Research And Design Of Bandwidth Reconfigurable Filter Based On Different Process Conditions

With the increasing demand for new wireless communication services and applications,the rapid development of high-level integrated RF circuit systems,the coexistence of multi-standard and multi-band operation in a highly integrated and single wireless communication device has become the mainstream trend of microwave filters design.Until now,the tunable filters reveal significant advantages as compared to the filter bank,particularly for reducing the size and complexity of wireless communication systems.Reconfigurable filters not only can resolve interference at different frequencies between signal channels in multi-band communication system,but also play an outstanding role in reducing filter size and realizing high integrated and portable wireless equipment.This thesis focuses on the above topics,the main innovation of this work includes the following points:First of all,through analyzing the characteristics of the filter topology and coupling structure,we proposed a microstrip based bandpass filter with compact,low cost and flexible design method,which bandwidth is independently tunable.The adoption of the variable-capacity diode enables the switch between one and three transmission zeros with the same central frequency,and the bandwidth of the proposed filter at central frequency of 1.5 GHz can be switched to narrowband and broadband response.The resonator used in the filter consists of a uniform resonant cavity,a PIN diode,and an open circuit ring.The PIN diodes are used to connect or isolate the open loop to the uniform resonator.When the open loop is loaded,the open loop will be connected with the uniform resonator,and the filter center frequency is 1.54GHz with the relative bandwidth is 33%,the in-band fluctuation is less than 1 dB.Regarding the three transmission zeros of the resonator,the filter bandwidth achieves broadband response.When the open loop is open,the open loop will not be connected to the uniform resonator,its center frequency is 1.55 GHz with relative bandwidth 9%,the minimum insertion loss in the band is 0.12 dB.The bandpass filter shows a narrowband response due to one transmission zeros of resonator.There is only one PIN diode in the filter,which can act as a switch,therefore the microstrip-based bandpass filter designed in this work favors characteristics of miniaturization and low insertion loss.Through the in-depth study of the secondary resonant unit,a LTCC bandpass filter is designed with reconfigurable bandwidth.Two transmission zeros are designed for the bandpass filter at the out-of-band,wherein the transmission zeros at the lower frequency enable the sufficient attenuation between the mirror frequency signal and interference signal,while the transmission zeros at upper frequency can suppress secondary and three harmonics.After the implementation of the circuit in LTCC configuration in which the filter has a multi-layer structure,the coupling between the capacitors can be enhanced through moving the capacitor plate closer or change of the overlap between the capacitor plates.The resultant cross-coupling will produce a parallel resonance and introduce the transmission zeros outside its band,so the electromagnetic coupling effect of the bandpass filter will be obviously improved.Therefore,the reconfigurable bandpass filter has been realized with and without the loaded capacitors.Without the capacitors,the bandpass filter works in the band of 2.4 GHz-2.5 GHz,and the standing wave ratio is less than 1.2,and the bandwidth can be further tuned through adjusting the capacitance of the three-dimensional layered structure in the filters.As the increment of the capacitance,the bandwidth of the filter at the lower frequency increases,while the performance of standing wave ratio becomes worse.The results indicate the capacitance values between 0-0.4 pF will meet filter requirement,i.e.,the insertion loss is less than 2.5 dB and S₁₁ is less than-10 dB.With the GaAs processing technique,a reconfigurable bandpass filter with transmission zero-point is proposed at radio frequency.Using a semi-lumped topology to replace the traditional full-lumped inductor and microstrip transmission line can not only reduce the circuit size,but also increase the operating frequency of chip filters.By adjusting the gate bias circuit of the field effect transistor(FET),the capacitance of the series resonant cavity is changed and the bandwidth of the filter is adjusted accordingly.Compared with the traditional reconfigurable filter,a miniaturized bandpass filter with two transmission zeros is proposed.A chip circuit sample was produced and the tape out uses 0.25mm Ga AspHEMT technology.The area of the chip filter is only 0.86×0.96 mm².The two modes are measured at the filter operation frequency of 10 GHz,one of which operates at 9.11 to 10.51 GHz with a relative bandwidth of 14.27%and an insertion loss of 2.4 dB.The other passband operates from 8.58 to 10.87 GHz with a relative bandwidth of 23.5%and an insertion loss of 2.2 dB.In this work,the working mechanism and design technology of bandwidth reconfigurable filter are in-depth studied under different process conditions,which is great of great importance to the development of the next generation multi-functional communication system.