A compact band-stop filter with wide bandwidth and far spurious stop bands

In this paper, a compact band-stop filter with wide bandwidth and far spurious stop band is presented. The traditional band-stop filter usually be designed with 1/4 wavelength admittance/impedance inverter, its volume is bulky and spurious stop band is near the working stop-band. In this paper, for realizing miniaturization, wide bandwidth and far spurious stop band, a capacitor is loaded in the band-stop filter´s resonators and a trench is dredged on the surface of the capacitors. At first, a rectangle cavity with a capacitor is proposed, its spurious stop band is 4.5 times far than the center frequency. Then several such cavities are connected in series to form a band-stop filter, its stop-band centered at 5GHz, relative bandwidth is 8%, and its spurious stop-band is higher than 23GHz. The filter has a transition of 100 MHz and the attenuation up to 40dB.