Microstrip disk cavities filter using gap capacitances coupling

A microstrip disk cavity bandpass filter using gap capacitance coupling is proposed and tested. A theoretical evaluation of the main capacitances and gap capacitances in a shielded microstrip multiconductor system is presented. The filter´s resonators are microstrip circular disks operating in the TM/sub 110/-mode and the coupling elements are the gaps between disks. Using a suitable substrate with high dielectric constant gives the microstrip disk cavity a high quality factor. The advantages of this filter are its small size, narrow passband, convenience for planar integration, and excellent electrical performance. In addition, its spurious passbands are far from the main passband. A foundation for analysis and synthesis of this filter is established. Experimental results are presented for a filter with five cavities.<>