Newnes Radio and RF Engineering Pocket Book, 3rd Edition

3

1.3 The isotropic radiator

A starting point for considering the propagation of radio- or lightwaves

is the isotropic radiator, an imaginary point source radiating equally

in all directions in free space. Such a radiator placed at the centre of

a sphere illuminates equally the complete surface of the sphere. As

the surface area of a sphere is given by 4πr

2

where r is the radius of

the sphere, the brilliance of illumination at any point on the surface

varies inversely with the distance from the radiator. In radio terms,

the power density at distance from the source is given by:

P

d

=

P

t

4πr

2

where P

t

= transmitted power.

1.4 Formation of radio waves

Radio waves ...