A compact coupled-line bandpass filter with multiple capacitive cross-couplings to create four transmission zeros is proposed. The locations of transmission zeros can be adjusted by varying the values of cross-coupled capacitances so as to improve the filter selectivity. The proposed filter is based on one-eighth-wavelength (λ/8) coupled-line sections and quarter-wavelength (λ/4) resonators, thus it occupies only half of the circuit area comparing with the conventional coupled-line bandpass filters. Specifically, a fourth-order microstrip coupled-line bandpass filter centered at 2.46 GHz with a 3-dB bandwidth of 10.2% and four transmission zeros is implemented and examined.
- Bandpass filter
- Multiple cross-couplings