Communications: radio wave antennas – Antennas – With aircraft
Reexamination Certificate
1999-01-19
2001-03-06
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
With aircraft
C343S705000, C343S767000, C343S860000
Reexamination Certificate
active
06198446
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a feed system for an antenna and, more particularly, to a feed system used in connection with a low observable, multifunction, conformal, load bearing structure, excitation notch antenna on an aircraft that provides radio communications and navigation functions over several frequency bands and communication modes.
2. Discussion of the Related Art
Modern manned and unmanned tactical aircraft require radio communications over several frequency bandwidths and communication modes to support the communications, navigation and identification (CNI) functions necessary for operation of the aircraft. These radio frequency bandwidths generally include the VHF frequency modulation (FM) band (30-88 MHz), the VHF amplitude modulation (AM) band (118-174 MHz) and the UHF band (225-400 MHz). To transmit and receive these frequency bands for aircraft communications purposes, a suitable antenna system is required that is positioned on the aircraft. Known antenna systems used on tactical aircraft for CNI functions have typically included blade antennas that have a fin protruding from the surface of the aircraft. Generally, multiple blade antennas are required for the CNI functions, including one for the VHF/FM frequency band, one for the VHF/AM frequency band and another one for the UHF frequency band.
Blade antennas have a number of drawbacks when used on aircraft. These drawbacks include requiring high speed electronics for synchronously tuning the antenna and the need to efficiently couple radio frequency (rf) currents to the aircraft skin. Coupling rf signals to the conductive portions of the aircraft is a known technique that is used when the only available antenna elements are electrically small in relation to the wavelengths of the signals being transmitted and received, as is the case for the VHF/FM band. Also, because the blade antenna protrudes from the aircraft, these antennas adversely effect the aircraft's aerodynamics. Additionally, broad band, electrically small, VHF/FM blade antennas have a very low gain because they have a poor matching network efficiency and a small radiation resistance.
Moreover, the available antenna installation sites on the aircraft may not support the number of antennas needed to install the proliferating number of CNI functions, if each function requires its own antenna. Excitation antennas for supporting CNI functions are installed on aircraft at sites that are not needed by other aircraft antennas and therefore provide an efficient use of the available “real estate” on the aircraft. Additionally, because many modern tactical aircraft are low observable aircraft, it is necessary that the antenna elements conform to the aircraft structure. Known conformal antennas do not cover all of the communications bands needed for the present CNI functions.
To overcome the requirement of multiple antennas to support the CNI functions, and eliminate the need for blade antennas, U.S. Pat. No. 5,825,332, filed Sep. 12, 1996, titled “A Multifunction Structurally Integrated VHF-UHF Aircraft Antenna System”, assigned to the assignee of the instant application and herein incorporated by reference, discloses an aircraft antenna that is totally integrated within the aircraft, and operates over a wide range of frequencies, including VHF/FM, VHF/AM and UHF. To operate in this manner, the antenna system uses an electrically conductive element that is part of the aircraft structure and an antenna element positioned and shaped to form a notch therebetween. The notch is generally uniform in width over part of its length and flares to a larger width over the remainder of its length. Broad band impedance matching electronics are provided to couple the antenna system to a transceiver to provide efficient transfer of energy to and from the antenna.
The broad band conformal antenna system of the '332 patent discussed above includes an antenna feed connected to the matching electronics and to a selected antenna feed point on the antenna element. The antenna feed excites the antenna element for transmission of signals, and conducts the received signals from the antenna element and electrically conductive element of the aircraft structure. The feed structure in the '332 patent is a single piece structure that provides electrical coupling between the antenna element and the matching network, but is not effective to provide the necessary coupling and impedance matching over all of the desired frequency bands of interest, including VHF/FM, VHF/AM and UHF.
What is needed is an antenna feed structure that provides impedance matched feeds for all of the frequency bands for CNI functions in connection with a single multifunction antenna. It is therefore an object of the present invention to provide such a feed structure.
SUMMARY OF THE INVENTION
In accordance with the teachings of the present invention, a multifunction antenna feed structure is disclosed that has a particular application as a feed for a multiple bandwidth antenna system used in connection with a modern tactical aircraft. The feed structure includes a first feed and a second feed electrically connected to first and second feed points on an antenna element at a location where the feeds are impedance matched to the desirable frequency bandwidths to be received and transmitted. In one embodiment, one of the feeds is impedance matched to the VHF/FM and UHF bandwidths and the other feed is impedance matched to the VHF/AM bandwidth. Also, in one embodiment, the first and second feeds are positioned within a flared notch between the antenna element and a conductive aircraft structural component. The feeds can take on different geometrical configurations, such as cylindrical feeds, cone feeds, or taper feeds.
The feeds are electrically isolated from the conductive aircraft component, and are electrically connected to a matching network. The matching network includes a first electrical circuit connected to one of the feeds and a second circuit electrically connected to the other feed. The first circuit impedance matches the signal from the antenna element to a transceiver circuit at the VHF/FM and UHF bands, and the second circuit impedance matches the second feed to the transceiver circuit at the VHF/AM band. The matching network would be positioned within the conductive aircraft component, proximate to the feed structure.
REFERENCES:
patent: 2701307 (1955-02-01), Cary
patent: 4245222 (1981-01-01), Eng et al.
patent: 4672685 (1987-06-01), Phillips
patent: 4723305 (1988-02-01), Phillips
patent: 4922259 (1990-05-01), Hall et al.
patent: 5825332 (1998-10-01), Camacho et al.
patent: 2329082 (1990-11-01), None
patent: WO 90/13152 (1998-10-01), None
Chea Haigan K.
Goetz Allan C.
Le Hoang-anh
TRW Inc.
Yatsko Michael S.
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