A Differential Multipoint Coupled-Fed Harmonic Suppression Patch Antenna With a Single-Layer and Filter-Free Structure

This letter introduces a differential multipoint coupled-fed patch antenna, which achieves wide out-of-band harmonic suppression with a simple single-layer and filter-free structure. First, the differential-fed technology is utilized, resulting in only TM₁₀, TM₁₂, and TM₃₀ modes being retained and nine modes being eliminated. Then, a multipoint coupled-fed technology is adopted for suppressing TM₁₂ and TM₃₀ modes. The coupling mechanism is studied in depth based on electromagnetic theory. By comprehensively considering the coupling effects along x-direction and y-direction, the coupling structure is designed elaborately for TM₁₂ and TM₃₀ modes suppression. Consequently, only TM₁₀ mode can be effectively excited. The proposed HSPA operates at the center frequency f₀ being 1.52 GHz, with a -3 dB out-of-band harmonic suppression in │S₁₁│ reaching up to 5.25 GHz. Additionally, the antenna efficiency of the design is suppressed to less than 25%, from 2 GHz to 5.25 GHz. A prototype was fabricated and measured to validate the design concept. The measured results agree well with the simulations, showing a decent out-of-band harmonic suppression up to 3.5