Mutual impedance between two short-circuited flat resonant dipoles

Explicit formulas are presented for the mutual impedance and coupling between two parallel or collinear short-circuited flat dipoles at resonance in terms of three dimensions with respect to wavelength. Experimental and theoretical results are in good agreement and show that the radiating dipoles are particularly well uncoupled and therefore are suitable for incorporation in short arrays for which superdirectivity can be achieved, or in large swept sector arrays.     

Mutual impedance of nonplanar-skew sinusoidal dipoles

The mutual impedance of nonplanar-skew sinusoidal dipoles is presented rigorously as a summation of several exponential integrals with complex arguments.     

Current distribution and input impedance of printed dipoles

Printed dipole antennas find increasing use in microwave as well as far infrared frequencies. The current distribution, input impedance, and radiation pattern are computed for wire antennas printed on a dielectric substrate. The current distribution is obtained by solving Pocklington's equation by moment methods. The Green's function pertinent to the problem involves improper Sommerfeld-type integrals. These integrals are computed by a real-axis integration technique which involves analytical and numerical steps. The effect of surface modes is carefully taken into account.     

Mutual coupling between microstrip dipoles in multielement arrays

An analytical method for evaluating mutual coupling in multielement microstrip arrays is discussed. The elements of the array are strip dipoles covered by an overlayer and excited by microstrip lines embedded in the substrate. In addition, two different ways of excitation are considered to evaluate the effect of the feeding lines on the coupling between the dipoles. Throughout the analysis, the transmission line and dipole widths are taken to be a fraction of the free-space wavelength, so that the longitudinal current component is the dominant contributor to the characteristics of the array. Under this assumption, the transverse component of the current is neglected without introducing appreciable error. The current distribution along the longitudinal direction is evaluated by solving an appropriate integral equation using Galerkin's method with piecewise continuous sinusoidal functions. All possible interactions between the currents on the feeding transmission lines and dipoles are included. Using the computed current distribution, transmission-line theory is applied on the feeding microstrip lines to evaluate self- and mutual impedances as well as scattering coefficients at chosen reference planes     

Mutual impedance between skewed patch antennas

This paper considers the mutual impedance between skewed rectangular microstrip patch antennas as a function of the skew angle. The analysis is done using the exact Green's function for the patch and the method of moments to solve for the field. The theoretical results obtained are compared with published experimental results     

The effect of a dielectric cover on the current distribution and input impedance of printed dipoles

The effect of the thickness and relative permittivily of a dielectric cover on a printed microstrip dipole has been analyzed. It is shown that the current distribution and the input impedance are, in general, very sensitive to variations of the cover parameters. For a dielectric plate with a constant thickness the dipole resonant length decreases substantially with an increase of the relative permittivity. Because of the limited bandwidth presented by single-element microstrip antennas the effects of the dielectric cover on the design of these antennas have to be carefully considered. For the calculation of the current distribution, the Hertz vector potential associated with the problem was determined for an element of current located in a stratified medium with four layers. Pocklington's integral equation was solved for the currents, using Galerkin's method with piecewise-sinusoidal expansion and weighting functions.     

Faster computation of mutual impedances between printed filamentarymonopoles

A coordinate transformation is used to reduce the dimensionality of impedance integrals coupling linear filamentary monopoles printed on grounded dielectric substrates. Computer processing times for the remaining numerical integrations are significantly reduced while accuracy is maintained     

Mutual impedance between probes in a waveguide

The general formulas for mutual impedance between two probes arbitrarily located in a rectangular waveguide are given by means of dyadic Green's function (DGF), field transformation, and reaction concept. In the formulation presented, the waveguide is semi-infinite. Lengths, feeding points, and orientations of the two probes in the waveguide are all arbitrary. As examples, expressions of mutual impedance for eight specific cases are given and discussed     

Low-cost antenna of series-fed printed strip dipoles

A newly developed antenna comprising series-fed printed strip dipoles is described. The effect of substrate permittivity on the radiation properties of the antenna is investigated, using an analysis model based on the general concept of the equivalent radius of cylindrical antennas. An antenna with a gain of >9 dB and VSWR⩽1.5 over the frequency range 1.8-2.2 GHz is presented     

Analysis of finite phased arrays of printed dipoles

The problem of a finite array of printed dipoles is treated, and results are presented in the form of reflection coefficient magnitudes, element patterns, and efficiency (based on power lost to surface waves). Various sized arrays are considered, and are compared with infinite array solutions. The excitation of surface waves is discussed in relation to the scan blindness phenomenon and the transition to an infinite array. Techniques for computational efficiency are also presented.     

Simplified mutual impedance of nonplanar skew dipoles

By including the point charges at the ends of the nonplanar skew monopoles with sinusoidal current distributions, the expressions given by Richmond and Geary [1975] are simplified. The simplified expressions satisfy reciprocity     

Bandwidth limitations of impedance matched ideal dipoles

Using circuit theory and Chu's network representations of the wave impedance of the lowest spherical multipole field, the Ideal dipole, an explicit expression is derived for the upper limit for the impedance bandwidth obtainable for an ideal, lossless, linearly polarized antenna. The expression embodies the network character of an ideal antenna and its role in the guidance of energy between the feed point and the free-space interface, making it more appropriate as a reference than the theoretical radiation quality factor (Q). Moreover, practical antennas do not always manifest a clear single-pole behavior, undermining the basic assumption of a reciprocal relation between Q and the bandwidth.     

Measurement of impedance transformation on practical dipoles

The measured input impedance of a practical dipole antenna is shown to be related to the theoretical input impedance of a delta-gap cylindrical dipole through a bilinear transformation. In order to determine the three complex constants which specify the transformation, the impedance of a dipole in front of a ground plane is measured and compared with the theoretical impedance. The comparison is performed by a curve-fitting procedure for bilinear transformation on a complex plane. The same measurement yields also the receiving efficiency of the antenna and its feeding network. Experiments show that the input impedance of a practical folded dipole, incorporating a balun transformer, may be predicted with an accuracy of better than four percent.     

Mutual coupling between slots printed at the back of ellipticaldielectric lenses

This paper presents calculations of the mutual admittance between two slots on a ground plane that are the primary feed of an elliptical dielectric lens antenna. This admittance may also be regarded as the basic constituent of a Galerkin method of moments formulation for the analysis of more complex feeding arrangements of slot antennas and coplanar waveguide circuits, it is found that the contribution of the reflection mechanisms inside the lens significantly affects the mutual admittance especially for H-plane coupling     

Scan blindness in infinite phased arrays of printed dipoles

A comprehensive study of infinite phased arrays of printed dipole antennas is presented, with emphasis on the scan blindness phenomenon. A rigorus and efficient moment method procedure is used to calculate the array impedance versus scan angle. Data are presented for the input reflection coefficient for various element spacings and substrate parameters. A simple theory, based on coupling from Floquet modes to surface wave modes on the substrate, is shown to predict the occurrence of scan blindness. Measurements from a waveguide simulator of a blindness condition confirm the theory.     

Input impedance of thin dipoles by moment method

The input impedance of half-wave dipoles with decreasing diameters has been calculated using the moment method of analysis with a stepped approximation of the current distribution. It is shown that the solution becomes increasingly inaccurate when the wire radius decreases and only a few segments for the antenna are used, and that it also diverges from the accurate answer when the length/diameter ratio of each segment is such that the axial-line-current and charge approximations become insufficient.     

Planar array design: approximation to mutual impedance between two remotely spaced 'half-wavelength' dipoles

The task of computing mutual coupling effects between remotely separated elements in the design of a large array is time consuming; the process may be hastened considerably by employing a very efficient approximation to the 'mutual impedance' integral, without seriously compromising the design parameters of the array.<>     

Scan blindness phenomenon in conformal finite phased arrays of printed dipoles

Scan blindness phenomenon for finite phased arrays of printed dipoles on material coated, electrically large circular cylinders is investigated. Effects on the scan blindness mechanism of several array and supporting structure parameters, including curvature effects, are observed and discussed. A full-wave solution, based on a hybrid method of moments/Green's function technique in the spatial domain, is used to achieve the aforementioned goals. Numerical results show that the curvature affects the surface waves and hence the mutual coupling between array elements. As a result, the array current distribution of arrays mounted on coated cylinders are considerably different compared to similar arrays on planar platforms. Therefore, finite phased arrays of printed dipoles on coated cylinders show different behavior in terms of scan blindness phenomenon compared to their planar counterparts. Furthermore, this phenomenon is completely different for axially and circumferentially oriented printed dipoles on coated cylinders suggesting that particular element types might be important for cylindrical arrays.     

Effective length and input impedance of the NIST standard dipoles

Computed values for the effective length and input impedance for a set of standard dipoles used at the National Institute of Standards and Technology are presented. These dipoles are used as calculable reference antennas in the calibration of dipole-like electromagnetic interference antennas in an open-area test site. Estimates for the uncertainty in the computed values of the effective length and antenna impedance are also given