太赫兹科学与电子信息学报  2020, Vol. 18 Issue (6): 1040-1044     DOI: 10.11805/TKYDA2019250

1. 西安交通大学 城市学院，陕西 西安 710018;
2. 南京理工大学 电子工程与光电技术学院，江苏 南京 210094

Design of a leakage canceller topology based on six-port network
YAN Xiulin1, FU Xuanli2, WANG Wenwei2, CHEN Chunhong2
1. City College, Xi'an Jiaotong University, Xi'an Shaanxi 710018, China;
2. School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing Jiangsu 210094, China
Abstract: A circuit topology based on six-port network is presented, which can be adopted to effectively suppress the leakage signal. This six-port network is mainly composed of three 3 dB hybrid couplers and an unequal Wilkinson power divider. Among the two output ports corresponding to the receiving signals, two leakage signals of the transmitting antenna are offset each other for their equal-magnitude and out-of-phase, which is benefit to achieve a high level of transmitting(Tx)-to-Rx isolation in the radar network. In order to demonstrate the Tx leakage canceller, a circuit topology is designed and simulated from 22 GHz to 26 GHz. In the operating band, the isolation of the Tx leakage canceller is lower than -29.5 dB, and it achieves the maximum isolation -44 dB at its center frequency. As shown, the circuit topology efficiently improves the isolation of single-antenna radar system and performs cancellation for the Tx leakage power.
Keywords: six-port network    leakage canceller    isolation

1 基于六端口网络的电路拓扑结构分析

 Fig.1 (a) continuous wave radar front-end system with leakage cancellation network; (b) circuit topology of six-port network 图 1 (a) 包含泄露对消网络的连续波雷达前端系统；(b)六端口网络的电路结构示意图

 ${U_{\rm{T}}} = {A_{\rm{T}}}\cos \;({\omega _{\rm{T}}}t + {\phi _{\rm{T}}})$ (1)

 Fig.2 Main leakage paths of transmission signals in the continuouswave radar front-end system 图 2 连续波雷达前端系统中主要的发射信号泄漏路线

 ${U_{BD{\rm{1}}}} = {A_{BD{\rm{1}}}}\cos \;({\omega _{\rm{T}}}t + {\phi _{BD}} - 180^\circ )$ (2)
 ${U_{BD{\rm{2}}}} = {A_{BD{\rm{2}}}}\cos \;({\omega _{\rm{T}}}t + {\phi _{BD}} - 90^\circ )$ (3)

 ${U_{L1'}} = {A_{L1'}}\cos \;({\omega _{\rm{T}}}t + {\phi _{BD}} - 180^\circ - {\phi _2} - 2{\phi _1})$ (4)
 ${U_{L2'}} = {A_{L2'}}\cos \;({\omega _{\rm{T}}}t + {\phi _{BD}} - 360^\circ - {\phi _2} - 6{\phi _1})$ (5)
 ${U_{L3'}} = {A_{L3'}}\cos \;({\omega _{\rm{T}}}t + {\phi _{BD}} - 90^\circ - 6{\phi _1} - {\phi _3})$ (6)

 ${U_{L - L1'}} = {A_{L1''}}\cos \;({\omega _{\rm{T}}}t + {\phi _{BD}} - 90^\circ - {\phi _2} - 2{\phi _1})$ (7)
 ${U_{L - L2'}} = {A_{L2''}}\cos ({\omega _{\rm{T}}}t + {\phi _{BD}} - 90^\circ - {\phi _2} - 6{\phi _1})$ (8)
 ${U_{L - L3'}} = {A_{L3''}}\cos ({\omega _{\rm{T}}}t + {\phi _{BD}} - 6{\phi _1} - {\phi _3})$ (9)

ϕ1为90°时，式(4)和式(5)的相位相差180°，式(7)和式(8)的相位相同，这2个端口的两路信号分别合成为一路信号。由于不等分功分器的影响，端口2的这部分合成信号和端口3的这部分合成信号等幅，经过定向耦合器的90°相移使其相位相反，便可以将这两路信号完美消除。

 ${U_{w'}} = \frac{{\sqrt {{\rm{10}}} }}{{\rm{5}}}{A_{L3'}}\cos \;({\omega _{\rm{T}}}t + {\mathit{\Phi } _{w'}})$ (10)

 ${I_{SO,{\rm{canceller'}}}} = 20\log \frac{{\sqrt {{\rm{10}}} {A_{L3'}}}}{{{\rm{5}}{A_T}}} - 3\;{\rm{dB}} = 20\log \frac{{\rm{1}}}{{\rm{2}}} - 3\;{\rm{dB}} - 3\;{\rm{dB}} - \left| {{S_{11}}} \right| - 3\;{\rm{dB}} = - 1{\rm{5}}\;{\rm{dB}} - \left| {{S_{11}}} \right|$ (11)

2 仿真结果分析与讨论

 Fig.3 (a) structure of wideband three–branch line hybrid coupler; (b) structure of unequal power divider with 90º phase change 图 3 (a) 宽带三分支线定向耦合器结构；(b)包含90°相位变化的不等分功分器结构

 Fig.4 Microstrip structure of six-port network 图 4 六端口网络微带结构
 Fig.5 S-parameter of six-port network 图 5 六端口网络S参数

 Fig.6 Microstrip structure of leakage cancellation network 图 6 泄漏对消电路的微带结构
 Fig.7 Simulated isolation results of the leakage cancellation network 图 7 泄漏对消电路的隔离度仿真结果
3 结论