Monoblock Antenna-Loaded Filter Pair: Synthesis, Model Extraction, and EM Design

This article proposes a monoblock module incorporating a dual-polarized patch antenna and two symmetrical channel filters, forming an integrated antenna-loaded filter (ALF) pair, for the first time. The module offers high-frequency selectivity, stable gain, compact size, and low insertion loss. To address design challenges, a generic synthesis and electromagnetic (EM) design framework is also proposed. In this framework, the antenna is treated as a frequency-variant complex load to the filter, and the filter network is synthesized by fully considering the antenna characteristics. This approach allows for higher design freedom. To preserve the intrinsic radiation characteristics and enhance the matching bandwidth, three practical strategies are innovated: introducing a buffer resonator to the antenna, creating an air cavity under the patch antenna, and feeding the patch antenna with a dielectric waveguide. The concept of a virtual-insignificant-port (VIP) model is introduced for extracting the overall circuit model of the ALF for deterministic EM design. The proposed framework is demonstrated with step-by-step details, showcasing its flexibility, convenience, and versatility for ALF modules. The validity of the monoblock ALF module is affirmed by a ceramic-based prototype, whose experimental results exhibit excellent impedance matching, frequency selectivity, and radiation properties.