Design of fourth order dual-mode microstrip filter by using interdigital capacitive loading element with high selectivity

In this letter, a novel fourth order filter using dual mode open loop resonators is proposed. Dual mode open loop resonators are performed by using capacitive loading element. The main advantage of this loading element is that it controls the passband frequency and bandwidth, sensitively. Also, use of the dual mode open loop resonator provides a compact and narrowband bandpass filter. In order to demonstrate the validity the filter is designed, simulated and fabricated. Measured result shows good agreement with simulated frequency response.