Capacitive Grid Research Articles

Constructing the phase converters consisting of arbitrary number of translucent surfaces

An effective analytical method of synthesis of an artificial anisotropic structure has been developed. At a design frequency, it ensures perfect match and a phase shift given. The structure may be formed by arbitrary number of inductive and capacitive grids. The method has been applied to constructing circular polarizers and twist polarizers. The geometrical parameters of the polarizers were found in the explicit form. Analytical criteria for an estimate of the bandwidth of the devices have been derived. Performance of the polarizers over a frequency band was studied. A circular polarizer has been proposed which consists of both a cascade of two inductive grids and a cascade of two capacitive grids. The polarizer can be used when very high axial ratio is needed. It ensures more than 10% bandwidth for 0.99 axial ratio. Measurements have been presented that prove adequacy of the mathematical model for real inductive and capacitive screens.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Wideband filters employing multilayer gratings

Multilayer surfaces, consisting of stacked inductive and capacitive strips or grids, have been used to design wideband filters in the 5–40 GHz range, with rapid transitions between reflection and transmission. For singly polarised applications, transmission bandwidths of 70–100% and edge transition ratios of 1.1–1.3 are realisable at 45° TM incidence using 4–8 layers of capacitive and inductive strips. Factors which constrain the passbands are highlighted. In dual polarised designs using doubly periodic grids, the widths are restricted to 35–40% by TE incidence grating responses at the upper passband edge. In TM they are even more restricted by a TE11 mode resonance. Wider passbands require high inductances to reduce the low frequency edge, implying very fine conductors.

Capacitive-grid beam splitters for far-infrared and millimeter-wave interferometers

A beam splitter intended for operation in Fourier transform spectrometers is described. The beam splitter, composed of metallic dots evaporated onto a transparent substrate, acts as a capacitive grid. Construction of the beam splitter and spectra obtained using it are presented. The effect of variation of dot size and interdot distance is discussed. Advantages and disadvantages of using this device in interferometers are presented.

4-layer inductive grid FSS at 45° incidence

Transmission/reflection-band centre ratios of about 1.3 can be attained with multiple layers of inductive or capacitive grids, or with single-layer arrays of more complex elements. The copolar losses and the linear crosspolar performance of a 4-layer inductive grid and a 2-layer array of concentric rings are compared to illustrate some of the problems that can arise experimentally.

Near millimeter wave bandpass filters

The properties of bandpass filters for broadband photometry are reported in the 3-12-cm(-1) frequency range. The filters are based on a combination of capacitive grids deposited on thick Mylar substrates and are designed to have very high out-of-band rejection. Low frequencies are blocked by a thick grill that consists of a hexagonal grid of circular holes in a thick metal plate.

Low-pass interference filters for submillimeter astronomy

Low-pass (long-wave transmitting) interference filters, suitable for broadband photometric observations, previously have been constructed from series of capacitive grids stretched on thin Mylar. These filters have the desired optical properties of high transmission, sharp cut-ons, and good blocking at short wavelengths. Their designs, however, do not scale from one wavelength to another and their performance can deteriorate at low temperatures due to differential contraction of the dielectric backing and the supporting structure. The deviation of these early filters from the predicted scaling was due primarily to the difference in refractive index between the backing material and the medium between the grids. In the present paper, filters are described in which dielectric spacers are used, instead of air, as the medium between the grids. This technique has improved the scaling and has reduced the distortion from differential contraction.

Preparation of Grids for Far Infrared Filters

Capacitive grids and similar structures, to be used as reflectors in far ir interference filters, are prepared from a 1-micro thick copper layer supported by a 2.5-micro thick dielectric film. The desired pattern is obtained by simple photolithographic contact printing of a suitable negative. The essential steps of this preparation and the generation of some relevant patterns are described.

Effective low-pass filters for far infrared frequencies

Capacitive grids (a structure complementary to metallic mesh) are used to construct effective low-pass filters for the far infrared and submillimeter wave region. These filters are closely related to optical interference filters and to microwave filters of the lris-coupled resonator type. In contrast to metallic mesh, used in reflection as a low-pass filter, the new filters are used in transmission. Further advantages are their high transmissivity in the passband, and the possibility to design them for any cut-off frequency in the submillimeter region. The slope of the cut-off characteristic increases very rapidly with the number of grids used in one filter. For a filter of 3 grids a slope of 50 dB/octave was measured. Normalizcd transmission curves are calculated to facilitate the practical design of these low-pass filters.

Far-infrared properties of metallic mesh and its complementary structure

The optical properties of thin metallic mesh (“inductive” grids) are compared theoretically and experimentally with the properties of the complementary structure (“capacitive” grids). Close interrelations are found. In the non-diffraction region (wavelength > grid constant), the optical properties of both types of grids can be described by simple transmission line equivalent circuits. The circuit parameters are determined as functions of the dimensions of the grids. This representation allows a fairly accurate calculation of interference filters consisting of two or more grids of either type. The new capacitive grids may be used advantageously in interference filters with non-harmonic lying orders, in filters with strongly differing peak transmissions, and in effective low-pass filters in the very far-infrared.