Varactor-Tuned Superstrate-Loaded Antenna and Filtenna for X-Band Applications

This article presents a novel superstrate-loaded frequency-agile cavity-backed slot antenna (CBSA) and filtenna for X-band (8-12 GHz) applications. The antenna is designed by combining the electromagnetic fields of a half-mode cavity and a radiating slot operating in their fundamental modes. Frequency tuning is achieved using a single varactor mounted on a superstrate to form a capacitive tuning network above the slot aperture. The superstrate design provides a simple yet effective means to reconfigure the frequency using fewer tuning elements, lower losses, and improved biasing feasibility than other semiconductor-based tunable slot antennas. Two in-house manufactured prototypes of the antenna, implemented using substrate-integrated waveguide (SIW) technology, demonstrated tuning ranges of 7.8-11.1 GHz (35%) and 9.6-11.1 GHz (14.5%). Finally, the proposed superstrate-loaded antenna element is co-designed with a contactless-tuned evanescent-mode (EVA-mode) cavity resonator within a filtenna unit. Due to the integrated filtering capability, the out-of-band radiation suppression is better than 20 dB across the tuning range. The filtenna presented in this article is the first in the literature to be implemented using high-Q cavities and SIW technology for applications above 6 GHz. Compared with other cavity-based SIW implementations at the X-band frequency range, the electronically tuned SIW-based antennas and filtenna presented in this article demonstrate the largest frequency tuning ranges with fast tuning speeds while maintaining a compact module.