Design of a microwave variable delay line using liquid crystal, and a study of its insertion loss

Kuki, Takao; Fujikake, Hideo; Nomoto, Toshihiro; Utsumi, Yozo

doi:10.1002/ecjb.1091

Cited by 24 publications

(19 citation statements)

References 12 publications

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“…A recent detailed study 10 published in 2010, has reported values of the effective loss tangent for conventional nematic LC devices at the millimeter wavelength range (30 GHz). Loss tangent, in static (from 0.01 to 0.06) and dynamic (from 0.04 to 0.001) regimes, were, in the worst case, one order of magnitude greater than that of conventional dielectrics such as teflon 11 and, therefore, were expected to be higher for microwave applications; this constraint has been treated as tolerable low losses.…”

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confidence: 99%

Note: Tunable notch filter based on liquid crystal technology for microwave applications

Urruchi

Marcos

Torrecilla

et al. 2013

Review of Scientific Instruments

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In this work, a compact design of an electrically tunable notch filter, based on liquid crystal (LC) technology, has been designed, manufactured, and characterized. The proposal has been achieved through particular configuration schemes with low cost inverted-microstrip structures and conventional spurlines structures due to its ease of integration. Central frequency tunability has been induced by applying low ac voltages, thus involving low power consumption. For these devices, filter responses have been approached specifically at microwave C-band frequency allocated for many satellite communications applications. Also, it has taken advantage of new highly anisotropic nematic LC mixtures at those frequency ranges. Recently, liquid crystal (LC) technology has begun to be used in nonoptical applications due to its promising features in further electronic applications ranging from kilohertz to megahertz frequencies. Intrinsic anisotropy of some LC properties, which implies different properties depending of the direction in which they are measured, allows new advanced devices to be designed with tunable features, by using these materials.The use of LC to design tunable devices at microwave frequency bands is not a new conception; nevertheless there has been an increasing interest in improving their performance, particularly in the last decade. Liquid crystals were recognized as candidates for microwave dielectric substrates in the early 1990s. 1 Although first approaches to LC devices in waveguides led to bulky and large consumption designs (due to strong magnetic fields for switching LC molecules), most of the recent prototypes, such as tunable phase shifters, 2, 3 capacitors, 4 filters, 5,6 or antennas, 7 have reported practical functions involving electric fields for orienting LC at those frequencies.Filters are very valuable devices because they represent a powerful tool for frequency response processing. They are designed in order to select or to remove bands of frequency. A band-rejection filter or band-stop filter is a filter that attenuates a frequency band, while the other frequencies remain unchanged. A notch filter is a band-rejection filter with a narrow stopband, with a high quality factor, that is mainly used to remove spurious frequencies and to filter noise signals.In this work, the design of a notch filter for about 5 GHz rejection frequency (f 0 ), based on the electric field switching of a LC, has been proposed and its feasibility has been demonstrated. Filters working at this frequency, allocated in the C-band, are intended to be used in satellite telecommunication systems or, for example, to avoid the interference a) Author to whom correspondence should be addressed. Electronic mail:vurruchi@ing.uc3m.es.between the UWB (Ultra Wide-Band) and WLAN (Wireless Local Area Networks) systems. 8 UWB systems are particularly promising for short-range high-throughput wireless communications. Multiple solutions have been proposed for providing tunability in microwave devices, such as varactors based on sem...

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mentioning

confidence: 99%

Note: Tunable notch filter based on liquid crystal technology for microwave applications

Urruchi

Marcos

Torrecilla

et al. 2013

Review of Scientific Instruments

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“…The most effective way to achieve a small value of τ d is to reduce d. When d is decreased, however, the transmission loss is increased in a delay line with the microstrip line structure, for example [9]. Thus, the following structural measure is much more important than the selection of the liquid crystal material: for high-frequency application, the value of d should not be decreased, but the effective thickness between the two rubbing layers should be minimized so that the orientation force required to return the orientation to the initial state of the liquid crystal is affected.…”

Section: Response Time Measurements and Discussionmentioning

confidence: 98%

“…(15), d must be decreased in order to achieve high speed. On the other hand, this increases the conductor loss in the microstrip line [9]. Consequently, in order to develop a delay line with low loss and small τ d , it is important to design a structure that can effectively reduce d by enhancing the orientation effect without decreasing the actual liquid crystal layer thickness.…”

Section: −4mentioning

confidence: 99%

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Measurements of the dielectric properties of nematic liquid crystals at 10 kHz to 40 GHz and application to a variable delay line

Kamei

Utsumi

Moritake

et al. 2003

Electron Comm Jpn Pt II

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SUMMARYIn support of the application of liquid crystals to adaptive devices such as variable delay lines in the microwave and millimeter band, the complex permittivities and response times of five different nematic liquid crystals after voltage application were measured. We measured both the real part ε // g of the relative permittivity, when the long axis of the liquid crystal molecule is parallel to the high-frequency electric field, and the relative permittivity ε ⊥ g when it is perpendicular to the high-frequency electric field. The values tanδ // and tanδ ⊥ were measured. In the range from 10 kHz to 13 MHz, the capacitance and conductance of a liquid crystal cell sandwiched between ITO glass plates processed by rubbing were directly measured. For 100 MHz to 40 GHz, we propose the new cutback method, in which two coaxial tubes with different lengths are filled with the liquid crystal and the dielectric properties are measured on the basis of their respective group delay and transmission loss. Dielectric relaxation is verified in the low frequency range. In particular, in the range from 3 to 40 GHz, dielectric properties are shown for a continuous change of frequency. It is found that ε // g and ε ⊥ g are kept almost constant regardless of the frequency, taking values of approximately 3 and 2.5, respectively. ∆ε′, which is the difference between the permittivities in two orientations, exhibits a large variation, from 0.4 to 0.8, depending on the material, which provides crucial data for selecting the optimal material. The response time was measured by placing the liquid crystal cell between two polarizers with the polarizing directions set parallel. The light from a He-Ne laser (632.8 nm) is directed onto the liquid crystal cell, and the transmitted light is detected by a photodiode. Assuming that the liquid crystal is used in an adaptive device, the speed of operation is investigated. Based on the measurement results for two different nematic liquid crystals, the design of a variable delay line for 20, 30, and 40 GHz is considered, and a principle of liquid crystal material selection is presented.

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“…Figures 2(c)-(d), to millimeter-or bulkier microwave devices for tunable -delay line, -phase shifter, -wavelength selector and beam steering devices [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], to name a few. Nematic liquid crystals are uni-axial, characterized by refractive indices n and the n ⊥ , for light polarization parallel and orthogonal to the director axis, respectively.…”

Section: F Figures 2(a)-(b)mentioning

confidence: 99%

MULTIPLE TIME SCALES OPTICAL NONLINEARITIES OF LIQUID CRYSTALS FOR OPTICAL-TERAHERTZ-MICROWAVE APPLICATIONS (Invited Review)

Khoo¹,

Zhao²

2014

PIER

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Abstract-We provide a critical account of the dynamics of laser induced refractive index changing mechanisms in nematic liquid crystals which may be useful for all-optical switching and modulation applications in the visible as well as the Terahertz and long-wavelength regime. In particular, the magnitude and response times of optical Kerr effects associated with director axis reorientation, thermal and order parameter changes, coupled flow-reorientation effects and individual molecular electronic responses are thoroughly investigated and documented, along with exemplary experimental demonstrations. Emphases are placed on identifying parameter sets that will enable all-optical switching with much faster response times compared to their conventional electro-optics counterparts.

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Design of a microwave variable delay line using liquid crystal, and a study of its insertion loss

Cited by 24 publications

References 12 publications

Note: Tunable notch filter based on liquid crystal technology for microwave applications

Note: Tunable notch filter based on liquid crystal technology for microwave applications

Measurements of the dielectric properties of nematic liquid crystals at 10 kHz to 40 GHz and application to a variable delay line

MULTIPLE TIME SCALES OPTICAL NONLINEARITIES OF LIQUID CRYSTALS FOR OPTICAL-TERAHERTZ-MICROWAVE APPLICATIONS (Invited Review)

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