Patents Of Interest to Amateur Radio Operators

Air Force Log Periodic Antenna

Fig 1—W8JF's log-periodic antenna consists of several concentric coplanar loops mounted about a balanced transmission line feed point.

Antenna Patents
Fig 2—Telex Communications' Parasitic Array With A Driven Sleeve Element. Elements 30 and 32 allow operation on the 10-m band.

This month's column features excerpts from recently issued patents in the fields of antennas and diversity receiving systems. Among the antenna patents, Jim Fisher, W8JF, was granted patent 4,595,930 for his design of a Planar Log-Periodic Quad Array r Fig 1 shows this antenna as consisting of several concentric coplanar loops mounted about a balanced transmission line feed point. Two twisted balanced lines extend diametrically from the feed point and drive each of the loops at two opposite corners.

The inventor terms this configuration as an improvement over the more conventional three dimensional log-periodic quad array. In this design, the current is distributed symmetrically in a single plane, producing a more uniform feed-point impedance over wide bandwidths. The planar LP array seems to have use in several applications, either as a standalone muitiband antenna or as a driven element in a muitiband parasitic array.

Telex Communications has patented a Parasitic Array With A Driven Sleeve Element (patent 4,604,628). The driven element is cut for 20 m and includes traps for 15 m. Operation on 10 m is provided by "open-sleeve" elements 30 and 32 (Fig 2) which are parasitically driven from the driven element. Element 30 is resonant in the 10-m band. Element 32 is shorter than element 30 by the distance between the elements. In addition to providing driven-element operation on 10 m without additional traps, the sleeve elements are claimed to reduce the SWR on the other bands.

Another muitiband antenna is described in patent 4,593,289, owned by Butternut Electronics and entitled MultiBand Dlpoie Antenna With Matching Stubs. The antenna, shown in Fig 3, uses a shortened bow tie-shaped dipole to resonate on 20,15 and 10 m by gamma rods driven from a centrally extending conductor. Gamma rods 122 and 124 resonate the antenna on 15 m, while rods 90 and 92 resonate the antenna on both 20 m and its harmonic, 10 m.

The "wingspan" of the 20- and 10-m version is approximately 12 feet, about one third the size of a full size 20-m dipole. The bandwidth of the antenna on

1 Notes appear on page 15. 14 qex each band is said to be about 600 kHz. Parasitic elements of similar design can be added to form a compact unidirectional array. In the Obvious-ln-Hindsight2 class of inventions is Honeywell's patent 4,584,716. Called the Automatic Dual Diversity Receiver, it is a simple diversity system for receiving signals concurrently broadcast on two frequencies, such as

Broadcast Band Antenna
Fig 3—The Multi-Band Oipofe Antenna With Matching Stubs. Its theory of operation is explained in the text.

NBS broadcasts on 5 and 10 MHz. No switching circuitry is involved. Instead, a broadband front end provides both the 5-and 10-MHz signals to a mixer. The local oscillator frequency is selected midway between the two receive frequencies (ie, 7.5 MHz) thereby producing an IF signal consisting of both received signals at 2.5 MHz. The remainder of the receiver circuitry is conventional and serves to demodulate the IF signal so as to recover the audio from both the 5- and 10-MHz broadcasts.

Preposterous Patents

On the lighter side, the Patent Office does not pass judgment on an invention's technical merits. It only checks to confirm that the invention is new, useful and nonobvious. Sometimes, technically questionable inventions slip by. One example is patent 4,584,586, a VHF-UHF TV antenna shown in Fig 4. A brief excerpt from the patent illustrates this point:

"It is believed that RF signals are magnetically drawn along patterns that conform to the magnetic field lines of the earth. Therefore, the configuration of the present array, which itself bears a general resemblance to the magnetic flux lines of the earth, contributes to its effectiveness. That is, it is believed that the shape of the present array contains spherical curvatures which conform to the curvature of the magnetosphere of the earth..."

The patent goes on to note that the hollow space inside the 0.325-inch tubing, from which the antenna is made, acts as a waveguide within which the signals captured by the array are carried to the twin-lead feed line.

Other recent patents of potential

Balanced Feedline

interest to the amateur community are:

4,578,819, Sony's Space Diversity Receiver.

4,580,092, Pocket Size Antenna Match Indicator For VSWR Measurement, owned by USA (through the Secretary of the Air Force).

4,591,867, Attenuation Apparatus For An Aerial Array (isolates transmit and receive antennas mounted on the same tower), owned by Telefonaktiebolaget LM Ericsson,

4,608,572, Broad-Band Antenna Structure Having Frequency- Independent Low-Loss Ground Plane (a variant of the discone antenna), owned by Boeing.

4,608,574, Backfire Helix Antenna, owned by USA (through Secretary of the Air Force).

Complete details on each of these inventions can be found in the associated patent. Copies of US patents are available for $1.50 each from The Commissioner of Patents and Trademarks, Washington DC 20231 (expect about a four-week delivery time).

Caveat: The US Patent laws provide that "Whoever without authority makes, uses or sells any patented invention, within the United States during the term of the patent therefor, infringes the patent."

Information on these patented inventions is printed here in accord with QEX's stated purposes of (1) providing a medium for the exchange of ideas and information; (2) documenting advanced works in the Amateur Radio field; and (3) supporting efforts to advance the state of the Amateur Radio art. These inventions may not be practiced, without permission of the patent owners, until seventeen years after the patents' issue dates. Nonethe-

Fig 4—Inventions that pass through the Patent Office are not Judged on their technical merits. This VHF/UHF TV antenna claims that because of its shape, its operation conforms to that of the Earth's magnetosphere.

less, it is believed that publicity of such advances in the state of the art will broaden the perspective of amateur experimenters and promote future technical advances within the amateur community.

Notes

1J. Fisher, "Development of the W8JF Waver-am: A Planar Log-Periodic Quad Array," Antenna Compendium, p 50. 2B. Conwell, "Patents," QEX, Apr 1986, p 16.

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