US3453630A - Wire antenna with moveable supports to change the shape - Google Patents

Description

July 1, 1969 D. J. THOMPSON 3,453,630

WIRE ANTENNA WITH MOVEABLE SUPPORTS TO CHANGE THE SHAPE Filed Sept. 21. 1966 Sheet Of 3 DOUGLAS 1/. 7Z/aMPsaM v BY/514,4

ATTORNEY y 1, 1959 D. J. THOMPSON 3,453,630

WIRE ANTENNA WITH MOVEABLE SUPPORTS TO CHANGE THE SHAPE Filed Sept. 21. 1966 Sheet ,3 of5 N VE/V 7'0 DOUGLAS d. Dam/ 5M Swiz /M July 1, 1969 D. J. THOMPSON 3,

WIRE ANTENNA WITH MOVEABLE SUPI"ORTS TO CHANGE THE SHAPE I Filed Sept. 21, 1966 Sheet 5 3" 3 FIG.5

Flag lNVEA/TOR DOUGLA s J. 7Z/oMPsoA/ sYl,/M

A Woe/w: v

United States Patent US. Cl. 343-757 9 Claims ABSTRACT OF THE DISCLOSURE An antenna formed by directing an electrical conductor around several support points. One or more of the supports is moveable to change the shape of the antenna.

This invention relates to UHF/VHF antennae, and more particularly to improvements in antenna systems for increasing the quality of the signals received thereby.

The development of antennae for UHF/VHF electromagnetic signal reception has included many innovations designed to increase the gain of the antenna (the amount of useful electrical energy derived through the antenna from a remotely-transmitted signal). A problem encountered in the reception of signals from commercial television broadcasting stations is that the antenna used must be suitable to receive signals from a plurality of transmitting stations of different frequencies, and the antenna must operate at a minimum standard of performance relative to all of the stations which may be received. In general, this problem has been solved by developing antennae having broad-band frequency characteristics of various highly-sophisticated designs such that, although optimum performance is not achieved with respect to any one station, acceptable performance is achieved with respect to all of them.

However, various interfering signals (such as other stations, noise and static) may not be adequately attenuated within a broad-band antenna relative to the strength of the signal received from the desired transmitting station. Therefore, an alternative solution to the multi-frequency requirements of receiver antennae has been to provide a tunable antenna. Tunable antennae heretofore available in the radio frequency bands have been comprised of telescopic elements, so as to permit extension and contraction of the receiving elements, and are exemplified by United States Patent No. 2,476,469 to Walker and United States Patent No. 2,599,048 to Dicke. At the lower radio frequencies, this design is useful, since the electrical length of the receiving element is varied as the physical size is varied. However, at higher frequencies, such as in the VHF and UHF television bands, the electrical properties of telescoping antennae become more complex, and sucha design no longer achieves optimum tuning. A first reason for this is that the antenna elements continue to have the same mass at any length to which they are tuned. As the length is decreased, elemental units of inductance tend to become elemental units of capacitance. The mass as a whole therefore tends to resonate at more nearly the same frequency, even though its physical length is changed. It follows that telescoping elements are less effective in achieving electrical tuning by changing physical size in the VHF and UHF bands.

An undesired transmitting station which is located at a great distance from the receiving antenna may at times tend to interfere with a desired transmitting station having the same frequency. Furthermore, noise, static and other spurious signals may tend to emanate from various sources within the effective range of the antenna. Rotating a directional antenna provides significant attenuation of all signals which do not emanate from the direction in which the antenna is pointed. But it is also known in the prior art that any transmitted signal received at the receiving elements of an antenna over a slightly remote path (such as being reflected thereto from a reflectory object) may have such a phase relationship with respect to another signal which arrives at the antenna receiving elements over a direct path, that the signals may add to or subtract from one another. This is due in part to the fact that transmitting stations transmit a pattern which is generally non-directional, therefore covering all points of the compass. It is also due to the fact that, although the transmitted electromagnetic radiation is generally horizontally polarized, the signals radiated from the transmitter are not all perfectly horizontal; thus some signals are directed somewhat downwardly, at a lower angle than other signals. These low-angle signals (called ground waves) are reflected from the ground, upwardly, and may be received at the receiving elements of the antenna at a time which is somewhat later than the time that the directly received, horizontally oriented signals are receivedv Similarly, radiation which is initially transmitted in a different direction may be reflected over a few degrees so that even though initially radiated horizontally, the horizontal distance to the receiver is longer than the comparable distance for simultaneously transmitted electromagnetic waves which are directly received from the transmitting station. Where the desired signals are of such a phase orientation as to be additive, they provide a relatively high-strength signal area, called space loops. Where they are subtractive, they provide a relatively lowstrength area called space nodes. The elimination of noise, interfering stations, and ghosts may therefore be fully achieved by using a tunable antenna having the directional ability described heretofore, and capable of being positioned within the space loops rather than the space nodes.

It is an object of the present invention to provide an improved multi-frequency UHF/VHF receiving antenna assembly.

Another object is to provide such an improved antenna assembly having a high gain characteristic at a variety of different frequencies.

It is also an object to provide such an antenna assembly having a high ratio of desired signal strength to noise and interfering transmitter station signals.

Still another object is to provide such an antenna assembly which is relatively economical and simple to manufacture and which is relatively simple in operation so as to be adapted to use with home television receivers.

A specific object is to provide a novel antenna assembly for receiving UHF/VHF signals which is capable of being properly oriented into a particular point in space to take advantage of maximum desired signal strength and capable of frequency adjustment without having unwanted conductor stubs and the attendant multiple signals which create ghost patterns and signal losses.

Other objects and advantages will be readily apparent from the following detailed description and the accompanying drawings wherein:

FIGURE 1 is a fragmentary rear perspective view of an antenna assembly embodying the present invention with a portion of the mast and mast stub broken away to reveal internal construction;

FIGURE 2 is a schematic illustration of an embodiment of the form of a bow tie antenna;

FIGURE 3 is a fragmentary front perspective view of an antenna assembly embodying the bow-tie design of FIGURE 2;

FIGURE 4 is a fragmentary rear view of another antenna assembly embodying the present invention;

FIGURE 5 is a fragmentary side elevational view of the antenna assembly shown in FIGURE 4 with a portion sectioned for clarity of illustration;

FIGURE 6 is a sectional view along the line 66 of FIGURE 5;

FIGURE 7 is a fragmentary rear view of a further embodiment of the present invention; and

FIGURE 8 is a fragmentary perspective view of still another embodiment of the present invention wherein a folded dipole antenna configuration is utilized.

It has now been found that the foregoing and related objects can be readily attained in an antenna assembly including at least one movable cable guide means with a flexible electrical conductor movably disposed with respect to the cable guide means and at least one fixed point so as to form a configuration of a receiving antenna element. Tuning means are provided for moving the cable guide means relative to the related fixed point so as to change the electrical dimensions of the receiving antenna element and thus provide adjustment in the size of the antenna elements which form the configuration of the antenna array.

More specifically, an antenna is formed by the disposition of flexible electrically-conductive wire disposed about pulleys or guides, the pulleys or guides being arranged so that they form a related length of electrical conductor into a receiving element of an antenna. The element of the antenna is increased in size by moving one or more of the pulleys or guides outwardly from a fixed point.

In accordance with a preferred aspect of the invention, the guides or pulleys are so arranged that the conductor, as it is removed from the antenna element formed thereby during contraction of the antenna element, becomes part of the television lead-in transmission line. Thus, there are no stray ends or tails to cause leakage or alternation of the resonant effect of the antenna. Further, as the desired frequency increases, the mass of the antenna decreases, and the elements within the antenna retain substantially the same electrical properties, proportionally altered by a reduction in size. Additionally, this design avoids the possibility of re-radiation of signals which could otherwise tend to create undesrable interference images in the received signal pattern (such as ghosts in the picture of a television receiver).

In accordance with still another aspect of the present invention, the antenna may be raised and lowered, or shifted laterally, so as to seek out space loops and to avoid space nodes, whereby the antenna itself is in a pattern of maximum signal strength to take advantage of the greatest possible electromagnetic field in the immediate area.

Relatively simple mechanical elements may be utilized for adjusting the physical size of the receiving elements of the antenna and for raising and lowering the antenna which permits employment of a simple configuration of electrical control and connection for the operation of motors which perform these functions. Additionally, a variety of alternative embodiments may be utilized for the manipulation of the size of the antenna elements which enable the choice for antenna assemblies of differing cost, reliability, and performance, as may be required to suit a variety of needs in the marketplace.

In one form the cable guide means includes two cable guides and the tuning means is adapted to move the cable guides along paths which diverge outwardly away from the fixed point and the flexible electrical conductor is disposed about the fixed point and the cable guides so as to define substantially a triangle. Preferably one end of the flexible conductor is disposed at the fixed point and the conductor follows a path from the fixed point around each of the guides and again past the fixed point so as to form a substantially closed triangular loop. In the preferred embodiment, a second triangular loop generally similar to the first herebefore described is disposed in the same plane and adjacent to the first loop. The fixed points of the two loops are spaced in proximity to one another so that the triangular loops comprise a double element array with one element being the mirror image of the other. The lengths of the flexible electrical conductors not included within the related triangular loops are disposed parallel to each other so as to form a transmission line.

In another embodiment, the cable guide means includes two cable guides each cooperating with a fixed point with the flexible electrical conductor being disposed relative to the two guides and cooperating fixed points so as to form a variable length folded dipole. Orienting means are additionally included which cooperate with the tuning means and which are disposed with respect to the two fixed points and the flexible electrical conductor so as to orient differential elements of the flexible conductor not included within the dipole in side-by-side relationship so as to form a transmission line. Most desirably, the orienting means spaces the side-by side conductors of the transmission line at a distance from one another which provides an impedance in the transmission line which is substantially equal to the impedance of the folded dipole.

In accordance with one aspect, the tuning means comprises a base having a slot therein and a member slidably disposed in the slot which supports the guide means. Suitable means drive and selectively position the slidable member at different points along the length of the slot so as to achieve the desired variation in dimension. The drive means may comprise a reversible motor, gear means driven by the motor, and a driver cooperating with the gear means and which is engaged with the slidable mem ber so that the drive means operates the slidable member in opposite directions within the slot in response to the direction of rotation of the motor.

Referring now in detail to FIGURE 1, an antenna assembly is shown connected to the upper end of a regular TV antenna mast 20 which is connected to the assembly by means of a coupling 22 which may be fastened thereto by any suitable means such as the bolt or rivet 24. Affixed to the coupling 22 is a housing 26 containing a gear train, a thrust bearing and other suitable apparatus (not shown) to drive the worm gear or lead screw 28 by the motor 30. Rotation of the worm gear or lead screw 28 is confined within an internal contact helical spur gear 32 so that, as the worm gear or lead screw 28 rotates, it will cause the helical spur 32 to advance thereon. The helical spur 32 is aflixed by suitable fastening means 34 to the inside of a vertically moving mast 36, so that advancement of the helical spur 34 will cause a raising or lowering of the vertical moving mast 36.

The vertically movable mast 36 is prevented from rotation due to stresses placed thereon through the action of the helical spur 32 by means of an eye bolt 38 which is afiixed to the helical spur 32 and which passes through a slot 40a in the fixed mast stub 40, within which the vertically movable mast 36 is slidably disposed. The eye ball 38 engages a limit switch operating rod 42 which is constrained by a pair of eye bolts 44, 46 rigidly affixed to the fixed mast stub 40.

Upon the limit switch operating rod 42 are fastened an upper limit switch rod driver 46 and a lower limit switch rod driver 48. When the helical spur 32 reaches its uppermost operating position relative to the limit switch operating rod 42, the eye bolt 38 will contact the upper limit switch rod driver 46 so as to raise the limit switch operating rod 42, thereby causing an eyelet 42a at the lower end thereof to operate a reversing limit switch 50 by moving its toggle arm 52 from a first position to a second position. Similarly, as the helical spur 32 reaches its lower limit of travel, the eye bolt 38 will contact the lower limit switch rod driver 48 so as to cause the limit switch rod 42 to move the toggle arm 52 from the second position to the first position (as shown in FIGURE 1). The worm gear or lead screw 28 is supported co'axially by the upper bearing 54 which permits free rotation thereof Within the vertically movable mast 36.

At the top of the vertically movable mast 36, a pair of U-bolts 56 firmly clamp the base member 58 thereto. On the base member 58 is an antenna assembly which includes a motor 60, preferably of the reversing type, which is connected through a gear train 62 to a drive drum or winch 64. In driving relationship with the winch 64 is a drive cable 66 which passes about the idler pulley 70 and has its opposite ends affixed to a central link 68 which is pulled to the right or left as seen in FIGURE 1 in response to the direction of rotation.

The central link 68 operates an upper link 72 and a lower link 74 which have one end pivotably fastened thereto by means of suitable pins or bolts 76. The opposite ends of each of the links 72, 74 are pivotally connected to ends of an upper post 80 and a lower post 82, respectively, and are held in place thereon by corresponding spring clip fasteners 84, 86.

The posts 80, 82 are slidable in the slots 88, 90- which are formed in a base 92 of the antenna proper, and wobbling is substantially eliminated by their respective collets or keepers 94, 96 which provide bearing surfaces and which restrict the longitudinal movement of the posts. Rotatably mounted on the opposite ends of the posts 80, 82 are a pair of idler pulleys 98, 100 about which a flexible electrical conductor 102 extends.

As seen in the embodiment of FIGURE 2, the flexible electrical conductor 102 is fixed at one end to the bearing support for the idler pulley 104 over which the conductor 102 also extends for movement along its length. This forms a left hand triangle 106 (as seen in FIGURE 2), which together with a similar right hand triangle 108 comprises a bow-tie type of antenna. The right hand triangle 108 is comprised of similar elements (designated with the reference subscript a) similar to correspondinglynumbered elements of the left-hand triangle 106. The flexible conductors 102, 102a terminate at corresponding terminals 110, 112 to which are also attached the two leads of a regular TV lead-in wire 114. As the pulleys 98, 98a, 100, 100a are caused to move outwardly from the guides 104, 10441, the size of the triangles 106, 108 formed by the flexible conductors 102, 102a is increased, and the length of flexible conductor 102, 102a disposed between the fixed pulleys 104, 104a and the terminals 110, 112 is lessened. As the size of the triangles increases, the tuned frequency of the antenna decreases.

Rotating with the winch 64 is a wrap-up pulley 116 having a cable :118 fixed thereto and wrapped thereabout so that, as the winch 64 rotates in either direction, the wrap-up pulley 116 will take up or release corresponding lengths of the cable 18. The cable 118 is fastened by means of a spring 120 to a companion cable 122 which is passed about an idler pulley 124 affixed to the bottom of the cable channel guide member 126. As may be seen, the other end of the cable 122, in the embodiments of FIGURES 5 and 6, is fixed to a cable channel so that as the antenna expands and contracts, the lengths of flexible conductor 102, 102a disposed between the fixed pulleys 104, 104a and the terminals 110, 112 are maintained taut by the operation of the wrap-up pulley 116 in combination with the spring 120.

Turning now to FIGURE 3 in detail, the base 92 has affixed thereto the cable channel guide member 126 together with a pair of support legs 128 (only one of which is seen in FIGURE 3), an end support 130, and a pulley support 132. The legs 128, support 130', and pulley support 132 may be aflixed to the cable channel guide memher 126 or formed as an integral part thereof. The pulley support 132 has a pair of angularly' disposed surfaces 134, 136 on each side thereof which preferably are defined by angles which divide between the related pulleys or guides 104 and 137, or 104a and 13741, the task of changing the course of the flexible conductor 102 or 102a from vertical to some angle above horizontal (considering that the base 92 is normally in a vertical plane). In the case where the flexible conductor 102 or 102a forms an included angle at the pulley 104 or 104;: of 30 (which ensures substantially a 300 ohm impedance for this type of antenna), the surface 136 may be at an angle of 35 with respect to the vertical edge of the cable channel guide member 126, and the surface 134 may be at an angle of 70.

A reversing upper limit switch 138 is mounted on the lowermost portion of the pulley support 132 in this embodiment but may be mounted otherwise at the upper limit of travel of the cable channel 140. For instance, the upper limit reversing switch 138 may be an integral part of a limit switch structure inserted into a recess provided therefore as illustrated by the dotted lines 142 or the switch 138 may be mounted at the rear of the pulley support 132, with an actuating means protruding therethrough.

The cable channel supports the terminals 110, 122 which join the flexible conductor 102a to the television lead-in wire 114. Aflixed to the cable channel 140 is the cable 122 which (as illustrated in FIGURE 1) maintains a constant downward tension (as seen in FIG- URE 3) on the flexible conductors 102, 102a without putting undue stress upon the posts 80, 82, 80a and 82a.

A second embodiment of driving means for the antenna illustrated in FIGURES l-3 is shown in FIGURE 4 with the antenna in its fully contracted position. The links 68, 68a are driven by a rack and pinion. assembly, rather than by the cable 66 and its associated apparatus as shown in FIGURE 1. In FIGURE 4, the motor and gear train (shown in FIGURE 1) rotate a pinion 152 Which drives the respective links 68, 68a inwardly or outwardly through the racks 154, 154a depending upon whether the antenna frequency is to be increased or decreased. The racks 154, 154a are suitably restrained by guides 156 and the links 68, 68a may be mounted on the forward and reverse sides, respectively, of the cooperating rack 154, 154a to avoid interference between the various parts. The pinion 152 also meshes with a spur gear 158 which may drive a potentiometer 160 (shown only schematically in FIGURE 4) to provide an indication of the positional setting of the antenna in a manner similar to the use of a potentiometer to provide an azimuth indication in conjunction with a television antenna rotor.

FIGURE 5 illustrates the antenna assembly shown generally in FIGURE 1 with the rack and pinion drive shown in FIGURE 4. Here, the pulley 104 has been moved slightly to the left of its natural position so as to illustrate the route of the flexible conductor 102 as it passes over the guides 98 and 100, and the end support 130 and pulley support 132 have been omitted for clarity. In addition, the left-hand end (the rear) of the post 80 has been broken away for simplicity, and none of the driving links 68, 72, 74 are shown except for the lower end of the link 74 as it is attached to the post 82. It can be seen that the pulley 116 together 7 with cables 118 and 122 are utilized to keep a relatively constant tension on the cable channel 140 at various positions of tuning of the antenna. In this embodiment, the spring tensioning means utilizes a spring loaded tension bolt assembly 164.

The cable channel guide member 126 has an additional support 166 with an extension 168 upon which an idler pulley or cable guide 170 is mounted (in the same fashion as the idler pulley or guide 124 is mounted to the cable channel guide member 126). The SuppOrting member 166 may be formed as an integral part of, or affixed to, the rear support member 172 to which the spring tension assembly 164 is also affixed, and the rear support memher 172 is atfixed to the base 92 by the fastener 174. At the bottom of the cable channel guide member 126 is a reversing lower limit switch 176, mounted so as to be operable by the cable channel 140 as it reaches its lower limit of movement.

As can best be seen in FIGURE 6, the cable channel 140 has a cross-section of generally lipped C-shaped configuration which permits it to slide up and down on the cable channel guide member 126, which is of generally T-shaped configuration, without interference from support members 128, 166.

Although the terminals 110, 112 are illustrated as simple bolt and nut assemblies in FIGURES 1 and 2, they preferably are constructed as shown in FIGURE 6, wherein a hole (such as a) is provided for clipping the flexible conductors 102 and 102a so as to completely terminate them within the terminals without the necessity of forming loops in the ends thereof, or without leaving tails within them which would cause dielectric leakage and loss of signal strength.

In FIGURE 7 there is shown a simplified side elevational view of an alternative embodiment similar to the rack and pinion of FIGURE 4 but having the advantage of driving parallel to the orientation of the slots 88 90. Therein, a worm gear 190 is used to drive a pan of helical spur gears 192, 194. Each of the helical spurs 192, 194 includes a related pair of worm gears or lead screws 196, 198 which have threads designed so that, as the spurs 192, 194 rotate, the threads 196 cause a motion to the left or to the right, respectively, by reason of their engagement with internal contact helical spur gears 204. The spurs 192, 194 include slots for keepers or bearings 200 and the lead screws 196, 198 have their outer extremities mounted in suitable bearings 206.

As the motor and gear train 60, 62 rotate in one d1rection or the other, the internal contact helical spurs 202, 204 will cause a contraction or an expansion of the antenna elements, which are not shown in FIGURE 7 due to the fact that the slots 80, 82 etc. appear beneath the worm gears or lead screws 196, 198. Since the internal contact helical spurs 202, 204 are adequately supported on the lead screws 196, 198, there is no binding or undue tension placed upon any of the parts of the antenna utilizing the arrangement of FIGURE 7. As an alternative, however, for an inexpensive design, the base 92 may be eliminated and a frame may be utilized to support a motor and bearings 202, 204, 206 thus eliminating the need for guide slots 80, 82. However, such an arrangement would not be as durable as an arrangement including both a base 92 with slots 80, 82 and the worm drive arrangement shown in FIGURE 7.

There are many possible alternatives in the method of driving the posts 80, 82 etc., so as to tune the antenna. In a variation of the cable drive of FIGURE 1, additional cable guides could be provided at the ends of the slots, and the links 68, 72, 74 etc. eliminated. This has the advantage that the force exerted on the posts 80, 82 and collets 94, 96 is now directly parallel with the orientation of slots 88, 90 so that there is no tendency for binding. As another alternative to the drive shown in FIGURE 1, the link 68 may be eliminated and the links 72 and 74 pivotably joined together.

For a simple design, a plurality of tension springs could be used to bias the antenna into its fully expanded position. The drive of the antenna would then be accomplished by causing the wrap-up pulley 116 (shown in FIGURES l and 5) to draw the antenna into a contracted position by exerting pressure on the cables 118, 122 so as to utilize the flexible conductors 102, 102a directly as a driving means for causing the posts 80, 82 to be drawn along the slots 88, 90. This would be a relatively simple and cheap apparatus, but it has the disadvantage of not being positively driven, which may backlash and additionally would not operate properly unless the antenna were completely housed in a protective environment as described hereinafter.

FIGURE 8 schematically illustrates an alternative embodiment of the invention in the form of a folded dipole antenna, wherein a plurality of pulleys or cable guides 104, 104a, 137, 137a perform functions similar to functions of like-numbered elements in FIGURE 3. The dipole itself is formed about a pair of non-conducting pulleys 114, 146 mounted on posts 145, 147 which are adapted for sliding in a pair of related horizontal slots 148, 150. The mechanism for causing the sliding of the posts holding the pulleys 144, 146 may be similar to that shown in FIGURE 1, wherein the cable 66 Would be connected directly to the back of the post 145 rather than to the link 68 although other embodiments of the bow-tie antenna drive means described hereinbefore may be adapted for operating the dipole antenna illustrated in FIGURE 8. The size of the guides 144, 146 is chosen to space the dipole elements less than of a wave length apart in accordance with well-known design principles. The drive motors 30, 60, and the controls therefor, may be of any suitable type. One system may use well known reversible motors, in which the drive action may be selected in either direction of rotation. For use therewith, the limit reversing switches 50, 138, 176 may be simple, double-pole, double-throw switches which reverse the connection to the motor whenever operated.

One of the great advantages of an antenna in accordance with the present invention over previous tunable antennae is that the impedance remains substantially constant, as does the quality factor (Q) which is the ratio between the impedance and the ohmic resistance. This means that the senstivity of the antenna, and its attendant ability to discriminate between the desired transmitted signal and spurious signals, will remain constant across the range of tuning capability of the antenna. Additionally, this aspect is further enhanced by the fact that an antenna having a 300 ohm impedance is easily manufactured, permitting use of regular, inexpensive TV lead-in wire. This impedance can be maintained at any size due to the fact that elements of flexible conductor 102, 1020 which are not included within the antenna array formed by the cable guides 104 and 98, or 144 are actually formed into a transmission line, which likewise has a 300 ohm impedance. Thus, as the antenna varies in frequency, the electrical characteristics at any given frequency remain substantially the same; similarly, there are no additional adjustments required due to the removal of flexible conductor from the antenna array as the size of the antenna is decreased. This particularly important because skin effects and other problems become more acute at the higher frequencies which occur when the antenna is at its smallest size.

Another advantage of an antenna in accordance herewith is that the good properties of an antenna array are not lost or reduced by space nodes, so that the theoretical advantages of a tuned antenna are made practical by the elevation adjustment proivded herein. A further advantage of this invention is that rather than being an oversized, heavy, complex array, the structure of this invention is small, light and simple. The rectilinear base design permits the structure to be inexpensively shielded from weather by a simple plastic housing, or other similar means.

Referring again to FIGURE 1, the materials for the base 92 and for the other structural pieces such as the cable channel guide member 126 should preferably be made of non-conducting materials such as suitable synthetic plastics. Since the motor 60 and gear train 62, as well as the rack and pinion structures, are mounted close to the antenna, they will have little effect on the operation thereof. In addition, the drums, cable pulleys or guides, the rack and pinion and the worm drive of FIG- URE 7 may all be made of synthetic plastic. The cable guides 104, 104a should provide electrical contact with running lengths of conductor 102, 102a and the ends of the conductors and, since non-moving guides are self cleaning to ensure good electrical contact, they are preferred.

A typical size of a bow-tie antenna in accordance with this invention for UHF channels would include a base which is 25 inches wide and 8 inches high, with about 6 /2 inches vertical distance between the outer extremities of the slots 88, 90 and the cable channel guide member 126 might be 24 inches long. Since the included angle between the flexible conductors 102, 102a on each side of the antenna is about 30, the antenna will have substantially a 300 ohm impedance between the flexible conductors 102, 102a at the terminals 110, 112, so that the assembly may utilize standard 300 ohm television lead-in wire of the flat variety in which the wires are approximately /2 inch apart. Therefore, the terminals 110, 112 and the pulleys 137, 137a should be slightly more than /2 inch apart to account for the fact that an air dielectric is used between the portions of the flexible conductors 102, 102a that form the transmission line between the pulleys 137, 137a and the terminals 110, 112. In the size illustrated for UHF commercial television, the slots would have an overall length of approximately 9 inches. For VHF recepition, the overall width of the base 92 would be about 66 inches, the other dimensions being proportional to those described hereinbefore. For the lower VHF channels (2-6), it is possible that the folder dipole embodiment of FIGURE 8 would be more feasible in terms of overall size and weight in view of the environment in which such antenna are to be used. Thus, the folded dipole could be constructed with a lower wind resistance, for instance, than the bow-tie antenna.

It should be understood that the detailed hardware illustrated in the various figures hereinare illustrative of various means for performing the expansion and contraction of the antenna as well as raising and lowering it, in accordance with the present invention. However, it can be seen that the present invention provides a relatively light, small, simple antenna system which has sufiiciently good electrical characteristics as to avoid the necessity for multiple arrays and equipmentation. This not only permits a lighter weight antenna, but because the antenna may be both tuned and vertically positioned (as well as rotated) to receive a maximum signal from a particular transmitting station, it eliminates spurious noise and other interference, and substantially prevents out-of-phase reflected signals from causing ghosts or images in the television receiver. By raising and lowering the antenna array so as to achieve recepition in a space loop rather than in a space node, the etfectiveness of the tunable antenna array is further enhanced. Thus, the signal from the pre ferred antenna assembly of this design maybe properly adjusted in three ways (rotation, elevation, and antenna size) and is not affected by the presence of objects in the area, indicating that maximum efliciency is being achieved.

Although the invention has been shown and described with respect to preferred embodiments thereof, it should be obvious to those skilled in the art that the foregoing and other changes and omissions in the form and details thereof may be made therein without departing from the spirit and the scope of the invention, which is to be limited only as set forth in the following claims.

What is claimed is:

1. A receiving antenna assembly comprising a base providing at least one guide channel; at least two cable guides slidably mounted in said channel and cooperating with at least one fixed point therebetween; a flexible electrical conductor movably disposed about said cable guides and fixed point so as to form the configuration of a receiving antenna element; and drive means distinct from said flexible conductor for moving said cable guides along paths in generally opposite directions in said channel so as to change the electrical dimensions of said receiving antenna element and provide a coplanar double loop array, one loop being substantially the mirror image of the other.

2. The antenna assembly of claim 1 wherein said base has a plurality of slots providing at least one of said channels in which said cable guides are slidably mounted for movement along said paths.

3. The assembly of claim 1 wherein said base provides at least two channels which, in turn, provide four paths, a first pair of said paths diverging from a first point on said base and a second pair of said paths diverging in substantially the same relationship from a second point proximate to said first point; wherein four of said guides are slidably mounted in said channels, a guide being movable by said drive means along each of said paths and said drive means simultaneously moving all of said guides toward or all away from said points; said cable being divided into two halves to provide two ends, one of said ends being fixed at said first point with the half of said cable associated therewith following a path from said first point about the two guides movable along said first pair of paths and past said first point, the other of said ends being fixed at said second point with the half of said cable associated therewith following a path from said second point about the two guides movable along said second pair of paths and past said second point to provide loops adjacently positioned and each in a substantially closed triangular configuration.

4. The antenna assembly of claim 1 including only two of said cable guides, each of said guides cooperating with a fixed point, and wherein said flexible electrical conductor is disposed relative to said two guides and their cooperating fixed points so as to form a variable length folded dipole.

5. The antenna assembly of claim 1 wherein there are two fixed points between said guides, and wherein said assembly additionally includes orienting means disposed with respect to the two fixed points and said flexible electrical conductor so as to orient diiferential elements of said flexible electrical conductor not included within said antenna element side by side so as to form a transmission line, elements of said flexible electrical conductor being added to and withdrawn from said antenna element by being drawn from and added to said transmission line whereby a substantially constant impedance and quality factor is maintained in said antenna element as its size is varied.

6. The antenna assembly of claim 5 wherein said orienting means is arranged to space the side by side conductors of said transmission line at a distance from one another which provides an impedance in said transmission line lsubstantially equal to the impedance of said folded lpO e.

7. The antenna assembly of claim 1 wherein said drive means comprises a reversible motor, gear means driven by said motor, and a driver cooperating with said gear means, said driver being engaged to said guides to move said guides in said channel in response to the direction of rotation of said motor.

8. The antenna assembly of claim 1 wherein said antenna assembly includes means for adjusting the position of said receiving antenna element in a direction selected from vertically and laterally.

9. The assembly of claim 1 wherein said assembly includes a mast having a fixed portion and a vertically 1 1 1 2 adjustable portion movably supported relative to said 2,861,268 11/1958 Tinsley 343902 fixed portion; and wherein said adjusting means includes 3,163,863 12/1964 Fujino 343823 means to move said movable portion vertically relative to said fixed portion. T ER REFERENCES 5 Smallwood: QST, August 1963, pp. 4840 References Cited UNITED STATES PATENTS 2,474,242 6/1949 Gieringer 343-823 2,702,345 2/1955 Walter 343-823 10 343803, 822, 823

ELI LIEBERMAN, Primary Examiner.

US. Cl. X.R.

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