B. Galocha

Far-field performance of linear antennas determined from near-field data

The main plane far-field radiation pattern of an antenna under test from the corresponding main plane near-field data, using a circular-line acquisition, is presented. The method is based on the reconstruction of equivalent magnetic currents (EMCs) using decoupled integral equations and one-dimensional source components. The resultant fast procedure is applicable to linear and quasilinear array antennas. Experimental data results and comparison with complete spherical acquisition and center-line acquisition are presented.

Equivalent source modelling and reconstruction for antenna measurement and synthesis

In this paper we present an algorithm that from a given 2D radiation pattern (in near, Fresnel or far field region) identifies a linear distribution of equivalent magnetic current. The equivalent current distribution radiates in an unbounded medium a field that best fits (in the sense of rms error) the given radiated field. The purpose of this paper is to discuss different alternatives of modeling the equivalent currents in terms of choosing the appropriate basis functions for each application. The first application is the obtention far field patterns of antennas, with separable distribution, from measurements in the near or Fresnel field regions. If we associate the given 2D radiation pattern to the field data measured in an anechoic chamber facility and we associate the equivalent currents to the tangential fields in the plane of the antenna under test (AUT) then we can obtain the field at any distance and thus the far field radiation pattern. The second application is the synthesis of linear arrays by associating the given 2D radiation pattern to the desired far field pattern and admitting a tolerance error in terms of the typical deviation at each aspect angle. The reconstructed equivalent current distribution can be used to synthesize an antenna by means of an array of slots or conducting patches (sampling of the reconstructed current distribution).

Shaped compact dual reflector antenna for Ku-band satellite pico-terminals

Pico-terminals for digital communications satellite systems need compact reflector antennas with a high aperture efficiency but with a controlled side lobe level. Shaped reflectors with an also shaped splash-plate meet both conditions satisfactorily. Such a solution was selected for the antenna of the remote user terminal of a CDMA satellite system (PRODAT project). This paper discusses its design and features.

On the radiation of horn clusters including mutual coupling and the effects of finite metal plates: application to the synthesis of contoured beam antennas

This work describes a model of the radiation of horn clusters for contoured beam antennas. The model includes internal mutual coupling (through a power divider network), modal conversions and reflections inside the horns, external mutual coupling and the effects of the edges of the metal plate that holds the cluster together. This model is applied to the synthesis of the direct broadcast satellite (DBS) antenna of the HISPASAT satellite, the computed immersed patterns of each horn being used in the optimization of the excitations. Results are given concerning model validation and optimization with immersed patterns. >

Beam mode expansion applied to horn system with meniscus lens: new application to radioastronomy receivers

Classical radioastronomy receivers are fed by a corrugated horn and independent lens, both of them placed in a cryostat to lower noise temperature. In addition, the beam is focused and driven using several elliptical and plane mirrors. The paper proposes to modify the initial feeding system, placing the lens onto the horn aperture, allowing a size reduction of the horn and lens and a simplification of their mechanical design. This profile lens is designed to correct phase error at the horn aperture. A quasi-optical model of horn plus lens system using beam mode expansion (BME) has been developed. Results using a spherical-elliptical lens and those from optical geometry theory (GO) have been compared.

Quasioptical Approach for Meniscus Lens Corrected Horn: Application to Cassegrain Systems

The Beam Mode Expansion (BME) approach for corrugated conical feed horn plus meniscus lens is presented. This approach is useful for providing the radiation pattern as it propagates through an optical system. A developed theoretical model has been verified measuring near and far field of a built horn and lens. These results have been used for designing the optical system of a Cassegrain antenna at 100GHz using the fundamental Gaussian beam mode (GBM) of the new approach. Multimode analysis has been performed with the pre-designed system in order to test the fundamental GBM results.

Design of Horn Clusters Including Edge Effects and Mutual Coupling

Computation of immersed patterns including mutual coupling and edge effects is proposed in order to define a new step for the synthesis of multifed antennas. This procedure has been applied to the DBS and AMERICA-GOV antennas of HISPASAT satellite reaching an improvement versus synthesis with isolated patterns.

Measurement of BepiColombo mission medium gain antenna parameters under realistic thermal conditions

This paper is focused on explaining the radiation test in temperature performed on the Engineering and Qualification Model of the Medium Gain Antenna Radiofrequency (MGA-RFA) Assembly of ESA’s BepiColombo mission. The goal of this program is to observe and study Mercury and its surroundings in a very demanding environment in terms of temperature and radiation. The MGA is an X-band two-axis steerable horn, which provides bidirectional communications between spacecraft and Earth as backup of the High Gain Antenna and also operates as primary communication link at several mission stages or conditions. The paper presents the measurement set-up for the qualification campaign of the antenna, where it was necessary to characterize the antenna in a representative thermal environment, and the results obtained from this test. Results of test up to 1508C show how gain and radiation pattern shapes are slightly affected by thermal stress, but without jeopardizing mission requirements. In addition, by analyzing correlation of this test with RF analysis in the same thermal conditions, it becomes possible to accurately extrapolate the MGA-RFA behavior up to temperatures of more than 5008C. This fact allowed the successful space qualification of this model.

Focalization of new 40 m radiotelescope of Centro Astronomico de Yebes

The paper presents the solution for the focalization of the new 40 m radiotelescope of the Centro Astronomico de Yebes (CAY) in Guadalajara, Spain. Quasi-optics theory is used for the propagation analysis of the beams through the different optical elements. The goal of the paper is to design the optical system that can focalize several bands reducing to the minimum number of possible optical elements, and sharing the maximum number of them. Hyperbolic lens and ellipsoidal mirror parameters, focal distances, and the feeder dimensions necessary for the focalization in each band are calculated.

An optical solution for the radioastronomic observation bands of the new 40 m radiotelescope of Centro Astronomico de Yebes

In this paper is presented a solution for the focalisation of the new 40 m radiotelescope of the Centro Astronomico de Yebes (CAY) in Guadalajara, Spain. Quasi-optics theory is used in this paper for the propagation analysis of the beams through the different optics elements. The goal of this paper is to design the optical system that can focalize several bands reducing to the minimum number of possible optic elements, and sharing the maximum number of them. Hyperbolic lenses and ellipsoidal mirrors parameters, focal distances, and the feeder dimensions necessary for the focalization in each band are calculated.