Patent ID: 12199357

DETAILED DESCRIPTION

The present disclosure relates to a method and apparatus for compensation of an antenna and/or an antenna array located at a surface that may experience extreme environmental conditions. Exemplary embodiments provide new architectures of surface-mounted antennas that can be conformally located on a surface, such as a vehicle surface of an air, land or sea vehicle surface. Exemplary embodiments can outperform known architectures, such as those that use a radome or covering for protection.

An exemplary apparatus as disclosed herein provides embedded compensation and/or calibration structures near the antenna that can be interrogated by an electromagnetic wave to determine surface properties. An exemplary method uses measurements of the compensation structures (e.g., calibrated compensation structures) to determine accurate beam pointing for dynamically varying surface conditions, thus allowing a system to perform sensing and/or seeking observation with high accuracy.

As disclosed herein, a compensation and/or calibration system can enable dynamic corrections of vehicle and/or surface antenna performance during flight. Dynamic operation is desirable because surface antennas contain features at the vehicle surface that are highly sensitive to a dielectric constant, a dielectric height and erosion, and/or temperature. High-velocity vehicles encounter extremes in both temperature and erosion which can lead to changes in an antenna pointing angle. If the actual pointing angle changes with respect to expectation, and these changes are uncompensated, then the vehicle cannot perform its mission because it will misinterpret positions of targets.

TheFIG.1exemplary embodiment shows a vehicle having compensation information related to a dielectric constant, dielectric height “h”, and periodicity of modulations, which information can change as a result of, for example, high temperatures and erosion present at a surface of a high-velocity vehicle and thereby change radiation angles of the antenna which can disrupt vehicle operation. InFIG.1, an exemplary configuration of a surface scattering antenna100includes a pointing angle defined as follows:

sin⁢θ=n0-λp=n0-cp⁢f

In the foregoing equation, the pointing angle is θ, and this is impacted by an index n0, a spatial periodicity of modulation, p, a frequency f, and wavelength, λ, wherein λ is related to frequency as λ=c/f where c is the speed of light.

The index “n0” is the “equivalent mode index” of the propagating surface wave. An “equivalent mode dielectric constant” is related to the dielectric constant, with index “n0”=sqrt (dielectric constant). The surface wave mode contains electromagnetic fields that are spread between the high temperature dielectric, such as the dielectric represented by a dielectric layer106inFIG.1; the air above the aperture; and also the interaction of the surface wave mode with reflections due to any refractory metal layer located below the dielectric. Because the interaction occurs with multiple materials, the “equivalent mode index” as referenced herein represents an average material property of the mode it sees. The “equivalent mode index” can be considered the material index for assessing a propagation velocity of a plane wave in the material, which velocity can thereby be equal to that of the surface wave mode, taking into account the geometry.

The dielectric constant is a constant of the high-temperature dielectric material described herein, as this material experiences the largest changes with temperature in exemplary embodiments. Changes to a dielectric constant or periodicity in flight due to extreme temperatures or erosion can cause angle discrepancies. An exemplary compensation system as disclosed herein can determine, or calculate, an amount of erosion along with changes to periodicity and a dielectric constant to allow accurate calculation of the radiation angle.

FIG.1illustrates a system which includes a surface antenna having an aperture; a compensation and/or calibration system containing plural compensation and/or calibration structures, each structure including: a dielectric layer covering at least a portion of the surface antenna aperture, a mode converter embedded within the dielectric layer; a carbon insulation layer; a refractory metal layer; a carbon-to-carbon (C-to-C, or C/C) layer positioned between the dielectric layer and the carbon insulation layer; a an electronic subsystem surface interface; an oxide insulation layer positioned between the carbon-to-carbon insulation layer and the electronic subsystem surface interface; and a waveguide dielectric interconnecting the surface antenna aperture and the electronic subsystem surface interface; and an electronic subsystem having a computer processor and a radio frequency (RF) module in operative communication with the compensation and/or calibration system.

InFIG.1, the external surface102can be, for example, a flat or vehicle-scale curved, surface. The lower half ofFIG.1is a perspective of the cross-sectional view shown in the upper half ofFIG.1. Electromagnetic wave propagation104is from left to right in the exemplary illustration across the dielectric layer106which can cover an entire antenna aperture radiating, for example, any number of 2-dimensional pencil beams.

The exemplary pencil beams inFIG.1show 1-dimensional steering. The aperture can radiate a beam in any direction for theta and phi, (in spherical coordinates).FIG.1shows three beams of the same azimuth but those skilled in the art will appreciate that any azimuth and elevation angles will be feasible and can be selected.

The dielectric layer106can be a relatively high temperature dielectric abutting a shorted wall108. The dielectric material is, for example, capable of being heated to high temperatures, such as >1000 C without decomposing or suffering damage. A mode converter110is included within the dielectric.

A refractory metal layer112and a carbon-to-carbon (C/C) layer114can be provided between the dielectric layer106and an exemplary a carbon insulation layer116. The refractory metal layer112uses the RF signal from an RF module to reflect at the metal interface and return without being transmitted via a waveguide dielectric122.

An exemplary embodiment can include additional (e.g., stacked) insulating layers. For example, theFIG.1embodiment includes an oxide insulation layer118to insulate an electronic subsystem120and/or an electronic subsystem surface interface which receives EM that has been received by the antenna surface and directed to the electronic subsystem via the waveguide dielectric122. Those skilled in the art will appreciate that the electronic subsystem is an electronic system, such as a radar, seeker or other electronic subsystem, that can be optionally mounted on or within a vehicle (e.g., aircraft, unmanned aerial vehicle (UAV), missile or any airborne device). The waveguide dielectric, or waveguide dielectrics if two or more such waveguide dielectrics are included, thereby interconnects the surface antenna aperture and RF received therein as electromagnetic energy to the surface interface.

The subsystem120(e.g., radar, or radar/seeker) can be configured in any known manner to receive electromagnetic energy (e.g., RF energy) and perform any desired seeking and/or radar function or other function. The subsystem can for example, include a computer processor and execute a software program stored on a non-transitory computer readable medium configured as a computer readable medium storing program code for performing data processing. A person having ordinary skill in the art will appreciate that embodiments of the disclosed subject matter can be practiced with one or more modules in a hardware processor device with an associated memory. A hardware processor device as discussed herein can be a single hardware processor, a plurality of hardware processors, or combinations thereof.

In an exemplary embodiment, control signals, processing algorithms, artificial intelligence capability and so forth can be provided to or from the electronic subsystem using any suitable local or remote database configuration. Suitable configurations and storage types will be apparent to persons having skill in the relevant art.

The exemplary computing device of the electronic subsystem can include a communications interface. The communications interface can be configured to allow software, control signals and data to be transferred between the computing device and external devices. Exemplary communications interfaces can include a modem, a network interface (e.g., an Ethernet card), a communications port, a PCMCIA slot and card, etc. Software and data transferred via the communications interface can be in the form of signals, which can be electronic, electromagnetic, optical, or other signals as will be apparent to persons having skill in the relevant art. The signals can travel via a communications path, which can be configured to carry the signals and can be implemented using wire, cable, fiber optics, a phone line, a cellular phone link, a radio frequency link, etc.

The waveguide dielectric122as shown in the perspective view can be represented as one or more feeds, located within a relatively small fraction of the aperture. The waveguide dielectric122can be the same, or different material relative to the material of which dielectric106is formed. Exemplary waveguide dimensions are shown in the perspective as λ and λ/2 where a periodicity in each dimension locks the dielectric to the carbon-to-carbon (C/C) layer.

As mentioned, theFIG.1surface scattering antenna system includes an embedded compensation and/or calibration system to compensate environmental influence on radiation angle. TheFIG.1embodiment can include an associated electronic subsystem, such as a seeker system, a radar system or other electronics, having a computer processor and a radio frequency (RF) module in operative communication with the compensation and/or calibration system as will be described herein.

FIG.2shows details of an exemplary system block diagram for a physical compensation and/or calibration system200of a surface antenna such as that ofFIG.1.

Referring toFIG.2, the exemplary surface antenna compensation and/or calibration system contains several components, such as embedded compensation and/or calibration structures204, each of which can be a compensation and/or calibration structure as described with respect toFIG.1and/orFIGS.3a-3e. For example, one or more such structures can be located at a surface of an external system such as a vehicle202. These structures can be configured to be interrogated with RF electromagnetic waves at one or more frequencies within the operating frequency range of the antenna to dynamically compensate for surface erosion, thermal expansion, and/or dielectric constant changes. The compensation and/or calibration system can be connected to an RF module206via transmission lines that allow RF signals to be input into the structures and then measured on an output. A magnitude and phase of these RF signals can provide information about surface properties.

The compensation and/or calibration structures can be configured with the same set of materials as the surface antenna to, for example, simplify manufacturing since the same manufacturing process can be used. This can provide more accurate calibrations since the surface antenna and calibration structures have the same material “stackup” (i.e., such as the material stackup shown inFIG.1). However, it is possible to use compensation and/or calibration structures of different materials and stackup as long as the relative impact of extreme conditions (e.g., higher temperature and/or airflow conditions) on the compensation and/or calibration structures vs. the antenna are known or can be predicted.

The apparatus for compensation and/or calibration of an antenna and/or antenna array can include a computer processor208configured to receive measurements of the compensation and/or calibration structure(s) to determine beam pointing for dynamically varying surface conditions, and to perform desired functions, such as those of: sensing and/or seeking observation within the electronic subsystem.

FIGS.3a-3eshows details of exemplary compensation and/or calibration structures of the compensation and/or calibration system204ofFIG.2.

InFIGS.3a-3e, exemplary embodiments of the compensation and/or calibration system are shown, and can include structures configured to be the same as that of the antenna which is being compensated, where an exemplary material stackup shown inFIGS.3a,3b,3c, and3ehas the same materials and thickness as the materials of the antenna. As such material compositions and thicknesses and order are, for example, the same in the compensation and/or calibration structures, and the antenna. The exemplary dielectric does not have modulations or periodicity. The compensation and calibration structures can be fabricated at the same time as the antenna and on the same material article so that all of the layers can have the same thicknesses and properties.

A high temperature dielectric can exist at a top surface where temperature is highest. Exemplary materials include hafnium silicate, boron nitride, aluminum oxide, hafnium oxide, calcium titanate, calcium zirconate, or any suitable material. The dielectric can, for example, be on the order of 0.1-10 mm thick, or lesser or greater depending on the frequency of operation.

An electrically conductive layer is placed below the high-temp dielectric in order to shield EM waves from the carbon-to-carbon (C—C) or insulating layers. Exemplary materials of metal include refractory metals (e.g., tungsten, niobium, tantalum, molybdenum, zirconium, rhodium, platinum), refractory metal alloys, nickel superalloys, or certain diborides (e.g. ZrB2), carbides, or nitrides that are electrically conductive at elevated temperatures.

A structural layer (e.g., an aeroshell, such as, for example a carbon-carbon (C—C) aeroshell) is located below the electrically conductive layer. This layer can be, e.g. materials which include carbon (C) and/or silicon(S) such as C/C, C/SiC, SiC/SiC, and/or nickel superalloy, refractory metal, or refractory metal alloy or any suitable material.

One or more thermally insulating layers can be placed below the C—C aeroshell in order to reduce the temperature to a desired level. More than one may be desired depending on the expected hot and cold side temperatures. Examples include porous carbon insulation and porous oxide insulation (e.g. Cal-carb, Zircar, min-K). Based on the surface temperature, one or more different insulating layers can be included. The composition of the insulating layers can be chosen based on the surface temperature and the desired temperature drop desired and/or needed (e.g., specified).

The insulation layers are not intended to interact with the electromagnetic fields. The waveguides are associated, for example with metal, by depositing a metal surface as the layer112below the high temperature dielectric to confine (e.g., reflect) the EM waves.

The waveguide(s)122can be used to connect between the RF module and the top surface. A mode converter launches a surface wave into a grounded dielectric. Grounded-dielectrics are known to support surface waves, and the mode converter can use a quarter-wave shorted reflector to launch in a forward direction.

In the exemplary embodiments ofFIGS.3a-3e, an exemplary compensation and/or calibration structure has three different, individual compensation/calibration structures which collectively perform compensation and/or calibration via the set of three waveguides (shown inFIG.3d). Each of the three waveguides is a calibration and/or compensation structure, but the set of all three can be used for calibrated compensation, which each have two RF connections to the RF module. In each case, exemplary sections are approximately one wavelength in width. The connections to the RF module are made by waveguides that transmit RF signals through the insulation layers and to the dielectric top surface.

FIG.3ashows a side view of a first exemplary compensation structure section. This section allows transmission of a surface wave along the dielectric. Surface waves are propagation modes that remain bound to a grounded dielectric structure. The phase velocity of propagation is dependent on dielectric height and dielectric constant. This section is a length L1which is, for example, in a range of 0.5-10 wavelengths, or lesser or greater.

FIG.3bshows side view of a second compensation structure. This structure can have a same geometry as the first section, but is length L2instead of L1. L2is, for example, between 0.5-10 wavelengths, or lesser or greater but should be different from L1by at least 0.1 wavelength (e.g., at least 0.5 wavelengths). The compensation structures can thereby perform, for example, TRL-type de-embedding via two different through waveguides, along with an additional calibration structure configured as a reflection-based structure for calibration described herein with respect toFIG.3c. Operation of a system incorporating different length (L1/L2) structures is known with respect to TRL calibration (see, e.g., an Internet page as follows:https://www.microwaves101.com/encyclopedias/trl-calibration).

FIG.3cshows an exemplary calibration structure having metal302covering the waveguides122at an interface between the waveguide and the high temperature dielectric. This causes the RF signal from the RF module to reflect at this interface and return without transmission. This is used as a calibration of the waveguide and RF module to account for changes in these layers that may occur during flight. Those skilled in the art will appreciate that the lengths L1and L2, shown inFIGS.3aand3b, respectively, are not the separations between the waveguides in those structures. In each case, L1and L2is a compensation structure length which can be greater than the waveguide separation. The exemplaryFIG.3ccalibration structure is shown with two waveguides separated by L3. However, it can have a different separation difference, or it can also be configured with a single waveguide to provide a calibration function.

FIG.3dshows a cross-sectional top view along cross-section lines D-D in each of theFIG.3a,3b,3ccross-sections: A-A, B-B and C-C. The exemplary compensation and/or calibration structures include the devices ofFIGS.3a,3b, and3cto perform an exemplary compensation and/or calibration in a manner as described herein. AFIG.3dtop view from above the compensation and calibration structures ofFIGS.3a-3cwould see only the dielectric because it fully covers the carbon-to-carbon (C—C) layer and the mode converters. Therefore this cross-sectioned view ofFIG.3dis a cross-section view cuts through the mode converter layer of the waveguide dielectrics122.

InFIG.3dthe compensation/calibration structures are all placed in parallel and arranged horizontally. However, other arrangements and orientations can be used as will as appreciated by those skilled in the art, provided the structures remain isolated from each other (e.g., separation greater than 0.5 wavelength, or lesser or greater as desired). In theFIG.3ccalibration structure, the waveguides exist below the dielectric for this cross section due to the added refractory metal302that separates them from the dielectric layer106.

In an exemplary embodiment, the compensation system can be located as close as possible to a vehicle's surface antenna so that vehicle conditions are the same on the compensation structure as the antenna.

FIG.3eshows an exemplary optional compensation and/or calibration structure that can be included in addition to other structures or in replacement. This structure has the same waveguide and mode converters asFIG.3balong with the same insulation layers, conductive layer, and high temperature dielectric. In this embodiment, only a single waveguide is present and the RF system measures reflection from this compensation structure.

Exemplary embodiments can interface with an RF module. The RF module can be configured to excite an RF signal into the calibration structure, and to measure the magnitude and phase of responses. This module can be a known printed circuit board (PCB) populated with commercial-off-the-shelf RF components for excitation and measurement of RF signals. The insulation layers in the compensation structures can be selected to reduce the temperature to levels where COTS (commercial-off-the-shelf) circuitry is usable.

The RF module can be coupled to the waveguides in the compensation circuit using known transmission lines (e.g., microstrip, stripline, coaxial cable, rectangular waveguide, circular waveguide, ridged waveguide, or other suitable transmission lines) to waveguide converters.

Magnitude and phase results from the RF module are sent to the processor such asFIG.2processor208with attendant power module212and data storage214which performs the calibration. In an exemplary embodiment, for each compensation structure, 2-port complex S-parameters are measured (S11, S12, S21, S22).

Returning toFIG.2, the exemplary system as shown can include a temperature sensor210located at a surface in contact with the surface antenna, and/or within one or more of the compensation and/or calibration structures. The temperature sensor210can be included as shown in the exemplary embodiment at a vehicle surface to provide a measurement of the temperature at this location. Alternatively, the temperature sensor can be inside one or more of the layers or at the interface of two layers. In such a case where the temperature sensor is embedded, a model of heat conduction through the entire structure can be used to estimate the temperature (or temperature distribution) within the compensation structures based on the temperature of the temperature sensor.

Alternatively there can be two or more temperature sensors, each of which can be at the surface of the vehicle, inside one or more of the layers, or at the interface of two layers. In this case, a local heat flux through the structure can be measured, assuming knowledge and/or characterization of the thermal conductivity. This, optionally coupled with a model of heat conduction through the entire structure, can be used to estimate the temperature or temperature distribution within the compensation structures. The temperature sensor can alternately be a resistance temperature detector (RTD), thermocouple, optical or infrared pyrometer, thermistor, transistor, or other suitable sensor which is selected to survive high temperatures in which the vehicle will operate.

TheFIG.2processor208can, for example, be a commercial off-the-shelf (COTS) processing device such as a microcontroller, FPGA, central processing unit, or other suitable device. The processor pulls information from the data storage214, the temperature sensor210, and the RF module206, and then calculates a current dielectric height, dielectric constant, and thermal expansion. These values are communicated to a vehicle electronic subsystem so that it can calculate accurate pointing angles.

The data storage214can be a COTS data storage electronics (e.g., flash memory, hard disks and so forth) used to store measured data about the compensation structures.

TheFIG.2system can include a power module in operative communication with the computer processor. The exemplary power module212can, for example, include COTS power electronics devices to receive a DC (and/or AC) voltage from the vehicle, convert that voltage to desired or required levels of each subsystem, and deliver sufficient current levels to each subsystem.

Referring toFIG.4, a multi-step method (400) can be used to compensate the surface antenna using the compensation system shown therein, whereby a surface antenna is identified for compensation (402). An exemplary embodiment uses a physical structure that is as closely matched as possible to the system that is being compensated. In such an exemplary embodiment, the surface antenna can be identified and this identification used in designing and configuring the compensation system.

In exemplary embodiments, data collection (404) prior to operation can be preferred. For example, to accurately run a compensation algorithm, it can be desirable to simulate or measure multiple aspects of the compensation structure. These simulations and/or measurements provide information about how physical changes to the structure impact the measured responses. Exemplary embodiments can measure or simulate compensation structure scattering parameters, S, as a function of dielectric constant, ε, and height, H. Such measurements can provide information about how erosion of the dielectric (changes in H) impacts scattering parameters. Similarly the measurements can provide information about how changes in dielectric constant impact the scattering parameters.

Exemplary embodiments can measure or simulate antenna periodicity, P, as a function of temperature, T: P(T). Increasing temperatures at a vehicle surface during operation will increase thermal expansion of the dielectric that will change periodicity P on the antenna. Measurement of thermal expansion as a function of temperature allows appropriate P to be utilized by a vehicle electronic subsystem.

Exemplary embodiments can measure a dielectric constant, ε, as a function of temperature, T: ε(T). Dielectric constant impacts antenna pointing and will also create changes in the scattering parameters of the compensation structures.

Data acquisition (406) can be performed to provide the compensation described herein, using, for example, a temperature sensor which can either be selected/designed and/or configured to continuously transmit temperature information to the processor, or it can be selected, designed and/or configured to respond to queries. Scattering parameters can be measured by collecting S-parameter data (S11, S12, S21, S22) from each of the compensation structures. The RF module can excite these signals and read magnitude and phases of the responses. This data is then provided to the processor.

A compensation calculation (408) can be performed using the acquired data. Unknowns for calculation are dielectric height, dielectric constant, and thermal expansion over frequencies of operation of a vehicle electronic subsystem. The compensation system can have several independent measurements:Structure 1 transmission: S12=S21Structure 2 transmission: S12=S21Structure 1 and structure 2 reflection: S11=S22Temperature sensor measurement: TStructure 3 calibration measurement: to calibrate results of structures 1 and 2.

The foregoing measurements, in reference to the stored data obtained prior to operation, can be used to calculate dielectric height, constant and expansion using a least squares fit (or other minimization technique) to provide a best estimate of the unknown properties. For example, a TRL calibration can be performed using the disclosed structure(s) with any known calibration process, including but not limited to that described on the Internet page https://www.microwaves101.com/encyclopedias/trl-calibration dated Aug. 2, 2022, the disclosure of which is hereby incorporated by reference in its entirety wherein a TRL calibration process includes selecting a TRL line standard for each designated frequency band with calculated frequency crossover points, and calculating quarterwave line lengths for each center frequency taking effective dielectric constants into account. After this calibration, an interpolation can be performed to go from the TRL calibration to an estimate of dielectric height, dielectric constant, and periodicity as those skilled in the art will appreciate.

Compensation results can be communicated (410) via transmission to the vehicle electronic subsystem. At any specified time interval (e.g., 100 microseconds, or shorter or longer) the acquisition-calculation-communication process can be repeated to update the compensation as a vehicle continues on its trajectory and surface conditions are changed.

It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.