A compact patch antenna with an inverted U-shaped radiating patch

We propose a new compact design of using an inverted U-shaped radiating patch to achieve a lower fundamental resonant frequency for a patch antenna with a thick air substrate. The proposed design is very suitable for applications with air-substrate patch antennas, and in the present study, it has been found that a significant lowering of the resonant frequency of about 32% can be achieved for the patch antenna with an air-substrate thickness about 5% of the wavelength of the center operating frequency. When the patch´s aspect ratio and desired operating frequency are fixed, this lowering in resonant frequency corresponds to an antenna size reduction of about 54%. Also, since the lengthening of the effective patch´s surface current paths is due to the additional downward paths in the added rims, different from the designs with meandered patches, relatively very small perturbation on the excited surface current distribution in the radiating patch is expected. This suggests that it is possible for the radiation characteristics of the proposed antenna to be as good as those of a regular patch antenna with a planar radiating patch.