RADAR ANTENNAS 315 



made to nod up and down about its horizontal axis by controllable amounts 

 up to a total of 65° and at a rate of 30° per second. 



In the sea search SCR-717 equipment, selsyn azimuth position data take- 

 offs are provided which drive a PPI type of indicator presentation. The 

 rotational speed about the vertical axis in this case is either 8 or 20 rpm 

 as selected by the operator. The reflector can also be tilted about its 

 horizontal axis above or below the line of flight as desired by the operator. 



It wUl be noted that the emitter moves with the reflector and accordingly 

 it is always located at the focal point throughout all orientations of the 

 antenna. 



16.3 T/ie AN/APQ-7 Radar Bombsight Antenna^^ 



Early experience in the use of bombing-through-overcast radar equip- 

 ment indicated that a severe limitation in performance was to be expected 

 as the result of the inadequate resolution offered by the then available air- 

 borne radar equipments. This lack of resolution accounted for gross errors 

 in bombing where the target area was not ideal from a radar standpoint. 



To meet this increased resolution requirement in range, the transmitted 

 pulse width was shortened considerably. In attempting to increase the 

 azimuthal resolution, higher frequencies of transmission were employed. 

 This enabled an improvement in azimuthal resolution without resorting to 

 larger radiating structures, a most important consideration on modern 

 high speed military aircraft. 



To extend the size of the radiating structure without penalizing the air- 

 craft performance, the use of a linear scanning array which would exhibit 

 high azimuthal resolution was considered. This array was originally con- 

 ceived in a form suitable to mount within the existing aircraft wing and 

 transmit through the leading edge. As development proceeded, the restric- 

 tions imposed on the antenna structure as well as the aircraft wing design 

 resulted in the linear array scanner being housed in an appropriate separate 

 air foil and attached to the aircraft fuselage (Fig. 62). 



The above study resulted in the development of the AN/APQ-7 radar 

 equipment, operating at the X-band of frequencies. This equipment 

 provided facilities for radar navigation and bombing. 



The AN/APQ-7 antenna consisted of an array of 250 dipole structures 

 spaced at | wavelength intervals and energized by means of coupling probes 

 extending into a variable width waveguide. The vertical pattern was 

 arranged to exhibit a modified esc distribution by means of accurately 

 shaped "flaps" attached to the assembly. 



" Written by L. W. Morrison. 



*' A large part of the antenna development was carried out at the M. I. T. Radiation 

 Laboratory. 



