US2642529A - Broadband loop antenna - Google Patents

Description

Patented June 16 195 3 UNITED STATES PATENT OFFICE B OA AND LOOP ANTENNA Sidney Frankel, Bergensfield, N. J., assignor to International Standard Electric Corporation, New :York, 'N. X, a nQnati n f .Dslamere:

fi lm eai nt 9$e a1.N9- W9 9 "7 Claims. 1

This invention relates to antennae and is particularly directed to improvements in loop antennae having high radiation conductance and broadband characteristics in the ultrahigh frequency range. are adapted for 'nondirection'al -br'o'adcasting.

It is desirable in ultrahigh frequency b'roadcasting to effic'iently load the generator of the energy to be radiated as well as to prevent frequency selectivity of the radiator -system over ayw-ide range of frequencies. -Unfortunately, both these conditions have not heretofore been realized in one antenna structure. While the reactive components of the load'ma-y-b'e tuned out by the addition of reactances of compensating signs, the resulting Q is high and broadband characteristics are sacrificed.

An object of this invention is an antenna that has both broadband characteristics and high ra=- diation conductance.

A more specific object of this invention is a loop-type antenna that is nondirectional.

A still more specific object of this invention is a nondirectio'nal loop antenna of simple, rugged, and easy-to-"nake construction.

The objects of this invention are realized by a longitudinally slotted sheet metal cylinder with the conductors of a coaxial transmission line extending into one end and through the cylinder.

The edges of the cylinder slot are connected; re-

spectively, with the inner .and outer conductors and the annular space betweenthe cylinder and outer conductor constitutes a tunable cavity resonator electrically in parallel-with the impedance at the slot. n

The above-mentioned and other features and objects of this invention and "the manner ofattaining them will become apparent and the invention itself will bebest understood by reference to the following description of --preferred embodiments of the invention taken in conjunction with the accompanying drawing,"wherein:

Fig. 1 is a perspective view, partly in section, of a single slot antenna structure of this invention;

Fig. 2 is an end view of the structure of Fig. 1;

Fig. 2a is a circuit diagram of the principal electrical parts of the structure of Fig. 2; and

Figs. 3 and 4 are end views of multi-cavity modifications of the antenna of Fig. 1.

The antenna of this invention comprises a symmetrical smooth sheet metal cylinder 1 closed at one end'with plate 2 having a longitudinal slot 4 extending from end-to-end. A coaxial transmission line is telescoped into said cylinder through one end, inner conductor 5 and outer conductor The antennae of this invention 6 extending through to the end plate. The high frequency voltage between the inner and outer conductors are applied, respectively, to opposite edges of the slot i by radially disposed 'vanes 1 and 8. The edges of vane I are joined'in'c'o'ntinuous line contact to one edge of the cylinder slot and the outer conductor, While the vane i8 extends centrally through a window in the outer conductor Band joins the inner conductor t'o' the other edge of the slot. Openings 9 and I0 between thevane 8 and either side of the window may-be predetermined as hereinafter described.

in Fig. 2a. It has been found that the imped ance Z of the cavity resonator presented at the input opening II] to the transmission line may be adjusted to capacitive or inductive value for any applied frequency merely by tuning the cavity resonator to resonance at a frequency above or below the applied frequency. such tuning is most conveniently'effected by moving the partition l2 toward oraway from the opening 10. It is found -ifurther ,,that the 'impe'dance'presented by the outside slot 4 to the transmission line is capacitive -C and resistive R only, the absence of inductive' ilnpedance being expected I when it is recalled the antenna cylindcr is closed at one end and can link 'withlno electromagnetic lines of force. That -'is, radi'o' frequency current flows radially over the opposed faces of the vanes l and 8 and from one edgeiof th'e' sl'ot to'the other along the'ou'ter surf-ace of the cylinder, and since the cylinder sides and end are impervious to such currents there can be no self induced voltages. Now, according to an important feature of this invention, the capacitive reactance of the loop circuit may be precisely balanced out by an equal and parallel inductive reactance that can be obtained at the opening I!) to the cavity by adjustment of the tuning partition l2. The load thus presented to the transmission line can be made entirely resistive and because the conductor and dielectric losses are small the largest portion of the resistance is attributable to radi' ation. For the smaller range of spacings between 7 and 8, the shunt capacitance varies in- 3 versely with the spacing. The efiiciency of radiation of this antenna is high.

More uniform radiation, increased radiation conductance, and still broader band characteristics may be obtained by employing a larger number of slots. In Fig. 3, for example, four equally spaced slots I3, I l, I5 and it are shown, although a larger or smaller number may be used if desired. As in Fig. 1 the two edges of each slot is joined byvanes 1 and 8 to the outer and inner conductors, respectively, of the transmission line. Each of thewider vanes 8 extends through, without contacting, the windows the outer conductor so that the fields within the line are open to both the antenna slots l3-!6 and'to cavity resonators ll. Each resonator is tuned by the short-circuit partition [2. In case the number of segments of the antenna cylinder, for the operating frequency, is large, and the circumferential distance between slots is too small to accommodate the full length. of the cavity resonators, the resonators may be folded as shown in Fig. 4. By the placement of sheet metal walls a cavity of desired length may be coiled within the limits of each segment. It is suggested in Fig.4 thatvthe vanes and curved wall portions of each segment be fashioned from single pieces of sheet metal, copper being one metal that has good conductivity and is easily bent.

While there has been described above the principles of this invention in connection with sp e cific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of this in vention.

What is claimed is: 1. An antenna comprising a coaxial transmission line, a longitudinally slotted cylinder encircling and coaxial with the conductors of said transmission line, the outer conductor of said line having a slot in registry and coextensive with the slot of said cylinder, the edges of the cylinder defining the slot being joined throughout the length of the cylinder slot to the inner conductor and outer conductor, respectively, of said transmission line.

the space inside said outer conductor, and a movable vane in said annular space to adjust the dimensions thereof.

4. The combination comprising a transmission line with coaxial conductors adapted to conduct high frequency energy, a loop antenna comprising a sheet metal cylinder telescoped over and concentric with the outer conductor of said line and provided with at least one longitudinal slot, the outer conductor of said line being slotted .-over its length within said cylinder, means con- 2. An antenna system comprising a sheet metal 5 cylinder and, concentric conductors of a transmission line, said cylinder and conductors being coaxial and being provided with. registering longitudinal slots in the cylnder and outer conductor,

a first radialvane joining one edge of the cylinder defining the slot therein to one edge of the outer conductor defining the slot therein, a second radial vane extending through the outer conductor slot and joining the other edge of the cylinder defining'the .slot therein to the inner conductor.

3. An'antenna system as defined in'claim 2 in which the annular space between said cylinder 7 and outer conductor is in communication with pling said transmission line and said antenna through said slots for impressing high frequency voltage across the edges of said slotfrom the electric field within said transmission line and for exciting the annular space between the cylinderand said outer conductor of the line 5. The combination of a loop antenna and transmission line, said line comprising coaxial conductors provided with windows in the outer conductor and said antenna comprising a metal cylinder telescoped over said line and provided with aplurality of longitudinal slots in said cylin der registering and coextensive with said windows in the outer conductor of said line, a vane extende ing radially from the inner conductor centrally through each of said windows to one edge of a said cylinder defining each of said slots, and vanes joining the opposite edge of said cylinder defining each slot to one edge in said outer conductor defining each window.

6. The combination as defined'in claim 5 in.

outer cylinder being provided with a slot, the

edges of said cylinder defining the slot being electrically connected to the inner cylinders, the first annular space between the outer two cylinders being provided with a communicating opening into the second space between the inner two cylin ders, and a radial short circuiting vane in said first space and adjustable in a circumferential direction along said first space.

. SIDNEY FRANKEL.

References Cited in the file of this patent UNITED STATES PATENTS Name Date Blumlein Apr. 15, 194i Barrow Aug. 26, 1941 Lindenblad Jan. 14, 1947 Riblet Jan. 6, 1948 Buchwalter Nov. 30, 1948 Chu July 26, 1949 Hansen Oct. 11, 1949 Masters 1 June 6, 1950 Number

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