Multibeam Applications Research Articles

EBG Focal Feed Improvements for Ka-Band Multibeam Space Applications

This letter presents the enhancement of an electromagnetic band-gap (EBG) antenna that is used to feed a reflector antenna for a space multibeam application in Ka band. One of the main difficulties in a typical focal feed cluster design is to obtain high illumination performances with neighbored and close radiating elements. The new structure presented in this letter tackles this difficulty by using a two-level EBG antenna as a multibeam focal feed. This last one is designed to illuminate a side-fed offset cassegrain antenna (SFOCA) working in Ka band and dedicated to a multibeam telecommunication coverage over Europe. A prototype has been measured, and the reflector antenna performances have been evaluated in order to show the good results obtained with this new multibeam focal feed.

Enhanced EBG Resonator Antenna as Feed of a Reflector Antenna in the Ka Band

Recent studies have shown that a multibeam reflector antenna could be illuminated by a multifeed electromagnetic bandgap (EBG) structure, in order to achieve a high gain multispot coverage with the simple feed by beam concept and only one aperture. This letter deals with the design of a metallic EBG antenna in the Ka band, feeding a side-fed offset cassegrain antenna (SFOCA) for a European multispot coverage. This reflector presents a high focal-length-to-diameter ratio limiting the defocusing effects for multibeam applications. It, therefore, requires focal feeds with a high directivity and a good radiation pattern quality. The well-known drawbacks of an EBG antenna are the narrow radiation bandwidth for high directivities and also the high sidelobes level reducing the reflector antenna efficiency. Consequently, the work presented in this letter consisted in improving the EBG antenna performances by using a more efficient feed. The replacement of the usual microstrip patch by a horn allowed to double the radiation bandwidth while decreasing the sidelobes level (-15 dB) of a 24-dB EBG antenna. A metallic prototype excited by a single horn has been manufactured at 30 GHz, and the measurements agree with the simulation. This device with one feed allows good SFOCA performances, similar to those obtained with a conventional focal feed like a Potter horn.

Designing Schwarzschild dual-reflector systems

The purpose of this paper is to provide readers an easy set of equations and design parameters to generate Schwarzschild dual-reflector systems. We consider the geometry of a Schwarzschild dual-reflector system, consisting of two rotationally symmetric reflectors, which form an aplanatic system that fulfills the Abbe sine condition. This dual-reflector system ensures freedom from spherical and primary coma aberrations when the feed horn is displaced from the axis of symmetry. This is a useful property for beam-scanning or multibeam applications

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.

Precise Incident Power Density Pattern Measurement through Antenna Pattern Deconvolution

Future cellular and fixed wireless loops (FWL) systems employing highly directive base stations antennas (5 to 8 degrees beamwidth) and moderately directive subscribers' antennas (15 to 25 degrees beamwidth) offer very large capacity due to reduced interference. An important property of the environment of such systems is the interference caused by scattering of the signal from a subscriber transmitter into directions other than the direct line of sight between the subscriber and the base station. In particular, for multibeam base station applications scattering could arrive at the base station in the direction being used by a different beam, resulting in interference that is difficult to reduce by normal nulling techniques. Thus interference can be highly dependent on the incident power density pattern (IPDP) caused by scattering of the signal radiated from the subscriber. We discuss herein the use of a uniformly illuminated array accompanied by electric field deconvolution to measure the crucial IPDP with the same performance as a low sidelobe array of the same size. The mathematical correction technique uses deconvolution of the measured complex electric field pattern with that of the antenna in free space by means of the Fourier Series and limiting the range of Fourier coefficients to those that are not negligible in the free space pattern. Application of the technique to an experimental uniform array with a 2.5 degree azimuthal beamwidth shows the practicality of the deconvolution with real antennas in real environments. The improved resolution and accuracy provided by Taylor weighting versus unweighted deconvolution when trying to measure weak scattered components in the presence of a nearby strong specular component is demonstrated. The IPDP was measured from many sites surrounding a suburban base station. A plot of the cumulative distribution of the ratio of the widely scattered power to that within a prescribed beamwidth summarizes the result of using the deconvolution technique on this experimental data.

Prototype negative electron affinity-based multibeam electron gun for lithography and microscopy

Negative electron affinity (NEA) photocathodes offer unprecedented capabilities as electron sources that promise to enable a new generation of microscopy and lithography instruments. Extremely low-energy spread and emission noise, high brightness, ultrafast blankerless switching, changeable emission area, and uniform multibeam emission are some of the advantages that this source offers. Their unique advantages in high-throughput multibeam applications have been discussed elsewhere. The main barrier to their widespread acceptance has been concern about lifetime and stability. A prototype electron gun based on NEA photocathodes has been constructed to demonstrate the performance, including stability, of NEA sources. Initial results, showing over 100 h of excellent stability from a single 2 μm emission area, show the paramount importance of in situ recesiation in attaining long cathode lifetime.

Nonlinear grating interactions in multibeam photorefractive recording: theoretical investigation

The nonlinear interactions between gratings generated during multibeam photorefractive recording with one reference and N object beams have been investigated theoretically. It is shown that nonlinear cross talk between gratings, which is well known in three-beam recording, persists and even increases for the practical relevant case in which the number of object beams N is large. The magnitude of the cross talk depends on the particular grating, and it is significant for a range of intensities commonly used in many multibeam applications. Finally, it is shown that for large N(N>5) the nonlinear interactions strongly suppress most gratings, whereas specific gratings can be selectively amplified.

Angle-etched facet laser arrays (fan laser arrays)

We present a novel individually addressable diode laser array that uses angle-etched facets. By arranging the lasers in a fan-like structure, all lasers emit in different directions from a common effective aperture. Using this device design, we demonstrate lasers with beam directions that are fixed and distinct, stable, single mode, and capable of simultaneous and random access operation. We analyze both the effect of facet roughness on the performance of etched-facet diode lasers, as well as the thermal crosstalk characteristics of angle-etched facet lasers. Thermal crosstalk characteristics of angle-etched facet lasers are experimentally compared to parallel stripe lasers. The combination of the aperture and thermal crosstalk reduction allows us to reduce the effective thermal coupling between array elements by over one order of magnitude. We show a novel two-dimensional scanner built with a fan laser array: results demonstrate the feasibility of these novel arrays for multibeam applications.

Space Laser Altimetry: Laser Engineering for Multi-Beam Applications.

The relatively new technique of laser altimetry, the measurement of Earth surface elevation by timing the propagation interval and digitizing the echo of short laser pulses, is in transition from an airborne remote sensing activity to space-based measurements of global topography. Space-based laser altimeters not only measure distance to the Earth's surface along the nadir track of a host spacecraft, but conduct a surface lidar investigation to reveal the complex shapes of land surface and its vegetation cover. Multi-beam concepts extend the coverage and accuracy of space applications of laser altimetry.

Matrix amplifiers for communication satellite applications

Matrix amplifiers architectures are capable of providing channel-to-beam allocation flexibility for the next generation of multibeam satellite applications. The paper considers the implementation aspects of such amplifiers. Network configurations which make the architecture possible are presented as well as measured results. Solid state power amplifier characteristics for satisfactory operation of matrix amplifires are considered and measured results on a unit are presented.

A coma-corrected multibeam shaped lens antenna, part II: Experiments

A dielectric lens based on the shaping technique described in Part I of this communication was fabricated and tested. This lens was shaped to control the sidelobes and zoned for improved scanning characteristics. Basic antenna measurements were conducted and excellent performance results have been observed. In the prototype lens system with unmatched surfaces, a 4 dB crossover between adjacent beams of -30 dB sidelobes was obtained. The beam was scanned up to \pm 12\deg without significant coma degradations. This coma-corrected zoned lens was developed for satellite multibeam applications. The multibeam antenna so designed not only reduces the total costs and the payload burden, but also enhances the system reliability and the overall gain compared to a conventional design because no complex feed network is required.

Antenna with multibeam applications

The design of a dual-reflector antenna that focuses an inclined incident plane wave to a point away from the axis of symmetry of the reflector is discussed. A useful application of such a system would be as a multibeam antenna for use in communication via satellites. Curves of path-length errors are presented for the feed positioned on the axis of symmetry, and the effects of refocusing are shown.