Design Method for Low-Profile, Harmonic-Suppressed Filter-Antennas Using Miniaturized-Element Frequency Selective Surfaces

A new technique for designing low-profile filter-antennas with wideband harmonic suppression capability is introduced. A filter-antenna element in a periodic infinite array consists of a radiating patch and an asymmetric frequency selective surface with an inductive wire grid and cascaded capacitive metallic strips. Based on this topology, a filter-antenna element operating at 2.12 GHz was designed with an extremely small thickness of approximately λ/27. A desirable second-order bandpass response and an excellent harmonic suppression of better than 30 dB over 2.4-10.0 GHz were achieved. Using this element, an 8 × 8-element filter-antenna array was designed. A maximum aperture efficiency of 60.3% was obtained within the operating band of the array. The aperture efficiency reduces to nearly zero over the frequency range from 2.3 to 10.0 GHz, which demonstrates the excellent filtering performance of the proposed filter-antenna outside of its band of operation.