THE RADAR RECEIVER 701 



made in terms of rectangular or other convenient coordinate systems re- 

 ferred to the ground itself. In certain applications, the characteristics of 

 the display or presentation device requires that coordinate conversion func- 

 tions be included within the radar receiver. The conversion and proper 

 presentation of all radar system coordinate information will, therefore, be 

 considered a necessary function of the radar receiver. 



Additional forms of radar receiver input signals encountered are those 

 primarily associated with the specific application of the radar system. 

 Reference coordinate axes data obtained from compasses or gyroscopes are 

 among the most common of these. Fn gun-fire control and bombing appli- 

 cations a considerable quantity of computed data must be accepted by the 

 receiver. These data may include predicted quantities which must be 

 jiresented in addition to the usual received present-time radar information. 

 In the case of airborne radar systems, provision must be included to properly 

 display navigational beacon and identification signals. The beacon is 

 operated by the radar transmitter in the aircraft and returns a coded signal 

 at a frequency slightly removed from the normal radar band. All aircraft 

 radar receivers are required to adequately detect and projierly display this 

 information. It has also become common practice to require provision 

 within the radar receiver for display of interrogator-response signals as 

 employed for military identification purposes. The identification equi])- 

 ment (IFF) proper is not a radar system component and, therefore, it will 

 not be considered here. 



1.22 Character of the Oulpul of a Radar Receiver 



The output of a radar receiver is required to be availaljlc to the observer 

 in a form which will permit immediate analysis and use of a maximum 

 of the received information. The consideration of some additional charac- 

 teristics of the radar information available and the military applications 

 will furnish a basis for choice of presentation means in the receiver. 



Because of the inherent ])ace of the constantly changing tactical mili- 

 tary scene, the basic requirements imposed upon the radar presentation 

 device are severe. For example, the use of radar in an aircraft, or on the 

 ground or sea directed against aircraft involves a process of obtaining in- 

 formation on targets having relative velocities upward of 500 feet per 

 second. If the radar system under consideration is being emj)loyed to fur- 

 nish data for the release of bombs or to direct gunfire, a fraction of a second 

 represents dimensions comparable to the target size. Such considerations 

 adequately emphasize the extreme imj)ortance of retaining the "immediacy" 

 characteristic of the information through the presentation device. 



Another factor influencing the design of the presentation components in a 

 radar receiver is found in consideration of the extreme complexity of the 



