Bandpass filters using grounded stub-loaded microstrip periodic structure for suppression of modes

Abstract In this paper, a grounded stub-loaded microstrip periodic structure (SL-MPS) is presented and its transmission characteristics are investigated. A new method of suppression of modes is proposed through adding grounded via holes on the grounded SL-MPS for the design of bandpass filters (BPFs). In order to validate the feasibility of suppression of modes of grounded SL-MPS, two cases of BPFs with different dimensions are designed. For the case of BPF with suppression of adjacent modes, the simulated and measured results of BPFs demonstrate that the fundamental and 2nd high-order modes can be effectively suppressed. For the other case of BPF with suppression of multiple modes, the fundamental, 1st, 3rd and 4th high-order modes can be successfully suppressed. The measurements of these BPFs are reasonably in agreement with their simulations. Observed from the theoretical analysis and experimental results, the proposed method can effectively widen the stopband of BPF by suppressing unwanted modes.