Patent Application
20070024505
The present invention relates to patch antennas for transmitting and receiving electromagnetic energy and more particularly to the design and use of patch antennas within high temperature environments.
Antennas are used to transmit and receive electromagnetic energy. Typically, they are used within ambient temperature environments and are used in such devices as mobile phones, radios, global positioning receivers, and radar systems. Patch antennas, sometimes referred to as microstrip antennas, typically are an antenna design consisting of a metallization applied to a dielectric substrate material. Many such designs are constructed with printed circuit board etching processes common in circuit board manufacture. The geometry of the design is typically rectangular or circular, but other geometries are possible to provide enhanced performance such as increased bandwidth or directionality.
Additionally, microwave-based sensors have been developed specifically for use in high temperature environments. Next generation sensor systems are used in high temperature environments that require an antenna to be exposed to combustion gases. These microwave systems enable advanced control and instrumentation systems for next-generation aircraft and power generating turbine engines.
Sensors operating within the environment of a turbine engine are frequently required to survive in gas path temperatures exceeding 2000° F. for over 12,000 operating hours. Traditional patch antennas found in consumer, industrial, and military systems are not built of construction methods or materials that can survive a short period of time in such high temperatures, let alone survive and operate reliability for thousands of hours. Patch antennas have not yet been implemented in such harsh environments to date.
Radomes have been used as dielectric windows to protect antennas from the elements as well as extended temperatures during missile vehicle re-entry into the atmosphere. These radomes are typically large structures made from a low dielectric constant that allow electromagnetic energy to pass through with a minimum of attenuation. Radomes on missile re-entry vehicles typically have to protect the antenna on the order of minutes and will often use ablative coating and additional thermal management systems to lower the temperature of the antenna. Traditional radome approaches to improving the survivability of a patch antenna are not well suited for extended life applications.
Finally, the dielectric constant of substrate materials changes as a function of temperature. Since patch antennas typically operate as a resonant structure whose resonance is closely coupled to the dielectric constant of the substrate, the center frequency of the antenna can change as a function of temperature. This requires that the transmit frequency be appropriately changed to match the center frequency of the antenna in order for the antenna to radiate electromagnetic energy efficiently. Therefore, in order to reduce system complexity and the total transmit bandwidth of the electronics, it is desirable to minimize the shift in antenna resonant frequency as a function of temperature.
Implementing a long-life patch antenna for high temperature environments requires a different approach than that found in the prior art. Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.
The present invention improves the performance and reliability of a patch antenna within a high temperature environment. The inventive patch antenna includes an antenna radiating element, typically placed within a housing or probe assembly having passages or orifices for distributing air within the housing and to the antenna radiating element. This combination of a patch antenna and housing is useful as a probe for use in measuring characteristics of equipment or devices that operate at a high temperature, typically greater than 600 degrees Fahrenheit. The 600 degrees Fahrenheit. The antenna radiating element typically comprises metallization (or solid metals) in contact with a ceramic, and may have a dielectric window consisting of a flame spray coating or a solid dielectric material in front of the radiating element. The antenna element is inserted into a probe body that mechanically captures the antenna and provides the necessary ground plane of the antenna to operate. The probe body may contain cooling orifices or passages, commonly referred to as cooling holes, to improve high temperature performance and may direct air through the antenna element itself. A high temperature microwave cable is inserted into the probe body and attached to the antenna radiator. These parts can be joined together with high temperature brazing, welding, or ceramic adhesive processes. The joining technology creates effective bonds that last in high temperature environments.
One aspect of the invention is the antenna radiating element, referred to as the puck, typically comprising a piece of solid dielectric material with a metallization applied. A high temperature metallization can be applied to the dielectric material via a standard thin film or thick film process, or a solid piece of metal can be brazed onto the dielectric material. The metallization shape or pattern provides the necessary geometry for the radiating element and, in addition, an attachment for the ground plane on the back side. The use of a dielectric material with a low change in dielectric constant as a function of temperature can minimize changes in the antenna center frequency as the temperature if the application environment changes. A dielectric window may be placed on top of the puck to provide additional thermal and environmental protection. The window may be of a standard plasma flame spray coating type, or it may comprise a solid piece of dielectric material. If a solid dielectric material is used, the patch geometry is preferably modified to provide the correct impedance match to the dielectric window, which will allow the antenna to radiate in the most efficient manner.
The probe body is a piece of metal that is used to mechanically retain the puck as well as provide the mechanical and electrical attachment between the microwave cable and the puck. The probe body outer dimensions allow the entire assembly to be installed into the system where the antenna is desired to be used. The probe body may contain cooling holes or other orifices that can be used as part of an active cooling system to improve the antenna performance in the hottest of environments.
The microwave cable allows the antenna to be connected to the transmitter and/or receiver electronics such that microwave energy can be efficiently transmitted via the antenna. The cable is of a high temperature construction that allows it to operate in the same environment as the probe. It is mechanically attached to the probe body to allow proper electrical connection to the ground plane.
Other systems, methods, features, and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.
Many aspects of the invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of exemplary embodiments of the present invention. Moreover, in the drawings, reference numerals designate corresponding parts throughout the several views.
a is the top view of an exemplary implementation of a patch antenna, with metallization applied using a thick film or thin film process in accordance with one embodiment of the present invention.
b is the side view of an exemplary implementation of a patch antenna, with metallization applied using a thick film or thin film process in accordance with one embodiment of the present invention.
a is the top view of an exemplary implementation of a patch antenna with a main radiator comprising a solid piece of metal attached to a dielectric substrate in accordance with one embodiment of the present invention.
b is the side view of an exemplary implementation of a patch antenna with a main radiator comprising a solid piece of metal attached to a dielectric substrate in accordance with one embodiment of the present invention
Exemplary embodiments of the present invention provide for a patch antenna capable of operating within a high temperature environment for extended periods of time. For the purpose of this disclosure, a high temperature environment is defined by an environment having a temperature of or greater than 600° F.
Exemplary embodiments of the present invention will now be described more fully hereinafter with reference to
This invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those having ordinary sill in the art. Furthermore, all representative “examples” given herein are intended to be non-limiting, and among others supported by exemplary embodiments of the present invention.
There are additional ceramics available for use as the dielectric substrate 101 that add titania or calcium oxide additives to an alumina formula; these materials are known to significantly reduce the dielectric constant change as a function of temperature. Exemplary embodiments of the invention use these materials to minimize the change in antenna center frequency as a function of temperature.
The high temperature metallization 101 is a metal that is applied to dielectric substrate 102. Although the dielectric substrate 102 is capable of withstanding very high temperatures with high survivability in corrosive environments, the metallization 101 can be vulnerable over longer exposures. Materials include platinum-palladium-silver, rhenium, elemental platinum, and even conductive ceramics such as indium tin oxide. The geometry of the metallization 101 can be of any standard antenna design. To date, exemplary designs include a circular path or variants of a circular path, including a U-slot patch and a straight slot patch. Any geometry that achieves the desired center frequency and bandwidth could be used to implement the metallization.
The feed to the antenna is through hole 103. In exemplary designs, the center conductor of a coaxial cable is fed through hole 103 and bonded to metallization 101 using a braze, TIG welding, laser welding, or any other metal-to-metal joining technique, as known to those versed in the art. The antenna could be fed using a pin rather than a coaxial cable, or the feed could be redesigned to accommodate any other type of patch antenna feed found in the prior art.
The exemplary patch antenna can operate in support of transmission and reception of electromagnetic signals, while exposed to high temperatures, based on a selection of high temperature materials to prevent melting, oxidation, or chemical attack, as described above in connection with
Disk 201 can comprise a high temperature nickel alloy metal, such as Hastelloy-X or Haynes 230. The disk 201 can be made as thick as desired. Exemplary designs include a disk 201 having a thickness of up to 0.050″. Larger thicknesses may be required depending on the application.
The cable 302 is typically a semi-rigid mineral insulated cable, using an insulator 306 such as silicon dioxide. These cables can be standard coaxial or triaxial cables with a traditional copper center conductor 303 and ground or a nickel alloy center conductor and ground for increased temperature resistance. The protective outer jacket of the cable 302 can be a stainless steel or a nickel alloy. The center conductor 303 is electrically attached to the patch antenna 100.
There are applications for the probe 300 where the air temperatures can exceed the melting points of the probe body 301. For these applications, passages or orifices, commonly referred to herein as holes, such as holes 304, can be drilled inside of the probe body 301. Additional passages or orifices, such as holes 305, can be drilled in the patch antenna 100. Exemplary installations of probe 300, such as in a gas turbine, can place the back of the probe body 301 within a cooler environment. Holes 304 and 305 allow cool air to pass through probe body 301 and radiator 100 to allow the probe to survive in the high temperature environment. An additional method of cooling uses an annular space or passage around the probe itself for cooling. For example, an annular passage can be placed adjacent to the dielectric material of the radiating element to support antenna cooling. These integral cooling orifices are useful for cooling and insulating the various components of the antenna 100.
Exemplary implementations of the patch antenna 100 include cooling holes 305 within the microwave design. The addition of cooling holes 305 into dielectric substrate 102 effectively reduces the dielectric constant by replacing high dielectric substrate material with air. With the addition of the cooling holes 305, the geometry of metallization 101 must be updated such that the resonant frequency of patch antenna 100 is at the desired frequency. The cooling holes 305 can be located outside of high temperature metallization 101 or placed in the geometry of high temperature metallization 101.
The cooling air distributed or passed by an orifice or passages provides other benefits for the inventive antenna, including 1) conductive cooling by direct contact with the probe surfaces (probe body, dielectric materials, conductive elements, and microwave cable); 2) providing an insulating layer of air in-between the probe body and the wall of the case; and 3) providing a boundary layer at the radiating element to protect it from high temperature gases.
Probe 400 is identical to the probe 300 of
The dielectric window 401 also can be implemented as a thick disk of material placed over patch antenna 100. The window material can include alumina, silicon dioxide, or any other material deemed appropriate for the application, with a thickness of up to or exceeding one half an inch thick. When a large dielectric window is placed in front of patch antenna 100, the microwave performance of the antenna can be impacted. Therefore, when a thick dielectric window 401 is used, the microwave design will have to properly account for its presence by impedance matching the patch to the dielectric window.
A large dielectric window 401 is typically attached using a ceramic adhesive to bond the dielectric substrate 102. Other standard metal to ceramic techniques can be used to attach the dielectric window 401 to the high temperature metallization 101.
Joint 702 is a ceramic to metal seal that attaches probe body 301 to the dielectric substrate 102. In exemplary designs, a vacuum brazed is used. However, air brazing, torch brazing, and diffusion bonding are additional ways to create the seal. Any conventional ceramic-to-metal seal methodology may be used to create the seal provided that the seal can handle the thermal and chemical environments where it is operating and provide the required hermetic seal for the cable.
Joint 704 attaches the center conductor of the cable 303 to the high temperature metallization 101 or disk 201. The attachment must provide sufficient electrical contact as to allow the microwave energy to transition from the cable to the patch antenna 100 with minimal signal reflections or losses. In exemplary implementations, a laser weld is used for the attachment. Brazing, TIG welding, induction heating, and any other metal to metal attachment process can be used without loss of generality.
In view of the foregoing, it will be understood that the present invention comprises an antenna operational within a high temperature environment. An antenna radiating element, typically comprising a patch formed by a conductive element in contact with a dielectric element, is operative to communicate electromagnetic signals. The dielectric element of the antenna radiating element typically comprises a dielectric material exhibiting a low change in dielectric constant as a function of temperature. A housing comprising conductive material is operable to accept the antenna radiating element. This housing has one or more cooling orifices supporting the passage of air for cooling the antenna radiating element within the high temperature environment.
A high temperature microwave cable can be coupled to the antenna radiating element. The cable is typically inserted within the housing and attached to the conductive element of the antenna radiating element for the passage of electromagnetic signals to or from the radiating element.
A dielectric window can be positioned in front of the antenna radiating element and adjacent to the housing. The dielectric window comprising a dielectric material operative to provide additional thermal and environmental protection for the antenna radiating element. The dielectric window typically comprises a flame spray coating or a dielectric material.
The antenna radiating element is typically housed within at least a portion of the housing and joined to the housing by a bond capable of withstanding the high temperature environment. The housing can comprise a conductive material having dimensions sufficient to operate as a ground plane for the antenna radiating element.
The conductive element can comprise a metallization applied to a surface of the dielectric element. In the alternative, the conductive element can comprises a solid conductive material joined to a surface of the dielectric element. The conductive element typically has a geometry suitable for communication of electromagnetic signals.
The dielectric element can comprises one or more orifices or cooling holes to support the passage of air for cooling the antenna within the high temperature environment. In the alternative, the dielectric element can comprise an annular passage to support the passage of air for cooling the antenna within the high temperature environment. The antenna also can include one or more passages positioned adjacent to the dielectric element to support the passage of air for cooling the antenna within the high temperature environment.
The present invention also provides a method of manufacturing an antenna for operation within a high temperature environment. An antenna radiating element can be formed by joining a conductive element to a dielectric material element. At least one orifice is added to a housing for housing the antenna radiating element. Orifices can be added to the conductive element of the antenna radiating element to further support the distribution of air for cooling the antenna. Each orifice or cooling hole supports the passage of air from the exterior of the housing to the interior of the housing for cooling the antenna within the high temperature environment. The antenna radiating element is inserted within at least a portion of the housing and joined to the housing.
The present application has presented alternative exemplary embodiments of a patch antenna operable within a high temperature environment. Different applications will require different frequencies of operation, mechanical dimensions and geometries, and materials, which can be designed using techniques known to one versed in the art.
Applicants claim priority under 35 U.S.C. 119 to an earlier-filed provisional patent application, U.S. Provisional Patent Application Ser. No. 60/652,231 filed on Feb. 11, 2005, entitled “A High Temperature Probe for Displacement Measurements”. The subject matter disclosed by this provisional patent application is fully incorporated within the present application by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 60652231 | Feb 2005 | US |
