Investigations On Rf Tunable Filter Technology And Its Application In Wireless Communications

Nowdays, due to the increasing demand of communication service, more and more frequency spectrum resource were needed. Thus, the high-effieciency utilization of spectrum is becoming reseach hotspot, such as cognitive radio, convergence of three networks and spectrum sharing technology. Different from the traditional communication technology, these advanced technologies can dynamically switch the frequency band and channel to communicate between different services and enhance the utilization of spectrum. However, the fixed-passband RF/Microwave filter could not suitable for the RF/Microwave front-end transceiver. Therefore, the miniature tunable filter with reconfigurable center frequency and bandwidth are highly demanded.In the dissertation, we major in the investigations on reconfigurable RF/Micorwave front-end transceiver and tunable bandpass filter, including the device designs and theory as well as verification by experiments. The major innovation achievements are listed as follows:1. This dissertation presents a general analytical approach to accurately predict the nonlinear distortion of varactor-tuned bandpass filters with arbitrary topology. The linearized circuit and its admittance matrix are derived to study the nonlinear behavior by means of the Volterra series representation. The effects on third-order intermodulation distortion (IMD3) are characterized for the principal filter parameters, such as tunable resonator configuration, susceptance slope, fractional bandwidth, unloaded quality factor and filter topology. The analytical results are fully coincident with the Harmonic Balance (HB) simulations using computer-aided design (CAD) varactor model. A two-pole 1.0-1.3 GHz tunable bandpass filter (BPF) with constant bandwidth 105MHz is fabricated and measured to validate the theory. The work mentioned above is already published in IEEE Trans. on MTT, vol.63, no.ll,2015.2. In this dissertation, a general approach is presented to synthesize the coupling matrix that matches to arbitrary frequency-invariant complex source and load. The approach converts the objective scattering matrix and reference impedances into an admittance matrix of multicoupled circuit based on the definition of power wave. The proposed method was verified by numerical and also simulated tests carried out with various complex reference impedances. The work mentioned above is already published in IEEE MWCL, vol.25, no.6, 2015.3. This dissertation proposes a two-path mixed coupling tunable bandpass filter with constant bandwidth. This compact configuration can achieve little bandwidth variation in a large tuning range. Presented with the equivalent circuit of the coupling structure, the analytical formulas of the two-path mixed coupling structure are derived to determine the initial dimensions of the resonator quickly. Furthermore, to enhance the selectivity and the out-of-band rejection, additional resonance circuit is introduced in the I/O structure to generate multiple adjustable transmission zeros. For verification, a tunable filter covering the frequency band of 0.78-1.35 GHz is implemented and measured. The experimental results are in good agreement with theory and simulations. The work mentioned above is already published in IEEE MWCL, vol.24, no.7,2014, IEEE MTT-SIMS2014.4. In this dissertation, a box-section bandpass filter consisting of hybrid λ/4 and dual-mode resonators at X-band is presented. Compared with the conventional even-odd mode method, the dual-mode resonator in the proposed filter is equivalent to separate λ/2 and λ resonators. A generalized synthesis approach is firstly proposed with extensive discussions on designing asynchronously tuned resonators. One prototype centered at 8.65 GHz, with 0.9 GHz passband is fabricated. Measured results of this filter demonstrate very high single-sided selectivity with 40dB skirt slope steepness of 1.98 and minimum in-band insertion loss of 1.43 dB. The work mentioned above is already published in IEEE MWCL, vol.24, no.12, 2014 and authorized patent (ZL 2013 1 0552948.3)5. Based on the previous research on tunable filter design and theory, the reconfigurable RF/Microwave front-end transceiver prototype was achieved. The narrow band tunable filter with constant bandwidth is used to switch channel and reject the interference signal.