Nearfield testing architecture

An open architecture design for a digital nearfield test system for nearfield testing of a phased array antenna allows the ability to use the components of an individual phased array antenna to be tested in conjunction with a nearfield scanner probe system allowing an efficient and cost-saving “radar testing the radar” scenario.

FIELD OF THE INVENTION

The present invention relates to nearfield testing of phased array RADAR.

BACKGROUND

Traditionally, when a phased array antenna is tested using a planar nearfield scanner, RF equipment is used to receive RF from an Array Under Test (“AUT”) or transmit RF to the AUT. In order to establish a concise reference point for obtaining the key phase and amplitude deltas for determining AUT performance, the equipment is configured in such a manner that establishes a reference point at the nearfield probe and a reference point at the AUT. Typically these points are established by placing a mixer in line and using a local oscillator to phase lock the points together. During nearfield scanning measurements, data is acquired via a RF receiver where amplitude and phase measurements are determined by the delta between the reference and test points. After the entire active aperture has been scanned and data collected, the data is post processed via a Fourier Transform to obtain a pattern of the farfield energy in visible space. This method works for phased arrays that use analog beamforming.

As phased arrays become more advanced, analog beamforming has evolved into digital beamforming, that is the traditional analog beamforming networks have been replaced by digital equipment. Analog receivers and exciters have been replaced by digital receivers and exciters which greatly improve key phased array performance parameters such as signal to noise, beamforming error elimination, and clutter attenuation aided by decorrelation.

The change to digital beamforming, however, has introduced new challenges in the nearfield test methodology. When a digital array transmits to the nearfield scanner probe, a digital word is translated by the exciter digital-to-analog converter and transmitted as RF to the nearfield scanner probe. When the digital array receives from the nearfield scanner probe, an analog-to-digital converter on the digital receiver converts the analog data to digital data comprising in-phase and quadrature-phase (I/Q) data components. This I/Q data stream is then bussed to various data processing locations within the phased array radar system. In existing nearfields, the nearfield scanner probe uses an analog receiver and exciter (RxEx). The existing nearfields thus have the cumbersome problem of having to correlate digital I/Q data from the digital array with analog RF data of the nearfield scanner probe.

This disclosure describes a new method of scanning a digital beamformed phased array in a nearfield by creating an open architecture approach to replacing the analog reference points with digital reference points and the ability to perform measurements.

SUMMARY OF THE INVENTION

In one aspect of the present invention, an open architecture design for a digital nearfield test system architecture for nearfield testing of a digital phased array antenna under test is disclosed, wherein the digital phased array antenna comprises a digital receiver/exciter and an onboard processor. The digital nearfield testing architecture comprises a digital nearfield scanner probe system comprising a nearfield scanner probe connected to the digital receiver/exciter and the onboard processor, wherein when the phased array antenna under test is in transmit mode, the nearfield scanner probe detects RF signal from the phased array antenna under test and sends detected RF Rx data to the digital receiver/exciter, and when the phased array antenna under test is in receive mode, the digital receiver/exciter generates and sends RF Tx data to the digital nearfield scanner probe which then transmits an RF signal to the phased array antenna under test which generates digital I/Q data. The digital nearfield testing architecture also includes a data processing and array control unit, wherein the digital receiver/exciter and the onboard processor formats the RF Rx data from the digital nearfield scanner probe and bus the RF Rx data back to the nearfield data processing and array control unit, and a local oscillator distribution network for synchronizing operations of the components of the digital nearfield architecture. The digital nearfield scanner probe system correlates the digital RF Tx and Rx data to the digital I/Q data from the phased array antenna under test.

The benefit of the present invention is the ability to use the digital Receiver/Exciter (DRx/Ex40inFIG. 2) and the processor (the processor50inFIG. 2) from an individual AUT and hook them up to a scanner probe to create a “radar testing the radar” scenario.

DETAILED DESCRIPTION

According to the present disclosure, in order to alleviate the problem of correlating digital I/Q data from the digital phased array with analog RF data of the nearfield scanner probe in the prior art nearfield phased array test architecture, the conventional RF subsystems containing the RF components necessary to perform RF data collection loops in phased array systems are replaced with a digitized RF subsystem to create a “bits-in-bits-out” solution.FIG. 1shows a high level schematic block diagram of an embodiment of such a digitized RF subsystem10. The RF subsystem10includes a digital phased array under test (“DAUT”)30and a nearfield scanner probe20for illuminating the DAUT during testing, where the digital nearfield scanner probe20along with its scanner probe equipment25(seeFIG. 2) creates a “bits-in-bits-out” nearfield test system. The “bits-in-bits-out” system is achieved by the digital nearfield architecture100shown inFIG. 2.

Referring toFIG. 2, the digital nearfield architecture100according to an embodiment of the present disclosure comprises a digital phased array system that includes the DAUT30, a data processing and array control unit60, a digital receiver/exciter (“DRx/Ex”)40and an onboard processor50. The digital nearfield architecture100also comprises a digital nearfield scanner probe system22. The digital nearfield scanner probe system22includes the nearfield scanner probe20and scanner probe equipment25that supports the operation of the nearfield scanner probe20during testing. According to the present disclosure, the scanner probe equipment25comprises the already existing components of the digital phased array system, the DRx/Ex40and the associated onboard processor50.

The digital nearfield architecture100also includes a local oscillator distribution network70, a local oscillator synthesizer75, a low noise central source80and a system reference85for synchronizing the operation of all components of the digital nearfield architecture100. The local oscillator synthesizer75creates the local oscillator signal used for RF mixing. The digital nearfield architecture100further includes a Digital Distribution35for distributing logic and data signals through the device under test. Different DAUTs have different distribution system.

InFIG. 2, the arrow120between the nearfield scanner probe20and a digital receiver/exciter (“DRx/Ex”)40represents both the transmit (“Tx”) and receive (“Rx”) RF data exchanged between the nearfield scanner probe20and the DRx/Ex40. The arrow125schematically represents the RF signal paths for both the Tx and Rx RF signals exchanged between the DAUT30and the nearfield scanner probe20. For example, when the DAUT30is in Tx mode and transmits RF signals, the nearfield scanner probe20receives the RF signal125and sends the detected RF Rx data120to the DRx/Ex40. When the AUT30is in Rx mode, the DRx/Ex40generates and sends RF Tx data120to the nearfield scanner probe20which then transmits an RF signal125to the DAUT30which generates digital I/Q data110. The digital I/Q data110is sent to the data processing and array control unit60of the DAUT30for further processing. The data processing and array control unit60is a data processing repository configured with various types of high speed and low speed processors and data storage devices.

Regardless of whether the nearfield scanner probe20is in Rx or Tx mode, the digital nearfield scanner probe system22correlates the digital RF Tx/Rx data to the digital I/Q data110from the DAUT30. The digital-to-digital correlation of the two data streams is enabled by interfacing a digital receiver/exciter (“DRx/Ex”)40and an onboard processor50to format the Rx signal120from the nearfield scanner probe20and bus the data back to the nearfield data processing and array control station60. The onboard processor50onboard the scanner probe equipment25would do the first stage of processing, that is, convert the RF signal to a digital signal. The data processing and array control unit60would then be in charge of correlating those digital data points to array data, essentially being the keeper of all data. The signals from the scanner probe's onboard processor50is correlated with the array data. Preferably, the DRx/Ex40connected to the nearfield scanner probe20implements the exact Rx function within the DAUT30when the DAUT is in Tx mode, and vice versa when the DAUT30is in Rx mode.

The digital nearfield architecture100allows for the inclusion of an RF signal drift monitor loop130to inject RF signal back onto the nearfield scanner probe's DRxEx40itself. By interleaving this drift measurement from the drift monitor loop130with the DAUT measurement during the testing of the DAUT30, the error/drift in the nearfield scanner probe's DRxEx40could be monitored and/or subtracted out of the measurement.

The DAUT30and the DRxEx40at the nearfield scanner probe20are tied to the system local oscillator distribution network70which is fed from a single low noise central source80. All timing synchronization is handled by the system reference85allowing all equipment and data recording to be in synch with each other creating a digital closed loop architecture.

Setting the Reference and Measuring

One of the challenges facing the development of a digital nearfield is the ability to set the correct reference point to derive phase and amplitude deltas between the DAUT30and the nearfield scanner probe20. These deltas are what are used to form a nearfield pattern and eventually a farfield pattern to assess phased array pattern performance of the DAUT30. In the digital nearfield system architecture100of the present disclosure, a digital reference point can be set at the nearfield scanner probe20during synchronization of the digital equipment using the DRxEx40. A correct reference point is necessary to derive phase and amplitude deltas between the AUT30and the nearfield scanner probe20. Once the reference point is established, the drift monitor loop130in the DRxEx40, will sample the I/Q data110at each dwell, i.e. a test event or a command execution in which a set of data points is captured. Conversely, a dedicated calibration channel on the DAUT30will have an identical loopback sampling the reference I/Q data established at the DAUT.

With the reference points established, the measurement process can take place by sampling data in the same manner as a traditional nearfield system would. As shown inFIG. 3, for the DAUT receive case, the nearfield scanner probe20is used to scan the active aperture32of the DAUT30where the active aperture32is defined into a planar data collection grid of (X1. . . Xn)/(Y1. . . Yn). The nearfield scanner probe20assembly is mounted on a scanner track22that is used to scan the nearfield scanner probe20through each X/Y grid position on the active aperture32.

As depicted in the high level illustration inFIG. 4, at each X/Y sampling position, the X/Y position data is fed back to the nearfield data processing and array control station60in real-time, a sample measurement is taken for each beam steer and frequency (dwell data), X/Y location, DAUT I/Q data, DAUT reference I/Q data, and Test reference I/Q data are stored in a data recorder90. Each sample point is tagged with an ID and all of the data is correlated by the data recorder90. Since everything is digital, the data recorder90can be configured to be able to take in the data and use a matrix to store and cross correlate the incoming data as shown inFIG. 4. A post processing workstation95can then locate and process the desired data set. The post processing workstation95is networked to access the data stored in the recorder90in non-real-time and post process the data to perform analysis and pattern synthesis.

The benefit of the digital nearfield architecture100is its open architecture which allows the nearfield scanner system to be fitted with specific DAUT performance hardware described herein. The openness of the architecture being referred to here is the ability of the digital nearfield architecture100to use a piece of the radar itself to test the radar rather than using additional off-the-shelf equipment. If the DAUT can be hooked into the nearfield system, then, any system can do the same operation. Due to the ever changing needs of various radar and phased array programs, the open architecture of the digital nearfield architecture100demonstrates the ability to integrate the hardware required to meet the specific performance needs of the radar system without purchasing new equipment as technology evolves. Since all that is required is the ability to capture and reference I/Q data, the burden of being limited by analog receivers/exciters is eliminated.

The open architecture of the digital nearfield architecture provides a clean and cost savings approach to testing a digital phased array. By integrating DAUT specific equipment into the nearfield system, the method of scanning remains the same. Only the data acquisition and manipulation is altered. Some of the improvements over the conventional analog nearfield testing architectures include: better accuracy via elimination of RF cable phase modulation with scanner motion; higher signal-to-noise ratio and therefore greater accuracy/and/or more accurate measurements as opposed to classic analog beamforming tapers for low sidelobes in analog arrays. The digital nearfield architecture of the present disclosure allows any digital receiver/exciter to be installed at the scanner probe along with supporting DAUT specific equipment to deliver the source tones to establish reference points and acquire nearfield measurements.