An Electronically Steerable Parasitic Array Radiator (ESPAR) Using Cavity-Backed Slot Antennas

The electronically steerable parasitic array radiator (ESPAR) is an inexpensive way to achieve beam steering. Planar ESPARs usually exhibit narrow fractional bandwidth (FBW) in terms of both impedance matching and beam squinting. Herein, an E-plane three-element ESPAR using cavity-backed slot antennas is presented to demonstrate a wider FBW, i.e., 4%, by investigating not only S11 but also beam squinting. It is found that a tunable load which uses a fixed inductor, a varactor, and a delay line can provide a much larger impedance tuning range compared to that without the inductor. This tunable load is critical to enhance the FBW by considering beam squinting. This ESPAR is able to scan from -26° to 20° in the E-plane, operating around 5.15 GHz. The measured peak gain is between 5.52 and 6.05 dBi at all scan angles. The radiation patterns are measured at different scan angles in the E-plane. In addition, they are measured at different frequencies to demonstrate the beam squinting performance.