Designing Modern Compact Microstrip Planar Quadband Bandpass Filter for Hand Held Wireless Applications

AbstractThis paper presents a modern compact quad-band bandpass filter (BPF) using dual-mode stub loaded half wave (λ/2) resonators, where a couple of directly fed resonators are loaded with two identical inner resonators such that the direct fed resonators will act as feeding structure for the loaded resonators. Based on the proposed stub loaded resonators, a modern filter with seven transmission zeros (TZs) is designed by folding the two identical inner resonators. The proposed design has a symmetrical geometry, therefore even-odd mode analysis is used to predict the resonant frequencies of the passbands. The first and second passbands are obtained through fundamental odd and even modes respectively while the third one is achieved by placing loaded inner resonators in the proposed design. The second even harmonic of the direct fed resonators is utilized to achieve the fourth passband and is controlled by the stubs loaded at the middle of the resonators. The filter is simulated and fabricated for the purpose of validation, wherein a good agreement can be seen in both simulated and experimental results.