Ceramic-elements-based distributed resonators and filters

The aim of this paper is to introduce a new family of low-profile resonators and filters that achieve high performance and low insertion loss without the need for post-production tuning. The new resonator is termed ceramic-element based distributed resonator and consists of a matrix of subwavelength-length ceramic posts connected in the inter-digital fashion to the top and bottom ground planes. Such a disposition of elements is beneficial for two main reasons. First, the frequency of operation of such a resonator becomes a function of its height, unlike in the case of standard ceramic resonators. Second, the ceramic element matrix performs inherent dimensional averaging, resulting in a filter that requires no post-production tuning. As a demonstrator of the proposed technology, a two-pole filter using a ceramic with a dielectric permittivity of 37 and a loss tangent of 0.0033 and operating at a centre frequency of 3.5 GHz was designed, fabricated and tested. The measured and predicted results are in excellent agreement and are extensively discussed.