Design and comparison of various coupled line Tx-filters for a Ku-band block upconverter

In this contribution common coupled line filter topologies are developed for their application as Tx-filter in a Ku-band block upconverter (BUC) from 13.75 - 14.5 GHz. Tough requirements of Rx-, LO- and second harmonic suppression were achieved by a detailed analysis of the metallic losses as well as equalizing even- and odd-mode velocities of the coupled line section. Four different filters were designed on an alumina substrate resulting in high measured performance values and small size compared to other work. By using a hairpin topology a designed filter achieves a low insertion loss (IL) less than 1.5 dB, a return loss (RL) of better than 20 dB, for a 3 dB fractional bandwidth (FBW) of 14.7% while maintaining a second harmonic suppression of more than 20 dB.