S.P. Rea

Liquid Crystal Tunable mm Wave Frequency Selective Surface

A frequency selective surface (FSS) which exploits the dielectric anisotropy of liquid crystals to generate an electronically tunable bandpass filter response at D Band (110-170 GHz) is presented. The device consists of two printed arrays of slot elements which are separated by a 130-mum thick layer of liquid crystals. A 3% shift in the filter passband occurs when the substrate permittivity is increased by applying a control signal of 10 V. Measured results show that the insertion loss increases from -3.7 dB to -10.4 dB at resonance (134 GHz), thus demonstrating the potential to create a FSS which can be switched between a transmitting and a reflecting structure.

Phase control of reflectarray patches using liquid crystal substrate

In this proof of concept study we employ numerical and measured results at X- band to demonstrate that the dielectric anisotropy of nematic state liquid crystal can be exploited to produce electronically controlled phase shifters for printed reflectarray antennas. Phase agility is realized by inserting a layer of liquid crystal in the region between the resonant patch array and the conductive ground plane. Applying a low frequency biasing voltage produces a small change in the permittivity of the substrate and this is shown to create a large shift in the phase of the reflected signal. Ansoft HFSS version 10.0 is employed to study the scattering behaviour of the array elements in the range 9¿11 GHz using the dielectric properties of commercially available liquid crystals. The simulated phase range, bandwidth and reflection loss are shown to be in close agreement with measurements that were obtained from a waveguide simulator. The most significant impact of this new active control strategy is in the mm and sub-mm wave band and therefore a technique is proposed for characterising the electrical performance of liquid crystals at these frequencies. This paper summarises the progress that has been made in the first stage of a collaborative academic/industrial project to investigate the feasibility of creating high frequency beam scanning reflectarray antennas for future space science instruments.

Dual polarised Sub-mm wave frequency selective beamsplitter

In this paper we describe the design of a Frequency Selective Surface (FSS) which gives a polarisation independent spectral response when the filter is orientated at 45° incidence. The structure consists of one or more freestanding screens each containing a closely packed array of nested short circuited annular slots. A computer model is used to design a two layer FSS which can separate the bands 316.5¿325.5GHz and 349.5¿358.5GHz with >20dB isolation and <1dB insertion loss in both the TE and TM incident planes. A single periodic array, which is the basic building block of the cascaded screen structure, has been fabricated using a precision micromachining technique. Quasi-optical swept frequency transmission coefficients which were measured over the range 305¿345GHz are shown to be in good agreement with the numerical results. A concept for improving the robustness of the structure in order to provide space qualified beamsplitters for future polarimetric atmospheric sounders is presented.

Performance of reflectarray cells printed on liquid crystal film

In this paper we demonstrate that the anisotropic property of liquid crystal can be exploited to control the phase of signals that are reflected from a reflectarray cell. Numerical and measured results at X-band are used to compare the plane wave scattering from two reflectarray cells which are constructed on liquid crystal film of thickness 200 mum and 500 mum. The phase agility, bandwidth and reflection loss are shown to be dependent on both the thickness and the voltage controlled permittivity of the tunable substrate. A tunable phase range greater than 250deg is achieved over a 6.1% bandwidth.

Electromagnetic modeling of aircraft air inlet Scoop

The attenuation/transmission characteristics and hence High Intensity Radiated Field (HIRF) immunity of a jet engine nacelle air vent, called a NACA Scoop, are reported. For the first time, results from simulations using a TLM based solver and measurements of the NACA Scoop in an anechoic chamber are discussed and compared.