And Now the Mini-Antenna

Cluttering rooftops, bristling from satellites and planes, protruding from walkie-talkies and TV sets, antennas are both a symbol and a necessity of the communications age. To transmit and receive signals efficiently, however, antennas must often be inconveniently large. Their sheer bulk adds crucial pounds to the weight of spacecraft, causes extra drag on the otherwise streamlined surfaces of supersonic aircraft, and is a dead giveaway to the location of radio operators on the battlegrounds of Viet Nam. Now, because of the persistence of an Air Force scientist, antennas are about to be cut down to size.

Ten years ago, Edwin Turner, a civilian electrical engineer in the Air Force Avionics Laboratory at Dayton's Wright-Patterson A.F.B., became convinced that a large antenna could be duplicated electronically by a smaller device. The solution, he felt intuitively, was a miniature antenna with an active, built-in transistor circuit. Unable to perfect the mini-antenna himself, he turned to other electronics experts for help but was told repeatedly that his concept was not feasible. To work efficiently, they said, an antenna had to be physically at least one-quarter as long as the wave length of its design frequency. In the frequency range used by television, for example, this requires antennas at least a few feet long.

Stubby Arms. Finally, during a 1963 visit to Germany, Turner mentioned his idea to Physicist Hans Meinke, a micro wave expert whose research is partially financed by the U.S. Air Force. Meinke immediately grasped Turner's concept, volunteered to work on it, and was awarded an Air Force contract. Now, after four years of mathematical analysis and laboratory work, he has finally built several prototype models of the mini-antennas that Turner visualized. The simplest of Meinke's devices, which the Air Force calls Subminiature Integrated Antennas (SIA), consists of three stubby, pencil-sized arms, each at tached to one of the three terminals of a transistor. Combined with the electrical properties of capacitance, inductance and resistance in the antenna arms, the transistor forms a circuit that has a low resonant frequency and thus "looks" physically bigger to incoming radio waves. Using the receiver to which it is attached as a power source, it can amplify by a factor of ten to 100 the small currents induced in the antenna by radio waves. Eliminated Ears. "Although the theory is pretty complicated," explains Turner, "we have in effect substituted a short antenna carrying a large current for a long antenna carrying a small current." Thus an SIA only a few inches long and weighing only an ounce or two is sufficient for the efficient reception of normal television signals over an extremely wide band in the 100-megacycle range.

By using SIAs, says the Air Force, it will be able to eliminate 10 lbs. to 500 lbs. from from the weight of aircraft and space space vehicles. Built-in SIAs will also eventually eliminate the conspicuous whip antennas on military radios and their civilian counterparts. And when the mini-antennas are mass-produced, Turner says, manufacturers will be able to build build them inside TV sets at a cost of only $2 or $3 apiece, eliminating familiar "rabbit ears" and costly, unesthetic roof antennas.

This file is automatically generated by a robot program, so reader's discretion is required.