Multi-Frequency And Broadband Technologies Of Negative Group Delay Microwave Circuits And Their Applications

As an important technical index to describe the linearity of phase-frequency characteristic of channels and devices,the group delay has attracted wide attention in the modern high-speed broadband wireless communication systems.The distortion of the group delay will cause inter-symbol interference and signal distortion,resulting in a series of problems such as the decrease in the signal-to-noise ratio and the increase in the bit error rate.As a novel method to compensate for the group delay,the negative group delay(NGD)circuit has shown significant advantages in satisfying the low-delay requirements of the fifth-generation mobile communications.Meanwhile,the wide application prospect of the NGD circuit has been detected in many fields,such as the performance improvement of microwave devices,the realization of the signal integrity and performance optimization of the array antennas.Consequently,the NGD microwave circuit has important research significance and application value.In order to satisfy the needs of multi-standard and broadband communication system,the NGD microwave circuit still has many problems to be solved.Multi-frequency and broadband technologies of the NGD microwave circuits are researched in this dissertation and the main innovative achievements are as follows:(1)Three multi-frequency NGD microwave circuits were presented.The first one is a dual-band NGD microwave circuit with wide frequency ratio range.The proposed dual-band NGD circuit had the same NGD characteristics in the two working frequency bands and the frequency ratio was increased to 1.1 ～ 6.3.Compared to the previous dual-band NGD microwave circuits,the frequency ratio of the proposed dual-band NGD microwave circuit was doubled.The second one is a low-loss dual-band NGD microwave circuit.With the lossy microstrip resonator,the insertion loss was decreased to 2.7 dB when the NGD value is -4.8 ns.Meanwhile,the two working frequency bands and the corresponding NGD characteristic could be controlled by the uncoupled parts of the stepped-impedance open-loop resonator,respectively.The measured results showed that the independent adjustment of the center frequency of high/low working frequency bands and the corresponding NGD value could be achieved.Compared to the previous dual-band NGD microwave circuits,the proposed dual-band NGD microwave circuit reduced the insertion loss and improved the design flexibility.The third one is a tri-band NGD microwave circuit.The influence of design parameters on circuit performance was analyzed,and the detailed design steps were given.A tri-band NGD microwave circuit with the working frequencies of 1.2 GHz,3.5 GHz and 5.8 GHz,NGD value of-1.1 ns was designed.The measurements showed that the expansion of the number of NGD working frequencies was achieved.(2)Two broadband NGD microwave circuits were presented.The first one is a broadband NGD microwave circuit with flat-NGD characteristic.The design equations were derived and the methods to improve the flatness of the group delay were given.Based on the design methods,a broadband NGD microwave circuit was designed and implemented.The flat-NGD bandwidth was increased to 46.3% with the group-delay fluctuation of ±8%.The measured results showed that the broadening of the flat-NGD bandwidth was realized.Compared to the previous broadband NGD microwave circuits,the proposed broadband NGD microwave circuits reduced the fluctuation of the group delay and broadened the flat-NGD bandwidth.The second one is a broadband NGD microwave circuit with low signal attenuation.The closed-form equations were obtained by the strict derivation of the design parameters and the detailed design steps were given.A broadband NGD microwave circuit with NGD value of -1.11 ns and the group-delay fluctuation of ±11.6% was designed and implemented.The maximum insertion loss within the flat-NGD bandwidth was reduced to 9.75 d B,which proved that the improvement of insertion loss was realized.Compared to the previous broadband NGD microwave circuits,the proposed broadband NGD microwave circuits improved the performance of the insertion loss.(3)A reconfigurable NGD microwave circuit with flat group delay was presented.The reconfiguration of the NGD value was realized by switching diodes and the tunable flatness of NGD was implemented with the varactors.The design equations at the center frequency were derived and the design steps were given.A reconfigurable NGD circuit with NGD reconfigurable range of -2.02 ～-5.84 ns and the group-delay fluctuation of ±8% was designed and implemented.And the flat-NGD bandwidth of 2.2 ～ 8.8% was obtained.The measurements showed that the NGD value could be reconfigured with the flat group delay characteristics.Compared to the previous tunable NGD microwave circuits,the proposed reconfigurable NGD microwave circuits reduced the fluctuation of the group delay and broadened the flat-NGD bandwidth.(4)Two kinds of microwave divices based on NGD circuit were presented.The first one is a broadband switch-less bi-directional amplifier based on NGD matching circuit.Based on the non-Foster characteristic of the modified RLC resonant NGD circuit,its reactance is equivalent to the negative capacitor for impedance matching.The design equations and steps are given.In order to verify the effectiveness of this circuit,the proposed amplifier was compared with the amplifier based on traditional LC matching circuit.The measured results showed that compared with the matching bandwidth of 5%(899 ～ 945 MHz)of the traditional LC matched bi-directional amplifier,the proposed one could improve the matching bandwidth to 32.8%(797 ～ 1095 MHz).And the broadband impedance matching characteristic was realized.The second one is a broadband phase shifter based on NGD microwave circuit.The proposed phase shifter took the broadband NGD circuit as the prototype and a microstrip line with characteristic impedance of 50 Ω was connected at the input-or output-port.And the different output phase shift could be realized by changing the length of the microstrip line.The measurements showed that the range of phase shift could be increased to -360° ～ 0° and the flat-phase bandwidth in the range of-180° ～ 0° were larger than 50%,which showed that the function of broadband phase shift was achieved with a small circuit size.