A compact dual-band passband filter

A microstrip dual-band bandpass filter based on mixed electronic and magnetic coupling is proposed in this letter. The proposed circuit consists of a second-order bandpass filter and a grounded couple-line, which can generate four transmission zeros at stopband to enhance the selectivity. A prototype operating at 1.5/1.85GHz has been designed, fabricated and measured. The measured results show the insertion loss of less than 1dB and the return loss of better than 15dB. The rejection level between these two pass-bands is larger than 30 dB, which are in good agreements with the simulated ones.