研究目的
To present a continuously tunable nonradiative dielectric waveguide (NRD) phase shifter based on liquid crystal (LC) technology at W-band.
研究成果
This paper presents the first phase shifter in nonradiative dielectric waveguide (NRD) topology at W-band based on liquid crystal (LC) technology. The LC is inserted in the NRD’s Rexolite core for tunability. An electrode system with parasitic mode suppressive structure is designed and fabricated on a thin Ultralam substrate. The measurement are performed with an electric biasing of ±150 V and a maximum Figure-of-Merit of 85 ?/dB was achieved with insertion losses including the transitions ranging between 2.9 dB to 4.9 dB.
研究不足
The difference in the measured and simulated differential phase shift of around 40 ?, caused by imperfect LC alignment, due to a not ideal homogeneous DC bias field. The measured insertion losses including the transitions are ranging between 2.9 dB to 4.8 dB, which is higher than the simulated insertion losses ranging between 1.8 dB to 2.8 dB. The difference is caused by manufacturing tolerances and the UV glue having an unknown loss, which could not be taken into account for the simulation.
1：Experimental Design and Method Selection:
The NRD is designed for the upper W-band using CST Studio Suite. The nonradiative characteristic is obtained by setting the plate separation to a =
2：32 mm. For the dielectric slab, Rexolite 1422 is chosen as material. The Rexolite slab has a width of b = 25 mm. To excite the LSM01 mode, a horn-like transition from the WR10 waveguide to the NRD is designed. The dielectric slab is plugged in the transition and both ends are tapered for better matching. Single mode operation is guaranteed by tapering the width of the metal waveguide. An LC cavity is added inside the Rexolite slab, with a length of 18 mm and two filling holes with a diameter of 5 mm. The ends of the cavity are tapered for smooth transition from the Rexolite to the LC. To orientate the LC an electric biasing system is designed, with which the DC field can be adjusted between parallel and perpendicular to the RF field. A thin substrate with three electrode strips is placed on each metal plate of the NRD. The electrodes’ influence on the RF field is minimized by using mode suppressing structures. Sample Selection and Data Sources:
The measurements are performed with a Keysight PNA with W-band extensions. Voltages of V = ±150 V were applied to the electrodes for LC orientation.
3：List of Experimental Equipment and Materials:
Keysight PNA with W-band extensions, Rexolite 1422, GT5-26001 LC mixture from Merck KGaA, Pyralux laminate.
4：Experimental Procedures and Operational Workflow:
The designed NRD is fabricated in split-block technology. Each part is milled together with two WR10 transitions out of a single piece of brass. The Rexolite slab is milled in two halves, in order to enable the milling of the LC cavity. Both halves are glued together with UV glue and the LC is injected through the filling holes. The holes are sealed with epoxy glue. The electrodes are etched on a 12 μm thick Pyralux laminate, which has a 18 μm thick single copper clad, and are then glued on the plates of the NRD.
5：Data Analysis Methods:
The measurements are performed with a Keysight PNA with W-band extensions. The measured and simulated S-parameters, differential phase shift, and Figure-of-Merit are compared.
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