A Research On Microwave Nonreciprocal Device

With the advent of 5G mobile communications,spectrum resources have become more strained.In order to improve spectrum utilization,full-duplex(full-duplex)duplexers will gradually replace half-duplex,and circulators,as a key component of full-duplexers,have become the focus of research.The traditional ferrite circulator is large and cannot be integrated,which is not beneficial to the miniaturization of 5G communication systems.Therefore,the research on non-ferrite circulators has become more and more extensive in recent years.Circulators implemented with transistors,due to the presence of transistor noise,cause the circulator to have an excessively high noise figure,which limits its application.Circulators implemented with components,such as inductors,capacitors and transmission line,are favored by researchers with good noise performance.Based on the analysis and comparison of various circulator structures,this paper proposes two integrated circulators based on switch transmission lines.The circulator is simple in structure,superior in performance,and easy to realize.The main work and innovations of this article are as follows:In this paper,the circulator based on switch transmission line is studied,and its loss mechanism is analyzed in detail,and an improvement scheme is proposed based on this.The existing circulator uses a coplanar waveguide to realize a quarter-wavelength transmission line.The structure area is large and the loss is large.In this paper,a lumped LC transmission line is used to replace the coplanar waveguide,which reduces the size of the transmission line while reducing losses;the inductor in the lumped LC transmission line uses the inductive effect of the wire to replace the ring inductor,simplifying the layout.In this paper,the first circulator chip is developed using the above improvement scheme.The first circulator achieves an insertion loss of 2.6dB from the transmitter to the antenna,an insertion loss of 3dB from the antenna to the receiver,and the isolation of the receiving end is 21.5dB,and the core area of the chip is0.93×0.85mm~2.Compared with the existing circulator,the insertion loss is reduced by about 0.5dB,and the chip area is reduced by 60%.In this paper,the factors affecting the linearity of the circulator are studied and analyzed.The switch in the existing circulator is located on the signal path,which causes the linearity of the circulator to be directly limited.In this paper,without changing the structure of the circulator,the position of the switch is moved so that the position of the switch becomes ac ground of the signal,which improves the linearity of the circulator.Experimental results show that the 1dB compression point of the circulator is as high as 25dBm,which is 4 dB higher than the compression point of the existing circulator.This paper studies the methods of generating quadrature signals,and proposes to use the internal integrated QVCO scheme to replace the existing poly-phase filter scheme,which eliminates the external interface of the modulation signal,avoids the loss of the poly-phase filter,and reduces the dissipated power of the modulation signal.In this paper,the second circulator is developed according to the above scheme.The second circulator chip achieves an insertion loss of 2.6dB from transmitter to antenna,an insertion loss of 2.6dB from antenna to receiver,and an isolation of 24dB from transmitter to receiver at the frequency of 18GHz.The core area of the chip is 0.93×0.94mm~2.The second chip achieved better insertion loss and isolation without obviously increasing the chip area,showing the effectiveness of the improvements proposed in this article.