Timothy E. Durham

Electromagnetic radiation from structures consisting of combined body of revolution and arbitrary surfaces

A formulation is developed to treat radiation from structures consisting of a body of revolution (BOR) in the presence of multiple arbitrarily shaped three-dimensional objects. An electric field integral equation is set up on the surface of the combined structure. The resulting integro-differential equation is solved using the method of moments. On the BOR, harmonic entire domain expansion functions are used for the circumferential dependence, while overlapping subdomain functions are used to model the axial curvature. The arbitrarily shaped portions of the structure are modeled using triangular surface patches. The resulting system matrix has a partial block diagonal nature, which provides a more economical solution for structures that have some rational symmetry. Numerical results are presented and compared to measurements of a unique cavity-backed patch fed antenna. >

Design of an 8–40 GHz antenna for the wideband instrument for snow measurements (WISM)

Measurement of land surface snow remains a significant challenge in the remote sensing arena. Developing the tools needed to remotely measure Snow Water Equivalent (SWE) is an important priority. The Wideband Instrument for Snow Measurements (WISM) is being developed to address this need. WISM is an airborne instrument comprised of a dual-frequency (X- and Ku-band) Synthetic Aperture Radar (SAR) and dual-frequency (K- and Ka-band) radiometer. A unique feature of this instrument is that all measurement bands share a common antenna aperture consisting of an array-feed reflector that covers the entire bandwidth. This paper covers the design and fabrication of the wideband array feed, which is based on tightly coupled dipole arrays. Implementation using a relatively new multi-layer microfabrication process results in a small, 6×6-element, dual-linear polarized array with beamformer that operates from 8 to 40 GHz.

Antenna characterization for the Wideband Instrument for Snow Measurements (WISM)

Experimental characterization of the antenna for the Wideband Instrument for Snow Measurement (WISM) under development for the NASA Earth Science Technology Office (ESTO) Instrument Incubator Program (IIP), is discussed. A current sheet antenna, consisting of a small, 6×6 element, dual-linear polarized array with integrated beamformer, feeds an offset parabolic reflector, enabling WISM operation over an 8 to 40 GHz frequency band. An overview of the test program implemented for both the feed and the reflector antenna is given along with select results for specific frequencies utilized by the radar and radiometric sensors of the WISM.

Integral equation analysis of dielectric and conducting bodies of revolution in the presence of arbitrary surfaces

A formulation is developed to treat radiation from structures consisting of conducting and/or dielectric bodies of revolution (BOR) in the presence of multiple arbitrary shaped three-dimensional objects. A set of integral equations is developed on the surfaces of the combined structure and the resulting integro-differential equations are solved using the method of moments. On the BOR, harmonic entire domain expansion functions are used for the circumferential dependence, while overlapping sub-domain functions are used to model axial curvature. The arbitrary shaped portions of the structure are modeled using triangular surface patch basis functions. The resulting matrix has a partial block diagonal nature which provides a more economical solution for structures which have some rotational symmetry. The accuracy of the BOR and arbitrary surface formulation is verified using the self-consistency method and measured data. >

Analysis and Measurement of EMI Coupling for Aircraft Mounted Antennas at SHF/EHF

The mutual coupling between antennas is an important aspect of the overall electromagnetic interference (EMI) between electronic systems on advanced aircraft. There are several existing systems level computer codes which can analyze coupling between aircraft mounted antennas, but these are inadequate for EMI analysis at frequencies above 2 GHz for many of the complex geometries encountered in modern aircraft. In order to develop improved coupling analysis models, an evaluation of all existing analysis techniques and computer programs has been carried out. In addition, an extensive set of coupling measurements have been performed to assess the accuracy of the different analysis techniques. This paper describes these evaluations and measurements including a comparison of theoretical and experimental results.

Investigation of a broad-band cavity-backed array antenna

A new multimode antenna consisting of a circular array of log periodic (LP) elements, suspended in dielectric material and placed in a circular cavity with a conical bottom, is presented and discussed. The conducting elements are contained within the dielectric. Far field patterns obtained using the method of moments (MoM) are compared to experimental measurements and show good agreement for both magnitude and phase. The effect of cavity cone angle on the antenna patterns is presented. Careful selection of the cone angle can result in significant suppression of undesirable higher order resonant modes on the LP elements.

Integral equation analysis of dielectric bodies of revolution in the presence of arbitrary surfaces

A general formulation is presented for bodies of revolution (BORs) in the vicinity of arbitrarily shaped three-dimensional surfaces. The formulation is capable of treating both perfectly conducting surfaces and dielectrics that are defined by a BOR. The formulation presented here allows a conducting BOR to be either open or closed. The arbitrary surfaces are perfectly conducting. A very general class of problems is solved by combining the solutions for BORs and arbitrary surfaces in a single formulation. The accuracy of the formulation has been confirmed by a series of self-consistency tests and comparisons with measured data.<<ETX>>

A method for treating junctions between bodies of revolution and arbitrary surfaces

The BOR/patch formulation can be applied to many types of antennas that involve a junction between these two basic elements of the structure. As an example, the cavity-backed patch antenna considered previously by the authors (1992) has such junctions. Although it was shown that accurate radiation pattern predictions for this particular antenna can be obtained without forming these junctions, they would be required in order to develop accurate input impedance models. The self-consistency technique is used to demonstrate the accuracy of the junction models.<<ETX>>

Composite body-of-revolution and arbitrary surface analysis using the method of moments

The need to predict the performance of a particular class of cavity-backed patch-fed antennas has motivated the development of combined body-of-revolution (BOR) and arbitrary surface analysis. The technique is general in the sense that it is useful for the radiation and scattering analysis of many objects which can be broken down into circularly symmetric portion and an arbitrary nonaxisymmetric portion. The use of special basis functions for the BOR part of the geometry results in substantial reductions in computation times as well as increased accuracy over using arbitrary surface models for the whole structure. Only the perfectly electrically conducting case is discussed. The cavity-backed antennas analyzed using the moment method are unique in that they are excited by large conducting patches in the plane of the aperture.<<ETX>>