Comparison of the Performance of Inline Filter Topologies Implementing Transmission Zeroes

Advancements in compact, high-performance filtering structures are crucial for high performance communication systems. Applications such as massive MIMO antenna arrays require filters which are at the same time strongly selective and highly miniaturized. Traditionally, transmission zeroes in the filtering response have been obtained using cross-coupling between multiple resonators. Recently, techniques have been developed for the retrieval of transmission zeroes with inline topologies. In this work, two of such techniques are compared, the extracted-pole and the path filter. The size and performance of these topologies are evaluated by creating and comparing a test filter for each of them, working around 3.7 GHz with a 5.4% bandwidth. Substrate Integrated Waveguide (SIW) prototypes have been fabricated and measured.