W. Hersch

Bio: W. Hersch is an academic researcher. The author has contributed to research in topics: Radiation pattern & Waveguide. The author has an hindex of 1, co-authored 1 publications receiving 11 citations.

The surface-wave aerial

Abstract: The radiation from the open-circuited end of an externally dielectriccoated metallic waveguide can be controlled by varying the size of the guide, the thickness and/or the dielectric constant of the coating. A new type of aerial designed around this principle is given the name `surface-wave aerial' and radiation-pattern measurements are used to confirm the theory underlying this type of radiator. According to its mode of operation it belongs to the category of end-fire aerials, which are briefly reviewed to show that surface-wave aerials occupy a place in their own right amongst the many possible arrangements that utilize the end-fire effect to produce a directional radiation pattern. The theory of the surface-wave aerial is developed in detail, a necessary preliminary step being a full theoretical analysis of the properties of the first-order cylindrical surface wave. It is shown that a dielectric-coated cylinder which is approximately a wavelength in circumference can act as a waveguide for higher-order surface waves, of which the first order is an example. The `characteristic equation' is determined for the general case from which the cut-off frequency, propagation coefficient and conditions under which propagation can take place are derived in turn. Two specific cases are evaluated numerically and the results are used to calculate the polar diagrams of surface-wave aerials operating at 9Gc/s. The wavelength constant as well as the continuous radiation loss of a surface waveguide for which λg/λ0≃1 are measured directly and the results obtained are used to account for the radiation pattern of very long aerials. In conclusion, an outline of future work is given.

Electrically short monopole antennas with dielectric or ferrite coatings

Abstract: A comprehensive analysis of the electrically-small material-clad monopole is performed by representing the various fields by discrete and continuous eigenvalue spectrums. The cladding creates a dominant quarter-wavelength resonant-cavity effect whereby the leakage of radiation at the terminal plane is transformed into a low impedance at the annular feed. The mode coupling taking place at both feed and terminal plane is solved by variational methods to yield the antenna radiation pattern, bandwidth, efficiency and input impedance as a function of electrical size and frequency. The agreement between the computed and measured results establishes the usefulness of the analysis, and design curves are presented; other factors that influence the system performance of the antennas in practice are discussed. It is concluded that the optimisation of this type of antenna centres on the choice of suitable low-loss material with comparable relative permeability and permittivity values at the frequency of interest. In general, this calls for research into improved materials, but useful antennas can be made with commercially available materials.

Theoretical investigation of cylindrical dielectric-rod antennas

Abstract: Present-day theory of uniform cylindrical dielectric-rod antennas rests on the three theoretical treatments of Horton, Bouix and Fradin (leaky-guide theory), and on Brown's end-fire theory A digression on the general relationship between Schelkunoff's equivalence principle and the vector Kirchhoff formula reveals that these radiation formulas may only be applied to regions in which the vector potentials are known to satisfy the inhomogeneous wave equation On applying this axiom to the theories, all but Brown's are shown to be fallacious A detailed application of the vector Kirchhoff formula to uniform cylindrical dielectric rods supporting the HE11 mode produces an expression for the far-field radiation pattern, which, when computed, gives good agreement with existing experimental data The analysis allows for dielectric losses and can also be extended to nonuniform dielectric antennas with gradual tapers Fresnel interaction of the apertures and lens effects are considered Finally, some design recommendations for dielectric rod antennas are made

Higher-Order Cylindrical Surface-Wave Modes

Abstract: A general theory of the propagation of higher-order modes on cylindrical surface-wave structures is examined and applied to the dielectric-clad rod. A theory is developed in which the boundary conditions at the guide are specified by an impedance dyadic. The characteristic equation for the structure is then obtained in terms of the elements of the dyadic. The equation is solved and yields a set of conditions which are satisfied by the values of the dyadic elements at the cutoff points for each of the higher-order modes. A mode without a cutoff frequency is shown to exist on the structure used. The relationship between the guide wavelength and frequency has been verified experimentally.

A study of absorption and scattering of microwaves by dielectric scatterers such as insects: with application to MIMO radar for imaging termites and UAV imaging MIMO radar and an investigation of modes without cutoff, open waveguides and artificial dielectrics

Abstract: Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 2016.

Revisiting the waves on a coated cylinder by using surface-impedance model

Abstract: The results of analytical and numerical study of the modes propagating on an impedance-surface circular cylinder are communicated. Besides the well-known axially symmetric Sommerfeld's mode, another hybrid mode, having a single azimuthal variation, can propagate at any frequency. For a realistic cylindrical conformal antenna, the both wavenumbers are quite comparable. This may cause additional coupling between array antenna elements.