Communications: radio wave antennas – Antennas – With spaced or external radio wave refractor
Reexamination Certificate
2000-12-06
2002-07-23
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
With spaced or external radio wave refractor
C343S909000
Reexamination Certificate
active
06424308
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a wideband matching surface for dielectric lens antenna radome absorbers. In particular, the present invention relates to a wideband matching surface for reducing electromagnetic wave reflection and attenuation in a dielectric lens antenna radome or absorber.
An antenna is often a critical element of a communication system. The physical design and construction of an antenna are the keys to providing exceptional electromagnetic energy collecting and radiation properties. A dielectric lens antenna, however, may be considered as a transmission line section. As a transmission line section, the antenna is susceptible to electromagnetic reflections, standing waves, and other interference that attenuate the electromagnetic signal that the antenna collects or radiates. An attenuated signal may not propagate reliably to its destination, may require additional transmit power, or additional receiver amplification, as examples.
Thus, prior lens antennas often included a surface matching structure. The surface matching structure presents an input or output impedance that matches the impedance of the antenna to its surrounding medium. As a result, electromagnetic reflections, and attenuation, are greatly reduced.
In the past, however, surface matching structures were effective only over a small range of frequencies. Thus, an antenna could not operate outside the small range of transmit or receive frequencies without incurring significant attenuation of the electromagnetic signal. As a result, a communication system that needed to operate over a wide range of frequencies required multiple antennas with individual surface matching structures, thereby significantly increasing the cost and complexity of the communication system.
A need has long existed in the industry for a wideband matching layer that addresses the problems noted above and others previously experienced.
BRIEF SUMMARY OF THE INVENTION
A preferred embodiment of the present invention provides a wideband matching structure for a dielectric lens antenna. The matching structure is formed from a first dielectric layer (e.g., Rexolite™) characterized by a first refractive index and a second dielectric layer characterized by a second refractive index supporting the first dielectric layer.
The refraction indicies (n
i
, i=1 or 2) of the first and second dielectric layers may be formed by periodically removing material from the dielectric layers along two orthogonal axes to form posts with fill factors (F
i
=w
i
/p, i=1 or 2) where p is the period of the lattice, and w
i
is the side length of the post.
The material is periodically removed along two axes to provide reduced reflection for both horizontally and vertically polarized electromagnetic waves.
As one specific example, the matching surface may be designed to provide 25 to 40 dB reflected power attenuation over 15 GHz to 35 GHz by providing a first refractive index of approximately 1.14 and a second refractive index of approximately 1.40, where the first Rexolite™ dielectric layer is approximately 0.107 inches thick and the second Rexolite™ dielectric layer is approximately 0.087 inches thick.
Another preferred embodiment of the present invention provides an antenna comprising a feed element, a dielectric lens antenna covering a feed element aperture, and a wideband matching surface supported by the dielectric lens antenna. The wideband matching surface comprises a first dielectric layer characterized by a first refractive index and a second dielectric layer characterized by a second refractive index supporting the first dielectric layer.
As noted above, at least one of the first dielectric layer and second dielectric layer have material periodically removed to provide at least one of the first and second refractive index. The material may be removed along two axes to form squares. The antenna dielectric may be Rexolite™, with the matching surface providing reflected power attenuation in the same fashion as a quarter wave matching section between the antenna dielectric and open space (or another boundary).
REFERENCES:
patent: 3886561 (1975-05-01), Beyer
patent: 4901086 (1990-02-01), Smith
patent: 4980696 (1990-12-01), Stone et al.
patent: 5426443 (1995-06-01), Jenness, Jr.
patent: 5543814 (1996-08-01), Jenness, Jr.
IEEE Transactions on Antennas and Propagation, Properties of Slotted Dielectric Interfaces, Robert E. Collin, Jan. 1959.
Optimal design for antireflective tapered two-dimensional subwavelength grating structures, Eric B. Grann M.G. Moharam, and Drew A. Pommet; Optical Society of America, vol. 12, No. 2, Feb. 1995.
Brundrett David L.
Hummer Kenneth A.
Roberts Andrew L.
Toland Brent T.
Wu Te-Kao
Nguyen Hoang
TRW Inc.
Wong Don
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