In this work, the feasibility of microwave liquid crystal based dielectric waveguide phased shifters is investigated in a phased rod antenna array for the first time. For this, a 1 × 4 rod antenna array is designed including the phase shifters as well as a cascaded E-plane power divider network. As core elements, the phase shifter are designed as continuously tunable subwavelength fibers, partially filled with a newly specifically synthesized microwave liquid crystal, exhibiting a maximum FoM 145 • /dB at 102.5 GHz. As proof-of-concept, a simplified electric biasing network is developed, demonstrating its beam steering capability by changing the scanning angle between 0 • , −25 • and +15 • with three different voltage distributions. The antenna array is well matched throughout the complete W-band with a input reflection below −10 dB. The measured antenna gain is between 11.5 to 9.1 dBi at 85 GHz accompanied with a side lobe level between −12 to −7 dB, depending on the steering configuration.INDEX TERMS Phased array, millimeter wave devices, microwave liquid crystal, dielectric waveguide.

This paper presents recent development of tunable microwave liquid crystal (LC) components in the lower millimeter wave (mmW) regime up to the W-band. With the utilization of increasing frequency, conventional metallic waveguide structures prove to be impractical for LC-based components. In particular, the integration of the electric bias network is extremely challenging. Therefore, dielectric waveguides are a promising alternative to conventional waveguides, since electrodes can be easily integrated in the open structure of dielectric waveguides. The numerous subcategories of dielectric waveguides offer a high degree of freedom in designing smart millimeter wave components such as tunable phase shifters, filters and steerable antennas. Recent research resulted in many different realizations, which are analyzed in this paper. The first demonstrators of phased array antennas with integrated LC-based phase shifters are reviewed and compared. In addition, beam steering with a single antenna type is shown. Furthermore, the possibility to realize tunable filters using LC-filled dielectric waveguides is demonstrated.

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In this paper, the gap waveguide technology is examined for packaging liquid crystal (LC) in tunable microwave devices. For this purpose, a line based passive phase shifter is designed and implemented in a ridge gap waveguide (RGW) topology and filled with LC serving as functional material. The inherent direct current (DC) decoupling property of gap waveguides is used to utilize the waveguide surroundings as biasing electrodes for tuning the LC. The bed of nails structure of the RGW exhibits an E-field suppression of 76 dB in simulation, forming a completely shielded device. The phase shifter shows a maximum figure of merit (FoM) of 70 • /dB from 20 GHz to 30 GHz with a differential phase shift of 387 • at 25 GHz. The insertion loss ranges from 3.5 dB to 5.5 dB depending on the applied biasing voltage of 0 V to 60 V. INDEX TERMS Liquid crystals (LC's), tunable phase shifter, phased array, gap waveguide, bed of nails.

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This paper presents for the first time a fully electronically reconfigurable waveguide filter tunable in bandwidth and center frequency based on liquid crystal (LC) technology. A continuously reconfigurable two pole bandpass filter is designed and characterized in the Ka-band at 30 GHz. To be able to tune both center frequency and bandwidth independently, the resonators and coupling structures are filled with LC as tunable material. Hence, the filter's center frequency and coupling strengths can be tuned and, furthermore, tuning with constant filter characteristic is possible. To tune the LC, a novel two-layer electrode design for waveguide structures is presented, which is simple to integrate and provides a high tuning efficiency with low insertion loss. By applying different bias configurations, the LC's effective permittivity can be varied, and therefore, also the resonators' electrical lengths. The presented two pole filter can adapt its center frequency from 29.8 GHz to 30.7 GHz with a maximum 3 dB bandwidth variation from 660 MHz to 870 MHz. The measurements are carried out with bias voltages up to ±250 V.INDEX TERMS Microwave filter, liquid crystals, millimeter wave communication, tunable circuits and devices, K-band.This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.

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In this paper we investigate the temperature dependent behavior of a liquid crystal (LC) loaded tunable dielectric image guide (DIG) phase shifter at millimeter-wave frequencies from 80 GHz to 110 GHz for future high data rate communications. The adhesive, necessary for precise fabrication, is analyzed before temperature dependent behavior of the component is shown, using the nematic LC-mixture GT7-29001. The temperature characterization is conducted by changing the temperature of the LC DIG’s ground plane between −10∘C and 80 ∘C. The orientation of the LC molecules, and therefore the effective macroscopic relative permittivity of the DIG, is changed by inserting the temperature setup in a fixture with rotatable magnets. Temperature independent matching can be observed, while the insertion loss gradually increases with temperature for both highest and lowest permittivity of the LC. At 80 ∘C the insertion loss is up to 1.3dB higher and at −10∘C it is 0.6dB lower than the insertion loss present at 20 ∘C. In addition, the achievable differential phase is reduced with increasing temperature. The impact of molecule alignment to this reduction is shown for the phase shifter and an estimated 85% of the anisotropy is still usable with an LC DIG phase shifter when increasing the temperature from 20 ∘C to 80 ∘C. Higher reduction of differential phase is present at higher frequencies as the electrical length of the phase shifter increases. A maximum difference in differential phase of 72∘ is present at 110 GHz, when increasing the temperature from 20 ∘C to 80 ∘C. Nevertheless, a well predictable, quasi-linear behavior can be observed at the covered temperature range, highlighting the potential of LC-based dielectric components at millimeter wave frequencies.