OMNI-DIRECTIONAL ANTENNA ARRAY

Abstract: An antenna array comprises four folded dipole elements each formed as an open-ended wire loop (9), the loops being angularly displaced about a vertical central axis (8) of the antenna and each being connected in common to respective terminal means (4, 5) at the central axis by twin feeder portions extending from the respective ends of the loop in a direction generally radial to the central axis. The open ended wire loops (9) forming the dipole elements are configured in such a manner that they lie in substantially a common plane extending at right angles to the central axis (8) and intended, in use, to be horizontal.

Description: OMNI-DIRECTIONAL ANTENNA ARRAY This invention concerns an improved omni-directional antenna array, more especially for signals in the television band. A known attenna array of this kind is described in International Patent Publication No. O86/03624, and comprises four folded dipole elements each formed as an open-ended wire loop, the loops being regularly angu¬ larly displaced about a vertical central axis of the antenna and each being connected in common to respective terminal means at the central axis and spaced apart in the direction of the central axis , by twin feeder portions extending from the respective ends of the loop in a direct¬ ion radial to the central axis. In this hitherto known arrangement the folded dipole elements were required to extend in vertical planes and were constructed as self-supporting elements incorporating the feeder portions, the latter serving as mountings for the elements of the array. While such an arrangement has proved successful as an omni-directional antenna there are none the less certain drawbacks in the existing construction. In order for the loop elements to be self- supporting they must be formed of wire that is of relatively large gauge in order to provide the required rigidity, so that not only the material cost, but also the requirement for relatively complex wire bending oper¬ ations leads to a relatively high manufacturing cost. Furthermore, the structure of the completed antenna array is relatively bulky and the appearance of the antenna is not always acceptable to users who may require a visu¬ ally attractive mobile antenna for attachment to passenger venicles, boats etc. The vertical height of the known- an t enna is also disadvantageous when used on motor homes or similar vehicles since it may increase the clearance eiαht ci tne vehicle to an unacceptable extent. It is accordingly an object of the present invention to provide an omni-directional antenna array providing a perfor anance that is at least comparable with that of the known array referred to, whilst mitigating some of the disadvantages outlined above. The invention accordingly provides an omni-directional antenna ' array of the kind initially referred to which is characterised in that the open-ended wire loops forming the dipole elements are configured in such a . manner that they lie in substantially a common plane extending at right angles to said central axis and intended, in use, to be horizontal. Preferably, the folded dipole elements are so angled in said common plane and arranged to extend adjacent one another that, collectively, they define an approximately circular array. In the antenna array in accordance with the invention, it has surprisingly been found that the performance of the array as an omni-directional antenna is not signifi¬ cantly reduced by the location ' of the wire loops forming the folded dipoles in a common horizontal plane, rather than in vertical planes. .Moreover this arrangement pro¬ vides a number of significant advantages not possessed by the known arrangement. For example, the antenna elements can be enclosed within a relatively flat outer housing of dielectric material the shape of which can be cnosen to provide an attractive appearance to the complete antenna. Thus, with the preferably circular an t enna array, the housing can take the form of a flattened disc. This also has the benefit of giving the antenna an aerodynamic form suitable for high speed vehicles. In accordance with a further preferred feature of the invention, che wire loops and feeders of the antenna array are formed of flexible wire or cable and are held in ~r_ε recu red con iguration y being wound around supports provided on a plate of dielectric material extending suostantially in said common plane. The support may be formed by injection moulding from an appropriate syn¬ thetic plastics material, the moulding incorporating integrally therewith any necessary guide means for locating the wire loops and the terminal means to which they are to be attached. Manufacturing costs are thereby sub¬ stantially reduced in comparison with the known arrange¬ ment. Such a moulding may comprise one half of a two-part disc-snaoed housing as referred to. above. In accordance with a further preferred feature of the invention the antenna array may be supplemented by means of a preferably telescopic rod or whip aerial connected to an appropriate one of the terminal means at the central axis of the antenna. The rod or whip antenna may be tuned to provide for reception and/or transmission of radio frequencies in a band other than that covered by the omni-directional antenna array, thus enabling a dual frequency or wide band antenna to be coupled to a receiving or transmitting apparatus by a common feeder. Surpris¬ ingly, in an antenna array having the configuration accord¬ ing to the present invention, the addition of a further antenna element on the central axis of the array does not interfere with the performance of the omni-directional array, as has been found to be the case with known arrays of other configurations. The invention is illustrated by way of example in the accompanying drawings, in which: Figure 1 s a perspective view of an antenna array m accordance with one embodiment of the invention illus¬ t ra t e d wi t h the casing partly fragmented to show internal derail, and o a: v ew similar to Fig ana - _ - Figure 3 is a perspective view of a moulded support for the omni-directional antenna array, shown without the antenna elements and associated terminal means. Referring to Figs.1 and 2 of the drawings, an antenna array in accordance with one embodiment of the invention com¬ prises an external housing in the form of a shallow disc and comprising a lower support portion 1 and an upper cover portion 2 shown partly broken away to- illustrate the internal components of the antenna array. The lower support 1 has, formed integrally therewith around ts central axis, a plurality of upstanding hook- snaped retaining lugs 3 which serve to retain in place against the surface of the support 1 an annular rectangular terminal plate 4 to which may be connected the outer screen of a coaxial aerial feeder cable not shown. The support 1 further comprises similar upstanding hook-shaped lugs 5 serving to retain a central rectangular terminal plate 5 to which may be connected the central conductor of the aerial feeder cable. ' The plate 6 is spaced from the surface of the support 1 by an upstanding wall portion 7 (Fig. 3 ) formed integrally with the support 1. It will be appreciated that tήe support I is formed of any suitable electrically insulating synthetic plastics material, and that the electrically conducting piates 4 and 6 are t us held in spaced relation relatively to a central vertical axis 8 of the antenna array and are electrically insulated from one another. Coupied to the terminal plates 4 and 5 are four regularly angularly spaced folded dipole antenna elements eacn formed from a lengt h of flexible wire or caole 9 that is anchored :: -ae lower annular plate 4, led in turn around a series of l ocating stays 10 za 15 formed integrally with the suppor t 1 ana then anchored to the terminal plate 5. The portion of eacn wire 9 extending between the stay 16 and the plate 6 s supported by a ramp 17 (Fig. 3 ) formed integrally with the support 1. The support 1 is also provided with a radially extending shelf 18 that may support any electrical circuitry required to be asso¬ ciated with the antenna array, e.g. an aerial amplifier, and the coaxial feeder cable (not shown) may be led from the central axis of the array to the circuitry supported by the shelf 18 via a groove 19 and an aperture 20. After assemoly of the internal components of the array, the cover 2 may be secured in place over the support 1 by fastening means extending through bosses 21 (Fig. 3 ) formed on the support 1. If desired the cover 2 may be provided with a removeable insert 22 concealing a socket by means of which a tele¬ scopic rod antenna may be electrically connected to the plate 5. The addition of a rod antenna to the array as described enables the complete unit to be used as a dual frequency or wide band antenna without interferring with the characteristics of the omni-directional array.

Claims: CLAIMS : 1. An antenna array comprising four folded dipole elements each formed as an open-ended ■ wire loop, the loops being regularly angularly displaced about a vertical central axis of the antenna and each being connected in common to respective terminal means at the central axis by twin feeder portions extending from the respective ends of the loop in a direction generally radial to the central axis, characterised in that the open ended wire loops forming the , dipole elements are configured in such a manner that they lie in substantially a common plane extending at right angles to said central axis and intended, in use, to be horizontal. 2. An antenna array according to claim I , characterised in that the folded dipole elements are so angled in said common plane and arranged to extend adjacent one another ' that, collectively, they define an approximately circular array. 3. An antenna array according to claim 1 or 2, characterised in that the antenna elements are housed in an outer shell of dielectric material. 4. An antenna array according to claim 3 characterised in that the said outer shell has the shape of a flattened disc. 5. An antenna array according to any one of claims 1 - 4, characterised in that the wire loops and feeders of the antenna array are formed of flexible wire or cable and are held in the required configuration by being wound around supports provided on a plate of dielectric material extending suostantially in said common plane. 5. An antenna array according to claim 3, characterised in that the said plate is formed by injection moulding from synthetic plastics material, the moulding incorporating said supports integrally therewith. 7. An antenna array according to claim 5 or 6 as appended to claim 3, characterised in that said plate forms one part of said shell, which is moulded in two parts from synthetic plastics material. 8. An antenna array according to any one of claims 1 to 7, characterised in . that it further comprises a supplementary rod or whip antenna element connected to one of said terminal means at the central axis of the antenna. 9. An antenna array according to claim 8 characterised in that said supplementary rod or whip antenna element is tuned to a frequency differing from that of said folded dipole elements.

Inventors: CLARK DEREK JAMES, CLARK, DEREK, JAMES
Applicants: MAXVIEW AERIALS LTD, MAXVIEW AERIALS LIMITED
Application year: 1991
Main classification: H01Q9
IPC codes: H01Q9, H01Q21