This thesis is a performance study of the paraboloidal antenna of the Dominion Radio Astrophysical Observatory and is an assessment of the quantity and distribution of radiation reaching the receiver input from all directions. This study deals first with the ideal reflector for which the radiation pattern is computed for small off-axis angles and for wide-angle radiation. The latter calculations make use of the stationary-phase principle in evaluating the radiation integrals. It has been found that the half-power beam-width is slightly more than 0.5° and the first side-lobe is at least 30 db down. In the following chapter, the surface imperfections of the reflector are considered, in addition to the radiation reaching the feed from the ground. The aperture field is divided into a number of zones perturbed slightly in phase so as to approximate the slowly-varying roughness of the reflector. The resulting increase in side-lobe level is then not only related to the surface tolerance, but to the average size of each zone. The radiation reaching the feed from the ground due to spillover, transmission through the reflector mesh and holes, and reflector surface loss, contributes about 16°K to the equivalent noise temperature of the antenna. The hollow dielectric spars supporting the feed horn are considered and are treated first as being infinite in length where the necessary boundary conditions are applied. The concept of scattering in cones about the cylinder axis is also developed. Then, for the finite cylinder, radiation is assumed to result from the same scattering width. Experimental studies are carried out and with Cassiopeia A as a source, the shape of the main beam is found to agree with the theoretical result, but the level of the first side-lobe is higher than expected. This discrepancy is believed to be due to reflector distortion. The sun is used as a source for detection of spar scattering and the presence of scattering cones is confirmed. An absolute temperature calibration is carried out with a resulting figure 27°K for the antenna pointed at the zenith. This temperature is measured at the input of a Dicke switch and is consistent with the theoretical 16°K presented to the input of the feed horn. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The various stages in the design and construction of a frequency standard for use in microwave spectroscopy is described. Procedures are laid down for the use of the instrument. The standard is of the variable frequency type which gives it several advantages over the fixed frequency machines. It is capable of providing complete coverage at microwave frequencies and is capable of determining the microwave harmonic generated without recourse to a wave-meter. Furthermore it can conveniently be used in conjunction with a calibrated communications receiver to measure frequency separations to a high degree of accuracy. A stable 200 kc crystal controlled oscillator is used as the base frequency. This frequency is multiplied by harmonic generators to 4800 kc and supplied to the oscillator grids of a balanced mixer. The variable 125 to 250 kc output from a BC221 signal generator is supplied to the signal grids of this same mixer. The mixer output is tuned with a band pass circuit passing 4925 to 5050 kc and consequently the two input frequencies are summed. The balanced mixer serves to eliminate several troublesome frequency components. The mixer signal is multiplied successively to 25 mc, 75 mc and 200 mc. An output from one of these VHF stages is chosen and impressed upon a 1N26 silicon crystal rectifier. This rectifier acts as a harmonic generator producing frequency markers in the microwave region. Since both the 200 kc oscillator and BC221 signals have a high degree of stability and can conveniently be calibrated relative to standard frequency broadcasts from the U.S. Bureau of Standards, these microwave frequency markers are known to a high degree of accuracy. This microwave standard signal is fed into the spectrometer waveguide and picked up by a crystal mixer. The spectrometer klystron signal is also detected by this crystal and consequently beats are produced equal to the difference between the standard harmonics and the klystron frequencies. This beat note is supplied to a tuned amplifier whose, output is applied to the Y plates of the spectrometer oscillograph. The time base of the latter is supplied by the sawtooth wave which sweeps the klystron frequency. When the beat note frequency is equal to the frequency to which the amplifier is tuned a marker pip will occur on the screen. Since the frequency of the standard signal and the tuning of the amplifier are known the frequency of the klystron at this point of the time base can be determined. By tuning the variable frequency oscillator, the pip can be moved across the horizontal axis until it is coincident with a spectrum line. Consequently the frequency of this line can be measured with an accuracy of 1 part in 10⁶. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

In radio-astronomy, spectra of noisy signals are often computed using digital auto-correlation techniques. To simplify the design of the many high-speed multipliers and averagers, coarse quantization is employed, using only a few digital levels. This thesis is a theoretical study of the penalty paid for such coarse quantization in the form of increased output noise. A degradation factor is defined and is calculated for a variety of logic schemes which have been used or proposed. For each scheme, results are given as a function of sampling rate and it is demonstrated that there is often significant improvement in sampling at rates faster than the Nyquist rate. A computer simulation technique was developed for verifying the computed results, and for extending the results to complicated schemes where analysis is very difficult. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

This thesis describes the design, construction, and testing of a radio-frequency interference monitoring system for use with the synthesis array telescope at the Dominion Radio Astrophysical Observatory near Penticton, B.C. The system is designed to provide continuous, automated surveillance of the radiospectrum around 408 MHz. Interfering signals are characterized and catalogued according to strength, duration, frequency, and direction. Although the monitor is presently a very useful tool for detecting and finding sources of interference, it is ultimately intended to communicate directly with the telescope's control computer, so that sporadic bursts of interference can be removed automatically. The system can detect a weak interfering signal that is within 5 dB of the smallest signal that can contaminate the astronomical observations. The smallest signal was calculated based on the following conditions, considered to be the case for which a synthesis telescope is most sensitive to interference, i.e., the worst case: a) observing at high declination (towards the North Pole), so that the fringes of the synthesis telescope are too slow to reduce the effects of the interference, and b) with the interference present continuously during the observation. These weak signals can be detected in the presence of other signals, nearby in frequency, which are up to 40 dB stronger, i.e., the dynamic range of the monitor is 40 dB. The monitor consists of an antenna system, a computer-tunable radio receiver, a fast Fourier transform (FFT) spectrum analyzer, and a microcomputer for control and data analysis. Everything except the microcomputer hardware was built as part of the project. A thorough survey of the literature on the design of dedicated FFT machines was required. It was discovered that there had been no investigation of the design details for fixed-point FFT machines which are required to do long integrations. In such situations, fixed-point errors limit the performance of the machine. A computer simulation of the Welch process was developed to analyze the effects of these errors and to optimize the design. Some new results concerning the detectability of small signals are presented. The FFT spectrum analyzer is used to estimate the power spectrum of 500 kHz-wide sub-bands using Welch's method of modified periodograms. It computes 256-point transforms in real-time with a resolution of 3.91 kHz (corresponding to one FFT every 512 μsec). This is comparable to the speed of a large array processor but at a fraction of the cost. Since the FFT is equivalent to a bank of contiguous filters, it can analyze the spectrum in much less time than the single swept filter found in most commercial spectrum analyzers, i.e., it is much more sensitive. The analyzer was specially designed and built using recently-available digital integrated circuits. The design draws upon several high-speed architectural concepts including pipelining, parallel arithmetic, and hard-wired control. Except for expensive array processors, the analyzer is much faster than any commercial FFT processors or FFT-based spectrum analyzers. As part of the antenna system, an array of helical antennas was designed and constructed, its characteristics were investigated and found to be suitable for the present application, and a method of remotely switching them on and off was devised. One more note - the radio spectrum is becoming more and more cluttered with man-made signals. Unprotected radio astronomy bands are being adversely affected and radio astronomers are turning to FFT spectrometers to cope with the relatively large interfering signals. The work herein on FFT-based design is applicable in such cases. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

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