Abstract
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.
Highlights
The ever-rising demand of higher data rates is an ongoing trend in today’s society
Besides the development of liquid crystal (LC) mixtures, the corresponding millimeter-wave components have undergone a change of topologies
The wave is completely guided in the dielectrics. (c) For the dielectric image line (DIL) a subwavelength waveguide is halved an mounted on a metal plane. (d) The parallel plate dielectric waveguide (PPDW) consisits of a dielectric slab which is inserted between to parallel metal plates. (e) The nonradiative dielectric waveguide (NRD) looks similar to the PPDW, except that the dimensions and polarization differ
Summary
The ever-rising demand of higher data rates is an ongoing trend in today’s society. It is predicted that the data traffic will be 10,000 times higher in 2025 than it was back in 2013 [1]. In order to achieve different time delay in the branches to each antenna element, tunable phase shifters are employed. Another important specification is the response time of the LC mixture, which depends on the viscosity γr and anisotropy at the frequency of the bias field (usually around 1 kHz) ∆ε 1 kHz. A higher ∆ε 1 kHz reduces the response time, while a higher γr increases the response time. In [9,10] it has been shown for the GT3-23001 mixture that the material properties are almost constant in the mmW regime up to several THz. Data provided by Merck KGaA at 19 GHz. Besides the development of LC mixtures, the corresponding millimeter-wave components have undergone a change of topologies. Afterwards, a tunable filter using a dielectric waveguide for band selection is presented, before conclusions are drawn at the end of the paper
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