introduces you to a downloadable
This is an
official U.S. Navy training course that will help you understand Wave
Propagation, Antennas, Transmission, and Waveguides. ~~~~~~~~~~~~~~~~~~~~~~~~~
The eyes and ears of a ship or shore radio station depend on sophisticated, highly computerized electronic systems. The one thing all of these systems have in common is that they lead to and fromantennas. Ship’s operators who must communicate, navigate, and be ready to fight the ship 24 hours a day depend on you to keep these emitters and sensors operational.
While radio waves traveling in free space have little outside influence to affect them, radio waves traveling in the earth’s atmosphere have many influences that affect them. We have all experienced problems with radio waves, caused by certain atmospheric conditions complicating what at first seemed to be a relatively simple electronic problem. These problem-causing conditions result from a lack of uniformity in the earth’s atmosphere.
this volume, we will review wave propagation, antenna characteristics,
shore-based and shipboard communications antennas, matching networks,
antenna tuning, radar antennas, antenna safety, transmission lines,
connector installation and weatherproofing, waveguides, and waveguide
couplings. When you have completed this chapter, you should be able to
discuss the basic principles of wave propagation and the atmosphere’s
effects on wave propagation.
Many factors can affect atmospheric conditions, either positively or negatively. Three of these are variations in geographic height, differences in geographic location, and changes in time (day, night, season, year).
To understand wave propagation, you must have at least a basic understanding of the earth’s atmosphere. The earth’s atmosphere is divided into three separate regions, or layers. They are the troposphere,the stratosphere, and the ionosphere. These layers are illustrated in figure 1-1.
all weather phenomena take place in thetroposphere. The temperature in
this region decreasesrapidly with altitude. Clouds form, and there may be
a lotof turbulence because of variations in the temperature,pressure, and
density. These conditions have a profound effect on the propagation of
radio waves, as we will explain later in this chapter.
stratosphere is located between the troposphere and the ionosphere. The
temperature throughout this region is almost constant and there is little
water vapor present. Because it is a relatively calm region with little or
no temperature change, the stratosphere has almost no effect on radio
This is the most important region of the earth’s atmosphere for long distance, point-to-point communi-cations. Because the existence of the ionosphere is directly related to radiation emitted from the sun, the movement of the earth about the sun or changes in the sun’s activity will result in variations in the ionosphere. These variations are of two general types:
(1) those that
more or less occur in cycles and, therefore, can be predicted with
reasonable accuracy; and (2) those that are irregular as a result of
abnormal behavior of the sun and, therefore, cannot be predicted. Both
regular and irregular variations have important effects on radio-wave
propagation. Since irregular variations cannot be predicted, we will
concentrate on regular variations.
The regular variations can be divided into four main
classes: daily, 27-day, seasonal, and 11-year. We will concentrate our
discussion on daily variations, since they have the greatest effect on
your job. Daily variations in the ionosphere produce four cloud-like
layers of electrically-charged gas atoms called ions,
which enable radio waves to be propagated great distances
around the earth. Ions are formed by a process called ionization.