Tunable Coaxial Resonator Filter based on Posts with Rectangular Bars

In this paper, a tunable microwave bandpass filter is presented which allows for different center frequency combinations while maintaining a constant bandwidth over a wide frequency range. The special T-shaped form of the coaxial resonator posts allows for adjustment of the center frequency and coupling factor while minimizing the amount of tuning screws. In total, only three tuning elements are used to control the input and inter-resonator coupling as well as the center frequency of the bandpass filter. The filter offers a 57MHz±3MHz bandwidth over a 400MHz frequency range. A demonstrator has been build to verify the concept and exemplary measurements have been taken at 1.73GHz, 1.93GHz and 2.10GHz. The simulations have been compared to the measurements, which validates the 57MHz bandwidth at the 20 dB return loss level for all tuning states.