Dual-Band Low-Profile Capacitively Coupled Beam-Steerable Square-Loop Antenna

In this paper, a dual-band low-profile switched beam square-loop antenna (SLA) fed by capacitively coupled feeding mechanism is presented. Two square loops are excited by four rectangular feeding patches which are fed with vertical probes. The capacitively coupled feeding arrangement introduces capacitance into the antenna input impedance and cancels the high inductance due to close proximity of ground plane and feeding probes. This feeding technique enables the antenna to be matched to 50 Ω feedline and helps in the realization of low-profile SLA. The antenna has a height of 3.04 mm; i.e., λ0 /26 for the operating frequency of 3.8 GHz. The dual-band capacitively coupled square-loop antenna (DBCCSLA) is developed for covering 3.8- and 4.7-GHz frequency bands, and each band possesses an impedance bandwidth of 120 MHz. In both frequency bands, when any of the four ports is excited, keeping other ports open circuited, the antenna generates a tilted beam directed away from the excited port, having a maximum directivity of 9.3 dBi. By exciting ports one at a time, the antenna can steer its tilted beam in four different quadrants to scan the entire space in front of the antenna.