A Miniaturized Surface Mount Compatible Quasi-elliptic Response Bandpass Filter Using Multilayer Substrates

In this paper, a miniaturized UHF band second-order quasi-elliptic response bandpass filter (BPF) is proposed. Traditional UHF transmission line filter suffers from large circuit size and large footprint area. For the purpose of miniaturization, spiral quarter-wavelength short-circuited resonators is used in this BPF filter design. For further footprint reduction, the proposed filter is implemented by stacking multilayer substrates. Coplanar waveguide (CPW) transmission lines are used as input and output ports on the same layer, which can be compatible with surface mounting technology (SMT) effectively. It is observed from simulation and measured results that the return loss and insertion loss at a center frequency of 433 MHz are about 15 dB and 0.7 dB, respectively, with a fractional bandwidth of 19%. Two transmission zeros are located on both sides of the passband. A good agreement is obtained between the simulated and measured results.