Multilayer Dual-Band Bandpass Filter With Multiple Transmission Zeros Using Discriminating Coupling

A multilayer dual-band bandpass filter with two independent paths combined between common input and output ports is proposed in this letter. Slot-coupled resonators and hairpin-line resonators form the two passbands centered at 2.4 and 5 GHz with 3-dB fraction bandwidth of 8% and 8.8%. Discriminating coupling is used in this letter to introduce a transmission zero (TZ) at third harmonic, validated by synthesis equations. And more TZs located at sideband of both passbands are obtained by source-load coupling. All these TZs contribute to high selectivity and extended stopband. The proposed filter is fabricated through a multilayer substrate to validate the design. Both simulated and measured results are in good agreement.