A Wideband suspended Microstrip Patch Antenna

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International Journal of Application or Innovation in Engineering& Management (IJAIEM)Web Site: www.ijaiem.org Email: [email protected]

Volume 4, Issue 11, November 2015 ISSN 2319 - 4847

Volume 4, Issue 11, November 2015 Page 95

ABSTRACT

In this paper we propose a circularly polarized (CP) microstrip antenna on a suspended substrate with a coplanar capacitive

feed and a slot within the rectangular patch. The antenna has an axial ratio bandwidth (< 3 dB) of 10.66%. The proposed

antenna exhibits a much higher impedance bandwidth of about 32.12% (S11 < −10 dB) and also yields return loss better

than −15 dB in the useful range of circular polarization. It has been found that this antenna offers higher directivi ty with

good radiation properties required for GPS system and mobile applications. The resulting circular polarization bandwidth (with

axial ratio ≤ 3 dB) has been found to meet that required for this application. The proposed antenna possesses a high gain of 6.0

dB overall the GPS (1575 MHz) and mobile (1800/1900 MHz) operation.

Keywords: GPS Microstrip Antenna, broadband antenna, suspended antenna, Circular Polarization, Axial Ratio.

I.INTRODUCTION

Although microstrip antennas in their basic form normally provide linear polarization, circular polarization (CP)

operation may be obtained by certain modifications to the basic antenna geometry and/or feed. These modifications

include adjusting the dimensions of the basic patch with one or more feeds, trimming the corners of a square patch,

feeding the patch at adjacent sides, feeding the patch (rectangular) from its corner along the diagonal, and cutting a slot

inside the patch [1]. Several such CP microstrip antennas are available in the literature. For example the antenna

reported by [2] yields an axial ratio (AR) bandwidth of 6.3% with straight feed and increases up to 14.1% with an L-

probe feed. This is a corner trimmed CP antenna with a U-shaped slot cut on the patch to ensure wide impedance bandwidth. There have been other works focusing on reducing the size of the antenna with a modest bandwidth for

circular polarization operation [3]. On the other hand, antennas reported by [4] and [5] offer AR bandwidths of 14%

and 23% respectively. However, these consist of stacked (multiple metal/dielectric) configurations and hence are

considered difficult to fabricate reliably. On the other hand, the antenna reported by Liu and Kao [6], is a simple probe

feed H-shaped microstrip antenna fed along its diagonal to excite the CP operation. But the AR bandwidth reported is

only about 1.3%.

This group has recently reported a linearly polarized coplanar capacitive fed wideband microstrip antenna

which provides input impedance bandwidth (S11 < −10 dB) of about 50% [7]. Furthermore, we have suggested the

use of fractal shaped boundaries for the radiating patch to get symmetric radiation patterns throughout the frequency

band [8].In the present work we investigate circular polarization operation of such a patch antenna with fractal

boundaries by introducing a suitably designed slot within.

In another effort, fractal geometry with fractal slots has been reported with an axial ratio bandwidth of about 2% [9].The current approach results in significantly higher AR bandwidth while retaining the simplicity of the feed

configuration.

II.ANTENNA DESIGN

The geometry of the antenna is shown in Figure 1. This is basically a suspended coplanar capacitive fed microstrip

antenna. Both antenna patch and the feed strip are etched on the same dielectric substrate, which is placed at a height

above the ground plane. The antenna is excited by connecting a coaxial probe to the feed strip by a long pin SMA

connector. The antenna was designed to operate with a center frequency of 1.6GHz.

A Wideband suspended Microstrip Patch

Antenna

Miss.Madhuri Gaharwal1, Dr,Archana Sharma

2

1PG student , EC department, TIT(E),Bhopal

2Assosiate Professor ,EC department, TIT(E),Bhopal






(a) Top view of wideband CP geometries

(b) Cross sectional view

Fig. 1. Proposed wideband CP antenna geometry.

III.SIMULATION AND RESULT DISCUSSION

In this study we use an FR4 substrate (dielectric constant=4.4, tan delta = 0.0023 and thickness=1.6mm) placed abovethe ground plane at a 6mm height. Minimum possible width of the feed strip is 9mm so that a hole can be made to

connect the probe pin. Its minimum length is approximately one fifth the side of the patch.

Due to fabrication constraints the minimum separation between the patch and the feed strip is 0.5mm. The physical

parameters of the antenna geometry with a slot are optimized using HFSS simulations and are listed in Table 1. These

geometrical parameters (Table 1) are optimized with HFSS software.

Table 1. Dimensions for the antenna geometry shown in.

Sr.no Parameters Dimensions (mm)

1. Patch Length(L) 63.0

2. Patch Width(W) 83.0

3. Substrate Length(Ls) 108.0

4. Substrate width (Ws) 132.0

5. Slot length(Ls1) 2.5

6. Slot length(Ws1) 11.07. Air gap(h) 9.0

8 Corner Slot length(Cs) 10.0

9. feed strip Length (fl) 12.0

10 feed strip Length (fw) 6.0

11. gap bet feed and patch(g) 0.5

Table 2. Comparisons table of different structure of patch.

Sr.

No.

Shape of MSA Freq

(GHZ)

Return

Loss(dB)

VSWR BW(M

Hz)

Axial

Ratio

(dB)

Gain

(dB)

1. RMSA Feed diagonal 1.52 -13.14 1.54 30 2.50 2.27

2. RMSA Corner Slits 1.54 -15.04 1.43 35 1.37 2.30

3. RMSA Corner Slits and

cross slits

1.58 -15.57 1.39 65 0.98 2.24






First, study of different shapes of microstrip patch have been investigated to understand their effects on impedance and

AR bandwidths. AR characteristics of the antennas are depicted in Figure 2. It can be noticed from Figure 2 that the

axial ratio decreases and bandwidth also increasing with adding cross cut slits.Table 2 Comparisons table of different shapes

Fig. 2. Axial ratio of different shape microstrip antenna.

The following section deals with the effects of air gap (h). By increasing h, the whole return curve shifts towards higher

frequencies. The air gap (h) has a significant effect on the matching to the input impedance. Increasing the height of

air gap it helps to improving the bandwidth of suspended microstrip antenna. Figure 3 shows performance of the

wideband circularly polarized antenna for different air gap varies from 3mm to 12mm.

Fig. 3. Effect of variation in air gap (h) on impedance Bandwidth.

Here we have study comparison three different techniques. As compared to conventional and suspended MSA we aregetting maximum bandwidth in coplanar suspended microstrip feed antenna. Figure 4 shows performance three

different techniques if microstrip antenna. It can be noticed from Fig. 4 that the impedance bandwidth increases forcoplanar suspended microstrip feed antenna.

Fig. 4. Effect of different techniques on impedance Bandwidth.






The simulated return loss characteristics of the proposed antenna in Fig.5, indicated that the return loss is below −15

dB in the CP operating range (1.60GHz–1.91GHz). The corresponding axial ratio characteristics are plotted in Figure

6.

It can be shown that axial bandwidth (with axial ratio ≤ 3 dB) has been found about 250Mhz i.e. 10.66%

The

radiation patterns are plotted in Fig.7, it can be noted that the gain of proposed antenna are 6 dB in the CP range of

operation.

Table 3. Comparisons table of different techniques of patch.

Fig. 5.Return loss of proposed antenna.

The corresponding axial ratio characteristics are plotted in Figure 6

Fig. 6.Axial ratio of proposed antenna.

Sr.No Shape of MSA Freq

(GHz)

Return

Loss(dB)

VSWR BW

(MHZ)

Axial

Ratio

(dB)

Gain

(dB)

1. RMSA 1.58 -15.57 1.39 65 0.98 2.24

2. Suspended RMSA 1.57 -15.23 1.42 140 0.31 3.24

3. Coplanar Suspended

RMSA

1.60 -19.04 1.25 465 1.01 5.93






Fig. 7.Radiation pattern of proposed antenna.

Fig. 8..Gain of proposed antenna.

IV.CONCLUSION

The coplanar suspended microstrip feed antenna was presented for circular polarization. This feed configuration has

been shown previously to improve the antenna’s impedance bandwidth. The CP geometry was used to get nearly

symmetrical radiation patterns.

A corner slits was used to excite circular polarization and slot dimensions were optimized to maximize the AR

bandwidth. The proposed geometry exhibits the return loss less than −15 dB and a gain above 5 dB in the CP operatingrange. By changing the slot orientation, antenna can be made to work in CP mode without changing any of the other

parameters of the antenna. With optimum slot dimensions this antenna offers an axial ratio bandwidth of 10.6% (AR<

3 dB). It has also been established that the proposed approach can be employed to design antennas with similar

performance for the desired operational.

REFERENCES

[1] Balanis, C. A., Antenna Theory, John Wiley & Sons, Inc., NewYork, 2004.

[2] Yang, S. L. S., K. F. Lee, and A. A. Kasha, “Design and study of wideband single feed circularly polarized

microstrip antennas,” PIERS Online, Vol. 80, 45–61, 2008.

[3] Chen, W. S., C. K. Wu, and K. L. Wang, “Novel compact circularly Polarized square microstrip antenna,” IEEE

Trans. Antennas Propagat., Vol. 49, No. 3, 340–342, 2001.

[4] Esselle, N. K. and A. K. Verma, “Optimization of stacked microstrip antenna for circular polarization,” IEEE

Antennas Wireless Propagat. Lett., Vol. 6, 21–24, 2007.

[5] Lien, H. C., Y. C. Lee, and H. C. Tsai, “Couple-fed circular polarization bow tie microstrip antenna,” PIERS

Online, Vol. 3, No. 2, 220–224, 2007.






[6] Liu, W. C. and P. C. Kao, “Design of a probe fed Hshaped microstrip antenna for circular polarization,” Journal of

Electromagnetic Waves and Applications, Vol. 21, No. 6, 857–864, 2007.

[7] Kasabegoudar, V. G., D. S. Upadhyay, and K. J. Vinoy, “Design studies of ultra wideband microstrip antennas

with a small capacitive feed,” Int. J. Antennas Propagat., Vol. 2007, No. Q4, 1–8, 2007.

[8] Kasabegoudar, V. G. and K. J. Vinoy, “A wideband microstrip antenna with symmetric radiation patterns,”

Microw. Opt. Technol. Lett., Vol. 50, No. 8, 1991–1995, 2008.[9] Rao, P. N. and N. V. S. N. Sarma, “A single feed circularly Polarized fractal shaped microstrip antenna with

fractal slot,” progress In Electromagnetics Research Symposium Proceedings, 95–197, Hangzhou, China, Mar. 24–

28, 2008.

AUTHORS

Miss.Madhuri Gaharwal received her Bachelor of Engineering in Electronics & telecommunication in 2009 from

Sant Gadage Baba Amravati University.She is currently pursuing her M.Tech in Electronics & Communication branch

from TIT college of Excellence, RGPV University Bhopal

Dr. Archana Sharma received her Bachelor of Engineering in Electronics & Communication in 2004 from RGPV

,Universit, Bhopal She received her M.tech in Microwave & Millimetre Waves from MANIT, Bhopal, India in 2008.She also received her Ph.D degree from the MANIT, Bhopal , India in 2014. She has many publications in various

international journals and conferences .Her research field focus on various antenna design and analysis , microstrip

antenna s, dielectric resonator antennas , microwave and millimeter wave systems, wireless communication . She is

presently working as Associate Professor in Department Electronics & Communication branch , TIT college of

Excellence, Bhopal, India.

Documents

A Wideband suspended Microstrip Patch Antenna