16 ELEMENTS OF AIRBORNE RADAR SYSTEMS DESIGN PROBLEM 



Despite this formidable advantage, the design of a jamming radar 

 system can be one of the most perplexing of all radar systems problems — 

 from the points of view of both systems engineering and hardware design. 

 This arises from the vast multitude of possibilities with which a jamming 

 system must cope. 



Scientific Research. Airborne radars are frequently utilized to 

 gather basic scientific data such as atmospheric transmission characteristics, 

 target reflectivity, and ground reflectivity and emission characteristics. 



The coming space age opens up several interesting possibilities. It is 

 very probable that the first glimpse of the surface characteristics of the 

 planet Venus will be provided by a radar picture taken from an inter- 

 planetary vehicle. The use of radar techniques would permit the penetra- 

 tion of the optically opaque atmosphere which completely obscures this 

 enigmatic planet, as well as provide a quantitative evaluation of its atmos- 

 pheric components. This could be accomplished by measurement of the 

 attenuation of the radar energy as a function of frequency. As will be 

 discussed in Chapter 4, water vapor, oxygen, and carbon dioxide exhibit a 

 marked efl^ect upon radar energy transmission characteristics at certain 

 frequencies. Passive radar techniques (microwave thermal mapping) 

 could be employed to ascertain the surface temperature distributions and 

 the heat balance. This type of scientific data would be invaluable for the 

 determination and prediction of weather conditions. 



1-5 THE MODULATION OF RADAR SIGNALS 



A radar system may perform a number of functions (Paragraph 1-4) 

 that involve the collection or transmission of intelligence for some defined 

 tactical objective. The intelligence is carried by modulations of the radar 

 microwave signal. The means used to create these modulations and the 

 means employed to extract information from them (demodulation) form 

 a convenient and mathematically useful way to describe and classify radar 

 systems. 



As will be seen in later portions of this book, the key to the understanding 

 and proper design of a radar system is a knowledge of the modulation proc- 

 esses that can take place. The various processes of modulation and de- 

 modulation are conveniently explained by the use of simple generic repre- 

 sentations of the three basic elements of a radar system: (1) the transmitter, 

 (2) the target, and (3) the receiving system. 



A simple transmitting system is shown in Fig. 1-10. It consists of a 

 means for generating alternating current power, a means for carrying this 

 power to an antenna, and an antenna that radiates some portion of this 

 power into the surrounding space. 



