Design of Monoblock Antenna-Loaded Bandpass Filters with General Synthesis Theory of Complex-Loaded Filters

This work presents a general synthesis and design framework for a monoblock antenna-loaded filter (ALF) module. The filter network is synthesized with full consideration of the antenna characteristics as a frequency-variant complex load, which is essentially different from traditional method where the antenna Q-factor is limited. Complex reflection zeros (RZs) are introduced as additional degrees of freedom to optimally satisfy the matching and rejection requirements. The integrated ALF module consists of a pair of symmetrical monoblock dielectric resonator (MDR) filters and a dual-polarized patch antenna in a monoblock fashion. To realize the designated asymmetrical transmission zeros (TZs), a quadruplet structure with a controllable diagonal coupling is used in the MDR filters. The fabricated prototype exhibits excellent matching, filtering, and radiation performance, demonstrating the effectiveness of the proposed synthesis approach and design concept.