Date of Award

Spring 1939

Document Type

Thesis

Department

Chemistry & Physics

Abstract

An understanding of the mechanism by which energy is radiated from an antenna is the purpose of this thesis. It was generally believed, until 1920, that radio waves traveled in an ever expanding circle, like the ripples created by a pebble falling into still water. If left to their own devices, radio waves from a vertical antenna will travel in this manner, but as the number of broadcasting stations increased it was necessary to control these radiations. Ways have been devised to make the waves travel in the form of a shamrock, a four-leaf clover, a double watermelon, or an airplane propeller. These are only a few examples of what are called field patterns. A radio engineer named Southworth explored this field and discovered 60 possible patterns for a two tower antenna installation. This same man worked out all the possible combinations up to 48 towers, and in this work discovered that a pencil of radio energy no wider than a highway which stretched for thousands of miles could be formed. This system is now used in trans-ooeanic broadcasting service. In 1927 the United States Government, by the creation of the Federal Communications Commission, placed restrictions as to frequency and power on all broadcasting stations within the territory belonging to the United States. This action resulted In an incomplete coverage of the broadcasting station’s territory. Increasing power was out of the question so the only way was to use a more efficient directive antenna. In the fall of 1933, WIND, at Gary, Indiana, was the second station in the United States to use a directive antenna. The purpose of the antenna was to concentrate as much energy as possible in Chicago, and not waste it covering Lake Michigan, Mae system worked well and established definitely the value of directive antennas.

The merit of a directional antenna is most conveniently measured in terms of the antenna gain, which is defined as "the power that must be supplied to a standard comparison antenna to radiate a given field strength in the desired direction, divided by the power that must be supplied to the directive antenna to accomplish the same result." A gain of 100 means that the directive antenna requires only 1/100 as much power to produce a given field strength in the desired direction as does the comparison antenna. The comparison antenna is usually taken either as a wire one-half wave length long and at an arbitrary orientation and height above the earth, or as a very short vertical wire.

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