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BELL SYSTEM TECHNICAL JOURNAL 



degrees was chosen as a suitable compromise between target angle sen- 

 sitivity (steepness of beam) and reduction of signal amplitude "on target". 

 This displacement required a phase shift of approximately 53 degrees 

 bet\veen the two halves of the array. From transmission line theory it can 

 be shown that this phase difference will be obtained with a capacitive 

 reactance equal to the characteristic impedance of the feed line when con- 

 nected at a point 0.176 wavelength from the feed point. It can also be 

 shown that this condition satisfies the requirem.ent for equal power division 

 to the two halves of the array. A capacitor of the required value (about 

 3 micromicrofarads) can readily be built to withstand the peak transmitted 

 power by proper condenser plate separation. A frequency variation of 

 about 40 megacycles can be tolerated without materially affecting the 

 antenna performance. 



Tablk it. — Antentia Characteristics 



Radat Mark 4 



Dimensions 



Apperture in Wavelengths 



Azimuth 



Elevation 



Eeam Width in Degrees (between half power 

 points in one way pattern) 



Azimuth 



Elevation 



.'\ntenna Gain in db 



Beam Shift in Degrees 



Azimuth 



Elevation 



6'x7' 



4.25 

 4.95 



12 

 12 

 22.5 



±3.0=" 

 ±3.0° 



A lobe switching unit similar to that described above was also applied to 

 the 3 ft. by 12 ft. antenna. Pertinent information regarding beam widths 

 and lobing angles for both antennas (together with information on the 

 antenna for Radar Mark 4 to be described later) is given in Table II. 



The effective beam widths as used in these radars were somewhat narrower 

 than the values given above due to the square law characteristic of the 

 second detector in the receiver, and the deflection sensitivity was such that 

 the specified tracking accuracy of ±15 minutes of arc could readily be 

 achieved. The "on target" position or axis of the antenna (lobe crossover) 

 was carefully aligned with the optical telescopes at the time of installation 

 so that either optics or radar angles could be used. The symmetrical design 

 of the antenna made this alignment substantially independent of small 

 changes in operating frequency. 



To minimize target confusion the signals presented on the Train or 

 Elevation Indicator (azimuth operator's oscilloscope) consisted only of 



