GB2375235A

GB2375235A - Multiple monopole aerial

Info

Publication number: GB2375235A
Application number: GB0128668A
Authority: GB
Inventors: Duncan John Telfer
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-12-07
Filing date: 2001-11-30
Publication date: 2002-11-06
Anticipated expiration: 2021-11-30
Also published as: GB2375235B; GB0128668D0

Abstract

A radio frequency aerial consisting of two or more electrically conducting monopole elements (e.g., E1, E2, Fig. 2) positioned so that they can interact with a ground plane (G, Fig. 2) to produce a near-spherical far-field pattern at right angles to the ground plane at the lowest resonant frequency. The elements are approximately one-quarter wavelength long at the lowest resonant frequency and consist of one or more components made from rods or wires. The elements are inwardly inclined, crossing over but not touching. The aerial feeder may be conventional conducting cable F and the feeder connection may include a matching unit M.

Description

MULTIPLE MONOPOLE AERIAL The invention relates to an aerial for wireless communication, or ionospheric sounding applications. It is of a type which has a plurality of electromagnetically coupled elements, approximately a quarter-wavelength in electrical length at the nominal operating frequency, and which is electrically associated with a groundplane. The ground-plane may be the natural earth or an artificial one consisting of a conducting sheet. Where the number of elements is greater than two, the invention is readily configured for circular polarisation.

The problem addressed by the invention concerns the need to exploit at high frequencies (HF) the naturally occurring propagation modes involving near vertical incidence skywave (NVIS) propagation for contact between ground stations separated by obstacles. Ideally, this requires a far-field (FF) pattern that is almost spherical and directed vertically, at right angles to the ground plane. Aerials for vertical propagation are well known, but generally have FF patterns that depart significantly from this ideal, or are less suitable for use in physically cluttered environments.

The object of this invention is to realise a near spherical FF radiation pattern, such that the configuration of the elements maximises gain in the direction at right angles to the ground plane at or near the lowest resonant frequency of operation. In this invention, the configuration of elements and their components allows simple and convenient connection to a conventional unbalanced feeder cable. Alternatively, balanced feed with appropriate matching arrangements allows the desirable FF pattern to be maintained over an extended frequency range. If the elements are made from wires, ease of assembly and low wind resistance are achievable. Embodiments for use at HF afford a relatively compact solution for NVIS propagation. Further compactness, e. g. , for vehicular operation at HF, may be achieved through the well known expedient of shortened inductively loaded elements. Embodiments at very high frequencies (VHF) or ultra high frequencies (UHF) use artificial ground planes and are physically smaller, and directionality of the FF pattern may be employed for reception of domestic television or orbiting satellite signals.

In this invention, the elements are tilted relative to the ground plane, each towards the other, so that they cross near the centre but do not physically touch. Preferably, the elements are made of metal, the conducting components being wires, rods or tubes.

Elements may consist of a plurality of such conducting components, in accordance with the requirements of bandwidth and of feeder matching. Plural components of an element are connected together at the end farthest from the ground plane. Element component configuration may be V-shaped, comb-like or bowed, with little change in the field pattern.

Three preferred embodiments of the invention are now described with reference to the accompanying drawing, in which: FIGURE 1 shows a 2-element HF embodiment constructed in wires, with the interleaving inclined 2-component elements positioned with reference to a conventional Cartesian coordinate system.

FIGURE 2 shows an HF 2-element embodiment without physical connection to the ground plane, but with which it interacts through the effects of close proximity.

FIGURE 3 shows an HF 4-element embodiment constructed in wires with interleaving inclined elements positioned with reference to a conventional Cartesian coordinate system.

FIGURE 4 shows the far-field radiation pattern of the 4-element embodiment, in a conventional Cartesian coordinate system, such that the'ground plane contains the X and Y axes and the lobe of the field pattern is directed along the Z axis.

As shown in Figure 1, an HF embodiment of the invention consists of a pair of tilted conducting elements. The angle of tilt elevation is near 45 degrees from the ground plane, with the cross-over point between one third and one half of the element length. as measured from the element end nearest to the ground plane. Each element is approximately one quarter of a wavelength long at the lowest resonant frequency of the aerial and formed from a pair of component wires. Wires 3 and 4 are the components of the'driven'monopole element El. Wires 1 and 2 are components of the parasitic monopole element E2. which develops its radio frequency current distribution by virtue of its proximity to the driven element. A conventional unbalanced feeder may be connected to any one of the element component wires, in this case F at wire 4, at or near the ground plane G. The remaining three component wires, 1,2 and 3, are connected to the horizontal ground plane. If more than one such feeder connection is made, due regard must be had of the phase relationship at the feed points. Alternatively, a conventional'gamma match'or inductive loop may be used for connection to the aerial. The wires are hung from non-conducting supports (not shown).

The embodiment of Figure 2 consists of an inclined pair of single component elements El and E2 mounted above a conducting ground plane, G. Each element is tilted towards the other, crossing but not touching, and connected, at the end nearest to the ground plane, to a balanced feed F, via a matching unit M. In this embodiment there is no direct connection between the aerial elements the ground plane, which interacts with the aerial electromagnetically to give the desired vertically oriented farfield pattern.

The embodiment of Figure 3 consists of four inwardly tilted conducting elements, Et, E2, E3, E4 on or near the ground plane G. The elements are tilted towards each other, without touching, at angles near 45 degrees from the ground plane. The cross-over region is preferably between one third and half the element length, as measured from the ground plane. Each element is approximately one quarter of a wavelength long at the lowest resonant frequency of the aerial. Elements are formed from wires or rods kept in position with non-conducting supports (not shown). Circular polarisation of the radiofrequency energy may be readily accommodated, for both transmission and reception of signals, by adjustment of the phase difference of the feed to each element, such that it is near 90 degrees between consecutive elements and near 180 degrees between opposite elements.

In Figure 4 the far-field radiation pattern for the aerial of Figure 1 is near-spherical, with very little vestigial side-lobe spread at the base. This type of field pattern geometry is realised with only slight differences for the other embodiments. This has been borne out by results of theoretical model calculations by the inventor, and practical testing with HF, VHF and UHF embodiments.

Acknowledgement.

For theoretical calculations, including generation of the'field pattern in Figure 4, use was made of the commercially available'EZNEC'C electromagnetic calculation software suite available through R. Lewallen at'EZNEC. COM'.

Claims

CLAIMS ]. A radio frequency aerial including a plurality of monopole elements positioned so that they can interact with a ground plane to produce a near- spherical far-field pattern at right angles to the ground plane at the lowest resonant frequency.
2. An aerial as claimed in I where the elements consist of one or more components made from rods or wires.
3. An aerial as claimed in I where the monopole elements are inwardly inclined An aerial as claimed in I whei I towards each other. crossing over but not touching.
4. An aerial as claimed in I where the elements are made from conducting material and of length approximately equal to one quarter wavelength at their lowest resonant frequency.
5. An aerial substantially as herein described and illustrated in the accompanying drawings.