Miniaturized bandpass filters using capacitor loaded folded slot coupled resonators

This paper introduces a new compact bandpass coupled resonator filter with Chebyshev response. The proposed filter consists of compact folded DGS resonators as building blocks of the filter. Some ways to reduce the resonant frequency by integrating a suitable lumped capacitor within slots is also presented. The filter has a compact size, which is 55% smaller than the conventional filter using unloaded DGS slots. Mixed coupling configuration is considered for design. In order to validate the feasibility of the proposed structure, a bandpass filter with centre frequency of 2.4 GHz is designed, fabricated, and measured. The filter has a passband from 2.175 to 2.79 GHz and a wide stopband with a rejection higher than 20 dB up to more than 11 GHz. Insertion loss of less than 0.7 dB is achieved within the passband. The experimental results agree well with the simulation ones.