A. Hessel

Scattering and guided waves at an interface between air and the compressible plasma

Propagation of waves in a compressible, isotropic, collisionless electron plasma is studied. Optical and acoustic modes of propagation are examined in detail. Scattering and guiding properties of a plane interface between free space and plasma are investigated. It is found that electromagnetic energy in theory can be completely converted into plasma waves. A surface wave is found whose properties are affected slightly by the compressibility for (\omega_{p}/\omega) > \sqrt{2} . In contrast to the case of purely dielectric plasma, this surface wave has no high-frequency cutoff. Formal expressions for electromagnetic and acoustic fields excited by a magnetic line source in free space, parallel to the interface, are obtained.

Element pattern of an axial dipole in a cylindrical phased array, Part I: Theory

Cylindrical array antennas are attractive for applications requiring uniform 360\deg azimuthal pattern performance. For very low sidelobe or precise angle measurement designs, an accurate knowledge of the mutually coupled element pattern becomes important. A modal solution is presented for an element pattern in a periodic array of axial dipole radiators placed coaxially over a circular cylindrical ground. This solution avoids the problems associated with asymptotic appproaches and displays a number of advantages: 1) it is exact, subject only to truncation errors; 2) it is uniformly valid in all spatial regions for both rectangular and, with a simple modification, for triangular isosceles lattice configurations; and 3) it provides absolute gain information. The analysis is presented along with numerical results for representative parameter values, selected to illustrate the various trade-offs. Comparison with published data employing the asymptotic approach and with planar array results is given.

Analysis of finite arrays-a new approach

A novel method for the analysis of finite arrays is presented. The method is based on a global array concept where the array problem (for single-mode elements) is reduced to a solution of a single Fredholm integral equation of the second kind. This formulation offers several types of solutions (not all explored yet) with illuminating results. The approximate solution of this integral equation, for example, yields finite array characteristics in terms of equivalent infinite array scattering parameters and mutual admittances. The method is general, i.e., applicable to any element-type and periodic array geometry. Presently, the method applies to single-mode elements (one unknown per element), however, it can be extended to a multimode analysis.

Element pattern of an axial dipole in a cylindrical phased array, Part II: Element design and experiments

The design and construction of a cylindrical array of axial dipoles is described. Dipole pattern amplitude measurements performed over practical scan and frequency ranges show excellent agreement with theoretically predicted results. Dipole pattern phase, feed line effects and radiator match are also discussed. These results provide strong evidence of the correctness of the analysis and numerical results presented in Part I of this paper, and furnish a firm basis for accurate prediction of array performance.

Element pattern of dually polarized element in infinite phased array

Explicit relations for the pattern of both field components of a dually polarized element in an infinite phased array are established. Calculations of the radiated field are made for an infinite array of circular waveguide apertures for several lattices and scan planes. The computed results are compared with the analytically obtained patterns of an ideal element. The effect of cross polarization on the element patterns is shown for nonprincipal plane scans.

Microstrip stacked strip element phased arrays

The frequency and scan performance of E-plane scanned, ideal probe-excited, broadband stacked strip element phased arrays are numerically investigated. Results indicate a 1.85:1 bandwidth over a 45 degrees E-plane scan range. The results clarify the operative physical phenomena and lead to an iterative element synthesis in the array environment. >

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

Modal analysis is presented for the realized element gain E and H plane patterns for two-dimensional cylindrical arrays with a concentric dielectric sleeve. Numerical results indicate that a dielectric window in the near field of a conformal phased array may cause significant deterioration of the element pattern due to guided wave effects. If the window is inappropriately configured, this deterioration manifests itself in appearance of pronounced dips and of an excessive off-broadside ripple. A design method of dielectric windows for conformal arrays to reduce the guided wave effects is proposed. The method is validated by direct evaluation of the E and H plane element patterns for optimized window geometries.

Linear phased array of coaxially-fed monopole elements in a parallel plate guide

Performance of a coaxially-fed monopole element in an infinite linear phased array radiating into a semi-infinite parallel plate guide is analyzed. Relations for the active admittance and element pattern are obtained. These expressions are required in the design of low sidelobe Rotman lens with probe elements. Numerical results based on theoretical analysis are presented. Comparison with experimental data will be given.

Conversion of transverse electromagnetic waves into a longitudinal wave at a dielectric-plasma boundary

Abstract : The document discusses the conversion of transverse acoustic waves into longitudinal plasma waves at the interface of a dielectric and an electron plasma.

3D scan performance of strip element microstrip phased arrays

An iterative design procedure taking into account the different scan performance in the E- and H-planes of strip element microstrip phased arrays is presented. The phased array model considered consists of perfectly conducting periodically spaced infinite strips of infinitesimal thickness on top of a grounded dielectric substrate. The strips are excited by ribbon current probes. Applying a linear phase taper simultaneously along the E- and H-planes allows the beam to be scanned in any arbitrary direction. Numerical results show the feasibility of a voltage standing wave ratio of less than two for a maximum scan of 40 degrees in the E-, H-, and D-planes and in a frequency band of +or-9%.<<ETX>>