Design of Switchable Dual-Balun Feeding Structure for Pattern-Reconfigurable Endfire Antenna

This letter proposes a microstrip switchable dual balun using a symmetrical three-coupled-line structure, which is used as a feeding network for designing a pattern-reconfigurable endfire antenna. By adding p-i-n diodes to the ends of the coupled quarter-wavelength lines, the proposed balun enables three-status operation while it has compact size and simple configuration. Based on this, a pattern-reconfigurable endfire antenna is designed, fabricated, and measured. Good agreement between the simulated and measured results can be observed. The peak gain of two directional statuses reaches 5.8 dBi and the front-to-back ratio (F/B) is more than 18 dB. Meanwhile, the peak gain of bidirectional status reaches 2.7 dBi and the F/B is less than 0.5 dB.