Synthesis of General Decoupling Networks Using Transmission Lines

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 $\pi$-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 $\pi$-network with transmission lines at all branches. A standard electrical length of $3\lambda/8$ and $5\lambda/8$ 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.