Single-Layer Low-Profile Patch Antennas with Improved CP Performance by Using Multiresonant Modes (Invited Paper)

In this letter, a novel design concept for circularly-polarized (CP) performance improvement of a single microstrip patch antenna (MPA) is studied and summarized via multiresonant modes. By investigating the internal E-field, it demonstrates that the direction of the equivalent magnetic currents (EMCs) at the patch edge are significantly changed under different feeding positions. Hence, two types of CP antennas are simulated and designed. Firstly, by reallocating three orthogonal modes in proximity to each other without sequential rotation, an extremely small frequency-ratio of about 1.04 is generated for the dual-polarized CP MPA. Secondly, by reallocating three orthogonal modes closely to each other with sequential rotation, the dual working bands of the MPA with same CP-polarization are merged to extend its CP bandwidth. In final, these MPAs are fabricated and measured. The measured results verify these predicted performances and the antenna keeps several advantages, i.e., low-profile, single-layer, single-element, wide AR-bandwidth, small frequency-ratio, and high efficiency.