Design of wideband and compact patch antennas


Student thesis: Master's Thesis

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  • Yuan LI

Related Research Unit(s)


Awarding Institution
Award date4 Oct 2004


This thesis presents the design and development of several novel small and wideband patch antennas. Microstrip antennas have the attractive features of low profile and light weight. However the antennas may be too large for practical applications at the lower microwave frequency range and may offer only a few percent of bandwidth. Several techniques have been proposed to reduce the size of the conventional half-wave patch, such as using high dielectric constant materials, using a shorting wall or shorting pin. Based on these techniques, several novel designs are presented here. First, a study on the quarter-wave patch with a vertical shorting wall is carried out. The bandwidth of the quarter-wave patch can only reach 8%. Then, two methods based on the traditional vertical shorting wall, lean shorting wall and folded shorting wall, are proposed for bandwidth enhancement. In which, the lean shorting wall method leads to a 17 % bandwidth which is about double of the bandwidth of the quarter-wave patch with a vertical shorting wall. Another folded shorting wall with a triangular patch has been developed to achieve 28.1% in bandwidth. However, the folded shorting wall causes an asymmetric E-plane copolarization pattern and high cross polarization in the H-plane. Secondly, a very wide bandwidth of 69.2% is achieved in a brand new dual-feed structure which is formed by combining two quarter-wave patch antennas. This antenna is much thinner, only about 0.026λ0. One disadvantage of the antenna is that the gain during the central frequency range is bellow zero. Effectively, the antenna acts as a dual-band antenna. With a “race-track” shaped patch, a stable gain of 3dBi is obtained over a bandwidth of 50% (S11<-10 dB). Comparison of different patch shapes on the S11 and gain are given. The use of shorting pins is an effective method to enhance the various performance characteristics of the antenna. In this thesis, relationship between the bandwidth, feed location and shorting pins locations on three types of rectangular patch antennas utilizing shorting pins are investigated. By analyzing the effect of the ratio of the shorting pin location to the probe feed location, it is found that optimum bandwidth is obtained when this ratio is close to the Golden Ratio for all three antennas. The Golden Ratio is closely connected with Fibonacci series and has a value of ( 5 −1) / 2 = 0.618. The usefulness of shorting pins in size reduction and bandwidth enhancement is further demonstrated by the performance of a new wideband small-size patch antenna with a cross-shaped probe feed. The antenna obtains 51.3% bandwidth when S11 is less than -10dB. A stable gain with a maximum value of 3.3dBi has been obtained. Also this structure is very simple and it covers DCS (1.71GHz—1.88GHz), PCS (1.85GHz—1.99GHz), UMTS (1.92GHz—2.17GHz), and 2.4GHz WLAN bands wireless communication applications. Finally, it is found most of the measurement results of the small antenna designs S11, radiation pattern and gain have been confirmed by using IE3D, a commercial EM simulation software package available from the Zeland Company.

    Research areas

  • Wireless communication systems, Microstrip antennas