700 BELI. SYSTEM TECH. \ UAL JOIR.XA/. 



exact choice of these parameters being dictated })y the specific a])plication 

 of each type of equipment. 



It has been customary to employ a common antenna system for both the 

 transmitting and receiving functions, the necessary protection of the sensi- 

 tive receiver input circuits from the high power transmitted pulse being 

 furnished by a TR switch or tube.^ The gas discharge TR switch assembly 

 attenuates the energy fed to the input terminals of the receiver for the 

 duration of ttie microwave outgoing pulse. At the time of decay of this 

 transmitting pulse, the TR switch is arranged to offer low attenuation be- 

 tween the antenna and the receiver to any received signal. 



The received microwave signal will be found to fluctuate in amplitude 

 between extremely wide limits. This amplitude characteristic of a re- 

 ceived radar signal is affected by the size and composition of the target, 

 the power of the radiated outgoing pulse, the distance or range to the target, 

 and miscellaneous propagation effects. Military requirements necessitate 

 designing the radar receiver to perform successfully with the minimum re- 

 ceived signal, while not unduly compromising this performance when sig- 

 nals of relatively high energy content are encountered. 



Other characteristics of the transmitted microwave signal, such as pulse 

 shape and repetition rate, are chosen to enable maximum {)erformance to 

 be attained for the specific application to be covered. The proper treat- 

 ment of these miscellaneous characteristics of the radar signal is of basic 

 concern to the receiver designer. 



The primary basic information which can be derived from the charac- 

 teristics of the received radar signal itself consists of data concerning the 

 range to the target under observation. This range data is made available 

 by a measurement of the elapsed time between the departure of the out- 

 going pulse and its return after reflection from the target and consideration 

 of the velocity of electromagnetic wave propagation. 



To determine the complete coordinates of a radar target, correlation of 

 the range information, as determined above, and the direction of radiation 

 from the antenna is necessary. Signals containing information as to the 

 instantaneous attitude of the antenna with respect to chosen reference axes 

 are, therefore, to be considered as essential inputs to the radar receiver. 



Though the natural coordinate system of radar is of a polar form, many 

 specific applications of radar systems require conversion of this information 

 into other forms more convenient of use. I-'or example, while in gun-])oint- 

 ing radar applications, it is desirable to present the final information in a 

 j)olar coordinate form, corresponding to the aiming axes of the guns in many 

 airborne radar bombing systems, it is necessary that the presentation be 



'"'I'lic (ias- Discharge Transmit- Receive Switcli," A. L. .Saimiel, J. W . (lark and \\ . 

 W. .Vluniford, Bell System Tcciinicol Journal, Vol. X.W, Jaiuiar> 1*M6. 



