THE RADAR RECEIVER 765 



dinate display system is here accomplished by magnetic deflection fields 

 perpendicularly disposed and produced by a pair of deflection coils located 

 at the junction of the neck and bulb as shown. In the polar form of dis- 

 play (PPI) usually only one deflection coil is employed for the ])roduction 

 of the radial sweep, the angular deflection being produced by rotation of this 

 coil about the neck of the cathode-ray tube in synchronism with the rotation 

 of the antenna. 



It is of interest to compare the relative characteristics of the electrostatic 

 and the magnetic-type of cathode-ray tubes from the standpoint of their 

 application to radar indicators. The electrostatic-type of cathode-ray 

 tube has a distinct advantage of lighter total weight for the tube itself and 

 the associated deflection circuits required, which in the case of airborne 

 radar equipment design is an important factor in its favor. In general, it 

 is desirable to present a large radar display field. For the larger diameter 

 cathode-ray tubes the magnetic-type tube has an advantage of shorter 

 over-all length which has proven an important equipment design factor for 

 airborne radar equipment where the available operating space is severely 

 limited. The magnetic-type cathode-ray tube requires weighty focussing 

 and deflecting assemblies and large power supplies to furnish the heavy 

 deflection current required, but because of the higher anode voltages which 

 may be employed here, the screen brightness achieved is considerably greater 

 than that available in the usual electrostatic type of cathode-ray tube. If 

 the anode potential of an electrostatic type of cathode-ray tube is increased 

 and hence the screen brightness, the deflection sensitivity is seriously im- 

 paired and a difticult deflection amplifier design results. From a deflection 

 point of view, it is possible to achieve somewhat better performance in re- 

 producing extremely high-speed sweeps by employing an electrostatic-type 

 of indicator which has somewhat less serious parasitic elements which act 

 to limit the high-frequency response. The final choice of type of cathode- 

 ray tube for the radar indicator is dependent on the specific detailed con- 

 siderations of the system in hand. Xo general and fast rules governing this 

 decision are evident. 



Characteristics of the Fluorescent Screen 



The fluorescent screen of the cathode-ray tul>e upon which the final radar 

 information is converted into the desired visual form consists of a deposit 

 of certain materials which exhibits fluorescence when bombarded with a 

 high-velocity electron stream. Phosphorescence, the continued emission 

 of visible light after bombardment has ceased, is also a property of all of 

 these screen materials. These screen materials, referred to as "phosphors", 

 have characteristics dependent on their physical form as well as their chem- 

 ical composition. 



