Compact phase shifter using arbitrary length of two coupled transmission lines

This article presents a compact structure of two coupled transmission lines with two reactive loads for the tunable phase shifter using a printed-circuit board. The proposed circuit offers size reduction and wide phase shift range. The conventional reflection-type phase shifter approach has large total electrical length and high insertion loss. To overcome such technical issues, arbitrary-length two coupled transmission lines were introduced in this work. After optimising the length and the even-mode characteristic impedance of the coupled transmission lines, tuning the odd-mode characteristic impedance can decide the variation of two adjustable reactive loads. Based on the proposed structure, further discussion of the wideband tuning operation and measurement of the phase shift range with -20 dB return loss are addressed in this article. The fabricated circuit is measured at 700 to 2400 MHz. The even- and odd-mode characteristic impedance of two coupled transmission lines are 100-ohm and 70-ohm having about 2.16 dB maximum insertion loss, while maintaining 181-degree phase shift range and 40-degree total electrical length of transmission lines at 700 MHz, respectively, providing about 78% to 89% size reduction compared with the previous research. Our data indicates that insertion loss, multi-band operation, and miniaturisation are superior to any published data.