on the polar-coordinate graph. The vertical axis on the rectangular-coordinate

graph corresponds to the rotating axis (radius) on the polar-coordinate graph.

4-56. Look at figure 4-11, view A. The numbered positions around the circle

are laid out on the horizontal axis of the graph from 0 to 7 units. The

measured radiation is laid out on the vertical axis of the graph from 0 to 10

units. The units on both axes are chosen so the pattern occupies a convenient

part of the graph.

4-57. The horizontal and vertical axes are at a right angle to each other. The

point where the axes cross each other is known as the origin. In this case, the

origin is 0 on both axes. Now, assume that a radiation value of 7 units is

measured at position 2. From position 2 on the horizontal axis, a dotted line

that runs parallel to the vertical axis is projected upwards. From position 7

on the vertical axis, a line that runs parallel to the horizontal axis is

projected to the right. The point where the two lines cross (intercept)

represents a value of 7 radiation units at position 2. This is the only point on

the graph that can represent this value.

4-58. As you can see from the figure, the lines used to plot the point form a

rectangle. For this reason, this type of plot is called a rectangular-coordinate

graph. A new rectangle is formed for each different point plotted. In this

example, the points plotted lie in a straight line extending from 7 units on the

vertical scale to the projection of position 7 on the horizontal scale. This is the

characteristic pattern in rectangular coordinates of an isotropic source of

radiation.

4-59. The polar-coordinate graph has proved to be of great use in studying

radiation patterns. Compare views A and B of figure 4-11. Note the great

difference in the shape of the radiation pattern when it is transferred from

the rectangular-coordinate graph in view A to the polar-coordinate graph in

view B. The scale of radiation values used in both graphs is identical, and the

measurements taken are both the same. However, the shape of the pattern is

drastically different.

4-60. Look at figure 4-11, view B, and assume that the center of the

concentric circles is the sun. Assume that a radius is drawn from the sun

(center of the circle) to position 0 of the outermost circle. When you move to

position 1, the radius moves to position 1; when you move to position 2, the

radius also moves to position 2, and so on.

4-61. The positions where a measurement was taken are marked as

0 through 7 on the graph. Note how the position of the radius indicates the

actual direction from the source at which the measurement was taken. This

is a distinct advantage over the rectangular-coordinate graph in which the

position is indicated along a straight-line axis and has no physical relation to

the actual direction of measurement. Now that we have a way to indicate the

direction of measurement, we must devise a way to indicate the magnitude of

the radiation.

4-62. Notice that the rotating axis is always drawn from the center of the

graph to some position on the edge of the graph (figure 4-11, view B). As the

axis moves toward the edge of the graph, it passes through a set of equally

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