US2700733A

US2700733A - Nonresonant antenna

Info

Publication number: US2700733A
Application number: US214190A
Authority: US
Inventors: Brueckmann Helmut
Original assignee: Individual
Current assignee: Individual
Priority date: 1951-03-06
Filing date: 1951-03-06
Publication date: 1955-01-25
Anticipated expiration: 1972-01-25

Description

Jan. 25, 1955 H. BRUEC KMANN 2,700,733

'NONRESONANT ANTENNA Filed March 6, 1951 2 Sheets-Sheet l FIG. 3

INVENTOR.

HELMUT BRUECKMANN FIG.2

Jan. 25, 1955 H. BRUE-CKMANN 2,700,733

N ONRESONAN T ANTENNA Filed March 6, 1951 2 Sheets-Sheet 2 FIG. 4 FIG. 5

FIG. 6 7

FIG. 8 9

SI 47 49 4a 50 45 46 FIG. IO

63 F I6. I I

INVENTOR. HELMUT BRUECKMANN 7| FIG. l2 7? United States Patent NONRESONANT ANTENNA Helmut Brueckmann, Little Silver, N. 1., assignor to the United States of America as represented by the Secretary of the Army Application March 6, 1951, Serial No. 214,190

2 Claims. (Cl. 25033.51) (Granted under Title 35, U. S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

The subject invention relates to antennas, and more particularly to directive, non-resonant antennas to cover a wide band of frequencies.

The name non-resonant antenna designates a certain kind of antenna which is widely used in radio engineering, especially in long range communication. The essential feature of a non-resonant antenna is that the voltage-current distribution along the radiating conductors represents a traveling or progressive wave. The simplest form of it is the well known Beverage wave antenna. Other forms are the rhombic antenna, the inverted-V antenna and the horizontal-V antenna.

The antenna described here can be considered as a combination of two rhombic antennas which have one common diagonal but two different planes. It has one application as a receiving or transmitting antenna for V. H. F. if high directivity and high substantially uniform gain over a very broad frequency range are desired. its input impedance is constant over the whole frequency range as is the case in any non-resonant antenna, and can be made as low as 300 ohms, providing perfect matching to common type transmission lines now available for television receivers. Another application is as a transmitting or receiving antenna for long range communication on high frequencies. In this latter case, the shipping weight and time for erection can be reduced considerably, as compared to an equivalent rhombic antenna, without sacrifice in directivity and gain, since only one pole is required to support the antenna.

It is therefore an object of this invention to provide an improved antenna.

It is a further object of this invention to provide an improved non-resonant antenna.

It is a further object of this invention to provide an antenna whose input impedance is constant over a wide range of frequencies.

It is a further object of this invention to provide an antenna with a non-reactive input impedance of 300 ohms over a wide range of frequencies.

It is a further object of this invention to provide a transmitting and receiving antenna having a high, substantially uniform gain over a wide range of frequencies.

Fig. 1 show a preferred embodiment of this invention.

Fig. 2 shows the electrical elements of this embodiment.

Figs. 3 to 9 are end views of the electrical elements of this invention, showing various connections.

Fig. 10 shows another embodiment of this invention and Figs. 11 and 12 show forms of the electrical elements of this invention.

The basic antenna is shown in Fig. 1 with a typical mechanical structure for mounting the antenna. The electrical elements of same antenna are shown in Fig. 2, without the mechanical structure, in order to make the form of this antenna more clear.

The antenna of Figs. 1 and 2 consists of eight straight conductors of equal length, which are numbered 21 to 24 and 26 to form two rhombuses, which have one common diagonal 25, but two different planes. For the sakeof brevity this antenna can be called a Double-rhombic antenna. At those two corners of each

rhombus

40, 41 or 42, 43

respectively, which are not common to the other rhombus,

29. They are arranged geometrically to 2,700,733 Patented Jan. 25, 1955 the conductors are connected directly. At the common corner 17, the conductors may be terminated in four resistors 30 to 33, as shown in Fig. 3. At the common corner 16, the conductors 34 may be connected to the transmission line in one of three diiferent ways. If two adjacent conductors are combined in parallel, as shown in Figs. 4 and 6, two combinations are possible which are not different in principle, but merely in the orientation of the electric field in space and the angles between the planes of conductors, which are connected in parallel. If two opposite conductors are combined in parallel as shown in Fig. 8, another possibility of feeding the antenna is obtained. By each combination, two symmetrical two-conductor lines are created in which the distance between corresponding elements of the conductors changes linearly along the line with the distance from the terminals. The characteristic impedance of each line is assumed to be substantially constant along the line or, at least, to change very gradually. Assuming that the characteristic impedance of both lines be equal, and that the terminating resistors 30 to 33 in Fig. 3 be impedance matched, the standing voltage-current waves on the conductors are eliminated and progressive voltage-current waves of equal magnitude travel along the conductors from one end-point of the common diagonal to the other endpoint. The input impedance of the antenna is half the characteristic impedance of the single line (with the other line present, of course), and independent of the operating frequency. If desired, the four resistors in Fig. 3 can be replaced by one, as shown by resistors 35 in Figs. 5, 7 and 9.

The antenna looks similar to the well known rhombic antenna, or to the inverted-V antenna when, in the latter case, the image below the ground is added. By a rhombic antenna is meant a directional array of four conductorsor virtual images of conductorsof /2 wavelength or more, terminated by a reel or inherent impedance substantially equal to that of the line. For the shorter wavelengths the array may be self terminated. However, it is ditferent from the conventional nonresonant antennas in respect to the arrangement of the conductors, which are located in two different, nonparallel planes with an arbitrary angle between them other than The distance between adjacent conductors may be comparable to the wave-length.

The conductors are fed and terminated at the two

common corners

16 and 17 of the rhombuses. At the other four

corners

40, 41, 42 and 43 which are not common to both rhombuses, the conductors are connected directly. However, the arrangement of the common corners on one side and non-common corners on the other side can be interchanged without abandoning the basic idea, which lies in the geometrical arrangement of the conductors, and their electrical excitation with progressive waves. The rhombic antennas may be fed as a single unit or as separate units in voltage phase (with voltage of the same or opposite polarity). For the purposes of this application and to distinguish over the prior art, the rhombic antennas here will be considered to be fed in phase to the extent defined above. If the length of one conductor is 2L; the angle between the plane through the

conductors

21 and 29 and the plane through the

conductors

26 and 24 may be 2A. The angle between the conductors 21 and 29 (or 26 and 24, etc.) may be 2B. All other dimensions follow from these data. For example:

Length of the common diagonal 25 (2p) :4L-cos A cos B Length of the non-common diagonals 37, 38 (2r) It is also possible to express these datain terms of the angle 2 between the planes of the two rhombuses 3 and the angle 26 between the

conductors

21 and 22 or 26"and 27; For example;

Length of the common diagonal 25 (2p):4L-sin 6 Length of the non-common diagonals 37, 38 (2r):4L

cos 6 Distance between the non-common corners 4t) and 43 (2m):4L cos fi-sin '1 Distance between the non-common corners 40 and 42 (2n):4L cos 6-cos y it will be noticed that the rhombic antenna can be considered as a special case of the new antenna with 5:0 (then 7:0 and 6=90A) and with an excitation according to Fig. 4. The inverted V-antenna above a perfectly conducting. plane ground can be considered as aspecial case of the new antenna with A20 (then :90 and 5:90B) and with an excitation according to Fig. 6, since the efiect of the ground on the radiation is equivalent to the presence of images of the conductors below the ground plane.

An application of the subject antenna as a transmitting or receiving antenna for V. H. F, especially as a receiving antenna for TV, is illustrated in Fig. l. The construction described in this figure lends itself to the possibility of rotating the antennas about a vertical axis. A metal pipe 25 is supported horizontally in its center by a vertical pole 30. Its total length may be designated 2p in order to be consistent with the formulas given here. Two

rods

37 and 38 are arranged in the plane through the center of the metal pipe 25 and perpendicular to it. The

rods

37 and 38 are of equal length Zr and made of non-conducting material, for example, Wood, tubes of plastic, or bamboo poles. Their tilt angles against a horizontal plane are equal. The center of each rod is fastened to the center of the metal pipe 25. At the other end, each rod supports two of the eight conductors of the antennas which preferably consists of aluminum wire. Some special forms of these conductors are shown in Figs. 11 and 12.

The eight conductors are excited electrically and terminated according to Figs. 4 and 5, resulting in polarization in the horizontal plane or perpendicular to the vertical plane through the metal pipe. The electrical properties of the antenna are not afiected by this pipe because the electric field strength of the antenna itself along the pipe is zero. The terminating resistor has a resistance of 300 ohms. At the input end 16 of the metal pipe the conductors are connected to a ground-symmetrical transmission line 34 with a characteristic impedance of 300 ohms, for example, a shielded balanced SOD-ohm line or two coaxial ISO-ohm cables. This line leads to the balanced input terminals of the receiver (or to the output terminals of the transmitter).

The radiation of this antenna has been calculated for various dimensions, and the following figures show the result when r p, 6:45 and :33", where r, p, 6, and 'y are defined above. This corresponds to A=40, B=22.6 and 2L=r- /2 where A, B and 2L are also defined above. If, for example, 2L is made equal to 9 6", corresponding to r=p=6 9", then the gain at 57 me. (average frequency of TV channel 2) is zero db over a matched half-wave dipole; at 177 me. (TV channel 7) the gain is 12 db. In this case, the side lobes of the horizontal radiation pattern are 10 db or more below the main lobe through the whole range from 57 to about 230 me.

The characteristic impedance of an element of the conductors as a function of the distance from the terminals can be made almost constant over the whole length when utilizing a two wire curtain as shown in Fig. 11 for the antenna of Fig. 1. Based on the dimensions r:p=6 9" and 'y=33, 6% of the total length of one conductor or 7 inches, counting from the

terminals

16 and 17, consist of one wire 69 of American wire gauge 6; the rest consists of two

wires

62 and 63 American wire gauge 10 connected in parallel. A spreader 65 is placed at the connections 40 to 43 of the four rods (see Figs. 1 and 2), and another spreader 66 is arranged between these wires at a distance from the terminals of 55% of the total length. The width b of all spreaders is 6" for the example given.

A certain and gradual increase of the characteristic impedancewith increasing distance from the terminals at 16 and 17 has been admitted in this example in order to enable a particularly simple and cheapconstruction.

g 4 This increase follows very closely to an exponential law in respect to s, as given by;

Ks=585 exp (0.229% in ohms Therefore the conductors behave in respect to voltage current distribution and input impedance as a so-called exponential line. In other words, the variation of the characteristic impedance does not cause noticeable refiection for electromagnetic waves progressing from one terminal to the other as long as 2L is greater than half a wavelength. Therefore, the eifect of this variation on the radiation pattern isnegligible and the input impedance is equal to the characteristic impedance near the terminals, independent of the frequency. However, it is by no means difficult to find an arrangement of wires or a shape of a tubular conductor which results in a' practically constant characteristic impedance along the conductors.

Incidentally, dimensions r=p=6' 9 and 'y=33-, can easily be altered in order to cover a higher frequency range by simply changing the position of the spreaders which are fastened to the tops 40 to 43 of the four rods and by shortening the wire accordingly. Dimensions p and b may remain unaltered. The resulting maximum gain is even higher than before at the same time, a wide frequency range is covered when r is decreased from 6 9" to 4 2" and p is kept at 6 9".

The advantages of the antenna described in Fig. l, with the dimensions r=p==6 9" and :33", therefore may be summarized as follows:

(1) The input impedance is practically independent of the frequency and equal to the generally accepted input impedance of TV receivers of 300 ohms. Consequently, it can be matched perfectly to a 300 ohm transmission linedand to a TV receiver over a very broad frequency ban (2) The actual gain is about equal to the actual gain of existing TV antennas at the lowest TV frequency and considerably higher at the higher TV frequencies.

(3) The directivity, which is important in respect to the elimination of ghosts and interference, is higher than in most of the existing TV antennas, averaged over the whole TV frequency band.

(4) The antenna also covers the PM frequency band.

(5) The antenna can easily be altered in order to cover a higher frequency range.

Another feature that may be important under special circumstances is that the direction of maximum radiation of the antenna can be changed easily by degrees without any change in the orientation of the antenna itself, simply by interchanging the connections of the antenna to the terminating resistor and to the transmission line at 16 and 17. For this purpose a 300 ohm two-wire transmission line may be run from the termination end 17 of the antenna to the receiver, in addition to the line from the input end 16, and the terminating resistor placed near to the receiver at the end of this line. The direction of maximum radiation then can be reversed by a switch located near to the receiver. No adjustment is necessary.

With an excitation of the antenna according to Fig. 4 or 8, the electric field at far distant points in a vertical plane through the common diagonal 25 is polarized perpendicularly to this plane. However, with an excitation according to Fig. 6 the electric field in the same plane is polarized parallel to the plane. This property makes it possible to change the polarization of the antenna Without any change in the antenna itself if each of the four

conductors

21, 26, 24 and 29 is connected at the input end 16 to an individual single-conductor line, preferably a coaxial cable. in this case all four single-conductor lines are run to the location of the receiver (or transmitter) and connected there according to Fig. 4, 6 or 8, depending upon the desired polarization. it is even possible to operate the antenna simultaneously, with an excitation according to' Fig. 6 and an excitation according to Fig. 4 or 8. For this purpose the balanced bridge circuit. similar in principle to the well-known phantomcircuit for multiple use of wire lines, can be used. When the circuit is properly adjusted, there is no coupling between the two pairs of terminals. Therefore the antenna can be used simultaneously by two transmitters or receivers without affecting each other, regardless of the operating frequencies, even if they are the same.

an antenna according to Fig. 11, with the Another application of this antenna, this time as a transmitting or receiving antenna for long range communication for frequencies from about 3 to mc., is illustrated in Fig. 10. The vertical pole with the height p above ground represents the sole supporting structure for this antenna. Two ground anchors 46 and 47, are arranged in the distance r from the pole, on opposite sides of it and on a straight line through the base of it. Two more ground anchors 48 and 49 are arranged in the same manner in another direction. The pole 45 and the anchors support four conductors to 53 of equal length, with the lines from 46 to 47 and 43 to 49 ineluding the angle 2 If the ground is plane and well conducting, its effect on the radiation is equivalent to the presence of images of the conductors below the ground plane. These images and the four conductors themselves establish the geometrical arrangement of conductors to Fig. 2, resulting in horizontal polarization in the vertical plane through the bisector of the angle 27. it does not matter whether the material of the pole 45 is metallic or insulating since the pole is located in the electrically neutral plane of the antenna.

Each conductor may consist of a three-wire curtain as shown in Fig. 12. Near both ends 70-71 of each conductor 73 the wires of the curtain can come together and at a certain point between the ends the wires are spaced by means of a spreader 75. The purpose of the curtain is to provide for a constant characteristic impedance along the conductor. The location and the width of a spreader that is adequate for this purpose depends upon the angles between the conductors and their length. As an example, for 'y=20, 6=10 and 2L=454 feet, the spreader 75 is located at a distance of 168 feet from the upper end of the conductors. If the width of the spreader is 7 feet, the characteristic impedance should be sufficiently constant. Some provision may be made to prevent the curtain from twisting, such as a small counterpoise at one end of the spreader or an insulating rope tied between one end of the spreader and ground.

The antenna of Fig. 10 is supposed to be fed at the points 46 and 43 through single-conductor transmission lines with a characteristic impedance equal to the impedance to ground of each conductor, which is half the characteristic impedance between two opposite conductors. In this example, the impedance to ground is close to 300 ohms. In order to avoid excessive ground losses in the single-conductor lines and undesired radiation from them, the energized conductor of these lines should be shielded, for example, by means of a wire cage. For practical reasons it should be arranged at the same height above ground as an ordinary two-wire transmission line, except at the feeding points 46 and 48. At these points the single-conductor line should be brought down to ground level in order to ground the wire cage, and the energized conductor of this line is connected directly to the lower end of the conductors. The single conductor line need not be longer than the distance 2m between the feeding points 46 and 48, which, in the above mentioned example, is 306 feet. However, its actual length is not important in electrical respect. At the center of the line the hot conductor is broken oif by insulators. The two ends are connected to a balanced two-wire transmission line with a characteristic impedance twice that of the single-conductor line, thus providing perfect matching for the two-wire line.

The termination of the antenna at the

points

47 and 49, can be established in the same manner as at the points 46 and 48, except that the two wire transmission lines may be replaced by a common type dissipation line, as normally used for terminating rhombic antennas. However, it can also be established by means of two separate terminating resistors (or dissipation lines), located at 47 and 49 and connected directly between the lower end of the

conductors

51 and 53, respectively, and ground. If a single-conductor line is preferred for termination, this line can be constructed as a dissipation line, by using resistive wire, for example, stainless steel wire.

The radiation of this antenna in the vertical plane through the bi-sector of the angle between 50 and 52 has been calculated for various dimensions. For example the dimensions 7:20", 6:10 and 2L=454 feet correspond to a height of the pole of 79 feet, although these dimensions do not necessarily represent an optimum. This antenna is comparable to a standard type C rhombic antenna with the smaller angle, 2A=40, the side length, 2L=3 l5 and a height of the poles of 63 feet at the snort diagonal (corresponding to an average height of the antenna of 57 feet). Since, in long range communication, one is interested mainly in the radiation at low elevation angles (that means at small vertical angles of response measured from the horizontal ground plane) the gain is considered for elevation angles between zero and 40 only, and the attenuation along the conductors has been assumed to be the same in both cases. In this case both antennas are the same with respect to gain for a very broad Irequency band, provided the antenna losses are the same.

The area covered by the subject antenna, however, is somewhat greater than the area covered by the equivalent rhombic antenna. in the typical cases compared above, the length and width of the subject antenna are 840 and 306 feet while those of the standard rhombic antenna are 596 and 222 feet respectively.

In order to keep the ground losses of the double rhombic antenna of Fig. 10 small, an adequate ground system should be provided, at least at the feeding points 46 and 48 and for a certain length below the

conductors

50 and 52, near their lower end. The question of what is to be considered as an adequate ground system depends, mainly, upon the ground conductivity, the operating frequency and the dimensions of the antenna. it is impossible to calculate the losses in the ground exactly, but an estimate of these losses has led to the conclusion that a copper mesh screen of rectangular shape about 16 feet wide and 70 feet long, at each feeding point, will be suflicient. When using a screen of this size the ground losses of the double rhombic antenna will be no higher than the ground losses of the standard rhombic antenna to which it is compared above.

The saving in shipping weight for supporting poles is estimated to be about 5000 lbs. when compared with conventional type construction, while the gross shipping weight of the additional copper mesh screen is only 374 lbs. Another advantage of the double rhombic antenna is the saving in erection time. Both of these advantages are particularly valuable in military applications.

What is claimed is:

1. An antenna for receiving radio waves comprising: first and second rhombic antennas having a common diagonal and situated in substantially perpendicular planes, each of said antennas having first and second terminals at one end of said diagonal and a matching impedance at the other end of said diagonal, a transmission line having first and second terminals, said first terminal of said transmission line directly connected to said first terminals of said first and second rhombic antennas, and said second terminal of said transmission line directly connected to said second terminals of said rhombic antennas.

2. An antenna for receiving plane polarized waves comprising: a first rhombic antenna having a diagonal in the direction of said waves, input terminals at one end of said diagonal and a matching impedance at the other end of said diagonal; said first rhombic antenna situated in a plane forming an angle of substantially 45 with respect to said plane of polarization; a second rhombic antenna having a diagonal coincident with said diagonal of said first rhombic antenna, input terminals at said one end of said diagonal and a matching impedance at said other end of said diagonal; said second rhombic antenna situated in a plane forming said angle of substantially 45 with respect to said plane of polarization and being at approximately right angles with respect to the plane of said first rhombic antenna, the respective terminals of said first rhombic antenna connected directly to the respective terminals of said second rhombic antenna.

References Cited in the file of this patent UNITED STATES PATENTS 760,463 Marconi May 24, 1904 1,132,569 Fessenden Mar. 23, 1915 1,626,803 Fishback May 3, 1927 2,145,024 Bruce Jan. 24, 1939 2,207,504 Bohm July 9, 1940 2,267,889 Aubert Dec. 30, 1941 2,298,034 Burrows Oct. 6, 1942 2,379,706 Hansell July 3, 1945