Enhancing Gain of Ring Slot Antennas With Shorting Strips

This paper proposes that ring slot antennas, loaded with shorting strips, can achieve broadside gain enhancement while maintaining a low profile and bidirectional radiation. Both circularly polarized (CP) and linearly polarized (LP) ring slot antennas are used to demonstrate this method. With infinite ground plane (GP), CP and LP ring slot antennas are observed to increase by at least 0.8 and 1.7 dBi in realized gains, respectively. Combined characteristic modes (CMs) are used to analyze and explain the working mechanisms of these antennas. It is shown that shorting strips could help to enlarge the radiation apertures of ring slots, while the center frequency remains constant; hence, broadside gains are enhanced successfully. It is also discussed that by replacing the infinite GP with a finite one of about 1.5λ × 1.5λ, gains of both CP and LP ring slot antennas change little at center frequencies. Prototypes of these two antennas are then fabricated and measured to experimentally validate the analysis and designing approach.