Compact Low-Loss Probe-Coupled Iris-Less Combline Filters

A new class of filters called as "Probe-coupled iris-less combline filters" are presented for wireless basestation applications. The main advantage of these filters is that even narrow band filters can be realized without using the metal partitions (de-coupling irises) between the resonator rods. The inter-coupling between the resonator rods can be controlled by changing the lengths and/or heights of the metal probes. This results in lesser milling cost and lower insertion loss. Moreover, attenuation poles at frequencies close to the passband frequencies can be obtained by the probes, resulting in higher selectivity. A typical insertion loss as low as about 0.4 dB has been measured for a full band PCS1900 filter with a selectivity of more than 60 dB in the transmit band. The overall size of the filter is only 4.7"×3.15"×1.7".