F. Venneri

Design and Validation of a Reconfigurable Single Varactor-Tuned Reflectarray

An aperture-coupled reflectarray element giving a full phase tuning range with a single varactor diode is proposed in this paper for pattern reconfigurability applications. The full phase agility is achieved by a proper optimization of the phase tuning line, thus providing an alternate inductive/capacitive effect able to avoid the use of two varactor diodes, usually adopted in similar existing configurations. The proposed active element structure is adopted to design a demonstrative reflectarray prototype of 3 × 15 radiators. Furthermore, an own synthesis procedure is applied to obtain the proper biasing voltages giving the prescribed H-plane field. Test examples of beam-scanning, multibeam, and shaped-beam patterns are discussed to demonstrate the effectiveness of the approach.

Aperture-Coupled Reflectarrays with Enhanced Bandwidth Features

An extensive analysis is performed on the aperture-coupled reflectarray configuration to highlight and quantify the bandwidth enhancement due to the use of reduced inter-element spacings. Bandwidth extension is directly evaluated on the phase curves relative to the reflection coefficient against frequency for different lengths of the tuning line. The operating frequency range computed with the proposed approach is numerically validated on the gain patterns of synthesized reflectarrays and a strong broadband behavior is demonstrated for reflectarrays of moderate aperture dimensions and reduced unit cell size.

Application of varactor diodes for reflectarray phase control

A new approach for beam steering in reflectarray applications is introduced in this paper. The progressive phase distribution is achieved by loading each microstrip patch element with a varactor diode on the radiating edge. In the following, the scattering characteristics of a single varactor loaded patch antenna will be presented. As a proof of concept, the beam steering capability of a five elements linear reflectarray has been experimentally investigated.

An improved synthesis algorithm for reflectarrays design

An improved synthesis procedure is presented in this letter for the design of microstrip reflectarray antennas. The iterative projection based algorithm is modified to include the effect of different incidence angles on the reflectarray elements in the evaluation of the design curve. Experimental results on an X-band prototype of unequal microstrip patch elements are reported.

Experimental investigation of a varactor loaded reflectarray antenna

A new approach for beam steering in reflectarray applications is introduced in this paper. The progressive phase distribution is achieved by loading each microstrip patch element with a varactor diode on the radiating edge. In the following, the scattering characteristics of a single varactor loaded patch antenna will be presented. As a proof of concept, the beam steering capability of a five elements linear reflectarray has been experimentally investigated.

Tunable reflectarray cell for wide angle beam-steering radar applications

An electronically tunable reflectarray element is proposed in this work to design beam-steering antennas useful for radar applications. A reduced size reflectarray unit cell is properly synthesized in order to extend the antenna beam scanning capabilities within a wider angular region. The radiating structure is accurately optimized to provide a full phase tuning range by adopting a single varactor load as phase shifter element. A 0.46λ-reflectarray cell is designed at the frequency of 11.5GHz, obtaining a phase agility of about 330°. The cell is successfully adopted for the design of a 21 × 21 reconfigurable reflectarray. The antenna is numerically tested for different configurations of the varactors capacitance values, and good beam-steering performances are demonstrated with in a wide angular range.

An experimental approach to active and passive reflectarray design

At variance of the numerical techniques conventionally used to analyse and design microstrip reflectarrays, in this paper a fully experimental approach is proposed. The overall procedure relies on the possibility to estimate the reflection phase of the single reflectarray cell by measuring the scattering characteristics of a small set of identical elements. This method, valid only when the mutual coupling can be ignored, has been successfully applied to both active and passive experimentally retrieved. In a second assessment, the phase curve of a varactor loaded microstrip antenna has been characterised. To prove the effectiveness of the proposed technique the experimentally generated data have been used to design two small reflectarrays. The measured radiation patterns are presented and discussed.

Design of a Reconfigurable Reflectarray Unit Cell for Wide Angle Beam-Steering Radar Applications

A reconfigurable aperture-coupled reflectarray element is proposed for the realization of beam steering antennas, suitable for radar applications. Each reflectarray element is coupled to a microstrip line, which is loaded by a single varactor diode acting as a phase shifter element, thus providing a continuously variable reflection phase. A reduced size reflectarray unit cell is properly designed in order to extend the antenna beam scanning capabilities within a wide angular region, but avoiding the occurrence of undesired grating lobes. The radiating structure is properly optimized to obtain a full phase tuning range at the frequency of 11.5 GHz, thus assuring a good agility and accuracy in the reconfiguration of the reflectarray radiation pattern.

Wideband aperture-coupled reflectarrays with reduced inter-element spacing

The bandwidth features of aperture-coupled reflectarrays are analyzed by varying the spacing between adjacent elements in the array grid. A bandwidth enlargement is obtained by reducing the reflectarray unit cell size. The wideband behavior is demonstrated through the comparison of phase curves as a function of the operating frequency for various lengths of the tuning stub. As further validation, the gain against frequency is calculated to compare bandwidth features of two 20 GHz reflectarray prototypes with different cell size.

Fractal Reflectarray Antennas: State of Art and New Opportunities

Fractal geometries are appealing in all applications where miniaturization capabilities are required, ranging from antennas to frequency selective surfaces (FSS) design. Recently, some fractal patches configurations, giving low losses, reduced size, and quite good phase ranges, have been proposed for the design of reflectarray unit cells. This paper reviews existing fractal-based reflectarrays, highlighting their benefits and limitations. Furthermore, a comprehensive analysis of an innovative reflectarray unit cell, using a fractal-shaped fixed-size patch, is presented. The miniaturization capabilities of the Minkowski fractal shape are fully exploited to obtain a compact cell offering quite good phase agility, by leaving unchanged the patch size and acting only on the fractal scaling factor. Experimental validations are fully discussed on a realized 10 GHz cell. This is subsequently adopted to synthesize various reflectarray prototypes offering single or multiple-beam capabilities over a quite large angular region (up to 50 degrees). Finally, experimental validations on a realized elements prototype are presented to demonstrate the wide angle beam-pointing capabilities as well as a quite large bandwidth of about 6%.