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Proposes the null steering method for the minimization of noise from real-time phased array systems. Low-performance digital signal processors; Variation of CLEAN technique.

For many applications, existing phased arrays prove to be costly, bulky and not flexible enough to meet operational requirements. This explains the present trends towards monolithic array design; integration of microwave front end; and beam-forming by using digital signal processing (DSP) techniques. This paper discusses a phased array direction finder based on programmable digital signal processing microdevices, whereby the basic task of beam scanning is carried out by digitally processing the down-converted antenna signals. [ABSTRACT FROM AUTHOR]

This paper discusses a type of multimode monopulse feed using corrugated circular waveguide. The 'difference' or error-signals are derived from the TE and/or TM modes, whereas the 'sum' or reference-signal is provided by the so-called hybrid modes. The optimization of the overall tracking performance is carried out in two steps. The horn dimensions are first chosen to give the optimum 'difference' mode illumination, then the 'sum' mode efficiency is optimized by shaping the ' sum ' pattern with the aid of higher-order hybrid modes. It is shown that the performance of a corrugated waveguide monopulse feed is, in many respects, superior to that of its conventional counterpart. [ABSTRACT FROM AUTHOR]

This paper presents a detailed description of an experimental corrugated feed horn designed to operate at the focus of a paraboloidal reflector. It is found that the corrugation depth does not critically restrict the bandwidth of the antenna, and the main requirement is that the thickness of the corrugation teeth must be small compared to the wavelength. The radiation pattern of the horn maintains a near-perfect cylindrical symmetry over a 10% bandwidth, and the V.S.W.R. is less than 1-1 within the same bandwidth. The overall efficiency of the antenna system is found to be within 3% of the maximum value predicted by the theory. In addition, the spill-over loss is very small, and is of the order of 3.5%. This indicates that a low-noise, high-efficiency antenna can be designed without the need of a massive and more costly conical horn used in dual-reflector systems to date. [ABSTRACT FROM AUTHOR]

Monopulse feeds which allow an independent optimization of the performance of the sum and difference modes have received much attention in the literature. This paper presents some experimental results obtained with a corrugated feed horn designed to operate at the focus of a paraboloid having =60degrees. The present indication is that a near-optimum performance in both the sum and difference modes can be achieved. [ABSTRACT FROM AUTHOR]

Large reflector antennas capable of high-power transmission and low-noise reception have been extensively used in the last decade. To improve the system performance, much effort has been concentrated on the design of a feed which optimizes the overall signal-to-noise ratio. As a result, corrugated waveguides have received a great deal of attention. The main reason is that this type of waveguide structure can support hybrid modes having cylindrically symmetrical radiation patterns (Minnett and Thomas 1966). To achieve high efficiency and signal-to-noise ratio, a large number of hybrid modes must be used. But, as the frequency changes, the mode composition also alters. The following section briefly discusses this effect on the bandwidth characteristics of a multi-mode corrugated feed horn. [ABSTRACT FROM AUTHOR]

The performance of corrugated waveguide borns for paraboloidal reflector antennas is optimized by shaping the radiation pattern with the aid of a high speed digital computer. The same basic program can be used for either the efficiency or signal-to-noise ratio of the system. It is shown that the effect of spill-over loss is to increase the contribution of ambient or ground temperature to the overall system noise. In addition, for the same reflector the optimum waveguide size required to give the maximum signal-to-noise ratio will increase as the ambient temperature increases. Results related to the overall efficiency are found to agree with those of published work. Finally, although the antenna performance is quite frequency sensitive, experimental results indicate that high performance corrugated feeds can in fact be realized.
Problems related to large radiotelescopes can be grouped into two main categories: those connected with antenna structure and surface irregularities, and those related to feed design. At present the feed problems have received increasingly more attention because, although the antenna gain can be increased simply by increasing the reflector diameter, the high cost of building these large antennas makes them uneconomical for certain applications. On the other hand, an efficient feed can significantly increase the capability of a smaller but more accurately built reflector. For this reason this paper only discusses some aspects of the problem of designing efficient feed horns using corrugated waveguide. This type of waveguide structure can support hybrid modes, and its radiation pattern is axially symmetric with zero cross-polarization (Minnett and Thomas 1966). For completeness, problems related to both efficiency and signal-to-noise ratio will be examined. [ABSTRACT FROM AUTHOR]

Theoretical investigation of random phase errors caused by surface irregularities in large reflector antennas has been the subject of many technical papers in recent years. This paper presents experimental results obtained by using a 4 ft diameter model whose reflector consists of an assembly of 54 triangular panels. Accurate control of artificial surface errors is achieved with the aid of micrometers attached to the corners of the panels. Thus the effect of random errors on the radiation characteristics of a large batch of nominally identical antennas can be successfully investigated. Good correlation between theoretical and experimental results has been obtained. The results also show that there is a significant advantage in using triangular panels to build antenna reflectors. [ABSTRACT FROM AUTHOR]

However, the aim of this correspondence is to point out the important fact that the effect of the root mean square phase-error on the radiation characteristics of the antenna is quite insensitive to change in the illumination function. In other words, the decrease in axial gain and the spread of the scattered radiation about the antenna axis are mainly determined by the size of the correlation interval and not by the illumination function. This can be observed by carefully examining the results given by Vu (1969). It is also important to note that the resultant radiation pattern of the antenna, and consequently its sidelobe structure, beamwidth, etc., can be obtained by superimposing the scattered radiation pattern on the error-free pattern (Ruze 1966). [ABSTRACT FROM AUTHOR]