"Impedance-Transforming Transdirectional Coupled Line Coupler Based on a Suspended Substrate"

"A new design of a quadrature 3-dB impedance-transforming transdirectional (TRD) coupled line coupler is proposed. The structure contains a base dielectric substrate with a grounded base and a suspended substrate with coupled strips, elevated with a small air gap, above a metal pad, which is galvanically connected to the grounded base of the base substrate by vias. The simulation was performed using the numerical conformal transformation technique with the center frequency calculation error of no more than 11.6%. The measured characteristics of the manufactured TRD coupler turned out to be close to the calculated ones and amounted to the following values in terms of the return loss of the upper line and isolation between the ports of the reference line of 10 dB: operating frequency band of 2.2\u20132.62 GHz (17%); amplitude and phase balances between the output ports of 4.4\u00b10.5 dB and 84\u00b13 deg., respectively; return loss of the reference line and isolation between the output ports of the upper line of more than 17 dB. A unique advantage of TRD coupler, which is absent in other types of the coupled line couplers (contra- and co-directional), is DC isolation between the input port and a pair of output ports, which is combined with a double impedance transformation (50:25). This will allow finding application of the new TRD coupler in development of balanced amplifiers, mixers, reflective phase shifters with increased controllable phase shift, phased antenna arrays, etc."

本文提出一种正交3分贝阻抗变换跨向（transdirectional, TRD）耦合线耦合器的新型设计方案。该结构包含带接地基层的基底介质基板与带有耦合导带的悬浮介质基板；悬浮基板通过微小气隙抬升于金属焊盘上方，该金属焊盘通过过孔与基底基板的接地基层实现导电连通。仿真采用数值共形变换技术开展，中心频率计算误差不超过11.6%。所制备的TRD耦合器实测特性与仿真计算结果高度吻合，针对10 dB的上线回波损耗与参考线端口间隔离度指标，其性能参数如下：工作频段为2.2~2.62 GHz（相对带宽17%）；输出端口间的幅度平衡与相位平衡分别为4.4±0.5 dB与84±3°；参考线回波损耗以及上线输出端口间的隔离度均优于17 dB。TRD耦合器具备一项其他类型耦合线耦合器（反向与同向耦合型）所不具备的独特优势：可实现输入端口与一对输出端口间的直流隔离，同时兼具双端口阻抗变换功能（变换比为50:25）。该特性可使新型TRD耦合器应用于平衡放大器、混频器、具备更大可控相移范围的反射式移相器以及相控天线阵列等器件的研发中。