A Composite Mode E-band Low Loss Bandpass Filter

This paper introduces a composite mode E-band low insertion loss bandpass filter. It is composed of two smaller TE<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</inf>-mode resonators and a large multi-mode resonator, where the resonant frequencies of TE<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">201</inf> and TE<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">301</inf> mode are adjusted to be closely aligned by inserting a tuning nail at the center of the large resonator, resulting in a composite mode. The input coupling is realized by offset feeding, leading to the generation of two transmission zeros (TZs) outside the passband. The measured results show that the filter operates within $73.96-76.14 \mathrm{GHz}$ frequency range with return loss better than 15 dB and the insertion loss as low as only $0.6 \pm 0.15 \mathrm{~dB}$, accompanied by two TZs located near 71.55 GHz and 73.31 GHz respectively, thereby demonstrating good electrical performance.