Research And Design Of Low-loss Negative Group Delay Microwave Circuit

The negative group delay effect refers to an abnormal electromagnetic transmission phenomenon in which the group delay is negative.The signal envelope at the output of the negative group delay circuit can appear earlier than the signal envelope at the input.This characteristic makes the negative group delay circuit often used in microwave communication systems and radio frequency devices,such as to reduce the size of the feedforward amplifier and improve its efficiency and bandwidth,to solve the problem of beam tilt in the array antenna,and to suppress bandpass.Significant positive delay at the edges of the passband of the filter,etc.Therefore,it is necessary to research and design a high-performance negative group delay circuit.Aiming at the problems of the current passive microwave negative group delay circuit with small bandwidth,low negative group delay value,and single center frequency point,three passive negative group delay circuits are designed.Each circuit elaborates the entire design idea and process from three aspects: theoretical method,ideal simulation and experimental verification.This paper first proposes a T-shaped negative group delay circuit based on a single open-circuit stub microstrip line.The actual measurement results show that the group delay,transmission coefficient,and reflection coefficient of the T-shaped circuit at the center frequency of 1.952 GHz are-9.85 ns,-33.56 d B,and-0.47 d B,respectively,and the negative group delay bandwidth is 144 MHz.Although the T-shaped negative group delay structure can achieve the goal of large bandwidth and large delay,the circuit needs to be solved in terms of loss and matching.Based on this,an IL-shaped circuit unit formed by a short-cut open-strip microstrip line and a coupling line is used as the main body to design a negative group delay circuit of the first stage,and then the IL-shaped circuit unit is designed by cascading The negative group delay circuit in the second and third phases improves the negative group delay value of the entire circuit.The actual measurement results of the third stage of the circuit show that the group delay and transmission coefficient and reflection coefficient of the circuit at the center frequency of 1.332 GHz are-13 ns and-7.86 d B,respectively,and the reflection loss of the port is better than 10 d B.It can be found that the designed multi-stage IL shape is a single-frequency circuit,so we will focus on designing a dual-frequency negative group delay circuit later.Therefore,a six-port coupling line and two unequal-length microstrip transmission lines are designed as a dual-frequency negative group delay circuit with a 0I0 structure.The specified center can be achieved by changing the length of the two microstrip lines.Frequency,the final measured results show that the two center frequencies of the circuit are 2.209 GHz and 2.941 GHz,respectively,and the negative group delay values at the respective center frequencies are-1.43 ns and-0.76 ns,respectively.In addition,the circuit has low insertion loss At 2.5d B,the reflection loss is better than 10 d B.