Analysis, Design and Applications of Reflectarrays

A brief overview of reflectarray antennas mainly focused on some efficient analysis and design techniques and on recent developments has been presented. A technique based on the local periodicity and Method of Moments in Spectral Domain has been presented as very efficient for the analysis of reflectarray antennas. The technique has been validated by comparing simulations and measurements in several breadboards. Based on the previous analysis technique, several design procedures have been implemented for different antenna performances, including requirements of broad-band, dualfrequency and stringent contoured beams. Finally some recent developments for applications in space and LMDS antennas are presented

Diseño construcción y medida de un reflectarray para antena terminal en banda KA

This contribution describes the design, manufacturing and test of a printed reflectarray for a Ka-band terminal antenna. The reflectarray has been designed to produce a focused beam at 30 GHz (uplink) in V polarisation and also at 20 GHz (downlink) in H polarisation. Two separate feeds are used to illuminate the reflectarray for H (20 GHz) and V polarisation (30GHz). The reflectarray element is made of two stacked varying-sized patches, being one dimension adjusted to focus the beam at 20 GHz in H polarization, and the other to focus the 30 GHz beam in V-polarization. A breadboard has been manufactured and tested. The measured radiation patterns show very good agreement with those obtained from the simulations. A 10% bandwidth has been obtained in both frequency bands, with an antenna efficiency of 62% at 30 GHz and 70% at 20 GHz

Reflectarray for K/Ka Band Terminal Antenna

Different satellite systems have been defined to provide broadband communications and internet access in remote geographical areas in Ka band (20-30 GHz) [1-2], being the up-link at 30 GHz and the down-link at 20 GHz. Costeffective antennas are required for fixed and portable terminals in Ka-band. Conventional reflectors are a preferred option to maintain reduced costs. However, the different receive (Rx) and transmit (Tx) frequencies obliges to use either a dual-frequency horn or two independent horns. The dual-frequency horn presents some difficulties, mainly because the phase-centre is different at each frequency, which would cause a reduction of the antenna gain. The use of independent feeds for Tx and Rx is simpler, but this solution is not possible using reflector antennas, because the two horns located at different positions cannot generate a beam in the same direction

Bandwidth Improvement in Large Reflectarrays by Using True-Time Delay

A significant improvement in the bandwidth of large reflectarrays is demonstrated using elements which allow true-time delay. Two identical, large reflectarrays have been designed using different phase distributions to generate a collimated beam. In the former, the phase distribution is truncated to 360deg as is usual in reflectarray antennas, while in the second, the true phase delay is maintained (three cycles of 360deg). The chosen phase-shifter elements are based on previously measured and validated patches aperture-coupled to delay lines. The radiation patterns for both reflectarrays have been computed at several frequencies and the gain is represented as a function of frequency for both cases. Bandwidth curves are presented as a function of the reflectarray size

Multifed Printed Reflectarray With Three Simultaneous Shaped Beams for LMDS Central Station Antenna

A two-layer reflectarray is proposed as a central station antenna for a local multipoint distribution system (LMDS) in the 24.5-26.5 GHz band. The antenna produces three independent beams in an alternate linear polarization that are shaped both in azimuth (sectored) and in elevation (squared cosecant). The design process is divided into several stages. First, the positions of the three feeds are established as well as the antenna geometry to produce the three beams in the required directions. Second, the phase distribution on the reflectarray surface, which produces the required beam shaping, is synthesized. Third, the sizes of the printed stacked patches are adjusted so that the phase-shift introduced by them matches the synthesized phase distribution. Finally, the radiation patterns are computed for the central and lateral beams, showing a shaping close to the requirements. A breadboard has been manufactured and measured in an anechoic chamber, showing a good behavior, which validates the designing methodology

Analysis of dual-reflector antennas with a reflectarray as subreflector

In this paper, a modular technique is described for the analysis of dual-reflector antennas using a reflectarray as a subreflector. An antenna configuration based on a sub-reflectarray and a parabolic main reflector provides better bandwidth than a single reflectarray, and has a number of advantages compared with a conventional dual-reflector antenna. Examples include the possibility of beam shaping by adjusting the phase on the sub-reflectarray, and potential capabilities to scan or reconfigure the beam. The modular technique implemented for the antenna analysis combines different methods for the analysis of each part of the antenna. First, the real field generated by the horn is considered as the incident field on each reflectarray element. Second, the reflectarray is analyzed with the same technique as for a single reflectarray, i.e., considering local periodicity and the real angle of incidence of the wave coming from the feed for each periodic cell. Third, the main reflector is analyzed using the Physical Optics (PO) technique, where the current on the reflector surface is calculated by summing the radiation from all the reflectarray elements. Finally, the field is calculated on a rectangular periodic mesh at a projected aperture, and then a time-efficient fast Fourier transform (FFT) algorithm is used to compute the radiation pattern of the antenna. The last step significantly improves the computational efficiency. However, it introduces a phase error, which reduces the accuracy of the radiation patterns for radiation angles far away from the antenna's axis. The phase errors have been evaluated for two integration apertures. It has been demonstrated that accurate patterns are obtained in an angular range of plusmn6deg, which is sufficient for large reflectors. The method of analysis has been validated by comparing the results with simulations obtained from GRASP8. Finally, the theoretical beam-scanning performance of the antenna is analyzed

A X-Band Planar Transmit-Array

Planar arrays are a very interesting option to substitute reflector antennas because of their well-known characteristics of low profile, potential low cost, reliability and flexibility in achieving contoured beams and multiple beams with a simple planar geometry. Suitable solutions using planar antennas for space applications have been proposed using reflect-arrays with countered beams and multibeam. Another proposed solution consists of transmit arrays. In this case, the antenna acts as a lens [1]. This consists of a periodic planar array having two patch antennas connected by a line. One element receives the signal from –z direction and the other transmits the signal in the +z direction. By a proper selection of the phase delay in the connection line, the phase distribution in the transmitting array can be adjusted. In an equal output phase configuration the transmitting array behaviour would be similar to the obtained with a parabolic reflector, having the advantage of removing the feed blockage

Demonstration of a Shaped Beam Reflectarray Using Aperture-Coupled Delay Lines for LMDS Central Station Antenna

A shaped-beam reflectarray based on patches, aperture-coupled to delay lines is demonstrated for local multipoint distribution system (LMDS) central station antennas, in the 10.10-10.70 GHz band. The antenna must cover a 60deg-sector in azimuth with a squared cosecant pattern in elevation. The design process consists of two steps. First, a phase-only pattern synthesis technique is applied to obtain the required phase-shift distribution on the reflectarray surface which generates the shaped pattern. The second stage consists of determining the length of the delay lines, aperture-coupled to the square patches, in order to achieve the phase distribution synthesized in the previous step. Two reflectarray antennas have been designed, one for vertical (V) and the other for horizontal (H) polarization. A breadboard for V-polarization has been manufactured and tested in an anechoic chamber, showing a good agreement between theoretical and measured radiation patterns

Reflectarray para Estación Base LMDS Basado en Parches Acoplados por Apertura

A shaped-beam reflectarray based on aperturecoupled elements is demonstrated as central station antenna for Local Multipoint Distribution System (LMDS) in the 10.10- 10.70 GHz band. The antenna must cover a 60° sector in azimuth with a squared cosecant pattern in elevation. The design process consists of two steps. First, a phase-only pattern synthesis technique is applied to obtain the required phase-shift distribution on the reflectarray surface which generates the shaped pattern. The second stage consists of determining the length of the delay lines, aperture-coupled to the squared patches, in order to achieve the phase distribution synthesized in the previous step. A reflectarray antenna has been designed for vertical (V) polarization. A breadboard has been manufactured and tested in an anechoic chamber, showing a good agreement between theoretical and measured radiation patterns

Dual-polarization transmit-receive reflectarray antenna made of cells with two orthogonal sets of coplanar parallel dipoles

A dual-polarization dual frequency focused beam reflectarray antenna is designed for transmit-receive (Tx-Rx) operation in Ku Band. A novel broadband reflectarray element is introduced, which consists of two orthogonal sets of three parallel dipoles. To adjust the dimensions of the elements in the antenna, we have used the local periodicity assumption, and we have analyzed a multilayered periodic structure surrounding each element by means of a home-made software based on the method of moments in the spectral domain. This strategy makes it possible to design reflectarray antennas within reasonable CPU times. The designed antenna shows a bandwidth of 10.9% in Tx-band and 7.1% in Rx-band for gain variations lower than 1 dB. Also, levels of cross-polar components 30 dB below the radiation maximum have been achieved. In order to improve the crosspolar discrimination, the elements of the designed reflectarray have been slightly rotated, and this has made it possible to achieve levels of cross-polar components 35 dB below the maximum in both the Tx and the Rx band