A novel wideband variable coupler employing liquid metal

This paper demonstrates a novel technique to obtain coupling variation for a wideband structure. A 5-element multisection broadside-coupled stripline coupler has been used to obtain a bandwidth of 2-8 GHz. Chambers have been cut in the dielectric between the middle pair of strips. The variable coupling has been achieved by pumping a liquid metal called Galinstan into the chambers of the middle section. The Galinstan essentially thickens the strips changing the spacing and thereby changing the coupling. The chambers are isolated from each other by the use of Kapton membranes. A coupling variation from around 20 dB to 10 dB has been achieved. Return loss is also better than 8 dB for all situations. A lubricant called DialaBX has been used to control the isolation. This lubricant has a similar dielectric constant as the Rogers substrate material, so it has been used to maintain the homogeneity of the structure. SONNET EM simulation software and ADS circuit simulation have been used to produce the results presented.