TABLE OF CONTENTS 
Since radio waves and alternating current (ac) signals are vital to all radar functions, any introduction to radar logically begins with them. Indeed, many radar concepts which at first glance may appear quite difficult are simple when viewed in the light of a rudimentary knowledge of radio waves and ac signals.
In this chapter we will consider the nature of radio waves and their fundamental qualities.
Radio waves are perhaps best conceived as energy that has been emitted into space. The energy exists partly in the form of an electric field and partly in the form of a magnetic field. For this reason, the waves are called electromagnetic.
While neither field can be perceived directly, fields of both types are familiar to everyone. A common example of an electric field is that due to the charge which builds up between a cloud and the ground and produces lightning (Fig. 1). On a much smaller scale, another example of an electric field is that due to the charge which builds up on a comb on a particularly dry day, enabling the comb to attract a scrap of paper.
Examples of magnetic fields are equally common. At...
