US2702345A

US2702345A - Radiation and interception of electromagnetic waves

Info

Publication number: US2702345A
Application number: US112270A
Authority: US
Inventors: Walter Ludwig
Original assignee: Individual
Current assignee: Individual
Priority date: 1949-08-25
Filing date: 1949-08-25
Publication date: 1955-02-15
Anticipated expiration: 1972-02-15

Description

Feb. 15, 1955 L. WALTER 2,702,345

RADIATION AND INTERCEPTION OF ELECTROMAGNETIC WAVES Filed Aug. 25, 1949 4 Shets-Sheet l 7 l'uowlq Warns.

Feb. 15, 1955 WALTER 2,702,345

RADIATION AND INTERCEPTION OF ELECTROMAGNETIC WAVES Filed Aug. 25, 1949 4 Sheets-Sheet 2 2 Luau/q Nature amm Feb. 15, 1955 WALTER 2,702,345

RADIATION AND INTERCEPTION OF ELECTROMAGNETIC WAVES Filed Aug. 25, 1949 4 Sheets-Sheet 3 ,ljgll mm 1 1/3112. I I00 [/5 WE loam: .smn/om/q WHVE 20770 7 I002 UNITY 2 12.6 METEKS' 5 Z w vaf/vqur 5 Z n m az/ven/ Iwuwq W4 T5178.

Feb. 15, 1955 L. WALTER RADIATION AND INTERCEPTION OF ELECTROMAGNETIC WAVES 4 Sheets-Sheet 4 Filed Aug. 25, 1949 (Zita 111%.

7 Lyon/1e II/HLTLTZ- United States Patent RADIATION AND INTERCEPTION 0F ELECTROMAGNETIC WAVES Ludwig Walter, Berlin, Germany Application August 25, 1949, Serial No. 112,270 7 Claims. (Cl. 250-33) This invention relates to improvements in the radiation and interception of electromagnetic waves. More particularly, this invention relates to an improved method and apparatus for matching antennas and feeders used in the radiation or interception of electromagnetic waves.

It is therefore an object of the present invention to provide an improved method and apparatus for matching the antennas and feeders used in the radiation or interception of electromagnetic waves.

In the radiation or interception of electromagnetic waves it is desirable that the electrical characteristics of the antennas and feeders be such that the impedances of the antennas and feeders match. Where this is done, there will be an efiicient transfer of energy between transmitter and antenna or between antenna and receiver.

Various types of feeders have been proposed and used, but most of them are comprehended within two categories: resonant feeders and non-resonant feeders. Resonant feeders are the easiest to construct, and they are readily adjusted for proper transfer of the electromagnetic waves between the antenna and the transmitter or receiver. However, feeders are often necessarily located adjacent trees, shrubbery or other objects which will absorb electromagnetic waves; and many of the electro magnetic waves that radiate from or should impinge upon the resonant feeders will be absorbed by those trees and shrubs. For this reason, resonant feeders are objectionable. Non-resonant feeders obviate this objection, but non-resonant feeders require rather precise impedancematching with the antennas. In the absence of such matching, the efficiency of transmission or reception of the electromagnetic waves will be low. For this reason non-resonant feeders are objectionable. The present invention obviates these objections by providing an improved antenna and non-resonant feeder which can easily be matched. It is therefore an object of the present invention to provide an improved antenna and non-resonant feeder which can easily be matched.

The non-resonant feeder provided by the present invention is a concentric transmission line, usually a coaxial cable; and the antenna provided by the present invention is a conductor that is coupled to both conductors of the concentric transmission line to form a loop. The matching is easily effected by varying the effective electrical length of the antenna, as by adjusting the distance between the leads from the two conductors of the concentric transmission line. This arrangement makes precise matching easy. It is therefore an object of the present invention to provide a concentric transmission line as the feeder and to provide a conductor, connected to both conductors of the concentric transmission line by adjustable leads, as the antenna.

The matching of the antenna and feeder provided by the present invention can also be effected by constructing the antenna so part of it is vertically-disposed and so the rest of it is horizontally-disposed; and so the length of the vertically-disposed part can be varied. By changing the length of the vertically-disposed part of the antenna, it is possible to change the effective electrical length of the antenna and thereby change the impedance of the antenna. Selection of the desired length for the vertically-disposed part of the antenna will facilitate matching of feeder and antenna. It is therefore an object of the present invention to provide an antenna with a vertically-disposed part and a horizontally-disposed part, and wherein the length of the vertically-disposed part can be adjusted.

The antenna provided by the present invention can take the form of a simple conductor or it can take the form of a tower, the downspout of a building, or another vertically-directed element of a building. In the latter instances considerable economies are possible; particu- 30 larly where tall antennas are desired, since the structural elements of the buildings will be immediately available and need not be constructed specially for the antennas. It is therefore an object of the present invention to provide an antenna and feeder arrangement wherein a tower, a downspout of a building, or another vertically-directed metal element of a building can serve as the antenna.

The antenna provided by the present invention Will usually radiate or intercept electromagnetic waves directly; but the antenna can be coupled to a resistive or reactive load that will radiate or intercept the electromagnetic waves. The antenna can be coupled to that load by conductive, inductive or capacitive methods; and such an arrangement will facilitate effective utilization of existing structures. It is therefore an object of the present invention to provide an antenna which can be coupled to a resistive or inductive load to cause that load to radiate or intercept electromagnetic waves.

It is desirable that matching of the antenna and feeder be efiected from a remote point. The present invention makes this possible by providing remote control of the effective electrical height of the antenna. It is therefore an object of the present invention to provide remote control of the effective electrical height of antennas.

Other and further objects and advantages of the present invention should become apparent from an examination of the drawing and accompanying description.

In the drawing and accompanying description a number of preferred embodiments of the present invention have been shown and described but it is to be understood that the drawing and accompanying description are for the purpose of illustration only and do not limit the invention and that the invention will be defined by the appended claims.

In the drawing, Fig. 1 is a schematic view of an antenna and feeder made in accordance with the principles and teachings of the present invention, and wherein the antenna is a simple conductor,

Fig. 2 is a schematic view of another form of feeder and antenna made in accordance with the principles and teachings of the present invention, and wherein a part of the antenna is a vertically-disposed tower or element of a building,

Fig. 3 is a schematic view of an antenna. and feeder similar to the antenna and feeder of Fig. 2, but wherein the feeder is suspended from the antenna and wherein the leads between the feeder and antenna are adjustable,

Fig. 4 is a schematic view of a feeder and antenna wherein the feeder is suspended from a tower and wherein the antenna consists of cables supported by a pulley system,

Fig. 5 is a side elevational view of one form of lead extending between and connecting a feeder andv an antenna,

Fig. 6 is a plan view of the lead, feeder and antenna shown in Fig. 5,

Fig. 7 is a schematic view of a feeder and antenna wherein the antenna is less than one half /2) a wave length in height,

Fig. 8 is a schematic view of the upper end of an antenna which has an extensible portion,

Fig. 9 is a broken view of the lower portion of an antenna and feeder similar to the antenna and feeder of Fig. 7, but wherein the feeder has a trombone adjustment,

Fig. 10 is a schematic view of a feeder and antenna wherein the effective vertical dimension of the antenna is varied by raising or lowering a float,

Fig. 11 is a chart obtained by plotting the voltage standing wave ratio of an antenna against variations in the distance between the leads which extend between the concentric transmission line and the antenna,

Fig. 12 is a chart obtained by plotting the voltage standing wave ratio of an antenna against variations in the length of the projecting end of the antenna,

Fig. 13 is a schematic view of the antenna and feeder with which the data for Figs. 11 and 12 was obtained,

Fig. 14 is a schematic view of an antenna and feeder, wherein the antenna has a vertically-disposed portion and a horizontally-disposed portion, and wherein the length of the vertically-disposed portion can be changed, and

Fig. 15 is a schematic view of another feeder and antenna, wherein the antenna has a vertically-disposed portion and a horizontallydisposed portion and wherein a float can be moved to adjust the effective vertical length of the antenna.

Referring to the drawing in detail, the numeral 20 denotes the outer conductor of a coaxial cable; that cable serving as the feeder for an antenna. Coaxial cables are just one form of concentric transmission line, and other concentric transmission lines such as sheathed conductors or the like can be used. However, the use of coaxial cables is preferred. The numeral 22 denotes the inner conductor of the coaxial cable; and an insulating endseal 24 coacts with a number of annular insulators within the coaxial cable to maintain the inner conductor 22 and the outer conductor 20 precisely coaxial.

The coaxial cable will be suitably coupled to the output of a transmitter, not shown, or to the input of a receiver, not shown; and it will conduct the electromagnetic waves to or from the antenna. The antenna is denoted by the numeral 26; and it takes the form of a simple conductor which is connected at one end to the inner conductor 22 of the coaxial cable, and which is connected at the point 28 to the outer conductor 20 of the coaxial cable. The vertically-directed portion of the antenna 26 is parallel to and closely adjacent the outer conductor 20 of the coaxial cable; the vertically-directed portion of the antenna being spaced only a small fraction of a wave length away from the outer conductor 24).

The antenna 26 will have a linear length, which when added to that portion of conductor 20 above the point 28, will provide a linear length greater than one wave length of the electromagnetic waves to be radiated or intercepted by the antenna. As will be obvious, the antenna 26 will have to be longer for electromagnetic waves with a long wave length than it need be for electromagnetic waves with short lengths. In constructing the antenna 26, a length should be selected which will make the combined linear length of antenna 26 and the portion of the conductor 20 above point 28 greater than the wave length of the longest electromagnetic waves to be radiated or intercepted. The antenna 26 can be enabled to radiate or intercept electromagnetic waves of shorter wave lengths by connecting lead 30, or lead 32, or both between antenna 26 and outer conductor 20. These leads will reduce the effective linear length of the antenna 26 and the outer conductor 20 as desired.

Proper setting of the

leads

30 and 32 will facilitate precise impedance-matching of antenna and feeder; thus securing efiicient radiation or reception of the electromagnetic waves by the antenna. It will usually be desirable to adjust the

leads

30 and 32 so the dimension h, the vertical distance between the lead 30 and the upper end of antenna 26, on Fig. 1 will be slightly less than one third /3) of a wave length and so the dimension i, the vertical distance between the

leads

30 and 32, on Fig. 1 will be one half /2) of a wave length of the electromagnetic waves to be radiated or intercepted. However, the dimensions h and i can be varied as desired to attain a standing wave on the antenna. By moving the lead 32 up and down it is possible to simultaneously change the dimensions h and i. This arrangement facilitates ready impedance-matching.

The antenna need not take the form of a simple conductor as indicated in Fig. 1; instead the antenna can take the form of a tower, a downspout, or any other vertically-directed element of a building. As shown in Fig. 2 a coaxial cable can be placed in parallel relation with and closely adjacent a tower; and it can utilize that tower as an antenna. In Fig. 2, the coaxial cable is denoted by the numeral 34 and the tower is denoted by the numeral 36. A lead 38 extends between the inner conductor of coaxial cable 34 and the tower 36, and a lead 40 extends between the outer conductor of cable 34 and the tower 36. In addition the outer conductor of cable 34 is grounded by lead 33. The leads 38 and 40 are shown spaced apart a distance equal to one half A) of the wave length of the electromagnetic waves to be radiated or intercepted by the antenna. The tower 36 will then act as the antenna and will radiate or intercept the electromagnetic waves.

Although shown as a tower, the vertically-directed element could be the down spout of a building, or it could be any vertically-directed metal element of a building adjacent the outer surface of the building. In making it possible to utilize the vertically-directed elements of buildings as antennas, the present invention minimizes the cost of feeder and antenna installations. In the installation shown in Fig. 2, the vertically-disposed portion of coaxial cable 34 will be supported by the tower 36, through the conjoint action ofleads 38 and 40. The horizontally-disposed portion of that cable can be rested upon or supported above the ground, as desired.

In Fig. 3, a tower 42 is shown; and that tower is similar to the tower 36 of Fig. 2. However, the tower 42 has a horizontally disposed arm 44 projecting outwardly from the top thereof. A cable 46 extends downwardly from the outer end of the arm 44 to engage and support a coaxial cable 48; the inner conductor of the coaxial cable 48 being electrically connected to cable 46. The coaxial cable 48 extends downwardly in parallel relation to the tower 42, and it is spaced only a small fraction of a wave length from the tower 42. A lead or connector 50 extends between and electrically connects the cable 46 and the tower 42; and a lead or connector 52 extends between and electrically connects tower 42 with the outer conductor of coaxial cable 48. In addition the outer conductor of cable 48 is grounded by lead 47.

Either or both of the

leads

50 and 52 can be moved up or down while electrically connecting the tower 42 with the conductors of coaxial cable 48. Lead 52 can be moved to change the distance subtended by

leads

50 and 52 without changing the length of the portion of tower 42 above lead 50. Lead 50 can be moved to simultaneously change the distance subtended by

leads

50 and 52 and the length of tower 42 above lead 50. The combination of lengths and distances possible with the movable leads 50 and 52, makes impedance-matching easy. The particular advantage of the arrangement shown in Fig. 3 is that the antenna 42 can be used to radiate and intercept a number of electromagnetic wave of different wave lengths, while still keeping the feeder and antenna Matched. In changing from electromagnetic waves of one wave length to another it is only necessary to move the

leads

50 and 52 to attain the desired matching for the new wave length.

Fig. 4 discloses a tower 54 which is provided with a horizontally disposed arm 56 at the top thereof; arm 56 being longer than arm 44 of tower 42 in Fig. 3. A cable 58 has one end secured to arm 56, and that cable extends downwardly to and is electrically connected with the inner conductor of a coaxial cable 60; that coaxial cable extending downwardly in parallel relation to tower 54. An extension of cable 58 extends upwardly from the point of connection of that cable with the inner conductor of coaxial cable 60; and that extension passes over the lower pulley of block 62, under the upper pulley of block 64, over pulley 66, and under the upper pulley of block 62 to arm 56 where it is held adjacent the said one end of cable 58. The block 64 is connected to tower 54 at the height of the upper end of coaxial cable 60, and it electrically connects the extension of cable 58 to that tower. By raising the end of the extension of cable 58 upwardly, it is possible to raise the block 62 upwardly; the upper end of coaxial cable 60 moving closer to tower 54 to permit upward movement of block 62. The outer conductor of the coaxial cable 60 is indirectly connected to ground by a cable 68; that cable extending under the upper pulley of block 70, over the lower pulley of block 64, under the pulley 72, and over the lower pulley of block 70 to ground. The outer conductor of coaxial cable 60 is connected directly to ground by conductor 61.

The extension of cable 58 and the cable 68 serve as a cable dipole; and the effective length of that dipole is determined by the vertical distance between the

blocks

62 and 70. Hence raising and lowering block 62 will vary that effective length and facilitate impedance matching of the feeder and antenna.

Fig. 7 discloses another form of vertically-directed conductor that can be used in radiating or intercepting electromagnetic waves. This conductor takes the form of a tower, and it is denoted by the numeral 72. A conductor 74 is connected to the top of tower 72; and it has a portion thereof which extends downwardly in closely-spaced, parallel relation with tower 72 to engage the inner conductor of a coaxial cable 78. Intermediate the ends of that portion of conductor 74 is a horizontallydisposed loop 76, and each of the sides of the loop is preferably longer than one quarter A) of a wave length. A lead or connector 75 extends between and electrically connects the sides of the loops; and adjustment of the position of this lead determines the efiective electrical length of the loop. A lead or connector 80 extends between and electrically connects tower 72 and conductor 74; and adjustment of the position of this lead determines the effective electrical height of tower 72.

The inner conductor of coaxial cable 78 is connected to tower 72 by loop 76, lead 75, conductor 74, and lead 80. The outer conductor of coaxial cable 78 is connected to tower 72 by ground. This particular arrangement is useful where the overall height of the tower 72 is less than one half of a wave length of the electromagnetic waves to be radiated or intercepted because the portions of conductor 74 and loop 76 between the

leads

75 and 80 can have an overall efliective length greater than the height of tower 72.

Figs. and 6 disclose one way in which the lead 80, the tower 72, and the conductor 74 of Fig. 7 can be made. The tower 72 will have a channel 82 formed at one side thereof in such a way that the channel provides an elongated, vertically-disposed recess. The conductor 74 will have upstanding sides 84 that will form a channel, and that channel will be positioned so the recess formed thereby opens into the recess formed by channel 82 on the tower 72. The lead 80 will have two metal discs 86 and a pulley 88 secured to a shaft 90; and the shaft 90 will be dimensioned so the discs 86 bear against and electrically connect the tower 82 and the sides 84 of conductor 74. Pulley 88 can receive a rope or cable; and that rope or cable can be used to adjust the position of the lead or connector 80.

Fig. 8 discloses a tower 92 which is equipped with an adjustable extension 94 at the upper end thereof. The extension 94 is held by two fasteners 96; the fasteners permitting selective setting of the extension 94 relative to the tower 92. A conductor 98 is connected to the upper end of tower 92; and a portion of that conductor extends downwardly in closely-spaced, parallel relation with the tower 92 to engage the inner conductor of a coaxial cable, not shown. A lead 100 extends between and electrically connects tower 92 with conductor 98; the lead being adjustable vertically. The particular advantage of this arrangement is its ready adjustment of the overall height of tower 92.

Fig. 9 discloses a tower 102 with a vertically-directed conductor 106 adjacent to it. The conductor has its lower end connected to the inner conductor of a coaxial cable 104, and its upper end, not shown, will be connected to tower 102 in much the same manner as the upper end of conductor 74 is connected to tower 72 in Fig. 7. Intermediate the top and bottom of conductor 106 is a loop 108; and that loop has a trombone adjustment 110. Shifting of the position of trombone adjustment 110 will determine the electrical length of loop 108.

In Fig. 10, the inner conductor of a coaxial cable 112 is connected to a cable 114; and cable 114 extends around pulley 116, under pulley 118, over pulley 120, under pulley 122, around pulley 124, over pulley 126, and under pulley 128 to ground. The

pulleys

118, 122, and 126 rotate about fixed pivots. Pulley 120 is carried at the upper end of a float 130 which is buoyed up by a liquid 132 held within a hole 134 in the ground, and pulley 128 is held to the lower end of float 130.

Pulleys

116 and 124 are supported by the opposite ends of a cable 136 which extends around two relatively fixed

pulleys

138 and 140 and around two fixedly mounted pulleys 142 and 144. The

pulleys

138 and 140 can be moved inwardly or outwardly to keep cable 136 taut and thus keep cable 114 taut. As the float 130 rises or falls, the vertical height of cable 114 will vary. The float 130 can be made to rise or fall by changing the level of the liquid 132 and by moving

pulleys

138 and 140 to change the downward force on float 130.

Cable 114 has one end thereof connected to the inner conductor of coaxial cable 112; the other end of cable 114 being connected to the outer conductor of coaxial cable 112 through ground. The cable 114 will serve as the antenna; and the effective portion of that antenna will extend from pulley 120 to pulley 116. Pulley 116 is electrically isolated from cable 136 by an insulator 117 and pulley 118 is electrically isolated from ground by insulator 119. Impedance-matching will be readily effected by changing the eflective vertical length of that cable, as by raising or lowering the float. The float 130 and its upwardly projecting mast can serve purely structural functions, or it can be made to serve electrical functions. In the latter case the mast can direct, reflect or radiate electromagnetic waves.

The elfectiveness of the matching done with the present invention is illustrated in Figs. ll-13. In Fig. 13 a tower 146 is shown that supports a coaxial cable 148 in closely-spaced parallel relation with it. Adjustable leads 150 and 152 extend between the tower 146 and the inner and outer conductors respectively of coaxial cable 148. The outer conductor of cable 148 is grounded by lead 149. The distance from lead 150 to the upper end of the tower 146 is denoted by the letter S, and the distance subtended by the

leads

150 and 152 is denoted by the letter B. Various changes were made in the distances S and B, and the voltage standing wave ratio was determined in each case. The data thus obtained was used in preparing the charts of Figs. 11 and 12; the ordinate in each case being the voltage standing wave ratio, and the abscissa in Fig. 11 being the distance B in terms of percent of wave length, and the abscissa in Fig. 12 being the distance S in percent of wave length.

This data was obtained by using radio waves with a wave length of twelve and six tenths (12.6) meters. Optimum matching of feeder and antenna was attained when S was approximately twenty eight percent (28%) of a wave length and when B was approximately fifty percent (50%) of a wave length. The distance between tower 146 and coaxial cable 148 was twenty (20) centimeters.

Another modification of the present invention is shown in Fig. 14. A tower 154 supports a pulley 156; and a cable 158 extends over the pulley 156. One end of cable 158 supports pulley 160 by the insulator 155, while the other end of that cable passes under movable pulley 161, and extends to pulley 164. The movable pulley 161 will be adjustably held in position by a rope or cable 162 which can be secured to a support.

The pulley 164 receives a rope or cable 166 which is attached to pulley 168, passes around pulley 170, passes around pulley 164, passes under pulley 172, passes over pulley 160 and is attached to block 174. Block 174 carlies a pulley 176, and that pulley receives the cable 178. That cable is secured to an insulator 180, it has a lead extending to the inner conductor of coaxial cable 182, it passes around one pulley of block 184, passes under pulley 186, passes over pulley 176, passes under pulley 188, passes around pulley 190, passes around the other pulley of block 184, passes around relatively fixed

pulleys

192 and 194, and passes around pulley 168 to ground. Insulator supports pulley 186.

The cable 178 will act as the antenna and it will have a vertically-disposed portion and a horizontally-disposed portion between pulley 176 and pulley 184. Changes in the length of the vertically-disposed portion of the antenna 178 can be effected by lengthening or shortening the rope 162 attached to pulley 161. Lengthening of that rope will enable the block 174 to drop downwardly and reduce the length of the vertically-disposed portion of the antenna. Shortening of that rope will pull upwardly on block 174 and increase the length of the verticallydisposed portion of the antenna. The interaction of the cables and pulleys will permit some lengthening and shortening of rope 162 without any need of shifting pulleys other than 161; but if further lengthening or shortening of rope 162 is desired the relatively fixed

pulleys

192 and 194 can be moved. Impedance-matching will be effected by changing the length of the vertically-disposed portion of cable 178.

Fig. 15 shows a coaxial cable 196 that has its inner conductor connected to a cable 198. The cable 198 has one end attached to an insulator 200; and that cable passes around a pulley 202, passes under a pulley 204, passes over a pulley 206, passes under pulley 208, passes around pulley 210, passes around pulley 212, and passes around pulley 214 to ground. Insulator 203 supports pulley 204.

Pulleys

202 and 210 are supported by the opposite ends of a rope or cable 217 which passes around pulleys 216 and 218; insulator 201 being between pulley 202 and the rope 217.

Pulleys

206 and 214 are supported by a rope or cable 220 which is connected to pulley 214, passes around pulley 222, passes under pulley 224, passes over pulley 226, passes under pulley 228, and passes over pulley 230 to engage pulley 206.

Pulleys

226 and 230 are rotatably mounted on horns at the upper end of a 7 hollow float 234, and that float is supported by the liquid 236 in a hole 238. A weight 232 is secured to the pulley 228; and that weight can hang downwardly within the hollow float 234 to keep cable 220 taut. When cable 220 is taut,

cables

198 and 217 will also be taut.

The cable 198 will be the antenna, and its effective length will be determined by

pulleys

202 and 206; and increasing or decreasing the liquid level in the hole 238 will raise or lower the float 234, thus increasing or decreasing the effective vertical height of the antenna. Such increases or decreases are easily effected, and they provide precise impedance-matching of the feeder and antenna. The cable 196 has its inner conductor directly connected to one end of cable 198, and it has its outer conductor connected to the other end of cable 198 through ground.

By using the present invention it is possible to attain precise impedance-matching of feeders and antenna, used in radiating or intercepting electromagnetic waves having wave lengths from about two one-hundredths (0.02) meter to two thousand (2000) meters. It is possible to have one antenna and feeder match for electromagnetic waves of different wave lengths. In addition, it is possible to effect the matching by remote control.

Whereas several preferred embodiments have been shown and described in the drawing and accompanying description, it should be apparent to those skilled in the art that various changes may be made in the form of the invention without affecting the scope thereof.

What I claim is:

1. An improved apparatus for radiating or intercepting electromagnetic waves that comprises an antenna, a feeder, said feeder being a concentric transmission line, said antenna being a vertically-directed elongated conductor, said conductor being parallel to and adjacent to but spaced from said concentric transmission line and being coextensive with a portion of said concentric transmission line, said antenna being always exposed to the path of movement of said electromagnetic waves, the inner conductor of said concentric transmission line being connected to said antenna at one point thereof, the outer conductor of said concentric transmission line being connected to said antenna at another point thereof, said points being spaced apart by a substantial portion of the length of said conductor, said antenna constituting an electrically conducting loop, and a lead connected to said conductor at a third point intermediate said one point and said other point, said lead extending to the outer conductor of said concentric transmission line, said third point and said one point subtending the principal radiating length of said conductor.

2. An improved apparatus for radiating or intercepting electromagnetic waves that comprises an antenna, a feeder, said feeder being a concentric transmission line, said antenna being a vertically-directed elongated conductor, said conductor being parallel to and adjacent to but spaced from said concentric transmission line and being coextensive with a portion of said concentric transmission line, said antenna being always exposed to the path of movement of said electromagnetic waves, the inner conductor of said concentric transmission line being connected to said antenna at one point thereof, the outer conductor of said concentric transmission line being connected to said antenna at another point thereof, said points being spaced apart by a substantial portion of the length of said conductor, said antenna constituting an electrically conducting loop, a lead connected to said conductor at a third point intermediate said one point and said other point, said lead extending to the outer conductor of said concentric transmission line, said third point and said one point subtending the principal radiating length of said conductor, and a second lead that has one end thereof adjustably connected to said conductor at a fourth point intermediate said one point and said third point, the other end of said second lead being connected to the inner conductor of said concentric transmission line, said leads subtending the radiating length of said conductor.

3. An improved apparatus for radiating or intercepting electromagnetic waves that comprises an antenna and a feeder, said feeder being a concentric transmission line, said antenna being a conductor that is adjacent to and is parallel to, and is coextensive with a portion of said concentric transmission line, the inner conductor of said concentric transmission line being connected to said antenna at one point thereof, the outer conductor of said concentric transmission line being connected to said antenna at another point thereof, a lead extending between said concentric transmission line and said antenna and a second lead extending between said antenna and said concentric transmission line to determine the effective electrical length of said antenna, said leads subtending a length on said antenna of approximately one half of a wave length.

4. An improved apparatus for radiating or intercepting electromagnetic waves that comprises an antenna and a feeder, said feeder being a concentric transmission line, said antenna being a conductor that is adjacent and is parallel to, and is coextensive with a portion of said concentric transmission line, the inner conductor of said concentric transmission line being connected to said antenna at one point thereof, the outer conductor of said concentric transmission line being connected to said antenna at another point thereof, a lead extending between said concentric transmission line and said antenna and a second lead between said antenna and said concentric transmission line to determine the effective electrical length of said antenna, said leads being intermediate the ends of said antenna.

5. An improved apparatus for radiating or intercepting electromagnetic waves that comprises an antenna and a feeder, said feeder being a concentric transmission line, said antenna being a conductor that is adjacent to and is parallel to, and is coextensive with a portion of said concentric transmission line, the inner conductor of said concentric transmission line being connected to said antenna at one point thereof, and the outer conductor of said concentric transmission line being connected to said antenna at another point thereof, a lead extending between said concentric transmission line and said antenna and a second lead between said antenna and said concentric transmission line to determine the effective electrical length of said antenna, said leads being intermediate the ends of said antenna, said leads being mounted for relative movement.

6. An improved apparatus for radiating or intercepting electromagnetic waves that comprises an antenna and a feeder, said feeder being a concentric transmission line, the inner conductor of said concentric transmission line being connected to said antenna at one point, the outer conductor of said concentric transmission line being connected to said antenna at another point, said antenna constituting an electrically-conducting loop which is connected to the inner and outer conductors of said concentric transmission line, and elements adjustable to determine the impedance-matching of said concentric transmission line and antenna, said elements being adjustable leads extending between said concentric transmission line and said antenna.

7. An improved apparatus for radiating or intercept ing electromagnetic waves that comprises an antenna and a feeder, said feeder being a concentric transmission line, the inner conductor of said concentric transmission line being connected to said antenna at one point, said antenna constituting an electrically-conducting loop which is connected to the inner and outer conductors of said concentric transmission line, the'outer conductor of said concentric transmission line being connected to said antenna at another point, and elements adjustable to determine the impedance-matching of said concentric transmission line and antenna, said elements being leads extending between said concentric transmission line and said antenna, said leads being/relatively movable to subtend portions of different lengths on said antenna.

References Cited in the file of this patent UNITED STATES PATENTS 2,124,424 Leeds July 19, 1938 2,138,906 Cork Dec. 6, 1938 2,153,768 Morrison Apr. 11, 1939 2,160,053 Barbour May 30, 1939 2,169,377 Walter Aug. 15, 1939 2,283,619 Wilmotte May 19, 1942 2,473,328 Brown June 14, 1949 FOREIGN PATENTS 457,468 Great Britain Nov. 3, 1936