Novel Miniaturized Bandpass Filters Using Spiral-Shaped Resonators and Window Feed Structures

In this paper, we present a new class of miniaturized microstrip bandpass filters with low-insertion loss, sharp-rejection and narrow-band performance.The proposed filters are composed of two spiral-shaped resonators and rectangle window feed structures.Both back-to-back and interdigital combinations of the resonators are adopted to obtain the miniaturized filter size.Compared to the traditional square loop bandpass filter, the sizes are reduced by 82% and 80%.It is also found that there is a pair of transmission zeros located on each side of the passbands, resulting in high selectivity.To validate the proposed idea, two demonstration filters with back-toback and interdigital spiral-shaped resonators are implemented.The measured results exhibit good agreement with the full-wave simulation results.