The present-day ocean remote sensing instruments that operate at low microwave frequencies are limited in spatial resolution and do not allow for monitoring of the coastal waters. This is due the difficulties of employing a large reflector antenna on a satellite platform, and generating high-quality pencil beams at multiple frequencies. Recent advances in digital beamforming focal-plane-arrays (FPAs) have been exploited in the current work to overcome the above problems. A holistic design procedure for such novel multi-beam radiometers has been developed, where (i) the antenna system specifications are derived directly from the requirements to oceanographic surveys for future satellite missions; and (ii) the numbers of FPA elements/receivers are determined through a dedicated optimum beamforming procedure minimizing the distance to coast. This approach has been applied to synthesize FPAs for two alternative radiometer systems: a conical scanner with an offset parabolic reflector, and stationary wide-scan torus reflector system; each operating at C, X and Ku bands. Numerical results predict excellent beam performance for both systems with as low as 0.14 % total received power over the land.
An algorithm for the computation of the solution to Laplace's equation in a 2-dimensional region is given in terms of equivalent sources on the boundary. The region may be of an arbitrary shape, and the boundary conditions may be an arbitrary combination of Dirichlet, Neumann and impedance types. The solution is obtained by a moment method, using either a step approximation to the source, or a piecewise-linear approximation. Point matching is used for testing the boundary conditions. Computer programs are available for the general problem, and some electromagnetic-field applications are discussed.List of symbols a, j8, y = arbitrary functions of c = solution to Laplace's equation V F, = potential from strip of uniform source on AC, A,-= length of element AC,-of curve C c = length variable along curve C g = conductivity k = constant Iji = elements of matrix [/] n = outward unit vector normal to curve C u = unit vector tangential to curve C w = complex function x, y -co-ordinates of point in space z -x + Jy = complex variable C = capacitance D = electric-flux density E = electric-field intensity H = magnetic-field intensity / = current J = current density P = power • P-, = pulse function Q -electric charge R = resistance V = constant potential Z o = characteristic impedance of a transmission line * denotes a complex conjugate
Novel antenna architectures for real aperture multi-beam radiometers providing high resolution and high sensitivity for accurate sea surface temperature (SST) and ocean vector wind (OVW) measurements are investigated. On the basis of the radiometer requirements set for future SST/OVW missions, conical scanners and push-broom antennas are compared. The comparison will cover reflector optics and focal plane array configuration. I.
Sammendrag-Performance of a dense focal plane array feeding an offset toroidal reflector antenna system is studied and discussed in the context of a potential application in multi-beam radiometers for ocean surveillance. We present a preliminary design of the array feed for the 5-m diameter antenna at X-band. This array is optimized to realize high antenna beam efficiency (∼ 95%) over a wide scan range (±20 • ) with very low side-lobe and cross-polarization levels.Index Terms-reflector antenna feeds, multi-beam antennas, microwave radiometry.
The Method of Moments (MoM), Physical Optics (PO) and Geometrical Optics (GO) are compared for analysis of dielectric lenses. It is found that MoM can be used (with normal computers) for diameters of the lens up to 15, being the wavelength, whereas the approximate methods PO and GO must be used at higher frequencies. Good agreement between the different methods is found and efficient calculation of PO and GO is discussed.
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