A MULTIPLE UNIT STEERABLE ANTENNA 



387 



generators, e^, static generators, e„, and resistances Ra- The input 

 circuits of the receivers are matched to the. antennas. 



In Fig. 32, A^ spaced antennas are shown connected in parallel. The 

 root-mean-square noise voltage. En, at the input to the receivers 

 represents the thermal noise originating in the receiver input circuits. 



ANTENNA I 

 R 



ANTENNA 2 

 R 



---rrri::j::S-I 



ANTENNA N 

 R 



input circuit 

 (impedance r) 



Es.Ea-En 



WAVE 

 DIRECTION UNIT 



^ANTENNA 



FIRST ASSUMPTION: 

 ALL LINES MATCHED 

 (line IMPEDANCES - R^ 

 PHASE SHIFTER IMP. = Ra 

 INPUT CIRCUIT MATCHED 

 TO IMP. Ra/n) 



SECOND ASSUMPTION: 



SINGLE WAVE. SIMILAR ANT 



(esi=es2 esN=es 



®ai~ ©az' 6qn= ©a) 



SIGNAL CURR. PHASED 

 STATIC CURR. RANDOM 



r-r 



6s K 



2Ra' 





_ N 



2Rr 



i/N 

 2Ra 



CONST X /r 



'^Wa 



CONST X /R 



Es ^ es 



■r-= Tn -7= CONST. 



1 ^r; 



Fig. 32 — Simple signal-to-noise analysis of a system of N spaced antennas. 

 Signal currents are phased and combined at the incoming frequency. The summa- 

 tion signs include addition on the power basis. 



For the matched condition this noise is constant and independent of 

 the number of antennas. A single wave is assumed and the signal 

 outputs of the antennas are phased by means of the phase shifters 0. 

 The maximum signal power obtainable from N antennas obviously is 

 N times that obtainable from one antenna. In terms of receiver noise, 



