Gerald F. Ricciardi

A flat laser array aperture

We describe a design concept for a flat (or conformal) thin-plate laser phased-array aperture. The aperture consists of a substrate supporting a grid of single-mode optical waveguides fabricated from a linear electro-optic material. The waveguides are coupled to a single laser source or detector. An arrangement of electrodes provides for two-dimensional beam steering by controlling the phase of the light entering the grid. The electrodes can also be modulated to simultaneously provide atmospheric turbulence modulation for long-range free-space optical communication. An approach for fabrication is also outlined.

Effects of channel mismatch and phase noise on jamming cancellation

Various hardware errors, including channel mismatch and phase noise, adversely affect the performance of jamming sidelobe cancellation in a digital beamforming array that combines array elements into overlapped subarrays for digital combining and uses auxiliary channels to obtain an estimate of the jammer signals. Analysis is needed to determine how much hardware error can be tolerated to obtain a desired level of jamming cancellation performance. We derive analytical, closed-form expressions that separately relate channel mismatch and phase noise to jamming cancellation ratio (CR) in a sidelobe cancellation system. We also validate our theoretical results using a high-fidelity simulation that models the phased array and signal processing chain, and obtain a close agreement between the theoretical and simulated results. By incorporating the errors in element- and subarray-level combining weights, we show that CR can be a misleading metric and it is more useful to consider the residue powers. We show that the residue power curve is proportional to the subarray pattern and provide design guidelines for improving jamming cancellation performance.

A Fast-Performing Error Simulation of Wideband Radiation Patterns for Large Planar Phased Arrays With Overlapped Subarray Architecture

We present an efficient solution for the fast computation of wideband radiation patterns of large planar arrays with overlapped subarray architecture, subject to beamforming errors. We obtain very good results fully hosting the simulation on a desktop platform, and even better results implementing a small portion of code on commercially-available graphical processing units (GPUs). Errors can be introduced throughout the beamforming chain and include random phase/magnitude errors, element failures, and surface deformation errors. At the core of the computational architecture are interchangeable primitives that quickly compute the entire far-field subarray pattern, subject to errors and user-defined tapers. The primitives are routines that address the general case of arrays with non-uniformly spaced elements (to model surface distortion) and the special case of arrays with uniformly-spaced elements. Both grid-type primitives are CPU hosted, while only the general non-uniform grid primitive type is GPU hosted due to its excellent run-time performance. The simulation quickly generates wideband patterns for the entire forward-looking hemisphere with sufficient resolution to accurately evaluate directivity and sidelobe metrics. Using only the non-uniform grid type hosted on the GPU, we show significant run-time improvement over both CPU-hosted implementations: 18.0 × over the general non-uniform grid and 5.7 × over the uniform grid.

Performance assessment of sidelobe jamming cancellation using stretch processing

We investigate via simulation the performance of the two major classes of algorithms that cancel sidelobe jamming in a wideband phased array radar that uses stretch processing of beamspace output. The deramper in stretch processing renders the statistics of the jamming non-stationary. One approach for addressing the non-stationarity is to divide the stretched output into segments and apply narrowband equalization on each segment. The other approach is to model the weight vector as time-varying. To each approach we also add subbanding to decrease the non-stationarity of the stretched jammer signals and time-taps to combat dispersion across the array. We show via simulation that since the jammers are in the sidelobe region, both approaches provide comparable performance in terms of cancellation ratio (CR) and loss in signal-to-interference-plus-noise ratio (SINR). But since the segmentation-based approach is approximately eight times less complex and channelization through subbanding aids in channel equalization, its subbanded variant is the preferred algorithm for wideband sidelobe cancellation.

Characterization of amplitude modulation bias coupling for solid-state high-power amplifiers

A method is developed and validated to empirically characterize unwanted spectral coupling from a non-ideal power supply bias to the radio frequency (RF) output for solid-state high-power amplifiers (HPAs) operating in saturation. Specifically, the method currently addresses how power supply ripple amplitude modulates the RF carrier output by characterizing an amplitude modulation bias coupling (AMBC) factor as a function of carrier frequency and power supply ripple frequency. With this coupling factor, one is able to use an analytical predictive model to understand the impact of various levels of bias ripple voltages on the HPA output spectrum. The approach examines the relative AM sideband levels in the frequency domain to empirically quantify the level of mixing that occurs since it is difficult to measure such small variations of interest in the time domain. A commercially available gallium nitride HPA and standard test equipment are used to demonstrate the characterization process.