Patent Grant
12062838
The disclosed subject matter relates to antenna systems, that is, antennas and associated electronics, for characterization of radio frequency (RF) systems, such as radar, communications, direction finding (DF), multi-input multi-output (MIMO) radar and communication systems, RF metrology, and other applications where antenna systems are used, and in particular to such RF emitter characterization systems requiring antenna systems with multiple ports and as may be used in implementations in which space is limited, such as in payload sections of unmanned aerial systems.
Multiport antenna systems are useful in a wide range of applications, including direction finding, radar, and any system using MIMO techniques. One platform of particular interest for such systems is unmanned aerial systems. For such platforms, however, there are significant constraints in terms of the size and weight of the payloads they can carry. It is therefore advantageous to develop antenna systems that (1) occupies as little space as possible, (2) allows re-use or concurrent use of much of the space to house electronic circuitry needed by the system, (3) covers wide bandwidths including low frequencies with wavelengths many times larger than the platform carrying the antenna, and (4) provides highly independent information from its ports in order to support high MIMO processing gain, high accuracy angle of arrival (AoA) estimation from any polarization and any angle, and sensitivity to any polarization wavefront from any angle, or in other words, no null to a wave with a certain polarization or coming from a certain direction.
A key problem of current RF emitter characterization systems is their large size, weight, power consumption, and setup time, when they must operate at low frequencies, such as a less than a few MHz.
Another problem for RF emitter characterization systems is the time required to compute the AoA for numerous signals of interest, such as the AoA of each packet from a large number of frequency hopping emitters. In this document the term “AoA” is used to mean either a single angle, such as azimuth, or a combination of angles, such as azimuth and elevation, in a defined coordinate system.
Given the extraordinarily wide frequency range and the associated wide range of patterns produced by the antenna across that frequency range, and given how the patterns can be significantly modified by different installations, which must all be comprehended by the RF emitter characterization system's estimator system, it will be appreciated that there exists a “array manifold” definition that can capture the wide range of patterns, and be used to clearly explain embodiments of an RF emitter characterization system (a) that embrace the dramatic pattern differences across the extraordinarily wide frequency range and span of installations, (b) that has processing gain to address the desire for a system that operates with enough sensitivity to enable characterization of small signals being listened to with nearby standard radio systems with larger antennas, and (c) that is able to estimate not only a signal's AoA, magnitude, and polarization, but also the AoA, magnitude, and polarization of a number of multipath terms associated with that signal. It should be understood that an array manifold can represent an isolated array, or an “as installed” array.
An array manifold is an antenna array's transfer function versus AoA and polarization, including a transfer function for each of its Np ports. An array manifold can be expressed as a five dimensional (5D) function or matrix that captures the complex output voltage (e.g. mag/phase phasor notation for a sine wave, cos(2πft) where t=0 is at a specified physical center point of the array), from the antenna's list of ports, when the antenna receives a standardized 1 V/m field strength electromagnetic (EM) wave arriving from a given angle and with a given polarization, and the antenna's ports are terminated with a specified load resistance RL. When expressed as a function, such as M(port, frequency, Az, El, polarization) (5 dimensions for the 5 arguments) the output is the complex output voltage from the given port resulting from an incoming signal with the given frequency, AoA, and polarization. When expressed as a matrix, the matrix as a whole captures the complex output voltages for (a) the array's list of ports, (b) a list of frequencies, a list of AoA (i.e., combinations of (c) azimuth and (d) elevation angles), and (e) two orthogonal polarizations (e.g., horizontal and vertical, or left and right hand circular, etc.). In this matrix case, the manifold might be expressed as the 5D matrix Mi,f,k,n,pol where the indexes i, f, k, n, pol (5 dimensions) correspond to (i) the port, (f) the frequency, (k) the azimuth, (n) the elevation, and (pol) the polarization. Interpolation between points in the matrix can be used to turn the matrix representation into a smooth functional representation.
It is often convenient to express the set of complex voltages from the set of antenna ports as a vector, at a given frequency, AoA (azimuth and elevation combo), and polarization. For example, a vector,
vi=Mi,f,k,n,0 1
where the pol=0 indicates the vector is for vertical polarization, and where, for brevity, the f, k, n indexes are “understood” to ultimately take on particular values associated with the context of the vector's use.
Similarly, the vector is sometimes made explicitly a function of the AoA, as in
vi(θk,ϕn)=Mi,f,k,n,0 2
where, for brevity, the frequency is not explicitly shown but “understood” to take on a particular value associated with the context of the vector's use.
The following are incorporated by reference in their entirety.
It would therefore be desirable to have a small multi-port antenna that provides the advantages described above. It would also be desirable to use such an antenna to provide for rapid and accurate characterization of RF signals, such as from radar and communication systems, including those using MIMO, frequency hopping, digitally coded, and other modulations, and where characterization includes such things as the range to the emitter, the angle of arrival of the signal, the signal's bandwidth, power, phase, modulation characteristics including joint time frequency characteristics, and etc. It is this context that the need for the subject matter disclosed herein arises.
The following presents a concise summary of one or more embodiments in order to provide a basic understanding of the embodiments. This summary is not an extensive overview of all contemplated embodiments and is not intended to identify key or critical elements of all embodiments nor delineate the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.
According to an aspect of an embodiment, there is disclosed an arrangement for a multiport antenna in which the antenna's conductive elements are arranged to define an at least partially enclosed interior volume. The interior volume is shaped and sized to accommodate a conductive enclosure containing electronic circuitry. The conductive enclosure and the antenna's conductive elements may also accommodate optical elements and optoelectronic circuitry. One or more window, which may be lenses, of optically transparent material may be placed in the antenna's conductive elements and a wall of the conductive enclosure to permit receipt and transmission of optical radiation. Preferably, the optically transparent material is electrically conductive. In this manner the combination the antenna and the conductive enclosure with its contents can be installed in spaces subject to size and volume constraints, such as the instrumentation payload section of an unmanned aerial system, without sacrificing functionality.
Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. It is noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.
The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the methods and systems of embodiments of the invention by way of example, and not by way of limitation. Together with the detailed description, the drawings further serve to explain the principles of and to enable a person skilled in the relevant art(s) to make and use the methods and systems presented herein. In the drawings, like reference numbers indicate identical or functionally similar elements.
This specification discloses one or more embodiments that incorporate the features of this invention. The disclosed embodiment(s) merely exemplify the present invention. The scope of the present invention is not limited to the disclosed embodiment(s). The present invention is defined by the claims appended hereto.
The embodiment(s) described, and references in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” “an exemplary embodiment,” etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
The disclosed subject matter relates RF characterization systems including multi-port antennas. Such an RF characterization system 100 is shown in
In terms of the isolation and characterization of an SoPI, or simply SoI, there may be two or more “parameter” lists. A first parameter list may be “SoI isolation parameters” comprising a list of criteria to isolate an SoI from other signals and noise. A second parameter list may be “signal parameters”, which are the parameters measured for SoI's from a given emission, or set of emissions, from an emitter, such as its center frequency, polarization, magnitude, bandwidth, AoA, range, SNR, modulation type, modulation parameters, time stamp, etc.
The SoI isolation parameters may specify that an SoI be within a center frequency range, bandwidth range, time duration range, etc., or have a hop-frequency set of parameters (such as hop duration range, rep-rate range, single-packet bandwidth range, total bandwidth range, packet start, stop and/or center frequency range, modulation characteristic such as chirp within a ramp-rate range, or NQ-QAM within an NQ range, or Npsk-PSK within an Npsk range, etc.), or that the SoI comes from a certain AoA range, or that one or more of those parameters have a variance, after a number of looks, that falls within a certain range. The SoI isolation parameters can be broken into different levels where each level is applied at different stages of processing.
At the highest level, there may be a receiver tuned to a band to cover all SoI's in that band, e.g., the entire 2-32 MHz high-frequency (HF) band. This may be regarded as an initial limitation or “parameter” on defining an SoI space—the lowest and highest frequency of interest (where to tune the radio and what bandwidth filter to use). These might be considered “pre-banding” or “pre-JTFA” parameters, with JTFA being an acronym for joint time frequency analysis.
Given whatever receiver bandwidth (e.g., 40 MHz), it is then possible to look more narrowly (more precisely on SoI) such as a 3 kHz bandwidth (BW) single sideband (SSB) signal at HF, versus a 25 kHz BW narrow band FM (NBFM) signal at V/UHF, versus a 200 kHz BW commercial FM signal, versus a 6 MHz BW TV signal, or versus a 10 MHz bandwidth radar signal at 3 GHz, etc. SoI isolation parameters such as these bandwidths of interest can be used to “aim” or precondition the JTFA processing to reduce processing load, in which case, they may be regarded as “pre-JTFA” parameters as well.
According to an aspect of an embodiment, JTFA may be used for this bandwidth refinement. JTFA detects time periods and frequency ranges where signals are located (or “pop up” or have high magnitude) in time and frequency. It is effectively equivalent to a parallel bank of filters of various bandwidths, wider bandwidth filters having finer time resolution, where the filter outputs allow an analysis that can trade time resolution for frequency resolution to optimize detection, or measurement of start and stop times, or measurement of the SoI's power spectral density or modulation characteristics, etc.
An initial SoI (i.e., post-JTFA) is declared (detected) when a higher magnitude time span and bandwidth JTF zone is found on one or more of the plurality of ports. In this case, an SoI data record, containing, for at least two of the plurality of ports, a finite length record covering the particular time span and frequency span detected, is made for that SoI. Generation of this record constitutes initial SoI “detection”. The individual records associated with each of the plurality of ports, is then cross-correlated—each port with at least one among all the ports.
According to an aspect of an embodiment, this use of JTFA detection and choosing of the length of the data record (in time or frequency) is performed using a constant false alarm rate (CFAR) detector, where the false alarm rate can be specified in the “SoI isolation parameters”. Other detectors could also be selected via the “SoI isolation parameters”.
Under control of the parameters, all the SoI's detected at this point can be output or they can be pruned and considered “preliminary”. That is, only those SoI's passing additional “post JTFA” or “pre-characterization” parameters' criteria are eligible for final output. An SoI record may be time-stamped with absolute time (e.g., GPS time) or a number associated with timing, so that the “post-JTFA”, “pre-characterization”, and post-characterization SoI isolation parameters can include time metrics, durations, periodicity, etc. along with any measured “signal parameters”. “Pre-characterization” SoI's (i.e., those passing the criteria provided in the “SoI isolation parameters”) are sent on either to the output or for further processing, according to the “SoI isolation parameters”.
Generally, the number of SoPI's is reduced at each stage of processing. SoPI's are typically pruned when they do not sufficiently match the “parameter ranges” associated with being passed on from a given processing stage. For example, only after JTFA processing can SoPI's be assessed as passing JTFA metrics like center frequency, bandwidth, time durations, and absolute time of occurrence, etc.
Using direction finding (AoA estimation) as an example of characterization, “Post DF” or “pre-clustering” parameters would add, for example, that an SoI must be within a range of AoA's, or have certain polarization or magnitude properties, or have certain multipath properties. Note that estimating an SoI's AoA also involves estimating its polarization and magnitude and can also include estimating the AoA, polarization, and magnitude of its associated multipath terms. All can be part of the characterization process. The AoA estimator system is configured to provide the measurements required by the SoI isolation parameters. For example, it might be configured to assume a known polarization signal or to estimate an unknown polarization signal, or to include or not include a number of multipath terms. SoI's passing the criteria as described by the “post-DF parameters” are sent on to output or for further processing, according to the “SoI isolation parameters”.
If the “SoI isolation parameters” include “post clustering” or “multi-look” parameters (i.e., the process is not finished after DF processing) then after DF processing, it is possible to output preliminary, not “final” but “next level” “pre-clustering”, SoI's. In this case, the system does not reduce to and output the “final” SoI's until after the “multi-look” or “clustering” step.
The “post clustering” “multi-look” parameters include things such as, for example, that a set of hops from the emitter of a batch of SoI's are all within 10 degrees of one another, or that the SoI's from an emitter have a variance in AoA or magnitude below a certain threshold (potentially after outlier removal), or have a polarization that (a) remains within a certain variance (such as from a stationary antenna), or (b) goes beyond a certain variance (such as from a mobile radio's whip antenna moving around), or (c) is within an absolute range (e.g., 10 degrees from vertical), etc.
Any measured “signal parameter” for an SoI at any stage can be output (i.e., under the control of the criteria in the SoI isolation parameters). Again, as opposed to SoI isolation parameters, “signal parameters” are the parameters measured for SoI's from a given emission, or set of emissions, from an emitter, like its center frequency, polarization, magnitude, bandwidth, AoA, range, location, modulation type, modulation parameters, time stamp, etc.
As indicated elsewhere, the lines of demarcation of the system are arbitrary and for explanation purposes only. For example, a single physical component may carry out multiple functions. For example, the functions could be performed by one or more suitably programmed microprocessors.
The RF characterization system 200 may be configured to identify a target based on at least one of the RF signatures of at least one of the uplink radio signals, the downlink radio signals, a direction to the target, and a location of the target. The RF characterization system 200 may further comprise a database of RF signature data that, for example, a processor accesses to identify the target. The RF signature data may comprise modulation information, and the database may comprise a modulation look-up table.
In one embodiment, Signal Detection/Filtering/Isolation block 410 is configured to perform a JTFA and perform CFAR detection of signals matching the time durations and frequency ranges specified in the pre-estimation SoI defining parameters it receives from the configuration and filtering parameters 210. A JTFA is typically comprised of a series of overlapping discrete Fourier transforms (DFT) but can also be done by other techniques. For signals passing the pre-estimation SoI defining parameters tests, Signal Detection/Filtering/Isolation block 410 outputs either (A) a set of filtered signal bursts covering the SoI's detected time duration or a parameter specified time duration carried by the configuration and filtering parameters 210, each SoI output as a data record with Ns time samples where each SoI can have a different Ns, or (B) a set of filtered signal bursts covering the SoI's detected bandwidth or a parameter specified bandwidth carried by the configuration and filtering parameters 210, each SoI output as a data record with Ns frequency samples, where each SoI can have a different Ns, where, for each SoI, the frequency domain output record in B is related to the time domain output record in A by a Fourier Transform. In either frequency or time domain cases, the Np row matrix coming out of Signal Detection/Filtering/Isolation block 604a is associated with an SoPI having Ns samples, forming an Np×Ns matrix.
That set of filtered signal bursts, which correspond to the set of port voltages, is accepted by On-Line Feature Computation block 420, which computes a feature vector for each SoPI burst that is output by Signal Detection/Filtering/Isolation block 410 and passes the computed feature vector to Signal Parameter Estimator block 430.
The feature vector computation: (1) characterizes a received SoPI, (which can contain a single wavefront or have multipath terms arriving from different angles of arrival), (2) is a fully phase coherent process that achieves high processing gain, (3) is agnostic to the phase of the incoming signal and only considers the differences in phase between the ports, and (4) reduces a record with many (Ns) samples down to a feature vector with a small number of real numbers.
In a first configuration, which eliminates estimator bias caused by noise in the receiver and noise picked up by each antenna port that is independent of noise picked up the other ports, the features are found by cross-correlating one of the ports with all the other ports, and the feature vector has 2(Np−1) real numbers.
In a second configuration, the features are found by cross-correlating each of the ports with all the ports, and the feature vector has Np2 real numbers. In other words, between the two configurations, the features are the cross-correlations between either (A) the digitized SoI records observed on the various ports in the antenna array, or (B) the digitized SoI record from a reference port and the digitized SoI records observed on the other ports in the antenna array.
The cross-correlations are done over a relatively large number of sample points (e.g., many narrow time samples over a long time period or many narrow band frequency-domain samples over a wide bandwidth), resulting in high processing gain. For example, on an SSB signal with 3 kHz of bandwidth voice syllables or energy bursts last, on average, about 0.5 seconds or more. A 0.5 second SoPI output record would have around 5000 data points to capture the 3 kHz bandwidth.
Continuing with the SSB signal example, the feature computation block 420 compresses the 3 kHz bandwidth energy that is spread across the many (5000 per port) data points on its input, to an effective processed bandwidth of 2 Hz and a low number of points on its output. For example, using the second configuration, a 6-port antenna array would generate around 6×5000=30000 points which would be compressed to a feature vector with only 36 real numbers. Using the first configuration, a 7-port antenna array would generate around 7×5000=35000 points which would be compressed to a feature vector with only 12 real numbers. The ratio of 2 Hz to 3 kHz ratio shows that for this example, the feature calculation process delivers about 32 dB of processing gain on each port. So, a weak signal with 7 dB of SNR which is marginally intelligible, will have a post-processing SNR of about 25 dB for the purposes of AoA estimation.
Off-Line Feature Computation block 440, using Array Manifold 160, either has precomputed, or computes, a set of matrixes needed by Signal Parameter Estimator 430, for each SoPI burst that is output by Signal Detection/Filtering/Isolation block 410. The matrixes needed by Signal Parameter Estimator 430 use the antenna system manifold to find, at the center frequency of each SoPI burst, the expected port outputs for a set of potential angles-of-arrival (azimuth and elevation) and for a set of two different and preferably orthogonal polarizations (e.g., vertical and horizontal or right and left hand circular polarization) (assuming the polarization of the incoming signal is also to be estimated) at each of the potential AoA's.
Signal Parameters Estimator 430 accepts the outputs from On-Line Feature Computation block 420, and Off-Line Feature Computation block 440, and uses a matching metric between the feature vector from On-Line Feature Computation block 420, and the matrixes from Off-Line Feature Computation block 440 to find a set of estimated signal parameters for each SoPI. In one embodiment, the estimated signal parameters include each SoPI's AoA, polarization parameters, magnitude, and if there are any associated multipath waves, how many there are, and each one's AoA, magnitude, phase, and polarization parameters. The polarization parameters are generally output as a Jones vector. Embodiments may also output a Stokes vector or other representations. Available for output are both the newly estimated signal parameters and the previously measured metrics allowing the signal to pass the pre-estimation SoI defining parameters tests. Also available are the time stamps applied to the SoPI bursts that generated the estimated signal parameters. Post-estimation SoI defining parameters could include ranges for one or more of the estimated signal parameters, such as ranges of angles of arrival to ignore or output, or polarizations to ignore or output. Either predefined/default post-estimation SoI defining parameters are used, or they are accepted from the configuration and filtering parameters 210. Only those signal parameters requested by the configuration and filtering parameters, and only for SoI meeting the SoI defining parameters are output from Signal Parameter Estimator 430, and thus RF characterization system 240.
The embodiment depicted in
The clustering system 510 also allows classification of emitters, such as moving versus stationary, by features such as how its polarization changes over time such as its randomness or its periodicity spectrum and the angular range over which it rotates. Configuration and filtering parameters 530 add additional parameters to those in configuration and filtering parameters 210. The additional parameters configure the clustering system 510 to optimize its performance under different operating scenarios. Configuration and filtering parameters 530 include such things as the number of estimates (or duration of time) the clustering system 510 should use to perform its clustering functions. Configuration and filtering parameters 530 can also include apriori probabilities that the SoI will be within a certain range of angles of arrival and probabilities that the SoI will not be in other ranges of AoA. Clustering system 510 can also use configuration and filtering parameters 530 to further isolate SoI from SoPI by filtering based on the addition parameters it generates. For example, parameters 530 may specify to only pass emitters that are stationary, or only those that are moving, or only pass those that are frequency hopping emitters, or pass all frequency hopping emitters that do not use a certain set of hop frequencies, or a certain frequency hop sequence, or a certain set of hoping frequency parameters.
In some embodiments, the estimator system generates an estimated AoA by finding, for a set of signals of interest, the angles in the array manifold that would produce port voltages most closely matching, according to a matching metric, those from each signal of interest (SoI). Different embodiments use different matching metrics and or different signal models to optimize the AoA estimation accuracy. For example, an embodiment may model the signal as being a single wavefront (i.e., a signal with no multipath) with a priori known polarization. When the polarization matches the model, and the signal actually has no accompanying multipath, this embodiment is capable of giving superior estimates. Some embodiments may model the signal as having multipath, where the polarizations of all terms are unknown and are estimated as part of the AoA estimation optimization process. This model is often the best performing model for some applications because, for example, (1) handheld radios and mobile radios are not held to be vertical or horizontal, but sway, and (2) signals almost always have a ground bounce reflection, and if the ground is tilted, or if the reflection is from a dihedral formed by random angle boulder edges or a tilted corner formed by a tree or building on tilted ground, the polarization will be rotated to an unknown angle. In some embodiments, the array manifold may be generated by combining an in-situ (as installed) measured array manifold and an array manifold generated via an EM simulator.
Besides signal models, matching metrics optimize different measures such as minimizing the mean square error (MMSE) (least squares) (Euclidean), minimizing the maximum error (mini-max), finding what is most likely (maximum likelihood), and other error minimization norms like H-infinity norm. Neural net based approaches aim to achieve similar combinations of high accuracy and robust performance in a wide variety of situations. Embodiments using a neural network require training with a large number of Monte Carlo noise instantiations added to all AoA and polarization combinations for all possible combinations of multipath terms, for every frequency in the array manifold, and preferably, many records of measured data with accompanying high accuracy truth data. While neural net based approaches require a lot of training data and compute time, once trained, they may be able to run with low latency on processors suitably small for portable systems.
Besides the signal model and the different measures for what is being optimized, the matching performance is affected by biases in the estimation process. Some estimator system embodiments are capable of jointly estimating the bias along with the AoA, mag/phase, and polarization of an incoming signal, and as such, minimize the impact of biases.
The above operations and all operations described herein can be carried out by one or more components of digital electronic circuitry, computer hardware, firmware, and software, for example, a suitable programmed processor or set of processors and associated memory which can include read-only memory and/or random access memory. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including, by way of example, semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD disks.
Implementations may also include one or more programmable processors, and one or more computer program products tangibly embodied in a machine-readable storage device for execution by one or more programmable processors. The one or more programmable processors can each execute a program of instructions to perform desired functions by operating on input data and generating appropriate output. Generally, the processors receive instructions and data from the memory. Any of the foregoing may be supplemented by, or incorporated in, specially designed ASICs (application-specific integrated circuits). These components may be physically centralized or be partially or wholly distributed throughout the embodiment.
The above-described arrangements bestow particular advantages from use as an antenna system 120 of antennae as described in U.S. Pat. No. 9,279,880 and U.S. patent application Ser. No. 17/038,600, both incorporated by reference above. These antennae may be balanced or unbalanced. These antennae may or may not include a reference port.
According to an aspect of an embodiment, the two or more port multiport antenna is comprised of two or more conductive pieces with two or more ports physically distributed around the two or more conductive pieces, each port having two terminals, a first terminal and a second terminal, wherein each port's first terminal is connected to one conductive piece, and each port's second terminal is connected to a different conductive piece, and at least two of the ports form current loops through each other via their connection to the two or more conductive pieces, wherein, for the purposes of explanation, each current loop has an axis, the axis being perpendicular to the plane centered on the loop and containing the at least two ports.
That all the ports contain both an E and H field induced output voltage component allow the ports to have well-defined patterns that are useful for direction finding, even when the antenna is extremely electrically small (i.e., at very low frequencies where the antenna's dimensions are less than 1/10 of a wavelength), and even when the antenna is electrically large (i.e., at high frequencies where the antenna's dimensions are multiple wavelengths). The width of conductive strips 610 and 620 along with the offset distance between them (i.e., the antenna's height) establishes the capacitance between the conductive strips and the antenna's sensitivity to low frequency E-fields. The area of the loop establishes the antenna's sensitivity to the H-field at low frequencies. By adjusting the length, width, height, and port termination impedance, the E and H field sensitivities can be made to match. By matching the sensitivities, the antenna produces two cardioid patterns with a high front-to-back ratio, one from each port, which is advantageous for direction finding or simply nulling signals that are interfering with a signal of interest. Many electronic components (e.g. transmission lines, amplifiers, mixers, baluns, etc.) are designed to work with a 50-ohm unbalanced impedance, or a 100-ohm balanced impedance. The antenna embodiment of
The conductive strips 610 and 620 are shown has having the same size and shape and oriented to be oppositely symmetrical, which makes the antenna balanced, and makes the antenna ignore E-field components aligned with the axis running between the centers of the port terminations.
More specifically,
In one embodiment, the ports themselves are coaxial in the sense that the first conductive piece 810 is shaped so that every port's first terminal can be a center conductor, by virtue of it being the tip of a triangular piece, and the second conductive piece 820 is shaped so that the each port's second terminal is a surrounding structure, that is, a hole, that forms a coaxial shield connection, connecting to the second conductive piece 820. The coaxial port configuration as just described allows every port to have a direct wide-band connection without any band limiting, or reliability limiting, or weight adding component such as a balun. Moreover, it allows the antenna to made easily configurable since a port can attach to a coaxial switch that can be configured to select between different terminations, such as a short, open, or a specific impedance, or select between bypassing or using an amplifier, or select between different filters in a filter bank. It also allows extremely low system noise figures because a low noise amplifier can be connected to the coaxial port, effectively without an intervening lossy cable. Of course, it will be apparent to one having ordinary skill in the art that other termination configurations may be used.
Also as shown in
As described above, a coaxial port configuration facilitates the antenna system being made configurable because a port can attach to a coaxial switch that can be configured to select between different terminations, such as a short, open, specific impedance, or specific length of transmission line, or select between bypassing or using an amplifier, or select between different filters in a filter bank. Each termination-configuration would require an associated array manifold. Similarly, the receiver system 130 may also have different configurations that present different termination impedances to the antenna, particularly at different frequencies, or with different cable lengths. Configuration and filtering parameters 210 can be used to communicate an appropriate manifold to estimator system 240 based on how the DF system configuration impacts the antenna's port terminations. Communication of the manifold via configuration and filtering parameters 210 allows the same system hardware to be easily and quickly used in different installations. In this case, the estimator system 240 would accept as part of the configuration and filtering parameters 210 or 530, an “as installed” array manifold for that particular installation.
These are merely examples of antenna elements that may be incorporated into the RF emitter characterizers described herein. Other suitable antenna elements may be found in U.S. Pat. No. 9,279,880 and U.S. patent application Ser. No. 17/038,600.
The displacement spacing between the generally rectangular planar portions of conductive elements 910 and 920 causes the antenna to be sensitive to an incoming E-field component aligned with the displacement spacing. As such, each port senses multiple EM field components, including an E-field component, and H-field components. At low frequencies (i.e., frequencies where the antenna is electrically small) all ports contain a common voltage induced by the incoming aforementioned E-field component, and each port also senses a voltage cause by the current flowing around each loop associated with that port, each loop having a current induced by the H-field component aligned with the axis of that loop. As illustrated, with the antenna oriented so the substantially planar sections of 910 and 920 are horizontal and displaced vertically, the four port antenna simultaneously senses three components, Ez, Hx, and Hy. As such, it can find the direction to any wave with a vertically polarized component, but cannot sense, and is blind to, a horizontally polarized wave from any direction. An array comprised of two such multiport antennas can have its antennas oriented so that they sense nominally orthogonal E-field components, such as Ez and Ex, as well as all three H-field components, Hx, Hy, and Hz. In this case the pair of antennas is not blind to any wave but has an AoA ambiguity for a wave arriving with a polarization and at an angle where the only E-field component is an Ey component. An array of three such antennas oriented to sense all three E-field components supports unambiguous AoA estimation of any incoming wave.
The four conductive surfaces in
In
The arrangement of the conductive surfaces and port connections in
Regardless of its orientation, between the four sensed EM field components, the antenna of
Provision of a second multiport antenna element oriented so it senses the missing EM field components missed by the first multiport antenna element provides for unambiguous direction finding on any polarization wave from any angle. Moreover, a two element system where each element senses two E and two H field components fits in a smaller volume of space than a three element system where each element senses one E and one H field component, such as the elements shown in
As can be seen, the conductive surfaces together define an at least partially enclosed interior volume. For some applications it may be advantageous to provide a lining to the conductive surfaces that provides enhanced sensitivity to the H-field picked up by a conductive surface pair.
From these transmission line embodiments, it will be obvious to one skilled in the art that other transmission line bundles with other structures or configurations are also valid, including each bundle having different termination mountings or bundles being comprised of a pair of shielded twin lead, a pair of shielded twin lead within a common shielded, or any of these where the twin lead is a twisted pair. In addition, a balun could be used on an antenna port so that a single coaxial cable, instead of two, could be used to bring the signal from an antenna port into the enclosure. All these configurations can also be used to bring the signal from the ports to an external system rather than the internal enclosure 1190.
To permit the optical components within enclosure 1190 to send and receive optical signals the enclosure 1190 and the antenna conductive sheets 1010, 1020, 1030, 1040 may be provided with one or more windows/lenses made of a transparent material, or preferably a conductive transparent material.
The transparent conductive material may include indium-tin-oxide. The transparent conductive material may include doped zinc oxide. The transparent conductive material may include carbon nanotubes. The transparent conductive material may comprise an amorphous material. The transparent conductive material may include a doped transparent semiconductor. The transparent conductive material may include a conductive polymer. The transparent conductive material may include a body comprising a transparent material and coating of a conductive material. The coating of a conductive material may include gold. The coating of a conductive material may include aluminum. The coating of a conductive material may include titanium. The coating of a conductive material may include chromium.
A wave's direction vector has three orthogonal directional components, for example, an x, y, and z component in a cartesian coordinate system. Two ports that sense one E and one H field component, such as the antenna configuration of
It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the present invention and the appended claims in any way.
The subject matter disclosed herein has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.
The foregoing description of the specific embodiments will so fully reveal the general nature of the present invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.
The embodiments can be further described using the following clauses:
1. A multiport antenna comprising:
2. The multiport antenna of clause 1, wherein the first, second, third, and fourth conductive elements are arranged symmetrically around a central axis.
3. The multiport antenna of clause 1 further comprising a high-mu lining on the inside of at least one of the conductive elements.
4. The multiport antenna of clause 1 further comprising an attachment to one or more port-pairs comprised of either a balun, or a pair of differentially connected coaxial cables or the same (a) wound to form a common mode choke, or (b) surrounded with ferrite to form a common mode choke, or both, or twin-lead, or twin-lead wound to form a common-mode choke, or twisted pair, or shielded twisted pair.
5. The multiport antenna of clause 1 further comprising a balun attached to each of one or more port-pairs.
6. The multiport antenna of clause 1 further comprising a twin-lead attached to each of one or more port-pairs.
7. The multiport antenna of clause 1 further comprising a twisted-pair or shielded twisted pair attached to one or more port-pairs.
8. The multiport antenna of clause 1, wherein, for one or more pair of conductive elements, each pair having a port-pair, a (a) length between the first vertex and second vertex, (b) a width of the conductive elements, (c) a distance across the central portion between the opposing pair of conducting elements, and (d) impedances terminating the ports, are adjusted to provide directional patterns from one or more of the ports.
9. The multiport antenna of clause 1, wherein, for one or more pair of conductive elements, each pair having a port-pair, a (a) length between the first vertex and second vertex, (b) width of the conductive elements, and (c) distance across the central portion between the opposing pair of conducting elements, are adjusted to provide directional patterns from one or more of the ports when the port termination is a standard value in an inclusive range of 50 ohms to 300 ohms.
10. The multiport antenna of clause 1 wherein at least one of the first, second, third, and fourth conductive elements comprises one or more transparent windows or lenses, or conductive transparent windows or lenses.
11. The multiport antenna of clause 1, wherein the first angle is equal to the second angle.
12. The multiport antenna of clause 11, wherein the first angle is a right angle such that the first sections together define a planar shape.
13. The multiport antenna of clause 11, wherein the first angle is an oblique angle such that the first sections together define a substantially conic shape.
14. The multiport antenna of clause 1 further comprising an electrically conductive enclosure arranged within the at least partially enclosed volume of the multiport antenna.
15. The multiport antenna of clause 14 further comprising at least one electronic component arranged within the electrically conductive enclosure.
16. The multiport antenna of clause 15 wherein the at least one electronic component arranged within the electrically conductive enclosure includes an RF receiver attached to the antenna.
17. The multiport antenna of clause 14 wherein the electrically conductive enclosure comprises at least one window.
18. The multiport antenna of clause 14 wherein the electrically conductive enclosure comprises at least one electrically conductive window.
19. The multiport antenna of clause 14 wherein at least one of the first, second, third, and fourth conductive element comprises at least one first window, optically aligned with at least one second window in the electrically conductive enclosure.
20. The multiport antenna of clause 14 wherein at least one of the first, second, third, and fourth conductive element comprises at least one conductive first window, optically aligned with at least one conductive window in the electrically conductive enclosure.
21. An RF emitter characterization system comprising:
22. An RF emitter characterization system comprised of an antenna array, a receiver system, and an estimator system,
23. The RF emitter characterization system of clause 22, wherein the estimator uses an array manifold.
24. The RF emitter characterization system of clause 23 wherein the array manifold is generated by combining an in-situ as installed measured array manifold and an array manifold generated via an EM simulator.
25. The RF emitter characterization system of clause 24 wherein the estimator finds a set of wavefront characteristics, for each of the one or more wavefronts received from an emitter, the set of wavefront characteristics comprising a magnitude, phase, polarization and AoA for a wavefront, wherein predicted output voltages are computed for the antenna array's ports based on the one or more sets of waveform characteristics by matching actual output voltages observed on the array's ports.
26. The RF emitter characterization system of clause 24 wherein the estimator finds a set of wavefront characteristics, for each of the one or more wavefronts received from an emitter, the set of wavefront characteristics comprising a magnitude, phase, polarization and AoA for a wavefront, wherein predicted features are computed from output voltages of the antenna array's ports predicted by the array manifold based on the one or more sets of waveform characteristics, wherein the predicted features best match the actual features computed from the actual output voltages observed on the array's ports.
27. The RF emitter characterization system of clause 24 wherein the estimator finds a set of wavefront characteristics for each of the one or more wavefronts received from an emitter, the set of wavefront characteristics comprising a magnitude, phase, polarization and AoA for a wavefront, by choosing from all combinations of one or more AoAs and one or more polarizations in the one or more sets of waveform characteristics, the combination of AoAs and polarizations that produces predicted features computed from the predicted output voltages on the antenna array's ports that best match the actual features computed from the actual output voltages observed on the array's ports.
28. The RF emitter characterization system of clause 24 wherein the estimator finds a set of wavefront characteristics for each of the one or more wavefronts received from an emitter, the set of wavefront characteristics comprising a magnitude, phase, polarization and AoA for a wavefront, by applying the observed port voltages to a computer learning algorithm that has been trained with one or both measured data and data predicted by the array manifold.
29. The RF emitter characterization system of clause 24 wherein the estimator finds a set of wavefront characteristics for each of the one or more wavefronts received from an emitter, the set of wavefront characteristics comprising a magnitude, phase, polarization and AoA for a wavefront, by applying features derived from the observed port voltages to a computer learning algorithm that has been trained with one or both measured data and data predicted by the array manifold.
30. The RF emitter characterization system of clause 29 wherein the features are the cross-correlations between either (A) the digitized SoI records observed on the various ports in the antenna array, or (B) the digitized SoI record from a reference port and the digitized SoI records observed on the other ports in the antenna array.
31. The RF emitter characterization system of clause 30 wherein
32. The RF emitter characterization system of clause 30
33. The RF emitter characterization system of clause 30 further comprising a clustering system adapted to refine the computed characteristics of the SoI including an estimated AoA based at least in part on more than one estimation of the SoI's characteristics prior to outputting a characterization of a signal that includes an angle of arrival of the signal and other characteristics of the signal as specified in configuration and filtering parameters.
34. A multiport antenna comprising:
35. A multiport antenna having a multiport antenna element with at least two ports, the antenna element comprising two or more conductive pieces with two or more ports physically distributed around the two or more conductive pieces, each port having two terminals, a first terminal and a second terminal, wherein each port's first terminal is connected to one conductive piece, and each port's second terminal is connected to a different conductive piece, and at least two of the ports form current loops through each other via their connection to the two or more conductive pieces, the two or more conductive elements being arranged around a center axis of the multiport antenna with their respective longitudinal sections together defining a circular periphery of the multiport antenna around an at least partially enclosed volume.
36. The multiport antenna of clause 35 wherein each current loop has an axis, the axis being perpendicular to the plane centered on the loop and containing the at least two ports.
37. The multiport antenna of clause 35 wherein the current loops are H-field sensing current loops having a current flowing through the same shared conductive pieces and across the same shared terminals of the same set of physically distributed ports, that are sensing E-fields, the E-fields inducing a voltage across those same ports.
38. The multiport antenna of clause 35 further comprising a second multiport antenna element with at least two second multiport antenna element ports, the second multiport antenna element antenna element comprising two or more second multiport antenna element conductive pieces with two or more second multiport antenna element ports physically distributed around the two or more second multiport antenna element conductive pieces, each second multiport antenna element port having two terminals, a first terminal and a second terminal, wherein each port's first terminal is connected to one second multiport antenna element conductive piece, and each port's second terminal is connected to a different second multiport antenna element conductive piece, and at least two of the ports form second multiport antenna element current loops through each other via their connection to the two or more conductive pieces, the second multiport antenna element being oriented to be capable of sensing EM field components not sensed by the multiport antenna element to permit unambiguous direction finding on any polarization wave from any angle.
39. A multiport antenna comprising a first multiport antenna element and a second multiport antenna element, wherein each of the first multiport antenna element and a second multiport antenna element senses two E-field components and two H field components, the first multiport antenna element and the second multiport antenna element being arranged to define an at least partially enclosed volume.
40. The multiport antenna of clause 39 wherein the second multiport antenna element is oriented to sense EM field components not sensed by the multiport antenna element to permit unambiguous direction finding on any polarization wave from any angle.
41. The multiport antenna of clause 39 wherein the multiport antenna is dimensioned and configured to fit within a payload compartment of an unmanned aerial vehicle.
This application is related to and claims the benefit of U.S. Provisional Application No. 63/172,949, filed Apr. 9, 2021, the contents of which are hereby incorporated into this application in their entirety. This application is related to U.S. patent application Ser. No. 17/038,600, filed Sep. 30, 2020, the contents of which are hereby incorporated into this application in their entirety. This application is also related to U.S. Pat. No. 9,279,880, issued Mar. 16, 2016, the contents of which are hereby incorporated into this application in their entirety.
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