A high performance K-band diplexer using high-Q micromachined cavities

Microwave diplexers are often used on transmit / receive systems to isolate a power transmit stage from a sensitive receive stage sharing a common antenna. With the ever-increasing need for efficient bandwidth usage, diplexers exhibiting close channel spacing, low insertion loss and small channel bandwidths are increasingly necessary. Utilizing two high Q cavity resonators, a Duroid-based high performance diplexer has been designed, fabricated and measured. This diplexer shows transmit / receive bandwidths of 2.39% and 1.8% and insertion losses of 2.38dB and 2.89dB, respectively. Channel center frequencies of 18.8GHz and 20.7GHz provide a channel separation of approximately 9% and channel to channel isolation greater than 24dB. Utilizing machined aluminum cavities and a Duroid substrate the diplexer design provides insight into cavity based diplexer construction, allowing for the design of a silicon based micromachined cavity diplexer. Simulation results from this silicon-based diplexer are also presented.