Diplexer with trisections synthesized by frequency-dependent coupling

Microstrip diplexer is realized with trisection bandpass filters synthesized by frequency-dependent coupling between nonadjacent stepped-impedance resonators. The trisection has a passband response of generalized Chebyshev form with two transmission zeros. The coupling is implemented by sliding both the high- and low-impedance sections to achieve the desired frequency-dependence characteristic at the design frequency. A trisection bandpass Alter at 3.5 GHz and a diplexer with passbands at 3.15 and 3.5 GHz are fabricated and measured. Measured data show good agreement with the simulated responses.