Based on a CMOS slow-wave coplanar-waveguide transmission-line topology, a novel compact millimeter-wave phase shifter is presented. The tunability is accomplished by using a liquid crystal (LC) material as a tunable dielectric between the coplanar signal strip and the shielding plane of the slow-wave transmission line. The device tunability is considerably enhanced by moving the free-standing signal strip with the application of a bias voltage. Combining the miniaturizing benefits of the slow-wave effect with the continuous tuning of LC material, the proposed device occupies only 0.38 mm² and exhibits high performance. The phase shifter was characterized up to 45 GHz for a maximum bias voltage of 20 V without significant power consumption. The reproducible measurements show a figure-of-merit (ratio between the maximum phase shift and the maximum insertion loss) of 51°/dB at 45 GHz.

This letter presents the realization of a miniaturized liquid crystal slow wave phase shifter at V-band. It is based on a microstrip topology, where the ground plane is realized by a porous alumina membrane filled with metallic nanowires, all of them being connected with each other by a metallic ground plane at the membrane's back. While the magnetic field can pass the nanowires almost unperturbed, the electric field is confined in between the signal electrode and the tips of the nanowires. After deembedding, the meander line phase shifter shows a matching always better than -10 dB, while exhibiting an insertion loss between 1.5 and 2.5 dB from 40 to 67 GHz. This results in a figure-of-merit for passive phase shifters of 33 dB to 45°/dB, accompanied with a phase shift of 55°-100°.

In this paper, a physical model of the slow-wave (SW) microstrip lines based on a metallic-nanowire-filled-membrane substrate is presented for the first time. The model properly predicts the behavior of the SW transmission lines as shown by the experimental results. Two sets of transmission lines differing in oxide thickness with various widths were fabricated and characterized up to 70 GHz. The electrical model is valid for both oxide thicknesses and microstrips width. High-quality factors are obtained, above 40 from 30 GHz up to 70 GHz, paving the way for further designs of passive circuits, like power dividers or hybrid couplers, with good performance.

This paper presents a highly miniaturized tuneable microstrip line phase shifter for 5 GHz to 67 GHz. The design takes advantage of the microstrip topology by substituting the ground plane by a metallic-nanowire-filled porous alumina membrane (NaM). This leads to a slow-wave (SW) effect of the transmission line; thus, the transmission line can be physically compact while maintaining its electric length. By applying a liquid crystal (LC) with its anisotropic permittivity as substrate between the transmission line and the NaM, a tuneable microstrip line phase shifter is realized. Three demonstrators are identically fabricated filled with different types of high-performance microwave LCs from three generations (GT3-23001, GT5-26001 and GT7-29001). The measurement results show good matching in a $50\ \Omega$ system with reflection less than −10 dB over a wide frequency range. These demonstrators are able to reach a maximum figure of merit (FoM) of 41 $^{\circ }$ /dB, 48 $^{\circ }$ /dB, and 70 $^{\circ }$ /dB for different LCs (GT3-23001, GT5-26001 and GT7-29001, respectively). In addition, experiments show that all three LCs should be biased with square wave voltage at approximately 1 kHz to achieve maximum tuneability and response speed. The achieved response times with GT3-23001, GT5-26001 and GT7-29001 are 116 ms, 613 ms, and 125 ms, respectively, which are much faster than other reported LC phase shifter implementations. Large-signal analysis shows that these implementations have high linearity with third-order interception (IP3) points of approximately 60 dBm and a power handling capability of 25 dBm.

A new through-substrate via (TSV) for millimeter-wave frequencies is proposed. The via is formed by copper nanowires connecting the bottom and top surfaces of a porous alumina membrane. It is shown here that the nanowire via is simple to fabricate using a low-cost technology. The nanowire vias were tested as coplanar waveguide transitions and characterized up to 110 GHz. The results show insertion loss better than 0.37 dB and return loss better than 14 dB per transition at 110 GHz. An electrical model for the vias was derived to give a design tool for circuit designers. These TSVs, along with the high-performance transmission lines already developed on the porous alumina membranes, contribute to a powerful platform for the design of high-performance circuits on this innovative interposer.