Miniaturized Low Insertion Loss Multilayer Capacitively Loaded Step-Impedance Interdigital Bandpass Filter

In this paper, a miniaturized low insertion loss interdigital bandpass filter with capacitively loaded stepped impedance resonators (SIR) in Low Temperature Co-fired Ceramic (LTCC) technology is introduced. By using SIR and capacitive loading structures based on epsilon(r) = 41.77 substrates, a wideband interdigital bandpass filter has been realized for the frequency range from 3.1 GHz to 4.8 GHz. Measurement shows insertion loss less than 0.8 dB, return loss better than 15 dB in the pass band with the center frequency at 3.95 GHz and bandwidth ratio of 43%. The filter has a size of 2.15 x 2.6 x 0.85 mm(3).