A Design Approach for Compact Pattern Reconfigurable Antenna Based on Short–Open-Circuited Transmission Line

A design approach is proposed for a compact pattern reconfigurable antenna based on short-open circuited transmission line. The designed antenna comprises a center-fed transmission line with two terminations and two dipoles. The currents on the dipoles that are deployed on the line with short and open circuited terminations have similar magnitudes but a large phase difference (about −140°), so the antenna radiates at endfire with high gain and high front-to-back ratio (FTBR). When the left termination is short-circuited (open-circuited) and the right one is open-circuited (short-circuited), the phase difference is about −140° (+140°) and the antenna can provide an endfire (backfire) beam at θ = +90° (−90°). By switching the states of the terminations with 2 PIN diodes, the endfire/backfire pattern reconfiguration can be achieved. With a compact size of 0.39λ0× 0.20λ0(λ0is the wavelength in free space at operating frequency), a prototype of the antenna is designed at 2.4 GHz, which reaches peak gains of 5.59/5.55 dBi and peak FTBR of 23.02 dB with a fractional bandwidth of 12.2% in different states.