Complementary diplexer

A contiguous planar diplexer in suspended stripline(SSL) technology is used in this article. The design of the diplexer is based on quasi-complementary LC lowpass and bandpass prototypes which are directly transformed into transmission line elements by using a quasi -lumped approach. This very straightforward design procedure requires no susceptance annulling networks and no introduction of unit elements which could limit the diplexer´s operation bandwidth. For achieving an optimal compatibility with external circuits, an ultra-broadband suspended stripline - microstrip line transition with a return loss of more than 10 dB from DC to 5 GHz was designed with very low channel insertion losses of typically less than 1 dB. The realized diplexer is extremely compact (63.5×14.9mm). This diplexer works at DC to 5GHz. The lowpass filter´s transmission band is from DC to 3GHz and the bandpass filter´s transmission band is from 4GHz to 5GHz.