Communications: radio wave antennas – Antennas – Wave guide type
Reexamination Certificate
2000-04-06
2001-11-27
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Wave guide type
C343S772000
Reexamination Certificate
active
06323818
ABSTRACT:
CROSS REFERENCES TO RELATED APPLICATIONS
This application is related to U.S. Provisional Application No. 60/041,669 by Koh et al entitled “A PREFERENTIAL CRYSTAL ETCHING TECHNIQUE FOR THE FABRICATION OF MILLIMETER AND SUBMILLIMETER WAVELENGTH HORN ANTENNAS” filed Mar. 25, 1997, and U.S. Provisional Application No. 60/042,065 by Bishop et al entitled “REPRODUCTION OF MILLIMETER AND SUBMILLIMETER WAVELENGTH HOLLOW WAVEGUIDES, CHANNELS, HORNS AND ASSEMBLIES BY CASTING/MOLDING TECHNIQUES” filed Mar. 25, 1997, both of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the fabrication of millimeter and submillimeter wavelength devices, and more particularly the fabrication of millimeter and sub-millimeter wavelength horn antennas integrated with waveguides, channels, and other components using lithographic and etching techniques.
2. Discussion of Background
In general terms, an electromagnetic waveguide is any structure which is capable of confining and guiding electromagnetic energy from one point to another in a circuit. A variety of structures have been devised to accomplish this goal. For example, coplanar waveguide is a type of waveguide which consists of thin strips of coplanar conductive material on a dielectric substrate. Another example is dielectric waveguide in which the radiation is confined in a coaxial dielectric tube by the principle of total internal reflection. A hollow metal electromagnetic waveguide is an electrically conductive hollow tube or pipe-like structure or a collection of such structures designed to confine and guide electromagnetic radiation. A horn is a tapered or flared waveguide structure which couples energy to or from free space and concentrates the energy within a defined spatial distribution (beam pattern). Only the inside surface of these structures must be conductive as the major fraction of the electrical current is constrained by nature to flow within a thickness known as the skin depth which is directly related to wavelength. Also the inner dimensions of such waveguides are determined by the radiation wavelength and are also generally proportional to wavelength.
Because of these relationships, the fabrication and design of hollow waveguides is strongly dependent on the operating wavelength. For example, in the case of microwaves with wavelengths on the order of centimeters, hollow waveguides can be easily fabricated by the extrusion of rectangular metallic tubes which have inside dimensions on the order of centimeters. Injection molded or extruded plastic waveguide components are also typically easily made for microwave wavelengths if they are coated with a sufficiently thick conductive material on internal surfaces. Also waveguide components for microwave frequencies can be made in sections which are joined by flanges and alignment is typically not difficult because of the relatively large dimensions.
However, the fabrication of hollow waveguide assemblies for millimeter and submillimeter wavelengths is typically much more difficult because the dimensions are correspondingly smaller. Also assemblies and subassemblies of waveguides must be combined with active electronic devices such as diodes or transistors and other passive components and circuits to make radio receiver and transmitter components such as heterodyne mixers. Therefore a complex network of accurately aligned, interconnected and very small hollow metal channels must be made and some of these channels must hold active and passive electronic components. This is generally not feasible with microwave style tubing.
A waveguide assembly designed for millimeter and submillimeter wavelengths is traditionally made by fabricating two machined metal “half” blocks, which when joined together, to form a structure comprised of air-filled metal channels. Because of RF electromagnetic field and current considerations, it is rare that any of the slots can typically be formed only in one half with the other half being a simple flat cover. Thus the blocks have slots of various shapes and sizes which are often the mirror image of each other and which require precise control of depth, width and position (i.e., alignment). This “split block” approach solves two basic problems: (1) the difficulty of monolithically forming complex and very small hollow metallic structures and (2) the need to insert a circuit deep within the structure.
In recent years high quality millimeter and submillimeter wavelength components have been manufactured using a technique based on direct machining of metal blocks, for example, as described by Siegel et al., “Measurements on a 215 GHz Subharmonically Pumped Waveguide Mixer Using Planar Back-to-Back Air-Bridge Schottky Diodes”, IEEE Trans. Microwave Theory and Tech., Vol. MTT-41, No. 11, pp. 1913-1921, November 1993, and Blundell et al., “Submillimeter Receivers for Radio Astronomy”, Proc. IEEE, Vol. 80, No. 11, pp. 1702-1720, November 1992.
FIG. 7
of Blundell et al is a drawing of machined horn antenna and waveguide fabricated using the described technique. A horn antenna is commonly used to couple electromagnetic radiation into the waveguide in communications applications. The primary benefits of machining the waveguide and the horn antenna into the metal block are that it is a well understood process which gives the designer great flexibility, the final structure is robust, and all internal components, such as semiconductor diodes, are protected from the environment. In addition, the machining process is essentially three dimensional, and therefore allows the integration of electromagnetic horns of nearly arbitrary shape.
Although the above-described direct machining technique has gained wide industry acceptance, the expense of the required machining equipment, the personnel expertise, and the fabrication time greatly increase the cost of fabricating millimeter and submillimeter wavelength components. Also, as the desired operating frequency of the components is increased (i.e., wavelength is decreased), the required dimensions of the metal block features shrink proportionally in relation to the decrease in wavelength, making fabrication even more costly and difficult.
Another common technique for fabricating millimeter and submillimeter wavelength components is known as electroforming, for example, as described by Ellison et al., “Corrugated Feedhorns at Terahertz Frequencies-Preliminary Results”, Fifth Intl. Space THz Tech. Symp., Ann Arbor, Mich., pp. 851-860, May 1994. In the electroforming technique, a metal mandrel is formed by high precision machining techniques and is then used as a metal core around which a second metal is deposited by electroplating. It is this second metal which eventually forms the hollow metal waveguide after the initial metal is chemically etched away. This technique is employed because it is often easier to machine the mandrel than the actual waveguide itself. Using this technique, components have been fabricated for frequencies up to 2.5 THz, however, the fabrication of the components is still costly and difficult.
Another technique for fabricating millimeter and submillimeter wavelength horn antennas is known as silicon micromachining, for example, as describe by Ali-Ahmad, “92 GHz Dual-Polarized Integrated Horn Antennas”, IEEE Trans. Antennas and Prop., Vol. 39, pp. 820-825, July 1991, and Eleftheriades et al., “A 20 dB Quasi-Integrated Horn Antenna”, IEEE Microwave and Guided Wave Letters, Vol. 2, pp. 73-75, February 1992, which are incorporated herein by reference. Using this technique, and as in the present invention, the horn antennas are fabricated using a preferential/selective wet etch and silicon wafers with a correct crystal orientation, such that the etch process proceeds very quickly in the vertical or (100) crystal plane direction but which virtually stops when the (111) crystal planes are. When the etch is carried to completion, only the (111) plane surfaces are exposed, and the result is a pyramidal shape etched into the silicon having a flare a
Bishop, Jr. William L.
Crowe Thomas W.
Hesler Jeffrey L.
Koh Philip J.
Mann Chris
Clinger James
Miles & Stockbridge P.C.
University of Virginia Patent Foundation
Wong Don
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