Compact-Transmission-Line Decoupling and Matching Network of Three-Element Array for Wireless Applications

Abstract

In this paper, a compact-transmission-line (TL) decoupling and matching network (DMN) for three-element circular arrays is presented. As a result of the miniaturization of wireless terminals, the antenna spacing is too close, leading to large couplings and deteriorating system performance. The DMN consists of an impedance transformation section and a star-shaped neutralization section which eliminates couplings between antennas while occupying a smaller area. The impedance transformation section converts the odd and even mode conductances of the antenna to the impedance of the feeding line, and the neutralization section eliminates the odd and even mode susceptances to complete the decoupling and matching of the antenna. The star-shaped circuit utilizes the area surrounded by the antennas in a more efficient manner than traditional triangle circuits. This facilitates the folding of the TL and the miniaturization of the circuit. A design formula is given for each module of the circuit after it has been analyzed analytically. A decoupling example is simulated and manufactured with the diameter of the area occupied by the DMN less than a quarter wavelength. At the working frequency, the port isolation is increased from 7.6 dB to 33.5 dB. The ECC between ports is reduced from 0.11 to 0.011, which validates the method proposed.