Performance Study of Defected Ground Structure Patch Antenna with Etched Psi (Ψ) Shaped Stubs

J. lnf. Commun. Converg. Eng. 16(4): 203-212, Dec. 2018 Regular paper Performance Study of Defected Ground Structure Patch Antenna with Etched psi (ψ) Shaped Stubs

Iram Nadeem and Dong-You Choi* , Member, KIICE Department of Information and Communication Engineering, Chosun University, Gwangju 61452, Korea Abstract In this article, a novel design of patch antenna with wide band characteristics is presented. The proposed antenna is having electrical dimensions of 0.14λ×0.11λ (at lower initial frequency) and footprints of 150 mm2. Structural parameters optimization shows 3.1–23.5 GHz frequency range for a (reflection coefficient) S11 ≤ -10 dB and simulated gain 6.8 dB is obtained. An equivalent circuit model is proposed to get an insight view of antenna. Advanced Systems Design (ADS) simulation results are obtain which confirm the validity of proposed model. Degenerated foster canonical form has been used to explain the reactance and capacitive behavior idea of simulated proposed antenna’s input impedance later on an equivalent circuit model and smith chart is also suggested. HFSS and CST have been used to analyze antenna behavior. The proposed antenna can be further used for microwave image detection applications.

Index Terms: Advanced Systems Design (ADS), Bandwidth ratio (BWR), Defected ground structure (DGS), Front to back ratio, Radio frequency (RF)

I. INTRODUCTION pole circular ring antenna for the applications of super wideband [6], are some of its examples. Other techniques used to Nowadays, rapid development has been observed in wire- increase the bandwidth of antenna include asymmetrical cou- less communication systems in term of wide band and ultra- pling feed of circular polarized microstrip antenna [7], and wide band applications. This includes microwave radar parasitic structures [8]. The interest is to achieve high band- imaging and positioning systems, high data rate systems, width along with reduction in size is also consideration [9]. ground penetrating radar systems (GPRS). Microstrip patch Among these techniques we will use the modified feeding antenna is very famous due to its simplicity, easy integration structure which is basically selecting the suitable feed line with rest of microwave integration circuits and low cost. A and position of slots so that input impedance at higher patch quarter circular patch with small vertical and horizontal cir- resonant mode can be modified [10, 11]. The use of partial cular sector extensions containing three different width ground surface or insertion of slots in ground surface can microstrip lines antenna of bandwidth (136%) held ultra- promotes the enlargement of bandwidth [12]. Intentionally wide band (UWB) application [1]. Different kind of antennas insertion of slot or stub in ground plane is known as defected has been discussed in literature, for instance, U-shaped nar- ground structure (DGS) which have a significant effect on row strip structures [2], hexagonal radiating patch antenna the performance of antenna [13, 14]. The goal of this work is [3], etched spiral slot on the patch [4], elliptic antenna with to design compact size planner antenna that can be used for inscribed third iteration sierpinski triangle [5], printed mono- wide bandwidth applications. The printed patch antenna that

Received 16 March 2018, Revised 23 October 2018, Accepted 24 October 2018 *Corresponding Author Dong-You Choi (E-mail: [email protected], Tel: +82-62-230-7060) Department of Information and Communication Engineering, Chosun University, 309, Pilmun-daero, Dong-gu, Gwangju 61452, Korea.

https://doi.org/10.6109/jicce.2018.16.4.203 print ISSN: 2234-8255 online ISSN: 2234-8883

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we proposed is miniaturized rectangular shape output band- lower side. Furthermore, it contains two psi (ѱ) shaped stubs width can satisfy wide band requirement including UWB. inside (middle) of the radiating patch. Feed line has been An equivalent circuit model of the patch antennas is related modified by incorporating a small rectangular slot along its to the physical dimensions of the antenna. Until now, litera- length satisfying 50 Ω requirement. A partial ground plane is ture has many proposed equivalent circuit models by taking obtained via DGS techniques, where multiple slots of vari- input impedance or admittance matching aspects. A degener- able lengths have been inserted. Ground plane is printed on ated foster canonical form for electrical and magnetic the bottom surface of the substrate. The antenna is designed antenna models are given in [15, 16]. Circuit refinement on Taconic TRF-45 material with thickness “h” of 1.58 mm methods consisting of narrow band and macro band are and relative permittivity (εr) of 4.5. The rectangular radiating explained in [17], rational admittance function to generate patch along the feed line of width of 1.2 mm is designed on passive circuits of antenna [18]. The tangential electric field the top surface of the substrate. The size of the proposed behavior in the form of near and far field is summarized in antenna is obtained by mathematical formulations of the [19], and exact parameters of the equivalent circuit model patch antenna. Further, the mathematical formulation which can be determine by nonlinear curve fitting optimization is complex due to the four cutting edge slots and insertion of techniques [20]. Lumped equivalent circuit model of antenna psi (ѱ) shaped stubs inside the radiating patch. In designing by using series and parallel RLC resonant circuits are stud- the patch antenna, one must account for the effect of the ied in [21–23], in which cavity model is implemented by slots in ground or radiating plane. Because the slots might taking basic parallel plate transmission circuit model. In this article, a compact planer antenna of area 15 x 10 mm2 is proposed. The antenna is simple in structure with few geo- metric parameters variation and DGS explained in Section II. Moreover, Section III gives a brief idea of current distribution around the radiating patch, stub and the ground plane. The geometry of proposed antenna where series and parallel combinations of lumped parameters are used to explain equivalent electric circuit behavior. Furthermore, by taking concept of degenerated foster conical method the capacitive and inductive behavior of the proposed antenna is explained in the form of smith chart shown in Section IV. Due to its good characteristics like small size, single layer and large bandwidth proposed printed antenna is an excellent candi- date for many wide band applications of the wireless communication systems. The simulation and measured results are explained in Section V. This reveals that the proposed antenna has achieved wide bandwidth ranging from 3.1 to 23.5 GHz for reflection coefficient below -10 dB. In addition, antenna displays good simulated radiation efficiency of around 88% to 90%. A small overview of the microwave imaging systems is given in the last part of the paper just to give brief idea about antenna use in this particular field in term of transmitter and receiver. Finally, conclusion is provided in Section VI.

II. MODEL AND GEOMETERY OF ANTENNA

Design of a miniaturized antenna for wide band function- ality is a real challenge. The proposed antenna geometry is shown in Fig. 1(a) and (b). The basic antenna is a rectangular patch that has endured through numerous changes to overcome the narrow bandwidth limitations at the origin. So, proposed antenna model consist of a rectangular radiating patch with level of two steps on upper side as well as on the Fig. 1. Antenna geometry (a) front side and (b) back side.

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have the effect of lowering the resonant frequency of the where effective permittivity (εeff) of the substrate material antenna. An increase in the step of the radiating patch and in can be determined by Eq. (2). Due to the fringing field effect the ground plane allows antenna better development of adap- the additional line length on ∆L both end of the patch length tion. Therefore, it has been optimized by using electromag- is given by netic solver software ANSYS HFSSv19 and in the second w with CST software. All dimensions of the proposed antenna ()ε + 0.3 × ⎛⎞------patch0.264 eff ⎝⎠h are given in Table 1. ΔL = ------.(4) w Radiating patch elements designing include the estimation ⎛⎞------patch ()εeff – 0.258 × 0.813 of its dimension. Width of the radiating patch Wpatch has ⎝⎠h small effect on resonance and has been attained by using the mathematical modeling as shown below [24]. where effective patch length Leff can be calculated by following formula c 2 W = ------(1) patch 2 ε + 1 fr r ------c Leff = .(5) 8 2fr εeff μoεo where c =3×10 is the free space speed of light, εr = 4.5 is the substrate material’s relative permittivity and f = 7.9 GHz r If antenna operates at center frequency f between lower of the proposed antenna. The microstrip patch is on top side c frequency f and upper frequency f (where f = (f + f )/2, of the substrate, therefore the electromagnetic wave has an 1 2 c 1 2 then fractional bandwidth (FBW) is given by effective permittivity (εeff) which is equal to

εr + 1 εr – 1 –0.5 ε = ------+ ------12------h + 1 f1 + f2 eff . (2) = ------2 2 wpatch FBW .(6) fc

The radiating patch length (Lpatch) also plays a crucial role Furthermore, initial lower frequency can be calculated by in determining the resonant frequency which is an important using following relation parameter to be considered while designing of patch antenna. The dimension of L can be calculated by using the following = – ⎛⎞------Bandwidth f1 fc ⎝⎠2 .(7) formula: Moreover, addition of variable length slots of antenna is L = L +2ΔL. (3) patch eff also equal to length of patch as well as width of the patch. Relation is shown in Eqs. (8) and (9) Table 1. Optimized dimensions of proposed antenna Parameter Value (mm) Parameter Value (mm) Lpatch = g1 ++fd1 +c1 +b1 15 1×0.5 Lsub a1 ≈ g2 ++wd2 +c2 +b2 (8) 10 1×0.5 Wsub a2 2.95 1×1 Wpatch = d2 ++++eg2 g1 d1 Lg b1 10 1×1 wg b2 ≈ c2 ++++b2 wf c1 b1 .(9) 6 1×1 Lf c1 1.2 1×1 wf c2 e 3.4 j 0.45×0.5 III. CURRENT DISTRIBUTION ANALYSIS

f 4.2 t1 0.59×2

q 1.2 t2 0.5×1.5 The current distribution usually gives the insight into the physical behavior of the antenna. In simulations, proposed p 1.6 t3 0.5×1.5 antenna etched with slots and stubs has been investigated. s 0.5 n1 1×2.2 The simulated (by HFSS) current distributions on resonant r 0.5 n2 0.875×2.5 frequencies of 7.9 GHz is shown in Fig. 2(a) and (b). We see u 0.6 m 0.45×2.2 1 a concentrated current flow on the lower edges of the radiat- v 0.81 m 0.6×2.5 2 ing patch and around all the corner of rectangular slots and 4.20 0.5×2 w k1 feed line. Moreover a strong current excites the whole side 1×1 0.5×2 d1 k2 of (ѱ) shaped stubs. 1×1 1×2 d2 k3 In addition, the concentrated current is observed on the 1×1 1×1 g1 g2 ground plane with the presence of defected ground tech-

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using power is validated in near resonance frequency ranges or where electrically small antennas are considered [15, 26]. Below Eq. (11) gives quality factor in term of power.

w ()I 2w XW() ------r r Qw()r ≈ (11) 4PA

where PA is the power accepted by antenna, by placing the formula of power the Eq. (11) can be simplified as

w XW() ------r r - Qw()r ≈ (12) 2Rw()r

where R(Wr) is the frequency dependent resistance of the antenna feeding point. It follows from [15, 27], that for any frequency W0, where the antenna is tuned to be resonant with Fig. 2. Simulated current distributions at resonant frequency 7.9 GHz front a series capacitor or lossless inductor, the quality factor Eq. side (a) and back side (b). (12) will be

W XW() nique, in the interior and exterior of the slots as depicted in ()= ------0 0 - Qw0 2 () (13) Fig. 2(b). The antiresonance properties of the antenna allevi- R0 W0 ate the impedance change by showing current concentration. where the subscript “0” signifies the tuned antenna. As described earlier the quality factor Eqs. (12) and (13) are IV. EQUIVALENT CIRCUIT MODEL valid only on the near resonance frequency ranges or for electrically small antenna. So, for frequency ranges away from resonance the quality factor expression would be A. Degenerated Foster Canonical Theorems change [27]. To follow this the tuned antenna quality factor can be approached from antenna impedance properties which The degenerated foster canonical form is found applicable W to model proposed antenna’s input impedance over all reso------0 - Qw()0 = []Z0()w0 (14) nance frequencies [20]. According to it, higher order modes 2R0()W0 can be represented by series of parallel RLC components Z w R w jX w [16]. The impedance at the feeding reference point where the where 0( ) = 0( ) + 0( ) is the impedance of the X W SMA connector can be connected was obtained by consider- antenna after it is tuned [ 0( 0) = 0] with lossless series ing HFSS (based on Finite difference time domain method) capacitor or inductor [27]. On the similar way antenna qual- tool. Simulated impedances in term of resistance and reac- ity factor can be approximated form bandwidth of matched tance of proposed antenna with slotted ground plane voltage standing wave ratio (VSWR) as (defected ground technique) are depicted in Fig. 3. The sim- 2 β ulated input impedance and admittance vs. frequency of the Qw()= ------(15) 0 FBW ()w proposed antenna is analyzed first. Then, to understand how v 0 antenna works according to foster theorem, a frequency s – 1 dependent equivalent circuit model is constructed on ADS as β = ------≤ 1 ,(16) shown in Fig. 4. According to [26], Foster reactance theorem 2 s is useable for the analysis of general antenna systems. Usu- fh – f1 ally frequency derivative of an antenna’s feed point reac- FBW ()w = ------(17) v 0 w tance X'(w) is related to reactive electric and magnetic 0 energy. This can be calculated as where VSWR = s, FBWv is the fractionally matched VSWR FBW 4[]we()w + wmw bandwidth. The v is chosen to approximate the quality X'()w = ------(10) factor because it exist in all resonance and antiresonance I 2 point of antenna. The fractional conductance bandwidth does where I is the current at feed point of the antenna, We(w) is not exist on antiresonance frequency ranges [15]. This was electric energy and Wem(w) is magnetic energy. For an antenna little theoretical background of degenerated foster canonical to have positive resonant factor X'(w) summation of both ener- theorems. gies should be assumed to positive [15]. The quality factor The simulated impedance [Z0(w) = R0(w) + jX0(w)] of the

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antenna feeding point reactance has positive (+ive) frequency derivative. Whereas at near antiresonance ranges antenna acts as parallel RLC circuits and corresponding frequency deriva- tives of the antenna’s feeding point reactance is negative (-ive) [16]. Hence the close observation of Fig. 3 starting from 3 GHz to 23 GHz range of bandwidth antenna reactance goes through three anti-resonance X'(w) (7.8, 9.7, 21.6 GHz) and two resonance points (8.8, 19.4 GHz) respectively. By using above Eqs. (14) and (15) of near resonance and antiresonance the antenna quality factor can be determined. By following the foster reactance theorems an equivalent circuit model has been proposed in ADS (advanced design Fig. 3. Simulated input impedance of the proposed antenna (HFSS only). systems) shown in Fig. 4. In a complete foster canonical theorem form, higher order modes can be represented by series RLC components, a capacitor of 5 pf and inductor 2.81 nH added in series when the antenna operates at second medium antiresonance (9.7 GHz). The higher order resonance frequencies are represented as two port LC circuit. Further, RLC namely 83.5 Ω, 2.65 nH and 5.24 pf component adds the effect of DGS of antenna. The equivalent circuit model is used to study the antenna impedance behavior. Number of simulations has been done for analyses and corresponding value of capacitors, inductors and resistors (used in Fig. 4 by hit and trial method) is determined. According to the foster reactance theorems antenna impedance should move about the smith chart in a certain direction. Typically the antenna impedance moves or shifts on the smith chart in clockwise direction with the increase in the Fig. 4. Equivalent circuit model of the proposed antenna. value of frequency. When the antenna impedance transition is from -ive (capacitance) to +ive (inductive) reactance. +ive impedance transitions is considered. Similarly, for the antenna proposed antenna is shown in Fig. 3. If we follow from impedance changing from +ive (inductive) to -ive (capaci- lower frequency (3.1 GHz) → higher frequency (23.5 GHz) tance) reactance is considered –ive and impedance transi- shown in Fig. 3 the first higher resonance point has been tions will also be reflected as negative) in a finite frequency observed at around 7.8 GHz which is caused by the parallel span [15, 17, 26, 27]. The simulated smith chart impedance (Capacitance) C=4.27 pf and (Inductance) L=0.68 nH. Then, of equivalent circuit model is shown in Fig. 5. Which is an antiresonance X'(w) at about 7.8 GHz is noticed which moving about the clockwise direction, even in the frequency might be introduced by adding psi (ѱ) shaped stubs in the ranges of negative reactance. Foster reactance theorem [15], radiating patch (as presented in Fig. 1). Since the antireso- concludes that the impedance moves anticlockwise or clock- nance X'(w) has a relative high capacitance value above the wise about the smith chart with increase in frequency. resonant frequency. The second resonance peak at around 9.6 According to this fact proposed antenna’s equivalent model GHz is determined by C = 8.54 pf, L = 1 nH and (Resis- is producing correct output. tance) R = 99 Ω. Similarly, the ground plane with a length of The study of impedance variation behavior can be useful 2.95 mm has chosen on which DGS techniques (Slots of for optimization of antenna in RF front end transceiver con- multiple widths and lengths) had been employed to achieve taining applications. higher bandwidth. Ground plane changes the impedance of antenna especially in region between 15 to 23 GHz (observed from simulated parametric analysis of antenna). V. RESULTS AND DISCUSSIONS This effect may be due to travelling of current along the all edges of the ground [16]. It has the ability to increases the The antenna parameters are optimized using the field antenna inductance [22]. solver software ANSYS HFSS ver.19 and CST. Fig. 6 shows According to the foster reactance theorem at near resonance the fabricated proposed antenna. The simulated and mea- ranges general antenna behaves as series RLC circuits and sured results of reflection coefficients |S11| ≤ -10 dB is given

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Fig. 6. Manufactured proposed antenna (a) front side and (b) back side.

Fig. 5. Impedance (red line) of the proposed antenna depicted on smith chart (obtained from ADS tool). in Fig. 7. This parameter was measured using an Agilent N5230A vector network analyzer. The simulated and measured result indicates that the antenna has accomplished a very wide bandwidth of 20.4 GHz, ranging from 3.1 to 23.5 GHz. The differences between the simulated and measured Fig. 7. Simulated and measured reflection coefficients vs. frequency. reflection coefficient |S11| results are probably due to the minor differences in substrate properties of the fabricated antennas as well as fabrication tolerances. Since the size is very small, the connectors were hand soldered and placed. The quality factor of the proposed antenna is determined from the Eqs. (14) and (15) by assuming antenna is well tuned. First, the measured VSWR is used to determine FBWv, where the VSWR = 2 is considered. The fractional 2:1 matched VSWR bandwidth is determined from frequency points in Eq. (17). The proposed antenna’s feed line characteristics impedance is deliberated equal to the antenna’s feed point resistance. Fig. 8 gives the approximation quality factor of the proposed antenna by using two different methods, Eqs. (14) and (15). The wide frequency range of 3.1–20 Fig. 8. Quality factor of the proposed antenna determined using the two GHz, covering the ranges of resonance and antiresonance is methods, (14) and (15). used. Since, Eq. (14) deals with antenna impedance properties and Eq. (15) works with VSWR. Fig. 8 presents the quality factor is in good agreement varying between 1–10 Additionally, it is related to directivity and gain of the over frequency 3–20 GHz. patch antenna. The simulated radiation efficiency and gain of Radiation efficiency εr of the antenna is defined as the the proposed antenna is shown in Fig. 9. Radiation efficiency ratio between radiated power to the input power (18). It also is varying between 88% to 99% for entire covered band- considers the conduction and dielectric losses. width. Similarly, gain is another important parameter in the designing of wideband microstrip patch antennas. The gain P ------radiated- εr = . (18)of the proposed antenna varies from -2 to 6.8 dB for the fre- Pinput quency band 3.1 to 23.5 GHz. The simulated gain and radia-

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observed at lower frequencies. Simulated and measured radiation patterns are almost similar.

A. Application

The proposed antenna can be used for microwave imaging system that contains antenna arrays enclosed to breast phan- tom. Breast cancer is the most common cancer among women leading huge death rate. Even though breast cancer treatment advancement have been in research, because the effectiveness of conventional breast cancer screening methods are questionable. Fig. 9. Simulated radiation efficiency and peak gain. Recent studies proved that X-ray mammography screening shows suspicious areas where no malignancy exists (≤20% of biopsied growth cancerous cell by a mammogram are identi- fied as malignancies). Furthermore, radiologists concluded that X-ray mammography images can manage to show 15% to 25% of cancer cells. The ongoing X-ray mammography process is severely uncomfortable specially; the imaging plates use can cause bruising in the breasts cells [18]. Use of microwave imaging in breast cancer detection is referred as “breast tumor radar” whose implementation involves computer; cou- pled to single antenna or an array of small antennas beaming 6 GHz pulsed microwaves [25]. Basically healthy breast tissue appears transparent or clear to microwave radiation but breast tumor holds more watery cell which can cause the scattering of microwaves beamed. The antenna can detect the scattered microwaves observable through network analyzer. The real Fig. 10. Simulated group delay (ns) and front to back ratio vs frequency. time data can be explored to construct a three-dimensional image showing both size and location of the tumor. Fig. 12 tion efficiency are attained by using HFSS only. Fig. 10 shows the overview diagram of use of microwave image describes the simulated group delay and forward to back detection systems. The process includes the transmitting ratio behavior of proposed antenna. The forward gain dra- microwave energy from (transmitting) first probing antenna at matically increases effective radiated power in a chosen the surface of breast inwardly through breast tissue, and the direction while the front to back ratio dramatically reduces receiving reflected microwave signal at the probe of second interference from signals to the antenna’s backside. In this antenna from the surface of breast. case, the antenna has varying front to back ratio from 4 to 18 The position of the transmitting antenna can be computed dB. The group delay signifies that the shape of the electrical by using position location techniques. Based upon radiation pulse transmitted should not be distorted by the antenna. For energy pattern, an image of the breast tissue’s tumor can be good pulse transmission and for the effective antenna verifi- investigated. In other words microwave transmitting antenna cation, the time domain response should be suitable and the configured to defective portions of breast to transmit energy. group delay must have very small or of constant value in the In case of antenna array systems each of the transmitting entire bandwidth during transmission. Fig. 10 indicates antennas must be moveable to provide the boarded inside group delay factor is varying from 0 to 1 ns. view. Fig. 11 presents the simulated and measured radiation pat- Table 2 provides the performance comparison of the pro- terns of the proposed antenna in E-plane or YZ-plane (ϕ = 0) posed antenna compare to earlier published papers. It proofs and H-Plane or XZ-Plane (ϕ = 90) at different resonance fre- that the proposed antenna has small size along with maxi- quencies. The radiation pattern is measured by using mum bandwidth. Proposed antenna is 80% smaller is size as anechoic chamber. At lower frequencies the radiation pattern compare with Ref [1], 30.5% small is size as compared with is omnidirectional in XZ-Plane while “8” like pattern or Ref [8], and 50% smaller is size compared from Ref [9]. In close to directional pattern is observed in YZ-Plane. How- future, we are planning to manufacture this proposed antenna ever, at 14 GHz or even higher frequencies, antenna converts and integrate with the hardware of the image detection to directional and additional back lobe appears. This is not which can lead to compact system design.

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Fig. 11. Simulated radiation pattern at (a) 4.9 GHz, (b) 9.8 GHz, (c) 14 GHz and measured radiation pattern at (d) 4.9 GHz, (e) 9.8 GHz, (f) 14 GHz resonance frequencies of the proposed antenna.

Table 2. Performance comparison of proposed antenna [1] [8] [9] Proposed Overall size 35×22 18×12 30×10 15×10

S11 ≤ -10 dB (GHz) 3.1–16.3 3.09–18.31 3.1–10.6 3.1–23.5 FBW (%) 136 140 112.1 153.3 BW (GHz) 13.2 15.2 7.5 20.4 Area (mm2) 770 216 300 150 BWR 5.25:1 5.92:1 3.42:1 7.58:1

Fig. 12. General setup of patch antenna proposed for image detection. observing the impedance reactance behavior. Smith chart is also shown which proves shift of impedance in clockwise direction for higher bandwidth. Antenna’s quality factor is VI. CONCLUSION calculated by using two different methods and a good approximation in results has been observed. The gain of the In this article, compact patch antenna containing multi-res- antenna is up to 6.8 dB having group delay value around 1 onance DGS patch antenna has been proposed. The proposed ns. It displays good omnidirectional radiation pattern at antenna is very compact having a size of 15 mm×10 mm. lower frequency having simulated radiation efficiency ≥88% Theory of degenerated foster canonical form is elaborated across the entire bandwidth. Lastly, an overview of printed and antenna equivalent circuit model has been proposed by patch antenna for imaging systems has been explained.

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Iram Nadeem received her M.S. in Telecommunication Engineering (Major: Optical Fiber Communication) and her B.S. in Electrical Engineering from the University of Engineering and Technology (UET), Taxila , Pakistan in 2014 and 2010, respectively. She achieved her M.Eng. degree in Information and Communication Engineering from Chosun University, Korea, in 2018. Currently, she is working as a research associate in the Department of Information and Communication Engineering, Chosun University. She had worked as Lecturer and Lab Engineer in different engineering institutes of Pakistan. Her research interests include optical fiber communication, microwave and satellite communication, UWB, MIMO antenna design, and WPT.

Dong–You Choi received his B.S., M.S., and Ph.D. degrees from the Department of Electronics Engineering, Chosun University, Gwangju, Korea, in 1999, 2001, and 2004, respectively. Since 2006, he has been professor and researcher in Department of Information and Communication Engineering, Chosun University, Korea. His research interests include rain attenuation, UWB antennas, mm-wave antenna design, wave propagation & microwave and satellite communication. He is a member of the IEEE, IEICE, JCN, KEES, IEEK, KICS, and ASK.

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