Ku-band substrate integrated waveguide bandpass filter design using mechanical tuning
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Substrate integrated waveguide (SIW) filters are widely used due to their easy fabrication techniques and relatively high quality factor. In microwave frequencies, manufacturing tolerances become comparable with wavelength and affect filter performance. Tuning resonator center frequencies and couplings between resonators allow correcting the errors that are caused by imperfections. An iris bandpass filter is designed in Ku-band using coupling matrix approach which relates mathematical coupling values to physical dimensions. SIW tuning is usually done by adding varactors to the circuit. This introduces nonlinearities which may be undesirable while also requiring external control voltages. A mechanical tuning method for SIW, similar to tuning screws that are used in waveguide filters, is analyzed for resonators and couplings. It is modified by using small surface mount resistors to achieve a more compact structure. Tuning mechanisms are inserted to designed filter and fabricated on a low loss substrate. Time domain method for tuning coupled filters is introduced as a tuning algorithm. Using mechanical tuners, SIW filter is tuned to desired filter performance.