Fundamental superstrate (cover) effects on printed circuit antennas

The fundamental effects of superstrate (cover) materials on printed circuits antennas are investigated. Substrate-superstrate resonance conditions are established which maximize antenna gain, radiation resistance, and radiation efficiency. Criteria are determined for material properties and dimensions for which surface waves are eliminated and a radiation efficiency due to substrate-superstrate effects ofe_{s} = 100percent is obtained. Criteria for nearly omnidirectionalbar{H}-plane patterns and nearly omnidirctionalbar{E}-plane patterns are presented. Finally, a general criterion is given for choosing a superstrate to optimize efficiency for the important case of nonmagnetic layers with the antenna at the interface.     

A bandwidth enhancement method for microstrip antennas

Bandwidth enhancement methods for electromagnetically coupled microstrip dipoles are discussed. It is demonstrated that if parasitic metallic strips are incorporated in the structure either co-planar and parallel to the embedded microstrip transmission line open end, or between the transmission line and the microstrip dipole, then substantial bandwidth enhancement results. Experimental verification of this model is introduced for a bandwidth definition based on the frequency range which satisfies a voltage standing-wave ratio (VSWR) < 2 criterion. Also, experimentalbar{E}- andbar{H}-plane patterns verify the theoretical model which accounts for radiation from the microstrip dipole, the parasitics, and the transmission line.     

Table of the field patterns of a loaded resonant circular loop

A table ofE- andH-plane patterns of the circular loop antenna withbeta b = 1.0loaded withZ_{L} = R + jXatphi = 180degis presented. The table gives useful information for determining the values of the load impedance for a given field pattern. The results were experimentally examined.     

The singularities of a Fourier-type integral in a multicylindrical layer problem

The singularities of the integrand of a Fourier-type integral obtained in solving the multicylindrical layer boundary value problem are discussed. The integrand is a function of the radial wavenumber k_{ip} of all the cylindrical layers, and the radial wavenumber in the ith layer is related to the axial wavenumber byk_{ip} = sqrt{k_{i}^{2} - k^{2}}wherek_{i}is the wavenumber of theith layer, andk_{z}is the axial wavenumber of all the layers which have to be the same by phase matching. On the complexk_{z}-plane, there seemingly are branch points of logarithmic type and algebraic type fork_{z} = k_{i}for all the layers. However, by invoking uniqueness principle in the solution of this boundary value problem, one can show that the only singularities on the complexk_{z}- plane are the branch-point singularity associated with the outermost medium which extends radially to infinity, and pole singularities which correspond to discrete guided modes in the multicylindrical medium.     

Radiation patterns of dielectric loaded rectangular horns

The effect of dielectric loading upon theE-plane radiation patterns of rectangular horns is shown to give higher directivity with raised sidelobes. The main beam and first sidelobe can be predicted accurately in terms of radiation from aTM_{y10}mode.     

Microwave holographic metrology of large reflector antennas

A microwave holographic technique for the determination of amplitude and phase of the principal and cross-polarized aperture fields of large reflector antennas is described. The hologram formation process utilizes the elevation over azimuth scanning system normally associated with these antennas, and, in this respect, appears to be unique among other proposed methods of field probing. The present work describes the means used to obtain vital information on the antenna structure such asE- andH-plane phase centers of the feed, and rms values of the reflector surface profile errors. Accurate prediction ofE- andH-plane radiation patterns in the near- and far-field is also demonstrated.     

On the quality factor of strip and line source antennas and its relationship to superdirectivity ratio

Exact formulas are derived for the quality factorQof strip and line source antennas. Contrary to popular opinion, none of them is equal to Taylor's superdirectivity ratiogammaor togamma - 1. But in the case ofE-plane strip sources (the complement of the type of strip source treated by Woodward and Lawson) the value ofQis precisely equal togamma_{alpha}^{-1/2}- 1, wheregamma_{alpha}^{beta}is a generalized superdirectivity ratio that reduces to Taylor'sgammawhen the edge exponentalphaand the pattern weighting exponentbetaare both zero. In the case ofH-plane strip sources the value ofQis approximately equal togamma_{alpha}^{1/2} - 1, and forH-plane line sources of vanishing widthait is approximately equal to[(2/pi) ln (2.516lambda/pi a)]gamma_{alpha}^{1}.     

Radiation performances of a modified rhombic dielectric plate antenna

An antenna consisting of the modified rhombic dielectric plate with double tapers in theH-plane excited by the open end of a transverse electric (TE_{10}) rectangular waveguide is proposed, and some antenna geometrical factors and radiation properties are given experimentally. It is found that these types of antennas have relatively narrow beamwidth and suppressed sidelobe in theH-plane, fairly flat main lobe in theE-plane, and medium performances of about 11.5 dB gain and 1.25 voltage standing-wave ratio (VSWR). It is also found that the radiation performances are virtually independent of frequency over a ten percent bandwidth about 10 GHz.     

Radiation by a probe through a substrate

Radiation by a probe through a grounded substrate layer is considered. The reaction concept is adopted and the coaxial line aperture effects are taken into account. Image theory is invoked to simplify the evaluation of the involved Sommerfeld type integrals. These integrals are computed through a real axis integration which combines numerical and analytical techniques. An interpolation method is introduced which eliminates repetitive calculation of reaction quantities. The properties of the probe such as input, mutual impedance, radiation pattern and radiation efficiency are examined as functions of substrate parameters such as thickness and dielectric constant. The probe length may be chosen to be smaller than, equal to or greater than the substrate thickness. The effect of substrate transverse magnetic (TM) surface wave modes is analyzed and it is found that at each mode cutoff omnidirectional radiation is obtained in thebar{H}-plane with maximum radiation along the horizon. The effect of small substrate loss on the probe parameters is also considered.     

Electric surface current model for the analysis of microstrip antennas on cylindrical bodies

An approach to the analysis of microstrip antennas on cylindrical bodies is presented. The printed radiator is replaced by as assumed surface current distribution, and the fields are solved taking into account the presence of the dielectric layer and the metallic cylinder. Calculation takes place in the Fourier domain. The far field, calculated asymptotically from this solution, is used to get the radiation patterns of the wraparound antenna for any dielectric and the half-wavelength patch forepsilon_{r} = 1.     

An improved element for use in array antennas

An antenna element consisting of a slot plus two parasitically excited wires has been found to exhibit many properties useful in array applications. The introduction of the wires provides a means of controlling both theE- andH-plane element radiation patterns. Specifically, the principal plane radiation patterns can be equalized and the directivity increased. If desired, the element pattern can closely approximate acos thetapattern in both planes. A 14-dB reduction in interelement mutual coupling is also achievable with this source as compared to a slot alone. A comparison of the characteristics of a four-quadrant 60-slot monopulse array with and without the wire elements indicates a 0.6-dB increase in gain and a significant reduction in back radiation for the former.     

Element pattern approach to design of dielectric windows for conformal phased arrays

Modal analysis is presented for the realized element gainE- andH-plane patterns for a two-dimensional circular cylindrical arrays with concentric dielectric sleeve. Numerical results indicate presence of significant surface wave effects. A design method of dielectric windows to reduce the guided wave effects is proposed. The method, validated by direct evaluation of the element pattern for the optimized window geometries, shows significant reduction of surface wave effects.     

Nonlinear optical susceptibility of AgI

We have measured the magnitude and absolute sign of the nonlinear optical coefficient in AgI to determine the importance of thed- electron contributions to the nonlinearity. The resultsd_{31} = +20.6 times 10^{-9}ESU andd_{33} = -41.1 times 10^{-9}ESU are in good agreement with theory.     

VHF TV full channel loaded circular loop antenna

A very high frequency (VHF) full channel room TV receiving antenna, with a voltage standing-wave ratio (VSWR)<2 in the full-band VHF is described. TheE- andH-plane patterns are nearly cardioid in shape, hence it has the advantage of eliminating the TV ghost interference caused by backward reflecting waves in a strong signal environment. The directional pattern and impedance of the loaded circular loop antenna are calculated. The theoretical and experimental data coincide with each other.     

Cross polarization caused by perturbed circular cross sections of waveguides and horn antennas

The cross polarization caused by a perturbed cross section of the conical hybrid-mode horn is analyzed. The perturbed cross section is assumed to be slightly elliptical. The theory previously presented for cross polarization in a smooth-walled waveguide supporting theTE_{11}- mode is referred and applied to theHE_{11}-mode as well. Simple analytical formulas which are sufficiently accurate for small ellipticites of the cross-section ellipse are presented. These show that the tolerances on the waveguide diameter are extremely strong, typically on the order of 2 to4 times 10^{-2}mm in the horn throat for typical horn geometries at 12 GHz.     

The rate-distortion function of a binary symmetric source when side information may be absent (Corresp.)

A binary symmetric source with binary side information is given. An encoder codes the source for data compression with no knowledge of the side information. It is then decoded, perhaps with and perhaps without the presence of side information. The rate-distortion function of this scheme is a function of two variables:D_{1}is the distortion when side information is present at the decoder, and D2 is the distortion when side information is absent at the decoder. The rate-distortion function is shown to reduce to previously solved problems in much of the(D_{1}, D_{2})-plane. Tight upper and lower bounds are found for the rate-distortion function in the rest of the(D_{1}, D_{2})-plane.     

A GTD analysis of the far-out sidelobes of cassegrain antennas

Using recent developments of the geometrical theory of diffraction (GTD), the completeE- andH-plane patterns of Cassegrain antennas are computed. The pattern in the main beam region is computed by conventional aperture integration methods and the GTD analysis is used to evaluate the far-out lobes caused by spillover and by various edge diffraction processes. The effects of the edge curvature and surface curvature are included in the computations.     

A corrugated horn antenna using V-shape corrugations

Corrugated horns use corrugations on theE-plane walls that are operating in the cutoff condition. In this paper, attention is focussed on replacing the rectangular shaped corrugation with a V-shaped corrugation. The properties of the V corrugations are obtained using an integral equation solution; the results of the computational studies indicate that for operation of the V corrugations in the forbidden zone the depth of the corrugations lie between0.3125 lambdato 0.625lambdain contrast to the rectangular corrugations where the corresponding depth is0.25 lambdato 0.5lambda. The radiation patterns and impedance of two identical rectangular horns with corrugatedE- plane walls using either V or rectangular corrugations are directly compared.     

a broad-band constant beamwidth corrugated rectangular horn

Using aperture field theory to predict the far-field radiation from a rectangular horn, a horn with substantially constantE- andH-plane beamwidths of17degand10degrespectively, is designed to operate over a 2.4:1 bandwidth. Assuming a cosine aperture field distribution in both theE- andH-planes of the horn, the general conclusion is first made that an aperture phase error of 0.37 wavelengths at the lowest operating frequency produces the least beamwidth variation (3 dB) over the band. A general design curve showing "constant" beamwidth as a function of horn throat length is produced, furthering the design of such horns with beamwidths in the range approximately9degto27deg. TheE-plane walls of the horn are corrugated, and to cover the bandwidth corrugations are comprised of "T-section" slots which are designed from a simple transmission line model. To realize the specified beamwidths, a compound horn configuration is adopted. Some experimental results obtained from a prototype horn are given.     

Microstrip disk antennas, Part I: Efficiency of space wave launching

A theoretical study on the problem of surface wave excitation of microstrip disk antennas is presented. The cavity model with magnetic sidewalls and dyadic Green's functions in stratified media is used to obtain the radiated fields in an integral form. Lossless media are assumed such that there is no cross coupling between the powers in the space (P_{SP}) and surface (P_{SU}) waves. The separate contributions of these two powers is examined. With the assumption thatP_{SU}does not contribute to the main radiation patterns of the antenna an efficiency of space wave launching and a corresponding antenna directivity are defined. Values of efficiency and directivity as functions of the dimensions of the antenna and for two values of dielectric constants of the substrate are shown. Agreement of these results with some of the available data is observed. It is worth noting thatP_{SU}may correspond to an appreciable portion of the total radiated power.