Micro-coaxial V-/W-band filters and contiguous diplexers

A millimetre-wave diplexer is demonstrated using two singly terminated bandpass filters fabricated using surface micromachined rectangular-coaxial transmission lines. Modified seventh order Chebyshev bandpass filters with 0.1 dB passband ripple are designed to operate from 50 to 75 GHz and from 75 to 110 GHz. These two filters are simply combined using a common junction to form a contiguous 50-75 GHz and 75-110 GHz diplexer. The singly terminated filter values are adjusted by use of a common factor that modifies the admittance properties of the filter to facilitate their parallel combination. The two filters and their diplexer combination are fabricated and the measurements are compared favourably to the theoretical models.