tunable RF bandpass filter

Hello everybody!

I need to design a tunable bandpass filter 910-1150MHZ center frequency and 20MHz bandwidth to included in a bigger design. I haven't been able to find many articles-white papers-books or former design in the web. Could please anybody help me, ideas, papers, resources? The idea is quite clear, suppose coplanar or microstrip interdigit or coupled lines and varactors in order to change electric lenght of the coupler in order to tune the center frequency. But I would appreciate any example, previous and similar design, any kind of resources to start with

Thanks a lot in advance

DAVID RF

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