Wideband mm-Wave Differential Bandpass Filter Using Micromachined Rectangular Coaxial Lines

This paper proposes a millimeter-wave (mm-wave) wideband differential bandpass filter (BPF) that utilizes rectangular micro-coaxial transmission lines as resonators. The differential BPF is ideal for application in high-sensitivity and integrated mm-wave systems due to its low loss and compact structure. The passband of the differential mode (DM) is formed by a fifth-order Chebyshev bandpass filter, and the wideband common mode (CM) suppression is improved by loading connecting lines on the symmetrical plane. The equivalent circuit of this symmetrical structure is analyzed with the use of microwave network parameters. Simulated results show that the differential BPF has an operating range of 30GHz to 50GHz, with a low insertion loss of 0.54dB and significant CM suppression over 26 dB.