W. Mark Dorsey

Design and Performance of Frequency Selective Surface With Integrated Photodiodes for Photonic Calibration of Phased Array Antennas

The design, fabrication, and integration of a frequency selective surface (FSS) with integrated photodiodes to allow for photonic calibration of phased array antennas is presented. The design includes embedding electrically short dipole antennas in each unit cell of the FSS, with a zero-biased photodiode placed across the gap of the diode. Fibers from an optical distribution network are passed through the honeycomb core of the frequency selective surface and pigtailed to the photodiodes. The RF performance of the frequency selective surface with integrated optics is investigated via simulations and measurements, and the results show that the structure maintains RF-transparency.

Phase-only synthesis of omnidirectional patterns with multiple nulls from a uniform circular array

An unconstrained optimization technique is presented for the phase-only synthesis of omnidirectional array patterns with multiple null regions from a circular array.

A hybrid global-local optimization approach to phase-only array-pattern synthesis

Phased array magnitude/power-pattern synthesis is in general a nonconvex optimization problem which can exhibit a large number of local minima. This is often exacerbated by the addition of (nonconvex) magnitude constraints on the array weights. Practical large-scale design of such patterns requires both efficient local optimization to quickly identify candidate minima, and nonlocal (“global”) optimization to provide new starting points and evaluate the resulting minima to find a suitable, if not global, solution. Here we combine a very efficient constrained local formulation based on a weighted pattern-error metric with a parameterized heuristic method for generating initial array weights and a global method for searching over the parameter space. We additionally show that passband point-nulls, a common local-minima artifact, can be reliably detected early in the local optimization allowing for quick termination.

Second-Order Cone Programming for Scan-Plane Reconstruction for the Wavelength-Scaled Array

The wavelength-scaled array architecture reduces the element count in large, ultrawideband antenna arrays by segmenting the aperture into subapertures of varying sizes and bandwidths. This results in an asymmetrical aperture of dissimilar elements with associated patterns that require significant correction. Here, we assess narrowband array performance using its far-field pattern as obtained in two steps. First, we characterize individual elements using planar near-field measurements. Second, we use second-order cone programming to optimize the complex element weights that generate the desired individual far-field element patterns derived from those measurements. This document details the far-field optimization technique, referred to here as optimized scan-plane reconstruction, and uses it to demonstrate that the asymmetric wavelength-scaled array can support low global sidelobe reduction, deep localized nulls, and/or mainbeam scanning like a conventional symmetric array.

Phase-only beam broadening in large transmit arrays using complex-weight gradient descent

Day recently obtained phase-only element weights for a large transmit array of arbitrary geometry by optimizing complex weights using an objective function that penalized amplitude variation. He used gradient descent modified with a classic SVD technique to create point and sector nulls as desired. Here Days approach is extended to allow for main-beam broadening as might be needed to illuminate multiple receive beams. This is done by adding a second objective term, one penalizing variation in array-factor amplitude across a grid of beamspace points covering the desired broad main beam. The tension between the two objective terms turns out to be challenging to manage, and at this preliminary stage of algorithm development, parameter scheduling across a sequence of stages of the optimization is required to obtain good solutions.

Transmit and receive circular array pattern synthesis for radar applications

Circular arrays are an appealing if underused option for radar systems that require 360° coverage in azimuth. They require no mechanical scanning and do not suffer from the high-angle scan loss and beam broadening of linear and planar arrays. The circular geometry, along with suitable pattern synthesis techniques, enables some unique capabilities. On transmit they provide the flexibilty to synthesize a continuum of beam shapes, from omnidirectional to sector to high gain. On receive, simultaneous high-gain beams can be formed to cover any desired azimuth footprint. In this paper we explore the capabilities of circular arrays through a series of pattern synthesis design examples.

Hybrid array pattern calculation technique

An array analysis technique is presented that uses nine embedded element patterns to approximate all embedded element patterns. The hybrid technique avoids shortcomings of other common approaches that use a single embedded element approximation, while also providing significant time/computational savings compared to exact approaches including simulations and/or measurements of all embedded element patterns. The technique is then applied to an array of dual-circularly polarized antenna elements.

SOCP design of monopulse sum and difference beams for a uniform circular array

Classical sum and difference beams for angle measurement in amplitude-comparison monopulse systems are constructed by adding and subtracting narrow beams slightly offset in pointing angle. Here instead beams with sum and difference behavior in azimuth are synthesized using second-order cone programs applicable to any array for which embedded complex element patterns are known. The computational example here is specific to a uniform circular array (UCA) because it uses embedded element patterns obtained by rotating a prototype pattern through angles uniformly spaced around the circle. That prototype was computed through electromagnetic simulation of a UCA of simple patch elements.

Fast synthesis of multiple nulls in an omnidirectional pattern

A fast and efficient nulling technique is presented which uses directional auxiliary beams to create nulls in an omnidirectional pattern. A combination of optimization methods and Fourier scanning techniques are used to create the auxiliary beams.

Transmit pattern synthesis for uniform circular arrays with active reflection constraints

Circular arrays offer many advantages over traditional linear and planar arrays in modern radar systems. The circular geometry facilitates design of omnidirectional, sector, and/or directional radiation patterns that can cover a full 360 degrees without the need for mechanical scanning and without degradation to beamwidth, gain, or sidelobe level. However, the design of these patterns is complicated by the need to account for unique embedded element patterns for all elements within the array and the sensitivity of the active reflections to the density of the array elements around the circle. In this paper we describe circular array pattern synthesis approaches that enable array pattern flexibility with bounds on the reflected power.