US2081162A - Antenna - Google Patents

Description

May 25, 1937. A. ALFORD v 7 2,081,162

ANTENNA Filed April 50, 1955 FIG. I G 7 8 FIG. 2

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ANDREW Al. FORD AT ORNEY Patented May 25', 1937 2 031,152:

UNITED STATES PATENT or ce Andrew Alford, New York, N. Y., assignor to Mackay Radio and Telegraph Company, New York, N. Y., a corporation of Delaware Application April 30, 1935, Serial No. 18,996 I 9 Claims. (cram-23) This invention relates to antenna systems, and flected, the radiation in direction 16 is reduced more particularly to a unidirectional antenna to zero. This requires an impedance capable-of. which may be used for the reception or transdissipating the energy at the same rate asit remission of short wave radio messages. ceives energy from the radiator. In a practical- It is the object of the present invention to coninstallation, where the impedance is usually struct a unidirectional transmitting or receiving called upon to dissipate large amounts of energy, antenna without the use of the customary resuch an impedance is of expensive construction. flectors, impedance matching device or termina- Another proposed arrangement, designed to actions. complish the same purpose, is to make the ra- 10 With this object in view an open-ended antenna diators so long that practically all of the energy 10 wire, preferably connected with a transmission will be radiated on the outward journey. When line, is supported at or near its open end in One considers'that a V with sides 16 wavelengths proximity to the ground, whereby the attenualong provides a front-to-back ratio of less than tion of currents traversing the antenna wire will 5 decibels, it is apparent that enormously long be so great near the open end that the reflection radiators will be required before the desired re- 15 of waves towards the other portions of the ansult may be accomplished to a reasonable extent. tenna wire and the transmission line will be I have found, on the other hand, that by maksubstantially completely prevented. A system ing the outer ends of the radiators trail very close. built up of such antenna wires will radiate in one to the ground, I can realize substantially uni- 2O direction only. lateral directivity with open-ended radiators of 20 My invention may be best understood by remoderate length. Thus, for example, in Fig. 2, is ferring to the following description in conjuncshown the side elevation of a typical radiator of tion with the accompanying drawing in which-- my invention, i. e., one side of a V. In Fig. 2, Fig. 1 shows a plan view of the antenna systhe ground surface 21 is shown level merely for tem, and convenience in delineation, only the relative dis- Fig. 2 is a perspective of one of the pairs of tance from the ground of the various portions of sagging radiators of Fig. 1. the conductor being important in a practical in- Referring to Fig. 1, I is a source of modulated stallation. The pole 22 supports the transmisradio frequency energy which is fed by any wellsion line end of the wire 23-17, the end 23 beknown coupling means to the transmission line 2. ing preferably about one-quarter wavelength 30 The latter is of the usual construction, its sole above the ground 2|. It is understood that when function being to transfer efficiently the energy a pole is said to support a wire that the cusit receives from the source I to the system of tomary construction using insulators is implied. open-ended radiators 3-6, 4-'|, 58, 9I2, The outer end of the wire 23-11 is supported by l0l3, and H--I4. These radiators are conthe very short pole l8 (five to ten feet high) al- 35 nected in pairs at successive points along the lowing sufficient sag as shown so that a considtransmission line, each pair in plan view forming erable portion of the wire runs close to the ground. a V as, for example, the pair 5-8 and H-I4. If required, the wire may be continued to an- The sides of the Vs formed by the other pairs are other similarly short pole 20 where the end I 9 is substantially parallel to the radiators 5-8 and supported. The portion of the wire |'ll9 runs 40 |4 close to the ground, i. e., about 5 feet above the Ordinarily, such an arrangement of radiators ground. radiates principally in the two directions shown The antenna of my invention will not work by the arrows I5 and I 6 which are in the verequally well over all types of ground. For extical plane bisecting the angle formed by the rample, over a relatively per ect ndu t 45 diators and is, therefore, said tobe bilaterally diground, such as sea water or salt marshes, I rective. It is desirable, however, to achieve unihave found that satisfactory results are difficult lateral directivity, e. g., no radiation in direction to obtain. Likewise, over a relatively insulat- IB and substantially all of the radiation in direcing ground, the results would doubtless be untion I 5. The practice generally followed in the satisfactory. Over intermediate or partially con- 50 art has been to terminate the outer ends in an ducting ground, such as would be encountered in impedance which will absorb all that remains a large percentage of installations, I have found of the outward flowing energy which reaches the that the attenuation per unit length in the porouter ends so that none is reflected back towards tion of the radiators very close to the ground the transmission line. Since no energy is reis enormously greater than in the remaining por- 55 tion further removed from the ground. In this invention, I utilize this high attenuation to reduce the outward travelling energy on the radiators to a negligible quantity so that substan tially none is left to be reflected. Furthermore, this is achieved with the radiating conductors extended only a moderate distance a few feet above the ground.

In practicing this-invention it is preferable to test the ground conditions in advance by installing an inexpensive test line such as portion l1|9 running about 5 feet above the ground. It is a relatively simple matter to measure the attenuation per unit length of the test line. This test provides information which enables one to estimate the attenuation of that portion of each radiator of the proposed antenna which will run close to the ground This attenuation should be made as large as practicable but need not be excessively great. It has been determined by experiment that an attenuation of ten to fifteen decibels is already sufficiently great to be useful. Over suitable ground this-may be attained with moderate lengths of wire. Furthermore, the construction of the portion near the ground is relatively inexpensive and may be extended to occupy any additional available space. Should the space available for the outer portion of the radiators be restricted, it is not necessary to extend the outer portions in the same direction as the higher or radiating portion. The resulting antenna system is substantially aperiodic so that the length is not critical with respect to wavelength. In determining the proper angle for the Vs, only the length from 23 to the bottom of the sag need be considered as active and due allowance must be made for the slope of this active portion in order to secure the proper angle of elevation for the beam.

Where more than three pairs of radiators are employed it will be worth while to provide impedance matching between the transmission line and the successive pairs of radiators in the manner well understood by one skilled in the art. In certain cases satisfactory results may be obtained with one or two pairs of sagging radiators without any impedance matching devices in the transmission line.

What I claim is:

1. An antenna system comprising a line, and antenna wires connected therewith, and each wire for a considerable portion of its length from the free end being positioned closeto the ground so as to have an attenuation per unit length greater than that of the remainder thereof.

2. An antenna system comprising a transmission line, and antenna wires connected therewith and forming a V, and each wire for a considerable portion of its length from the free end being positioned close to the ground so as to have an attenuation per unit length greater than that of the remainder thereof.

3. An antenna system comprising a transmission line, and antenna wires connected therewith and forming a plurality of parallel Vs, and each wire for a considerable portion of its length from the free end being positioned close to the ground so as to have an attenuation per unit length greater than that of the remainder thereof.

4. An antenna system comprising a transmission line, means for supporting said line at a certain elevation, two antenna wires with one end connected to the line at said certain elevation, and means for supporting the other ends at a substantially lower elevation than the other portions, the length of said other portions being a substantial percentage of the total length of the antenna wires and being positioned a few feet above the ground so as to make the antenna substantially uni-laterally directive.

5. An antenna system comprising a transmission line, means for supporting said line at a certain elevation, two antenna wires forming a V and with one end connected to the line at said certain elevation, and means for so supporting the other ends that for a considerable portion of the length therefrom such antenna wires are at a substantially lower elevation, whereby said portions of the wires have substantially higher attenuation per unit length than the portions nearest the line.

6. An antenna system comprising a line, means for supporting said line at a certain elevation, an antenna'wire with one end connected to the line at an elevation a substantial part of a wave length above ground, and means for supporting ,a substantial length of the free portion of the wire at a substantially lower elevation with said substantial length running close to ground so as to increase the attenuation of waves traversing said antenna wire thereby to reduce substantially the reflection of said waves over the antenna wire towards said line.

7. An antenna system comprising a line, a pair of radiators connected therewith at an elevation above the ground of the order of magnitude of a quarter wavelength, and means for supporting the outer ends of said radiators with a substantial portion of the length thereof from the outer endsnear the ground so that the attenuation offered by said substantial portions of the radiators in proximity to the ground to the waves traveling therethrough will substantially completely prevent the reflection of waves over the radiators towards the transmission line.

8. An antenna system according to claim '7, and in which a plurality of pairs of said radiators are connected with the transmission line substantially parallel with one another.

9. An electrically long antenna comprising a wire, one part of which is supported at a distance above ground equal to a substantial part of a wave length and another part of which is supported very close to ground, said second part being of such length that the antenna is substantially uni-laterally directive.

ANDREW ALFORD.

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