Claims:1. A method for calibrating an active phased array antenna in a radar system, the method comprising:
receiving, by each of analog-to-digital converters (ADCs), signal of a predefined amplitude through multiple calibration channels;
determining amplitude and phase of the signal received by each of the ADCs;
determining calibration factor for each of the channel; and
adjusting each of the channels using the determined calibration factors digitally by applying correction factors to the received signals.
2. The method as claimed in claim 1, wherein adjustment of each of the channel is done before performing beam forming on a field programmable grid array based hardware, and wherein the received signal is intermediate frequency (IF) signal.
3. The method as claimed in claim 1, wherein the correction factors adjust phase of the received signals.
4. The method as claimed in claim 1, wherein the correction factors adjust the amplitude of the received signals, and wherein the correction factors are generated in complex form, and wherein the correction factors are multiplied by the IF signal for correction.
5. The method as claimed in claim 1, wherein phases of the channel are brought to 0 deg. by subtracting the corresponding phases of each channel during calibration.
6. A system for calibrating an active phased array antenna in a radar system, the system comprising:
one or more analog-to-digital converters (ADCs) configured to receive signal through multiple calibration channels to convert analog signal to digital signal;
one or more digital down-converters (DDCs) operatively coupled to an output end of the one or more ADCs;
one or more calibration units operatively coupled to an output end of the one or more DDCs; and
one or more digital beam former units coupled to an output end of the one or more calibration units.
7. The system as claimed in claim 6, wherein the one or more ADCs are configured to compute calibration coefficients for amplitude and phase calibration of the received signal in digital domain, and wherein the received signal is intermediate frequency (IF) signal.
8. The system as claimed in claim 6, wherein the one or more DDCs are configured to convert a digitized, band limited signal to lower frequency signal at lower sampling rate, wherein each of the one or more DDCs comprises a direct digital synthesizer (DDS), a low-pass filter (LPF) and a downsampler.
9. The systems as claimed in claim 6, wherein the one or more calibration units are configured to align phase and gain of the channels, and wherein calibration is done for amplitude and phase to compensate mismatches across the channels.
10. The system as claimed in claim 6, wherein in DBF unit is adjusted to reduce the errors introduced by the antenna elements, and wherein in the DBF unit complex weights of both amplitude and phase are applied to the baseband signal, and results are summed up to produce baseband signal with desired directional pattern.

, Description:TECHNICAL FIELD
[0001] The present disclosure relates to a system and method for calibrating an active phased array antenna before beamforming in a radar system.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art
[0003] Active phased array antennas are well known for their capability to steer the beam electronically with minimum side-lobe levels and with high resolution beam width. Now a day, active phased array radars are progressing towards digital hardware and digital beam former is one of the important sub systems in the receiver. These systems are capable of carrying out antenna system real-time calibration in the digital domain. Therefore, amplitude and phase matching can relax the requirements for a close match of amplitude and phase between transceivers, because variation in these parameters can be corrected in real time.
[0004] For multichannel receiver and digital beam former, it is very critical that all channels are phase and gain aligned. However, considerable amplitude and phase difference among the channels can occur due to the different RF (radio-frequency) hardware connected to each antenna element. Characteristics of most RF devices depend on the frequency and temperature and vary with time. For successful beam shaping and scanning in phased array radars, it is essential to precisely set the amplitude and phase of each element channel. In order to equalize the phase and amplitude effects of the channels, phased array radars need to be calibrated periodically.
[0005] The measurements are repeated at different frequencies that the radar is required to operate. For calibration, it may not be necessary to measure the actual phase/amplitude responses of each channel. Since the input signals are equal, then calibration can be done by simply measuring the output signals relative to each other and matching inter channel phases and amplitudes.
[0006] Therefore, there is need in the art to provide a simple and efficient system and method for digital down conversion, online calibration for phase and gain matching and digital beam former for active phased array radars.

OBJECTS OF THE PRESENT DISCLOSURE
[0007] Some of the objects of the present disclosure, which at least one embodiment herein satisfies are as listed herein below.
[0008] It is an object of the present disclosure to provide a simple and efficient solution which can overcome the limitations of the prior art.
[0009] It is an object of the present disclosure to provide a system and method for online calibration and receive digital beam formation in a radar system.
[0010] It is an object of the present disclosure to provide a system and method for calibrating an active phased array antenna in a radar system.
[0011] It is an object of the present disclosure to provide a simple and efficient system and method which can be easily implemented for calibrating an active phased array antenna before beamforming in a radar system.
[0012] It is an object of the present disclosure to provide an improved multichannel digital receiver and digital beamformer.
[0013] These and other objects of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.

SUMMARY
[0014] The present disclosure relates to a system and method for calibrating an active phased array antenna before beamforming in a radar system.
[0015] In an aspect, the present disclosure provides a method for calibrating an active phased array antenna before beamforming in a radar system, the method can include: receiving, by each of analog-to-digital converters (ADCs), analog signal of a predefined amplitude through multiple calibration channels simultaneously; determining/computing amplitude and phase of the signal received by each of the ADCs; determining/computing calibration factor for each of the channel; and adjusting each of the channels using the determined calibration factors digitally by applying correction factors to the received signals.
[0016] In an embodiment, the antenna array includes a number of transmitting antenna elements.
[0017] In an embodiment, the received signal is intermediate frequency (IF) signal.
[0018] In an embodiment, adjustment of each of the channel is done before performing beam forming on a field programmable grid array based hardware.
[0019] In an embodiment, the correction factors can adjust phase of the received signals.
[0020] In an embodiment, the correction factors can adjust the amplitude of the received signals.
[0021] In an embodiment, the correction factors can be generated in complex form.
[0022] In an embodiment, the correction factors can be multiplied by the IF signal for correction.
[0023] In an embodiment, the phases of the channel can be brought to 0 deg. by subtracting the corresponding phases of each channel during calibration.
[0024] In another aspect, the present disclosure provides a system for calibrating an active phased array antenna in a radar system, the system can include one or more analog-to-digital converters (ADCs) configured to receive signal through multiple calibration channels to convert analog signal to digital signal; one or more digital down-converters (DDCs) operatively coupled to an output end of the one or more ADCs; one or more calibration units operatively coupled to an output end of the one or more DDCs; and one or more digital beam former units coupled to an output end of the one or more calibration units.
[0025] In an embodiment, the one or more ADCs can be configured to compute calibration coefficients for amplitude and phase calibration of the received signal in digital domain
[0026] In an embodiment, the received signal is intermediate frequency (IF) signal.
[0027] In an embodiment, the one or more DDCs can be configured to convert a digitized, band limited signal to lower frequency signal at lower sampling rate. In an embodiment, the digital down conversion can be done individually after phase and amplitude calibration across the channels.
[0028] In an embodiment, the each of the one or more DDCs can include a direct digital synthesizer (DDS), a low-pass filter (LPF) and a downsampler.
[0029] In an embodiment, the one or more calibration units can be configured to align phase and gain of the channels.
[0030] In an embodiment, the DBF unit can be adjusted to reduce the errors introduced by the antenna elements. In the DBF unit complex weights of both amplitude and phase are applied to the baseband signal, and results are summed up to produce baseband signal with desired directional pattern.
[0031] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. The diagrams are for illustration only, which thus is not a limitation of the present disclosure.
[0033] FIG. 1 illustrates an exemplary block diagram of the proposed system for calibrating an active phased array antenna in a radar system, in accordance with embodiments of the present disclosure.
[0034] FIG. 2 illustrates an exemplary block diagram representation of calibration procedure of the proposed system, in accordance with embodiments of the present disclosure.
[0035] FIG. 3 illustrates an exemplary flow diagram of the proposed method for calibrating an active phased array antenna before doing beamforming in a radar system, in accordance with embodiments of the present disclosure.
[0036]
[0037] FIG. 4A illustrates exemplary simulated waveforms at ADC output before phase calibration, and FIG.4B illustrates aligned data of all channels after running online calibration, in accordance with embodiments of the present disclosure.
[0038] FIG. 5 illustrates an exemplary graphical representation of the beam pattern achieved after calibration in the RADAR system, in accordance with embodiments of the present disclosure.
[0039] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION
[0040] In the following description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. It will be apparent to one skilled in the art that embodiments of the present invention may be practiced without some of these specific details.
[0041] If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[0042] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0043] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0044] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.
[0045] Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those of ordinary skill in the art. Moreover, all statements herein reciting embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure).
[0046] Embodiments explained herein relate to a system and method for calibrating an active phased array antenna before beamforming in a radar system.
[0047] In an aspect, the present disclosure provides an improved multichannel digital receiver and digital beamformer for a radar system that can include multichannel analog-to-digital converters (ADCs) to receive anolg intermediate frequency (IF) signal. This led to realisation of computationally intensive software in single field-programmable gate array (FPGA) using Multiplexing and Demultiplexing technique which reduced hardware resource requirements drastically. Digital Down conversion and Digital Beam Formation can be done in a simple, efficient and cost effective manner. Each element is digitally controlled for phase and gain matching using a receive beam calibration software modules resulting in higher accuracy and flexibility of the system. Complex weight selection for modifying array beam pattern to enhance the reception of desired signal while simultaneously suppressing interfering signals is done in such a way that the resource utilization can be minimal.
[0048] In another aspect, a method of phase and amplitude calibration is disclosed wherein known single frequency is added to the analog-to-digital converters and compensation is done after down conversion wherein signal is brought to base band signal with in- phase and quadrature phase components.
[0049] In another aspect, in the method disclosed, complex calibration coefficients can be computed using simulated beat frequency after down conversion and these coefficients are used in the DBF for compensating the errors in the phase and gain across different channels.
[0050] FIG. 1 illustrates an exemplary block diagram of the proposed system for calibrating an active phased array antenna in a radar system, in accordance with embodiments of the present disclosure. In an embodiment, for multiple receive channels, intermediate frequency (IF) signal is passed through multiple analog-to-digital converters (ADCs) and Digital Down Conversion is done individually after phase and amplitude calibration across the channels.
[0051] In an embodiment, the ADCs at block a 102 is used to convert received Analog IF signal to digital signal. Here, multichannel analog inputs can be converted to respective multichannel digital outputs.
[0052] In an embodiment, digital down-converter (DDC) at the block 104 is operatively coupled to an output end of the ADCs. The DDC is configured to converts a digitized, band limited signal to lower frequency signal at lower sampling rate. The DDC can include three subcomponents including a DDS (Direct Digital Synthesizer), a low-pass filter(LPF) and a Downsampler (decimate).
[0053] In an embodiment, the DDS can generate a complex sinusoid at the intermediate frequency (IF). Multiplication of intermediate frequency with ADC input signal can create images centered at the sum and difference frequency. The low pass filter may pass the difference (i.e. Baseband) frequency and then it is Downsampled so that it can be conveniently used in further stages.
[0054] In an embodiment, a calibration unit at block 106 is operatively coupled to an output end of the DDC. The calibration unit input to Digital Beam Former (DBF) at block 110 through multiplier at block 108. The DBF can be adjusted to reduce the errors introduced by the antenna elements. In DBF block, the complex weights of both amplitude and phase can be applied to the baseband signal, and the results can be summed up to produce baseband signal with desired directional pattern.
[0055] In an embodiment, known single frequency can be added to ADC and compensation can be done after down conversion wherein signal is brought to base band signal with in- phase and quadrature phase components.
[0056] In an embodiment, complex calibration coefficients can be computed using simulated beat frequency after down conversion, and these coefficients are used in the DBF for compensating the errors in the phase and gain across different channels.
[0057] In an exemplary embodiment, the disclosed system can be based on a single FPGA using Multiplexing and Demultiplexing technique which may reduce hardware resource requirements drastically.
[0058] In an exemplary embodiment, detailed calibration procedure for any ‘N’ channel Radar is explained herein below, as shown in FIG. 2. The calibration procedure can be adapted for any ‘N’channels of IF entering DBF hardware. The disclosed procedure can be implemented on (FPGA) a field-programmable gate array based hardware using System Generator modules of MUX (Multiplexer) and Arc_Tan.
[0059] In an embodiment, in amplitude calibration mode, all ADC channels can be fed a known simulated input signal. In order to find out the amplitude difference of each channel from the known data, calibration values are computed for all input channels by dividing known signal value with magnitude of each ADC channel. Amplitude is computed for each channel and normalised to get the ‘N’ Cal values where ‘N’ is number of channels. This is done to bring all channels to signal level as expected i.e, equal to known simulated signal given.
[0060] In an embodiment, amplitude Cal factor can computed by the below formula when known signal fed is 0dBm :

[0061] Numerator in above Formula can be modified depending upon the value of the known signal entering ADC. Calibration factors for all channels are computed in this mode and stored in the look up table.
[0062] In an embodiment, phase calibration values can be computed by finding the phase of each ADC channel using the below formula:
=O°

[0063] All ADC channels can be compensated to bring phase of all channels to zero degree. This can be done by negating the calculated O° and storing it as phase calibration value i.e -O° channel wise.
[0064] Both phase (-O°) and amplitude (ß) calibrated values are used for multiplication with I and Q data before doing digital beam forming.
Cal Coefficients :
DDC output (After Calibration) : DDC output * Cal output
*

I Data(calibrated):
Q Data(calibrated):
[0065] As given in above equation, amplitude and phase can be calibrated with new amplitude and phase values as and respectively.
[0066] Referring to FIG. 2, N channels of DDC output of I and Q is fed to the Arc_Tan block via a Mux to calculate the phase. The phase obtained is converted to the range +180 degree to -180 degree and negated to compensate the phase variations across the channels. Negated phase values can be multiplied by Sin and Cos block to convert into standard complex form.
[0067] For amplitude Calibration, values are computed using formula as explained earlier. Then both phase and amplitude of respective I & Q values is fed to Multiplier block followed by Demultiplexer block to get I & Q calibrated values for all channels. Phase and gain matched channels are fed to the digital beam forming module for multiplication with the complex coefficients to generate multiple beams.
[0068] FIG. 3 illustrates an exemplary flow diagram of the proposed method for calibrating an active phased array antenna before doing beamforming in a radar system, in accordance with embodiments of the present disclosure. In an embodiment, the disclosed method 300 can include at a step 302, receiving, by each of analog-to-digital converters (ADCs), analog signal of a predefined amplitude through multiple calibration channels simultaneously, at step 304 determining/computing amplitude and phase of the signal received by each of the ADCs; determining/computing calibration factor for each of the channels; and at step 308, adjusting each of the channels using the determined calibration factors digitally by applying correction factors to the received signals.
[0069] In an embodiment, the antenna array includes a number of transmitting antenna elements.
[0070] In an embodiment, the received signal is intermediate frequency (IF) signal.
[0071] In an embodiment, adjustment of each of the channel is done before performing beam forming on a field programmable grid array based hardware.
[0072] In an embodiment, calibration of multichannel analog signals for catering to different spot frequencies can be done as per the radar property/ specifications.
[0073] In an exemplary embodiment, the disclosed method can be implemented by computationally intensive software module that can be realised on a single FPGA using Multiplexing and Demultiplexing technique with minimal resource utilization.
[0074] In an embodiment, the correction factors can adjust phase of the received signals.
[0075] In an embodiment, the correction factors can adjust the amplitude of the received signals.
[0076] In an embodiment, the correction factors can be generated in complex form.
[0077] In an embodiment, the correction factors can be multiplied by the IF signal for correction.
[0078] In an embodiment, the phases of the channel can be brought to 0 deg. by subtracting the corresponding phases of each channel during calibration.
[0079] FIG. 4A shows Simulated Waveforms at ADC output before Phase calibration. FIG. 4A shows the data captured at the ADC for multiple channels before calibration wherein phase and amplitude are not aligned. FIG 4B shows aligned data of all channels after running online calibration/after running calibration unit. Phase and gain of all channels are aligned as shown in FIG. 4B.
[0080] FIG. 5 illustrates an exemplary graphical representation of the beam pattern achieved after calibration in the RADAR system, in accordance with embodiments of the present disclosure. As shown in FIG. 5, it is observed that strength of beams are gradually reducing as expected.
[0081] Thus, it will be appreciated by those of ordinary skill in the art that the diagrams, schematics, illustrations, and the like represent conceptual views or processes illustrating systems and methods embodying this invention. The functions of the various elements shown in the figures may be provided through the use of dedicated hardware as well as hardware capable of executing associated software. Similarly, any switches shown in the figures are conceptual only. Their function may be carried out through the operation of program logic, through dedicated logic, through the interaction of program control and dedicated logic, or even manually, the particular technique being selectable by the entity implementing this invention. Those of ordinary skill in the art further understand that the exemplary hardware, software, processes, methods, and/or operating systems described herein are for illustrative purposes and, thus, are not intended to be limited to any particular named.
[0082] While embodiments of the present invention have been illustrated and described, it will be clear that the invention is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to those skilled in the art, without departing from the spirit and scope of the invention, as described in the claim.
[0083] In the foregoing description, numerous details are set forth. It will be apparent, however, to one of ordinary skill in the art having the benefit of this disclosure, that the present invention may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form, rather than in detail, to avoid obscuring the present invention.
[0084] As used herein, and unless the context dictates otherwise, the term "coupled to" is intended to include both direct coupling (in which two elements that are coupled to each other contact each other)and indirect coupling (in which at least one additional element is located between the two elements). Therefore, the terms "coupled to" and "coupled with" are used synonymously. Within the context of this document terms "coupled to" and "coupled with" are also used euphemistically to mean “communicatively coupled with” over a network, where two or more devices are able to exchange data with each other over the network, possibly via one or more intermediary device.
[0085] It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refers to at least one of something selected from the group consisting of A, B, C …. N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.
[0086] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE PRESENT DISCLOSURE
[0087] The present disclosure provides a simple and efficient solution which can overcome the limitations of the prior art.
[0088] The present disclosures provide system and method for online calibration and receive digital beam formation in a radar system.
[0089] The present disclosure provides a system and method for calibrating an active phased array antenna in a radar system.
[0090] The present disclosure provides a simple and efficient system and method which can be easily implemented for calibrating an active phased array antenna before beamforming in a radar system.
[0091] The present disclosure provides an improved multichannel digital receiver and digital beamformer.