Two designs are constructed based on a two-layer dual-patch antenna with coaxial feed. One of the shorter edges of the upper patch is connected to the lower patch and the other shorter edge is connected directly to the ground by another vertical wall without touching the lower patch. In the first design the upper patch is rectangular and the shorting wall to the ground is narrower than the width of the whole patch. In this case the resonant frequency of the patch can reduce by 72/100 when compared with the conventional halfwave patch. It has a bandwidth of 8.8/100 and a gain of -1.7dBi in the broadside direction. The pattern has a maximum gain 0.5dBi occurring at θ = -40. In the second design, the upper patch is modified into a trapezoidal shape. The resonant frequency of this patch can reduce by 72/100 when compared with the conventional halfwave patch. It has a bandwidth 8.3/100 and a gain of - 1.7dBi in the broadside direction. The pattern has a maximum gain 1.5 dBi at the direction of-35 direction. Compared with the first design, a 1 dBi gain improvement is obtained.
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