US3573841A

US3573841A - Television receiving antenna

Info

Publication number: US3573841A
Application number: US732427A
Authority: US
Inventors: Harry Greenberg
Original assignee: Avnet Inc
Current assignee: Avnet Inc
Priority date: 1968-05-27
Filing date: 1968-05-27
Publication date: 1971-04-06
Anticipated expiration: 1988-04-06
Also published as: BR6908689D0

Abstract

A dual band, front fed television receiving antenna comprises upper and lower crossarms forming an acute angle in a vertical plane, and supporting a plurality of dipoles of graduated length decreasing toward the front of the array. Each dipole has a pair of arms with one arm of each dipole being connected to one crossarm and the other arm connected to the other crossarm, the arms of each dipole extending horizontally in opposite directions and transversely from their associated crossarms. An outboard, close-spaced parasitic element is associated with each arm of those dipoles which have an effective length of approximately one full wavelength at a frequency in the high VHF band. Certain of the dipoles have a centrally located close-spaced parasite associated with each of their two dipole arms. UHF elements may be similarly connected to the respective crossarms with at least some of the UHF elements physically located between the two frontmost VHF dipoles.

Description

United States Patent 72] Inventor Harry Greenberg Kerhonkson, N.Y. [21] Appl. No. 732,427 [22] Filed May 27, 1968 [45] Patented Apr. 6, 1971 [73] Assignee Avnet, Inc.

New York, N.Y.

[54] TELEVISION RECEIVING ANTENNA 17 Claims, 11 Drawing Figs.

[52] US. Cl. 343/802, 343/815, 343/885 [51} Int. Cl ..H0lq 21/12 [50] Field of Search 343/792.5,

[56] References Cited UNITED STATES PATENTS 2,955,289 11/1960 Winegard 343/815 3,259,904 7/1966 Blonder et al. 343/814 3,274,605 9/1966 Rauch 343/792.5 3,355,739 11/1967 Bell et a1 343/792.5

Primary ExaminerEli Lieberman Attorney-Darby and Darby ABSTRACT: A dual band, from fed television receiving antenna comprises upper and lower crossarms forming an acute angle in a vertical plane, and supporting a plurality of dipoles of graduated length decreasing toward the front of the array. Each dipole has a pair of arms with one arm of each dipole being connected to one crossarm and the other arm connected to the other crossarm, the arms of each dipole extending horizontally in opposite directions and transversely from their associated crossarms. An outboard, close-spaced parasitic element is associated with each arm of those dipoles which have an effective length of approximately one full wavelength at a frequency in the high VHF band. Certain of the dipoles have a centrally located close-spaced parasite associated with each of their two dipole arms. UHF elements may be similarly connected to the respective crossarms with at least some of the UHF elements physically located between the two frontmost VI-IF dipoles.

Patehted April 6, 1971 3,573,841

6 Sheets-Sheet 2 INVENTOR HARRY GREENBERG ATTORNEYS Patented April 6, 1971 6 Sheets-Sheet '5 R R S O Y T E NE N w i m N T A Patented April 6, 1971 6 Sheets-Sheet 4 FIG. 4

I Y J T m 1 DBL) 2o 4U 04 y /D4U 30 oau c3u 03L f au v Pal. a 30 02L) :CZU [DZU o 1P i k 1 3 22 on. 30 l 20 2o 1 PIU 40 2 [ML C 50 IO 47 INVENTOR HARRY GREENBERG ATTORNEYS Patented April 6, 1971 3,573,841

6 Sheets-Sheet 5 FIG. 10 30 FIG. 7 8M) DTL osu

TELEVISION RECEIVING ANTENNA The present invention relates to antennas intended principally for the reception of electromagnetic energy of radio frequency within the Very High Frequency (VHF) and Ultra High Frequency (UHF) bands presently allotted to commerhigh and low bands), substantial difficulty has been encountered in providing commercially practicable antennas capable of satisfactory performance over both bands, although, presently, a number of such antennas are being marketed.

These antennas incorporate various design compromises intended to provide optimized performance from a number of different, and sometimes conflicting, viewpoints. For example, such viewpoints may concern mechanical considerations with regard to the wind resistance and rigidity of the antenna as well as its ease of installation. The primary electrical considerations, as well-known, include a properly shaped gainversus-frequency curve (including increased gain of the high band over the low band), a good impedance match with respect to the signal transmission line which is coupled to the receiver over the frequency range of interest, and a properly formed radiation pattern (i.e. high front-to-back ratio and a minimum of side lobes) for each of the channels. There are other known design criteria including, of course, the cost of manufacture and the necessity of transporting the manufactured product in commerce.

The most advanced antenna which has been commercially available for television reception is illustrated in US. Reissue Pat. No. 25,604, dated Jun. 16, I964, entitled End-Fire Planar Dipole Array With Line Transposition Between Dipoles and Impedance Increase Towards Feed," and as signed to the assignee of this application. The antenna shown in FIGS. 6 and 7 of that patent comprises a front-fed array of dipoles of graduated length increasing toward the front, with a line transposition between each pair of adjacent dipoles. A close-spaced parasitic element is associated with each of the dipoles so as to cause the active elements to have a frontwardly oriented directivity characteristic over both the high and low bands. The parasitic elements additionally serve the important function of adjusting the impedances of the individual dipoles desirably: relative to each other, to increase the ability of the rearward dipoles to contribute to the overall signal strength which is supplied by the array through the signal transmission line to the television receiver.

The present invention provides an antenna which is a sub stantial improvement over the antennas disclosed in reissue U.S. Pat. No. 25,604, particularly with respect to the gain provided in a given length. The antenna of the present invention is such that a desired gain can be achieved with an antenna array which is approximately two-thirds as long as an array providing the same gain and constructed pursuant to the above-mentioned reissue patent. This substantial increase in gain in a given length is achieved without any reduction in the remaining highly desirable electrical characteristics provided by the prior antenna, while providing substantial benefits from a mechanical viewpoint, including benefits additional to those which would normally accrue from the reduction in length of an antenna.

Also, according to the invention, an array of simplified and relatively inexpensive construction is provided which is capable of use over both the VHF and UHF television bands wherein a further reduction in length of the overall array is provided in addition to that described above.

Briefly, according to the invention, a front-fed antenna array comprises upper and lower crossarms fonning an acute angle in a vertical plane, the apex of the angle being at the front of the antenna, facing the transmitting station in the case of a receiving antenna. A plurality of dipoles of graduated length, decreasing toward the front of the antenna, have the so that a respective dipole arm is connected to each crossarm. A pair of close-spaced, outboard parasitic elements is associated with each of those dipoles which are approximately one-half wavelength long at the high end of the low VHF band. Certain of the dipoles have associated therewith a central close-spaced parasite for the purpose of providing the desired impedance relationship referred to above. Where the array is to be used for the reception of UHF signals, the UHF active dipole elements are arranged similarly to the VHF elements but at least some of the UHF elements are located between the shorter VHF elements.

The invention will be better understood from the appended drawings, in which:

FIG. 1 is a perspective view of a preferred embodiment of the antenna looking up from beneath the antenna;

FIG. 2A is a top plan view of the upper crossarm assembly shown in FIG. 1;

FIG. 2B is a top plan view of the lower crossarm assembly shown in FIG. 1;

FIG. 3 is a side elevational view of the antenna shown in FIG. 1;

FIG. 4 is a top plan view of the antenna shown in FIG. 1;

FIGS. 5 to 8 are schematic illustrations of different embodiments of a VHF antenna according to the invention;

FIG. 9 is a top plan view of a portion of an antenna array incorporating the active elements required for the reception of the UHF band; and

FIG. 10 is a side elevational view of the portion of the array shown in FIG. 9.

The antenna illustrated in FIGS. 1-4 is intended for reception of VHF signals. It comprises an upper conductive crossarm U and a lower conductive crossarm L which lie in the same vertical plane and are arranged to form an acute angle. The two crossarms are held separated by a preferably tubular support member 58 at their open ends, and are joined at their juxtaposed ends by an insulating bracket 12 described more in detail below. The antenna is supported from a mast 64 secured to both crossarms U and L.

In this particular embodiment, seven dipoles Dl-D7 of graduated length decreasing toward the apex 10 of crossarms U and L are supported on and electrically connected to the crossarms U and L. Each of these dipoles consists of two separate arms, one of which extends from and is electrically connected to crossarm U and the other of which extends from and is connected to crossarm L. In the drawings and the following description, each of the dipole arms is identified by the letter D, a number corresponding to its position with respect to the front of the antenna (the apex 10 of the crossarms U and L), and the letter U or L indicating the crossarm to which that particular dipole arm is connected. For example, the first dipole consists of a first ann DIU extending transversely from the upper crossarm U and a second arm DlL extending transversely in the opposite direction from the lower crossarm L. Each of the remaining dipoles D2D7 consists of the arms DZL, DZU to D7U, D7L, respectively, as most clearly shown in FIG. 4. The two arms of each dipole lie in the same vertical plane. In the form shown in FIGS. 1-4, the successive dipoles are staggered; that is, the successive dipoles alternate as to the direction in which they extend from each crossarm. Thus, in FIG. 2, dipole arm DlU is shown extending to the left of crossarm U, arm D2U extends to the right, arm D3U to the left, and so on. A signal transmission line 12 is electrically connected to the front of crossarms U and L and serves to feed signals from the array to the television receiver.

Each of the dipole arms is secured to rigid conductive bracket 20 and fastened (as by riveting) at 22 to its associated crossarm so as to electrically connect the dipole arm to the crossarm so that the crossarms U and L can serve both as a transmission line for the dipoles DI through D7 and as the supporting means for the dipoles. This arrangement, whereby successive dipole arms extend in opposite directions from the same crossarm, provides an array of dipoles having effectively opposed arms thereof connected to the respective crossarms, a line transposition between adjacent dipoles. The effect of such a line transposition on a front-fed antenna array is to reduce the ability of the antenna to receive signals from the rear, thereby increasing its front-to-back ratio, as more fully described in the aforementioned Reissue US. Pat. No. 25,604.

The dipoles may be equally spaced, that is, the distances between successive dipoles, arms DlU, D2U, etc., as measured along crossarm U (and arms DlL, D2L, etc., as measured along crossarm L) may be the same. This feature is desirable with respect to considerations relating to the manufacture of the array. If desirable for practical purposes, the spacing of the dipoles may be varied slightly to improve the response of the array at certain channels.

Close-spaced central parasitic elements C2U-C7U are fastened at 24 to respective insulating brackets 26 supported on the upper crossarm U. These parasitic elements are close to their respective dipole elements, and for mechanical reasons are preferably mounted below the crossarm slightly below and to the rear of the dipole arms D2U-D7 U, respectively.

However, thislocation is not essential, and they may be suitably mounted anywhere close to their respective dipole arms so as to give the appropriate electrical effect. The parasites are parallel to their associated dipole arms and symmetrically disposed with respect to crossarm U. Identical central close-spaced parasites C2L-C7L, associated with the dipole arms D2L-D7L,' respectively, are similarly secured to the lower crossarm L. All these central parasites are insulated from the crossarms and function in essentially the same fashion as the close-spaced central parasites illustrated in FIGS. 6 and 7 (at ld--60d) of the aforementioned reissue Pat. No. 25,604, which sets forth applicable criteria for determining parasite length and spacing. As explained in said reissue patent, the close-spaced central parasites C2U, C2L to C7U, C7L cause the respective dipoles D2-D7 to have (1) a bidirectional directivity characteristic (as opposed to multilobed) on the upper VHF band, and (2) an impedance relationship relative to the remaining dipoles such that it will not be required to provide a disproportionate share of the total energy fed by the downlead to the receiver.

The parasite arrangement C2U, etc. of the present invention differs from that of the reissue patent in having a separate parasite for each arm of each dipole having an effective length of three halves of a wavelength of more on the high band. (For example, in FIGS. l--4, shortest dipole D] has no central parasite, while all others do). The desired effect of the parasite is not fully achieved where only a single parasite is associated with a single dipole or where one half of a full length parasite (having a length of about one-fourth of a wavelength in the high band) is associated with each arm of a single dipole.

In addition to the central parasites, each of the shorter dipole elements D1, D2 and D3 has associated therewith a pair of close-spaced outboard-parasites, PlU, PlL; P2U, P2L; and P3U, P3L, respectively. Each outboard parasite, such as PlU, is mechanically supported directly in front of its associated dipole arm (DlU in this instance) on two suitable insulators 30 so that the parasite extends slightly beyond the free end of its associated dipole arm. The preferred length of the outboard parasites is 24.5 inches or approximately one-half of a wavelength at the center of the high VHF band.

It has been observed that the outboard parasites materially improve the performance of the antenna although the reason for such improvement is not fully understood. It is believed that in the case of the shorter dipole elements such as D1, D2 and D3 (the lengths of which preferably vary from 54 to 71 inches), the dipoles would operate (in the absence of the parasites) in a full wavelength mode on the high VHF band which would render them ineffective on the high band. Moreover, at a full wavelength, a central close-spaced parasite (such as C2U, etc.), is not fully effective in reducing dipole impedance. As a result, the shorter dipoles would not properly contribute to the gain of the antenna over the high band. The outboard parasites may possible induce in-phase currents in the ends of the associated dipole arms to create a current distribution in the shorter dipoles providing a current in the dipole ends in phase with the current in the center portion of the dipole over the high VHF band, to cause those dipoles to contribute effectively to the gain on the high band. However, it has also been observed that the currents existing in an out board parasite at certain frequencies will be out of phase with the currents existing in the adjacent portions of its associated dipole. This may indicate that the dipole and its outboard parasites operate in combination as an individual endfire array. Regardless of the theory of operation of these outboard parasites, the addition of such parasites permits selection of dipole lengths satisfying low-band criteria while enabling subsequent adjustment (by means of the outboard parasites) of the high-band operation so as to optimize high-band performance without degrading low-band performance.

The use of both outboard parasites and central parasites with dipoles D2 and D3 provides a noticeable performance improvement in the preferred embodiment. However, the use of a central parasite with the shortest dipole D1 would not materially affect performance and therefore it has been omitted.

A pair of vertical insulating plastic blocks 40 and 42 (see FIGS. 3 and 4) are secured (as by riveting) to the front ends of crossarms U and L to brace the forward portion of the antenna. Two contact strips 43 and 44 electrically connect respective crossarms U and L to two

terminals

45 and 46 which are mounted on block 42.

Terminals

45 and 46 serve as the connecting means for the signal transmission line 12 or downlead to the television receiver.

If it is desired to add a director unit for the array, a horizontal rod 47 may be secured as shown at 48 to the

plates

40 and 42 to support a conventional director unit such as shown at 50. A suitable director unit is described in US. Pat. No. 3,277,491 assigned to the assignee of this invention. Since director unit 50 forms no part of the present invention, a detailed description of it is not included here.

At the rear of the array, a pair of reflectors RU and RL are mounted on the upper and lower crossanns U and L, respectively. As shown in FIGS. 2, 2A each of the reflectors may comprise a pair of

arms

52 and 54 suitably mounted on a conductive bracket 56 on the respective crossarm U or L, with the

arms

52 and 54 extending generally transverse to the erossarm. Since the

arms

52 and 54 are electrically connected together by the bracket 56, the

arms

52 and 54 form a single continuous conductor which operates in a well-known fashion as a reflector to improve the front-to-back ratio of the antenna. For mechanical rigidity, vertical tubular support member 58 is mounted on insulating

brackets

60 and 62 extending toward each other from the crossarms RL and RU, respectively.

Where the dimensions and spacings of the active and parasitic elements are properly selected, in accordance with the considerations described in the aforementioned reissue U.S. Pat. No. 25,604, 604, it has been found that the current flow in the transmission line formed by crossarms U and L is extremely low to the rear of the dipole D7. Consequently, it is possible to electrically connect the crossarms in that location without substantially affecting antenna performance. Thus, the

brackets

60 and 62, as well as the tubular support member 58, can be constructed of a metallic material and connected together and to the crossarms U and L without the use of insulating means. This simplifies construction of the antenna, thereby reducing production costs while at the same time improving the mechanical characteristics of the antenna as a commercial television receiving antenna. Of course, where desired, support 58 may be insulated from one or both crossarrns.

A typical TV antenna mounting mast is shown at 64. According to the preferred embodiment of the invention, the antenna, as herein described, is mechanically supported on the mounting mast 64 by standard means, but in a novel fashion. Thus, two insulating

plastic mast brackets

66 and 68 are connected to the crossarms U and L, respectively (by rivets 70,

for example), and extend toward each other so that the mastmounting portion of the bracket 66 is substantially below the upper crossarm U. This permits a conventional U-shaped clamp 72 to be firmly mounted around mast 64 with the top of the mast, shown at 64', terminating beneath the upper crossarm U. It was discovered that where the mast extended above the upper crossarm (pursuant to standard antenna mounting practices), there existed a capacitive coupling between the upper crossarm and the mast, causing a current flow in the mast which produced a detrimental effect on the high-band performance of the antenna.

Because of the low current flow in the rear of the antenna, it is possible to combine the functions of the supporting tube 58 and mast 64 by mounting the antenna on mast 64 such that the mast is to the rear of the longest or last dipole. In effect, the mast becomes an extension of support 58. This further simplifies the manufacture and installation of the antenna but is not generally mechanically feasible for longer arrays.

As noted previously, the full theory of operation of the antenna is not fully understood. It has been found that the central close-spaced parasites (i.e., C2U, C2L, etc.) may be conveniently placed below and slightly behind their associated dipole arms, although not restricted to this location. With respect to the outboard parasites (i.e., PlU, PlL), the best results have been achieved where the outboard parasites are positioned in front of their associated dipole arms, although this location is not essential to obtaining an improvement in antenna performance by use of the outboard parasites. As in the case of most antennas, the specific location, dimensions and spacing between elements can be determined in large part by empirical observations, although the general consideration discussed in reissue U.S. Pat. No. 25,604 should be followed. This is also the case with respect to the angle between the crossarms U and L which is selected as a compromise between gain and directivity. In the preferred embodiment, the angle between the crossarms U and L is approximately 12, although this can be varied somewhat.

The invention is not dependent upon the number of elements employed. FIGS. 58 illustrate schematically different arrangements of antenna elements pursuant to the invention, with the elements in each drawing being identified in the same fashion as the elements in FIGS. 1-4. Where nine dipoles are used (FIG. 8) it is preferred to use two separate directors which are identified as 50 and 50'. In FIGS. 58, where an element is identified by the notation U & L it means that such an element is mounted on both the upper and lower crossarms which, of course, are not separately shown in the schematic drawings of FIGS. 5--8.

The VHF embodiments of the invention illustrated in FIGS. 18 may be provided with active elements for reception on the UHF band, and FIGS. 9 and illustrate a preferred embodiment of such an array according to a further feature of the invention. Since the VHF array has been previously described, only those portions necessary to explain the novel features of the combined antenna are described below.

In FIGS. 9 and 10 the two frontmost VHF dipoles D1 and D2 are illustrated. The UHF antenna in this case consists of ten additional dipole elements which are shown as F l-Fl0. Each of these UHF dipoles Fl-Fl0 is similar to the previously described VHF dipoles DlD7 in that it consists of two arms, one of which is connected to the upper crossarm U and the other of which is connected to the lower crossarm L. As in the VHF antenna of FIGS. l4, successive dipole arms (e.g. FlU, F2U, etc.) extend in opposite directions from alternate sides of the associated crossarm (e.g. crossarm U). The arms of dipoles F10, F9, and F8 are mounted on the top of their associated crossarms U and L, the remaining dipoles Fl-F8 being supported on the underneath portions of the crossarms, with dipole F7 being directly beneath dipole D1. An important feature of this aspect of the three rearmost dipoles F10, F9 and F8 between the two frontmost VHF active dipole elements D1 and D2.

The use of the crossarms U and L as both the transmission line and supporting means for the active UHF elements F1- F10 simplifies and reduces costs of manufacture and installation. The placement of a portion of the UHF portion of the array between elements of the VHF portion provides a substantial reduction in overall length which is an important consideration with respect to commercial television receiving antennas.

A standard UHF director assembly may be mounted on a suitably dimensioned tubular support member such as shown at 46 in FIG. 3. With respect to the combined VHF-UHF array, it is preferred not to use the VHF director element 50 shown in FIGS. 1-4. However, a known three-element director assembly 82 may be employed, the three

elements

82a, 82b and 82c being colinear, with the outer elements acting as high-band directors on the high VHF band. If desired, the array shown in FIGS. 9 and 10 may be employed without the UHF director assembly 80.

The following table states the dimensions of the active and parasitic elements employed in the preferred embodiments of the inventions illustrated in FIGS. 14, 9 and 10. The distance between adjacent dipoles, as measured along each of the crossarms, is 12 inches.

Each central parasite (i.e. C2U, C2L, etc.) is 4 inches behind and 2% inches below its associated dipole arm. Each of the outboard parasites (i.e. PlU, P1L, etc.) is spaced 3 inches in front of its associated dipole arm (i.e. D1U, DlL, etc.). Each outboard parasite is 24%inches long and extends 6% inches beyond its associated dipole arm (i.e. the distance X shown in FIG. 2 is 6% inches). In the following table, the stated dimensions are in inches and represent in all cases the tip-to-top length of the associated part. With respect to the dipoles D1-D7, and F1Fll, by tip-to-tip length is meant the effective length of the dipole considering the two arms as being colinear (e.g. with respect to dipole D7, the dimension Y indicated in FIG. 4). The spacing between successive dipoles F1F9 is 3 inches, and the spacing between dipoles F10 and F11, and F11 and F12 is 4 inches:

Element Length D1 54 D2 65 D3 71 D4 79 D5 88 D6 96 D7 102 C2 (U and L)- 22 C3 (U and L)- 23. 5 C4 (U and L) 25. 5 C5 (U and L) 27 C6 (U and L) 29. 5 C7 (U and L) 32 R (U and L) 108 F1 6. 5 F2 7. 0 F3 7. 5 F4 8. 0 F5 8. 5 F6 9. 5 F7 10. 0 F8 11. 0' F9 12. 0 F10 13. 0

Where the reflector R is 12 inches behind dipole D7, and

director 50 is l2 inches in front of dipole D1, the total length of the VHF portion of the antenna is approximately 8 feet. An antenna constructed according to the preferred embodiment of the invention has been found to have approximately 50 percent greater gain than the gain of an antenna having the equivalent elements and constructed strictly according to the above-mentioned US. Pat. u.s. Pat. No. 25,604.

While the invention has been described as a receiving antenna, it will be obvious that it can equally well be used as a transmitting antenna. By appropriate scaling, the invention may be used on other frequencies than the conventional television VHF and UHF bands.

Although preferred embodiments of the invention have been illustrated and described, numerous modifications thereof will be obvious to those skilled in the art. For example, it is possible to incorporate the benefits of different features of the invention despite changes in dimensions, spacings, or relative positions of the previously described parts. In certain cases, the benefits of the invention can be achieved, although not in full measure, by omitting certain of the parts, particularly certain of the central close-spaced parasites associated with the longer dipole elements.

Modification of the spacing between the various elements is also contemplated, the basic criteria for such spacing being generally discussed in the aforementioned reissue US. Pat. No. 25,604. Where it is desired to substantially change the spacing between active elements, the invention contemplates the use of conventional means for properly phasing the signals contributed by such elements so as to maintain a satisfactory front-to-back ratio. Various other modifications of the invention will also be obvious to those skilled in the art and the invention should be defined primarily with reference to the following claims.

I claim:

1. A multiband antenna array for the reception of VHF television broadcast signals having a direction of greater effectiveness extending from its front, comprising two conductive crossarms forming an acute angle in a vertical plane with the apex of said angle at the front of the array, means for connecting a signal transmission line to said crossarms at the apex of said angle, a plurality of dipoles of graduated length decreasing toward the front of the array, each dipole having two arms, one arm of each dipole being connected on one crossarm and the other arm of each dipole being connected to the other crossarm, with the two arms of each dipole extending in opposite directions from a crossarm, and with successive dipole arms extending outwardly from an associated crossarm alternately on opposite sides thereof, the tip-to-tip lengths of said dipoles including a range from approximately one-half wavelength at the low end of the low VHF band to approximately one full wavelength within the high VHF band, at least some of said dipoles operating in a harmonic mode greater than the second harmonic for frequencies within said high VHF band, and means associated with individual ones of said last-named dipoles for increasing the effectiveness thereof towards the front of the antenna for such frequencies.

2, An antenna array according to claim 1, further including outboard parasites associated with at least one dipole which has a length such that it is effectively one wavelength long at a frequency in the high VHF band, each of said outboard parasites being close-spaced to and extending outwardly beyond a respective associated dipole arm.

3. An antenna array according to claim 2, wherein the length of each of said outboard parasites is approximately onehalf wavelength long at a frequency in the high VHF band.

4. An antenna array according to claim 3, wherein each of said outboard parasites is positioned in front of its associated dipole arm.

5. An antenna array according to claim 1, further including a pair of outboard parasites associated with each of said dipoles which has a length such that it is approximately one wavelength long at a frequency in the high VHF band, each said outboard parasite being close-spaced to and extending outwardly beyond a respective dipole arm.

6. An antenna array according to claim 5, wherein the length of each of said outboard parasites is approximately onehalf wavelength long at a frequency in the high VHF band.

7. An antenna array according to claim 1, wherein said means for increasing the effectiveness comprises close-spaced parasites associated with at least one of the dipoles which has an effective length of about three-halves of one wavelength at 9. An antenna array according to claim 1, further including 1 two close-spaced parasites respectively associated with the arms of each of said dipoles which has a length approximately equal to three-halves of one wavelength at a frequency in the high VHF band,

10. An antenna array according to claim 9, wherein each of said close-spaced parasites is symmetrically disposed relative to the crossarm on which its associated dipole arm is mounted.

11. An antenha array according to claim 5, wherein said means for increasing the effectiveness comprises a respective close-spaced parasite respectively associated with each arm of each of said dipoles having an effective length approximately equal to three-halves of one wavelength at a frequency in the high VHF band.

12. An antenna array according to claim 11, wherein each of said last-named close-spaced parasites is symmetrically disposed relative to the crossarm on which its associated di ole arm is mounted.

3. An antenna array according to claim 1, further including a metallic bracing member at the rear of the rear-most dipole and electrically interconnecting both crossarms.

14. An antenna array according to claim 1, further including a plurality of additional dipoles of graduated length decreasing toward the front of the array, said additional dipoles being dimensioned for the reception of UHF radio energy, each additional dipole including two arms, one of which is connected to one crossarm and the other of which is connected to the other crossarm, at least some of said additional dipoles being positioned between the shortest of two of said first-named dipoles.

15. An antenna array according to claim 1, further including a mast for mounting the array and means for reducing capacitive coupling between said array and mast.

16. An antenna array according to claim 15, wherein said means for reducing said capacitive coupling comprises means for clamping said array to said supporting mast with the upper crossarm above the top of said mast.

17. A dual band VHF television antenna array having a direction of greater effectiveness extending from its front, comprising two conductive crossarms forming an acute angle in a vertical plane with the apex of said angle at the front of the array, means for connecting a signal transmission line to said crossarms at the apex of said angle, a plurality of dipoles of graduated length, each having a pair of arms, one arm of each dipole being connected to one crossarm and the other arm of each dipole being connected to one crossarm, with the two arms of each dipole being in a common vertical plane and extending horizontally in opposite directions each transversely of its crossarm, the dipole elements having their lengths graduated and decreasing toward the front of the array, with successive dipole arms extending outwardly from the crossarm alternately on opposite sides thereof, at least one of said dipoles having an effective length of three-halves of one wavelength at a frequency in the high VHF band, and a pair of parasitic elements associated with at least one of said latter dipoles, each of such parasitic elements being in closely spaced relation with respect to a respective dipole arm, and parallel thereto, and symmetrically disposed with respect to the respective crossarm, at least some of said dipoles having a length approximately one-half wavelength at the high end of the low VHF band, and each arm of such latter dipoles having associated with it a close-spaced parasitic element parallel to and juxtaposed to the outer end of said dipole arm and extending outwardly beyond said dipole arm, each of said latter parasitic elements being effectively one-half wavelength long at a frequency in the high VHF band.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 573 841 Dated April 6 1971 Harry Greenberg Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 44, "of", third occurrence, should read line 74 "possible" should read possibly Column 4,

line 56 "25 ,604 ,604" should read 25 ,604 Column 5 line 73, before "three" insert invention is the location c the Column 7 line 34, "on" should read to Column line 51 "one" should read the other Signed and sealed this 11th day of April 1972 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM F G-1050 (10-691 USCOMM no 603

Claims

1. A multiband antenna array for the reception of VHF television broadcast signals having a direction of greater effectiveness extending from its front, comprising two conductive crossarms forming an acute angle in a vertical plane with the apex of said angle at the front of the array, means for connecting a signal transmission line to said crossarms at the apex of said angle, a plurality of dipoles of graduated length decreasing toward the front of the array, each dipole having two arms, one arm of each dipole being connected on one crossarm and the other arm of each dipole bEing connected to the other crossarm, with the two arms of each dipole extending in opposite directions from a crossarm, and with successive dipole arms extending outwardly from an associated crossarm alternately on opposite sides thereof, the tip-to-tip lengths of said dipoles including a range from approximately one-half wavelength at the low end of the low VHF band to approximately one full wavelength within the high VHF band, at least some of said dipoles operating in a harmonic mode greater than the second harmonic for frequencies within said high VHF band, and means associated with individual ones of said lastnamed dipoles for increasing the effectiveness thereof towards the front of the antenna for such frequencies.

2. An antenna array according to claim 1, further including outboard parasites associated with at least one dipole which has a length such that it is effectively one wavelength long at a frequency in the high VHF band, each of said outboard parasites being close-spaced to and extending outwardly beyond a respective associated dipole arm.

3. An antenna array according to claim 2, wherein the length of each of said outboard parasites is approximately one-half wavelength long at a frequency in the high VHF band.

6. An antenna array according to claim 5, wherein the length of each of said outboard parasites is approximately one-half wavelength long at a frequency in the high VHF band.

7. An antenna array according to claim 1, wherein said means for increasing the effectiveness comprises close-spaced parasites associated with at least one of the dipoles which has an effective length of about three-halves of one wavelength at a frequency in the high VHF band, each arm of said dipoles having one of said parasites associated therewith.

8. An antenna array according to claim 7, wherein each of said close-spaced parasites is symmetrically disposed relative to the crossarm which its associated dipole arm is mounted.

9. An antenna array according to claim 1, further including two close-spaced parasites respectively associated with the arms of each of said dipoles which has a length approximately equal to three-halves of one wavelength at a frequency in the high VHF band.

11. An antenna array according to claim 5, wherein said means for increasing the effectiveness comprises a respective close-spaced parasite respectively associated with each arm of each of said dipoles having an effective length approximately equal to three-halves of one wavelength at a frequency in the high VHF band.

12. An antenna array according to claim 11, wherein each of said last-named close-spaced parasites is symmetrically disposed relative to the crossarm on which its associated dipole arm is mounted.

13. An antenna array according to claim 1, further including a metallic bracing member at the rear of the rear-most dipole and electrically interconnecting both crossarms.