EP3017502B1

EP3017502B1 - Airborne antenna system with controllable null pattern

Info

Publication number: EP3017502B1
Application number: EP14811958.9A
Authority: EP
Inventors: Kevin Le
Original assignee: Intel Corp
Current assignee: Intel Corp
Priority date: 2013-07-01
Filing date: 2014-07-01
Publication date: 2019-08-21
Anticipated expiration: 2034-07-01
Also published as: EP3017502A2; WO2015001425A8; WO2015001425A2; CN105264712A; WO2015001425A3

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention.

The present application, generally relates to a system for adjusting antenna pattern having a vertical polarization omni-directional radiation pattern.

2. Description of the Prior Art.

Existing antenna systems located on aircraft to enable wireless communications are difficult to implement to full effect as a result of their operating environment. When operated in receive mode, the antenna is configured for receiving signals in the line of sight either from ground or other aircraft. However, reception of signals from other aircraft mounted transmit antennas is highly undesirable. Filtering or notching of these nearby transmitted signals is not possible due to a number of operational factors. Output power reduction of offending transmitters renders communication links inoperable since these nearby antennas cannot provide adequate coverage area on the ground and air to air. Implementation of conventional large metallic structures to reduce inter antenna interference on the aircraft body is not readily possible due to a number of factors such as aerodynamic constraints, visual appearance, and regulatory requirements.
What is needed is an airborne antenna system that resolves the problems providing sufficient signal strength while addressing interference considerations experienced on aircraft
US 2003/0052825 A1 relates to a spatial null steering microstrip antenna array comprising two concentric microstrip patch antenna elements. An inner circular antenna is used as an auxiliary element in nulling interference received by an outer annular ring antenna disposed around the inner antenna. The outer annular antenna is resonant in a higher order mode but forced to generate a right hand circularly polarized lower order (TM11) far field radiation pattern, thereby allowing co-modal phase tracking between the two antenna elements for adaptive cancellation. Each antenna element is appropriately excited by symmetrically spaced probes.
US 2009/0023383 A1 shows an apparatus that comprises a distributed array of antenna elements for receiving a radio frequency signal on a satellite communications link, wherein the radio frequency signal includes a known preamble; a plurality of mixers for translating the radio frequency signal to a plurality of baseband signals having in-phase and quadrature components; a processor for applying weights to the baseband signals, wherein the weights are found adaptively in response to the preamble in combination with decision-directed feedback when the preamble is not present; and a receiver for processing the weighted baseband signals. A pre-processor can be used to create sub-arrays of the antenna elements using maximal-ratio weighting.
US 2006/0229104 A1 discloses a system implementing soft handoffs in a cellular communications system on a mobile platform. The system employs an antenna controller in communication with a beam forming network that generates two independently aimable lobes from a single beam. The single beam is radiated by a phased array antenna on the mobile platform. In an Air-to-Ground implementation involving an aircraft, a base transceiver station (BTS) look-up position table is utilized to provide the locations of a plurality of BTS sites within a given region that the aircraft is traversing. The antenna controller controls the beam forming network to generate dual lobes from the single beam that facilitate making a soft handoff from one BTS site to another.
US 2006/0114164 A1 discloses a phased array antenna system accommodating onto a platform for tracking a target moving relatively to the platform. The antenna system comprises a first planar active subsystem operable for receiving/transmitting an RF signal of a certain linear polarization direction and for selectively performing electronic scanning; a second, roll subsystem coupled to the active subsystem and operable for rotational movement of the active subsystem about a first axis perpendicular to a plane defined by the planar active subsystem; a third, elevation subsystem coupled to the second, roll subsystem and to a fourth azimuth subsystem, the azimuth subsystem defining a central axis of the antenna system and being operable for providing rotational movement of the first planar subsystem about the central axis. The elevation subsystem provides a certain angular orientation between the plane defined by the active subsystem and a plane defined by the azimuth subsystem, thereby allowing positioning the first planar active subsystem with respect to the target such that the linear polarization direction is substantially aligned with a linear polarization direction of RF radiation received and/or transmitted by the target.
US 2006/0227048 A1 discloses a hybrid antenna for use with satellite communications systems that may be mounted to a fuselage of an airframe and contain an electronic phased-array assembly to electronically steer the pitch of the antenna beam fore and aft of the airframe and mechanically roll the phased-array assembly to provide below-the-horizon coverage.
US 2006/0040660 A1 relates to an air-to-ground cellular network for deck-to-deck call coverage which provides call coverage to customers who are located in aircraft that are flying within the arrival/departure airspace of an airport by trifurcating the spatial coverage regions or volumes of space to solve the problems of inter-network interference while yielding air-to-ground cellular network coverage at any altitude.

SUMMARY OF T HE INVENTION

The present invention is defined by the subject matter of the independent claims. Advantageous embodiments are subject to the dependent claims. The invention generally relates to a system configured to provide airborne antenna functionality through the application of a controllable null pattern. Coupled to a transceiver, the antenna of the invention is operable in the same frequency band with other transmit and receive antennas mounted in near proximity on the aircraft body. In a particular operational configuration the antenna radiation pattern is varied so that the antenna radiation main beam direction can be controlled over a defined range. The present antenna system addresses the aforementioned problems of interference, signal strength and structural limitations by forming the transmit (or receive) antenna radiation, beam shape away from the transmitter antenna so as to mitigate nearby transmitter interference, while improving receive system performance without having power reduction requirement from nearby co-located, co-band operating transmitters.
The invention provides an omni-directional coverage antenna having a controlled elevation radiation pattern so as provide signal reduction from co-located, co-band operating transmitters mounted on an airborne platform. In an embodiment, the receive antenna is adapted to reduce the interference by combining electrical down tilt with a reverse mechanical up tilt by creating an augmented elevation plane downward pointing pattern with a deep null oriented toward nearby transmit antennas.
Advantages of the invention can further be found in the following description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows an airborne platform (fixed wing, but can be rotor as well) used with the present antenna.
Fig. 2 is a side view of an airborne platform showing detail of the placement of the composite Transmit (TX)-Receive (RX) antenna relative to other dedicated transmit antennas mounted on the airframe.
Fig. 3 is a block diagram representing functional blocks of TX-RX antenna and dedicated TX antennas mounted on the aircraft.
Fig. 4 is a diagrammatic representation of the TX-RX antenna combining mechanical and electrical tilt to achieve radiation pattern null relative to dedicated TX antennas mounted on the aircraft.
Fig. 5 shows an antenna 3-D radiation pattern with a center donut representing the main lobe of the antenna pattern.
Fig. 6 shows an antenna 3-D radiation pattern tilted down slightly to the left due to mechanical tilt of the antenna center axis with the center donut representing the main lobe of the antenna pattern.
Fig. 7 shows an antenna 3-D radiation pattern tilted down slightly to the left due to mechanical tilt and combined with the effect of the electrical tilt (bottom most side lobes are attenuated) with the center donut representing the main lobe of the antenna pattern.
Figs. 8A and 8B provide comparisons of elevation radiation patterns (2D) due to electrical and mechanical tilts (not combined).
Fig. 9 is a representation of radiation elevation patterns (2D) due to a resulting combination of electrical and mechanical tilts at -90 deg with the deep null that provides receiver overload protection from nearby transmit antennas.
Figs. 10A-10C provide comparisons of the antenna's azimuth radiation patterns (2D) due to electrical, mechanical and combined tilts.

DETAILED DESCRIPTION OF THE INVENTION

A system of the present invention for providing an airborne antenna with a controllable null pattern is shown in FIGS. 1-3. The system is embodied in tiltable antenna 14, which is affixed to underside 16 of the fuselage of aircraft 10. The antenna 14 is a transmit and receive antenna, and it may be a tri-band antenna as shown. It is spaced from an existing dedicated transmit antenna 12 of the aircraft 10 by distance S. The antenna 14 is coupled to a transceiver configured to generate and receive signals in a frequency range of interest. The antenna may be shielded from impingement such as with cowl 17. An example of a suitable transceiver is represented in FIG. 3 as transceiver 18. The transceiver 18 includes an S-band receiver filter circuit, a C-band receiver filter circuit and an S-band transmit filter circuit. The dedicated transmit antenna 12 may be a combination of two or more antennas, such as antennas 12-1 and 12-2, each of which is separately coupled to an S-band transmit filter circuit, either or both of which may be co-banded with the transmit and/or receive bands of the antenna 14.
As shown in FIG. 4, the antenna 14 can be configured with an electrical tilt, a mechanical tilt or a combination of the two. The antenna 14 is adapted to reduce from relatively closely located transmit antennas such as antenna 12 interference by combining electrical down tilt with a reverse mechanical up tilt. That configuration creates an augmented elevation plane downward pointing pattern with a deep null oriented toward nearby transmit antennas. That is, through selection of the configuration of the signal transmitted by the transceiver 18, electrical tilt resulting in the radiation patterns shown in FIGS. 5, 8A and 10A. That adjusts the lobe positioning in the way shown. Through mechanical movement of the antenna 14, mechanical tilt of the antenna 14 is achieved, such as through joining the antenna 14 to a controllable motor. That mechanical tilt also changes the lobe positioning to generate the radiation patterns shown in FIGS. 6. 8B and 10B. The combination of both electrical down tilt and reverse mechanical up tilt produces the radiation patterns represented in FIGS. 7, 9 and 10C. It can be seen in FIGS. 9 and 10C that the combination of mechanical and electrical tilt generate a null pattern substantially aligned with the direction of antenna 12. As a result, interference is minimized without excessive signal boost or additional structural elements.
While the present invention has been described with respect to a specific embodiment, it is to be understood that variants may be included as aspects of the invention described by the following claims.

Claims

An airborne antenna system comprising:
an omnidirectional coverage antenna (14);

a co-located second transmit antenna (12) that is co-banded with the transmit and/or receive bands of the omnidirectional coverage antenna (14); and

a transceiver (18) coupled to the omnidirectional coverage antenna (14);

characterized in that the omnidirectional coverage antenna (14) and co-located second transmit antenna (12) are attachable to an underside (16) of an aircraft (10); and

the omnidirectional coverage antenna (14) is arranged for both electrical down-tilt and mechanical up-tilt to create, from a vertical polarization omnidirectional radiation pattern of the omnidirectional coverage antenna (14), an augmented elevation plane downward pointing pattern with a deep null oriented toward the co-located second antenna (12) so that interference from the second antenna (12) is reduced.
The antenna system of claim 1, wherein the second antenna comprises a plurality of dedicated transmit antennas.
The antenna system of claim 1 wherein the electrical down-tilt is achieved by selection of a configuration of a signal transmitted by the transceiver (18).
The antenna system of claim 1 wherein the pointing pattern with the deep null is aligned with the direction of the second antenna (12).
A method of reducing antenna interference comprising:
receiving by an omnidirectional coverage antenna (14) attached to an aircraft fuselage, from a transceiver (18) coupled to the omnidirectional coverage antenna (14), signals in a frequency range of interest;

characterized by

creating, by a combination of electrical down-tilt and mechanical up-tilt of the omnidirectional coverage antenna (14) and from a vertical polarization omnidirectional radiation pattern of the omnidirectional coverage antenna (14), an augmented elevation plane downward pointing pattern of the omnidirectional coverage antenna (14), the pattern having a deep null oriented toward a co-located second transmit antenna (12) that is also attached to the aircraft fuselage and co-banded with the transmit and/or receive bands of the omnidirectional coverage antenna (14), so that interference from the second antenna (12) is reduced.
The method of claim 5 wherein the second antenna (12) comprises a plurality of dedicated transmit antennas.
The method of claim 5 wherein the electrical down-tilt is achieved by selection of a configuration of a signal transmitted by the transceiver (18).
The method of claim 5 wherein the pointing pattern with the deep null is aligned with the direction of the second antenna.