Novel Miniaturized Light-Weight Coaxial Cavity Filters With Electrical Mainline Couplings

This paper provides a comprehensive discussion for a novel class of miniaturized light-weight coaxial filters employed in 700 MHz supported 5G stations. The proposed resonators are characterized with square top plates and zigzag “arms”. All the zigzag arms are inter-coupled in an overlapped fashion, reducing the filter length and specially providing electrical/capacitive (negative) mainline couplings. Owing to the capacitive loadings and large-area square top plates, resonant frequencies can be decreased to very low frequency bands inside a compact size, which further boosts the light-weight application in communication systems. Besides, with the simple construction with only metal structures, this type of filter features low costs. The implementation of both negative and positive cross couplings is also discussed to adapt to the proposed filter configuration, ensuring the flexible placement of transmission zeros (TZs) and the customization of sophisticated filter responses. The good results of a 12-pole Tx filter and a fabricated 10-pole Rx filter have validated the effectivity of the presented structures. Moreover, implemented with the proposed configuration, the weight of a network comprising six quadplexers is expected to be reduced by 32% compared with the device based on conventional technology.