An investigation of CPW bandpass filters using end-coupled resonators and square dual-mode rings

CPW bandpass filters employing end-coupled half-wavelength resonators or dual-mode ring resonators on alumina substrates are investigated. One filter employs three half-wavelength resonators with a combination of both edge and end coupling, and has a centre frequency of 23 GHz with a 1 GHz bandwidth and a measured insertion loss of 3.5 dB. The second filter is a CPW square dual-mode ring resonator filter with less than 1.2 dB insertion loss and 400 MHz 3dB bandwidth centred at 6.3 GHz. In addition to presenting successful results of these novel filters, the important effects of grounding are discussed and investigated experimentally.