A compact band-stop/band-pass filter using a narrow gap capacitive as J-inverter and a new octagonal defected ground structure (DGS)

In this paper, we proposed a new compact DGS band-stop filter with broad passband and low insertion loss in the stop-band. The philosophy of the structure behind this new microstrip band-stop filter is simple as it is composed of a pair of octagonal DGS-slots and an open-stub as compensated microstrip capacitance. The filter will be realized through direct electromagnetic coupling and slow wave effect methods. With this configuration, the BSF with higher compactness, broad passband and sharp transition characteristics was realized. Additionally we present a novel compact band pass filter employing metal-loaded slots etched in the ground plane (DGS) and a simple capacitive gap on the top. With the proposed technique, a simple transformation from LPF to a corresponding BPF was realized. In order to validate the feasibility of the proposed design method, a band-stop filter with 0.9-dB ripple is designed, fabricated, and measured. The experimental results agree well with the simulation results.