Keith D. Trott

Wideband phased array radiator

Raytheon has developed a novel wide-band, dual-polarized, element with excellent cross-polarization isolation to populate the AMRFC high band transmit array. The electrically short crossed notch (ESCN) element consists of an orthogonal pair of tapered crossed-notch radiators with a balanced feed to increase polarization purity. The ECSN provides excellent polarization performance vs. scan (better than current notch capabilities). The measured co-pol and x-pol performance of the embedded element in the E-, H-, and diagonal planes and the swept gain performance will be discussed. Also discussed will be the modeling techniques used to design this wideband radiator.

A UTD type analysis of the plane wave scattering by a fully illuminated perfectly conducting cone

A uniform high-frequency asymptotic solution, based on the physical optics (PO) approximation, is obtained in the format of the uniform geometrical theory of diffraction (UTD) to describe the fields diffracted by the tip of a semi-infinite, perfectly conducting cone when it is fully illuminated by an electromagnetic plane wave. The solution is expressed in terms of an integral, over finite limits which can be integrated numerically without difficulty. The results computed from the uniform asymptotic PO solution compare well with previously published results given for narrow-angle semi-infinite cones. In addition, they compare well with measurement and with an independent moment method (MM) solution for the scattering by a finite flat-backed cone in which several higher order wave interactions are found to be significant; one such interaction is between the tip and the base of the cone. Expressions are provided which are useful for calculating this tip-base interaction and confirm its relative importance. These expressions also provide tip diffraction effects which are important within the forward paraxial zone for the radiation by antennas on cones. >

Steerable phased array antennas using single-crystal YIG phase shifters-theory and experiments

A phased array antenna containing four linear microstrip patch elements has been fabricated and tested. The elements were fed through single-crystal yttrium-iron-garnet (YIG) phase shifters. By varying the bias magnetic field, the input phases to the antenna elements can thus been tuned, resulting in steering of the radiation beam in one dimension. Measurements compared reasonably well with calculations.

Modeling conformal antennas on metallic prolate spheroid surfaces using a hybrid finite element method

In this paper, the hybrid finite element-boundary integral (FE-BI) method appropriate for modeling conformal antennas on doubly curved surfaces is developed. The FE-BI method is extended to model doubly curved, convex surfaces by means of a specially formulated asymptotic dyadic Greens function. The FE-BI method will then be used to examine the effect of curvature variation on the resonant input impedance of a cavity-backed, conformal slot antenna and a conformal patch antenna recessed in a perfectly conducting, electrically large prolate spheroid surface. The prolate spheroid shape provides a canonical representation of a doubly curved mounting surface. The numerical results for conformal slot and patch antennas on the prolate spheroid are compared as a function of curvature and orientation.

Single-crystal YIG phase shifter using composite stripline structure at X band

A tunable phase shifter at X band using single-crystal YIG film material grown on GGG substrates is fabricated. The phase shifter is a quarter wavelength in the absence of a bias magnetic field. The phase can be tuned 120° by varying the bias magnetic field from 3440 to 3720 Oe. The resultant variation in insertion loss was 0.5 dB. Measurements compared very well with calculations.

A Practical Approach to Modeling Doubly Curved Conformal Microstrip Antennas

Designers are increasingly integrating conformal microstrip antennas into the curved structures of either air or land vehicles. Quite often, these structures are doubly curved (e.g. curved along two orthogonal surface directions). This practice necessitates the development of accurate codes versatile enough to model conformal antennas with arbitrarily shaped apertures radiating from doubly curved surfaces. Traditional planar-structure-based design techniques are not well suited for this application. A hybrid finite element-boundary integral formulation appropriate for the high-frequency analysis and design of doubly curved conformal antennas is introduced in this paper. The novelty of this approach lies in its use of an asymptotic prolate spheroidal dyadic Green’s function to model the physics of curved surface diffraction. To demonstrate the utility of this approach, the effects of curvature on the resonant frequency and input impedance of both a doubly curved conformal square and circular patch antenna are investigated. Different feed positions are also considered. Due to a paucity of published experimental data, the numerical results are benchmarked by comparison with the results for planar square and circular patch antennas. The planar results are obtained by using an experimentally validated planar finite element-boundary integral code. 296 Macon, Trott, and Kempel

7-21 GHz wideband phased array radiator

Raytheon has developed a novel wideband, dual-polarized, element with excellent cross-polarization isolation to populate the AMRFC high band transmit array. The electrically short crossed notch (ESCN) element consists of an orthogonal pair of tapered crossed-notch radiators with a balanced feed to increase polarization purity. The ECSN provides excellent polarization performance versus scan (better than current notch capabilities). The 2X (3-9 GHz) measured co-polarisation and x-polarisation performance of the embedded element in the E-, H-, and diagonal planes and the swept gain performance were discussed at the 2003 Phased Array Conference. This paper discusses the measured performance of the 1X (7-21 GHz) version with the fully integrated balun. The measured embedded element performance for the E-, H-, and diagonal planes is discussed as well as the novel balun design which enables the outstanding performance.

Application of the integral equation-asymptotic phase (IE-AP) method to three-dimensional scattering

An approach for numerically analyzing electromagnetic scattering from convex conducting obstacles which possess large, relatively smooth surfaces is discussed in this work. In this approach, the current density induced on the scatterer is represented in terms of basis functions which are capable of representing rapid phase variation with very few unknowns per square wavelength. The unknowns associated with the surface current are then determined through testing of appropriate surface integral equations. A special technique is introduced to accelerate calculations of portions of the resultant matrix equation associated with shadow regions and edges. The results of a series of numerical experiments on canonical objects demonstrate the efficiency and accuracy of the technique.

Single-crystal yttrium iron garnet phase shifter at X band

A tunable phase shifter at X band using single-crystal yttrium iron garnet film material grown on GGG substrates is fabricated. The phase shifter is a fourth wavelength in the absence of a bias magnetic field. The phase can be tuned 120° by varying the bias magnetic field from 3440 to 3720 Oe. The resultant variation in insertion loss was 0.5 dB. Measurements compared very well with calculations.

Polarization isolation limit for dual-polarized phased array systems

Polarization isolation in dual polarized phased arrays is studied as an expansion of the unit cell behavior. It concludes that a fundamental polarization isolation limit exists in the diagonal far-field planes, while the principal planes exhibit no polarization limit. The diagonal plane polarization isolation limit is scan dependent, reaching a 0 dB maximum at 90°, or end-fire scan. While aperture design features may approach this limit, and manufacturing tolerances modulate it, it apparently is not exceeded in phased array test results. Polarization compensation circuits may improve on the aperture polarization isolation, but are also fundamentally limited by it.