System and method for near-field testing of a phased array antenna

A near-field test system for a phased array antenna includes a probe, a beam forming network, and a computing system. The probe is disposed at a fixed position in a near-field of the antenna and is configured to receive at least a portion of a test beam radiated by the antenna. The beam forming network is coupled to the antenna and includes a plurality of phase shifters configured to steer the test beam to a position in the near-field when radiated by an array of antenna elements of the antenna. The computing system is coupled to the probe and is configured to normalize received power of the test beam based on the position of the beam in the near-field relative to the fixed position of the probe, and generate a far-field antenna pattern for the antenna from normalized received power of the test beam.

FIELD

The field of the disclosure relates generally to testing of phased array antennas and, more specifically, to a system and method for near-field testing of a phased array antenna to produce a far-field pattern.

BACKGROUND

Conventional testing of electronically scanned antennas, such as phased array antennas including, for example, single-beam or multi-beam active array antennas found on space vehicles, communication systems, aircraft, radio towers, or other platform operating at radio frequencies, involves either far-field characterization or near-field characterization that is then translated to a far-field antenna pattern. Near-field characterization conventionally includes rastor-scanning the amplitude and phase of the near-field electromagnetic radiation of the antenna, and then using a two-dimensional Fourier transform to translate the near-field measurements to a far-field antenna pattern. For a multi-beam antenna, the rastor-scan and translation to far-field are repeated for each beam.

In far-field testing, for example, of a phased array antenna on an orbiting space vehicle, e.g., a satellite, each beam is pointed in a different direction and differentiated from the next by frequency (e.g., frequency division multiple access, or FDMA), by time (e.g., time division multiple access, or TDMA), or by code (e.g., code division multiple access, or CDMA). A portion of each beam is received at a reference antenna, e.g., on the ground. Given that the azimuth and elevation of each beam relative to the reference antenna is known, and given that each beam is differentiated in some manner from the next, the received power of each beam can be normalized and mapped to represent a far-field pattern.

BRIEF DESCRIPTION

One aspect of the present disclosure includes a near-field test system for a phased array antenna includes a probe, a beam forming network, and a computing system. The probe is disposed at a fixed position in a near-field of the phased array antenna and is configured to receive at least a portion of a test beam radiated by the phased array antenna. The beam forming network is coupled to the phased array antenna and includes a plurality of phase shifters configured to steer the test beam to a position in the near-field when radiated by an array of antenna elements of the phased array antenna. The computing system is coupled to the probe and is configured to scale received power of the test beam, and generate a far-field antenna pattern for the phased array antenna from scaled received power of the test beam.

Another aspect of the present disclosure includes a method of near-field testing of a phased array antenna having an array of antenna elements, the method includes steering a test beam to a beam position in a near-field of the phased array antenna. The method includes disposing a probe at a fixed position in the near-field of the phased array antenna. The method includes phase shifting the test beam supplied to each element of the array of antenna elements to apply a spherical phase taper across the array to generate a spherical wave front focused at the probe and to equalize path length phase from each element of the array to the probe. The method includes receiving at least a portion of the test beam at the probe. The method includes scaling received power of the test beam. The method includes generating a far-field antenna pattern for the phased array antenna from scale received power of the test beam.

Yet another aspect of the present disclosure includes a beam forming network for near-field testing of a phased array antenna, the beam forming network includes a plurality of phase shifters and a microcontroller. The plurality of phase shifters is coupled to a signal generator. Each phase shifter is configured to receive a test beam from the signal generator and apply a corresponding phase shift to the test beam. The phase shifter supplies the test beam to an element of an array of antenna elements of the phased array antenna. The microcontroller is coupled to the plurality of phase shifters for controlling the corresponding phase shift of each element of the array. The microcontroller is configured to adjust the corresponding phase shift of each element to steer the test beam to a position in the near-field of the phased array antenna when radiated by the array, and adjust the corresponding phase shift of each element to apply a spherical phase taper across the array to generate a spherical wave front focused at a probe disposed in the near-field of the phased array antenna and to equalize path length phase from each element of the array to the probe when the test beam is radiated by the array.

Yet another aspect of the present disclosure includes a near-field test system for a phased array antenna. The near-field test system includes a probe, a beam forming network, and a computing system. The probe is disposed at a fixed position in a near-field of the phased array antenna and is configured to transmit a test beam toward a fixed location on the phased array antenna. The beam forming network is coupled to the phased array antenna and includes a plurality of phase shifters and a beam summer. The plurality of phase shifters is configured to steer received beams for each antenna element of the phased array antenna to form a planar wave front when radiated by the probe. The beam summer is coupled to the plurality of phase shifters and is configured to combine power of the received beams. The computing system is coupled to the beam forming network and is configured to scale combined power of the received beams and generate a virtual spectrum for the phased array antenna from scaled power of the received beams.

Yet another aspect of the present disclosure includes a method of near-field testing of a phased array antenna having an array of antenna elements. The method includes transmitting a test beam toward a fixed location on the phased array antenna from a probe at a fixed position in the near-field of the phased array antenna. The method includes receiving at least a portion of the test beam at each antenna element. The method includes phase shifting the received beams from each antenna element to apply a spherical phase taper across the array to correct a spherical wave front detected by each antenna element resulting from unequal path length phases from each antenna element to the probe, thereby producing a planar wave front. The method includes combining power of the received beams. The method includes scaling combined power of the received beams. The method includes generating a virtual spectrum for the phased array antenna from scaled power of the received beams.

Yet another aspect of the present disclosure includes a beam forming network for near-field testing of a phased array antenna. The beam forming network includes a plurality of phase shifters and a microcontroller. The plurality of phase shifters is coupled to respective antenna elements of the phased array antenna. Each phase shifter is configured to receive a received beam from the respective antenna element, apply a corresponding phase shift to the received beam, and supply the received beam to a beam summer. The microcontroller is coupled to the plurality of phase shifters for controlling the corresponding phase shift of each element of the array. The microcontroller is configured to adjust the corresponding phase shift of each element to apply a spherical phase taper across the array to correct a spherical wave front detected by each antenna element resulting from unequal path length phases from each antenna element to the probe, thereby producing a planar wave front.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. Although specific features of various examples may be shown in some drawings and not in others, this is for convenience only. Any feature of any drawing may be referenced and/or claimed in combination with any feature of any other drawing.

DETAILED DESCRIPTION

Embodiments of the systems and methods described generally include a near-field test system and a method of near-field testing for a phased array antenna. As an example, the phased array antenna is installed on an orbiting space vehicle, e.g., a satellite. However, the disclosed systems and methods are not limited to satellite applications and can be utilized with phased array antennas in most any communication system and/or radar antenna platform, e.g., installed on aircraft, balloon, radio towers, etc. and operating at radio frequencies, optical frequencies, and/or sonar frequencies. For example, the systems and methods provide near-field testing to produce a “snapshot” of a far-field antenna pattern by electronically scanning the phased array antenna over a probe at a fixed position in the near-field, and using power measurements at the probe to generate the far-field antenna pattern with a single measurement, or “snapshot.” The systems and methods may apply to both single-beam and multi-beam phased array antennas, and enable far-field characterization for all beams with as few as a single near-field scan. The systems and methods may include multiple beams simultaneously radiated from the phased array antenna, and each beam is steered to a rastor position in the near-field. At least some embodiments apply a linear phase progression over the antenna elements during beam forming to steer the beam to its corresponding rastor position. In an example, each beam has a unique feature, or discriminator, that enables differentiation of the beams at the probe upon receipt. The unique features may include, for example, a different frequency for each beam, a different timing for each beam, or a different coding for each beam. The systems and methods may also apply a spherical phase taper during beam forming to form a spherical wave front that focuses each beam's energy at the probe and equalizes path length phase among the different elements of the phased array antenna, which are each offset from a center of the phased array antenna by some distance.

In some example systems and methods, the probe receives at least a portion of each beam. A far-field antenna pattern is generated based on the received power of each beam once it is normalized for each beam's known rastor position relative to the fixed position of the probe. Embodiments of the systems and methods implement near-field testing without mechanically rastor-scanning a probe over the surface of the phased array antenna, but instead by taking advantage of the electronic scanning capability native to the phased array antenna under test. Moreover, the far-field pattern is generated with simple power measurements instead of conventional amplitude and phase measurements that must undergo a two-dimensional Fourier transform to arrive at the far-field antenna pattern. Accordingly, the disclosed systems and methods reduce complexity, time, and cost necessary to characterize a phased array antenna in the far-field.

In alternative embodiments, the near-field test system and a method of near-field testing may be used for a receiving phased array antenna. In such embodiments, beams are transmitted by the probe and received by the phased array antenna. Although functionally reversed, the near-field test system and method of near-field testing operate in the same manner for the receiving phased array antenna as for a transmitting phased array antenna. Each system and method effectively tests the phased array antenna, one by transmitting from the phased array antenna and the other by receiving at the phased array antenna. Accordingly, although certain aspects of the following embodiments are described in terms of a transmitting phased array antenna, the same description applies equally when testing a receiving phased array antenna. Likewise, descriptions of certain aspects of some embodiments in terms of a receiving phased array antenna also apply to testing a transmitting phased array antenna.

FIG. 1is a block diagram of a near-field test system100for a phased array antenna102. Near-field test system100includes a probe104disposed at a fixed position in the near-field of phased array antenna102. Near-field test system100includes a signal generator106and a beam forming network108that feed phased array antenna102. Near-field test system100includes a computing system110that controls various components of near-field test system100, including a microcontroller112that itself controls components of beam forming network108and, in certain embodiments, signal generator106. In alternate embodiments, signal generator106is controlled directly by computing system110. Computing system110includes an RF receiver113, a processor114, a memory116, and a communication interface118. In alternative embodiments, any one of RF receiver113, processor114, memory116, or communication interface118may be implemented in combination with any other of the components of computing system110. For example, communication interface118may be implemented to include RF receiver113.

FIG. 2is a diagram illustrating near-field testing of phased array antenna102shown inFIG. 1. Phased array antenna includes an array of antenna elements120, each of which simultaneously radiates multiple beams122,124,126that are pointed to respective rastor positions in the near-field128of phased array antenna102.FIG. 2illustrates three beams122,124,126, however, in various embodiments, the number of beams radiated may be one or more.FIG. 2illustrates probe104disposed at its fixed position in near-field128, as opposed to in the far-field130of phased array antenna102, which is generally many-times the wavelength of the beams radiated by phased array antenna102.

Referring toFIGS. 1 and 2, processor114is configured to execute instructions, or program code, stored in memory116or any other suitable local or remote memory device. Processor114, for example, is configured to gain access to program code for receiving, via communication interface118, and processing test data collected by probe104for phased array antenna102. Such test data can be stored, for example in memory116. Processor114is further configured to gain access to program code for instructing microcontroller112, via communication interface118, to independently control phase shifters (not shown) to adjust phases of the electromagnetic waves to be fed to antenna elements120of phased array antenna102to shape, e.g., steer, the emitted beams122,124,126. Computing system110instructs both probe104and microcontroller112to collect test data, e.g., power measurements, for each beam.

Processor114is further configured to gain access to program code for processing the test data collected by probe104to scale received power measurements. Such scaling may include, for example, normalizing received power measurements for each beam based on each beam's pointing position, or rastor position, in azimuth and elevation relative to the fixed position of probe104. In alternative embodiments, processor114may reference measured power to a gain standard. Processor114maps the scaled power measurements to a far-field antenna pattern.

FIG. 3is a block diagram of beam forming network108shown inFIG. 1. Beam forming network108and its various components may be implemented digitally using, for example, a digital signal processor, or may be implemented using discrete analog components. Beam forming network108is fed by a plurality of signal generators106. Each signal generator106produces a beam signal having a unique feature, such as a unique frequency, a unique timing, or a unique coding, that distinguishes each beam radiated by phased array antenna102from each other. Beam forming network108includes, for each beam, a signal divider302and a plurality of phase shifters304. Beam forming network108also includes, for each antenna element120, a beam summer306. Beam divider302, or splitter, receives the beam signal from a corresponding signal generator106and supplies it to each of its corresponding plurality of phase shifters304, one phase shifter304per antenna element120. Phase shifters304adjust the phase of the beam being supplied to each antenna element, for example, to steer the beam. To steer the beam, phase shifters304apply a linear phase progression to antenna elements120as a function of each elements position relative to the center of the array. Phase shifters304further adjust the phase of the beam to apply a spherical phase taper to equalize path length phase to probe104for each antenna element120and focus the beam's energy at probe104. All the phase-shifted beams for a given antenna element120are then combined by a corresponding beam summer306, such that all beams are simultaneously radiated by each antenna element120. In certain embodiments, beam forming network108includes a plurality of amplitude control elements for each antenna element120. Such amplitude control elements may include, for example amplitude taper control.

Microcontroller112controls, for example, each of the plurality of phase shifters304of beam forming network108independently to modify the respective phase shifts applied to the beam signals supplied by signal generators106. Further, in certain embodiments, microcontroller112is configured to control signal generators106to modify, for example, frequency, timing, or coding of the beam signals supplied to beam forming network108.

Signal generator106can include one or more RF or baseband circuits or components, such as, for example, a modulator, amplifier, oscillator, or other wave generator.

Probe104includes, for example, an antenna, such as a Potter horn, or other suitable type of antenna for receiving portions of the beams radiated from phased array antenna102. Probe104may also include a power meter for measuring received power from the beams. In alternative embodiments, received power may be measured by RF receiver113.

FIG. 4is a plot400of an antenna pattern402in power, or directivity, expressed in decibels on a vertical axis404, versus pointing angle, expressed in degrees on a horizontal axis406. Antenna pattern402includes a main beam408centered at zero degrees, and a plurality of side lobes410measured at pointing angles relative to main beam408. The power shown in antenna pattern402is expressed in decibels (dB) relative to main beam408, main beam408accordingly being measured at 0 dB. Side lobes410generally exhibit a side lobe power level412that is reduced from the power level of main beam408. For example, in antenna pattern402, the side lobe power level412is about −15 dB relative to the power level of main beam408.

Referring toFIG. 2andFIG. 4, probe104is configured to receive, at its fixed position, at least a portion of beams122,124,126radiated from phased array antenna102. Because each of beams122,124,126is pointed to a corresponding rastor position in near-field128, the main lobe of each beam, e.g., main beam408, is not necessarily received by probe104. Rather, depending on the pointing angle in azimuth and/or elevation relative to the pointing angle of the fixed position of probe104, probe104may receive main beam408or one of side lobes410.FIG. 5is a diagram of near-field test system100illustrating main beam408steered to a rastor position502in near-field128. Rastor position502is defined in degrees azimuth and elevation, or pointing angles, one of which is illustrated inFIG. 5as pointing angle504defined relative to the position of probe104in near-field128. Accordingly, the power received at probe104is a function of pointing angle504, as shown on antenna pattern402inFIG. 4. Likewise, given a received power at probe104and a known pointing angle504, or a known rastor position502, the received power can be normalized and mapped to a far-field antenna pattern. In alternative embodiments, the received power can be scaled to produce a far-field antenna pattern by referencing received power to a gain standard determined based on a power measurement at a same distance as the far-field.

FIG. 6is a plot600of a wave front602directed at probe104. Wave front602is shown in power, expressed in decibels on a vertical axis604, versus pointing angle, expressed in degrees on a horizontal axis606. Wave front602includes, for example, beams122,124, and126shown inFIG. 2, each of which is aimed at a different pointing angle608,610, and612, respectively. Beam122is aimed at probe104and, accordingly, is referred to as having a pointing angle608of zero. Beams124and126have pointing angles610and612that are non-zero relative to the pointing angle of beam122, or are offset from probe104. Consequently, the power received by probe104from beams124and126is reduced from that of beam122, and can be expressed as a function of pointing angle. Because each of beams122,124, and126includes unique features, e.g., frequency, time, or coding, the power received at probe104can be divided among its components corresponding to those features. For example, probe104detects beam122with the greatest power, represented by a point614(illustrated as a triangle). Probe104detects beam124, aimed at pointing angle610, with a lesser power represented by a point616(illustrated as a square), and beam126, aimed at pointing angle612, with an even lesser power represented by a point618(illustrated as a circle).

FIG. 7is a plot700of a virtual antenna pattern702derived from power received at probe104from beams122,124, and126. Virtual antenna pattern702is shown in power, expressed in decibels on a vertical axis704, versus pointing angle, expressed in degrees on a horizontal axis706. More specifically, normalized power levels corresponding to points614,616, and618are plotted against their respective pointing angles608,610, and612to produce virtual antenna pattern702. Virtual antenna pattern702may also be referred to as a “snapshot” of the actual antenna pattern, which can be compared to an expected antenna pattern for the purpose of validating, for example, phased antenna array102and beam forming network108.

FIGS. 6 and 7illustrate three beams for clarity only. Concepts illustrated inFIGS. 6 and 7apply equally for any number of beams and for any number of antenna elements120in phased array antenna102.

FIG. 8is a diagram of near-field test system100illustrating a spherical phase taper applied to antenna elements120of phased array antenna102. For a given antenna element120, a path length802from the antenna element to probe104is a function of a probe distance804, D, or the distance from the center of the array of antenna elements120and probe104, and a distance806, di, of the ithantenna element120from the center of the array. More specifically, path length802is represented by √{square root over (D2+di2)}. Generally, the further a given antenna element120is from the center of the array, the longer its path length802. A longer path802manifests as a negative phase shift in the signal received at probe104. A spherical phase taper applied to the phase shifter304for each antenna element120focuses the energy at probe104by applying a positive phase shift as a function of the relative position of a given antenna element120. For example, a phase offset for the ith antenna element120, ∝i, is computed according to the following equation:

∝i⁢=2⁢πλ⁢(D2+di2-D)
where, λ is the wavelength of the beam.

FIG. 9is a diagram of near-field test system100illustrating a linear phase progression applied to antenna elements120of phased array antenna102to steer a radiated beam900to a pointing position in the near-field by directing the generated wave front by a given pointing angle, or scan angle. Near-field test system100is located in a Cartesian reference frame where phased array antenna102lies in an X-Y plane902and probe104is positioned in the near-field at probe distance804along a Z-axis904. Accordingly, a given antenna element120, or the ithantenna element120, is positioned at an x-y coordinate (xi, yi). The pointing angle for a given beam, generally expressed in azimuth and elevation angles, is translated to a polar coordinate system expressed as an angle, θ, defined between beam900and Z-axis904, and an angle, Φ, defined as an angle of rotation about Z-axis904, relative to an X-axis, of a projection of beam900onto X-Y plane902. The linear phase progression yields a phase shift, σi, to be added to spherical phase taper, ∝i, and applied by an ithphase shifter304for the ithantenna element120for beam900. The linear phase progression is computed according to the following equation:

FIG. 10is a flow diagram of a method1000of near-field testing of a phased array antenna, such as phased array antenna102shown inFIGS. 1 and 2, having an array of antenna elements120. Method1000includes steering1002test beam408to beam position502in near-field128of phased array antenna102. Test beam408is steered by applying a phase shift at phase shifters304corresponding to the test beam, where each phase shifter304also corresponds to an antenna element120in phased array antenna102. More specifically, the phase shift may be applied as a linear phase progression as a function of beam position502and the position of a given antenna element120relative to the center of the array of phased array antenna102.

Method1000further includes disposing1004probe104at a fixed position in near-field128. In certain embodiments, method1000may further include moving probe104to a second fixed position in near-field128to capture a second “snapshot” far-field antenna pattern.

Method1000includes phase shifting1006test beam408supplied to each antenna element120of phased array antenna102to apply a spherical phase taper across the array. The spherical phase taper is added to the phase shift applied to steer1002test beam408. The spherical phase taper forms the wave front radiated by phased array antenna102into a spherical wave front focused at the fixed position of probe104. The spherical phase taper equalizes the path length phase from each antenna element120of the array to probe104.

Method1000includes receiving1008at least a portion of test beam408at probe104. Test probe104receives at least some power from either a main lobe of beam408or from one of side lobes410. The received power is normalized1010based on beam position502relative to the fixed position of probe104. The far-field antenna pattern for phased array antenna102is generated1012from the normalized received power of test beam408.

FIG. 11is a graph1100of an example normalized received power1102, or virtual antenna pattern, measured by near-field testing system such as near-field testing system100shown inFIGS. 1 and 2, and a corresponding far-field antenna pattern1104, expressed in power, measured in the far-field for reference. Power is represented on a vertical axis1106and expressed in dB relative to a main beam power. Power is plotted versus scan angle shown on a horizontal axis1108and expressed in degrees relative to boresight. Generally, normalized received power1102matches the far-field antenna pattern1104, thereby validating near-field testing system100. The far-field antenna pattern1104features a main lobe1110and a plurality of side lobes1112.

FIG. 12is a block diagram of an example near-field test system1200for phased array antenna102. Near-field test system1200is similar to near-field test system100shown inFIG. 1, in that both can effectively test phased array antenna102, for example, for the purpose of validating far-field antenna patterns. However, where near-field test system100is configured to transmit one or more test beams from phased array antenna102toward probe104positioned in the near-field128, near-field test system1200is configured to transmit one or more test beams from probe104toward phased array antenna102. Accordingly, certain elements of near-field test system100are also used in near-field test system1200, and certain other elements of near-field test system1200are at least not shown in near-field test system100as illustrated, for example, inFIG. 1, or vice-versa.

Near-field test system1200includes computing system110, microcontroller112, phased array antenna102, and probe104positioned in the near-field128. Phased array antenna102is coupled to beam forming network108, which will process received signals from phased array antenna102in a functionally-reversed sequence as compared, for example, to the description of beam forming network108shown inFIG. 3.FIG. 13is a block diagram of near-field test system1200and beam forming network108shown inFIG. 12. In certain embodiments, for example, embodiments of beam forming network108using analog components, the same components of beam forming network108process both transmitted and received signals. However, in alternative embodiments, for example, certain embodiments of beam forming network108that use digital components, the transmit and receive paths through beam forming network108are distinct.

Generally, probe104transmits a test beam composed of multiple signals generated by signal generators106. Computing system110controls signal generators106to generate each signal with a unique feature, such as frequency, time, or coding. The signals are then combined by a beam summer1202before being emitted by probe104. As in near-field test system100shown inFIG. 1, the test beam is aimed at a fixed location, however, each antenna element120of phased array antenna102receives varying levels of power from each of the test beams components and, more specifically, reduced power as the position of a given receiving antenna element120moves away from the fixed location at which the test beam is aimed. For example, if the test beam is aimed at a central antenna element, power received at antenna elements120on the perimeter of phased array antenna102will generally receive less power than the interior antenna elements.

The test beam is received at antenna elements120and is directed into beam forming network108. In the functionally-reversed use case (i.e., receiving), beam forming network108produces a spectrum, or “virtual spectrum,” of signals corresponding to the original signals generated by signal generators106and having the corresponding unique features. The spectrum can be recorded as data in memory or, for example, can be viewed on computing system110or another computing system, such as a spectrum analyzer1204.

Beam forming network108, as stated above, may include common components for both the receive path and transmit path, or may include distinct components for the receive path and transmit path.FIG. 13illustrates beam forming network108functionally, and thus certain components are illustrated as distinct from those shown inFIG. 3. However, the functional aspects of certain components shown distinctly inFIGS. 3 and 13may be combined into a single device in certain implementations. For example, beam forming network108, as shown inFIG. 13, includes beam dividers1206that separate a beam received by a given antenna element120into its components by their respective unique features, e.g., by frequency, timing, or coding. Conversely, beam forming network108, as shown inFIG. 3, includes beam summers306that combine phase shifted beams into a single beam for emitting from a given antenna element120. In certain embodiments, beam summers306and beam dividers1206may be implemented by a single bidirectional component that performs the summing and dividing functions appropriately for transmitted and received signals, respectively. In alternative embodiments, beam summers306and beam dividers1206may be implemented as distinct components, each residing appropriately on the transmit path or the receive path of beam forming network108.

As described above, for a given antenna element120, a received beam is divided by beam dividers1206into its component signals based on their respective unique features. The component signals then pass through phase shifters304(also shown inFIG. 3). Phase shifters304adjust the phase of each signal to “steer” the beam. The original test beam radiated by probe104was aimed at the fixed location, however each antenna element120detects a distinct beam in phase and amplitude based on its position on phased array antenna102. Consequently, the signals that pass to phase shifters304are skewed in phase (and amplitude) from the original test beam. Thus, phase shifters adjust the phase of each signal to correct for that “steering” introduced by antenna elements120. Phase shifters304apply the same phase progressions and, in certain embodiments, spherical phase taper as in the transmit use case described above and shown inFIG. 3. Phase shifters304yield a plurality of signals that form a generally planar wave front.

Beam forming network108includes a plurality of beam summers1208, generally one for each unique feature, i.e., each signal, generated by signal generators106. Beam summers1208combine phase shifted signals from each antenna element120for a corresponding one of the unique features of the signals generated by signal generators106. For example, if the original test beam emitted by probe104is a composite of six signals generated by signal generators106, each having a unique frequency, all six signals are received at each antenna element120and divided into the six components by beam dividers1206. The six components from each antenna element120are then phase shifted appropriately for that antenna element120, and combined into six signals by beam summers1208. Accordingly, in this example, a virtual spectrum having six frequency components may be shown on spectrum analyzer1204.

FIG. 14is a plot1400of an example virtual spectrum1402, or “snapshot,” measured by near-field test system1200shown inFIGS. 12 and 13, and derived from a test beam radiated by probe104at phased array antenna102. Virtual spectrum1402is shown in power, expressed in decibels on a vertical axis1404, versus feature (e.g., frequency, timing, code) on a horizontal axis1406. In the example described above, signal generators106produce six signals, each having a unique frequency. Accordingly, for that example, virtual spectrum1402includes six signals1408,1410,1412,1414,1416, and1418having distinct frequencies as their respective unique features1420,1422,1424,1426,1428, and1430. Virtual spectrum1402may be displayed, for example, on spectrum analyzer1204.

FIG. 14illustrates six signals for clarity only. Concepts illustrated and described with respect toFIGS. 12-14apply equally for any number of signals and for any number of antenna elements120in phased array antenna102.

FIG. 15is a flow diagram of an example method1500of near-field testing of a phased array antenna, such as the phased array antenna102shown inFIGS. 12 and 13. Method1500begins with transmitting1502a test beam toward a fixed location on phased array antenna102from probe104at a fixed position in the near-field128of the phased array antenna102. In certain embodiments, probe104is coupled with a plurality of signal generators106and a beam summer1202. In such embodiments, each of the plurality of signal generators106produces a test signal having a unique feature, such as, for example, a unique frequency, a unique timing, or a unique coding. The plurality of test signals is then combined by beam summer1202into the test beam.

At least a portion of the test beam is received1504at each antenna element120. The received beams from each antenna element120are phase shifted1506to apply a spherical phase taper across the array to correct a spherical wave front detected by each antenna element120resulting from unequal path length phases from each antenna element120to probe104, thereby producing a planar wave front. The power of the received beams is combined1508by a beam summer1208.

In embodiments where multiple test signals are combined into the test beam, received beams from each antenna element120are separated by beam dividers1206into components according to the unique features of the test signals. For example, where the unique features of each test signal are unique frequencies, beam dividers1206separate received beams into frequency components, each received component being passed along to a different set of phase shifters304. Powers of the received components from each antenna element120are then combined by beam summers1208after phase shifting1506. Combined power is scaled1510and used to generate1512a virtual spectrum for the phased array antenna.

The technical effects of embodiments of the systems and methods described herein include, for example: (a) providing a near-field testing system with a single probe disposed at a fixed position in the near-field; (b) reducing the time, expense, and complexity of near-field testing by using a fixed probe position rather than mechanically scanning the probe over the face of the antenna under test; (c) electronically scanning multiple beams over a grid of rastor positions in the near-field to capture a single “snapshot” of the near-field power; (d) generating a far-field antenna pattern from near-field received power from the multiple beams normalized for each beam's rastor position relative to the fixed position of the probe; (e) generating a far-field antenna pattern without phase and amplitude measurements for each beam and without rastor scanning over the face of the array; (f) generating a far-field antenna pattern without two-dimensional Fourier transform to translate the near-field characterization to the far-field; and (g) applying a spherical phase taper over the antenna elements to generate a spherical wave front focused on the probe at the fixed position.

Some embodiments involve the use of one or more electronic processing or computing devices. As used herein, the terms “processor” and “computer” and related terms, e.g., “processing device,” “computing device,” and “controller” are not limited to just those integrated circuits referred to in the art as a computer, but broadly refers to a processor, a processing device, a controller, a general purpose central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, a microcomputer, a programmable logic controller (PLC), a reduced instruction set computer (RISC) processor, a field programmable gate array (FPGA), a digital signal processing (DSP) device, an application specific integrated circuit (ASIC), and other programmable circuits or processing devices capable of executing the functions described herein, and these terms are used interchangeably herein. The above embodiments are examples only, and thus are not intended to limit in any way the definition or meaning of the terms processor, processing device, and related terms.

In the embodiments described herein, memory may include, but is not limited to, a non-transitory computer-readable medium, such as flash memory, a random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), and non-volatile RAM (NVRAM). As used herein, the term “non-transitory computer-readable media” is intended to be representative of any tangible, computer-readable media, including, without limitation, non-transitory computer storage devices, including, without limitation, volatile and non-volatile media, and removable and non-removable media such as a firmware, physical and virtual storage, CD-ROMs, DVDs, and any other digital source such as a network or the Internet, as well as yet to be developed digital means, with the sole exception being a transitory, propagating signal. Alternatively, a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD), or any other computer-based device implemented in any method or technology for short-term and long-term storage of information, such as, computer-readable instructions, data structures, program modules and sub-modules, or other data may also be used. Therefore, the methods described herein may be encoded as executable instructions, e.g., “software” and “firmware,” embodied in a non-transitory computer-readable medium. Further, as used herein, the terms “software” and “firmware” are interchangeable, and include any computer program stored in memory for execution by personal computers, workstations, clients and servers. Such instructions, when executed by a processor, cause the processor to perform at least a portion of the methods described herein. The systems and methods described herein are not limited to the specific embodiments described herein, but rather, components of the systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein.

The systems and methods described herein are not limited to the specific embodiments described herein, but rather, components of the systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein.

For example embodiments of the systems and methods may include:

A near-field test system for a phased array antenna, the near-field test system comprising: a probe disposed at a fixed position in a near-field of the phased array antenna and configured to receive at least a portion of a test beam radiated by the phased array antenna; a beam forming network coupled to the phased array antenna and comprising a plurality of phase shifters configured to steer the test beam to a position in the near-field when radiated by an array of antenna elements of the phased array antenna; and a computing system coupled to the probe and configured to: scale received power of the test beam; and generate a far-field antenna pattern for the phased array antenna from scaled received power of the test beam.

The near-field test system above, wherein the computing system is further configured to normalize received power of the test beam based on the position of the beam in the near-field relative to the fixed position of the probe.

Any of the near-field test systems above, wherein the beam forming network further comprises: a plurality of phase shifters for each of a plurality of test beams, the plurality of test beams each having a unique feature, the plurality of phase shifters configured to steer the plurality of test beams to corresponding rastor positions in the near-field when radiated by the phased array antenna; and a plurality of beam summers corresponding to the array of antenna elements of the phased array antenna, the plurality of beam summers configured to combine the plurality of test beams to be radiated by each element of the array of antenna elements; and wherein the computing system is further configured to: normalize received power of each beam of the plurality of test beams based on the corresponding rastor position determined based on the unique feature of the beam, and generate the far-field antenna pattern for the phased array antenna from normalized received powers of the plurality of test beams.

Any of the near-field test systems above, wherein the plurality of phase shifters for each of the plurality of test beams is configured to apply a spherical phase taper across the array of antenna elements to generate a spherical wave front focused at the probe and equalize path length phase from each element of the array to the probe.

Any of the near-field test systems above, further comprising a plurality of signal generators coupled to the beam forming network and corresponding to the plurality of test beams, wherein each signal generator is configured to supply a beam signal having the unique feature to the plurality of phase shifters for a corresponding test beam.

Any of the near-field test systems above, wherein each of the plurality of signal generators is configured to generate the beam signal having a unique feature selected from the group consisting of: a unique frequency, a unique timing, and a unique code.

Any of the near-field test systems above, wherein the plurality of phase shifters is further configured to apply a linear phase progression across the array of antenna elements based on a distance from a center of the array to each element of the array to steer the plurality of test beams to the corresponding rastor positions.

A method, comprising: steering a test beam to a beam position in a near-field of a phased array antenna; disposing a probe at a fixed position in the near-field of the phased array antenna; phase shifting the test beam supplied to each element of an array of antenna elements of the phased array antenna to apply a spherical phase taper across the array to generate a spherical wave front focused at the probe and to equalize path length phase from each element of the array to the probe; receiving at least a portion of the test beam at the probe; scaling received power of the test beam; and generating a far-field antenna pattern for the phased array antenna from normalized received power of the test beam.

The method above, further comprising phase shifting the test beam to apply a linear phase progression across the array of antenna elements based on a distance from a center of the array to each element of the array to steer the test beam to the beam position.

Any of the methods above, further comprising: applying a linear phase progression to each of a plurality of test beams to steer the plurality of test beams to corresponding rastor positions in the near-field when radiated by the phased array antenna, the plurality of test beams each having a unique feature; summing the plurality of test beams for each element in the array of antenna elements; normalizing received power of each beam of the plurality of test beams based on the corresponding rastor position determined based on the unique feature of the beam; and generating the far-field antenna pattern for the phased array antenna from normalized received powers of the plurality of test beams.

Any of the methods above, further comprising generating a plurality of beam signals corresponding to the plurality of test beams having the unique feature, wherein the unique feature is selected from the group consisting of: a unique frequency, a unique timing, and a unique code.

Any of the methods above, further comprising comparing the far-field antenna pattern to an expected far-field antenna pattern to verify integrity of the phased array antenna and its beam forming network for all of the plurality of test beams.

Any of the methods above, further comprising: disposing the probe at a second fixed position in the near-field of the phased array antenna; and repeating the near-field testing of the phased array antenna to obtain signatures of at least one radiating property of the array of antenna elements.

Any of the methods above, wherein scaling comprises normalizing received power of the test beam based on the beam position relative to the fixed position of the probe.

A beam forming network for near-field testing of a phased array antenna, the beam forming network comprising: a plurality of phase shifters coupled to a signal generator, each configured to: receive a test beam from the signal generator, apply a corresponding phase shift to the test beam, and supply the test beam to an element of an array of antenna elements of the phased array antenna; and a microcontroller coupled to the plurality of phase shifters for controlling the corresponding phase shift of each element of the array, the microcontroller configured to: adjust the corresponding phase shift of each element to steer the test beam to a position in the near-field of the phased array antenna when radiated by the array, adjust the corresponding phase shift of each element to apply a spherical phase taper across the array to generate a spherical wave front focused at a probe disposed in the near-field of the phased array antenna and to equalize path length phase from each element of the array to the probe when the test beam is radiated by the array.

The beam forming network above, wherein the microcontroller is further configured to adjust the corresponding phase shift of each element to apply a linear phase progression across the array of antenna elements based on a distance from a center of the array to each element of the array to steer the test beam to the position in the near-field.

Any of the beam forming networks above, further comprising a plurality of beam summers corresponding to the array of antenna elements of the phased array antenna, the plurality of beam summers configured to combine a plurality of test beams to be radiated by each element of the array of antenna elements.

Any of the beam forming networks above, further comprising a plurality of phase shifters for each of the plurality of test beams, the plurality of test beams each having a unique feature, the plurality of phase shifters further configured to steer the plurality of test beams to corresponding rastor positions in the near-field when radiated by the phased array antenna.

Any of the beam forming networks above, wherein the microcontroller is further configured to be coupled to a computing system over a communication channel, wherein the computing system is coupled to the probe, and wherein the microcontroller is further configured to communicate the rastor positions of the plurality of test beams and the unique feature of each of the plurality of test beams to the computing system over the communication channel.

Any of the beam forming networks above, wherein the microcontroller is further configured to be coupled to a computing system over a communication channel, wherein the computing system is coupled to the probe, and wherein the microcontroller is further configured to communicate the position of the beam to the computing system over the communication channel.

A near-field test system for a phased array antenna, the near-field test system comprising: a probe disposed at a fixed position in a near-field of the phased array antenna and configured to transmit a test beam toward a fixed location on the phased array antenna; a beam forming network coupled to the phased array antenna and comprising: a plurality of phase shifters configured to steer received beams for each antenna element of the phased array antenna to form a planar wave front when radiated by the probe; and a beam summer coupled to the plurality of phase shifters and configured to combine power of the received beams; a computing system coupled to the beam forming network and configured to: scale combined power of the received beams; and generate a virtual spectrum for the phased array antenna from scaled power of the received beams.

The near-field test system above, wherein the computing system is further configured to normalize combined power of the received beams based on positions of corresponding antenna elements for the received beams on the phased array antenna relative to the fixed location to which the test beam is directed.

Any of the near-field test systems above, further comprising: a plurality of signal generators configured to generate a corresponding plurality of test signals, the plurality of test signals each having a unique feature; and a beam summer coupled to the plurality of signal generators and the probe, the beam summer configured to combine the plurality test signals into the test beam.

Any of the near-field test systems above, wherein the beam forming network further comprises: a beam divider for each antenna element of the phased array antenna, each beam divider configured to separate a received beam into received components corresponding to the unique feature for each of the plurality of test signals; a plurality of phase shifters for each of the plurality of test signals, the plurality of phase shifters configured to steer the received components of the received beam to form the planar wave front; and a plurality of beam summers corresponding to the plurality of test signals, the plurality of beam summers configured to combine power of the received components for each of the plurality of test signals; wherein the computing system is further configured to: normalize combined power of received components for each of the received beams based on the position of corresponding antenna elements for the received beams on the phased array antenna relative to the fixed location to which the test beam is directed; and generate the virtual spectrum for the phased array antenna from normalized combined powers of the plurality of test signals.

Any of the near-field test systems above, wherein the plurality of phase shifters for each of the plurality of test signals is configured to apply a spherical phase taper across the array of antenna elements to correct a spherical wave front detected by each antenna element of the phased array antenna resulting from unequal path length phases from each antenna element to the probe.

Any of the near-field test systems above, wherein each of the plurality of signal generators is configured to generate the beam signal having a unique feature selected from the group consisting of: a unique frequency, a unique timing, and a unique code.

Any of the near-field test systems above, wherein the plurality of phase shifters is further configured to apply a linear phase progression across the array of antenna elements based on a distance from a center of the array to each element of the array to steer the received beams to form a planar wave front.

Any of the near-field test systems above, wherein the computing system comprises a spectrum analyzer configured to measure power of the received beams.

A method of near-field testing of a phased array antenna having an array of antenna elements, the method comprising: transmitting a test beam toward a fixed location on the phased array antenna from a probe at a fixed position in the near-field of the phased array antenna; receiving at least a portion of the test beam at each antenna element; phase shifting received beams from each antenna element to apply a spherical phase taper across the array to correct a spherical wave front detected by each antenna element resulting from unequal path length phases from each antenna element to the probe, thereby producing a planar wave front; combining power of the received beams; scaling combined power of the received beams; and generating a virtual spectrum for the phased array antenna from scaled power of the received beams.

The method above, further comprising phase shifting the received beams to apply a linear phase progression across the array of antenna elements based on a distance from a center of the array to each element of the array to steer the received beams to form a planar wave front.

Any of the methods above, further comprising: generating a plurality of test signals having unique features; and combining the plurality test signals into the test beam.

Any of the methods above, further comprising: dividing a received beam from each antenna element into received components corresponding to the unique feature for each of the plurality of test signals; applying a linear phase progression to the received beams to steer the received components of each received beam to form the planar wave front; and combining power of the received components from each antenna element for each of the plurality of test signals; normalizing combined power of received components for each of the received beams based on positions of corresponding antenna elements for the received beams on the phased array antenna relative to the fixed location to which the test beam is directed; and generating the virtual spectrum for the phased array antenna from normalized combined powers of the plurality of test signals.

Any of the methods above, wherein generating the plurality of test signals comprises generating the plurality of test signals having a unique feature selected from the group consisting of: a unique frequency, a unique timing, and a unique code.

Any of the methods above, further comprising comparing the virtual spectrum to an expected spectrum to verify integrity of the phased array antenna and its beam forming network for all of the plurality of test signals.

Any of the methods above, further comprising: disposing the probe at a second fixed position in the near-field of the phased array antenna; and repeating the near-field testing of the phased array antenna to obtain signatures of at least one receiving property of the array of antenna elements.

Any of the methods above, wherein scaling comprises normalizing combined power of the received beams based on positions of corresponding antenna elements for the received beams on the phased array antenna relative to the fixed location to which the test beam is directed.

A beam forming network for near-field testing of a phased array antenna, the beam forming network comprising: a plurality of phase shifters coupled to respective antenna elements of the phased array antenna, each phase shifter configured to: receive a received beam from the respective antenna element, apply a corresponding phase shift to the received beam, and supply the received beam to a beam summer; and a microcontroller coupled to the plurality of phase shifters for controlling the corresponding phase shift of each element of the array, the microcontroller configured to adjust the corresponding phase shift of each element to apply a spherical phase taper across the array to correct a spherical wave front detected by each antenna element resulting from unequal path length phases from each antenna element to a probe from which a test beam originated, thereby producing a planar wave front.

The beam forming network above, wherein the microcontroller is further configured to adjust the corresponding phase shift of each element to apply a linear phase progression across the array of antenna elements based on a distance from a center of the array to each element of the array to steer the received beams to form a planar wave front.

Any of the beam forming networks above, further comprising a plurality of beam dividers corresponding to the array of antenna elements of the phased array antenna, the plurality of beam summers configured to separate a received beam into received components corresponding to a unique feature for each of a plurality of test signals combined into a test beam received by the array of antenna elements.

Any of the beam forming networks above, further comprising a plurality of phase shifters for each of the plurality of test signals, the plurality of test signals each having a unique feature, the plurality of phase shifters further configured to steer the received components of the received beam to form the planar wave front.

As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or steps unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present disclosure or “an example embodiment” are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. To the extent the terms “includes,” “including,” “has,” “contains,” and variants thereof are used herein, such terms are intended to be inclusive in a manner similar to the term “comprises” as an open transition word without precluding any additional or other elements.