Dual band filter with quad-mode stripline resonator

This paper presents a quad-mode resonator with a square patch and via holes, which connects to the upper and lower ground planes through the via holes. This resonator has four fundamental modes, incorporating three transmission resonance modes and one quasi-lumped component resonance mode. The resonant frequencies of these modes can be shown to be easily handled by an increase and decrease in the number of via holes connected to the square patch and the ground. Furthermore, the dual band filter in the size of 5.0 mm × 5.0 mm × 1.5 mm is designed by a single resonator and demonstrated.