US2919441A

US2919441A - Radio-frequency-energy transmission line and antenna

Info

Publication number: US2919441A
Application number: US501570A
Authority: US
Inventors: Chu Lan Jen
Original assignee: Individual
Current assignee: Individual
Priority date: 1955-04-15
Filing date: 1955-04-15
Publication date: 1959-12-29
Anticipated expiration: 1976-12-29

Description

Dec. 29, 1959 LAN JEN CH RADIO-FREQUENCY-ENERGY TRANSMISSION LINE'AND ANTENNA Filed April 15. 1955 FIG. 3

INVENTOR. LAN JEN CHU A TTORNEYS United States Patent RADIO-FREQUENCY-ENERGY TRANSMISSION LINE AND ANTENNA Lan Jen Chu, Lexington, Mass.

Application April 15, 1955, Serial No. 501,570

'4 Claims. (Cl. 343-810) The present invention relates to radio-frequency-energy transmission lines and antennas, and, more particularly, to transmission lines and antennas that are especially adapted for use in the high and ultra-high-frequency bands.

Various transmission lines and antennas of special configuration have heretofore been evolved in an attempt not only to reduce the manufacturing and maintenance cost of the transmission-line and antenna structures, but, also, to render such structures more efficient. As an illustration, it has been proposed to simplify conventional coaxial or parallel-wire transmission lines through the expedient of printing or depositing conductor strips upon opposite sides of a dielectric layer. This proposal, as well as many others, however, is subject to several disadvantages. In the first place, the velocity of propagation of the radio-frequency energy along such transmission lines is considerably less than the very desirable free-space velocity of electromagnetic energy in air, that is, the velocity of light. This is because the radio-frequency energy must travel through the medium of the dielectric support for the two conductors of the transmission line or antenna system. In addition, the radio-frequency energy is subject to appreciable attenuation as a result of losses occurring in the said dielectric medium.

An object of the present invention, accordingly, is to provide a new and improved transmission line and antenna structure that, unlike the before-mentioned priorart transmission lines and antenna systems, permits the radio-frequency energy to travel with substantially the velocity of light and with substantially no attenuation.

An additional object is to provide such a transmissionline and antenna structure that, though particularly adapted for balanced-line operation, can easily be designed to have any desired impedance characteristics.

Still a further object is to reduce the manufacturing and maintenance costs of transmission lines and antennas.

Other and further objects will be explained hereinafter and will be more particularly pointed out in the appended claims.

The invention will now be described in connection with the accompanying drawings, Fig. 1 of which is a fragmentary perspective view illustrating a preferred form of the present invention as applied to a transmission line;

Fig. 2 is an exploded view illustrating the application of the transmission-line structure of Fig. 1 to a preferred antenna;

Fig. 3 is a fragmentary perspective view of the assembled antenna of Fig. 2 encased within a tubular housing; and

Figs. 4 and 5 are fragmentary views of modifications.

Referring to Fig. 1, a balanced two-conductor transmission line is shown comprising a pair of opposing substantially planar similar conductors 1 and 3 extending longitudinally along the inner surfaces 5 and 7 of a pair of dielectric-sheet supports 9 and 11. The supports 9 and 11 may assume the form of Bakelite, fiberfilass or other dielectric sheets or layers and the planar conductors 1 and 3 may be of sheet copper or brass and the like, attached at 13 as by cementing or gluing along the inner surfaces 5 and 7 of the dielectric supports 9 and 11. If desired, the conductor strips 1 and 3 may also be sprayed or printed upon the surfaces 5 and 7 of the dielectric-layer supports 9 and 11. The dielectric supports 9 and 11 are positioned substantially parallel to one another with the conductors 1 and 3, which are substantially co-planar with the respective surfaces 5 and 7 of the supports 9 and 11, disposed in capacitive opposition. Radio-frequency energy may be applied to the left-hand terminals of the conductors 1 and 3 and propagated along the two-conductor balanced transmission line formed by the conductors 1 and 3, the radio-frequency energy being guided between the opposing inner faces of the planar conductors 1 and 3.

In accordance with the present invention, this radiofrequency energy guided in the space between the planar conductors 1 and 3 is permitted to travel with substantially the velocity of light. This end is achieved by utilizing a dielectric spacer 15 external to the space I between the conductors 1 and 3 so that the space I may be constituted solely of air. By displacing the spacer 15 away from the side edges of the conductors 1 and 3, that energy which is guided at the side edges of the conductors 1 and 3 may similarly travel in an air medium II. The spacer 15 is preferably in the form of a honeycomb structure having cells of air and that may be glued or otherwise secured to the inner surfaces 5 and 7 of the dielectric layers 9 and 11 in order rigidly to unite them. The radio-frequency energy thus travels unimpeded through substantially an air medium com pletely along the transmission line, achieving the desired advantageous end of permitting the energy to travel with substantially the velocity of light. The use of the preferably porous air-filled honeycomb structure 15, moreover, provides a minimum of dielectric material in the path of stray field.

In addition, in accordance with the present invention, there is negligible attenuation of the radio-frequency energ since there is no dielectric medium besides the air in the space I between, and the space II immediately to the side of, the conductors 1 and 3, and a minimum amount of dielectric material is present further to the side. In addition, the structure of the present invention is not subject to the reflections that give rise to undesirable standing-wave ratios and that are inherent in prior transmission lines that require dielectric media between the conductors or other dielectric supports therebetween. This result is attained in Fig. 1, moreover, with an entirely symmetrical and balanced-line feed. The ends of the structure, moreover, may be sealed over and it may be rendered air-tight or gasfilled with a gas at any desired pressure. The simplicity of manufacture of the component parts and of assembly of the same provides, in addition, a relatively low-cost article.

Transmission lines constructed in accordance with the present invention, furthermore, are adapted for simple adjustment to any desired characteristic impedance. This may be easily accomplished, for example, merely by varying the spacing between the dielectric layers 9 and 11, as by utilizing honeycomb or other spacers 15 of different heights, or by varying the relative widths of the conductors 1 and 3 as shown, for example, in the embodiment of Fig. 4.

Not only is the structure of the present invention extremely advantageous as a transmission line, but it is of important utility, also, in connection with radiating or receiving antenna structures and particularly those constituted of a number of antenna elements. In view of the fact that the phase velocity of the radio-frequency energy guided along the line is substantially that of light because of the construction of the present invention, an antenna so constructed will be of extremely high gain. This is because the gain of an antenna is proportional to the ratio of the length of the antenna to the wavelength in free space. The present invention thus renders the Wavelength along the antenna substantially equal to that of free space, thus providing maximum gain conditions for the same number of antenna elements. In=addition to the before-mentioned results of extremely low-1 attenuation, furthermore, an antennasystem so constructed is less subject to the type of standing-wave phenomena before-described.

As an illustration of the application of the transmission-line structure of the present invention to an antenna system, a beacon-type dipole array antenna is shown in Fig. 2. The dielectric layers 9, 11 are there shown spaced apart in order to illustrate the details of construction. Upon the surface 7, a main longitudinally extending planar conductor 3 is mo'unted,.the width of the dielectric support 11 being wider than that of the conductor in order to permit the use of the spacer connecting member 15. At intervals along the main planar conductor 3, there are provided a plurality of transverse branch conductors 2, 4, 6 and 8. It is to be understood that more or less branch conductors than the four illustrated may, of course, be employed. The corresponding main planar longitudinally extending conductor 1 is shown secured to the inner surface 5 of the dielectric support 9 and is provided with similar rightangularly extending transverse branch

planar conductors

10, 12, 14 and 16. At each end of the transverse branch extensions 2, 4, 6 and 8 are downwardly extending respective dipole-element

planar conductors

22, 24, 26 and 28. At the ends of the

transverse conductors

10, 12, 14 and 16 there are similarly provided upwardly extending dipole-element planar conductors 3 32, 34 and 36, respectively. When the dielectric supports 9 and 11 are sandwiched together, with the honeycombed spacer material 15 disposed therebetween in regions preferably external to the spaces I and II, for the reasons heretofore explained, a balanced dipole array is produced having the before-mentioned advantages over present-day antenna arrays. of Fig. 2, the polarization of the radio frequency energy is vertical in view of the vertical orientation of the dipole elements. The dipoles constituted of the

elements

22 and 30, 24 and 32, 26 and 34, and 28 and 36, may be successively spaced along the main-line conductors 1 and 3 at intervals of, for example, awavelength of the energy for which the antenna was designed. It is pref erable for impedance-matching purposes that the width of the conductors 1 and 3 be successively decreased or reduced in the intervals between successive dipoles as shown at 13', 13 and 1"'3". Radio-frequency energy may be fed directly to the bottom of the transmission lines 1 and 3 and a high-power gain radiation pattern, omni-directional in the horizontal plane, will be produced which is highly suitable for radio-beacon purposes. If desired, this antenna may be enclosed in a tubular housing such as a radio-wave permeable plastic cylinder 19, as of polystyrene, preferably end-sealed against the eifect of the atmosphere or pressurized with air or any other gas media at any suitable pressure.

It is to be understood, of course, that the above-do scribed structure is equally useful as a receiving antenna and that many different types of antenna elements and arrays may be constructed utilizing the technique herein disclosed.

As a typical illustration, an experimental line of the type illustrated in Fig. 1 having a pair of six-inch wide Fiberglas planar supports 9 and 11 of about one thirtysecond of an inch thickness, separated by Fiberglas honeycomb spacers 15 about a quarter of an inch in height,

In the system iii) and having copper-strip conductors l and 3 about one inch wide and about 2 thousandths of an inch thick, glued to the inner surfaces 5 and 7, was found to propagate radio-frequency energy in the ultra-high-frequency band with a phase velocity equal approximately to ninety-five percent of the velocity of light. The characteristic impedance of the line was about'fifty ohms and the losses along the line were far less than those encountered with the prior-art strip-line systems before-mentioned and other prior-art lines.

Another way of achieving the end of eliminating substantially all dielectric mountings or supports for a twoconductor transmission line from the radio-energy-propagating space between the conductors is illustrated in Fig. 5. The planar conductors 1 and 3 are there shown provided with substantially co-planar right-angularly extending extensions 21 and 23 which are secured to a planar dielectric support 25. Actually, since there is some slight capacitance between the extensions 21' and 23 and the dielectric support 25 directly bounds the lower edges of the conductors 1 and 3, unlike the structures of Figs. 1 to 4, a small quantity of radio energy will be propagated between the extensions 21 and 23 through the dielectric support 25. Substantially all of the radiofrequency energy, however, travels between the inner opposing faces of the substantially parallel planar conductors 1 and 3 with almost the velocity of light and with low attenuation. As in the case of the transmission lines of Figs. 1, 2 and 4-, the characteristic impedance may easily be varied by, for example, adjustin the spacing between the planar transmission-line conductors 1 and 3 or by varying the dimensions of the same;

Further modifications will occur to those skilled in the art and all such are considered to fall Within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. A radio-frequency-energy transmissionline'and" antenna having a pair of longitudinally extending'substantially planar main conductors each provided with aplurality of transverse planar branch conductors substantially co-planar with the main conductors connected at intervals therealong and mounted upon the inner surfaces of a pair of spaced substantially parallel planar dielectric supports of greater transverse dimension than the conductors, the conductors of the pair of conductors and the corresponding branch conductors being disposed in opposition, and a plurality of longitudinally extending planar dipole-element conductors mounted upon the inner surfaces of the supports at the ends of the branch conductors with the dipole elements mounted upon each support extending in the opposite direction from the direction of extension of the dipole elements mounted upon the other support of the pair of supports.

2. A radio-frequency-energy transmission line and antenna having a pair of longitudinally extending substantially planar main conductors each provided with a plurality of transverse planar branch conductors substantially co-planar with the main conductors connected at intervals therealong and mounted upon the inner surfaces of a pair of spaced substantially parallel planar dielectric supports of greater transverse dimension than the conductors, the conductors of the pair of conductors and the corresponding branch conductors being disposed in opposition with the width of the portions of the main conductors between the successive intervals therealong successively decreasing, and a plurality of longitudinally extending planar dipole-element conductors mounted upon the inner surfaces of the supports at the ends of the branch conductors with the dipole elements mounted upon each support extending in the opposite direction from the direction of extension of the dipole elements mounted upon the other support of the pair of supports.

3. A radio-frequency-energy transmission line and antenna having a pair of longitudinally extending substantially planar main conductors each provided with a plurality of transverse planar branch conductors substantially co-planar with the main conductors connected at intervals therealong and mounted upon the inner surfaces of a pair of spaced substantially parallel planar dielectric supports of greater trans-verse dimension than the conductors, the conductors of the pair of conductors and the corresponding branch conductors being disposed in opposition with the width of the portions of the main conductors between the successive intervals therealong successively decreasing, a plurality of longitudinally extending planar dipole-element conductors mounted upon the inner surfaces of the supports at the ends of the branch conductors with the dipole elements mounted upon each support extending in the opposite direction from the direction of extension of the dipole elements mounted upon the other support of the pair of supports, and porous dielectric spacer means disposed between the supports.

4. A radio-frequency-energy transmission line and an tenna having a pair of longitudinally extending substantially planar main conductors each provided with a plurality of transverse planar branch conductors substantially co-planar with the main conductors connected at intervals therealong and mounted upon the inner surfaces of a pair of spaced substantially parallel planar dielectric supports of greater transverse dimension than the conductors, the conductors of the pair of conductors and the corresponding branch conductors being disposed in opposition with the width of the portions of the main conductors between the successive intervals therealong successively decreasing, a plurality of longitudinally extending planar dipole-element conductors mounted upon the inner surfaces of the supports at the ends of the branch conductors with the dipole elements mounted upon each support extending in the opposite direction from the direction of extension of the dipole elements mounted upon the other support of the pair of supports, and porous dielectric spacer means disposed between the supports in regions external to the space between opposing conductors.

References Cited in the file of this patent UNITED STATES PATENTS 2,556,224 Scott June 12, 1951 2,721,312 Grieg June 30, 1951 2,794,185 Sichak May '28, 1957 2,800,634 Grieg July 23, 1957 2,819,452 Arditi et a1. Jan. 7, 1958 FOREIGN PATENTS 655,803 Great Britain Aug. 1, 1951