GB2621460A

GB2621460A - Omnidirectional vehicle antenna apparatus

Info

Publication number: GB2621460A
Application number: GB2309571.4A
Authority: GB
Inventors: John Boyes Stephen
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 2022-06-27
Filing date: 2023-06-26
Publication date: 2024-02-14
Also published as: GB202309571D0; GB202209353D0; WO2024003695A1

Abstract

A vehicle 101 may have multiple directional antennas 102 mounted in an equal spaced distributed array around the vehicle (e.g. car, boat, aircraft, satellite), pointing away from the vehicle, maybe in an azimuth plane. In transmit and/or receive the directional antennas 102 operate only on a single polarisation and in phase, providing a combined omnidirectional radiation pattern 103. Polarisation may be linear, vertical, horizontal, slant, right or left hand circular polarisation. The directional antennas 102 may be planar inverted-F PIFA antennas housed in a radome, and equal-phase signals may be output or combined using a Wilkinson power divider. The antenna apparatus my mitigate interference or distortion of radiation by the vehicle 101 and reduce wasted signal energy.

Description

OMNIDIRECTIONAL VEHICLE ANTENNA APPARATUS

Technical Field of the Invention

The invention relates to omnidirectional antennas, specifically omnidirectional vehicle antennas.

Background to the Invention

Antennas convert electromagnetic signals (typically radio frequency signals) into electric currents and vice versa. Electric currents do not inherently provide information on the direction of a signal transmitted or received by an antenna. In order to obtain directionality, an antenna radiation pattern can be designed to provide a peak gain in a particular direction that is substantially higher than the gain in any other direction.

The direction of peak gain is typically referred to as the main beam of the antenna. For example, this may be achieved mechanically by focussing the signal using a reflector such as a parabolic dish or electronically using an array of antenna elements.

The main beam can be used to focus the power radiated from a transmitting directional antenna towards a particular direction. Similarly, a receiving directional antenna can be used to detect the angle of an emitter by sweeping the main beam across the emitter.

In some situations, it is desirable for an antenna to be omnidirectional i.e. to provide equal gain in a wide range of directions. Such an omnidirectional antenna therefore provides very limited or substantially no directionality. The omnidirectional antenna may radiate substantially equal power in substantially all directions or all directions in a given plane e.g. all azimuth or all elevation directions.

Omnidirectional antennas are used in many communications applications, in particular in applications where the line of sight between a transmitter and receiver is unknown. This has conventionally been achieved using monopole or dipole 'whip' type antennas. However, mounting such an antenna onto an electrically large (i.e. physically large with respect to the wavelength) platform such as a vehicle can distort the radiation patterns and cause shadowing effects. Recently, in GB2571632, it has been shown that interference can be mitigated by mounting at least two dual polarised directional antennas around a vehicle and operating them in phase to provide a combined omnidirectional performance in each of two polarisations. However, this solution wastes energy in certain applications and there is an ongoing demand for increasing antenna efficiency to allow for higher data transfer rates.

Therefore it is an aim of the present invention to provide an omnidirectional vehicle antenna apparatus with improved efficiency.

Summary of the Invention

According to a first aspect, the invention provides an omnidirectional vehicle antenna apparatus comprising a plurality of directional antennas configured to be mountable in a substantially equi-spaced distributed array around and pointing away from a vehicle, wherein the antenna apparatus is configured such that, when operated in transmit and/or receive, the directional antennas operate in phase with each other to deliver a combined omnidirectional performance, wherein the directional antennas operate only on a single polarisation. Providing directional antennas that operate only on a single polarisation increases the efficiency of the apparatus. The inventor has shown that the energy of a signal transmitted or received by a dual polarised apparatus of the prior art is generally either absorbed or reflected by a nearby surface (such as the ground or an object such as a wall). For some applications, such as sensing or communications, the absorbed energy is typically wasted. For other applications, such as ground penetrating radar, the absorbed energy may be beneficial. In either case, the wasted energy reduces the power of the signal and is thus inefficient.

An omnidirectional vehicle antenna apparatus is an antenna configuration for communicating wireless signals from a vehicle or receiving wireless signals at a vehicle. The apparatus provides omnidirectional coverage by radiating in substantially all directions or in substantially all directions within a geometrical plane. Typically the geometrical plane is an azimuth plane.

Generally, a vehicle is electrically large relative to the signal wavelength. In some embodiments, the vehicle is a ground vehicle such as a car, a maritime vessel such as a boat, an aircraft or satellite. The apparatus comprises a plurality of directional antennas i.e. an antenna that has directivity or a radiation pattern with a peak gain towards a particular direction that is substantially higher than other directions. The directional antennas are mountable on a vehicle i.e. the directional antennas can be attached upon, or integrated with the bodywork of the vehicle using adhesive, screws, welds or other fastening means which may be permanent or detachable to allow for replacement or servicing. The fastening means typically maintains the position of the directional antennas on the vehicle when the vehicle is in use.

The directional antennas are mountable in a substantially equi-spaced distributed array around a vehicle. This balances the mutual coupling between the directional antennas 15 such that when driven in phase the electromagnetic fields combine to provide a smooth omnidirectional pattern The directional antennas are mountable to be pointing away from the vehicle. Typically the directional antennas direct the radiation pattern substantially away from the vehicle to minimise interference with the vehicle resulting in distortion of the radiation pattern.

The apparatus is configured such that when operated in transmit and/or receive, the directional antennas operate in phase with each other to deliver a combined omnidirectional performance. Generally, the directional antennas operate in phase with each other to deliver a combined omnidirectional performance at a single polarisation.

The signals to/from each directional antenna are divided/combined and matched in phase with each other. This may be achieved by passing both signals through an active phase shifting component configured to modulate the phase of each signal such that they are aligned in phase. Alternatively it may be achieved by designing the propagation paths of each signal to be the same length i.e. the electrical paths are the same length i.e. the cable lengths are the same.

The directional antennas operate solely on a single polarisation for example horizontal, vertical, ±45° slant or Left Hand Circular (LHC) or Right Hand Circular (RHC). Generally, the polarisation refers to the plane of the electric field of the signal. The directional antennas may be designed to operate on a single polarisation. Alternatively, the directional antennas may be capable of operating on a plurality of polarisations but are configured to or arranged to only operate on a single polarisation.

Preferably, the single polarisation is a single linear polarisation. Less of the signal is wasted when a single linear polarisation is used and thus it is more efficient than other types of polarisation such as circular.

Preferably, the directional antennas are combined using one or more Wilkinson power dividers. The Wilkinson power dividers split a transmitted signal into two or more equal phase output signals which are then fed out of the directional antennas. Similarly, the Wilkinson power dividers combines two or more equal-phase signal received by the directional antennas. Furthermore, the Wilkinson power dividers ensure full isolation between the directional antennas.

Preferably, the directional antennas are directional planar antenna elements. A planar 20 antenna has a reduced profile and therefore has minimal mechanical impact on the vehicle such as minimal impact on the vehicle aerodynamics and is less visible externally around the vehicle Preferably, the directional antennas are planar inverted-F antennas (PIFA). Generally a PIFA comprises a ground plate and a radiating top plate. A PIFA has a reduced profile however can be manufactured to be wideband in operation -for instance the resonant frequency and fractional bandwidth of a PIFA can be carefully optimised by varying the dimensions of a PIFA.

Preferred embodiments of the apparatus are configured to operate at 1800MHz to 6000MHz. Other embodiments operate at 800MHz to 2500MHz. The directional antenna elements may be configured to provide such frequencies by virtue of using different planar antenna design topologies, or inclusion of parasitic radiators.

Preferably, each directional antenna is housed within a respective radome. The radome may comprise hardened plastic. The radome protects the directional antenna from damage. The radome is typically transparent to radiation at the operational frequencies.

According to a second aspect, the invention provides a vehicle comprising the omnidirectional vehicle antenna apparatus of the first aspect of the invention. Mounting an apparatus of the first aspect of the invention onto a vehicle provides efficient omnidirectional coverage whilst mitigating interference or distortion of the radiation by the vehicle and provides increased efficiency compared to the prior art.

Preferably, the single polarisation is vertical linear polarisation. A vertical linearly polarised signal generally reflects off the surface thereby providing enhanced radiation compared to other polarisations. In some embodiments, the Electric field (E field) of the vertical linear polarisation is substantially orthogonal to the ground, sea or object in use when the apparatus is mounted onto the vehicle. Therefore, this minimises the amount of signal absorbed by the ground.

Preferably, the single linear polarisation is horizontal polarisation. Typically, the E field of the horizontal linear polarisation is substantially parallel to a surface near the vehicle. A horizontally polarised signal generally couples into the surface. In some embodiments, the horizontal polarisation is parallel to the ground, sea or object in use when the apparatus is mounted onto the vehicle.

Preferably, the directional antennas are mounted at ground level. Ground level may include the surface on which the vehicle travels such as the land, sea etc. Preferably, the vehicle is a car. In some embodiments the apparatus may be used to 30 provide communications for example 2G, 3G, 4G and/or 5G telecommunications for communications devices/systems in the car.

Preferably, there are at least 4 directional antennas mounted in an azimuth plane around the car. This provides omnidirectional coverage in an azimuth plane around the car. This arrangement may be suitable for communications purposes.

Preferably, the at least 4 directional antennas are mounted on each corner of the car.

The corners of the car include the nearside front, offside front, offside rear and nearside rear of the car. This reduces distortion of the radiation pattern by the vehicle.

According to a third aspect, the invention provides a method of omnidirectional lo communication to or from a vehicle, the method comprising the steps of: providing a vehicle according to the second aspect of the invention; and then receiving or transmitting a signal using the omnidirectional vehicle antenna apparatus. Typically, it is desirable to minimise wasting the signal energy. Therefore, by receiving or transmitting a signal using the omnidirectional vehicle antenna apparatus on the car, less of the signal is wasted and the efficiency is improved.

Any feature in one aspect of the invention may be applied to any other aspects of the invention, in any appropriate combination. In particular apparatus aspects may be applied to method or use aspects and vice versa. The invention extends to an apparatus, method or use substantially as herein described, with reference to the accompanying drawings.

In all aspects, the invention may comprise, consist essentially of, or consist of any feature or combination of features.

Brief Description of the Drawings

The invention will now be described, purely by way of example, with reference to the accompanying drawings, in which; Figure la is a schematic, side on view of an embodiment of the invention mounted onto a car; Figure lb is a schematic, overhead view of the vehicle of Fig. la; and Figure 2 is a schematic, overhead view of the vehicle of Figs. la and lb and the gain profile of the apparatus in use.

The drawings are for illustrative purposes only and are not to scale.

Detailed Description

Fig. la and Fig. lb illustrates an embodiment of the invention 100 mounted onto a car 101 from a side on view and overhead view respectively. The car 101 is shown in the side on view as being substantially rectangular shaped. A vertically polarised directional antenna 102 is mounted on each of the four corners of the car 101. The directional antennas 102 are low profile P IFA antennas comprising a radiating top plate and ground planes (not shown). Each antenna 102 is encased inside a radome to protect against damage. In use, the Electric field (E field) of the antennas 102 is substantially orthogonal to the ground 103. The antennas 102 are capable of transmitting and/or receiving a high band communications signal between 1800MHz to 6000MHz. Each antenna 102 is connected to an RF transceiver by cables (not shown) operating on a high band communications signal between 1800MHz to 6000MHz.

In use, the signals transmitted and/or received by each of the antennas 102 are driven in phase with each other and divided and/or combined using a Wilkinson power divider (not shown). Fig. 2 illustrates a transmit and/or receive omnidirectional antenna pattern 103 of an embodiment of the invention mounted onto a car 101. The radial distance from the car 101 is intended to illustrate gain (i.e. greater radial distances from the car 101 indicate higher gain). The resulting antenna pattern 103 is shown as substantially symmetrical in the azimuth plane around the car 101; indicating that the antenna pattern 103 has not been distorted by the car 101 and is therefore substantially omnidirectional.

The invention has been described with specific reference to vertically polarised antennas mounted on a car for communications. It will be understood that this is not intended to be limiting and the invention may be used more generally. For example, the invention may be used more generally for any other wireless application such as sensing. The invention may be implemented on any type of vehicle such as a boat, aircraft or satellite and so on and may operate on any other single polarisation such as horizontal, ±45° slant, LHC or RHC.

Claims

CLAIMS1. An omnidirectional vehicle antenna apparatus comprising a plurality of directional antennas configured to be mountable in a substantially equi-spaced distributed array around and pointing away from a vehicle, wherein the antenna apparatus is configured such that, when operated in transmit and/or receive, the directional antennas operate in phase with each other to deliver a combined omnidirectional performance, wherein the directional antennas operate only on a single polarisation.
An omnidirectional vehicle antenna apparatus according to claim 1, wherein the single polarisation is a single linear polarisation.
3. An omnidirectional vehicle antenna apparatus according to claim 1 or 2, wherein the directional antennas are combined using one or more Wilkinson power dividers.
An omnidirectional vehicle antenna apparatus according to claim 1, 2 or 3, wherein the directional antennas are directional planar antenna elements.
5. An omnidirectional vehicle antenna apparatus according to claim 4, wherein the directional antennas are planar inverted-F antennas.
An omnidirectional vehicle antenna apparatus according to any preceding claim, configured to operate at 1800MHz to 6000MHz.
An omnidirectional vehicle antenna apparatus according to any of claims 1 to 5, configured to operate at 800MHz to 2500MHz.
An omnidirectional vehicle antenna apparatus according to any preceding claim, wherein each directional antenna is housed within a respective radome.
9. A vehicle comprising the omnidirectional vehicle antenna apparatus of any preceding claim.
10. A vehicle according to claim 9, wherein the single polarisation is vertical linear polarisation.
11. A vehicle according to claim 9, wherein the single polarisation is horizontal linear polarisation.
12. A vehicle according to any of claims 9 to 11, wherein the vehicle is a car.
13. A vehicle according to claim 12, wherein there are at least 4 directional antennas mounted in an azimuth plane around the car.
14. A method of omnidirectional communication to or from a vehicle, the method comprising the steps of: providing a vehicle according to any one of claims 9 to 13; and then receiving or transmitting a signal using the omnidirectional vehicle antenna apparatus.