Design Of The Stepping Variable Bandpass Filter

With the rapid development of modern communication technology and the speeding up of informatization,electromagnetic environment is increasingly complex while the frequency resources are scarce.Tunable transceiver bandpass filter are playing an important role in improving the wireless electromagnetic compatible environment,enhancing the receiving sensitivity and increasing the utilization rate of radio frequency spectrum,etc.Compared with the fixed bandwidth filter,continuous tunable bandpass filter is inadequate in power capacity,reliability and cost.Therefore,considering actual performance and demand balance of the engineering application,the stepping adjustable bandpass filter offers broad application prospect.Tunable resonator filters are generally constituted by two parts of resonator and adjustable device.The resonator used in this paper is microstrip rectangular ring resonator and the adjustable device adopted is the PIN diode switch.With the two parts,the stepping variable bandpass filter can be designed.Firstly,the switch features of the PIN diode switch is analyzed by ADS simulation,in which passive equivalent lumped model of the PIN diode switch can be obtained in the frequency selected.Then the basic working principle of ring resonator is analyzed.Finally,two kind of step variable bandpass filter are designed.(1)Microstrip rectangle ring is loaded with uniform line internal and the PIN diode switch to realize stepping variable bandpass filter.When the PIN diode switch turns to OFF state,the center frequency of the passband is at 2.8GHz,the insertion loss is 0.88GHz,absolute bandwidth equals to 150MHz,relative bandwidth is 5.4%,and the attenuation outside the band is about 15dB.when the PIN diode switch turns to ON state,the center frequency of the passband is at 5.4GHz,the insertion loss is 1.48GHz,absolute bandwidth equals to 1.2GHz,relative bandwidth is 22%,and attenuation outside the band is more than 20dB.(2)Microstrip rectangle ring is loaded with stepped impendance line internal and the PIN diode switch to realize stepping variable bandpass filter.when the PIN diode switch turns to OFF state,the center frequency of the passband is at 2.8GHz,the insertion loss is 1.06GHz,absolute bandwidth equals to 100MHz,relative bandwidth is 3.6%,and the attenuation outside the band is more than 15dB.when the PIN diode switch turns to ON state,the center frequency of the passband is at 5.4GHz,the insertion loss is 1.1GHz,bsolute bandwidth equals to 1.1GHz,relative bandwidth is 20%,transmission zero appears at the right side band and attenuation outside the band is more than 30dB.