A compact dual-mode bandpass filter for GPS, Compass (Beidou) and GLONASS
A dual-mode bandpass filter with compact size is proposed by using a new type of rotational symmetric dual-mode rectangular resonator. Due to the feed structure, two transmission zeros are generated near the lower and upper passbands to improve the skirt-selectivity of the filter. By adjusting the mutual coupling between the loading meander-line loop resonators, one transmission pole and neighboring transmission zero can be controlled. Two capacitors are added between each meander-line loop resonator and feedline to improve in-band performance. Based on this topology, a compact filter for GPS/Compass (BeiDou)/GLONASS applications has been designed, analyzed and fabricated. Measured results verified the validity of this design methodology. This proposed filter exhibits the small size of 0.11 λg×0.10 λg.