Reflector Antenna Patterns Research Articles

ATMS Radiance Data Products’ Calibration and Evaluation

The Advanced Technology Microwave Sounder (ATMS) is a passive microwave radiometer for the current generation of polar-orbiting meteorological satellites operated by the National Oceanic and Atmospheric Administration (NOAA). The first two ATMS instruments are manifested onboard the Suomi National Polar-orbiting Partnership (S-NPP) and NOAA-20 satellites. Several critical changes have been made to ATMS operational calibration algorithm since March 2017. The calibration processing has been revised from a Rayleigh–Jeans approximated algorithm to a full radiance algorithm in order to reduce the error introduced by the approximation over cold radiances in the higher frequency channels. In addition, based on the lessons learned from S-NPP and NOAA-20 postlaunch calibration/validation tests, some major improvements have been made in the updated operational algorithm. These include reflector emission and antenna pattern corrections. Details of the radiance-based ATMS on-orbit calibration are documented in this report, and results of prelaunch calibration error budget analysis and postlaunch calibration accuracy evaluation are also presented for reference.

Frequency-dependent radiation properties of negative permittivity metamaterial reflector antenna

This paper reports a novel type of microwave reflector antenna that uses the frequency-dependent properties of an epsilon negative (ENG) metamaterial medium. The frequency-dependent characteristics of this artificial plasma medium is analyzed using the dispersive auxiliary differential equation finite difference time domain (ADE-FDTD) method by employing a Gaussian pulse and the results are verified experimentally using an artificial plasma medium fabricated by an array of thin conducting wires. The radiation pattern of plain and corner plasma reflector antennas modeled using Drude equations are obtained and are compared with a plasma reflector and conventional metallic reflector antennas. The results obtained for the plasma reflector antenna is experimentally verified using a 90° corner reflector antenna fabricated using wire medium. This new class of plasma antennas show marked variations in radiation pattern for frequencies above and below plasma frequency, which may find potential use in various frequency selective applications.

Electromechanical Coupling Analysis of Shaped Reflector Antenna Based on Standard Discrete Parabola Set

The mechanical-electromagnetic-field-coupling-model (MEFCM) is widely used in analysing the effect of structural deformation on radiation pattern of reflector antennas. Due to lack a closed-form optical path difference expression for shaped reflector antennas, the MEFCM cannot be directly applied. For this shortcoming, in order to apply the coupling model into shaped dual-reflector antennas, we proposed a new shaped surface description approach based on standard discrete parabola set. By employing this approach, the MEFCM can be applied to analyse the radiation pattern of shaped dual-reflector antenna with different types of structural deformation. Application on a 25 m shaped Cassegrain antenna shows the effectiveness of the proposed approach for the pattern analysis of shaped dual-reflector antennas.

Second-Order Expansion Computation of Average Power Pattern of Cylindrical Reflector Antennas With Random Surface Errors

To consider the effects of random surface errors on the radiation pattern of cylindrical reflector antennas, a second-order expansion computation method is proposed to calculate the boresight gain loss and average power pattern. The additional phase error caused by random surface distortion is expanded into a second-order Taylor series expansion in radiation integral. Based on the probabilistic Gaussian distribution of phase errors, the boresight gain loss and average power pattern can be simplified into a second-order expression of a root-mean-square (rms) value of random surface errors. Simulation results on a Ku/Ka-bands parabolic cylindrical reflector illustrate that the second-order expansion can account for the boresight gain loss within a computational accuracy of 0.1 dB when the rms value of random surface errors is below $\lambda /22$ for the Ku-band, as well as $\lambda /24$ for the Ka-band. When the rms value of random surface errors is below $\lambda /50$ for the Ku-band, or $\lambda /100$ for the Ka-band, the second-order expansion can also account for the first sidelobe in an average power pattern.

The Beam Pattern of Reflector Antennas With Buckled Panels

On high precision reflector telescopes the transient thermal panel buckling can have an effective rms-value comparable to the errors in the adjustment of the reflector panels. Under this condition, high signal-to-noise radio holography of high spatial resolution can reveal the characteristic signature of panel buckling in the beam pattern and can map the surface deformation of the buckling, while lower signal-to-noise Moon limb scans may see the buckling only under favorable conditions. Detailed diffraction calculations, and some observations, indicate (1) that the panel buckling produces diffraction rings and/or diffraction spokes, (2) that panel buckling in azimuthal direction may have a smaller degrading effect than panel buckling in radial direction because for azimuthal buckling the energy is spread more uniformly over a large solid angle, and (3) that the coverage of the reflector aperture with buckled panels determines the multiplicity of the diffraction rings and/or diffraction spokes.

Performance analysis of spaceborne SAR systems

This paper describes a software tool for performance analysis and parameter prediction for conventional and special SAR modes. Several aspects of design, performance analysis and parameter optimization for Spotlight and interferometric SAR systems are examined. After the description of relevant principles the synthesis of antenna dimensions and efficient modeling of parabolic reflector antenna patterns are demonstrated. The influences of range migration and yaw steering on the PRF selection are shown along with a design example. The tool presented here was used on the Shuttle Radar Topography Mission (SRTM) flown on the Shuttler Endeavour for the X-SAR performance prediction in the preparation phase and was also used in near realtime during the mission.

Uniform asymptotic solution for electromagnetic reflection and diffraction of an arbitrary Gaussian beam by a smooth surface with an edge

A closed form solution is obtained to describe, in a physically appealing manner, the reflection and diffraction of a general astigmatic Gaussian beam which is incident on an arbitrary smooth, electrically large, slowly varying curved, perfectly conducting screen (or reflector). This closed form solution is obtained via an asymptotic evaluation of the radiation integral for the fields scattered from the reflector, to within the physical optics approximation that remains valid for the present situation. The analysis developed here is particularly well suited for the fast analysis of electrically large reflector antennas by representing the feed illumination by a relatively small set of Gaussian beams launched from the feed plane. Each of these Gaussian beams after being launched undergoes reflection and diffraction at the reflector; the expressions for the reflected and diffracted fields are developed in this paper and utilized by Chou [1996] to compute the radiation pattern of large reflector antennas in a matter of a few seconds as compared to the conventional numerical physical optics integral method which takes hours on the same computer.

Equivalent edge current technique for reflector antenna patterns in the boresight caustic region

AbstractIt is shown that the equivalent edge currents (EEC) obtained in terms of the uniform geometrical theory of diffraction coefficients (EEC‐UTD) yield accurate values of the radiated far field in the boresight caustic region of a paraboloid. Failure of the equivalent edge current technique to provide the correct values for boresight region fields in a previous article is attributed to the reflector edge representation in that article. Radiation patterns computed by the EEC‐UTD method are found to blend well with the pattern obtained by the UTD technique. © 1995 John Wiley & Sons. Inc.

Average Pattern and Beam Efficiency Characterization of Reflector Antennas with Random Surface Errors

Random errors on a reflector surface will result in antenna gain loss, beam efficiency reduction, and sidelobe level degradation. In this study, an improved mathematical model is presented for handling correlated random surface errors. The average power patterns of arbitrarily distorted antennas are determined by performing a complete numerical integration. Furthermore, in the case of a parabolic reflector antenna with random surface errors that have relatively short correlation length, the effective aperture distribution parameters, Be and pe, can be defined and analytically derived. Numerical data for a parabolic reflector antenna with dimensions recommended by a recent NASA study are generated to investigate the effects of uniform and linear random surface errors on power pattern, boresight gain loss, and beam efficiency. The results properly characterize the pattern degradation and the beam efficiency reduction as a function of random surface errors. For high beam efficiency and low sidelobe specifica...

A versatile reflector antenna pattern computation method: Shooting and bouncing rays

AbstractBased on shooting and bouncing geometrical optics rays, this paper describes an aperture integration method for computing the secondary pattern of reflector antennas. The method is versatile and flexible. Within the geometricdl optics accuracy, there is virtually no restriction on the number of reflectors, the coating material, radome, or the feed configurations. Pattern computations are shown for an antenna with six reflectors, coated with dielectric material and covered by a spherical radome.

Synthesis of shaped-beam reflector antenna patterns

The paper describes the synthesis of shaped-beam dual-reflector antenna patterns using two methods. In the first, for a prescribed far field the antenna aperture field is obtained initially and then a Geometric Optics synthesis method used to define the reflector coordinates. In the second method an optimisation procedure is employed to shape the reflectors directly, so as to generate, through Physical Optics, the desired far field. The two methods are compared for the pattern corresponding to the EUTELSAT 2 spacecraft. Close agreement is found and differences ascribed to initial constraints.

Radiation pattern analysis of reflector antennas

AbstractA method is proposed for accurately calculating the radiation pattern of reflector antennas in the entire angular range from the main beam direction to the off axis region. The principle of the method is similar to the physical optics diffraction theory, and consists of the result obtained by conventional physical optics corrected with the contribution from the edge current calculated by the geometrical theory of diffraction. However, the edge current is expressed in a simple form by means of a local coordinate system defined by the peripheral line and the mirror normal at each edge point and of the incident electromagnetic vector components in reference to this coordinate system. Therefore, it is possible to treat an arbitrarily shaped mirror surface and an antenna with a primary radiator using an arbitrary pattern. It is confirmed that the results obtained by the present method approach those obtained by the physical optics method near the main beam and those obtained by the geometrical theory of diffraction at the off axis. Accuracy is tested by applying the present method to the problem of diffraction from a circular disk for which a rigorous solution exists. The present method makes unnecessary the distinction of the use of physical optics (main beam) and the geometrical theory of diffraction (off axis) performed so far, in an empirical manner. It is possible systematically to obtain the pattern near the first‐third side lobes where two methods may be connected.

Secondary pattern and focal region distribution of reflector antennas under wide-angle scanning

A new numerical method, Fourier-Bessel series techniques, has been developed to investigate the far-field pattern and focal region distribution of reflector antennas under wide-angle scanning. In this Fourier-Bessel series technique, the current on the reflector surface is first expanded in terms of elementary sinusoidal functions via the well established fast Fourier transform (FFT) algorithm and the surface integration involved in physical optics integration is then carried out analytically. The derivation of Fourier-Bessel series and its convergence as applied to parabolic reflectors are described. The secondary patterns and focal region distributions of a parabolic reflector with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F/D = 0.48</tex> and scanning up to 48 beamwidths are presented.

A transform technique for computing the radiation pattern of prime-focal and Cassegrainian reflector antennas

An efficient numerical method based on the use of the fast Fourier transform (FFT) algorithm is developed for computing radiation patterns of aperture antennas with given aperture distributions. The method is also readily applicable to the problem of computing the radiation pattern of paraboloidal reflector antennas when the induced surface currents on the surface of the reflector are known. Using an efficient launching and scanning scheme for subreflector analysis, the method is extended to a Cassegrainian reflector antenna system.

Reviews and abstracts - A transform technique for computing the radiation pattern of prime-focal and cassegrainian reflector antennas

Reviews and abstracts - A transform technique for computing the radiation pattern of prime-focal and cassegrainian reflector antennas