LOW LOSS METAL DIPLEXER AND COMBINER BASED ON A PHOTONIC BAND GAP CHANNEL-DROP FILTER AT 109 GHZ

In this paper we present the design, fabrication and measurements for a Wband metal Photonic Band Gap (PBG) Channel-Drop Filter (CDF) diplexer, which can also be employed as a combiner to combine signals of different frequencies into a single waveguide. A PBG CDF is a device that allows channeling of a selected frequency from a continuous spectrum into a separate waveguide through resonant defects in a PBG structure. A PBG CDF transmits straight through all the frequencies except for the resonant frequency, and thus it represents a diplexer. Reversing the wave flow directions causes it to combine signals of different frequencies from two different waveguides into a single channel, representing a combiner. The device is compact and configurable and can be employed for mm-wave spectrometry with applications in communications, radio astronomy, and radar receivers for remote sensing and nonproliferation. High ohmic losses in metals constitute the main challenge in realization of a metal CDF at W-band. To mitigate the problem of ohmic losses, the filter was designed to operate at coupled dipole resonant modes instead of coupled fundamental monopole modes. The experimental samples were fabricated in two different ways: by conventional machining and by electroforming. The comparative results of the samplesʹ testing are presented in the paper. Frequency selectivity of 30 dB with a 0.3 GHz linewidth at 108.5 GHz was demonstrated. In addition, we suggest an experimental method to check the frequencies of separate resonant cavities of fabricated samples which do not properly operate and a possible way to adjust the geometry of the cavities for the frequencies to meet the required specifications.