Carlo Bencivenni

Synthesis of Maximally Sparse Arrays Using Compressive Sensing and Full-Wave Analysis for Global Earth Coverage Applications

Global optimization methods can be employed to design aperiodic array antennas that accurately account for their electromagnetic (EM) behavior and complex performance specifications. However, they are computationally expensive and, therefore, limited to small to midsized array problems. On the other hand, analytical methods do not suffer from this problem, but often assume idealized antenna elements and fully adjustable excitation controls, thereby excluding beam degradation effects caused, e.g., by mutual coupling (MC) and quantized phase shifters. We present a fast design method for large maximally sparse arrays that is capable of handling the aforementioned limitations. It is based on the previously published combined EM-Compressive Sensing approach, which has been herein generalized for multibeam optimization, and where we also exploit array symmetry in order to reduce the design complexity. Results are obtained for a circular array (100λ diameter) of horn antennas operating in a multibeam SATCOM scenario, and demonstrate that even weak MC effects and small phase quantization are important when very demanding sidelobe and cross-polarization levels are required.

Optimization of the 0.35–1.05 GHz Quad-Ridged Flared Horn and Eleven feeds for the Square Kilometer Array baseline design

Initial optimization results for the wide-band Eleven antenna and Quadruple-Ridged Flared Horn (QRFH), designed to operate as the reflector antenna feeds at 350 - 1050 MHz, are presented and discussed in the context of the next generation radio telescope - the Square Kilometer Array (SKA). First, we describe the procedure that has been developed to carry out time-efficient optimization of the feeds for multiple antenna optics configurations at the system level (so as to maximize the antenna-receiver sensitivity), and then cross-compare the two feed types by assessing the main antenna system characteristics and radio-astronomy performance metrics.

System noise performance of ultra-wideband feeds for future radio telescopes: Conical-Sinuous Antenna and Eleven Antenna

Next generation radio telescopes can greatly benefit from reflector antenna feeds that demonstrate very wide frequency bandwidth and can potentially realize low noise performance of the receivers. In this paper, we provide an overview of the current developments at the national radio observatories in Sweden and USA that make use of novel multi-port antenna feeds, such as the Sinuous Antenna and Eleven Antenna. The focus of this overview is on the system performance, when using this technology at high or very low frequencies, i.e. when the feed-receiver system is fully or partially (cryogenically) cooled.

MIMO channel capacity gains in mm-wave LOS systems with irregular sparse array antennas

This paper investigates potential advantages of linear irregular sparse antenna arrays over their regular counterparts in a mm-wave line-of-sight (LOS) multiple-input multiple-output (MIMO) scenario. The comparison is based on numerical computations of MIMO eigenvalues of the corresponding channel matrices and the resulting channel capacity. Identical linear antenna arrays are assumed at the transmitter and the receiver sides. The compared regular and irregular arrays have an equal aperture length. Mutual coupling between elements within an array is assumed negligible due to the array sparsity. A 4×4 MIMO channel is studied, where we change the position of the two inner elements to obtain irregularly spaced arrays. It is shown that for some specific distances between TX and RX, the irregular array distribution can significantly improve the channel capacity in LOS. This observation opts for reconfigurable array designs.

Effects of regular and aperiodic array layout in multi-user MIMO applications

In MIMO applications, antenna arrays adopt a uniform regular lattice. However, in phased array applications, it is a well-known fact that aperiodic or irregular arrays can offer several advantages. In this paper, we present initial investigations on the effects of regular and aperiodic layouts in Multi-User MIMO applications. We aim at explaining and providing an intuitive understanding on why aperiodic arrays are superior to regular ones. Additional results and quantification of the advantages will be presented in an upcoming journal publication.

Synthesis of circular isophoric sparse arrays by using compressive-sensing

A design approach for large-scale sparse arrays based on Compressive Sensing has been recently introduced in the literature and extended to include complex EM effects and scan performance. However, that approach cannot directly control the number of excitation amplitudes. Here, we apply a two-step procedure that first synthesizes continuous rings with unconstrained amplitudes using an iterative ℓ1-norm minimization approach, and then replaces them with a circular isophoric ring array with a number of elements proportional to the original amplitude of each ring. The procedure is demonstrated for an isotropic array of a 10λ radius, for which a reference solution based on the analytical density-taper approach is available in the literature. Results show the capability of the proposed method to achieve a significant reduction of the array aperture (20%) with 25% less elements or 4dB lower peak side lobe level.

Multi-element aperiodic array synthesis by Compressive Sensing

In recent years, Compressive Sensing has attracted considerable attention in various areas of antennas and electromagnetics, including the synthesis of sparse array antennas. The CS synthesis of arrays achieves higher accuracy than analytical methods and allows for the fast and deterministic design of large complex arrays, without resorting to computationally expensive Global Optimization methods. The CS approach presented here has been previously studied by the authors for the design of maximally sparse arrays in the presence of mutual coupling effects, beam scanning degradation, as well as the imposition of symmetries for design modularity. In this manuscript the authors demonstrate another (yet unexplored) capability of such an approach, i.e., to incorporate different element types and determine their optimum combination in the course of the array synthesis procedure. Numerical examples are illustrated for large arrays comprising uniform circular aperture elements and operating in a SATCOM multi-beam scenario. It is shown that by exploiting this capability it is possible to simultaneously reduce the number of elements and gain scan loss.

Aperiodic isophoric slotted waveguide antenna for point-to-point communications at Ka-band

We report the intermediate results on a novel slotted waveguide antenna for point-to-point communications at Ka band. The antenna adopts an aperiodic layout with uniformly-excited elements capable of meeting the ETSI class II radiation pattern envelop in all planes with high aperture efficiency. A total of 16 regular waveguide subarrays with an aperiodic inter-column spacing along the E-plane are fed by a corporate feed network located underneath. The prototype was milled in three layers of aluminum and bonded by vacuum brazing. Measurements confirm a 15% impedance bandwidth. The simulated patterns satisfy the radiation pattern envelop and have a gain above 28.5 dBi over 29–31 GHz, corresponding to an efficiency better than 80%.

Point-to-point 3 × 3 MIMO performance gains with aperiodic sparse arrays in pure LOS channels

Analyzed is the topology of a 3-element linear array antenna with vertically polarized isotropic antenna elements. The focus has been on point-to-point (PtP) multiple-input multiple-output (MIMO) communication over pure line-of-sight (LOS) channels. An empirical equation is presented for the mid-elements relative position achieving near-optimal 3 × 3 MIMO capacity. The position is a function of the transmit and the receive antennas separation distance and the wavelength of the transmit signal. The capacity gains of aperiodic over uniform array antenna configurations are presented, which at some distances can be a factor 2.5.