Miniature wideband patch antennas


Student thesis: Doctoral Thesis

View graph of relations


  • Ricky CHAIR

Related Research Unit(s)


Awarding Institution
Award date2 Oct 2002


This thesis presents the design and development of several novel small and wideband multi-layer patch antennas. Microstrip antennas have the attractive features of low profile and light weight. They can be made conformal to mounting structures. In the lower microwave frequency range, their size, however, may be too large for practical applications. They also suffer from narrow bandwidth and low radiation efficiency at higher frequencies. Several techniques have been proposed to reduce the size of the conventional half-wave patch. One approach involves the use of expensive high dielectric constant materials. Another approach is to use either a shorting wall or a shorting pin. Adding the shorting wall leads to a quarter-wave patch. Although the shorting pin method can achieve a size of less than 20% in resonant length, in general, it can only provide narrow impedance bandwidth and the design is very sensitive to the location of the shorting pin. In this thesis, a detailed study on the quarter-wave patch is presented. The bandwidth of the quarter-wave patch can reach 17.7% of the resonant frequency with a thickness of only 0.053b. Due to the vertical wall radiation, the cross-polarization level increases and causes the E-plane radiation pattern to tilt away from the broadside direction and increase the radiation in the H-plane cross-polarized field. Another study is on the addition of a shorting pin between the feed and the shorting wall, it shows that the bandwidth has enhanced further and reaches 21.6% of the resonant frequency. Both designs can attain more than 95% of radiation efficiency. Several novel multi-layer patch antennas with low cross-polarization are described. They can be divided into 2 categories, the folded patch antenna and the stacked patch antenna. Both of them can provide low cross-polarization level. This is because all vertical walls are formed in pairs and their radiated fields are cancelled in the broadside direction. The size reduction of the folded patch antenna is achieved by effectively increasing the resonant length of the antenna. Among the three folded patch designs, the smallest one can reduce its physical length by 37.4% when compared with the conventional rectangular patch antenna with the same projection area. The stacked patch antenna involves two layers, and they are connected together by two vertical walls. A simple transmission line model is used to demonstrate the physical operation of this stacked patch antenna. The size of this antenna has reduced by 60% in length and a bandwidth of 12% of the resonant frequency is achieved. By combining the stacked patch and the quarter wave patch techniques, another three novel designs have been developed. These designs reduce the size hrther with the smallest one achieving only 28% of the conventional rectangular patch in length and it has a bandwidth of 8.8% of the resonant frequency. Radiation efficiency is an important parameter for analyzing the small antennas. As the gain is reduced with the size, it is hard to tell whether the gain is high or not. Wheeler Cap efficiency method has been employed to measure the radiation efficiency of the designed antennas. Most of the multi-layer small antennas design have achieved over 90% of radiation efficiency. Finally, most of the measurement results of the small antenna designs have been confirmed by using IE3D, a commercial EM simulation software package developed from the Zeland Company. Acceptable agreement has been obtained on the SWR, radiation pattern, gain and radiation pattern.

    Research areas

  • Microstrip antennas