Comparative Study of Pentagon Shaped Patch Antenna with Different Substrates Operating at WLAN Frequency

 

K. Karthika*, T. Jaspar Vinitha Sundari, S. David

Assistant Professor, Department of Electronics and Communication Engineering, Kumaraguru College of Technology, Coimbatore- 641048, Tamilnadu, India.

 

ABSTRACT:

Microstrip antenna finds a great attention for the past four decades due to their low profile, low cost and ease of fabrication. This work presents a design and analysis of pentagon shaped patch antenna operating at 5.8GHz (WLAN frequency). Substrate plays a vital role in the design antenna in terms of Miniaturization and bandwidth broadening. The comparative study is made by choosing different substrates such as FR4 and Roger in the design of proposed antenna. The effect of changing substrate material for the given antenna is observed in term of its gain, directivity, return loss, VSWR and Bandwidth. Size of the antenna is 25×25×1.6 mm³ makes it convenient for wireless communication systems. High Frequency Structure Simulator (HFSS) software is used to simulate the proposed antenna design.

 

 

 

INTRODUCTION:

The recent development of wireless communication system has created a need for compact, high gain microstrip patch antenna. MSA are very common antenna due to their low profile, low cost, light weight and many more. In this paper, a pentagon shaped microstrip antenna is designed with one probe feed and it is designed to operate at WLAN frequency (5.8 GHz). Characteristics of an antenna such as radiation, efficiency, bandwidth, input impedance, mutual impedance, and radiation pattern can be optimized by a choice of substrate relative permittivity and thickness value [1]. Rectangular patch antenna requires multiple feeds to get circular polarizations whereas the pentagonal patch antenna provides circular polarization with only one feed [2].

 

The radiated power is sensitive to the dimensions of the substrate and to control the radiation and maximize the radiated power, a thin substrate is preferred [3]. Proper selection of substrate will improve gain and efficiency of an antenna without shifting the resonant frequency significantly [4]. An electromagnetic property of magnetic substrate has effect on antenna’s gain [5]. For better impedance matching, antenna is fed with a 50 ohm coaxial cable [6]. Thus the designed antenna which is operating at 5.8 GHz is chosen to be a pentagonal patch antenna and fed with a 50 ohm coaxial cable for better impedance matching. Roger 4350 results in maximum efficiency but the size and price are the issues in it. FR- 4 substrate is an optimal solution but it sometimes requirement dependent [7]. By incorporating axially symmetric distribution of shorting pillars, the isolation between feeding probes is increased [8].

 

Structure with superstrate layer has strong effect on the resonant frequency and half-power bandwidth of the superconducting rectangular patch than that of the structure without superstrate layer as both the thickness and permittivity of the superstrate increase [9]. Though MSA finds lots of advantages, there are some limitations such as low gain. Numerous techniques have been advised to apply on patch antennas to improve its narrow bandwidth and gain. Here the comparative study is made between pentagon shaped patch antenna operating at WLAN frequency (5.8 GHz) using FR4 substrate [10] and Roger substrate.

 

ANTENNA DESIGN AND ANALYSIS:

When compared to rectangular patch antenna, pentagonal microstrip patch antenna offers better performance. Both linear and circular polarizations will be supported by pentagon antenna. To get circular polarizations, rectangular patch antenna requires multiple feeds whereas the pentagonal patch antenna provides circular polarization with only one feed. The geometry of regular pentagonal shape is shown in Fig 1.

 

Fig. 1: Geometry of regular pentagonal shape [1]

 

The relationship between the circles (r1) to the side arm of the regular pentagon (r2) is given in formula (1.1)

 (1.1)

 

side arm of the pentagon is calculated using formula (1.2)

(1.2)

 

In the derivation of the formula (1.1), the patch is assumed to be a resonant cavity with perfectly conducting side walls. The resonant frequency of the dominant as well as for the higher order modes can be calculated from the formula given below

 (1.3)

 

where   are the zeros of the derivative of the Bessel function  of the order n, as is true for TE mode circular waveguides, however for the lowest order modes     

 (1.4)

 

Using formulae 1.1 and 1.2, the proposed pentagon shaped patch is designed and the designed parameters are given in Table 1.

 

Table 1: Design Specifications

Parameters	Pentagonal Antenna with FR4 Substrate [1]	Pentagonal Antenna with Roger Substrate
Side arm length	8.9 mm	7.8 mm
Dielectric Constant	4.4	3.48
Thickness of Substrate          1.6 mm                                1.6 mm
Loss Tangent	0.002	0.002
Centre frequency	5.8 GHz	5.8 GHz
Feed location	Xf =1 mm, Yf =0.7 mm	Xf =1 mm, Yf =0.7 mm
Coaxial cable dimension	Inner radius: 0.5 mm Outer radius: 0.7 mm	Inner radius: 0.5 mm Outer radius: 0.7 mm

 

Different substrate has different dielectric constant. Dielectric constant of Roger is 3.48 whereas dielectric constant of FR4 is 4.4. Variation in dielectric constant will have effects in antenna’s parameter. By changing it, the size of an antenna gets varied. The size of a designed antenna with Roger substrate is 20×20×1.6 mm³.

 

Fig. 2: Geometry of antenna using Roger substrate at 5.8 GHz

 

Based on the calculated parameters shown in table 1, the pentagon shaped patch antenna is designed and simulated. The front view of proposed antenna is shown in Fig 2.

 

RESULTS AND DISCUSSION:

HFSS software is used to simulate the pentagon shaped antenna. Different parameters like return loss, gain, VSWR and directivity are measured using that software. The parameter return indicates the amount of power is reflected back to the antenna. The designed antenna with Roger substrate exhibits the return loss of -25.99 dB and it is shown in Fig 3.

 

SWR is defined as the ratio of the maximum radio-frequency (RF) voltage to the minimum RF voltage along the line. VSWR values between 1 to 2 indicates that the antenna has better impedance matching. Fig 4.shows the VSWR of the designed antenna with Roger substrate and it is 1.10

 

Fig. 3: Return loss of the pentagon shaped antenna with Roger substrate

 

Fig. 4: VSWR of the pentagon shaped antenna with Roger substrate

 

The measure of the ability of the antenna to direct the input power into radiation in a particular direction is defined by the term Gain and is measured at the peak radiation intensity. Fig 5. Shows the gain of the antenna with Roger substrate and it is 5.93 dB.

 

Fig. 5: Gain of the pentagon shaped antenna with Roger substrate

 

Fig 6. Directivity of the pentagon shaped antenna with Roger substrate

 

Measure of the concentration of radiation in the direction of the maximum is termed as Directivity. Fig 6. shows the directivity of the antenna with Roger Substrate and it is 5.97 dB.

 

Table 2: Comparison of Results

Parameters	With FR4 Substrate [1]	With Roger Substrate
Return Loss	-44.03 dB	-25.99 dB
VSWR	1.0126	1.10
Gain	3.8 dB	5.93 dB
Directivity	5.5 dB	5.97 dB

 

Based on the simulation results the comparison is shown in Table 2. From this it observed that, by using dielectric material with low dielectric constant, gain and directivity gets increased and there is a significant change in return loss, VSWR and bandwidth.

 

CONCLUSION:

There are number of substrates being used in the design of microstrip patch antenna. The pentagon shaped patch antenna with Roger substrate is designed to operate at 5.8 GHz. The corresponding return loss for the antenna is -25.99 dB and VSWR is 1.10 while the resulted gain is 5.93 dB and the directivity is 5.97 dB. By comparing the obtained results with results of pentagon antenna with FR4 substrate, the size of an antenna gets reduced and parameters like gain and directivity are better when using the substrate Roger. Return loss, VSWR and Bandwidth are comparatively good with FR4 substrate. Thus increasing the dielectric constant results in decreased gain and directivity.

 

ACKNOWLEDGEMENT: 

The authors are grateful to the authorities of Kumaraguru College of Technology, Coimbatore for the facilities.

REFERENCES:

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8.       Yinting Liu, "Multiband Antenna for Satellite Navigation System", IEEE Antennas and Wireless Propagation Letters, vol. 15, pp. 1329-1332, 2015. 

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Received on 29.07.2017                             Accepted on 30.09.2017        

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