A Ku-band transversal filter with a center frequency of 12 GHz and a bandwidth of 6 GHz using directional couplers made of a multilayer ceramic has been proposed and developed. The directional coupler can realize a wide range of frequency characteristics, e.g. coupling of 3.50.5 dB in the frequency range of 10 to 17 GHz and a wide range of coupling values, i.e. 3 to 35 dB. Calculations have confirmed that the increase in insertion loss due to a decreasing Q-factor can be much less than that for a resonator filter. The transversal filter was fabricated without additional tuning, and measured results agreed well with calculated values.

A TE010 mode dielectric resonator is proposed to be used in a millimeter-wave filter. The resonator was fabricated using the photolithographic technique, and high unloaded Q of 1610 was obtained at 60 GHz. A planar circuit type millimeter-wave filter, using TE010 mode dielectric resonators, was fabricated using NRD guides as input and output circuits. The measured filter characteristics agreed with calculated values well. The filter can be applicable to future millimeter-wave mobile communications systems.