A compact dual-frequency square ring antenna with filtering characteristics

In this paper, a compact square ring antenna is presented, which shows dual-frequency filtering characteristics. The antenna is designed for the 5.2 and 5.8 GHz wireless frequencies with between-band gain suppression of approximately 18 dB at 5.45 GHz. The dual-frequency response is realized through a multilayer design, where the antenna uses triangular perturbation elements within the square ring element, along with a C-shaped aperture and L-shaped microstrip feed. The resonant frequencies, bandwidths, and between-band gain suppression can be modified through optimizations of the antenna dimensions. The antenna is compact in size, with a square ring length of 11.4 mm, or 0.21λ, on each edge. The antenna shows broad beam radiation patterns at both resonant frequencies and over the vertical and horizontal polarizations.