US2153298A - Aerial - Google Patents

Description

April 4, 1939. E, Q CORK 2,153,298

AERIAL Filed NOV. 21, 1936 INVENTOR EDWARD CECIL CORK ATTORNEY Patented Apr. 4, 1939 UNITED STATES PATENT OFFICE signor to Electric &

ited, Hayes, Middlesex,

company Musical Industries Lim- England, a British Application November 21, 1936, Serial No. 112,024 In Great Britain November 30, 1935 4 Claims.

This invention relates to aerials and isconcerned with aerials for the reception of carrier wave signals of short wave lengths such as are encountered in the reception of television signals.

The form of a short wave aerial is dictated chiefly by the electrical characteristics which it is desired that the aerial should have; for example, a dipole aerial is usually composed of a conductor or a pair of conductors, the physical length of which is equal to one-half of the carrier wave length, the two arms or portions of the aerial being arranged to lie substantially wholly in the same straight line with the result that the overall length of the aerial corresponds substantially to one-half a wave length. The radiation resistance, and the reactance at frequencies slightly removed from. the resonant frequency of the aerial are further important electrical characteristics, the reactance of the aerial, together with the radiation resistance, determining the effective selectivity.

In some circumstances, for example, where it is desired to erect an aerial within a limited space, it may prove impossible to employ an aerial of the form usually adopted when a certain state of electrical characteristics is desired. Thus, the space in which the aerial is to be erected may be insufficient to permit the use of a straight wire dipole. It is not desirable to reduce the overall dimensions of the aerial by reducing the physical length of the conductor to the required dimensions, since, in this case, the aerial is not self-tuned at the carrier frequency and will, therefore, require a loading inductance to effect tuning. Since the loading inductance will have at any side band frequency a greater ratio of reactance to resistance than the length of conductor it replaces, the selectivity of the aerial loaded in this manner will be greater than that of the plain dipole, that is'to say, less suitable for the reception of a wide range of side band frequencies, more especially as the radiation resistance of the shorter conductor will be less.

It is, therefore, the chief object of the present invention, to provide an improved aerialsuitable for erection in a limited space without shortening the physical length of the conductor or conductors but in which the overall length of the aerial is reduced while, at the same time, the variation of electrical characteristics of the aerial due to the reduction in its overall length are counteracted.

According to the invention, a short wave aerial for the reception of a carrier Wave and a wide side band range of frequencies is provided comprising a conductor, the physical length of which is approximately equal to a half wave length of the carrier frequency, and which is bent, coiled or otherwise arranged so that its overall length is less than that of a half wave length and wherein, for the purpose of maintaining an adequately low selectivity, the surface area of the conductor is increased so as tocounteract or substantially counteract the increase of selectivity that would otherwise be produced by the deformation of the conductor. I

Thus, by bending, coiling or otherwise arranging the conductor, the aerial can be disposed in a relatively confined space, but since the deformation of the aerial itself entails a reduction of the radiation resistance thereof, while the reactance thereto is not correspondingly reduced, the selectivity of an aerial deformed in this manner is greater than that of an undeformed aerial. Hence, the selectivity is restored to the required low value by increasing the surface area of the conductor, for example by using as the conductor a wide fiat strip, or several conductors in parallel, the reactance of which at any side band frequency is considerably less than a single conductor of relatively small area. The wide flat strip aforesaid may be made of copper or other suitable conducting material, and in place of using a strip of copper, metal gauze or foil may be used.

In some cases the aerial may be constituted by an array of conductors, the physical length of each of which is approximately one-half wave length and being separated by a relatively large distance and fed in parallel at their centers. An aerial of this kind, in order that it may be erected in a limited space, may have one or more of the elements deformed as aforesaid and constructed so as to counteract the effect produced by the deformation.

An aerial constructed in accordance with the present invention by virtue of its low characteristic impedance has a relatively low reactance.

In order that the said invention may be clearly understood and readily carried into effect, the same will now be more fully described with reference to the accompanying drawing which illustrates one embodiment of the invention.

As shown, the aerial is composed of a pair of elements I and 2, constituting the conductor, the physical lengths of each element being approximately one-quarter of the operating wavelength, the elements being fed at theadjacent ends by means of a concentric feeder, one of the elements being connected to the central conductor of the feeder and the other to the sheath thereof, the aerial thus constituting a half wave length dipole. The elements, in order to reduce the overall length of the aerial, have their ends bent at right angles as shown, or at any other suitable angle, so that each element is of a substantially L-shape. The elements are. mounted upon a support 3, which may be in the form of a pole or wooden frame with the interposition of suitable insulators, not shown, so that the vertical limbs of the element lie in substantially the same straight line. The conductor has, therefore, a substantially Z-shape. For an aerial for the reception of signals on a carrier wave length of about 7 meters, each element may be composed of copper strip about 6" wide and about thick, the vertical limb of each element being about 4 feet long, while the bent end of each element is about 1 /2 feet long. In the example shown, the adjacent ends of the elements I and 2 are connected to a feeder system as aforesaid, the feeder system being associated with a rejector (i. e., tuned trap circuit) in the form of a wire conductor connected at one end to the sheath and disposed substantially parallel to the sheath in the manner described in the specification of British Patent No. 438,506. In the drawing, the reference numeral 4 indicates the feeder which, as aforesaid, is associated with a rejector 5 connected to the element, the feeder being supported adjacent to the inner ends of the elements I and 2 by a suitable support 6. The rejector 5 serves to prevent the flow of current at the signal frequency along the outside of the sheath of the feeder.

In an aerial of the form described, there is a concentration of distributed capacity at the ends of the aerial elements remote from the feeder; the distribution of the current in the aerial is thus more uniform than in the case of a straightwire dipole aerial.

It is not possible to give a formula for determining the increase of area necessary, having regard to the deformation of the conductor and, consequently, the required area can best be determined empirically.

I claim:

1. A short wave aerial for the reception of a carrier wave and a Wide range of side band frequencies, comprising a conductor the physical length of which is approximately equal to a half wavelength of the carrier frequency and a feeder system coupled to the midpoint of said conductor, said conductor being so constructed and arranged that its overall length is less than that of a half Wavelength of the carrier frequency, the surface area of said conductor being relatively large compared to a straight aerial of the same physical dimensions, whereby the selectivity that would otherwise be produced by the arrangement of the conductor is substantially counteracted, said surface area being so arranged that the distributed capacity of the aerial increases toward the ends of said conductor.

2. A short wave aerial for the reception of a carrier wave and a wide range of side band frequencies, comprising a conductor the physical length of which is approximately equal to a half wavelength of the carrier frequency, said conductor being so constructed and arranged that its overall length is less than that of a half wavelength of the carrier frequency, the surface area of said conductor being relatively large compared to a straight aerial of the same physical dimensions, whereby the selectivity that would otherwise be produced by the arrangement of the conductor is substantially counteracted, the surface area of said conductor being composed of a plurality of adjacent spaced wires in parallel relationship with respect to one another.

3. A short wave aerial for the reception of a carrier wave and a wide range of side band frequencies, comprising a conductor the physical length of which is approximately equal to a half wavelength of the carrier frequency and a feeder system coupled to the midpoint of said conductor, said conductor being so constructed and arranged that its overall length is less than that of a half wavelength of the carrier frequency, the surface area of said conductor being relatively large compared to a straight aerial of the same physical dimensions, whereby the selectivity that would otherwise be produced by the arrangement of the conductor is substantially counteracted, the surface of said conductor being composed of a wide strip of electrical conducting material said surface area being so arranged that the distributed capacity of the aerial increases toward the ends of said conductor.

4. A short wave aerial for the reception of a carrier wave and a wide range of side-band frequencies, comprising a conductor the physical length of which is approximately equal to a half wavelength of the carrier frequency and a feeder system coupled to the midpoint of said conductor, said conductor being of general Z form and so constructed and arranged that its over-all length is less than that of a half wavelength of the carrier frequency, the surface area of said conductor being relatively large compared to a straight aerial of the same physical dimensions, whereby the selectivity that would otherwise be produced by the arrangement of the conductor is substantially counteracted said surface area being so arranged that the distributed capacity of the aerial increases toward the ends of said conductor.

EDWARD CECIL CORK.

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