Communications: radio wave antennas – Antennas – Spiral or helical type
Reexamination Certificate
1981-12-11
2001-05-01
Blum, Theodore M. (Department: 3662)
Communications: radio wave antennas
Antennas
Spiral or helical type
Reexamination Certificate
active
06225963
ABSTRACT:
BACKGROUND OF THE INVENTION
It is desirable to have radar detection systems which can detect emissions over a wide frequency range. For such systems to operate effectively, suitable antennas are required which can efficiently capture the radar signals. When the antennas are to be located on aircraft, a significant problem exists in finding space for the antennas both because suitable space on aircraft is extremely limited and there is a need that the detection antenna not interfere with normal aircraft operations.
Several antennas exist that cover the 0.5 GHz to 18 GHz frequency band. These antennas provide lower band coverage either by wiring helices around a cylindrical surface placed at right angles to the beam or by using a normal 2-18 GHz antenna at the 0.5-2 GHz frequencies and accepting additional gain losses and pattern degradation. For the prior art antennas which include helices, excessive depth behind the mold line is required, and additional space is required around the antenna at the mold line to allow energy to reach the helices. This in turn increases the required spacing to adjacent antennas affecting the phase tracking ability of such antenna when arrayed. The gain of the helix antennas at the low end of the frequency band is only −15 dBi while the gain of the normal 2-18 GHz antenna, at the low band is only −30 dBi. The pattern performance of the normal 2-18 GHz antennas is poor at low frequencies because of the small antenna aperture available.
Other antennas exist that cover the lower band efficiently having large radiating areas which make them efficient. However, the antennas of this type do not operate effectively at the higher frequencies and therefore multiple antenna locations must be provided which is difficult especially when the antennas are retrofitted to an existing aircraft.
It is also possible to construct an antenna that will efficiently operate over the total frequency band of 0.5-18 GHz including the lower frequencies by enlarging the diameter of conventional spirals to include the lowest desired frequency. This antenna at 0.6 GHz would require a diameter of about 6.8 inches. Such an antenna, although large, would work as a radar warning antenna. However, it could not be used in an array because of the required excessive spacing between adjacent antennas. This severely limits its usefullness in radar detection because bearing information which can be obtained from an array is almost as important to determine as the existance of the radar emission in the first place.
BRIEF DESCRIPTION OF THE PRESENT INVENTION
The present cloverleaf antenna basically is a spiral antenna having a pair of printed circuit elements which are circularly spiral at the center portion thereof. Four other similar spiral antennas can be included at the sides of the center portion to form longitudinal and lateral arrays with the center portion. The elements of the center portion are extended outwardly in a cloverleaf fashion so that the four cloverleaf lobes formed by the spiral elements are located on the diagonals between the other array forming spiral antennas. The element portions of the cloverleaf lobes convert a normal 2 to 18 GHz spiral array into one that can also handle frequencies down to 0.6 GHz while keeping the same array envelope and providing a higher gain than prior art antennas of larger size.
Therefore it is an object of the present invention to provide a wide band antenna and antenna array in the same array envelope as existing arrays of smaller frequency range.
Another object is to provide a wide band radar warning antenna which can be produced easily and simply using printed circuit techniques.
Another object is to provide a radar warning array which requires a minimum of depth for incorporation into a moving platform such as an aircraft.
Another object is to provide an antenna which can be flush mounted and is relatively small in size having a nominal beamwidth near 80° and a near constant gain over most of a wide frequency band.
These and other objects and advantages of the present invention will become apparent to those skilled in the art after considering the following detailed specification in conjunction with the accompanying drawings wherein:
REFERENCES:
patent: 2482767 (1949-09-01), Hansen
patent: 2977594 (1961-03-01), Martson et al.
patent: 3246245 (1966-04-01), Turner
patent: 3343089 (1967-09-01), Murphy et al.
patent: 4309706 (1982-01-01), Mosko
patent: 271592 (1970-05-01), None
Blum Theodore M.
McDonnell Douglas Corporation
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