Compact circularly polarized asymmetric-slotted microstrip patch antennas

A technique is demonstrated to generate circularly polarized (CP) radiation of the compact diagonally asymmetric-slotted microstrip patch antennas. Design rules for the single-feed, compact, circularly polarized microstrip antennas (CPMA) with any arbitrary-shaped slots along the diagonal directions are first summarized. Four, compact, CPMA with circular-, square-, cross-, and square-ring-shaped slots along the diagonal directions are proposed and compared based on a fixed overall antenna size. A compact, CP, cross-shaped slotted, microstrip antenna is fabricated and measured to verify the proposed technique experimentally. The measured 3-dB axial-ratio bandwidth of about 6.0 MHz is achieved with 10-dB return loss bandwidth of 19.0 MHz while measured gain of the antenna is 4.0 dBic at 930 MHz.