Dual band low-profile switched beam Square Loop Antenna with capacitively coupled feeds

Abstract

A low profile dual-band switched beam Square Loop Antenna (SLA) with capacitively coupled feeds is presented. Two co-centered square loops are capacitively coupled to the four vertical feeding probes by four rectangular feeding patches. The capacitively coupled feeding mechanism introduces capacitance into the antenna input impedance and cancels the high inductance due to the feeding probe and the close proximity of the ground plane. This feeding technique allows the antenna to be matched to a 50 ohm feed line and helps in the realization of a low profile SLA. The antenna has a height of 6 mm and it is developed for operating in 3.1 GHz and 3.8 GHz frequency bands. In both frequency bands when any of the four ports is excited, keeping other ports open circuited, the antenna generates a radiation beam tilted by 31 degrees from the broadside and directed away from the excited port, having a maximum directivity of 9.1 dBi. Thus by exciting one port at a time, the antenna can steer its tilted beam in four different quadrants to scan the entire space in front of antenna.