This work presents an interference based W-band single-pole double-throw (SPDT) in rectangular waveguide and liquid crystal technology. In radiometers, this kind of SPDT can be used e.g. for switching to the calibration load for power calibration. The SPDT is designed with an E-plane power divider, two different paths for the phase shifting regions, being separated by 30 mm to provide enough space for the used magnets for proof-of-concept, and a coupled line combiner, where the interference is taking place. Rexolite 1422 is serving as liquid crystal cavity. The matching is better than -12 dB between 88 GHz to 110 GHz, except a peak around 102 GHz. The insertion loss is less than 3 dB between 89 GHz to 105 GHz, while exhibiting an isolation of at least 9 dB in this frequency range. From 90 GHz to 100 GHz, isolation is even between 10 dB to 12 dB.