Research On Microwave Circuits Integrated With Negative Group Delay Function

In recent years,the negative-group-delay(NGD)microwave circuits have been got widely attentions and applications due to their unique negative group-delay characteristics.It can be applied to the antenna array feeding network to solve the beam tilt problem of the antenna array,and it can compensate the group delay of the circuit to achieve high linearity and improve the efficiency of the feed-forward amplifier.In addition,microwave circuits such as filters,power dividers,and couplers are essential components in modern wireless communication systems.Therefore,this thesis studies the function integration design of the NGD circuit with the filter,power divider and coupler to reduce circuit size and improve system performances.The main works completed include:(1)An NGD circuit based on a lossy L-shaped coupling stub is designed.The NGD characteristic of this circuit is realized by coupling a quarter-wavelength lossy L-shaped stub to the main transmission line.The lossy L-shaped stub is mainly composed of a quarter-wavelength transmission line and a loading resistor.The phase shift of the designed NGD circuit at the center frequency is 90°,which can be used to replace the quarter-wavelength transmission line in the traditional microwave circuit for realizing the function integration design of the microwave circuit with the NGD circuit.Measurement results show that the NGD circuit has an NGD value of-1.19 ns at 1.997 GHz,an insertion loss of 1.43 dB,an insertion phase shift of 90.53°,and a return loss of more than 15 dB.It has low insertion loss and good matching performances.(2)A band-pass filter with the NGD function is designed.The filter consists of two half-wavelength open-circuited coupled resonators to implement the band-pass filtering function,The coupling between the lossy L-shaped stub and the resonator is used to obtain the NGD characteristic in the passband.In addition,an open-circuited stub is loaded inside each resonator at a suitable position,and two transmission zeros are generated in the upper stopband to improve the filtering performance.The measurement results show that the NGD value at the center frequency of 1.995 GHz is-1.08 ns,and the NGD bandwidth is 34 MHz.In the NGD band,the insertion loss is less than 7.5 dB,and the return loss is greater than 20 dB.Furthermore,compared with traditional band-pass filters,three transmission zeros at 1.520,2.495,and 2.735 GHz are achieved with good stopband attenuation.(3)A Wilkinson power divider integrated with the NGD function is designed.The power divider is realized by replacing the quarter-wavelength transmission line of the traditional power divider with an NGD circuit having the input and output impedances of 70.71Ω.At the center frequency of 1.997 GHz,the measured NGD values for two output ports are-1.34 ns and-1.36ns,respectively,the insertion loss is 5.63 dB and 5.67 dB,and the NGD bandwidth is 39 MHz.In the NGD band,the return loss is greater than 11 dB,and the isolation is greater than 20 dB.The NGD power divider has low insertion loss and good input matching performances.However,due to the narrow NGD bandwidth of this power divider,an NGD wideband power divider was designed.It is mainly realized by coupling a two-section coupled-line power divider with two pairs of the lossy L-sh,aped stubs.The measurement results show that the NGD bandwidth is broadened to be 79 MHz.(4)An equal-power-dividing coupler integrated with the NGD function is designed.Two NGD circuits with input and output impedances of 35.35 Ω and 50 Ω are designed to replace the quarter-wavelength transmission lines of the traditional branch-line directional coupler.Due to the isolation of the coupler deteriorated by NGD cir,cuits,short-circuited stubs are added at the through-and coupling-ports to improve the isolation.At the center frequency of 1.999GHz,the measured insertion losses for the through-and coupling-ports are 6.075 dB and 6.077 dB,respectively,and the corresponding NGD values are-1.415ns and-1.042ns.The measured NGD bandwidth is 36 MHz,in which the return loss is greater than 11 dB,the isolation is greater than 18 dB,and the phase difference between the through-and coupling-ports is 90°±2.4°.The measurement results show that the NGD function of the equal power dividing directional coupler is realized.