Electronically controlled asymmetric microstrip line coupler underpinned by an hybrid right-/left-handed line

This work presents a microstrip coupler based on an hybrid right-/left-handed (RH/LH) line whose coupling ratio is electronically controlled. After some considerations on the LH line theory, the asymmetric RH/LH coupler is presented focusing on the parameters yielding the coupling ratio and the frequency range. The dependence of the coupling ratio on the number of cells constituting the coupler is highlighted. From these results, a prototype of a coupler with an electronically switched ratio has been developed. The variable coupling ratio is obtained by switching ON or OFF some cells in the structure of the coupler. The isolation of the OFF mode of the electronic switch implemented is carefully studied. Measurements and calculus are presented in order to estimate the isolation factor required to obtain a significant variation of the coupling ratio as well as to illustrate the original behaviour of such couplers. A functional electronically controlled coupler with one switch implemented is finally characterised and its performances are discussed.