J. Ruze

Bio: J. Ruze is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Antenna aperture & Radiation pattern. The author has an hindex of 1, co-authored 1 publications receiving 648 citations.

Antenna tolerance theory—A review

Abstract: The theoretical basis of antenna tolerance theory is reviewed. Formulas are presented for the axial loss of gain and the pattern degradation as a function of the reflector surface rms error and the surface spatial correlation. Methods of determining these quantities by astronomical or ground-based electrical measurements are described. Correlation between the theoretical predictions and the performance of actual large antenna structures is presented.

Planck 2013 results. VII. HFI time response and beams

Abstract: This paper characterizes the effective beams, the effective beam window functions and the associated errors for the Planck High Frequency Instrument (HFI) detectors. The effective beam is the angular response including the effect of the optics, detectors, data processing and the scan strategy. The window function is the representation of this beam in the harmonic domain which is required to recover an unbiased measurement of the cosmic microwave background angular power spectrum. The HFI is a scanning instrument and its effective beams are the convolution of: a) the optical response of the telescope and feeds; b) the processing of the time-ordered data and deconvolution of the bolometric and electronic transfer function; and c) the merging of several surveys to produce maps. The time response transfer functions are measured using observations of Jupiter and Saturn and by minimizing survey difference residuals. The scanning beam is the post-deconvolution angular response of the instrument, and is characterized with observations of Mars. The main beam solid angles are determined to better than 0.5% at each HFI frequency band. Observations of Jupiter and Saturn limit near sidelobes (within 5 degrees) to about 0.1% of the total solid angle. Time response residuals remain as long tails in the scanning beams, but contribute less than 0.1% of the total solid angle. The bias and uncertainty in the beam products are estimated using ensembles of simulated planet observations that include the impact of instrumental noise and known systematic effects. The correlation structure of these ensembles is well-described by five errors eigenmodes that are sub-dominant to sample variance and instrumental noise in the harmonic domain. A suite of consistency tests provide confidence that the error model represents a sufficient description of the data. The total error in the effective beam window functions is below 1% at 100 GHz up to multiple l similar to 1500, below 0.5% at 143 and 217 GHz up to l similar to 2000.

An overview of near-field antenna measurements

Abstract: After a brief history of near-field antenna measurements with and without probe correction, the theory of near-field antenna measurements is outlined beginning with ideal probes scanning on arbitrary surfaces and ending with arbitrary probes scanning on planar, cylindrical, and spherical surfaces. Probe correction is introduced for all three measurement geometries as a slight modification to the ideal probe expressions. Sampling theorems are applied to determine the required data-point spacing, and efficient computational methods along with their computer run times are discussed. The major sources of experimental error defining the accuracy of typical planar near-field measurement facilities are reviewed, and present limitations of planar, cylindrical, and spherical near-field scanning are identified.

Fundamental limitations in antennas

Abstract: Four fundamental limitations in antennas have been identified in the areas of: electrically small antennas, superdirective antennas, superresolution antennas, and high-pin antennas. All exhibit roughly exponential increase in cost factors with performance increase beyond the robust range. This paper reviews these limitations. Electrically small antennas are analyzed via spherical mode theory, with the antenna enclosed in a virtual sphere. Minimum Q varies inversely as the cube of sphere radius in radian wavelengths when the radius is much less than the latter. This limits the achievable bandwidth. Superdirective apertures require a constraint; the optimization is generally intractable except for line sources. Superdirective arrays have spacing below half-wavelength, and for small spacings a constraint is desirable to limit Q, tolerances, efficiency, sidelobes, etc. This is accomplished by expressing constrained directivity as a ratio of two Hermilian quadratic forms, for which a solution exists. Array Q varies exponentially with directivity so only modest increases are practical. Superresolution arrays use maximum entropy processes to improve spatial frequency resolution for short samples (short arrays), analogous to spectral analysis processing. An amplitude-tapered autocorrelation function is extended by linear least square prediction and autoregression; the latter contributes filter poles. This extension is with minimum added information, hence maximum entropy. In contrast to superdirective arrays which are all zero functions, superresolution maximum entropy uses an all pole function. Results are dependent upon the sampling subarray size and upon signal/noise (S/N). Required S/N increases exponentially with inverse angular resolution. Achievable gain of high-gain reflector antennas is limited by cost of the structure. For random surface errors maximum gain is proportional to the mechanical tolerance ratio (antenna diameter/1σ tolerance) squared. Since cost increases rapidly with diameter and with tolerance ratio this comprises a gain limitation. Current best reflectors have maximum gain in the range of 90 to 100 dB.

The Atacama Pathfinder EXperiment (APEX) : a new submillimeter facility for southern skies

Abstract: APEX, the Atacama Pathfinder EXperiment, has been successfully commissioned and is operational. This novel submillimeter telescope is located at 5107 m altitude on Llano de Chajnantor in the Chilean High Andes, on what is considered one of the world’s outstanding sites for submillimeter astronomy. The primary reflector with 12 m diameter has been carefully adjusted by means of holography. Its surface smoothness of only 17–18 µm makes APEX suitable for observations up to 200 µm, through all atmospheric submm windows accessible from the ground. First scientific results will be presented in the accompanying papers of this special issue.

Deployable Tensegrity Structures for Space Applications

Abstract: This thesis deals with the development of deployable structures, based on the tensegrity concept, for applications in space. A state-of-the-art review of deployable masts and reflector antennas for space applications is presented. A comparison is made between the various reflector antennas in terms of deployed and stowed sizes, mass and accuracy. The key step in the design of tensegrity structures is the form-finding analysis. Several methods proposed for this step are scrutinised and classified into two groups, kinematic and static methods, and the advantages and disadvantages of each method are investigated. Two of the statical methods seems to be identical. It is concluded that several form-finding methods are available, but no single method is suitable for general tensegrities. The force method, for the analysis of the kinematic and static properties of large bar frameworks, is presented. The analysis and design of deployable tensegrity masts, with three struts per stage, is described. A routine for the manufacturing of physical models is proposed and evaluated. Different schemes for deployment are investigated. A way to deploy the struts using self-deployable hinges is introduced and demonstrated by fourand eight-stage mast models. Finally, the tensegrity mast is compared with an existing deployable mast with respect to stiffness. The mast is relatively stiff in the axial direction but very weak in bending. The requirements for a deployable reflector antenna used on small satellites are formulated. A concept, which uses a triangulated cable network to approximate the reflecting surface, is adopted. The kinematically determinate triangulated cable network is thoroughly analysed. The achievable surface accuracy of the net, both to systematic errors arising from the triangular approximation of the surface and random manufacturing errors, is evaluated. The underlying principles and the statical and kinematical properties of the new concept are presented. A physical model is built to analyse the feasibility of the concept and to test various deployment schemes. The scheme using telescopic struts are identified as the most suitable and a preliminary design an antenna, with a diameter of three metres, for a future space mission is performed. Numerical computations show that the antenna is stiff and extremely light.