Enhancing coupling of capacitively loaded combline resonators

Using an interresonator tap will significantly enhance interresonator coupling. In general, the tap being wide, short, and positioned far away from ground will all enhance coupling even further, though there is an upper limit on the coupling. Resonant frequency will increase as coupling increases. Using capacitive loading and a tap allows coupling three times stronger than quarter-wave resonators can provide. Using capacitive loading will also enhance coupling and reduce the physical length of a resonator. But the stopband will narrow and the layout will become more complex. Adding digits to the capacitively loaded resonator will further reduce the length, but the layout becomes even more complex. Adding an interresonator tap will expand the stopband, but it will still be narrower than the stopband of a quarter-wave resonator.