A Miniature Low-Loss Slow-Wave Tunable Ferroelectric BandPass Filter From 11-14 GHz

This paper presents for the first time a miniature, tunable slow-wave 2-pole ferroelectric filter with low loss operating from 11.5-14 GHz (20% tuning). The filter consists of sections of coplanar waveguide transmission lines that are loaded with high quality factor tunable ferroelectric capacitors with BST material. Each resonator section is loaded with a total of 12 capacitors resulting in a very compact size. Coupling between the slow-wave resonators, as well as matching with the input/output ports is achieved via inductive stubs. The measured insertion loss varies from 5.4 to 3.3 dB from 11.5-14 GHz and a bias voltage range from 0-30 V. The third-order intercept of the filter was found to be around 31 dBm. To the best of our knowledge, this is the smallest loss performance for such a filter in the 11-14 GHz range.