Research On High-performance Tunable Microwave Devices

With rapid development of modern wireless communication technology,the communication system is required to operate in multiple frequency bands with a smaller size and lower cost.In order to meet the requirements,the reconfigurable wireless communication systems are researched and developed.As a key component of the reconfigurable wireless communication transceiver,the tunable microwave devices play an irreplaceable role to improve performance of the communication system.Therefore,the development of high-performance tunable microwave devices has become an urgent requirement.Among them,the research on tunable diplexers with constant absolute bandwidth and high-order balanced tunable filters with multiple zeroes is still undeveloped.In addtition,as a basic component,the high-order tunable filter applied to design other high-performance microwave active and passive devices is also a research hotspot.Aiming at these issues above,this dissertation has done the following researches:1.Based on tri-mode synchronously-tuned resonator,a wide-tuning-range tunable diplexer with equal constant absolute bandwidth is proposed and firstly realized.By using a tri-mode synchronously-tuned resonator with flexible tuning behaviours,a three-pole tunable filter is designed.The designed filter,which is used as the tunable diplexer's lower channel,has constant absolute bandwidth,wide-tuning range and low insertion loss.Using the same design method,the upper channel realizes the same constant absolute bandwidth as the lower channel's,wide-tuning range and low insertion loss.The measurement results show that the two channels of the diplexer has a frequency-tuning range of 1.47-2.5 GHz(52%)and 2.2-3.5 GHz(45.6%),respectively.At the same time,they own a synchronously-tuned bandwith of 1.03 GHz.The 3d B-bandwidth of the two channels is 247.5±26.5 MHz,isolation between two channels is around 32 d B and insertion loss is better than 4.3 d B over the entire frequency tuning range.2.A wide-tuning-range diplexer with low insertion loss,high isolation and equal constant absolute bandwidth is proposed.By introducing source-load coupling and crosscoupling,each channel of the diplexer has three transmission zeros which are in mirrorsymmetric distribution.By placing two transmission zeros on the side where the other channel locates,the isolation between channels and the passband frequency selectivity of the diplexer are improved.Experimental results show that the two channels of the diplexer has a frequency-tuning range of 1.35-2.25 GHz(50%)and 1.9-3.0 GHz(44.9%),respectively.The achieved synchronously-tuned bandwith is 900 MHz and insertion loss better than 3.3 d B.While the isolation between two channels is around 38 d B and 3d Bbandwidth is 194±8 MHz.3.The high-order balanced tunable filters with constant absolute bandwidth and multiple transmission zeros are proposed.In this chapter,the proposed new banlanced filter structures introduce source-load coupling and cross-coupling simultaneously,which achieves differential-mode frequency responses with three transmission zeroes and four transmission zeroes.To obtain the high common-mode rejection ratio,a short microstrip stub and lumped resistor are loaded at the center of the resonator.Under common-mode excitation,each resonator in the common-mode equivalent circuit of the filter is loaded with a same resistor.As a result,the high common-mode rejection ratio is realized within the frequency tuning range.The measurement results show that the realized differentialmode resposnes have approximately constant absolute bandwidth,three transmission zeros for three-pole filter and four transmission zeros for four-pole filter.While high common-mode rejection ratio is also achieved.4.The wideband low-phase-noise voltage-controlled oscillator based on quasielliptic tunable filter is proposed.By employing a quasi-elliptic tunable filter with widetuning range and constant absolute bandwidth,steep in-band phase variation and high constant in-band group delay are obtained.On the one hand,the steep phase variation realizes phase compensation of a voltage controlled oscillator in a wide-frequency range.On the other hand,the high constant in-band group delay achieves constantly low-phase noise.By employing quasi-elliptic tunable filter as frequency selective device in the oscillator loop,a voltage-controlled oscillator with wide-tuning range and constantly lowphase noise is realized.The measured results show that the tuning range of the proposed voltage-controlled oscillator is 1.352-2.12 GHz(44.4%).At the frequency offset of 100 k Hz and 1 MHz from oscillation frequency,the phase noises are better than-101 d Bc/Hz and-127.8 d Bc/Hz.5.Based on quasi-elliptic balanced tunable filter,a low-phase-noise differential voltage-controlled oscillator is proposed.By employing quasi-elliptic balanced tunable filter with constant absolute bandwidth as frequency stabilizing element,a parallelfeedback differential voltage-controlled oscillator is firstly realized.The steep in-band phase variation and high constant in-band group delay of the differential-mode response provides the constantly low-phase noise for a differential voltage-controlled oscillator.The measured results show that the tuning range of the proposed differential voltagecontrolled oscillator is 1.72-2.12 GHz(20.8%).At the frequency offset of 100 k Hz and 1 MHz from oscillation frequency,the phase noises are better than-99 d Bc/Hz and-129.1 d Bc/Hz.