Compact Broadband Microstrip Antenna For Radionavigation

Prof.Ms.R.P.Labade Asst. Prof., Department of E&TC

AVCOE,Sangamner Sangamner, India

rplabade@gmail.com

Dr.S.B.Deosarkar Principal VPCOE VPCOE, Baramati

Baramati, India sbdeosarkar@yahoo.com

Mr.Ankit Dangi Student, Department of E&TC

AVCOE,Sangamner Sangamner, India

ankitdangi89@gmail.com

Abstract -- Proposed compact broadband microstrip patch antenna has been designed by increasing the substrate height and inserting the slots at different angles. At the center frequency of 2.9955 GHz impedance bandwidth of 153.6 MHz, return loss of -35.6595 dB, Gain of 8.57dBi and very good radiation pattern in the broadside direction is achieved. Which can be used for radio navigation and in radar for detecting positions of living and non living objects. MSA is simulated by Zeland IE3D software using Method of Moment (MoM) technique [7]. Keywords – MSA; radio navigation; broadband antenna.

I. INTRODUCTION

The major disadvantage of the microstrip-patch antenna is its inherently narrow impedance bandwidth of only a couple of percent. [3] Number of researcher has been presented a bandwidth-enhancement techniques. Such as utilization of thick substrates with a low dielectric constant and stacked or co-planar parasitic patches. The use of an electronically thick substrate only results in limited success, because a large inductance is introduced by the increased length of the probe feed, resulting in a maximum bandwidth of less than 10% of the resonant frequency. By using stacked patches. Bandwidths of 10%-20% can be obtained, but this design has the disadvantage of added complexity of fabrication. To counteract the inductance introduced when using a thick substrate, capacitance can he introduced by adding a concentric annular gap around the probe feed, resulting in 16% bandwidth. [3] Bandwidth can also be increased by cutting a resonant slot inside the patch or by using multi resonator gap coupled and stacked configurations [6].

II. PROPOSED DESIGN A broadband RMSA is shown in fig 1. It is designed on glass epoxy substrate (εr= 4.3, loss tangent=0.02) The RMSA has a length of 30mm and width 40mm. As height increases, fringing field from edges increases, increasing effective length of patch thus increasing the efficiency and decrease in resonant frequency. Also directivity increases and aperture area increases due to increase in length and thus finally bandwidth get enhanced. [4] Also bandwidth is increased by decreasing the effective dielectric constant as patch size increases which in turn increases the fringing fields. So the

proposed uses two substrates i.e. FR4 (εr = 4.4, loss tangent=0.002, h1=1.6mm) and Foam (εr = 1.07, h2=3mm). Now to reduce the increased area horizontal and vertical slots are inserted as they increase the effective path length of surface current.[7] The slot width and feed point will be optimized to keep the loop in the impedance plot inside the VSWR = 2 circle. The feed used is 50 ohms coaxial SMA connector due to its ease of availability and also produces less spurious radiation. [5] The “fig. 1” shows the geometry of antenna.

(a) Top View

(b) Side View

Figure 1. Antenna Geometry (L=40mm, W=30mm, h1=1.6mm, h2=3mm)

For an efficient radiator the width and length leads to a good

radiation efficiency is given by,

(1)

(2)

Center frequency is given by “(3)”,

(3)

Effective dielectric constant of the antenna calculated for w/h ≥1,

(4)

III. RESULTS AND OBSERVATION The above designed geometry is simulated using IE3D software which is based on Method of Moment (MoM) technique. [7] The following results were obtained by the simulation software. All the results show that they meet the required values for effective functioning of the antenna. [1]

A. Return Loss The graph shown the return loss of -35.6595 dB which is actually the good, ideally return loss should be RL ≥ -9.5dB.[1] At the center frequency of 2.9955 GHz a reasonable impedance bandwidth of 153.6 MHz is achieved.

B. VSWR For perfect matching between the transmitter and the antenna, Γ = 0 and RL = ∞ which means no power would be reflected back, whereas a Γ = 1 has a RL = 0dB, which implies that all incident power is reflected. For practical applications, a VSWR of 2 is acceptable, since this corresponds to a return loss of -9.55 dB.[1]

Figure 2. S11 Vs Frequency

Figure 3. VSWR Vs Frequency (simulated)

Figure 4. VSWR Vs Frequency (measured)

Fig.3 graph shows the VSWR of -1.05015 dB which is actually the good. Graph of “fig.4” shows measured VSWR on Anritsu vector network analyzer. Which is in good agreement with simulated result.

C. Radiation Pattern: From fig 5. plot we can see the radiation pattern of E – plane (phi = 0 deg) and H-plane (phi = 90 deg).

Figure 5. Radiation Pattern

1r

2

f r2

v0

1r

2

0μ0f r2

1W

+∈

=+∈∈

=

( ) ∈∈+=

∈∈

=

0μ 0reff2ΔΔL2

1

0μ 0reffL eff2

1f

1/2

w

h121

2

1r

2

1r

effr

−

++−∈

++∈

=∈⎥⎥

⎦

⎤

⎢⎢

⎣

⎡

L 2Δ 0μ0refff r2

1L −

∈∈=

The maximum gain is 8.11 dBi at theta = 0 deg. The 3 db beam width of the antenna is 83.975 deg at phi = 0 deg and 67.87 deg at phi = 90 deg.

D. Current Distribution

Fig.(5) shows that radiation is effective along the width as compared to length. Also we can see that due to the X – shape slot, the path length of the current (i.e. flow of current) from feed point towards edges increases which indicates efficient radiation. The width is called as radiating edge as maximum radiation along it whereas length as non-radiating edge of the antenna.

IV. CONCLUSION Thus the proposed antenna works satisfactorily for the frequency of 2.9 GHz which can be used for Radio navigation assigned by ITU-T standards with a S11 of -35 dB with an impedance bandwidth of 150 MHz, Gain of 8.57dBi and very good radiation pattern in the broadside direction. This meets all the requirements of the antenna used for radio navigation. Measured results are in good agreement with the simulated result. The actual manufactured antenna is as shown in (Fig.7)

Figure 6. Current Distribution

Figure 7. Manufactured MSA

REFERENCES

[1] C.A.Balanis “Antenna Theory and Design”, second edition, John Wiley and Sons, New York, 1997. [2] G Kumar and K.P.Ray, “Broadband Microstrip Antennas”, Willey and Sons, Inc., New York, 2002. [3] R. Garg, P. Bhartia, I. Bahl, A. Ittipiboon, “Microstrip Antenna Design Handbook”, ARTECH HOUSE, Boston 2001. [4] Aaron K. Shackelford, Kai-Fong Lee,and K.M.Luk Design Of small size wide web bandwidth Microstrips antenna” IEEE Antenna and Propogation Magazine, Vol.45 No,1 February 2003. [5] W Chan and K F Lee, “Input impedance of coaxially fed RMSA on electrically thick substrate”, Microwave Optical Technology. Lett, 6, 1993, pp.387-390. [6] R.Q.Lee, K F Lee and J Bobinchak, “Electromagnetically Coupled Rectangular Patch Antenna”, Electron.Lett. 23, 1987, pp.1070-1072. [7] S.A.Malekabadi, A.R.Attari, M.M.Mirsalehi, “Compact and broad band circular polarized microstrip antenna with Wide band axial ratio bandwidth”, 2008 International Symposium on Telecommunications. [8] IE3D 11.05 Manual, Zeland Software Inc. Freemont, California (Dr.BATU,Lonere MS). [9] E.H. Newman and P. Tylyathan, “Analysis of Microstrip Antennas Using Moment Methods,” IEEE Trans. Antennas Propagation, Vol. AP-29, no. 1, pp. 47- 53, January 1981.