Investigation of Broadband Printed Biconical Antenna with Tapered Balun for EMC Measurements

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Article Investigation of Broadband Printed Biconical Antenna with Tapered Balun for EMC Measurements

Abdulghafor A. Abdulhameed 1,2,* and ZdenˇekKubík 1

1 Department of Electronics and Information Technology, Faculty of Electrical Engineering, University of West Bohemia, 301 00 Pilsen, Czech Republic; [email protected] 2 Department of Electrical Techniques, Qurna Technique Institute, Southern Technical University, Basra 61001, Iraq * Correspondence: [email protected]

Abstract: This article investigates the design, modeling, and fabrication of small-size (150 × 90 × 1.6 mm) broadband printed biconical antenna. The proposed antenna is intended for use a reference antenna for electromagnetic interference measurement inside the EMC chamber. The reflection coefficient (S11-parameter) is verified by modeling the equivalent circuit of the structure in terms of lumped elements. This structure offers a −10 dB impedance bandwidth (from 0.65 GHz to 2.3 GHz) with the tapered balun feeding method. Therefore, it has a high probability of estimating the electromagnetic waves emitted from several applications such as GSM, LTE, UMTS, 3G, Wi-fi, Bluetooth, ZigBee and more. The simulated standard antenna parameters are compatible with the measured parameters results. Furthermore, azimuth omnidirectional radiation pattern and well-realized gain (3.8 dBi) are achieved, reflecting good values of antenna factor compared to the commercial design. Keywords: antenna factor; balun feeding technique; biconical antenna; EMC measurement; wideband Citation: Abdulhameed, A.A.; Kubík, Z. Investigation of Broadband Printed Biconical Antenna with Tapered Balun for EMC 1. Introduction Measurements. Energies 2021, 14, Recently, electronic devices have become more popular and are becoming smaller 4013. https://doi.org/10.3390/ in size. According to their applications, the radiation of these devices is occupying the en14134013 electromagnetic spectrum from DC frequency to GHz. Furthermore, electromagnetic interference (EMI) will occur between these devices as long as they share the same range [1]. Academic Editor: Andrea Mariscotti The devices’ ability to work together without any effect against each other is called electromagnetic compatibility (EMC) [2]. Emission and immunity are essential criteria for Received: 7 June 2021 EMI measurements. Three mandatory aspects should exist to generate EMI phenomena, Accepted: 25 June 2021 Published: 3 July 2021 the source of the electromagnetic waves, the victim affected by the source, and the path between the source and the victim. This path can be either radiated or conducted [3,4].

Publisher’s Note: MDPI stays neutral There are three radiation regions for each radiated element, near field region, reactive with regard to jurisdictional claims in near-far field region (Fresnel), and far-field region (Fraunhofer) [5]. These regions have published maps and institutional affil- their radius (R) related to their wavelength and the higher dimension D, as shown in iations. Figure1 . Two methods were proposed for EMI measurement based on radiated element regions and the power of the interference source. The far-field method uses an antenna to estimate the propagated electrical field inside the chamber [6]. In contrast, the near-field method utilizes probes to collect the induced magnetic and electrical field above the printed circuit board (PCB) [7]. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. The antennas used for the EMC test should have specific characteristics such as wide This article is an open access article bandwidth, high gain, omnidirectional radiation pattern, and good antenna factor. These distributed under the terms and designed antennas are intended to work in the very high frequency (VHF) and ultra-high conditions of the Creative Commons frequency (UHF) bands (30–1000 MHz and 1000–3000 MHz, respectively) [8], to detect Attribution (CC BY) license (https:// the interference emitted from the most critical applications in these bands such as GSM creativecommons.org/licenses/by/ (850–900 MHz), LTE (1800 MHz), UMTS or 3G (2100 MHz), Wi-fi, Bluetooth, Zigbee 4.0/). and more (2400 MHz) [9,10]. VHF and UHF bands are classified based on the European

Energies 2021, 14, 4013. https://doi.org/10.3390/en14134013 https://www.mdpi.com/journal/energies Energies 2021, 14, x FOR PEER REVIEW 2 of 14

interference emitted from the most critical applications in these bands such as GSM (850– Energies 2021, 14, 4013 900 MHz), LTE (1800 MHz), UMTS or 3G (2100 MHz), Wi-fi, Bluetooth,2 of 15 Zigbee and more (2400 MHz) [9,10]. VHF and UHF bands are classified based on the European Telecom- munications Standards Institute (ETSI). The VHF band is covered by a biconical or log Telecommunications Standards Institute (ETSI). The VHF band is covered by a biconical or logperiodic periodic antenna,antenna, while while the horn the antennahorn antenna covers the covers UHF band the above UHF 1 GHz band [11 ].above 1 GHz [11].

FigureFigure 1. Three 1. Three field regions field regions for any radiated for any element. radiated element. Several structures of the antennas were proposed to utilize in EMC measurement. In [12],Several the authors structures propose using of the characteristics antennas of were the sleeve proposed dipole antenna to utilize for EMCin EMC measurement. In measurement,[12], the authors which offerspropose 86% sizeusing reduction characteristics compared to of the the conventional sleeve dipole biconical antenna for EMC meas- antenna. The log-periodic dipole antenna’s frequency performances were improved in [13] usingurement, a saw-tooth which shape offers feedline. 86% The successive size reduction dipoles will compared be arranged in to the the horizontal conventional biconical an- planetenna. and The eliminate log-periodic the unwanted dipole vertical antenna’s electric field frequency component. performances A complementary were improved in [13] log-periodicusing a saw-tooth dipole array shape with cross-polarization feedline. The successive was proposed dipoles in [14]. will This structurebe arranged in the horizontal has an array of dipole antennas orthogonal to dipoles of conventional log-periodic dipole antennas,plane and offering eliminate a circular the polarization unwanted without vertical any hybrid electric junction. field The widthcomponent. of the A complementary ridgelog-periodic of the double dipole ridge guide array horn with (DRGH) cross-polarization antenna was tapered was linearly proposed in [15]. in This [14]. This structure has processan array maximized of dipole the effective antennas radiation orthogonal aperture and to reduced dipoles the of beamwidth conventional compared log-periodic dipole an- to conventional 1–18 GHz DRGH. tennas,Classical offering antennas a circular are large inpolarization size and heavy without in weight. any Therefore, hybrid using junction. printed The width of the ridge circuitof the technology double ridge (PCB) forguide antenna horn design (DRGH) is the antenna best choice was for thistapered purpose. linearly The in [15]. This process microstripmaximized antenna the has effective many advantages radiation such aperture as its low and cost, reduced low profile, the and beamwidth ease to compared to con- fabricateventional [16]. On1–18 the GHz other hand,DRGH. it suffers from the narrow bandwidth and low efficiency. The limited bandwidth is considered a big issue in EMC applications, which makes using the monopoleClassical and dipoleantennas printed are antennas large the in best size way and to overcome heavy thisin issue.weight. Therefore, using printed circuitThere technology will be a trade-off (PCB) between for theantenna impedance design bandwidth is the and best the size,choice especially for this purpose. The mi- forcrostrip this band antenna from 0.5 tohas 3 GHz many since advantages low frequency such needs as a largeits low size. cost, Different low kinds profile, and ease to fabri- of printed antennas were proposed to serve EMC applications. In [17], a wideband (0.8–2.5cate [16]. GHz) Onlog-periodic the other printed hand, antenna it suffers with 12from dipoles the was narrow presented. bandwidth The authors and low efficiency. The oflimited [18] show bandwidth the design and is developmentconsidered of a abig broadband issue in bi-conical EMC applications, printed dipole an- which makes using the tenna,monopole where a wideand impedancedipole printed bandwidth antennas was obtained the withbest theway help to of overcome balun feed and this issue. matching network. Ultra-wideband biconical (700 MHz–20 GHz) bilateral tapered slot antenna withThere dual-polarization will be a trade-off was investigated between for EMC the measurements. impedance Two bandwidth studies [19,20 and] the size, especially presentedfor this aband new UWB from Skeletal 0.5 to antenna 3 GHz for since EMC low measurements; frequency the needs VSWR a was large better size. Different kinds of thanprinted the classical antennas antenna were that was proposed used for the to sameserve purpose. EMC In applications. [21], the bulb shape In [17], was a wideband (0.8–2.5 proposed with ultra-wideband (0.79–1 GHz and 1.37–15 GHz), where the wide impedance matchingGHz) log-periodic was achieved with printed the help antenna of using the with stepped 12 partdipoles and feeding was presented. line. In [22], The authors of [18] show the design and development of a broadband bi-conical printed dipole antenna, where a wide impedance bandwidth was obtained with the help of balun feed and matching network. Ultra-wideband biconical (700 MHz–20 GHz) bilateral tapered slot antenna with dual-polarization was investigated for EMC measurements. Two studies [19,20] presented a new UWB Skeletal antenna for EMC measurements; the VSWR was better than the classical antenna that was used for the same purpose. In [21], the bulb shape was proposed with ultra-wideband (0.79–1 GHz and 1.37–15 GHz), where the wide impedance matching was achieved with the help of using the stepped part and feeding line. In [22], the design and model of a small elliptical planner dipole antenna for ultra-wideband EMC applications are presented.

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EMC measurement needs an accurate and low uncertainty antenna to achieve a reli- theable design antenna and factor model (AF) of a small[23], where elliptical the planner AF represents dipole antenna the ratio for of ultra-wideband the electrical EMCfield applicationsstrength on the are surface presented. of the antenna to the induced voltage across the antenna terminals [24]. EMC measurement needs an accurate and low uncertainty antenna to achieve a reliable antennaThis factor paper (AF) presents [23], wherethe design, the AF modeling, represents and the fabrication ratio of the of electrical an electrically field strength small-size on theprinted surface biconical of the antenna tothat the serves induced as a voltage reference across antenna the antenna in the EMC terminals measurements. [24]. The projectionThis paper of presents the classical the design, antenna modeling, inspires and the fabricationprinted biconical of an electrically shape to offer small-size wide printedbandwidth biconical from 0.65 antenna to 2.3 that GHz. serves Furthermore, as a reference suitable antenna values in of the AF EMC along measurements. the covering The projection of the classical antenna inspires the printed biconical shape to offer wide frequency reflect the accuracy and low certainty of this design. This paper is organized as bandwidth from 0.65 to 2.3 GHz. Furthermore, suitable values of AF along the covering follows: Section 2 presents the antenna design with the parametric study. The standard frequency reflect the accuracy and low certainty of this design. This paper is organized as antenna parameters and the antenna factor result are illustrated in Section 3. Section 4 follows: Section2 presents the antenna design with the parametric study. The standard highlights a comparison between the proposed antenna and commercial design, and antenna parameters and the antenna factor result are illustrated in Section3. Section4 finally, Section 5 presents a brief discussion. highlights a comparison between the proposed antenna and commercial design, and finally, Section5 presents a brief discussion. 2. Design Procedures 2. DesignThe choice Procedures of a biconical antenna has a significant advantage related to the shape of the radiationThe choice pattern. of a biconical To be more antenna specific, has the a significant radiation emission advantage from related the device to the shapeunder ofthe the test radiation (DUT) has pattern. an unpredicted To be more form specific, and tends the radiation to be omnidirectional emission from rather the device than underpresent the directive test (DUT) radiation. has an unpredictedTherefore, using form a and directive tends to antenna be omnidirectional may lead to rather a missing than presentEMI calculation directive due radiation. to the fact Therefore, that the directive using a directiveradiation antennapattern cannot may lead cover to athe missing whole EMIradiation calculation emitted due from to theDUT, fact i.e., that omnidirectional the directive radiation antennas pattern such as cannot biconical cover antennas the whole are radiationpreferred emittedin these from applications DUT, i.e., rather omnidirectional than directional antennas antennas such as such biconical as horn antennas antennas are preferred[25]. in these applications rather than directional antennas such as horn antennas [25].

2.1. Antenna Design This antenna consists of two horizontal trapezoidal shapes based on FR-4FR-4 substratesubstrate with relativerelative permittivitypermittivity of ofε r휀==4.3 4.3and and loss loss tangent tangenttan tan훿δ = 0.025 = 0.025, as illustrated, as illustrated in [16 in]. Some[16]. Some modiﬁcations modifications were were made made in bothin both shape shape and and feeding feeding methods methods to to suit suit thethe EMCEMC application. The idea of this design came from the dipole characteristics and the fact that the thicker width of the dipole leads to the wide bandwidth, and this thicker was changed to planner biconical, biconical, in orderorder toto achieveachieve widewide bandwidth bandwidth [[11].11]. TheseThese twotwo trapezoidaltrapezoidal shapes were placed placed in in the the top top and and bottom bottom layer layer of of the the structure, structure, and and hence hence they they created created a w λ avirtual virtual triangular triangular slot slot with with a awidth width 푤 g betweenbetween them them with with (0.25 (0.25 λ monopole) for eacheach shape [[26].26]. Therefore, when L = 0.25 λ == Wp = 71 mm, the length L dimension is adjustedadjusted to obtain the optimal result. The geometrical shape of thethe biconicalbiconical printedprinted antennaantenna withwith a balun feed method is shownshown inin FigureFigure2 2,, while while Table Table11 list list the the optimum optimum dimensions dimensions of of antenna parameters

(a) (b)

Figure 2. The geometrical shape of the proposed antenna, (a)) frontfront view,view, ((bb)) backback view.view.

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Table 1. The optimal values of the overall parameters of the antenna. Parameter Value/mm Parameter Value/mm

푤 150 퐿 90 푤 71 퐿 80 푤 3 푤 14 푤 1.5 푤 40

Energies 2021, 14, 4013 푤 40 퐿 4 of 15 18

2.2. Feeding Method Table 1. The optimal values of the overall parameters of the antenna. Balun is a transformer between the unbalanced port (antenna) and the balanced port (coaxialParameter cable). It controls Value/mm the current Parameter and decreases Value/mm feeder radiation by providing a ws 150 Ls 90 balancedwp current at each71 antenna’s legs.L Itp prevents the 80current from propagation on the transmissionw f 1 line outer surface,3 to avoidw f 2distortion of the14 radiation properties [27]. The wo 1.5 wg 40 balun feedw f line provides40 wideband impedanceL f matching.18 Therefore, it is more than suitable for this type of application, which requires broadband bandwidth. Two cases are studied2.2. Feeding here Method (the top and bottom transmission lines have the same and different widths). The Balunbalun is afeed transformer method between is dedicated the unbalanced to feeding port (antenna) this andstructure the balanced [28]. Tapered transmission port (coaxial cable). It controls the current and decreases feeder radiation by providing linesa balanced are currentprinted at each in antenna’sthe substrate legs. It preventslayer’s the front current and from back propagation face with on the same length and the transmission line outer surface, to avoid distortion of the radiation properties [27]. different width. The front transmission line (at the port side) has a width of 푊 = 3 mm The balun feed line provides wideband impedance matching. Therefore, it is more than connectedsuitable for this to type the of 50 application, Ω of coaxial which requires cable, broadband while bandwidth.the tapered Two end cases areof this line has a width of 푊studied = 1.5 here mm (the top connected and bottom transmissionto the front lines face have theof samethe andantenna. different widths).On the other hand, the back The balun feed method is dedicated to feeding this structure푊 [28=]. Tapered 14 mm transmission transmissionlines are printed line in the width substrate (at layer’s the port front andside) back is face with the same length connected and to the 50 Ω of coaxial cable,different which width. Theworks front as transmission the ground line (at plane, the port while side) has the a width tapered of Wf 1end= 3 mmof this line also has a width connected to the 50 Ω of coaxial cable, while the tapered end of this line has a width of of 푊 = 1.5 mm connected to the back face of the antenna. Wo = 1.5 mm connected to the front face of the antenna. On the other hand, the back transmission line width (at the port side) is Wf 2 = 14 mm connected to the 50 Ω of coaxial cable,2.3. Parametric which works asStudy the ground plane, while the tapered end of this line also has a width of Wo = 1.5 mm connected to the back face of the antenna. This antenna was modeled and simulated with CST Microwave studio [29]. The 2.3.parametric Parametric Study sweep is one of the critical facilities in this software that allowed us to sweep This antenna was modeled and simulated with CST Microwave studio [29]. The parametricany parameter sweep is onevalue of the to critical achieve facilities the in desired this software result. that allowed CST Microwave us to sweep studio uses the finite anyintegration parameter value technique to achieve (FIT) the desired for result. its transient CST Microwave solver studio by uses discretizing the ﬁnite the integral form of integrationMaxwell’s technique equations. (FIT) for Figure its transient 3 shows solver the by discretizinggrid shape the of integral this method; form of three parameters were Maxwell’s equations. Figure3 shows the grid shape of this method; three parameters were sweptswept as follows.as follows.

Figure 3. The mesh system of ﬁnite integration technique. Figure 3. The mesh system of finite integration technique.

2.3.1. The Width of the Virtual Slot between Two Trapezoidal Shapes 푤

This parameter presents the transition from the trapezoidal shape (푤 > 0) to the rectangular shape (푤 = 0). Since the 푤 value is still constant, the parameter 푤 is swept from 0 to 90 mm, and the corresponding S-parameter, as shown in Figure 4.

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2.3.1. The Width of the Virtual Slot between Two Trapezoidal Shapes wg Energies 2021, 14, x FOR PEER REVIEW 5 of 14 This parameter presents the transition from the trapezoidal shape (wg > 0) to the rectangular shape (wg = 0). Since the wp value is still constant, the parameter wg is swept from 0 to 90 mm, and the corresponding S-parameter, as shown in Figure4.

Figure 4. Return losses vs. frequency for different values of w . Figure 4. Return losses vs. frequency for differentg values of 푤.

It can be seen that there is no matching at wg = 0 mm (rectangular shape), while the return losses offer −12 dB at w = 20 mm. The resonance frequency remained at the It can be seen that thereg is no matching at 푤 = 0 mm (rectangular shape), while the same point for different values of wg, and the effect is only carried on the bandwidth. The bestreturn value losses of the slot offer width −12 that dB offers at a푤 good = reflection 20 mm coefficient. The resonance and higher impedance frequency remained at the same bandwidthpoint for is differentwg = 40 mm. values The discontinuity of 푤, and of the each effect trapezoidal is only shape carried increases on the the bandwidth. The best reactive part of the input impedance of the antenna and hence, increases the standing wave ratio.value The of reactive the slot part ofwidth the input that impedance offers can a begood minimized reflection with an increasecoefficient in the and higher impedance conebandwidth angle ∅c (w isg = 푤40 mm)= 40 reflecting mm. wide The bandwidth discontinuity [30]. of each trapezoidal shape increases the

2.3.2.reactive Balun Feedingpart of Method the input with the impedance Straight Line and of Tapered the antenna Line and hence, increases the standing waveAs mentionedratio. The above, reactive the balun part lines of are the printed input at theimpedance top and bottom can side be of minimized the with an increase substratein the cone to be oneangle part of∅ the (푤 planner = 40 biconical mm) antenna. reflecting Figure wide5 shows bandwidth the difference [30]. between the use of straight lines and tapered lines. It is clear that the tapered lines provide an impedance bandwidth wider than straight lines. 2.3.2. Balun Feeding Method with the Straight Line and Tapered Line 2.3.3. The Separation between the Trapezoidal Shapes (d) TheAs gap mentioned distance between above, the two the opposite balun trapezoidal lines are shapes printed signiﬁcantly at the affects top and bottom side of the bothsubstrate impedance to bandwidthbe one part and theof the gain, planner as shown inbiconical Figure6a,b, antenna. respectively. Figure The 5 shows the difference bestbetween value of the separation use of distance straight is at lines d = 0 mm,and as tapered shown in lines. the green It curve,is clear reﬂecting that the tapered lines provide the maximum realized gain of 4 dBi gain and suitable impedance matching with broad bandwidthan impedance (0.7–2.3 GHz)bandwidth [31]. wider than straight lines.

Figure 5. Return losses vs. frequency for both straight and tapered feeding lines.

2.3.3. The Separation between the Trapezoidal Shapes (d) The gap distance between the two opposite trapezoidal shapes significantly affects both impedance bandwidth and the gain, as shown in Figure 6a,b, respectively. The best value of separation distance is at d = 0 mm, as shown in the green curve, reflecting the maximum realized gain of 4 dBi gain and suitable impedance matching with broad bandwidth (0.7–2.3 GHz) [31].

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Figure 4. Return losses vs. frequency for different values of 푤.

It can be seen that there is no matching at 푤 = 0 mm (rectangular shape), while the return losses offer −12 dB at 푤 = 20 mm. The resonance frequency remained at the same point for different values of 푤, and the effect is only carried on the bandwidth. The best value of the slot width that offers a good reflection coefficient and higher impedance bandwidth is 푤 = 40 mm. The discontinuity of each trapezoidal shape increases the reactive part of the input impedance of the antenna and hence, increases the standing wave ratio. The reactive part of the input impedance can be minimized with an increase in the cone angle ∅ (푤 = 40 mm) reflecting wide bandwidth [30].

2.3.2. Balun Feeding Method with the Straight Line and Tapered Line As mentioned above, the balun lines are printed at the top and bottom side of the substrate to be one part of the planner biconical antenna. Figure 5 shows the difference

Energies 2021, 14, 4013 between the use of straight lines and tapered lines. It is clear that6 of the 15 tapered lines provide an impedance bandwidth wider than straight lines.

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FigureFigure 5. 5.Return Return losses losses vs. frequency vs. frequency for both straight for andboth tapered straight feeding and lines. tapered feeding lines.

(a) (b)

FigureFigure 6. 6.(a)( aReturn) Return losses losses vs. vs. frequency frequency for differentdifferent values values of of d d in in mm; mm; (b )(b Realize) Realize gain gain vs. vs. frequency frequency for different for different values values of ofd in d inmm. mm.

2.4.2.4. Equivalent Equivalent Circuit TheThe change inin thethe widthwidth of of the the dipole dipole affected affected the the bandwidth bandwidth directly. directly. An equivalent An equivalent circuitcircuit is is involved inin performingperforming a comprehensivea comprehensive study study of thisof this antenna. antenna. The biconicalThe biconical antennaantenna is is derived from from the the classical classical planner planner dipole, dipole, and and the the most most common common lumped lumped elements model consists of series impedance (C0 and L0) and parallel resonator (C1,L1 elements model consists of series impedance (C0 and L0) and parallel resonator (C1, L1 and and R1)[32]. The series component presents the transmission line point while the parallel Rresonator1) [32]. The is equivalent series component to the two resonance presents the arms transmission of the dipole, line as shown point in while Figure the7. parallel resonator is equivalent to the two resonance arms of the dipole, as shown in Figure 7.

Figure 7. Equivalent circuit of the typical dipole with default values of lumped elements.

Figure 7 presents the equivalent circuit for a narrowband dipole. Moreover, extra parallel resonators must be loaded to enable a wide frequency band to cover the whole frequency band from 0.7 to 2.3 GHz. Figure 8 presents the equivalent circuit modeling of a wideband biconical antenna in AWR Design Environment Software. The achieved S11- parameter from CST Microwave studio is imported to AWR Software, and the whole lumped elements are tuned to achieve the same response as imported S11-parameters. The return losses for both the proposed antenna and its equivalent circuits are shown in Figure 9, while Table 2 illustrates the optimum values of the equivalent circuit lamped elements.

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(a) (b) Figure 6. (a) Return losses vs. frequency for different values of d in mm; (b) Realize gain vs. frequency for different values of d in mm.

2.4. Equivalent Circuit The change in the width of the dipole affected the bandwidth directly. An equivalent circuit is involved in performing a comprehensive study of this antenna. The biconical antenna is derived from the classical planner dipole, and the most common lumped elements model consists of series impedance (C0 and L0) and parallel resonator (C1, L1 and R1) [32]. The series component presents the transmission line point while the parallel Energies 2021, 14, 4013 resonator is equivalent to the two resonance arms of the7 of 15dipole, as shown in Figure 7.

FigureFigure 7.7.Equivalent Equivalent circuit of circuit the typical of dipole the with typical default values dipole of lumped with elements. default values of lumped elements. Figure7 presents the equivalent circuit for a narrowband dipole. Moreover, extra parallel resonators must be loaded to enable a wide frequency band to cover the whole frequencyFigure band 7 from presents 0.7 to 2.3 GHz. the Figure equivalent8 presents the circuit equivalent for circuit a modelingnarrowband dipole. Moreover, extra parallelof a wideband resonators biconical antenna must in AWRbe loaded Design Environment to enable Software. a wide The achieved frequency band to cover the whole Energies 2021, 14, x FOR PEER REVIEW S11-parameter from CST Microwave studio is imported to AWR Software, and the whole 7 of 14 frequencylumped elements band are tuned from to achieve 0.7 to the 2.3 same GHz. response Figure as imported 8 S11-parameters. presents the The equivalent circuit modeling of a widebandreturn losses for bothbiconical the proposed antenna antenna and in its equivalentAWR Design circuits are shownEnvironment in Figure9, Software. The achieved S11- while Table2 illustrates the optimum values of the equivalent circuit lamped elements. parameter from CST Microwave studio is imported to AWR Software, and the whole lumped elements are tuned to achieve the same response as imported S11-parameters. The return losses for both the proposed antenna and its equivalent circuits are shown in Figure 9, while Table 2 illustrates the optimum values of the equivalent circuit lamped elements.

FigureFigure 8. Equivalent 8. Equivalent circuit circuit of the of the wideband wideband biconical biconical printed printed antenna.

Table 2. The optimum values of the lumped elements.

Element No. 1 2 3 4 5 6 R/Ω - 51 19.5 36 5.5 - L/nH 0.37 5.6 1.22 1.5 0.6 4.8 C/pF 9 5.5 4.3 5.4 10 6.3

Figure 9. S11-parameter for wideband biconical antenna and its equivalent circuit.

Table 2. The optimum values of the lumped elements.

Element No. 1 2 3 4 5 6 R/Ω - 51 19.5 36 5.5 - L/nH 0.37 5.6 1.22 1.5 0.6 4.8 C/pF 9 5.5 4.3 5.4 10 6.3

3. Fabrication Process and Measurement Results The standard antenna parameters that measure whether this design is suitable for the EMC applications are estimated directly using the CST Microwave studio, except the antenna factor parameter, which is calculated from the achieved gain from the CST Microwave studio. This antenna was fabricated using the printed circuit technology, and the prototype of the fabricated design is shown in Figure 10. The RIGOL DSA875 Spectrum Analyzer, with directional coupler RIGOL VB 1032, is used to estimate the S- parameter, as shown in Figure 11. While the radiation characteristics are obtained using an anechoic chamber, the simulated and the measured results have a good agreement.

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Energies 2021, 14, 4013 8 of 15 Figure 8. Equivalent circuit of the wideband biconical printed antenna.

FigureFigure 9. 9.S11-parameter S11-parameter for wideband for wideband biconical antennabiconical and antenna its equivalent and circuit. its equivalent circuit.

3. Fabrication Process and Measurement Results Table 2. The optimum values of the lumped elements. The standard antenna parameters that measure whether this design is suitable for theElement EMC applications No. are 1 estimated directly 2 using the 3 CST Microwave 4 studio, except 5 6 the antenna factor parameter, which is calculated from the achieved gain from the CST MicrowaveR/Ω studio. This antenna - was fabricated 51 using 19.5 the printed circuit 36 technology, and 5.5 - the prototypeL/nH of the fabricated 0.37 design is 5.6 shown in Figure 1.22 10. The RIGOL 1.5 DSA875 Spectrum 0.6 4.8 Analyzer, with directional coupler RIGOL VB 1032, is used to estimate the S-parameter, Energies 2021, 14, x FOR PEER REVIEW C/pF 9 5.5 4.3 5.4 8 of 14 10 6.3 as shown in Figure 11. While the radiation characteristics are obtained using an anechoic chamber, the simulated and the measured results have a good agreement. 3. Fabrication Process and Measurement Results The standard antenna parameters that measure whether this design is suitable for the EMC applications are estimated directly using the CST Microwave studio, except the antenna factor parameter, which is calculated from the achieved gain from the CST Microwave studio. This antenna was fabricated using the printed circuit technology, and the prototype of the fabricated design is shown in Figure 10. The RIGOL DSA875 Spectrum Analyzer, with directional coupler RIGOL VB 1032, is used to estimate the S- parameter, as shown in Figure 11. While the radiation characteristics are obtained using an anechoic chamber, the simulated and the measured results have a good agreement. (a) (b)

FigureFigure 10. 10.FabricationFabrication shape shape of the of thebiconical biconical antenna: antenna: (a) (fronta) front view, view, (b) (backb) back view. view.

Figure 11. Measurement of S11-parameter using the Spectrum analyzer.

3.1. Return Losses and VSWR The reflection coefficients and the voltage standing wave ratio (VSWR) are the same coin’s two sides. Figure 12a shows the simulated and measured reflection coefficients of the design. It expresses about –30 dB return losses at a resonance frequency of 1 GHz, and the –10 dB impedance bandwidth starts from 750 MHz to 2.5 GHz. The measured result (S11-parameter) offers good agreement with the simulated result, reflecting VSWR < 2 in this broadband, as shown in Figure 12b, and it covers most of the EMC applications such as GSM (850–900 MHz), LTE (1800 MHz), UMTS or 3G (2100 MHz), Wi-fi and more (2400 MHz), which has a high probability of interference occurred.

(a) (b) Figure 12. (a) Simulated and measured return losses vs. frequency, and (b) simulated and measured VSWR vs. frequency.

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Figure 10. Fabrication shape of the biconical antenna: (a) front view, (b) back view. (a) (b) Figure 10. Fabrication shape of the biconical antenna: (a) front view, (b) back view.

Figure 11. Measurement of S11-parameter using the Spectrum analyzer. Figure3.1.Figure Return 11. 11. Measurement LossesMeasurement and VSWR of S11-parameterof S11-parameter using the Spectrumusing the analyzer. Spectrum analyzer. 3.1.The Return reflection Losses andcoefficients VSWR and the voltage standing wave ratio (VSWR) are the same 3.1.coin’s Return twoThe reflectionsides. Losses Figure coefficients and 12a VSWRshows and the voltagesimulated standing and measured wave ratio reflection (VSWR) are coefficients the same of thecoin’s design. two It sides. expresses Figure about 12a shows –30 dB the return simulated losses and at a measured resonance reflection frequency coefficients of 1 GHz, of and thethe –10 design.The dB impedance reflection It expresses bandwidth about coefficients –30 dB starts return fromand losses 750the at MHz avoltage resonance to 2.5 standingGHz. frequency The measured of wave 1 GHz, andratio result (VSWR) are the same coin’s(S11-parameter)the –10 two dB impedance sides. offers Figuregood bandwidth agreement 12a starts shows with from the 750 the simulated MHz simulated to 2.5 result, GHz. andreflecting The measured measured VSWR result < 2reflection in coefficients of this(S11-parameter) broadband, as offers shown good in Figure agreement 12b, withand it the covers simulated most result,of the EMC reflecting applications VSWR < such 2 theasin GSM thisdesign. (850–900 broadband, It MHz),expresses as shown LTE (1800 in about Figure MHz), –3012 b,UMTS anddB it returnor covers 3G (2100 mostlosses MHz), of the at Wi-fi EMCa resonance and applications more (2400 frequency of 1 GHz, and theMHz),such –10 aswhich GSMdB has (850–900impedance a high MHz), probability LTEbandwidth (1800 of interference MHz), starts UMTS occurred. orfrom 3G (2100 750 MHz), MHz Wi-fi to and2.5 more GHz. The measured result (2400 MHz), which has a high probability of interference occurred. (S11-parameter) offers good agreement with the simulated result, reflecting VSWR < 2 in this broadband, as shown in Figure 12b, and it covers most of the EMC applications such as GSM (850–900 MHz), LTE (1800 MHz), UMTS or 3G (2100 MHz), Wi-fi and more (2400 MHz), which has a high probability of interference occurred.

(a) (b) FigureFigure 12. 12. (a)(a Simulated) Simulated and and measured measured return return losseslosses vs.vs. frequency,frequency, and and (b ()b simulated) simulated and and measured measured VSWRVSWR vs. vs. frequency. frequency. 3.2. Surface Current Distribution The surface current distribution is the best way to explain the antenna’s behavior, since it describes the currents’ directions. Figure 13 shows the front and back view of the surface current distribution at 1 GHz. The tapered balun’s role of balancing currents in the red arrows in both front and rear sights is highlighted. (a) (b) Figure 12. (a) Simulated and measured return losses vs. frequency, and (b) simulated and measured VSWR vs. frequency.

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3.2. Surface Current Distribution 3.2. Surface Current Distribution The surface current distribution is the best way to explain the antenna’s behavior, The surface current distribution is the best way to explain the antenna’s behavior, since it describes the currents’ directions. Figure 13 shows the front and back view of the since it describes the currents’ directions. Figure 13 shows the front and back view of the surface current distribution at 1 GHz. The tapered balun’s role of balancing currents in Energies 2021, 14, 4013 surface current distribution at 1 GHz. The tapered balun’s role of balancing currents10 of 15 in the red arrows in both front and rear sights is highlighted. the red arrows in both front and rear sights is highlighted.

(a) (b) (a) (b) Figure 13. Surface currents distribution at 1 GHz: (a) front view, (b) back view. FigureFigure 13. 13. SurfaceSurface currents distributiondistribution at at 1 1 GHz: GHz: (a )(a front) front view, view, (b) back(b) back view. view. 3.3. Gain and Radiation Efficiency 3.3.3.3. TheGain Gain gain and measures Radiation EfficiencyEfficiencyhow much the antenna gained the electromagnetic waves in one direction,TheThe rathergain gain measures measures than the how total much received the antenna waves. The gained gain thethe standards electromagnetic are related waveswaves to in in the one radiationdirection,one direction, pattern; rather rather thanhigh than the gain the total is total achieved received received in waves. waves. the directive The The gain gain radiation. standards standards Furthermore, are related related to tothe the omnidirectionalradiationthe radiation pattern; pattern; radiation high high offers gain gain islow is achieved achieved gain relativity, in in the the directive directiveand it is radiation. certainly radiation. Furthermore, suitable Furthermore, for theEMC the applications.omnidirectionalomnidirectional Figure radiationradiation 14a presents offersoffers the low low simulated gain gain relativity, relativity, and measured and and it is it certainly gainis certainly versus suitable frequency.suitable for EMC for The EMC measureapplications.applications. gain values Figure 14 14aarea presents presentsestimated the the using simulated simulated the andcomparison and measured measured method gain gain versus with versus frequency. the frequency. help Theof an The measure gain values are estimated using the comparison method with the help of an anechoicmeasure chamber. gain values An acceptable are estimated level usingof gain the was comparison achieved with method a maximum with the value help of 3.8of an anechoic chamber. An acceptable level of gain was achieved with a maximum value of dBianechoic at 1.69 chamber.GHz. The An radiation acceptable efficiency level of describes gain was the achieved ratio of with the gain a maximum to the directivity value of 3.8 3.8 dBi at 1.69 GHz. The radiation efficiency describes the ratio of the gain to the directivity ofdBi ofthe the at antenna. antenna.1.69 GHz. More More The than than radiation 85% 85% of of simulatedefficiency simulated describes radiation efficiency efficiencythe ratio is ofis obtained obtainedthe gain for tofor the the the overall directivity overall operationofoperation the antenna. band, band, asMore as shown shown than in in 85% Figure Figure of simulated 14b.14b. radiation efficiency is obtained for the overall operation band, as shown in Figure 14b.

(a) (b) FigureFigure 14. 14. (a()a Gain) Gain in in dBi dBi( avs.) vs. frequency, frequency, ( (b) radiation efficiencyefficiency vs. vs. frequency. frequency. (b) Figure 14. (a) Gain in dBi vs. frequency, (b) radiation efficiency vs. frequency. 3.4.3.4. Antenna Antenna Factor Factor (AF) (AF) The antenna factor plays a critical role in measuring how useful the antenna is for use The antenna factor plays a critical role in measuring how useful the antenna is for 3.4.as a Antenna reference Factor antenna (AF) for EMC measurements. Antenna factor can be defined as the ratio use as a reference antenna for EMC measurements. Antenna factor can be defined as the betweenThe theantenna incident factor electrical plays field a critical and the role received in measuring voltage [ 33how,34]. useful Equation the (1)antenna is used is for usefor calculatingas a reference the antennaantenna factor for EMC from measurements. the simulated and Antenna measured factor gain, can respectively be defined [35 ].as the p AF(dB) = 19.76 − 20 log(λ) − 20 log Gr (1)

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ratio between the incident electrical field and the received voltage [33,34]. Equation (1) is used for calculating the antenna factor from the simulated and measured gain, respectively [35]. Energies 2021, 14, x FOR PEER REVIEW 10 of 14

퐴퐹(푑퐵) = 19.76 − 20 log(휆) − 20 log퐺 (1)

where 휆 is the wavelength, and 퐺 is the gain of the antenna in dBi. ratio betweenFigure 15the highlights incident electrical the calculated field and antenna the received factor voltage for printed [33,34]. biconical Equation antenna (1) is from usedboth forsimulated calculating and themeasured antenna gain. factor It can from be theseen simulated that above and 650 measured MHz, they gain, are well- respectively [35]. matched, and hence, the antenna factor increases in regular steps with an increase in the

frequency reaching 2.5퐴퐹 GHz.(푑퐵) = The 19 . antenna76 − 20 log factor(휆) − increases20 log퐺 in non-regular steps(1) as the Energies 2021, 14, 4013 frequency increases above 2.5 GHz, despite reduced matching11 of 15 due to the antenna being where 휆 is the wavelength, and 퐺 is the gain of the antenna in dBi. directional rather than omnidirectional at 2.5 GHz. Figure 15 highlights the calculated antenna factor for printed biconical antenna from

bothwhere λsimulatedis the wavelength, and andmeasuredGr is the gain gain. of the It antenna can inbe dBi. seen that above 650 MHz, they are well- matched,Figure 15 and highlights hence, the calculatedthe antenna antenna factor factor forincreases printed biconical in regular antenna steps from with an increase in the both simulated and measured gain. It can be seen that above 650 MHz, they are well- frequencymatched, and hence, reaching the antenna 2.5 GHz. factor increases The antenna in regular steps factor with increases an increase in in the non-regular steps as the frequencyfrequency reaching increases 2.5 GHz. above The antenna 2.5 GHz, factor despite increases inreduced non-regular matching steps as the due to the antenna being frequency increases above 2.5 GHz, despite reduced matching due to the antenna being directionaldirectional rather rather than omnidirectional than omnidirectional at 2.5 GHz. at 2.5 GHz.

Figure 15. Antenna factor in dBm−1 vs. frequency for printed biconical antenna.

3.5. Radiation Pattern Figure 16 shows the 3-D radiation pattern of the antenna. It can be seen that the FigureFigureazimuth 15. 15.Antenna Antenna line factor or infactorlongitude dBm−1 invs. dBm frequency line−1 vs. forcan frequency printed be biconicalobtained for antenna. printed with biconical ph = 90° antenna. (the red line), where this line 3.5.is Radiationalmost Pattern equal in value along its radius. Furthermore, the elevation line or latitude line 3.5.will FigureRadiation be 16achieved shows Pattern the 3-Dat ph radiation = 0° pattern [35]. ofBoth the antenna. planes It can(azimuth be seen that and the elevation) for four frequency azimuth line or longitude line can be obtained with ph = 90◦ (the red line), where this line is almostbandsFigure equal (0.85 in value16 GHz,shows along its 1 radius.the GHz, 3-D Furthermore, 1.5radiation GHz, the elevationpattern and 1.9 line of or GHz) latitudethe antenna. are line will shown It can in be Figure seen that 17. the At lower azimuthbefrequencies, achieved line at ph or = 0the ◦longitude[35 ].omnidirectional Both planes line (azimuth can be andbehavior obtained elevation) forwithappears four ph frequency = clearly. 90° bands (the Onred theline), other where hand, this linewith high (0.85 GHz, 1 GHz, 1.5 GHz, and 1.9 GHz) are shown in Figure 17. At lower frequencies, isthefrequencies, almost omnidirectional equal the behaviorin value radiation appears along clearly. pattern its Onradius. the tends other Furthermore, hand, to with be high directional frequencies,the elevation rather line than or latitude omnidirectional, line willthesupporting radiation be achieved pattern the tends at gain ph to be = directional distribution0° [35]. ratherBoth than curveplanes omnidirectional, with(azimuth increasing supporting and elevation) the frequency for four in Figurefrequency 14a. The gain distribution curve with increasing frequency in Figure 14a. The radiation pattern bandsmeasurementradiation (0.85 setup pattern GHz, is shown 1measurement GHz, in Figure 1.5 18. GHz, setup and is 1.9 shown GHz) in are Figure shown 18. in Figure 17. At lower frequencies, the omnidirectional behavior appears clearly. On the other hand, with high frequencies, the radiation pattern tends to be directional rather than omnidirectional, supporting the gain distribution curve with increasing frequency in Figure 14a. The radiation pattern measurement setup is shown in Figure 18.

FigureFigure 16. 3-D 16. Simulated 3-D Simulated radiation pattern radiation of the printed pattern biconical of antenna. the printed biconical antenna.

Figure 16. 3-D Simulated radiation pattern of the printed biconical antenna.

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Energies 2021, 14, x FOR PEER REVIEW 11 of 14 Energies 2021, 14, 4013 12 of 15

(a) (b)

Figure 17.FigureFigure Simulated 17. Simulated17. and Simulated measured and measured radiation and radiation measured pattern: pattern: (a) radiationsimulated (a) simulated azimuth, pattern: azimuth, (b ()b measured()a measured) simulated azimuth, azimuth, azimuth, (b) measured azimuth, (c) simulated(c()c simulated) simulatedelevation, elevation, (d) elevation,measured (d) measured elevation. (d elevation.) measured elevation.

Figure 18. Radiation pattern measurements setup inside the anechoic chamber.

4. Comparison between the Proposed Design and the Commercial Design A brief comparison between the proposed and commercial designs (BicoLOG 20300) offered for sale on the AARONIA AG website by company of AARONIA in Germany is Figure 18. Radiation pattern measurements setup inside the anechoic chamber. illustratedFigure in Table 18. 3 Radiation [36]. The specifications pattern measurements of the (BicoLOG setup 20300) inside are taken the anechoicfrom the chamber. datasheet posted on the website. It can be seen that both designs are based on the biconical shape, which4. Comparison provides an omnidirectional between the radiation Proposed pattern. DesignThe proposed and design the Commercialis small Design and lightweight compared to the classical one, because it is based on the printed circuit technique. ThisA technique brief comparison has the disadvantage between of small the bandwidthproposed (650 and MHz–2.3 commercial GHz) designs (BicoLOG 20300) comparedoffered to the classicalfor sale antenna on the (20 AARONIA MHz–3 GHz). AG In contrast, website the by planar company bi-conical of AARONIA in Germany is antenna illustrated offers an acceptable in Table realized 3 [36]. gain The of a specifications maximum value ofof 3.8 the dBi, (BicoLOG while the 20300) are taken from the classical antenna’s maximum gain is 1 dBi. Finally, both designs have good values of datasheet posted on the website. It can be seen that both designs are based on the biconical shape, which provides an omnidirectional radiation pattern. The proposed design is small and lightweight compared to the classical one, because it is based on the printed circuit technique. This technique has the disadvantage of small bandwidth (650 MHz–2.3 GHz) compared to the classical antenna (20 MHz–3 GHz). In contrast, the planar bi-conical antenna offers an acceptable realized gain of a maximum value of 3.8 dBi, while the classical antenna’s maximum gain is 1 dBi. Finally, both designs have good values of

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4. Comparison between the Proposed Design and the Commercial Design Energies 2021Energies, 14, 2021x FOR, 14 PEER, x FOR REVIEW PEER REVIEW 12 of 14 12 of 14 A brief comparison between the proposed and commercial designs (BicoLOG 20300) offered for sale on the AARONIA AG website by company of AARONIA in Germany is illustrated in Table3[ 36]. The speciﬁcations of the (BicoLOG 20300) are taken from the datasheet posted on the website. It can be seen that both designs are based on the antennaantenna factor, whichfactor,biconical makeswhich shape, themmakes which suitable providesthem suitable for an omnidirectionaluse foras ause reference as radiation a reference antenna pattern. antenna inside The proposed theinside EMC the EMC chamber.chamber. design is small and lightweight compared to the classical one, because it is based on the printed circuit technique. This technique has the disadvantage of small bandwidth (650 MHz–2.3 GHz) compared to the classical antenna (20 MHz–3 GHz). In contrast, the Table 3.Table Numerical 3. Numerical comparison comparison of antenna of antenna factor of factor the proposed of the proposed antenna antenna with the with commercial the commercial planar bi-conical antenna offers an acceptable realized gain of a maximum value of 3.8 dBi, antennaantenna (BicoLOG (BicoLOG while20300). the 20300). classical antenna’s maximum gain is 1 dBi. Finally, both designs have good values of antenna factor, which makes them suitable for use as a reference antenna inside SpecificationsSpecificationsthe EMC chamber. BicoLOG BicoLOG 20300 20300 Proposed Proposed Design Design Dimensions/mmDimensions/mm 350 × 160 350 × ×140 160 × 140 150 × 90150 × 1.6 × 90 × 1.6 Table 3. Numerical comparison of antenna factor of the proposed antenna with the commercial Designantenna Design (BicoLOG 20300). Biconical Biconical Printed Printed biconical biconical Substrate - FR-4 SubstrateSpeciﬁcations BicoLOG - 20300 Proposed Design FR-4 Weight/gWeight/g Dimensions/mm 350 350 × 350160 × 140 150 × 5090 × 1.6 50 Gain/dBiGain/dBi Design −45–1 Biconical −45–1 Printed 2–3.8 biconical 2–3.8 Substrate - FR-4 FrequencyFrequency range/MHz range/MHzWeight/g 20–3000 20–3000 350 650–2300 50 650–2300 AntennaAntenna Factor *Factor1)/dBm Gain/dBi*−11) /dBm−1 22–44 22–44−45–1 24–36 2–3.8 24–36 Frequency range/MHz 20–3000 650–2300 Antenna Factor *(1)/dBm−1SMA FemaleSMA22–44 Female 24–36 SMASMA Female FemaleSMA Female SMA Female RF ConnectorRF Connector RF Connector PicturePicture Picture

*(1) frequency range from 0.6 to 2.3 GHz. *1) frequency*1) frequency range from range 0.6 from to 2.3 0.6 GHz. to 2.3 GHz. The achieved antenna factor values for the proposed design are in line with commercial The achievedThe achievedantenna antenna design antenna valuesfactor BicoLOG factorvalues 20300, values for as the illustrated for proposed the in Table proposed design4. design are in are line in with line with

commercialcommercial antennaTable antenna design 4. Antenna designvalues factor comparisonvaluesBicoLOG BicoLOG of 20300, the proposed as20300, illustrated antenna as illustrated with in the Table commercial in 4. Table antenna 4. (Bi- coLOG 20300). Table 4.Table Antenna 4. Antenna factor comparison factor comparison of the proposed of the proposed antenna antenna with the with commercial the commercial antenna antenna Frequency/GHz AF (BicoLOG 20300)/dBm−1 AF (Proposed Design)/dBm−1 (BicoLOG(BicoLOG 20300). 20300). 0.5 22 24 1 28 38 −1 −1 −1 −1 Frequency/GHzFrequency/GHz AF1.5 (BicoLOG AF (BicoLOG 20300)/dBm 20300)/dBm 29 AF (Proposed AF (Proposed 30Design)/dBm Design)/dBm 0.5 0.5 2 22 22 39 24 33 24 2.5 42 36 1 1 28 28 38 38 1.5 1.55. Conclusions 29 29 30 30 2 2 An electrical small-size 39 printed 39 biconical antenna is designed, modeled, 33 and 33 fabricated to serve as a reference antenna in EMC measurements. The proposed antenna uses a tapered 2.5 2.5balun transformer to provide 42 a balanced 42 current and offers an impedance 36 bandwidth 36 from 650 MHz to 2.2 GHz with an acceptable VSWR. The realized gain of the antenna has a 5. Conclusions5. Conclusions good value related to the omnidirectional antennas. This antenna’s behavior reﬂects an omnidirectional radiation pattern at the lower frequencies and gradually being a directional An electricalAn electricalantenna small-size with small-size an increase printed in printed the biconical rate toward biconical antenna 2.5 GHz. antenna isThis designed, design is was designed, compared modeled, modeled, with and and fabricatedfabricated to serve theto as commercialserve a reference as a antenna reference antenna design antenna (BicoLOGin EMC in 20300)measurements. EMC for measurements. EMC measurement The proposed The and achievedproposed antenna a antenna good performance. It is worth mentioning that this antenna can be reconﬁgured to cover uses a tapereduses a tapered balun transformer balun transformer to provide to provide a balanced a balanced current current and offers and an offers impedance an impedance bandwidthbandwidth from 650 from MHz 650 to MHz 2.2 GHz to 2.2 with GHz an with acceptable an acceptable VSWR. VSWR. The realized The realized gain of gainthe of the antennaantenna has a good has avalue good related value relatedto the omnidirectional to the omnidirectional antennas. antennas. This antenna’s This antenna’s behavior behavior reflectsreflects an omnidirectional an omnidirectional radiation radiation pattern pattern at the lower at the frequencies lower frequencies and gradually and gradually being being a directionala directional antenna antenna with an with increase an increase in the inrate the toward rate toward 2.5 GHz. 2.5 This GHz. design This design was was comparedcompared with the with commercial the commercial antenna antenna design design(BicoLOG (BicoLOG 20300) 20300)for EMC for measurement EMC measurement and achievedand achieved a good a performance. good performance. It is worth It is worthmentioning mentioning that this that antenna this antenna can be can be reconfiguredreconfigured to cover to lower/higher cover lower/higher frequency frequency bands atbands the expense at the expense of size. of For size. instance, For instance, an antennaan antenna size of size297 ×of 200 297 mm × 200 will mm cover will a cover frequency a frequency band starting band starting at 330 MHzat 330 up MHz to up to 2.3 GHz.2.3 On GHz. the Onother the hand, other increasing hand, increasing the higher the frequencyhigher frequency band for band this for design this designrequired required changingchanging the sharp the lines sharp of lines the virtual of the virtualtriangular triangular into curvature into curvature lines toward lines toward the antenna. the antenna.

Author AuthorContributions: Contributions: Conceptualization, Conceptualization, A.A.A. andA.A.A. Z.K.; and methodology, Z.K.; methodology, A.A.A.; A.A.A.;investigation, investigation, A.A.A. A.A.A. and Z.K.; and resources, Z.K.; resources, A.A.A. A.A.A. and Z.K.; and writing—review Z.K.; writing—review and editing, and editing, A.A.A. A.A.A.and Z.K. and All Z.K. All authors authorshave read have and read agreed and toagreed the published to the published version versionof the manuscript. of the manuscript.

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lower/higher frequency bands at the expense of size. For instance, an antenna size of 297 × 200 mm will cover a frequency band starting at 330 MHz up to 2.3 GHz. On the other hand, increasing the higher frequency band for this design required changing the sharp lines of the virtual triangular into curvature lines toward the antenna.

Author Contributions: Conceptualization, A.A.A. and Z.K.; methodology, A.A.A.; investigation, A.A.A. and Z.K.; resources, A.A.A. and Z.K.; writing—review and editing, A.A.A. and Z.K. All authors have read and agreed to the published version of the manuscript. Funding: This research was supported by the Ministry of Education, Youth and Sports of the Czech Republic under the project OP VVV Electrical Engineering Technologies with High-Level of Embedded Intelligence CZ.02.1.01/0.0/0.0/18_069/0009855 and by the project SGS-2021-005: Research, development and implementation of modern electronic and information. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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