Communications: radio wave antennas – Antennas – Antenna components
Utility Patent
1998-09-10
2001-01-02
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Antenna components
C343S753000, C343S767000, C343S792500, C343S91100R
Utility Patent
active
06169525
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of wireless communications, and more particularly to high-performance sectored antenna systems using low profile broadband feed devices.
BACKGROUND OF THE INVENTION
A high performance sectored antenna system is discussed generally in U.S. patent application Ser. No. 08/677,413 now abandoned entitled Focused Narrow Beam Communication System, incorporated herein by reference. Such a sectored antenna system utilizes a lens device with multiple focal points that serve as ports for the RF signals associated with each respective sector. Feed devices are typically mounted in close proximity to each desired focal point of the lens and the design of such feed devices is crucial to the performance of the sectored antenna system.
Performance parameters for a sectored antenna system include gain, side lobe and back lobe performance, and isolation among sectors. Feed device design affects all three of these parameters. It is desirable to have high gain in the desired direction of each sector, with low side lobe and back lobe levels to minimize the amount of radiation into other sectors. These objectives can be accomplished by increasing the size of the sectored antenna system, but it is also desirable to keep the antenna system as small as possible. If such a sectored antenna system is to cover more than 90 degrees, it is likely that some feed devices will partially block the signals of other feeds, reducing the effective gain of those sectors of the antenna system. Such blockage should be reduced, but should also minimize detrimental effect of other design parameters.
In order to reduce blockage that results in high side lobes, small feed devices are often used. Unfortunately, small feeds result in broad primary patterns, which in turn reduce aperture taper and result in high side lobes. Until recently, most work has involved waveguides as the primary feed devices for lens antennas. Some recent work has involved microstrip patch feeds and has had some success in lowering overall side lobe levels. These microstrip patch feed devices have the advantage of a constant phase center over their operating band but have the disadvantage of a large structure. Microstrip patch antenna feeds can be made smaller through the use of a higher dielectric constant substrate material, but they have relatively narrow bandwidth and typically require separate transmit and receive feeds, thereby doubling the size.
Ordinarily, broadband feed devices would not be used with lens antennas in a high performance sectored antenna system because of the nature of their operation. Among other drawbacks, such feed device phase centers move over frequency, making broadband operation difficult. As discussed in
Antenna Theory Analysis and Design
by Constantine Balanis on p. 556 and typically accepted in the field of high performance sectored antenna systems, “The movement of the active region of the antenna, and its associated phase center, is an undesirable characteristic in the design of feeds for reflector and lens antennas.” The present invention successfully utilizes low profile broadband feed devices in a lens-based sectored antenna system, resulting in higher performance with lower back lobes and side lobes.
SUMMARY OF THE INVENTION
An object of this invention is to create a high-performance, yet compact sectored antenna system that reduces side lobe and back lobe radiation using low profile broadband feed devices.
A related object of this invention is to create an efficient method of feeding signals into and out of a dielectric lens device.
Another object of this invention is to reduce coupling among sectors in a sectored antenna system.
Yet another object of this invention is to create a sectored antenna system for broadband operation across a wide range of frequencies.
Another object of this invention is to create a sectored antenna system capable of supporting a high capacity communications system.
In accordance with a preferred embodiment of the invention, a sectored antenna system comprises one or more dielectric lenses, each having a surface and one or more low profile broadband feed devices next to the lens surface In a preferred embodiment, such feed devices may be log periodic dipole arrays and/or notch antenna feeds. Other low profile broadband feed devices could also be used. The feed devices radiate signals into the lens that emerge as separate directional beams in the transit operating mode, or the lenses receive incoming signals from different directions and focus them onto different antenna feed devices in the receive operating mode, or a combination thereof. In the preferred embodiment of this invention, a Luneberg lens is employed whose focal point by design or construction is on or outside the surface of the lens, but other types of lenses can also be used. The low profile broadband feed devices minimize blockage and scattering to improve overall side lobe level performance.
Other objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, embodiments of the present invention are disclosed.
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Carey Douglas F.
Dziadek Edward F.
Ho Tan
Spike Technologies, Inc.
Wolf Greenfield & Sacks P.C.
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