spark Gap Switches for Radar 



By F. S. GOUCHER, J. R. HAYNES, W. A. DEPP and E. J. RYDER 



Introduction 



AN ESSENTIAL feature of radar is the generation, by means of an 

 •oscillator, of high-energy pulses of short duration, repeated many 

 times a second. The energy for these pulses is furnished to the oscillator 

 from a power supply in a variety of ways. One of the most widely used of 

 these is the "line type modulator" in which a pulse-forming network made 

 up of a series of condensers and inductances is charged from the power supply 

 through a choke and is then discharged by a switch so that a substantially 

 constant current will flow for a predetermined short time through the pri- 

 mary of a pulse transformer coupled to the oscillator. This switch is, 

 therefore, an essential component of this type of modulator. 



To meet the pulsing requirements of radar as it developed during the war, 

 this line modulator switch was required to withstand thousands of volts 

 between pulses and to carry hundreds of amperes for the pulse duration 

 which was of the order of microseconds. Also, the switching operation had 

 to be repeated from a few hundred to a few thousand times a second for a 

 total operating time of hundreds of hours. Furthermore, the dissipation 

 of energy within the switch had to be very small in comparison with the 

 energy delivered to the oscillator for efficient operation. 



The switch which had the widest application in this type of modulator 

 was that employing an electric spark. Of over 50,000 radars of various types 

 manufactured by the Western Electric Co. during the war, over half em- 

 ployed the electric spark in switching. One form of this switch was a rotary 

 spark gap, operating in air, in which the timing of breakdown was controlled 

 mechanically. These gaps were successfully adapted to a variety of radar 

 types including airborne radar. However the demands for a more compact 

 and lighter weight switch capable of operating at lower voltages for airborne 

 radar led to the development of fixed sealed unit type gaps which, when 

 connected in series, can be broken down electrically in a simple circuit. 



Many problems had to be solved in the development of these switches. 

 They required a considerable amount of study, and with the aid of new tech- 

 niques developed during the war, a number of significant measurements 

 have been made which have extended our knowledge of sparks generally. 

 It is the object of this paper to describe the results of some of these studies, 



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