US2311872A - Antenna system - Google Patents

Description

1 Feb. 23, 1943. M. A. ROTE ANTENNA SYSTEM Filed April 12, 1941 2 Sheets-Sheet 1 ATTORNEY WWI/14521477 Feb. 23, 1943. ROTE 2,311,872

' ANTENNA SYSTEM Filed April 12, 1941 2 Sheets-Sheet 2 IN VENTOR Ma V/A/ fl- #072 I g A TTORNE Y Patented Feb. 23, 1943 Melvin A. new, Newark, N..l, assigns-r .to Fed eral Telephone & Radio Corporation; a-corporation urn-aware Application=April-12, 1941, Serial N'. -388;223 Claims; (01. 25-0 33? This invention; relates to improvements in antenna systems. and more particularlyto antenna. systems :Of the high. frequency loop type.

High. frequency lo'op type antennae have been proposed having certain desirable features in simplicity of construction; Gne such type of high frequency loop antennae is disclosed in: the applicationlof Andrew Alford, entitled-Antenna systems, Ser. No- 270,173,,filed'April-25, 1939, Patent No.. 2,283,897,. granted May 26, 1942. This highzfrlequency loop: antenna particularly when designedlto -operate with two radiant acting elements surfers from v thec-difiiculty that. voltage maximal: occur at the. feeding point of the loop. 'I'hisloop when" applied .to aircraft has the voltage maximum points aligned with the. longitudinal axis of the craft. Thus, sleet formations tend to detune .the loop,.pbei1'1g- "deposited .at. 'a relatively high impedancepoint. This can be partly overcome by -v providing-1a covering Var-- rangementsaround the loop but such covers crease-theair drageandlare', therefore; undesirable. The constructionzof the loopxdoes not lend itself: readily to mountingliif .1 turned attright angles on thecraft;

Since these loops have current maximaat lat, erally; disposed points-oft the craft', they. are: slightly more effective onthe sidesiof the aircraft than longitudinally. type of charam teristic is not generally desirablesince the signals received usually come-from tl-ie fi ont or rear of the'craft.

Furthermore; when sueh-a loop-is mountedabove-thefuselageof the craft the-distorting f fects'ofthe-airplane -parts-themselves tend tofurther accentuate the 'elliptieity of the hormon tal characteristic;

It is aprincipal object of my invention-tome: vlde a. loop antenna forhigmfrequencyenergy in which'th'ese difficulties are minimized or'com pletely overcome.

Ifi accordance with a feature of 'myinvention a loop of the general character described above but arranged to have w more than two current maxima around the peripherj thereof is provided: so that the characteristic pattern of the in therplane of the loop issub'stantially circular or elongated in the direct-ion of the longitudinal axis .ofan aircraft, or elongated in thisaxisto.

The objects and features "of: my invention will be :more: clearly understood-from the particular description-of my invention'zma'd'e with reference 1 to the accompanyingdrawings, in which- Fig;;l shows diagrammatically one-form of my invention;-

Figt 21is'a modified: antenna arrangement incorporating the features of my invention;

Figsy3 and 4 are experimental curves in polar I coordinates of the field pattern illustrating the performance of anantenna of the form of Fig; 2;

Fig; 5'is a 'stillfurthermodified embodiment of my invention which has characteristics similar to thearrangement of :Fig. 2 when properly adjusted; and g Figs; 6;? and 8 are still further modified embodiments incorporating the features of my invention.

. InFig." 1 is shown aloop antenna consisting of threeradiant acting members 1, 2 and 3, arranged to form; asubstantially enclosed peripheral space: These elements are substantially equaliinrlength andare each short with respect tothe operatingwavelength preferably in the order oftwo-tenths of a'wavelength' long. v Connectedto the adiacenteends of sections I, 2; 2, 3 and 3, l, are non-radiating, transmission lines A, 5, 6=. Theconductors 4A';;5Aand6A,-and 4B, 5B, 613; may 'berespectively interconnected and coupledto acommon translating'device 1 over a transmissionrlines; Each of lines 4, 5 andli are adjusted-to have substantially. equal electrical lengths and impedancesr 7 By this arrangement current maxima are pro duced at the centers of each. of the members l,- 2 and-- 3. The current distribution around the entire periphery ofthe antenna system is thus maintained fair-ly constant and a substantially circularradiation-pattern: in the plane ot the loop ;is\produced-. Furthermore, the energy-radiated or-rcollectedby the loop will be polarized with: the electric .vector in planesparallel. to the loop.

In. thearrangement of Fig.- .l complications arise because symmetry must be maintained in compensate the distorting effects of the aircraft" the-radiating members and feeding lines inorder tQ'. maintain; proper. balance a and secure uniform feeding of the radiatingmembers- Furthermore,

4 a the loopaof Fig; 1 is not of-suoh-construction as to readily lend itselt tesuitablesupport onthe fuselage etanzaircraftt. V

The structu-ral arrangement shown in- Fig. 2 overcomes-the disadvantages present the loop of Fig; 1;. m this arrangement the a radiant act lngportiomoftheantenna consists of three members 20,224 andgZZ, preferably, but notnecessari ly of .equaL-length forming a substantially closedperiphery-.- These members need-not be symmetrically -arrangedas in the. case of Fig, l,

Member 26 is coupled at its opposite ends to members 2| and 22, respectively, by means of a capacitive coupling which may comprise merely an overlapping portion of the respective memers. This structure, utilizing the inherent capacity of overlapping conductors may be readily availed of when the antenna is made of flat strips, but in the case of other conductor shapes the provision of separate coupling condensers or other constructions permitting suitable capacitive coupling must be provided. In the case of Fig. 2 a translation device 21 is coupled over a transmission line 28 to the free ends of members 2 I 22.

This arrangement provides a current maximum at the center of conductor 26 and two current maxima intermediate the ends of conductors 2|, 22. By adjusting the coupling capacities between members 26 and members 2|, 22, the current maxima in members 2 I 22 may be shifted toward or away from the junction point of transmission line 28 with members 2 I, 22 to vary the distribution in the plane of the loop. By decreasing the capacity at 24, 25, the current maxima are shifted toward transmission line 28 and a field pattern elongated in the plane of symmetry of the loop is achieved. By increasing capacities 24, 25, the current maxima in members 2 22 are shifted away from transmission line 28 and a more nearly circular pattern is produced.

In Fig. 3 curve 36 shows the field pattern experimentally obtained from a loop antenna of the prior art. It will be noted that curve 30 has its major axis in such a direction that it would be laterally disposed to an aircraft if it were mounted thereon in the conventional way. Curve 3| is a pattern plotted utilizing an antenna of the form shown in Fig. 2 having the dimensions indicated in the small diagram in the plot of the curve. It will be noted that curve 3| has its major axis at right angles to the major axis of curve 36, thus securing a more desirable distribution. These measurements were made for both types of loop at 110 megacycles.

In Fig. 4 curve 40 illustrates another experimental pattern obtained at 110 megacycles using a loop similar to Fig. 2, in which the current maxima are adjusted in members 2|, 22 to substantially the midpoints of these members. It will be noted that the pattern here is substan tially circular.

It should be further noted that with the an tenna structure of Fig. 2 a voltage node occurs substantially mid-way of member 20 and a relatively low voltage may be similarly obtained at the junction point of transmission lines 28 with members 2|, 22. Accordingly, when such a loop is mounted in the normal manner on an aircraft fuselage, the troublesome effects of sleet formations at high voltage points is greatly reduced.

The arrangement shown in Fig. is similar to that shown in Fig. 2, except that in place of a unitary member 20, the energy is supplied at this end of the loop necessitating the provision of two sections 50, 5| connected to supply line 52. Two members 53, 54 corresponding to 2| 22 of Fig. 2, are capacitively coupled through capacitances 55, 56 with sections 56, 5|, respectively, and a condenser 51 is provided to intercouple the other end of the member 53, 54. In this arrangement, each of the capacitors 55, 56 and 51 may be made adjustable to secure the desired current distribution in the loop. The same distribution of current may be achieved in this arrangement as in the arrangement of Fi 2. This loop, however, has the advantage that a low impedance line 52 may be used for coupling the loop to a translating device whereas the arrangement of Fig. 2 requires a relatively high impedance transmission line. In addition the use of a low impedance line provides a more efiicient transfer of energy without the use of impedance matching elements. Furthermore, the tuning of the loop is less critical with this connection than with the previously described connection.

In Fig. 6 a further modification of my invention in which four current maxima are produced around the periphery of the loop is disclosed.

This antenna comprises four radiant acting members 60, GI, 62, 63, arranged to form a substantially closed periphery. A transmission line 64 is connected to members 60, 6|, so that coupling to a suitable translator may be made. The other end of members 60, 6|, and adjacent ends of members 62 and 63, are interconnected by a transposed tie-line 65 and the other ends of members 62, 63 are arranged in overlapping relation. Thus, the current distribution in conductors 62 and 63 starting from a current minimum at their open ends will be effectively in overlapping relationship, producing by addition current maxima either in the center or on both sides of a plane of symmetry. Similarly, two current maxima will exist in conductors 60, 6|, generally located intermediate the ends of these conductors. Adjustment of the current maxima can be made by bridging a tuning element, such as the condenser, across line 65, preferably at its midpoint. Adjustment of this tuning element will serve to shift the maxima considerably in conductors 60, 6|, but will have only slight effect on the position of the maxima relative to conductors 62, 63.

Figure 7 illustrates a loop antenna similar to that of Fig. 6, but in place of the tie-line 65, two open ended transmission line sections 10, H, are provided. This antenna will produce substantially the same type of current distribution as is achieved in the circuit arrangement of Fig. 6. However, the distribution may be readily varied by adjusting the length of lines I0, 1|. These lines should, of course, be adjusted the same amount to maintain symmetry of the system.

If desired, transmission line sections 10, ll, may be replaced by coupling condensers, preferably variable condensers.

In Fig. 8 a preferred structural arrangement of the antenna circuit shown in Fig. 7 is illustrated. In this arrangement the transmission line sections I0, II, are formed by continuing elements 60, 62, and 6|, 63 in substantially parallel overlapping relation. This is in efiect merely a straightening of the two conductors of transmission lines 16, so that they are substantially aligned with the periphery of the loop. This loop arrangement will produce precisely the same type of field pattern as will the loop of Fig. '7. However, from a mechanical standpoint, particularly for mounting on aircraft, air resistance is considerably reduced by this construction since cross structural elements are avoided. V

In each of the arrangements of Figs. 6, 7 and 8, the same advantages with respect to the shaping of the pattern and the avoidance of excessive sleet formation on high voltage points is achieved. i

It should be noted that in the various arrangements according to my invention, particularly as disclosed in Figs. 2 to 8, the various radiant acting members are arranged to form a tially in each of the radiant acting members is provided. At least one of these current loops is produced in a radiant acting member or in the members at a point less than half the length of the particular member or members from this plane of symmetry.

While I have diagrammatically disclosed a number of embodiments of my inveniton, it is clear that various changes in the structural arrangement may be made without departing from the scope of my invention. The loops may be made in substantially any geometric form which will provide a single axis of symmetry with respect to each of the loop constructions.

A preferred structural arrangement for use on aircraft is one in which the loop, as a whole, has substantially a rectangular or square form. This loop is made with the longitudinal members of a bomb shaped streamline form and with the lateral members in the form of streamlined connecting struts, so that the whole structure forms a hollow substantially rectangular arrangement in which all members are streamlined. This construction produces less air resistance than would be produced by a single streamlined housing enclosing the entire loop. Furthermore, such an arrangement is subjected to less strain, upon change of attitude of the aircraft, than asingle elevated housing of streamline form about the entire loop. Also, this arrangement still retains the desirable effective height for the antenna which would be lost were a housing of the blister type used.

While I have described specific embodiments of my invention, this description should not be considered as a limitation on the scope of my invention. Various changes and modifications within the scope of my invention will readily be apparent to an expert in the art.

What is claimed is:

1. A loop antenna system for short wave operation comprising at least three radiant acting means arranged to form a substantially closed periphery, said radiant acting means being less than a quarter-wavelength long at the operating frequency and arranged to have a single plane of symmetry, a translating means, a transmission line coupling said translating means to at least one of said members substantially at said plane of symmetry, and coupling means for controlling distribution of energy in said loop to produce a single current loop in each of said radiant acting means, said coupling means being adjusted to produce at least one current maximum at one side of said loop less than half the length of one of said radiant acting means from said plane of symmetry.

2. A loop antenna system according to claim 1, further comprising means for adjusting said distribution to shift the position of at least one of said current loops.

3. A loop antenna according to claim 1 provided with three radiant acting elements as the radiant acting means, one of said elements having its center coinciding with said plane of symmetry, and the other members being arranged with one end of each coupled to said first named member and their other ends substantially in said plane of symmetry, said means for controlling the distribution of current comprising means for effecting said coupling.

4. A loop antenna according to claim 1 provided with three radiant acting elements as the radiant acting means, one of said elements having its center coinciding with said plane of symmetry, and the other members being arranged with one end of each coupled to said first named member and their other ends substantially in said plane of symmetry, said means for controlling the distribution of current comprising means for efiecting said coupling, and said transmission line being coupled substantially at the center of said first named member.

5. A loop antenna according to claim 1, provided with four radiant acting members as said radiant acting means, two of said members being connected at one end to said transmission line and at their other ends coupled to one end of the other two members, the other ends of said other two members being arranged in overlapping relation.

MELVIN A. ROTE.

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