Novel Microstrip Bandpass Filter With Slotted Hexagonal Resonators And Capacitive Loading

A compact microstrip elliptic-function bandpass filter (BPF) is introduced in this paper. The techniques, etching slot and adding open stubs with capacitive loading, are applied to enhance the self-inductance and self-capacitance of the hexagonal open-loop resonators, which increases the electrical length of the resonator. At the same time, the capacitive coupling between two hexagonal resonators is enhanced. So, size reduction and improved insertion-loss performances are obtained. Compared to the conventional design, the central frequency and insertion loss of the proposed filters are reduced by 28% and 3.1 dB, respectively. Measurements show that the proposed filter, called type II, has a fraction bandwidth of 23% at central frequency 1.84 GHz and its insertion loss in passband is less than -1.5dB. The BPF occupies only 12times21.2 mm².