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Multiple simultaneous beams exist when an array of N elements is connected to a beamformer with 1M beam ports, where N and 1M may be different. Multiplebeam systems have many uses: in electronic countermeasures, in satellite communications, in multiple-target radars, and in adaptive nulling, for example. The last application uses adaption in beam space as it avoids several serious difficulties that arise with adaption in array space. (Mayhan, 1972). Not included in this chapter are array feeds for parabolic reflectors, where amplitude and phase control of the elements allows coma correction, beam switching, adaptive nulling, and to a limited degree. | Phased Array Antennas. Robert C. Hansen Copyright 1998 by John Wiley Sons Inc. ISBNs 0-471-53076-X Hardback 0-471-22421-9 Electronic CHAPTER TEN Multiple-Beam Antennas INTRODUCTION Multiple simultaneous beams exist when an array of N elements is connected to a beamformer with M beam ports where N and M may be different. Multiplebeam systems have many uses in electronic countermeasures in satellite communications in multiple-target radars and in adaptive nulling for example. The last application uses adaption in beam space as it avoids several serious difficulties that arise with adaption in array space. Mayhan 1972 . Not included in this chapter are array feeds for parabolic reflectors where amplitude and phase control of the elements allows coma correction beam switching adaptive nulling and to a limited degree correction of reflector shape errors Rudge and Davies 1970 Blank and Imbriale 1988 Smith and Stutzman 1992 . Also not included are horn arrays feeding reflector antennas on communication satellites to provide tailored earth coverage patterns Clarricoats and Brown 1984 Richie and Kritikos 1988 Bird 1990 . BEAMFORMERS This section deals with the methods for forming multiple beams. Multiple beamformers are either networks or quasi-optical lenses. It is customary to call either type a beamforming network BFN . In general with a network BFN beam crossover levels are independent of frequency while beamwidths and beam angles change with frequency. With a lens BFN beam angles are fixed while beamwidths hence crossover levels change with frequency. Each class of BFN is discussed. 330 BEAMFORMERS 331 Networks Power Divider BFN. Probably the simplest BFN uses power dividers to split the received signal from each array element into N outputs the 1 outputs from the dividers are connected through fixed phasers to a combiner to provide beam 1 etc. Figure sketches such a configuration. Since there is a signal decrease to 1 7V preamplifiers .