Compact dual-band bandpass filter for GNSS bands deploying octagonal open-loop resonators

A compact microstrip dual-band bandpass filter for Global Navigation satellite System (GNSS) receivers using a direct RF front-end is presented in this paper. The proposed filter is based on half-wavelength octagonal open-loop resonators. Dual band characteristic is obtained by integrating quarter-wavelength resonators into the octagonal open-loop resonators. The resulting filter covers the two bands; 1164-1300 MHz and 1559-1610 MHz, which are currently used by the operational GPS and GLONASS constellations, and will also be used by the upcoming Galileo system. The filter is designed and implemented in microstrip technology, with its operation validated. It is compact, light and low cost. Experimental and simulated results are presented that demonstrate close agreement. Around 2.6 dB insertion loss and more than 25 dB stop-band attenuation in two bands is achieved with the proposed filter.