Radiation Performance of Log Periodic Koch Fractal Antenna Array with Different Materials and Thickness

Journal of Scientific & Industrial Research Vol. 77, May 2018, pp. 276-281

V Dhana Raj1*, A Mallikarjuna Prasad2 and G M V Prasad3 *1,2Department of Electronics and Communication Enggineering, JNTUK, Kakinada, A. P, India 3Department of Electronics and Communication Enggineering, BVCITS, Amalapuram, A. P, India

Received 13 February 2017; revised 19 September 2017; accepted 22 January 2018

A frequency independent Printed Log Periodic Dipole antenna (PLPDA) with and without fractals for different materials and thickness is proposed for UWB applications. The impedance bandwidth of PLPD without fractal for FR4 of 4.71GHz to 9.99GHz. Similarly, for the RT/Duroid, the impedance bandwidth of 3.09GHz to 12.13GHz with VSWR less than two is achieved. The radiation patterns for different combinations are also observed to be an end-fire radiation pattern. In this paper, the first iteration is proposed, the parametric and performance observations are also made for different thickness (63mil, 62mil, and 31mil) of the dielectric substrate. Antennas are fabricated, and its performance is authenticated using vector network analyzer (E5071C) to carry out return loss and VSWR measurements. The obtained results are insensible agreement with the theoretical results.

Keywords: UWB Ultra Wide Band , S-parameter, VSWR Voltage Standing Wave Ratio, FR4, RT/Duroid, Koch fractal

Introduction fractal concepts in log periodic antennas to realize An antenna is often explicated as a transformation communication, reported in earlier literature6. structure between the free space and a guiding device. In 1950, Isbell et al. have first introduced the log PLPDA design considerations periodic antenna and depicted various curves relating In the proposed PLPDA, 10 elements were σ, τ and antenna gain for the LPDA antenna design1. considered. The layout of the proposed antenna In order to overcome interference issues existing in structure is shown in Figure 1(a). Three important wireless communications systems due to overlapping measures required for the designing procedure of the with that of the UWB systems, introducing Log Periodic Dipole Array. Multiple notch bands are helpful2. For Wireless  The scaling factor, τ = 0.61, spacing factor, σ = communications, because of their good bandwidth, 0.155 and number.of elements, N=10 is chosen. stable gain over the entire frequency range, simple  The dimension of the longest dipole L_1 computed architecture, and ease of fabrication the periodic log using the formula, L_1=λ_me/4, which responses 3 antennas are suitable . The Printed Log Periodic to the lowest resonance frequency fmin , where me Dipole Array (PLPDA), conjointly radiates in an end- is the longest operating wavelength. fire direction inside ultra-wide waveband. With the  The value of λ_me is determined using the multiple resonance properties, its data rate increased formula, where c is the velocity of light and ε_eff by increasing the amount of the dipole components. is effective dielectric constant by which Miniaturization has become the primary necessary 4 propagation delay is estimated. objective at a frequency(RF) . Currently, the needs of  The relation between the spacing factor and the a communication system with a wide bandwidth range length of the dipoles are related by, are large enough. Enhancement of the gain and S_ (n+1) =4σL_n, Where, n=1, 2, 3,…9 bandwidth of the antenna also be subject to on the  Finally, once the scale of the lengthiest dipole shape and size of the patch, reported in earlier element determined, the space of different dipoles studies5. Wide bandwidth achieved by introducing often determined in terms of the subsequent —————— relationship: *Author for Correspondence E-mail: [email protected] L_ (n+1)/L_n =W_ (n+1)/W_n =τ DHANARAJ et al.: RADIATION PERFORMANCE OF LOG PERIODIC KOCH FRACTAL ANTENNA ARRAY 277

Fig. 1— a)Log periodic antenna Structure b) Koch curveFractal c) Simulated PLPDA d) Simulated PLPKDA e) Fabricated PLPDA on FR4 f) fabricated on RT/Duroid 5880 g) PLPKDA on FR4 h) PLPKDA on RT/Duroid 5880

Table 1 shows the dimension of the proposed Table 1—Physical dimensions of the PLPDA PLPDA ParameterValue(mm)Parameter Value(mm) ParameterValue(mm)

L1 16 W1 2.7 S1 6.35 Design specifications of Printed Log Periodic Dipole Antenna (PLPDA) L2 9.6 W2 2.1 S2 9.7 The following dimensions are used in the design of L3 5.9 W3 1.3 S3 6.3 PLPDA. Operating frequency (f_o) =4.5 GHz, Height L4 3.6 W4 0.8 S4 3.85 of the substrate (h) = 1.6003mm, Dielectric constant L5 2.2 W5 0.5 S5 2.35 (ε_r) =2.2, Loss tangent (δ) =0.0009, and the half L6 1.3 W6 0.3 S6 1.5 angle of the structure, vertex angle, α=2〖tan〗^ (-1) ((1-τ)/4σ) =〖32.8258〗^o. The RT-Duroid with L7 0.8 W7 0.2 S7 0.85 double-sided copper clad is used as substrate material. L8 0.5 W8 0.2 S8 0.6 L9 0.3 W9 0.2 S9 0.4 Design issues of Printed Log Periodic Koch Dipole Antenna L10 0.2 W10 0.2 S10 0.3 (PLKDA) well as conformal antennas are considered. The HFSS With the fractal antenna as the dipole, the simulated and fabricated antennas are shown in miniaturization is achieved. Using HFSS simulation, Figure1(c) and Figure 1(d). The fabricated antennas the Koch curve is generated which replace the are shown in Figure 1(e) to Figure 1(h). intermediate segment by one-third of the line with a bent giving rise to original one-third span.Using this Results further miniature is achieved shown in Figure 1(b). In the proposed work, the analysis is made for Different dielectric materials such as Teflon, mica, ordinary log periodic and Koch fractal log periodic glass FR4, RT/Duroid 5880 and RT/Duroid 6006 are antennas for various frequency bands of operation and used with a diversity of mechanical, thermal and observed an increase in percentage band width and electrical characteristics are appropriate for planar as gain. In addition, the work is extended to different 278 J SCI IND RES VOL 77 MAY 2018

dielectric materials and thicknesses. Low dielectric log periodic antenna with FR4 substrate operates from constant materials have exhibited good performance 3.88GHz to 13.71GHz and log periodic antenna with characteristics. In the below Table 2, the comparative RT/DUROID 5880 substrate operates from 3.02GHz analysis is given for PLPDA and PLPKDA with FR4 to 13.89GHz. Printed Log periodic antenna with Koch and RT/Duroid5880 substrates with a thickness of fractal antenna with FR4 substrate operates from 63mil. The radiation characteristics are observed to be 2.77GHz to 10.25GHz and with RT5880 substrate end-fire with broadband characteristics. From the operates from 2.81GHz to 14GHz .It is apparent from radiation pattern, it was observed that for ordinary the Table 2 ,the radiation performance of the antenna PLPDA a small back lobe is observed, by using Koch degrades at larger dielectric constant. The radiation fractal dipole array the back lobe is almost performance of PLPDA and PLPKDA implemented suppressed. The gain of the antenna increases with the on the RT/Duroid 5880 material of different thickness thickness of the substrate is as observed from the are shown in Figure 2(a) to Figure 2(h).The gain Table 3 and radiation patterns of the proposed performance of the proposed antennas implemented antennas with different dielectric materials of 63mil Table 3—Comparison of Gain of PLPDA and PLPKDA with thickness are shown in Figure 3. For the perfect different substrate materials and thickness design of antenna at microwave or higher frequencies, Substrate material Gain tolerance of the substrate is crucial. It is found that RT/Duroid 5880 given a better response. The PLPDA PLPKDA 4.76 5.82 performance of the both PLPDA and PLPKDA on Mica( r = 5.7) , h=63mil 4.66 5.65 different materials investigated and observed a Glass ( r = 5.5) , h=63mil consistent performance exhibited by the RT/Duroid 3.84 4.07 FR4 ( r = 4.4) , h=63mil 5880 material with a gain of 6.4dB and wideband Arlon (  = 3.58) , h=63mil 5.68 5.14 ranging from 3.2 GHz to 13.89 GHz with good r RT5870 (  = 2.33) , h=63mil 6.51 6.17 reflection coefficient performance. Its bandwidth is r 5.92 5.61 10.69 GHz for PLPDA and multi-band response from RT5880 ( r = 2.2), h=31mil 6.45 6.18 2.9-4.8GHz, 5.7-6.3GHz, 7.2-8.2GHz and 10.7- RT5880 ( r = 2.2), h=62mil 6.46 6.21 13GHz for PLPKDA. The proposed antenna is RT5880 ( r = 2.2), h=63mil suitable for the S, C, X and Ku bands. Practically the 6.28 6.22 Teflon ( r = 2.1) , h=63mil Table 2—Comparison of PLPDA and PLPKDA with different materials Antenna Printed Log Periodic dipole Antenna Printed Log Periodic dipole Antenna with Koch Fractals Substrate FR4 RT5880 FR4 RT5880 r = 4.4  = 0.02 r = 2.2  = 0.0009 r = 4.4  = 0.02 r = 2.2  = 0.0009 Sim./Expt. Sim Expt. Sim. Expt. Sim. Expt. Sim. Expt. No. of Bands 4 4 1 1 3 3 3 3 Return -12.71 -10.82 -31.42 -34.5 -36.90 -34.42 -21.63 -30.05 Loss -18.58 -28.62 -25.87 -28.69 -13.42 -30.06 -18.22 -20.27 -19.94 -20.28 -26.36 -36.03 -18.21 -24.71 VSWR 1.60 1.81 1.29 1.02 1.35 1.04 1.18 1.1 1.27 1.08 1.36 1.08 1.54 1.03 1.28 1.20 1.98 1.23 1.10 1.05 1.28 1.12 Resonant frequency 5.04 5.19 5.6 5.19 6.08 6.09 4.16 3.8125 7.0 6.96 8.44 8.23 7.58 7.625 9.9 10.19 11.97 11.86 12.29 12.25 11.9 12.19 Frequency 4.71-5.32 4.96-5.41 3.2-13.89 3.09-12.13 2.56-6.62 2.43-6.69 2.88-4.91 2.81-4.56 Range 6.55-7.40 6.51-7.38 7.90-10.47 7.89-10.27 7.13-8.27 6.0-9.19 8.10-10.59 7.98-10.64 11.43-14 11.41-14 10.68-13.04 11.81-14 11.35-14 11.32-14 %BW 12.10 8.67 190.54 174.18 66.77 69.95 48.79 45.93 12.14 12.5 30.45 28.92 15.83 41.84 25.15 26.1 21.47 21.83 19.20 17.88 22.27 21.98 DHANARAJ et al.: RADIATION PERFORMANCE OF LOG PERIODIC KOCH FRACTAL ANTENNA ARRAY 279

Fig. 2—Thickness influence on the proposed antenna structures fabricated on RT 5880 material

on several dielectric substrate materials various a significant reduction in back lobe thereby increased thickness (h=31mil,62mil, and 63mil) are furnished in FBR is observed with the introduction of fractals. The Table 3. The Radiation patterns of designed antennas measured radiation pattern of the Log periodic Koch with different dielectric substrate materials with dipole array (LPKDA) is presented below with Vertical thickness, h=63 mil are shown in Figure 3,4. There is and Horizontal polarizations using anechoic chamber. 280 J SCI IND RES VOL 77 MAY 2018

Fig. 3—Radiation patterns of log periodic antennas with different dielectric substrate materials, h=63mil

Conclusions The systematic design procedure of a printed log periodic dipole antenna and log periodic Koch fractal dipole has been presented. The designed antennas were fabricated, and the features are measured to validate its performance like Return Loss (S11), VSWR, Radiations patterns, and gain. The advantages of these antennas are that the compact size and wide bandwidth better than the conventional log periodic antennas. Consequently, it is interested in various applications like X-band and Ku-band that are mainly used for satellite applications. The radiation patterns for different thickness and dielectric combinations are simulated and measured, and good performance with end-fire characteristics is observed. In future, the work can be extended for higher iterations and for

Fig. 4—Measured Far-field for both E and H of log periodic different fractal geometries to improve the bandwidth, dipole array with Koch fractal, RT5870 with thickness 63mil gain and better VSWR of the antenna. DHANARAJ et al.: RADIATION PERFORMANCE OF LOG PERIODIC KOCH FRACTAL ANTENNA ARRAY 281

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