Observing methods to cancel atmospheric fluctuations

The information collected by a radio telescope has the characteristic of noise, which is normally not discernible from the inherent thermal noise of the antenna-receiver system. The signal is generally broad-band, continuous radiation. The only exception is the presence of spectral lines of cosmic molecules and atoms, which appear at discrete frequencies, but otherwise are noise-like as well. The signals in communication channels are modulated in a particular fashion and therefore easier to...

The ALMA Prototype Antennas

For more than 15 years astronomers in the USA, Japan and Europe have been making plans for a large millimeter array, placed at a superb site. In 2000 these plans were merged into the ALMA project, which is joint project of North America (USA and Canada) and Europe (ESO, representing 12 European countries) under participation of Japan and Taiwan. The project comprises 54 antennas of 12 m diameter, suitable for observations at 1 THz (0.3 mm wavelength) and equipped with receivers in the entire...

Introduction and historical development

Some history of the parabolic reflector antenna In highschool I was taught that the great Greek scientist Archimedes (287 - 212 BC) was instrumental in the defence of his city Syracuse on Sicily against the Roman fleet and army of Marcellus during the Punian War. Among the defensive devices, developed by him, he used parabolic mirrors to concentrate the reflected light from the Sun to set the Roman ships afire. The frontispiece picture on page vi of this book represents this feat....

The Heinrich Hertz Submillimeter Telescope HHT

The first good experiences with a CFRP mirror and the excellent thermal and mechanical properties of the material, along with its relative low weight, made it an attractive, be it relatively expensive, choice for structures with specifications more stringent than those of the MRT. The requirements for the mobile antennas of the IRAM Millimeter Interferometer (Guilloteau et al., 1992) included transportability along rail tracks between observing stations, suppression of thermal deformations and...

The IRAM 30m Millimeter Radio Telescope MRT

In chapter one we mentioned that the development of large reflector antennas has been spurned strongly by the needs of radio astronomers. Interestingly, this is not entirely the case for the spectral range, called millimeter-wave radio astronomy, which we define as the frequency range from 30 - 300 GHz (wavelength 10 to 1 mm). The first reflectors, sufficiently accurate to operate at 3 mm wavelength, were the 4.9 m diameter antenna at the University of Texas (Tolbert et al.,1965) and the 4.6 m...

Geometry of reflector antennas

In this chapter we deal with a description of the geometry of a paraboloid of revolution. We shall collect the geometrical relationships, which we need for the description of the electromagnetic radiation characteristics of the paraboloidal reflector antenna. Because many radio telescopes and communication antennas actually employ the Cassegrain or Gregorian layout, we include the formulas for those systems too. These are dual reflector systems, where a relatively small secondary reflector,...

Axial defocus

In Chapter 2 we described the geometrical relations of the paraboloid and presented the formulae for the path length differences caused by defocusing. Their influence on the characteristics of the radiation pattern will now be discussed. In general terms this is called the theory of aberrations. We will not give an exhaustive treatment (for this see e.g. Born and Wolf, 1980), but will derive the changes in beam parameters, like gain, beamwidth, sidelobe level, etc. First we treat the effects of...

Antenna characteristics in practical applications

After the development of the basic equations, we now turn to application of these to practical situations in antenna theory, like calculations of efficiency, beamwidth and sidelobe level as well as the influence of defocus and other errors on the antenna's characteristics. We shall develop formalisms and present results which are of use in the daily work of the antenna engineer and the radio astronomer. We first introduce as basic quantity the aperture efficiency, defined as where A is the...

The Effelsberg 100m radio telescope

Radio Telescope Cross Section

Radio astronomy in Germany was established at the University of Bonn with the construction of a 25-m telescope in 1957. In 1962 Otto Hachenberg was appointed professor of radio astronomy. He came from the Heinrich-Hertz-Institute in Berlin, where, together with industry, he had built a 32-m transit instrument. Lacking finite element analysis and computing power, they had studied experimentally how spaceframe structures deform under gravity. Here an indication of homologous deformation became...

List of Figures and Tables

Dwingeloo telescopes Wurzburg and 25-m antenna 3 3. The 75 m diameter Lovell radio telescope at Jodrell Bank Observatory 4 4. ESA deep space ground station in Western Australia 5 5. The NRAO 140-ft telescope at Green Bank 6 6. The Green Bank Telescope GBT of NRAO 7 7. The 15 m diameter JCMT on Hawaii 8 8. The 10 m diameter CSO submillimeter wavelength antenna on Hawaii 8 9. The 12 m diameter APEX antenna on the ALMA site in Chile 9 10. The 25 m long Little...

Info

Gain loss due to axial defocus of the feed from the primary focus for 3 mm wavelength and uniform illumination. The dashed red curve uses the exact phase error of Eq. 2.29 , the green curve is for Eq. 2.28 , essentially coinciding with the red, and the blue curve Eq. 4.22 , barely separated from the other two. The cyan line is the quadratic approximation of Eq. 4.22 to the blue function, adequate for b lt 15. We return now to Eq. 4.21 which is the expression for the gain loss as...