Tunable Bandpass Filters for Multi-Standard Applications

In this paper the results of a demonstrator of a tunable five pole bandpass filter for multi-standard applications is presented. The couplings and frequencies of the resonators are controlled by a moveable tuning plate located at the bottom side of the assembly. The filter is laid out to have a constant passband bandwidth of 25 MHz and continuous tuning capability of the center frequency from 1810 MHz to 2170 MHz. The frequencies are tuned by ceramic tuning elements to guarantee a high quality factor. The measured insertion loss is less than 1.8 dB for the whole frequency range. Furthermore a novel filter tuning concept for base station assemblies will be discussed, which shows more flexibility and requires less mechanical accuracy.