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

Transcription

1 Journal of Scientific & Industrial Research Vol. 77, May 2018, pp Radiation Performance of Log Periodic Koch Fractal Antenna Array with Different Materials and Thickness V Dhana Raj 1 *, A Mallikarjuna Prasad 2 and G M V Prasad 3 *1,2 Department of Electronics and Communication Enggineering, JNTUK, Kakinada, A. P, India 3 Department 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 An antenna is often explicated as a transformation structure between the free space and a guiding device. In 1950, Isbell et al. have first introduced the log periodic antenna and depicted various curves relating σ, τ and antenna gain for the LPDA antenna design 1. In order to overcome interference issues existing in wireless communications systems due to overlapping with that of the UWB systems, introducing Multiple notch bands are helpful 2. For Wireless communications, because of their good bandwidth, stable gain over the entire frequency range, simple architecture, and ease of fabrication the periodic log antennas are suitable 3. The Printed Log Periodic Dipole Array (PLPDA), conjointly radiates in an endfire direction inside ultra-wide waveband. With the multiple resonance properties, its data rate increased by increasing the amount of the dipole components. Miniaturization has become the primary necessary objective at a frequency(rf) 4. Currently, the needs of a communication system with a wide bandwidth range are large enough. Enhancement of the gain and bandwidth of the antenna also be subject to on the shape and size of the patch, reported in earlier studies 5. Wide bandwidth achieved by introducing *Author for Correspondence profvdr@yahoo.com fractal concepts in log periodic antennas to realize communication, reported in earlier literature 6. PLPDA design considerations In the proposed PLPDA, 10 elements were considered. The layout of the proposed antenna structure is shown in Figure 1(a). Three important measures required for the designing procedure of the Log Periodic Dipole Array. The scaling factor, τ = 0.61, spacing factor, σ = and number.of elements, N=10 is chosen. The dimension of the longest dipole L_1 computed using the formula, L_1=λ_me/4, which responses to the lowest resonance frequency f min, where me is the longest operating wavelength. The value of λ_me is determined using the formula, where c is the velocity of light and ε_eff is effective dielectric constant by which propagation delay is estimated. The relation between the spacing factor and the length of the dipoles are related by, S_ (n+1) =4σL_n, Where, n=1, 2, 3, 9 Finally, once the scale of the lengthiest dipole element determined, the space of different dipoles often determined in terms of the subsequent relationship: L_ (n+1)/l_n =W_ (n+1)/w_n =τ

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

3 278 J SCI IND RES VOL 77 MAY 2018 dielectric materials and thicknesses. Low dielectric constant materials have exhibited good performance characteristics. In the below Table 2, the comparative analysis is given for PLPDA and PLPKDA with FR4 and RT/Duroid5880 substrates with a thickness of 63mil. The radiation characteristics are observed to be end-fire with broadband characteristics. From the radiation pattern, it was observed that for ordinary PLPDA a small back lobe is observed, by using Koch fractal dipole array the back lobe is almost suppressed. The gain of the antenna increases with the thickness of the substrate is as observed from the Table 3 and radiation patterns of the proposed antennas with different dielectric materials of 63mil thickness are shown in Figure 3. For the perfect design of antenna at microwave or higher frequencies, tolerance of the substrate is crucial. It is found that RT/Duroid 5880 given a better response. The performance of the both PLPDA and PLPKDA on different materials investigated and observed a consistent performance exhibited by the RT/Duroid 5880 material with a gain of 6.4dB and wideband ranging from 3.2 GHz to GHz with good reflection coefficient performance. Its bandwidth is GHz for PLPDA and multi-band response from GHz, GHz, GHz and GHz for PLPKDA. The proposed antenna is suitable for the S, C, X and Ku bands. Practically the log periodic antenna with FR4 substrate operates from 3.88GHz to 13.71GHz and log periodic antenna with RT/DUROID 5880 substrate operates from 3.02GHz to 13.89GHz. Printed Log periodic antenna with Koch fractal antenna with FR4 substrate operates from 2.77GHz to 10.25GHz and with RT5880 substrate operates from 2.81GHz to 14GHz.It is apparent from the Table 2,the radiation performance of the antenna degrades at larger dielectric constant. The radiation performance of PLPDA and PLPKDA implemented on the RT/Duroid 5880 material of different thickness are shown in Figure 2(a) to Figure 2(h).The gain performance of the proposed antennas implemented 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 r = 4.4 = 0.02 RT5880 r = 2.2 = FR4 r = 4.4 = 0.02 RT5880 r = 2.2 = Sim./Expt. Sim Expt. Sim. Expt. Sim. Expt. Sim. Expt. No. of Bands Return Loss VSWR Resonant frequency Frequency Range %BW Table 3 Comparison of Gain of PLPDA and PLPKDA with different substrate materials and thickness Substrate material Gain PLPDA PLPKDA Mica( r = 5.7), h=63mil Glass ( r = 5.5), h=63mil FR4 ( r = 4.4), h=63mil Arlon ( r = 3.58), h=63mil RT5870 ( r = 2.33), h=63mil RT5880 ( r = 2.2), h=31mil RT5880 ( r = 2.2), h=62mil RT5880 ( r = 2.2), h=63mil Teflon ( r = 2.1), h=63mil

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

5 280 J SCI IND RES VOL 77 MAY 2018 Fig. 3 Radiation patterns of log periodic antennas with different dielectric substrate materials, h=63mil Fig. 4 Measured Far-field for both E and H of log periodic dipole array with Koch fractal, RT5870 with thickness 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 (S 11 ), 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 different fractal geometries to improve the bandwidth, gain and better VSWR of the antenna.

6 DHANARAJ et al.: RADIATION PERFORMANCE OF LOG PERIODIC KOCH FRACTAL ANTENNA ARRAY 281 References 1 DuHamela R H & Isbell D E, Broadband Logarithmically Periodic Antenna Structures, IRE Nat Conv Rec, Part I(1957) Chao Y, Wei H, Leung C, Guohua Z, Chen Y, Wei Q & Zhen Q K, Ultra-wideband Printed Log-Periodic Dipole Antenna with Multiple Notched Bands, IEEE Trans on Ant and Prop, 59(2011) Hsu H T & Huang T J, A Koch-shaped log-periodic dipole array (LPDA) antenna for universal ultra-high frequency (UHF) radio frequency identification (RFID) handheld reader, IEEE Trans on Ant and Prop, 61(2013) Giovanni A C, Paolo M, Giuseppe M & Giorgio M, Design of a printed log periodic dipole array for ultra-wideband applications, Prog in Electromag Res, 38(2013) Srija D, Poulami S, Sushanta S, Debasree S, Sushanta B & Partha P S, Microstrip array antenna with wideband and high gain, Ind Jour Pure App Phy, 54(2016) Amindyasari R A & Achmad M, Ultra high-frequency log periodic antenna for digital TV application, IEEE Int Conf on Wire and Tele, 2(2016)