Compact Low Loss L-Band Diplexer for Space Applications

For application in satellite multibeam arrays, a compact low loss diplexer has been developed.´ Branch filters using temperature compensated cylindrical dielectric resonators mounted in a circular cut-off waveguide give a mechanically simple and robust construction with excellent on board power handling capability. Techniques for manufacture of composite resonators with LiNbO3 to close tolerances on frequency and temperature coefficient have been developed, and bandpass filters with uniform and temperature invariant properties were fabricated. A special input/output cross-coupling is applied in order to give enhanced rejection in part of the filter stopbands. As part of an ESA (European Space Agency) project concerning a multibeam array model, L-band diplexers having less than 0.5 dB loss in 15 MHz passbands and up to 80 dB rejection in a 15 MHz band 100 MHz from passband centers have been manufactured and tested in a 60°C temperature range.