RX and TX Coherence in Radar Antennas Using Near-Field Antennas

Abstract

A method and system for calibrating and cohering at least one radar antenna in receive (RX) mode and transmit (TX) mode includes performing RX mode calibration on the at least one radar antenna using a radio frequency (RF) far-field calibration source, and using the RF far-field calibration source for each of the at least one radar antenna to calibrate an RF phase Φ RXn operating the at least one radar antenna with the at least one near-field antenna in an RX mode to determine a plurality of RX mode phases for the at least one radar antenna and the at least one near-field antenna; operating the at least one radar antenna with the at least one near-field antenna in a TX mode to determine a plurality of TX mode phases for the at least one radar antenna and the at least one near-field antenna; and deriving a TX mode calibration phase as a function of the determined RX mode phase and the determined TX mode calibration phase.

Description

[Background technology]

[0001] Installing large radar antennas in remote locations is difficult and expensive. Large radar antennas require large buildings or facilities and require lengthy installation, integration, and testing before operation. Therefore, the portability of large radar antennas is severely limited. Instead, several smaller radar antennas can be transported to remote locations. Such small radar antennas must be coherent in both receive (RX) and transmit (TX) modes to achieve the functionality of large radar antennas. This allows for the rapid transport and installation of large radar antenna functionality in remote locations while keeping costs down. Key to this concept is the need for the smaller radar antennas to be coherent with each other; otherwise, system sensitivity would be significantly reduced. U.S. Pat. No. 9,979,084, incorporated herein by reference, discloses a method for cohering multiple radar antennas in RX mode using satellite calibration (SatCal). However, TX mode coherence is more difficult and complicated to achieve.

[0002] Deep space radar antennas require large arrays of dish antennas spanning distances of approximately 1 km. Such dish antennas must be calibrated and properly tuned to make their radiated radio frequency (RF) coherent, or to combine their received signals in phase (coherence). Without coherence, the radar antenna will not function properly. While calibration in RX mode has been demonstrated, achieving TX coherence is more complex and has not been demonstrated without the need for an RF far-field calibration source. Summary of the Invention

[0003] In accordance with the concepts described herein, exemplary methods and systems provide TX coherence in radar antennas.

[0004] In accordance with the concepts described herein, exemplary methods and systems provide a near-field horn calibration method for coherently aligning multiple independent radar antennas in a TX in the field.

[0005] In accordance with the concepts described herein, exemplary methods and systems provide a portable radar antenna for remote locations.

[0006] In accordance with the concepts described herein, exemplary methods and systems are provided that allow radar antennas to be physically detached and quickly transported and instantiated as a coherent radar network.

[0007] The methods and processes for making and using the disclosed embodiments may be understood by reference to the accompanying drawing figures. It should be understood that the components and structures shown in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the concepts described herein. Like reference characters designate corresponding parts throughout the different views. Moreover, embodiments are illustrated in the drawings by way of example, and not by way of limitation. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram of an active array radar antenna being calibrated using a near-field horn antenna in accordance with the present disclosure. [Figure 2] FIG. 1 is a diagram of a dish antenna being calibrated using a near-field dish antenna with a feed horn in accordance with the present disclosure. [Figure 3] FIG. 1 is a diagram of a calibrated dish antenna and phase parameters according to the present disclosure. [Figure 4] FIG. 1 is a diagram of a dish antenna calibrated using a near-field horn antenna and phase parameters according to the present disclosure. [Figure 5]FIG. 1 is a diagram of an active array radar antenna calibrated using a near-field horn antenna and phase parameters according to the present disclosure. [Figure 6] 1 is an exemplary method for calibrating a radar antenna using a near-field antenna according to the present disclosure. [Figure 7] 1 is an exemplary method for synchronizing, equalizing, and calibrating a radar antenna using a near-field antenna according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present disclosure provides exemplary methods and systems for rapidly achieving large aperture radar performance at remote locations where the autonomous radar antennas are not mechanically anchored to one another, but instead are made coherent through near-field antennas in both RX and TX modes.

[0010] The aperture and performance of a large radar antenna can be obtained in the field by coherently combining many smaller, portable radar antennas. To perfectly steer the TX beam, the phase center of the radar antenna (e.g., active array radar antenna or dish antenna) must be known. The phase of the quadrature waveforms is determined by a perfect 20 log 10 It must be related to the phase of the common radar waveform to recover the (N) Effective Isotropic Radiated Power (EIRP), where N is the number of TX antennas.

[0011] TX calibration of multiple dish antennas can be achieved using satellite radar targets (e.g., RF far-field calibration sources). To calibrate using satellite targets, it is necessary to know which satellites are present in the region of the sky being surveyed. It is also necessary to precisely know the phase centers of the TX antennas. Furthermore, a measurement sequence must be achieved in which each TX antenna radiates an orthogonal waveform in addition to the common waveform utilized by all TX antennas during radar operation. Such methods are complex and time-consuming. Other methods involve mechanically coupling the radar array to a single large aperture, which is often not possible.

[0012] Exemplary methods of the present disclosure (e.g., calibration methods for both RX and TX modes) utilize both the RX and TX operation of each radar antenna being calibrated. RX calibration and antenna phase center can be quickly determined using an RX calibration method (e.g., SatCal, although any suitable RX calibration method may be used). A one-step TX calibration process follows from RX calibration using a near-field RF antenna (e.g., a horn antenna or a dish antenna with a feed horn). A feed horn is a small horn antenna used to couple a waveguide to a dish antenna (e.g., a parabolic dish antenna or an offset dish antenna) for receiving or transmitting microwave signals. The result is a solution to a problem that limits the application of large radar antennas (e.g., large phased array antennas or dish antennas) in remote locations.

[0013] There are several ways to combine several radar antennas into one system, including (1) coherently combining the RX signals and incoherently combining the TX signals, and (2) coherently combining all the RX and TX signals. With incoherent combining, the signal-to-noise ratio (SNR) of the radar antenna array is 20log 10N, where N is the number of coupled radar antennas, and the coherence is in RX mode only. Coherently combining RX and TX increases the SNR by 30log 10 N, where N is the number of coupled radar antennas. The net improvement in RX and TX coherence vs. RX-only coherence is 10log 10 N. Coherent combining of RX and TX is a method to obtain maximum large aperture radar performance using multiple smaller aperture radar antennas.

[0014] 1 is a diagram of at least one active array radar antenna 101 being TX calibrated by at least one near-field horn antenna 103 in accordance with the present disclosure. In an exemplary embodiment, one near-field horn antenna 103 may be used to TX calibrate each of the at least one active array radar antenna 101 by moving the near-field horn antenna 103 to each position of the at least one active array radar antenna 101. In an exemplary embodiment, more than one near-field horn antenna 103 (e.g., at least two, a number equal to the number of active array radar antennas 101, or a number greater than the number of active array radar antennas 101) may be used to TX calibrate the at least one active array radar antenna 101 by moving and / or arranging the near-field horn antenna 103 relative to the position of the at least one active array radar antenna 101. When multiple near-field horn antennas calibrate a single common active array radar antenna, the resulting relative calibration factors of the multiple near-field horn antennas can be determined and compensated for by comparing the resulting calibration factors of the multiple near-field horn antennas.

[0015] 2 is a diagram of at least one dish radar antenna 201 being TX calibrated using at least one near-field dish antenna 203 with a feed horn in accordance with the present disclosure. In an exemplary embodiment, one near-field dish antenna 203 may be used to TX calibrate each of the at least one dish radar antenna 201 by moving the near-field dish antenna 203 to each location of the at least one dish radar antenna 201 or by pointing the near-field dish antenna 203 at each of the at least one dish radar antenna 201. In an exemplary embodiment, more than one near-field dish antenna 203 (e.g., at least two, a number equal to the number of dish radar antennas 201, or a number greater than the number of dish radar antennas 201) may be used to TX calibrate the at least one dish radar antenna 101 by moving and / or arranging the near-field dish antenna 103 relative to the location of the at least one dish radar antenna 101. When multiple near-field horn antennas calibrate a single common active array radar antenna, the resulting relative calibration factors of the multiple near-field horn antennas can be determined and compensated for by comparing the resulting calibration factors of the multiple near-field horn antennas.

[0016] An exemplary method of the present disclosure relocates radar antennas to remote locations (e.g., on pre-cast footings) that are interconnected (e.g., by fiber stabilization and / or fiber short-open-load (SOL) methods) to a common processor and synchronized to a common source.

[0017] An exemplary method of radar antenna calibration of the present disclosure includes calibrating a radar antenna (e.g., an active array antenna or a dish antenna) in RX mode (e.g., using SatCal or any other suitable RX calibration method), and then calibrating the radar antenna in TX mode using orthogonal waveforms for each radar antenna. Optionally, a common waveform for each TX radar antenna may then be calibrated in phase.

[0018] Radar antenna calibration in RX mode can be done with a single pulse if the SNR is high enough. For example, a GEO (geosynchronous equatorial orbit) satellite with a sufficiently high RCS (radar cross section) can be used for RX calibration if the signal is integrated long enough and if the transmitted radiation power impinging on the satellite is high enough. If an array of radar antennas is utilized for this calibration, using only orthogonal waveforms per radar antenna, there may be a loss of sensitivity of 10logN (where N is the number of TX radar antennas) compared to using the same waveform and making all TX antennas coherent.

[0019] Optionally, the relative positions of the radar antennas may be measured (e.g., using laser retroreflective targets) to aid in RX or TX calibration. While precise position measurements of the radar antennas are not required, such measurements may speed up the acquisition of TX mode coherence. Multiple radar apertures are aligned and the RX modes are made coherent (e.g., using SatCal or any other suitable RX mode calibration method). This process may be performed for multiple satellites at multiple angles to refine radar position metrics. Next, the near-field antenna (e.g., horn antenna or dish antenna with feed horn) method of the present disclosure is used to transfer the RX mode calibration to the TX mode calibration for each radar antenna, rapidly achieving RX and TX mode coherence for multiple radar antennas in the field, achieving a full 30 log10 N radar performance sensitivity can be obtained.

[0020] After RX calibration of all radar antennas is achieved using a method such as SatCal, and after each radar antenna is calibrated in TX mode, one or more near-field antenna calibration vehicles may move on to the next radar antenna to be calibrated in TX mode. In an embodiment, only one near-field antenna is used to TX calibrate all radar antennas. If necessary, more near-field antennas may be used due to redundancy requirements or because a single near-field antenna cannot reach or illuminate all radar antennas in the radar antenna farm. In this case, multiple near-field antennas must be used to calibrate at least one common radar antenna. The insertion phase difference between the near-field antennas is then determined. This phase correction is then used to accurately calibrate a radar antenna calibrated using one near-field antenna (e.g., near-field antenna A) to a radar antenna calibrated using another near-field antenna (e.g., near-field antenna B). The calibration is insensitive to the distance between the radar antenna and the near-field antenna calibration vehicle, side lobes, etc.

[0021] While RX mode calibration at a single pointing angle of the radar antenna may be achieved within one dwell using SatCal, antenna calibration and coherence at multiple pointing angles requires knowledge of the relative radar antenna phase center offset or variation as the radar antenna is scanned or mechanically pointed. This phase center position can be determined by RX SatCal at multiple scan angles (assuming repeatable radar antenna phase center motion) or by precise mechanical measurement of the antenna position.

[0022] This disclosure discloses an exemplary method for TX mode calibration, which can be performed quickly and with low risk using a single-polarized or dual-polarized instrumented horn or dish antenna on a tower near the TX radar antenna (hereinafter referred to as RF test horn calibration). RF test horn calibration leverages the following electromagnetic reciprocity (e.g., coupling from an RF test antenna to radar antenna n is the same for both RX and TX operation), the use of TX / RX radar antennas, and whether a single RF test antenna may be used, or if two or more test antennas are used (e.g., for redundancy or shielding), each test antenna must be calibrated. This can be accomplished by calibrating one radar antenna using at least two test antennas.

[0023] In traditional methods using active array radar antennas, each active array radar antenna is calibrated in RX mode only (e.g., using SatCal), which determines the relative phase of the active array radar antenna from a reference plane, which may utilize digital beamforming (DBF) at the receiver input.

[0024] In an embodiment, an RF test radar antenna may be installed on a tower and pointed at a radar antenna to be calibrated in TX mode. The polarization of the radar antenna to be calibrated and the RF test antenna must be aligned. Each radar antenna to be calibrated may then be pointed at the RF test antenna, and phase measurements may be made in both RX and TX operation. Once the RX calibration of the radar antenna to be calibrated is known, the TX phase calibration may then be determined. Typically, only phase calibration is required in TX mode, since amplitude is not adjustable. This method dramatically reduces the risk and complexity of TX calibration.

[0025] In this disclosure, RX calibration of each radar antenna must be accomplished using an RX calibration method (e.g., SatCal), and time stability of the TX and RX components must be maintained between the initial RX calibration and subsequent TX calibration methods.

[0026] FIG. 3 is a diagram of at least one dish antenna 300 and phase parameters to be calibrated in accordance with the present disclosure. FIG. 3 illustrates that the relationship between TX and RX phase calibration is the same whether the reference plane of an RF antenna calibration or an RX calibration method (e.g., SatCal) is measured. TX phase calibration is then achieved relative to the RX phase calibration for each of the at least one dish antenna 300 by establishing a reference plane at the waveguide input to the RF feed horn of the at least one dish antenna 300. This calibration is only as accurate as the RX calibration method (e.g., SatCal), but is independent of the multipath error of the RF horn antenna relative to the measurement of dish n.

[0027] The purpose of the RF test horn calibration is to match the TX mode calibration to a separately performed RX mode calibration. The TX mode calibration may have the same errors as the RX mode calibration (e.g., SatCal), if any. The RX mode calibration may be performed in the reference plane of a plane wave incident on the front face of the antenna assembly. The result is a parameter Φ RXn The RF horn calibration method is RXn Φ for TXn Determine where Φ TXn is a TX calibration relative to the same (e.g., arbitrary) reference plane. RF horn calibration aligns the TX and RX signals in at least one dish antenna 300 at the same, common TX / RX path element in at least one dish antenna 300. In this case, the common path element is the horn waveguide feed input. This reference plane may be different from the reference plane for RX calibration (e.g., SatCal).

[0028] In general, the temporal stability of the TX and RX components relative to each other can be ensured by using a common array calibration receiver / exciter to send a calibration signal from the calibration exciter to the coupled path inputs at each antenna receiver channel and sending an RF signal with each antenna exciter channel coupled off and back to the common calibration receiver. A separate method can be used to remove phase drift from the calibration signal cable. For long distances, RF over fiber can be used to minimize loss of the calibration signal. Calibration data from these coupled paths can be used to apply corrections for any TX or RX phase drift during the time of the initial RX calibration and TX calibration according to the RF horn method of this disclosure.

[0029] Exemplary method embodiments achieve these goals because the remaining path elements are common to both TX and RX and have the same effect on wave propagation due to electromagnetic (EM) reciprocity. Because the method utilizes reciprocity at the RF horn input, the method is not affected by errors such as multipath. Such errors are common to both TX and RX horn measurements and are canceled out.

[0030] FIG. 4 is a diagram of at least one dish antenna 401 calibrated using at least one near-field horn antenna 403 and phase parameters according to the present disclosure.

[0031] The first step in the near-field horn method is to calculate Φ RXn calibrating at least one dish antenna 401 in RX mode using an RX calibration method (e.g., SatCal) to determine Φ RXn is the RF phase from the reference plane of the RF far-field calibration source of the at least one radar antenna to the RX RF port of the at least one radar antenna in RX mode.

[0032] Then, at least one dish antenna n401 operates in RX mode, as in the active array antenna embodiment shown in Figure 5 and described below. measRXn is determined by equation (1) as follows: where all phases are known or measured, and where Φ measRXn is the RF phase from the reference plane of the RF far-field calibration source of the at least one radar antenna to the RX RF port of the at least one radar antenna measured during the RX mode calibration, where Φ measRXno is the RF phase measured at the RF port of at least one near-field antenna during RX mode calibration, where Φ propn is the RF phase from the reference plane of at least one radar antenna to the reference plane of at least one near-field antenna, where Φ oRX is the RF phase from the reference plane of the at least one near-field antenna to the RX RF port of the at least one near-field antenna, where Φ o is the RF phase on at least one near-field antenna to the digital receiver exciter (DREX) of at least one radar antenna.

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[0033] Then, at least one dish antenna n401 operates in TX mode. measTXno is determined by equation (2) assuming that the command phase = 0 at the TX port of dish antenna n, as follows: where Φ measTXno is the RF phase measured at the RF port of at least one near-field antenna in TX mode, where Φ TXn is the RF phase from the reference plane of the RF far-field calibration source of the at least one radar antenna to the TX RF port of the at least one radar antenna in TX mode, where Φ oTXis the RF phase from the reference plane of the at least one near field antenna to the TX RF port of the at least one near field antenna, where n is a positive integer that denotes one of the at least one radar antenna.

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[0034] Next, Φ from Eq. (3) TXn is calculated using equation (4) as follows:

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[0035] This is assumed to be the case for at least one dish antenna 401 Φ, assuming the same RF test horn (e.g., near-field horn test vehicle) is used for all of the at least one dish antenna 401. TXn At least one 401Φ dish antenna TXn Alternatively, if a different RF test horn (e.g., a different near-field horn test vehicle) is used to calibrate at least one portion of the dish antenna 401, a different RF test horn must be used to calibrate at least one common dish or radar antenna.

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[0036] Figure 5 is a diagram of at least one active subarray or phased array n501 and phase parameters being calibrated using at least one near-field horn antenna 503 in accordance with the present disclosure. The steps of the near-field horn method for determining the TX phase of the radar array of Figure 5 are the same as those of Figure 4 described above, except that at least one dish antenna n401 is replaced with at least one active subarray n501.

[0037] When calibrating multiple phased array antennas, unlike the reflector case,

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[0038] For example, if N=32,

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[0039] FIG. 6 is an exemplary method 600 for calibrating a radar antenna using a near-field antenna according to this disclosure.

[0040] Step 601 of method 600 comprises: RXn This involves calibrating the radar antenna (e.g., a dish antenna or an active array antenna) in RX mode to determine . SatCal or any other suitable RX mode calibration method may be used.

[0041] Step 603 of method 600 includes operating radar antenna 401 in RX mode. measRXn is determined by equation (6) as follows: where all phases are known or measured.

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[0042] Step 605 of method 600 includes operating the radar antenna in TX mode. measTXno is determined by equation (7) assuming a command phase=0 at the TX port of dish antenna n as follows:

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[0043] Step 607 of method 600 calculates Φ by equation (8) as follows: measRXn -Φ measTXno where ΔΦ is the dropout.

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[0044] Step 609 of method 600 calculates Φ in equation (9) as follows: TXn (e.g., TX mode calibration of a radar antenna) involves solving equation (8).

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[0045] This is assumed to be the case for at least one dish antenna 401 Φ, assuming the same RF test horn (e.g., near-field horn test vehicle) is used for all of the at least one dish antenna 401. TXn At least one dish antenna 401Φ TXn Alternatively, if different RF test horns (e.g., different near-field horn test vehicles) are used to calibrate at least one portion of the dish antenna 401, then a different RF test horn must be used to calibrate at least one common dish or radar antenna.

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[0046] When calibrating multiple phased array antennas, unlike reflectors,

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[0047] For example, if N=32,

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[0048] Possible errors in RF horn calibration can include RX calibration (e.g., SatCal), reflections within the dish antenna network, and multipath errors. Any errors in the RX calibration may not be removed by the RF horn calibration method and may carry over to the TX calibration. By applying reciprocity to the phase shift, reflections can be assumed to be small. Assuming a voltage standing wave ratio (VSWR) of 1.5:1 at the input of the feed horn and at the circulator output, the resulting reflection error is approximately -28 dB, or there may be a 2° phase error. Multipath errors, for example, can affect the accuracy of the on-axis comparison but do not affect the relative TX-to-RX calibration of the horn antenna.

[0049] FIG. 7 is an exemplary method 700 for synchronizing, equalizing, and calibrating a radar antenna using a near-field antenna according to this disclosure.

[0050] Step 701 of method 700 includes synchronizing radar antennas using a common clock signal and stable distribution method. Step 703 of method 700 includes performing radar antenna equalization / time delay compensation using RF over coaxial cable or RF over fiber optic injection. Step 705 of method 700 includes determining a relative radar antenna RX phase calibration using SatCal or an equivalent method. Step 707 of method 700 includes determining a relative radar antenna TX phase calibration from the RX phase calibration using a near-field antenna method (e.g., the method shown in FIG. 6 and described above). Step 709 of method 700 includes achieving RX and TX radar antenna coherence, where step 705 provides RX radar antenna coherence and step 707 provides TX radar antenna coherence.

[0051] Step 707 does not have to be performed after step 705, but may be performed if followed by the other calibration steps outlined above, and Φ TXn -Φ RXn may be performed before step 705 and at a different location if phase stability is maintained throughout the process.

[0052] While illustrative embodiments of the present disclosure have been described, it will be apparent to those skilled in the art that other embodiments incorporating these concepts may also be used. The embodiments contained herein should not be limited to the disclosed embodiments, but rather should be limited only by the spirit and scope of the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

[0053] Elements of different embodiments described herein can be combined to form other embodiments not specifically described above. Various elements that are described in the context of a single embodiment may be provided separately or in any suitable subcombination. Other embodiments not specifically described herein are also within the scope of the following claims.

[0054] Various embodiments of the concepts, systems, devices, structures, and techniques for which protection is sought are described herein with reference to the associated drawings. Alternative embodiments may be contemplated without departing from the scope of the concepts, systems, devices, structures, and techniques described herein.

[0055] It should be noted that in the above description and drawings, various connections and relationships (e.g., above, below, adjacent, etc.) are described between elements. These connections and / or relationships may be direct or indirect unless otherwise specified, and the described concepts, systems, devices, structures, and techniques are not intended to be limiting in this regard. Thus, coupling of entities can refer to direct or indirect coupling, and relationship between entities may be direct or indirect relationship.

[0056] As an example of an indirect relationship, references in this description to forming layer "A" above layer "B" include situations in which one or more intermediate layers (e.g., layer "C") are between layer "A" and layer "B," so long as the relevant properties and functions of layer "A" and layer "B" are not substantially altered by the intermediate layer(s). The following definitions and abbreviations should be used for interpreting the claims and the specification. As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," "contains," or "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, mixture, process, method, article, or device that includes a list of elements is not necessarily limited to only those elements and may include other elements not expressly listed or other elements inherent to such composition, mixture, process, method, article, or device.

[0057] Moreover, the term "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The terms "one or more" and "at least one" are understood to include any integer number greater than or equal to one, i.e., 1, 2, 3, 4, etc. The term "plurality" is understood to include any integer number greater than or equal to two, i.e., 2, 3, 4, 5, etc. The term "connected" can include an indirect "connected" and a direct "connected."

[0058] References in the specification to "one embodiment," "an embodiment," "an exemplary embodiment," etc. indicate that the described embodiment may include a particular feature, structure, or characteristic, but that all embodiments may include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with one embodiment, it is believed to be within the knowledge of one of ordinary skill in the art to affect such feature, structure, or characteristic in connection with other embodiments, whether or not explicitly stated.

[0059] For purposes of this description, the terms "above," "below," "right," "left," "vertical," "horizontal," "top," "bottom" (to name a few) and their derivatives refer to the structures and methods described, as well as the orientation of the drawings. The terms "overlying," "atop," "ontop," "positioned on," or "positioned atop" mean that a first element, such as a first structure, is above a second element, such as a second structure, and intervening elements, such as interfacial structures, may be present between the first and second elements. The term "direct contact" means that a first element, such as a first structure, and a second element, such as a second structure, are connected without intervening elements. Such terms may also be referred to as directional or positional terms.

[0060] The use of ordinal numbers such as "first," "second," and "third" in the claims to modify claim elements does not, in and of itself, imply a priority, precedence, or ordering of one claim element over other claim elements, or the chronological order in which method actions are performed, but is merely used as a label to distinguish one claim element with a particular name from another element with the same name (other than the use of the ordinal number) to distinguish between claim elements.

[0061] The terms "approximately" and "about" may be used in some embodiments to mean within ±20% of a target value, in some embodiments within ±10% of a target value, in some embodiments within ±5% of a target value, and even in some embodiments within ±2% of a target value. The terms "approximately" and "about" may include the target value. The term "substantially equal" may be used in some embodiments to refer to values ​​that are within ±20% of each other, in some embodiments within ±10% of each other, in some embodiments within ±5% of each other, and even in some embodiments within ±2% of each other.

[0062] The term "substantially" may be used in some embodiments to refer to values ​​within ±20%, in some embodiments within ±10%, in some embodiments within ±5%, and even in some embodiments within ±2% of a comparison measurement. For example, a first direction that is "substantially" perpendicular to a second direction may in some embodiments refer to a first direction that is within ±20%, in some embodiments within ±10%, in some embodiments within ±5%, and even in some embodiments within ±2% of a 90° angle with the second direction.

[0063] It is to be understood that the disclosed subject matter is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings, as the disclosed subject matter is capable of other embodiments and of being practiced and carried out in various ways.

[0064] It is also to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. Thus, those skilled in the art will appreciate that the conception underlying this disclosure may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out some of the purposes of the disclosed subject matter. Accordingly, the claims should be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the disclosed subject matter.

[0065] While the disclosed subject matter has been described and illustrated in the foregoing exemplary embodiments, it should be understood that the disclosure is made by way of example only, and that many changes may be made in the details of the implementation of the disclosed subject matter without departing from the spirit and scope of the disclosed subject matter.

Claims

1. 1. A method for calibrating and cohering at least one radar antenna in receive (RX) and transmit (TX) modes, comprising: performing an RX mode calibration on the at least one radar antenna using a radio frequency (RF) far-field calibration source; using the RF far-field calibration source for each of the at least one radar antenna, an RF phase Φ ＲＸｎ determining where Φ ＲＸｎ is the RF phase from an RF far-field calibration source reference plane of the at least one radar antenna to the RX RF port of the at least one radar antenna in RX mode, and n is a positive integer indicating one of the at least one radar antenna; operating the at least one radar antenna in an RX mode together with at least one near-field antenna; determining a plurality of RX mode phases at the at least one radar antenna and the at least one near-field antenna; operating the at least one radar antenna in a TX mode together with the at least one near-field antenna; determining a plurality of TX mode phases at the at least one radar antenna and the at least one near-field antenna; deriving a TX mode calibration as a function of the determined RX mode phase and the determined TX mode phase; A method comprising:

2. the at least one radar antenna is one of at least one active array antenna and at least one dish antenna; The method of claim 1.

3. the RF far-field calibration source is a satellite; The method of claim 1.

4. the at least one near-field antenna is one of at least one horn antenna and at least one dish antenna; The method of claim 1.

5. The step of operating the at least one radar antenna together with the at least one near-field antenna in an RX mode includes: [Equation 1] operating the at least one radar antenna together with the at least one near-field antenna in an RX mode to determine where Φ ｍｅａｓＲＸｎ is the RF phase from the RF far-field calibration source reference plane of the at least one radar antenna to the RX RF port of the at least one radar antenna measured during RX mode calibration; where ΔΦ is the RF phase difference between the RF far-field calibration source reference plane and the at least one near-field antenna reference plane; where Φ ｐｒｏｐｎ is the RF phase from a reference plane of the at least one radar antenna to the reference plane of the at least one near field antenna; where Φ ｏＲＸ is the RF phase from the reference plane of the at least one near field antenna to the RX RF port of the at least one near field antenna; where Φ ｍｅａｓＲＸｎｏ is the RF phase measured at the RF port of the at least one near field antenna during calibration of the RX mode; where Φ o is the RF phase on the at least one near-field antenna to a digital receiver exciter (DREX) of the at least one near-field antenna; where n is a positive integer indicating one of the at least one radar antenna. The method of claim 1.

6. The step of operating the at least one radar antenna together with the at least one near-field antenna in a TX mode includes: [Equation 2] operating the at least one radar antenna together with the at least one near-field antenna in a TX mode to determine where Φ ｍｅａｓＴＸｎｏ is the RF phase measured at the RF port of the at least one near field antenna during calibration of the TX mode; where Φ ｐｒｏｐｎ is the RF phase from a reference plane of the at least one radar antenna to the reference plane of the at least one near field antenna; where Φ ｏＴＸ is the RF phase from the reference plane of the at least one near field antenna to the TX RF port of the at least one near field antenna; where Φ ＴＸｎ is the RF phase from the RF far-field calibration source reference plane of the at least one radar antenna to the TX RF port of the at least one radar antenna in TX mode; where ΔΦ is the RF phase difference between the RF far-field calibration source reference plane and the at least one near-field antenna reference plane; where Φ ｏ is the RF phase on the at least one near-field antenna to a digital receiver exciter (DREX) of the at least one near-field antenna; where n is a positive integer indicating one of the at least one radar antenna. The method of claim 1.

7. deriving a TX mode calibration as the function of the determined RX mode phase and the determined TX mode phase; [Equation 3] determining a [Equation 4] To determine [Equation 5] This is the step to obtain the result of where Φ ｍｅａｓＲＸｎ is the RF phase from the RF far-field calibration source reference plane of the at least one radar antenna to the RX RF port of the at least one radar antenna measured during RX mode calibration; where Φ ｍｅａｓＴＸｎｏ is the RF phase measured at a digital receiver exciter (DREX) RF port of the at least one near-field antenna during calibration of the TX mode; where Φ ＲＸｎ is the RF phase from the RF far-field calibration source reference plane of the at least one radar antenna to the RX RF port of the at least one radar antenna in RX mode; where Φ ｏＲＸ is the RF phase from the reference plane of the at least one near field antenna to the RX RF port of the at least one near field antenna; where Φ ｏＴＸ is the RF phase from the reference plane of the at least one near field antenna to the TX RF port of the at least one near field antenna; where Φ ｍｅａｓＲＸｎｏ is the RF phase measured at the DREX RF port of the at least one near field antenna in RX mode; where Φ ＴＸｎ is the RF phase from the RF far-field calibration source reference plane of the at least one radar antenna to the TX RF port of the at least one radar antenna in TX mode; where Φ ｏ is the RF phase on the at least one near-field antenna to a digital receiver exciter (DREX) of the at least one near-field antenna; where n is a positive integer indicating one of the at least one radar antenna; The method of claim 1 , comprising:

8. the at least one near-field antenna includes one near-field antenna that is repositioned to calibrate and coherently match each of the at least one radar antenna; The method of claim 1.

9. the at least one near-field antenna includes at least one near-field antenna for each of the at least one radar antenna; The method of claim 1.

10. The method further comprises: calibrating and cohering the at least one radar antenna in receive (RX) and transmit (TX) modes at a plurality of different airborne locations; The method of claim 1.

11. The method further comprises: synchronizing the at least one radar antenna using a common clock signal and a stable distribution method; The method of claim 1.

12. The method further comprises: performing equalization / time delay compensation of the at least one radar antenna using RF over a coaxial cable; The method of claim 1.

13. The method further comprises: performing equalization / time delay compensation of the at least one radar antenna using optical fiber injection; The method of claim 1.

14. 1. A system for calibrating and cohering at least one radar antenna in a receive (RX) mode and a transmit (TX) mode, comprising: at least one radar antenna; a radio frequency (RF) far-field calibration source; performing an RX mode calibration on the at least one radar antenna and using the RF far-field calibration source for each of the at least one radar antenna, adjusting an RF phase Φ ＲＸｎ and determining a where Φ ＲＸｎ is the RF phase from the RF far-field calibration source reference plane of the at least one radar antenna to the RX RF port of the at least one radar antenna in RX mode, and n is a positive integer indicating one of the at least one radar antenna. an RF far-field calibration source; at least one near field antenna; operating the at least one radar antenna in an RX mode to determine a plurality of RX mode phases at the at least one radar antenna and the at least one near-field antenna; operating the at least one radar antenna in a TX mode with the at least one near-field antenna to determine a plurality of TX mode phases at the at least one radar antenna and the at least one near-field antenna; deriving a TX mode calibration as a function of the determined RX mode phase and the determined TX mode phase; at least one near field antenna configured as follows: Including, the system.

15. the at least one radar antenna is one of at least one active array antenna and at least one dish antenna; The system of claim 14.

16. the RF far-field calibration source is a satellite; The system of claim 14.

17. the at least one near-field antenna is one of at least one horn antenna and at least one dish antenna; The system of claim 14.

18. Operating the at least one radar antenna together with the at least one near field antenna in an RX mode includes: [Equation 6] operating the at least one radar antenna together with the at least one near-field antenna in an RX mode to determine where Φ ｍｅａｓＲＸｎ is the RF phase from the RF far-field calibration source reference plane of the at least one radar antenna to the RX RF port of the at least one radar antenna measured during RX mode calibration; where ΔΦ is the RF phase difference between the RF far-field calibration source reference plane and the at least one near-field antenna reference plane; where Φ ｐｒｏｐｎ is the RF phase from a reference plane of the at least one radar antenna to the reference plane of the at least one near field antenna; where Φ ｏＲＸ is the RF phase from the reference plane of the at least one near field antenna to the RX RF port of the at least one near field antenna; where Φ ｍｅａｓＲＸｎｏ is the RF phase measured at the RF port, the RF port including a digital receiver exciter (DREX) RF port of the at least one near-field antenna in RX mode; where Φ ｏ is the RF phase on the port of the at least one near field antenna up to the DREX of the at least one near field antenna; where n is a positive integer indicating one of the at least one radar antenna. The system of claim 14.

19. Operating the at least one radar antenna together with the at least one near-field antenna in a TX mode includes: [Equation 7] operating the at least one radar antenna together with the at least one near-field antenna in a TX mode to determine where Φ ｍｅａｓＴＸｎｏ is the RF phase measured at a digital receiver exciter (DREX) RF port of the at least one near-field antenna during calibration of the TX mode; where Φ ｐｒｏｐｎ is the RF phase from a reference plane of the at least one radar antenna to the reference plane of the at least one near field antenna; where Φ ｏＴＸ is the RF phase from the reference plane of the at least one near field antenna to the TX RF port of the at least one near field antenna; where Φ ＴＸｎ is the RF phase from the RF far-field calibration source reference plane of the at least one radar antenna to the TX RF port of the at least one radar antenna in TX mode; where ΔΦ is the RF phase difference between the RF far-field calibration source reference plane and the at least one near-field antenna reference plane; where Φ ｏ is the RF phase on the port of the at least one near field antenna to a digital receiver exciter (DREX) of the at least one near field antenna; where n is a positive integer indicating one of the at least one radar antenna. The system of claim 14.

20. Deriving a TX mode calibration as the function of the determined RX mode phase and the determined TX mode phase comprises: [Equation 8] and determining [Equation 9] To determine [Equation 10] The goal is to obtain the results of where: Φ ｍｅａｓＲＸｎ is the RF phase from the RF far-field calibration source reference plane of the at least one radar antenna to the RX RF port of the at least one radar antenna measured during RX mode calibration; where Φ ｍｅａｓＴＸｎｏ is the RF phase measured at a digital receiver exciter (DREX) RF port of the at least one near-field antenna during calibration of the TX mode; where Φ ＲＸｎ is the RF phase from the RF far-field calibration source reference plane of the at least one radar antenna to the RX RF port of the at least one radar antenna in RX mode; where Φ ｏＲＸ is the RF phase from the reference plane of the at least one near field antenna to the RX RF port of the at least one near field antenna; where Φ ｏＴＸ is the RF phase from the reference plane of the at least one near field antenna to the TX RF port of the at least one near field antenna; where Φ ｍｅａｓＲＸｎｏ is the RF phase measured at the RF port of the at least one near field antenna in RX mode; where Φ ＴＸｎ is the RF phase from the RF far-field calibration source reference plane of the at least one radar antenna to the TX RF port of the at least one radar antenna in TX mode; where Φ ｏ is the RF phase on the port of the at least one near field antenna to a digital receiver exciter (DREX) of the at least one near field antenna; where n is a positive integer indicating one of the at least one radar antenna. Seeking results and The system of claim 14 , comprising:

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