Concentric distributed resonators and filters

In this paper we present a concentric, multiple resonant elements realization of a distributed filter. The proposed filter has 3 poles and is designed to operate at a frequency of 1.8 GHz with an absolute bandwidth of 40 MHz, equivalent to 2.22 %. Each resonant chamber of the presented filter consists of 25 individual resonant elements arranged in an interdigitated fashion along the circumference of three concentric rings. The resonator occupies a volume of 40 × 40 × 5 mm3 and has an unloaded quality factor of over 1800. The internal height of the filter (5 mm or 10.8°) is lowest reported in the literature. The measurements of the filter are in an excellent agreement with simulations — the measured insertion loss is 0.44 dB, while the theoretically predicted value stands at 0.37 dB.