Broadband Monopole Patch Antenna Optimization
*Randy L. Haupt, rlh45@psu.edu
Rodney Martin, ram232@psu.edu
Joseph Flemish, jflemish@psu.edu
The Pennsylvania State University, Applied Research Laboratory,
State College, PA 16801
Introduction
There have been several attempts at designing a broadband monopole patch
antenna. The tab monopole proved to be a simple yet functional design that served
as a basis for several spin-offs [1]. Further refinements to this concept have been
presented in the literature [2][3][4]. We built this monopole and measured its
reflection coefficient over a broad bandwidth. Next, we developed a computer
model of the antenna using FEKO [5]. The computed and measured s11 results
agreed well. Next, we optimized the design over a 20% bandwidth for both a
coplanar fed and microstrip line fed versions. Both of these designs have much
smaller ground planes than the original tab monopole.
The Tab Monopole
An experimental model of a tab monopole antenna was built (see Figures 1 and 2)
according to the specifications in [1] where Tx=25.4, T1=5.1, T2=4.2, T3=4.0,
Gx=63, Gy=51, and M=4 mm and εr=2.2, substrate thickness=1.6 mm. A computer
model of the tab monopole was modeled using FEKO. The magnitude of s11 for
the experimental model and the computer model are shown in Figure 3. The
experimental antenna (bandwidth = 62.7%) and computer model (bandwidth =
47.3%) s11 results are very close. Consequently, we have confidence in the
computer model, so that we can use it to optimize this antenna design.
Figure 1. Picture of the experimental antenna.
1-4244-0878-4/07/$20.00 ©2007 IEEE
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Figure 2. FEKO tab monopole.
Figure 3. Computed vs. measured reflection coefficient.
Optimized Broadband Monopole
Our goal is to simplify the design of the tab monopole while optimizing its
bandwidth. Our target center frequency is 2.0 GHz with a 20% bandwidth. Part of
the simplification is making the ground planes smaller at Gx=32.1 and Gy=30 mm.
After a few iterations with a genetic algorithm, the following dimensions were
found: Tx=16.1, T1=2.3, T2=18.8, T3=6.1, and, M=4.6 mm. The resulting graph of
s11 and a picture of the new monopole model are shown in Figure 4. Far field
plots at 1.8, 2.0, and 2.2 GHz appear in Figure 5 for θ=90o and θ measured from
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the z-axis and φ measured from the x-axis. The patterns are doughnut-shaped with
the maximum radiation at φ=180o.
Figure 4. Picture of optimized co-planar fed patch monopole and a graph of
its s11 performance.
Figure 5. Directivity patterns for optimized co-planar fed patch monopole.
Next, a microstrip line fed version of the broad band monopole was
optimized to get Gx=29.1, Gy=30, Tx=13.1, T1=7.9, T2=16.7, T3=4.5, and, M=3.4
mm. A picture of the new monopole and a graph of its s11 are shown in Figure 6.
The tab portion of the monopole is thinner and taller than the coplanar fed
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version. The width of the ground plane is 16mm on either side of the tab. The
height of the ground plane was set at 30mm.
Figure 6. Graph of s11 for and picture of optimized microstrip line fed patch
monopole.
Conclusions
The tab monopole is a very useful broadband microstrip antenna. This paper
optimized the shape and size of the tab monopole at a lower frequency. A
microstrip line fed version was also optimized.
Acknowledgement
This work was partially sponsored by Army CECOM under contract N00024-02D-6604 DO-295.
References:
[1] J.M. Johnson and Y. Rahmat-Samii, "The tab monopole," IEEE AP-S Trans. ,
vol. 45, no.1, Jan 1997, pp.187-188.
[2] K. Wong and Y. Lin, "Stripline-fed printed triangular monopole," Electronics
Letters, vol. 33, no. 17, 14 Aug 97, pp. 1428-1429.
[3] J. Kim, T. Yoon, J. Kim, and J. Choi, "Design of an ultra wide-band printed
monopole antenna using FDTD and genetic algorithm," vol. 15, no. 6, Jun
2005, pp. 395-397.
[4] H.R. Chuang, C.C. Lin, and Y.C. Kan, "A printed UWB triangular monopole
antenna," Microwave Journal, Jan 2006.
[5] FEKO Suite 5.1, EM Software and Systems (www.feko.info), 2005.
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