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Synthesis of General Decoupling Networks Using Transmission Lines

Binbin Yang

TL;DR

The paper tackles mutual coupling in multi-port radiators by proposing a transmission-line based generalized $\pi$-network (TL-DN) that is inherently lossless and reciprocal. It develops a Y-parameter based synthesis workflow, starting from the load S-parameters $S_L$, deriving $S_{DN}$, then $Y_{DN}$, and solving for branch TL parameters to satisfy $Y_{\Pi}=Y_{DN}$. To reduce implementation complexity, it fixes a standard TL length with $a = -\frac{1}{\sqrt{2}}$ (corresponding to $l = \frac{3\lambda}{8}$ or $\frac{5\lambda}{8}$) and determines $Z_0$ per branch; eventual decoupling is achieved by conjugate matching with the $N$-port load. Two numerical demonstrations (a 2-port patch at 1.2 GHz and a 3-port monopole at 1 GHz) show perfect decoupling at the design frequencies using TL-DN, validating the approach and its scalability and consistency with lossless TL implementations.

Abstract

In this paper, we introduce a synthesis technique for transmission line based decoupling networks, which find application in coupled systems such as multiple-antenna systems and compact antenna arrays. Employing the generalized $π$-network and the transmission line analysis technique, we reduce the decoupling network design into simple matrix calculations. The synthesized decoupling network is essentially a generalized $π$-network with transmission lines at all branches. A standard electrical length of $3λ/8$ and $5λ/8$ are chosen to simplify the physical implementation, leaving the characteristic impedances of the transmission line branches the main design parameters. The advantage of this proposed decoupling network is that it can be implemented using transmission lines, ensuring better control on loss, performance consistency and higher power handling capability when compared with lumped components, and can be easily scaled for operation at different frequencies. A two-port microstrip antenna system at 1.2 GHz and a three-port monopole antenna system at 1 GHz are investigated respectively to demonstrate the validity of the proposed synthesis method, and perfect decoupling ($S_{21}<-50$dB) are achieved at both design frequencies.

Synthesis of General Decoupling Networks Using Transmission Lines

TL;DR

The paper tackles mutual coupling in multi-port radiators by proposing a transmission-line based generalized -network (TL-DN) that is inherently lossless and reciprocal. It develops a Y-parameter based synthesis workflow, starting from the load S-parameters , deriving , then , and solving for branch TL parameters to satisfy . To reduce implementation complexity, it fixes a standard TL length with (corresponding to or ) and determines per branch; eventual decoupling is achieved by conjugate matching with the -port load. Two numerical demonstrations (a 2-port patch at 1.2 GHz and a 3-port monopole at 1 GHz) show perfect decoupling at the design frequencies using TL-DN, validating the approach and its scalability and consistency with lossless TL implementations.

Abstract

In this paper, we introduce a synthesis technique for transmission line based decoupling networks, which find application in coupled systems such as multiple-antenna systems and compact antenna arrays. Employing the generalized -network and the transmission line analysis technique, we reduce the decoupling network design into simple matrix calculations. The synthesized decoupling network is essentially a generalized -network with transmission lines at all branches. A standard electrical length of and are chosen to simplify the physical implementation, leaving the characteristic impedances of the transmission line branches the main design parameters. The advantage of this proposed decoupling network is that it can be implemented using transmission lines, ensuring better control on loss, performance consistency and higher power handling capability when compared with lumped components, and can be easily scaled for operation at different frequencies. A two-port microstrip antenna system at 1.2 GHz and a three-port monopole antenna system at 1 GHz are investigated respectively to demonstrate the validity of the proposed synthesis method, and perfect decoupling (dB) are achieved at both design frequencies.
Paper Structure (8 sections, 15 equations, 3 figures, 2 tables)

This paper contains 8 sections, 15 equations, 3 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Theory of the TL-based Decoupling Network
  3. DN Synthesis Process
  4. DN Synthesis with Standard Electrical Length
  5. Design Examples
  6. Two-port Antenna System
  7. Three-port Antenna System
  8. Conclusions

Figures (3)

  • Figure 1: The topology of the generalized TL $\pi$ network (two-port case). Ports 3 and 4 can be connected to a coupled two-port system, and ports 1 and 2 provide access to a decoupled two-port response.
  • Figure 2: (a) the geometry of the two-port square patch antenna, (b) the original S parameter behavior of the two-port patch, (c) the S parameter of the two-port patch with DN synthesized using standard electrical length ($S_{12}$ overlaps with $S_{21}$).
  • Figure 3: (a) the geometry of the three monopoles, (b) the original S parameter behavior of the three monopoles, (c) the S parameter of the three monopoles with DN synthesized using standard electrical length.