Using Kirchhoffs diffraction theory, scalar field analyses of two off-axis focused antenna systems, the Fresnel-zone plate antenna (FZPA) and parabolic reflector antenna, are presented. Expressions which describe the gain patterns of both antennas are derived and used to examine the scan properties of the two systems and to reveal and discuss similarities and differences between them. The results of the analysis give good insight into future applications of the FZPA as a multibeam antenna. © 1993 John Wiley & Sons, Inc.

The scan performance of the fresnel-zone plate antenna: A comparison with the parabolic reflector antenna

Near-field designs of Fresnel and Gabor zone plates are computationally analyzed by using versions that allow the foci to be brought closer to the plate than in the usual far-field applications. It is found that the Fresnel plate has a dominant primary conjugate pair of foci well inside the far-field region and a more intense primary focus and smaller off-focal-plane sidelobes than the near-field Gabor systems, thus yielding a superior imaging performance.

Computational study of diffraction patterns for near-field Fresnel and Gabor zone plates

1. General introduetion 1.1. Background and scope 1.2. Brief survey 2. Review and extension of the theoretical description of propagation on tropospheric radio paths 2.1. Introduetion 2.2. Large-scale refraction and reflection on the 30 GHz l.o.s. path 2.2.1. Reflection at the earth surface 2.2.2. Temporal and spatial variatien of the k-factor 2.2.3. Amplitude and phase distortien 2.2.4. Ray tracing 2.3. Tropospheric scintillation 2.3.1. Weak-scattering theory 2.3.2. Application of weak-scattering theory 2.4. Precipitation 2.4.1. A model for the propagation medium in the presence of rain 2.4.2. Attenuation, depolarisation and signal distartion 2.4.3. Rain-induced scintillations 3. Instrumentation of experiments 3.1. Introduetion 3.2. The 30 GHz measuring system 3.3. The local weather station 3.4. Baseband signal processing and data colleetien 4. Experimental verification of theory 4.1. Introduetion 4.2. Large-scale refraction and reflection on the 30 GHz l.o.s. path 4.2.1. Signal fluctuations, depolarisation and distortien 4.2.2. Angle-of-arrival measurements 4.2.3. Ray tracing 4.3. Scintillation 4.3.1. Amplitude and phase scintillation measurements on 8.2 km line-of-sight path at 30 GHz (reprint) 3 3 5

The influence of tropospheric irregularities on the dynamic behaviour of microwave radio systems

Auxiliary defocused feeds with weak excitation can be used to cancel or reduce specific near-angle sidelobes of double reflector antennas. Existing earth terminals may be upgraded in this way to provide improved isolation between interfering satellites when the tight station-keeping tolerances agreed at WARC-79 come into force.

Improved orbit utilisation by interferometric sidelobe suppression

A theoretical investigation of the defocused Schwarzschild antenna system is described. Scan properties have been compared with those of the Cassegrain antenna system. It is shown that both the focused and defocused radiation patterns of the two systems are almost identical.

Scan Properties of the Schwarzschild Antenna

Computation of the far field of a defocused reflector antenna using the stationary phase method is described. The positions of the stationary phase points are determined, to eliminate one of the two numerical integrations of the radiation integral. Examples of scan patterns and computational time saving are presented.

F.J.J. Gielkens

Papers

Stationary phase method for far-field computation of defocused reflector antennas