Low-profile Annular Patch Antenna for Pattern Diversity Applications

A low-profile pattern diversity antenna based on short-ended annular microstrip antenna is proposed in this paper. The characteristic equation is used to solve the resonant frequencies of the different modes in theory. By tuning the ratio of the inner and the outer diameters of the annular patch, the resonant frequencies of TM11 and TM01 modes can overlap at a specific frequency. Numerical results show that the proposed antenna can provide a broadside and an omnidirectional radiation patterns in 5.8-GHz Wireless Local Area Network (WLAN) band and the height of the antenna is only 0.09 lambda(0). Besides, the isolations between all ports are better than 20 dB and the envelope correlation coefficients (ECCs) are lower than 0.002, which ensure a good diversity performance.