Liquid Crystal Based SPDT with Adjustable Power Splitting Ratio in LTCC Technology

This paper presents the design and characterisation of a new liquid crystal (LC) based single-pole double-throw (SPDT) with continuously adjustable power splitting ratio in low temperature co-fired ceramic (LTCC) technology. It is designed for a centre frequency of 30 GHz, including a key component, the fully embedded LC phase shifter in stripline topology. The SPDT shows a good matching with $\vert S_{11}\vert =-10\mathrm{dB}$ over a bandwidth of 18 %. It exhibits an insertion loss of 9 dB to 11 dB and an isolation between 22 dB to 32 dB. The continuous tuneability not only allows the selection of each preferred power splitting ratio at the output ports, but also a tuning of the centre frequency. The high insertion loss arises from a certain surface roughness as well as a decreased conductivity of the gold metallisation used.