Phase-only Optimization Research Articles

A Phase-Only Optimization Null Control Method for FDA-MIMO Based on ADMM

This paper investigates null control within the transmit–receive beampattern of Frequency Diverse Array-Multiple-Input and Multiple-Output (FDA-MIMO) systems, presenting a novel phase-only optimization approach for achieving null control in FDA-MIMO. We employ an alternating multiplier framework, which transforms the intricate and inherent constant modulus constraint and numerous amplitude constraints in optimization into more manageable projection problems. By employing a phase-only optimization strategy, the intricate hardware and computational burdens associated with null control in FDA-MIMO are effectively alleviated. The simulation results indicate that the algorithm proposed in this paper exhibits excellent null control ability while precisely maintaining constant modulus constraints, and it possesses an extremely high computational efficiency.

Antenna Excitation Optimization with Deep Learning for Microwave Breast Cancer Hyperthermia.

Microwave hyperthermia (MH) requires the effective calibration of antenna excitations for the selective focusing of the microwave energy on the target region, with a nominal effect on the surrounding tissue. To this end, many different antenna calibration methods, such as optimization techniques and look-up tables, have been proposed in the literature. These optimization procedures, however, do not consider the whole nature of the electric field, which is a complex vector field; instead, it is simplified to a real and scalar field component. Furthermore, most of the approaches in the literature are system-specific, limiting the applicability of the proposed methods to specific configurations. In this paper, we propose an antenna excitation optimization scheme applicable to a variety of configurations and present the results of a convolutional neural network (CNN)-based approach for two different configurations. The data set for CNN training is collected by superposing the information obtained from individual antenna elements. The results of the CNN models outperform the look-up table results. The proposed approach is promising, as the phase-only optimization and phase–power-combined optimization show a 27% and 4% lower hotspot-to-target energy ratio, respectively, than the look-up table results for the linear MH applicator. The proposed deep-learning-based optimization technique can be utilized as a protocol to be applied on any MH applicator for the optimization of the antenna excitations, as well as for a comparison of MH applicators.

In-Band Scattering Reduction of Wideband Phased Antenna Arrays With Enhanced Coupling Based on Phase-Only Optimization Techniques

A novel systematic methodology based on phase-only optimization techniques is proposed for the realization of in-band scattering reduction of wideband phased antenna arrays with intentionally enhanced electromagnetic (EM) coupling. By only optimizing the phase excitation that can be implemented using a coaxial delay line at the feed port of each element, the array with lower monostatic scattering cross section (SCS) can be accomplished in the designated angular region with little degradation of radiation performances within the operating band. Based on fast and efficient synthesis expressions of scattering and radiation properties of the array with additional phase contributions, where all the mutual coupling effects are taken into account, and it is capable of realizing a systematic and fast optimization methodology of the phase excitations. Then, a joint optimization approach is adopted to achieve a balance between radiation and scattering characteristics of the array. A $1\times16$ linear array operating in 8–12 GHz for scanning up to ±60° is designed to validate the proposed approach. The simulated and measured results are in good agreement, indicating that the monostatic SCS of the optimal array is considerably reduced compared to that of the uniform array with equal phase excitations.

Phase-Only Beam Broadening of Contiguous Uniform Subarrayed Arrays

In modern antenna systems, beam broadening of subarrayed arrays provides continuous coverage of a wide angular extent in a cost-effective manner. While many methods have been published that address beam broadening of traditional (non-subarrayed) arrays, there is a knowledge gap in the published literature with respect to efficient beam broadening of contiguous uniform subarrayed arrays. This article presents efficient methods for beam broadening of contiguous uniform subarrayed arrays where the excitation of each element is not individually controlled, but the elements of the array are grouped together as subarrays to have the same element excitations. Particularly, this article focuses on phase-only optimization to preserve maximum power output. Three modilied iterative Fourier transform (IFT) methods and one genetic algorithm (GA) are presented to efliciently search the vast solution space of possible phase settings for a solution that satislies the desired broadened pattern. These methods are evaluated on idealized 1 x 40 and 1 x 80 linear arrays with live element subarrays and 40 x 40 and 80 x 80 element rectangular arrays with 5 x 5 element subarrays. The proposed modilied IFT methods are found to be faster than the GA approach, while the GA approach only offers a few percentage points of better effectiveness.

Optimizing single-nanoparticle two-photon microscopy by in situ adaptive control of femtosecond pulses

Single-nanoparticle two-photon microscopy shows great application potential in super-resolution cell imaging. Here, we report in situ adaptive optimization of single-nanoparticle two-photon luminescence signals by phase and polarization modulations of broadband laser pulses. For polarization-independent quantum dots, phase-only optimization was carried out to compensate the phase dispersion at the focus of the objective. Enhancement of the two-photon excitation fluorescence intensity under dispersion-compensated femtosecond pulses was achieved. For polarization-dependent single gold nanorod, in situ polarization optimization resulted in further enhancement of two-photon photoluminescence intensity than phase-only optimization. The application of in situ adaptive control of femtosecond pulse provides a way for object-oriented optimization of single-nanoparticle two-photon microscopy for its future applications.

Phase-Only Optimization of Asymmetric Multiple Beams Reflectarray with Single Feed Using the Invasive Weed Optimization

Phase-only optimization of asymmetric multiple beams reflectarray with single feed is investigated in this paper. The conventional design approaches are first reviewed. Secondly, for design of asymmetric multiple beams reflectarray with arbitrary gain levels and beam directions, a general method based on invasive weed optimization is proposed. Then, practical considerations for applying the proposed method to design multiple beams reflectarray are talked over. For illustrating the effectiveness of the proposed method, several multiple beams design cases with different design requirements are optimized through this method, and the optimized results are analyzed through simulation approach based on array theory. The simulation results show that the optimized cases demonstrate the satisfactory multiple beams performance.

Design and Optimization of a Single-Layer Planar Transmit-Receive Contoured Beam Reflectarray With Enhanced Performance

This paper presents the design and optimization of a 1.2-meters single-layer planar contoured beam reflectarray in Ku-band. The reflectarray is optimized to fulfill the requirements of a Direct Broadcast Satellite mission, which covers a South American coverage in both transmit and receive frequency bands for dual linear polarization. The reflectarray is designed using a direct optimization approach where all the array elements are optimized simultaneously, thus resulting in a design with enhanced performance compared to designs obtained using a phase-only optimization approach. The reflectarray fulfills all the coverage requirements in both transmit and receive frequency bands and the performance is validated by means of full-wave Method of Moments simulations.

AN IMPROVED PREDESIGN PROCEDURE FOR SHAPED-BEAM REFLECTARRAYS

This article describes an improved design procedure for shaped-beam reflectarrays, which is advanced mainly in accuracy and concision. Specifically, the excitation has been computed by a new approach named local simulation instead of mathematical modeling, which demonstrates more advantage in precision. The intersection approach has been applied to optimization, and it is improved by introducing a new multi-stage strategy into the synthesis process to avoid local minima. Moreover, the phase-only optimization, calculation of the reflection phase data table and the simulation verification processes are combined as a co-simulation procedure by VBScript (Visual Basic Script). This procedure is very beneficial to design reflectarrays with efficiency. As an example, a reflectarray consists of 621 dual-loop elements is optimized, and a good sectored-cosecant squared beam result is obtained.

Direct Optimization of Printed Reflectarrays for Contoured Beam Satellite Antenna Applications

An accurate and efficient direct optimization technique for the design of contoured beam reflectarrays is presented. It is based on the spectral domain method of moments assuming local periodicity and minimax optimization. Contrary to the conventional phase-only optimization techniques, the geometrical parameters of the array elements are directly optimized to fulfill the contoured beam requirements, thus maintaining a direct relation between optimization goals and optimization variables, and hence resulting in more optimal designs. Both co- and cross-polar radiation patterns of the reflectarray can be optimized for multiple frequencies, polarizations, and feed illuminations. Several contoured beam reflectarrays, that radiate a high-gain beam on a European coverage, have been designed and compared to similar designs obtained using the phase-only optimization technique. The comparisons show that the designs obtained using the proposed direct optimization technique are superior in performance, both for multi-frequency and dual-polarization designs. A reflectarray breadboard has been manufactured and measured at the DTU-ESA Spherical Near-Field Antenna Test Facility to validate the proposed technique. An excellent agreement of the simulated and measured patterns is obtained.

APPLICATION OF ELECTROMAGNETISM-LIKE ALGORITHM TO PHASE-ONLY SYNTHESES OF ANTENNA ARRAYS

In this paper, a novel stochastic approach, i.e., the electromagnetism-like (EM-like) algorithm, is applied to phase-only syntheses of antenna arrays. The goal is to minimize the pattern sidelobe under null-steering constraints by phase-only adjusting. The mechanism of EM-like algorithm results from the Coulomb's Law of Electromagnetics. It does not require gradient calculations, and can automatically converge at a good solution through the virtual charge of each particle. Simulation results show that the EM-like algorithm can well treat the phase-only optimization of antenna arrays. Although the null-steering constraints will affect the optimization in sidelobe reduction, it can be easily included in the EM-like based optimization scheme. The EM-like algorithm can be applied not only to problems of antenna arrays, but also to many other nonlinear optimization problems in electromagnetic waves.

Study of deployed and modular active phased-array multibeam satellite antenna

A deployed, self-cooled and modular (tile-based) active phased array for multibeam applications has recently been proposed in the literature. This novel antenna facilitates the implementation of large array antennas in space with many beams from the same aperture, offering a flexible payload with the potential for high traffic capacity. However, the configuration also raises some questions about degradation in antenna performance, due to constraints such as non-circular aperture, frame gap, uniform amplitude excitation, and a calibration boom deployed in front of the array. Methods dealing with these issues are discussed in this paper. It is shown that a phase-only optimization technique can effectively reduce interference between same-frequency spatially reused beams, and can compensate for EIRP and C/I degradation for tile-correlated errors and failures.

Radiation pattern synthesis for arrays of conformal antennas mounted on arbitrarily-shaped three-dimensional platforms using genetic algorithms

A domain-decomposition/reciprocity procedure is presented which allows the radiation patterns of microstrip patch antennas mounted on arbitrarily-shaped three-dimensional perfectly electric conducting (PEC) platforms to be computed accurately as well as efficiently. The utility of this technique is demonstrated by considering an example consisting of a nine-element conformal array of microstrip patch antennas mounted axially along a finite-length PEC circular cylinder. It is shown that the elements close to the ends of the cylinder have significantly different patterns than those close to the center of the cylinder. The results from this example suggest that the common practice where all the individual element patterns are assumed identical is not always valid and, in fact, can lead to significant performance degradation in the design of conformal phased arrays. This observation is supported by the fact that an attempt to steer the main beam of the nine-element conformal array to an angle /spl theta//sub 0/=60/spl deg/ using a standard uniform progressive phase shifting technique proves unsuccessful. Next a genetic algorithm (GA) synthesis procedure is introduced that is capable of determining the optimal set of element excitation phases required to yield a desired or specified far-field radiation pattern. The results of this GA phase-only optimization are shown to yield the desired main beam steered to the correct angle for this nine-element linear array mounted on a circularly cylindrical platform. The GA radiation pattern synthesis procedure introduced appears to be a highly effective means of correcting for platform effects on the individual element patterns of a conformal phased array.

Phase-only optimization for the generation of wide deterministic nulls in the radiation pattern of phased arrays

Some analytical and experimental results of the phase-only optimization of each array element for the generation of wide deterministic nulls in the sidelobe region of the radiation pattern of a phased-array antenna are presented. The technique derives from the adaptive null-steering theory and is applied in the radar field to the spatial filtering of strong clutter echoes or jammers. A wide deterministic null has been realized in the elevation pattern of a phased-array antenna, with electronic scanning in elevation, without any hardware change; the calculated performances are compared to the measured data.