Design of Compact, Low-Profile, Wideband, Dual-Frequency Patch Antennas Based on Complementary Co-Directional SRRs

A traditional microstrip antenna is capable of exhibiting good dual-band operation via slotting a complementary codirectional split resonant ring (CCSRR) unit on the rectangular radiating patch. Thanks to the advantage of low mutual coupling between the co-directional ring-slots in such a complementary co-directional split resonant ring unit, the antenna´s operating frequency band, which originates from the complementary co-directional split resonant ring´s resonance, is significantly expanded with the addition of more co-directional ring-slots. Antennas comprised of zero, a single, dual, and triple complementary co-directional split resonant rings were designed, fabricated, measured, and comprehensively compared. According to our investigation, besides operating in their inherent TM₁₀₀ modes, the proposed antennas have the advantages of providing a lower and much wider operating range than that in the TM₁₀₀ mode. This is especially more than a 9% impedance bandwidth, even with such a low profile (only 0.0316λ0 in height). More importantly, uniformly good radiation characteristics, including excellent broadside main beams with high polarization purity, and large front-to-back ratios (FTBRs), were achieved in both frequency ranges, on the whole.