Research Of Miniaturized Reconfigurable Microwave Circuits Based On Tunable Devices

With the improvement of living standards,the need for military development,multi band and reconfigurable microwave devices have a wider demand.This dissertation has carried out the research work on the technical problems arising from this background.And the main innovative contributions are summarized as follows:1.This paper presents a new quadrature hybrid coupler model that can be used for multi beam electronic toll collection(ETC)systems.In order to adapt to different frequency band ETC system,the orthogonal coupling model proposed in this paper is designed to cover the two common ETC system frequency range: 2.4 GHz(2.2-2.6 GHz)and 5.8 GHz(5.4-6.0 GHz).The quadrature coupler with different power distribution characteristics in the two frequency band,in the 2.4 GHz band is equally quadrature output,in the 5.8 GHz band is orthogonal output in the 0.5 dB to 7 dB range.The orthogonal divider presented in this dissertation with wide band width,the circuit of small size,is in good agreement with the real test and simulation data.2.This paper presents a novel wideband quadrature hybrid with tunable power dividing ratio.It consists of a broadband hybrid power divider and two varactor diodes.By verifying the reverse voltage of the varactor diodes,the power dividing ratios between the two output ports(i.e.,port 3 and port 4)of the hybrid can be easily controlled.Analytical design equations are derived using the even-odd mode method.To verify the design concepts,a miniaturized tunable power dividing ratio hybrid working at 1.85 GHz is designed and tested.When verifying the reverse voltage of the varactor diodes from 0 to 16 volt,the power dividing ratios between the two output ports of the hybrid can be tuned from-1 to 7.3 dB within a wide bandwidth(1.7-2.0 GHz).Good isolation and return loss performance have been maintained for different power-dividing ratios.And the output phase difference is nearly 90 degree.Moreover,the working bandwidth is larger than 200 MHz for different values of reverse voltage.3.Three adjustable frequency couplers are proposed.The principle and design method of variable frequency coupler with variable capacitance diode are discussed.The design method of dual frequency band central frequency tunable coupler is also discussed.(1)Center frequency tunable coupler.Simulation and measurement results show that by varying biasing voltage of the varactor diodes,the center operating frequency can be tuned continuously from 1.46 to 2.01 GHz(31.7%).In the working frequency band under different bias voltage,the coupler can keep the output port phase quadrature and amplitude balance,and the whole circuit size is relatively small(21.55×26.1mm2 or 0.227?g× 0.275?g).(2)Wide frequency band center frequency tunable coupler.By changing the voltage at both ends of the variable capacitance diode,the center frequency can be adjusted,and the resonant frequency of the coupler is continuously varied in the range of 705 to 1050 MHz(39.3%).When the bias voltage is 22 V,the bandwidth of the test is 41.1%(850-1290 MHz).The bias voltage varies from 1V to 22 V,covering the operating bandwidth of 635 MHz-1290 MHz(68.1%).In the operating frequency band under different bias voltage,the coupler can keep the output port phase quadrature and amplitude balance.The entire circuit size is relatively small(3.9×3.7cm2,0.092?g1× 0.087?g1 or 0.137?g2×0.130?g2).(3)Dual band center frequency tunable coupler.The coupler covers two frequency bands.When the bias voltage at the ends of the varactor diode changes from 1 volt to 23 volts,the center frequency of the low frequency band varies from 0.72 GHz to 0.96 GHz(28.6%),and the center frequency of the high frequency band varies from 2.5 GHz to 2.72 GHz(8.4%).In the 0.72 GHz to 0.96 GHz band,the output power is divided into equal parts,and in the 2.5 GHz to 2.72 GHz frequency band,the power ratio between the output ports varies from 0 to 2 dB.The circuit size is relatively compact,the core circuit occupies an area of 4.6×4.9 cm2(0.13?g1× 0.14?g1 or 0.4?g2×0.43?g2).4.The topology of the power divider with small size and adjustable bandwidth is proposed by using lumped components.This circuit has two transmission zero points near the edge of the pass band of Wilkinson divider,and can independently adjust the zero position of the series and parallel resonant circuit respectively,and flexibly realize the adjustment of the upper and lower sideband respectively,and obtain the corresponding bandwidth of Wilkinson power diviedr.Through simulation and test,the circuit shows good power distribution performance and adjustable characteristics of the upper and lower sidebands respectively.The maximum band range is 1.91-2.98 GHz,and the band width is 1070 MHz(43.8%).The minimum band range is 2.32-2.47 GHz,and the bandwidth is 150 MHz(6.3%).In the frequency band,S21 and S31 are-4 dB,the reflection coefficient S11 is less than-15 dB,and the isolation degree of S23 is greater than 15 dB.The influence of the spacing and the distribution position of the series parallel resonant circuit on the output S parameters is also analyzed.Due to the use of lumped elements,the circuit is very compact.