Silicon-Micromachined Wideband Sub-THz Frequency-Diverse Antenna

This article presents the first compact, wideband, silicon-micromachined frequency-diverse antenna, operating across the 220–330 GHz range, designed explicitly for sub-THz imaging applications. The antenna consists of 80 slot radiating elements of twelve distinct sizes corresponding to half of the uniformly sampled wavelengths within the operating bandwidth. These elements are arranged in a Mills-Cross configuration for antenna designs A and B, supported by an innovatively shaped air-filled cavity. The cavity is engineered to support multiple higher-order, high-Q resonance modes, generating highly frequency-diverse, pseudorandom radiation patterns. The frequency-diverse antenna is fed by a three-section impedance-matching transitional direct waveguide and is fabricated using advanced silicon micromachining technology. This article comprehensively analyzes the antenna's radiation patterns and impedance matching across the entire waveguide band. The compact prototype, with an overall size of 18 mm × 16 mm × 0.933 mm (effective antenna dimensions of 11$\lambda \times 11\lambda \times 0.85\lambda$), is the most compact air-filled, cavity-backed frequency-diverse antenna reported to date. It demonstrates high radiation efficiency and is designed for direct mounting on a standard WR-3.4 waveguide flange. The antenna achieves a fractional bandwidth of 34%, with a return loss better than 10 dB, extending to 40% with a return loss better than 5 dB.