Microwave and Wireless Communications Technology

18 MICROWAVE PROPAGATION

Figure 2-3 Propagation paths: tropospheric, direct, and reflected.

so low that ions can travel relatively long distances before recombining with op-

positely charged ions to form electrically neutral atoms. As a result, the ionos-

phere remains ionized for long periods of the day, even after sunset. At lower

altitudes, however, air density is greater and recombination thus occurs rapidly. At

those altitudes solar ionization diminishes to nearly zero immediately after sunset,

or never achieves any significant levels, even at local noon. Some authorities be-

lieve that ionization and recombination ...