A MULTIPLE UNIT STEERABLE ANTENNA 417 



substantial improvement in quality is obtained by reducing the 

 distortion associated with selective fading. It is both interesting and 

 important to note that whereas so often one advantage is gained only 

 at the expense of another, in the MUSA system the best quality im- 

 provement and the greatest signal-to-noise advantage are obtained 

 together, without compromising. 



The system developed is expensive and might be thought to illustrate 

 the law of diminishing returns. As a part of a point-to-point radio- 

 telephone system, however, it has certain compensating features not 

 mentioned thus far. One of these is the broad frequency band 

 feature. 



With essentially aperiodic unit antennas the MUSA possesses a 

 broad frequency range; i.e., the directional pattern, despite its sharp- 

 ness, is substantially the same over a band of a hundred or more kilo- 

 cycles provided the terminal equipment is made sufficiently broad. 

 (See Appendix I.) The broad-band feature is important for its possi- 

 bilities in multiplexed operation of telephone circuits; i.e., it makes 

 possible, insofar as the antenna system is concerned, the adaptation of 

 some of the carrier telephone methods to radio circuits. It is to be 

 expected that, excepting certain critical cases, fairly large percentage 

 frequency bands will follow virtually the same paths. This assump- 

 tion was verified by a few experiments in which pulses were received 

 simultaneously from GBS (Rugby, 12,150 kilocycles) and GBU 

 (Rugby, 12,290 kilocycles) 140 kilocycles apart. These tests showed 

 that, although the pulse fading was, of course, not synchronous, the 

 angles involved were alike. 



Another compensating feature of the MUSA receiving system is that, 

 with suitable terminal equipment, reception may be carried on from 

 several points at once provided they lie within the horizontal angular 

 range of the unit antenna. Some sacrifice in vertical angular selec- 

 tivity occurs but this is confined to low angles where it is least im- 

 portant. 



Certain features of the system make for economies in plant cost. 

 The fact that a great many components are identical permits manu- 

 facturing economies. Also, spare units need be provided only for a 

 few vital functions, since the failure of one of the many similar parts 

 does not disrupt service. 



The development of steerable directivity has thus far been concerned 

 with receiving antennas. In receiving, one has the obvious ad- 

 vantage of having, in the monitoring branch, a criterion to dictate the 

 steering adjustments. The lack of such a direct criterion for adjusting 

 transmitting directivity does not, however, rule out the possibility, at 



