Criteria for nearly omnidirectional radiation patterns for printed antennas

Radiation from printed antennas is investigated with emphasis placed on producingbar{E}- andbar{H}-plane radiation patterns that are as nearly omnidirectional as possible. This is achieved using criteria which are derived for a nonzero radiation field extending down to the layer surface (radiation into the horizon). It is determined that this phenomenon arises when a surface wave pole coincides with a branch point in the complex plane. A simple ray optics interpretation is given for the phenomenon, and graphs are presented to easily enable design of printed antenna geometry to achieve nearly omnidirectionalbar{E}- orbar{H}-plane patterns.     

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.     

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}.     

On the relationship between the transmitting and receiving properties of an antenna

The response of a linear, passive antenna in free space to an incident plane wave is related to its far-field radiation in the reverse direction bybar{h}^{r}=bar{h}^{t}. The vector effective heightbar{h}^{r}characterizes the voltage across the open-circuit antenna terminals induced by an incident plane-wave field, and the correspondingbar{h}^{t}characterizes the far-field radiation of the antenna when driven by a current injected into the same terminals. This relationship, which is shown to follow from the well-known reciprocity principle, both includes phase and makes mathematically explicit the polarization relation involved in the identity of the transmit and receive patterns of an antenna.     

Numerical solution of nonuniform surface wave antennas

An integral equation is used to numerically study microwave surface wave antennas. The source is chosen as a horizontal magnetic line current which is placed parallel to a planar surface having a one-dimensional nonuniform surface reactance. The integral equation is numerically solved exactly taking full account of radiation from both the feed and the termination, and their mutual interaction. By varying the profile of the surface reactance and the antenna length, radiation characteristics such as directivity, beam width and sidelobe level are discussed. The optimum excess phase delay is found to be aboutpi/3for an antenna length of3lambda_{0}, gradually increasing topi/2for a length of8lambda_{0}. When a feed transition in the reactance profile is used to achieve a good surface wave launching efficiency near the source, the first sidelobe can be reduced to less than-10 dB below the main beam level with little effect upon the directivity. Optimum reactance profiles are suggested for antennas from3lambda_{0}to8lambda_{0}long.     

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.     

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.     

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.     

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.     

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.     

Loaded horizontal antenna over an imperfect ground

The Fresnel reflection coefficient technique is employed to establish anE-field integral equation for the antenna current. A resistive loading of the formLambda(x) = Lambda_{0}/(1 - |x|/L)is used to load the antenna. An optimization technique is discussed for determining the value of critical loadingLambda_{0}^{c}, which enforces a traveling wave current on the antenna. Results are given for the critical loading parameters, antenna currents, input impedances and radiation patterns versus different antenna dimensions and ground permittivities and conductivities. Some representative time-domain results for such loaded antennas are also included.     

Current distribution and input admittance of an infinite cylindrical antenna in anisotropic plasma

The current distribution and input admittance of an infinitely long cylindrical antenna driven by a slice generator and immersed in an anisotropic plasma are investigated. The applied dc magnetic field is along the axis of the antenna. By superimposing the characteristic waves guided along the antenna, the current solution is obtained in the form of a one-dimensional integral, which is examined both analytically and numerically. WhenK_{perp} > 0, the magnitude of the current decays slowly with the distance from the source, and its phase is nearly linear with a "propagation constant" equal tosqrt{K_{perp}}k_{0}for an antenna with very small radius. WhenK_{perp} < 0, the magnitude of the current decreases rapidly away from the source, and its phase is no longer linear. The input admittance decreases with the radius of the antenna.     

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.     

Antenna radiation characteristics with partially coherent illumination

The radiation characteristics of a partially coherent illuminated antenna are found for both a circular aperture and a linear antenna. The antenna illumination function is assumed to be Gaussian, and the phase structure function in the plane of the antenna is assumed to be of the formcr^{nu}, withnu = 1, 5/3, and 2. The beam broadening and reduction in gain in decibels are found to be of the formKb^{alpha}, whereKandalphaare functions of the antenna illumination and the "law" of the phase structure function, andbis a function of the "level" of the phase structure function.     

Investigation Into the Effects of the Patch-Type FSS Superstrate on the High-Gain Cavity Resonance Antenna Design

Results of modeling, design, simulation and fabrication are presented for a high-gain cavity resonance antenna (CRA), employing highly-reflective patch-type superstrates. In order to determine the resonant conditions, the antenna is first analyzed using the transverse equivalent network (TEN) model, as well as the well known simple ray-tracing method. Prior to that, a highly-reflective patch-type frequency selective surface (FSS) is designed in order to be employed as the superstrate layer of the CRA. Next, a 2.5-D full-wave analysis software package, based on the method of moments (ANSOFT Designer v4.0), is utilized to analyze the antenna structure. Using this full-wave analyzer, the input impedance properties of an actual antenna are investigated as well. Then, a 3-D full-wave analyzer, based on the finite element method (ANSOFT HFSS), is used to extract the directivity and radiation patterns of the CRA, taking into account the finiteness of the substrate, superstrate and ground plane. Some previously unaddressed issues, such as the effects of the FSS superstrate on the input impedance characteristics of the probe-fed microstrip patch antenna, acting as the excitation source of the CRA are also studied. The effects of the highly-reflective FSS superstrate size on the CRA directivity, and explicitly its aperture efficiency, are investigated as well. A comparative study is also performed between CRAs with patch-type FSS and high permittivity dielectric superstrates. Measurement results are provided to support the modelings and simulations.      

Resonant Meta-Surface Superstrate for Single and Multifrequency Dipole Antenna Arrays

The design of a multifrequency dipole antenna array based on a resonant meta-surface superstrate is proposed. The behavior of a single element that is closely placed to a meta-surface is experimentally investigated. The proposed meta-surface is based on resonating unit cells formed by capacitively loaded strips and split ring resonators. By tuning a dipole antenna to the pass band of the meta-surface, the physical area is effectively illuminated enhancing the radiation performance. The gain, radiation efficiency and effective area values of the whole configuration are compared to the ones obtained with a single dipole without superstrate. Radiation efficiency values for the proposed configuration of more than 80% and gain values of more than 4.5 plusmn 1 dB are obtained. Based on this configuration, simulated results of a multifrequency antenna array are presented. Distinctive features of this configuration are high isolation between elements (20 dB for a distance of lambda₀/4), and low back radiation.     

Radiation from a gyro-plasma sheathed aperature

It is shown that the presence of a gyrotropic plasma sheath covering a rectangular slot radiator may not alter significantly the radiation pattern when the static magnetic field is perpendicular to the slot. The plasma covered antenna remains omnidirectional and the radiated power is not significantly reduced when the cyclotron frequencyomega_{b}, the collision frequencynu, and the operating frequencyomega, fulfill the inequalityomega_{b}^{2}ggomega^{2}+nu^{2}. It is also found that the matching between the plasma covered antenna and its surrounding is sharply improved for certain combinations of the plasma sheath parameters and the operating frequency. This finding may have an application in plasma diagnostics, the slab widthLand the plasma frequencyomega_{p}can be determined by varyingomega_{i}andomegaaccording to an expression derived in this paper.     

Radiation patterns of a mode transducing antenna

Radiation patterns for the general case ofTE_{0n}excitation of Wengenroth's mode transducing antenna are derived. The antenna seems well suited for application as a launcher for electron cyclotron resonance heating (ECRH) plasma heating. Gain and launching efficiency are calculated. Very good agreement is found between predictions and experimental results forTE_{01}mode excitation.     

Impedance of a finite insulated antenna in a cold plasma with a perpendicular magnetic field

A variational formulation is developed for the impedance of a finite strip antenna embedded in a planar dielectric slab which is surrounded by a magnetoionic medium (cold electron plasma) with a static magnetic field impressed in a direction perpendicular to the antenna surface. Closed form expressions are obtained in the limit of low frequencies, and for a short antenna in a uniaxial medium. The impedance becomes large at the plasma frequency, near the upper hybrid resonance frequency, and further resonances are observed near the gyro-frequency if the gyro-frequency exceeds the plasma frequency. The reactance of a short antenna is inductive at low frequencies, but becomes capacitive as the thickness of the insulation around the antenna is increased. For very thin insulating layers the wave number of the variationally approximated current distribution exceedssqrt{sqrt{epsilon_{1}} sqrt{epsilon_{3}}} k_{0}(epsilon_{1}andepsilon_{3}are the two diagonal elements of the permittivity matrix), whereepsilon_{1}andepsilon_{3}may have positive or negative real parts. However, this approximation does not apply to current distributions along an insulated antenna. The present calculations are also compared with earlier work on antenna impedances.