Cascaded LPF/BSF with Stepped Impedance Loop Resonator for RF Applications

In this paper a microstrip based low-pass filter (LPF) cascaded with band stop filter (BSF) structure is presented. Usually, microstrip filters are designed as stepped impedance resonators. The size of microstrip filter depends on the order of filter and its length is decided by the wavelength. Here the stepped impedance resonator is modified into square loop with impedance variation. Different energizing techniques are studied and optimized. The filter with embedded band-stop structure with closed loop structure designed at 1.5 GHz center frequency and is fabricated on an FR4 epoxy substrate and validated experimentally using Field fox Analyzer.