Dual‐frequency circularly‐polarized microstrip antenna with switchable polarization sense

A dual‐frequency circularly‐polarized (CP) microstrip antenna capable of switching polarization sense is presented. The antenna is fed by a microstrip line through aperture coupling. First, it is found that a CP mode can be excited when the radiating patch is square and an open‐ring slot is used as the coupling aperture. Then, by truncating the radiating patch, another CP mode can be obtained. The two CP modes have reversed polarization senses, and their operating frequencies are different. For the proposed dual‐frequency CP microstrip antenna, two prototypes with frequency ratios of 1.07 and 1.23 were constructed, and voltage‐controlled diodes are employed to achieve the electrical switching between the two CP modes.