Emerging radar cross section (RCS) measurement needs are making it increasingly necessary to take the measurement system to the target, rather than take the target to a fixed measurement site. With this in mind, QuarterBranch Technologies Inc. set out to build the first truly portable pulsed-IF RCS measurement system without sacrificing capabilities that most users require. The result is RadarMan, with a core unit that can attain measurement speeds rivaling the practical limits of other systems, with equal measurement sensitivity.


Real-time plotting capabilities are extensive, including near real-time inverse synthetic-aperture radar (ISAR) and SAR imaging. In addition to the real-time plotting package, each RadarMan system includes a single-seat license of QuarterBranch’s offline processing/plotting package, Data Display.

RadarMan is a compact, lightweight, pulsed-IF radar system that is engineered to be cost-effective, highly reliable and supportable at a level not achievable in other mainstream RCS measurement systems. These key attributes revolve around the remarkably unique architecture and physical package of the product in contrast to other pulsed-IF acquisition systems. Specifically, all of RadarMan’s core functions, including all digital control, data and timing circuitry, IF circuitry, a frequency-agile synthesizer, and all frequency up- and down-conversion are contained in a single seven-inch tall box that weighs approximately 25 pounds.

Specifications Summary

RadarMan operates at frequencies from 2 to 18 GHz, with optional frequency expansion down to 100 MHz. It has 10 kHz frequency resolution and a frequency switching speed of less than 5 μs. The frequency table allows full polarization matrix operation. Up to eight waveform table entries (chirps) can contain 1 to 8192 steps, with up to 65,536 coherent integrations in increments of powers of two. The system can be placed in any of a number of diagnostic loop modes, including IF, RF converter, low-power transmit drive and HPA. Any one of these loops can be configured as a “fast loop” to be included within a target collection run for monitoring system stability.

RadarMan has a selection of two video bandwidths, 100 and 250 MHz. A/D conversion is 14 bits each for the I and Q video channels. Instantaneous dynamic range is 65 dB.

The system supports pulse repetition frequencies (PRF) ranging from 3 kHz to 2 MHz. Range delay can be set from 0 to just under 328 μs in 1 ns steps, and pulse widths can range from 5 ns to 2 μs, also in 1 ns increments. All timing parameters as well as transmit drive levels are adjustable on a band/sub-band basis.

The IF module contains a phase modulator that allows 16-state polyphase operation to correct for I/Q circularity errors, as well as for ambiguous clutter suppression. Phase agility operates in a number of selectable sequences. These sequences include: fixed phase (at any of the 16 phase states), biphase, complementary, incremental and pseudo-noise (PN). For each setting of coherent integrations, the start value of the PN sequence can be set by the user to optimize the multiple-time-around suppression for specific range conditions. In addition to the built-in phase sequences, the user can execute a custom phase sequence by creating a simple ASCII format file.

User Interface Software

The user interface software allows for full control of all radar hardware parameters, data collection and storage and real-time data processing/display. This intuitive program also features integrated target/antenna motion control, simple calibration and background subtraction reference collection, an image parameter calculator and range walk with real-time transmit/receive bracket adjustments. Measurement parameter setups can be saved and recalled, as well as calibration and background subtraction reference vectors.

Plot types include line plots (magnitude or phase vs. frequency, FFT-based range profiles, or Doppler plots, for example), time/position charts, intensity charts (magnitude/phase vs. frequency/range/Doppler vs. time) and ISAR or SAR images. For each plot type, the user can select the desired X- Y- and Z-axis data sources from a plot type-specific list for each plot axis. The user may dynamically enable or disable processing functions such as calibration, background subtraction, R^4 correction, weighting function and zero-Doppler subtraction as data is collected. Scaling for all plot axes can be either auto-scaled or adjusted manually.

The software includes a series of automated system diagnostics tests. These tests include A/D statistics, long-term system stability using loop mode tests, receiver linearity and I/Q circularity.

Data Display Offline Processing Software

Data Display is a full-featured RCS processing package for offline processing and plotting of RadarMan data (see Figure 1). A single-seat license of Data Display is included with the purchase of each RadarMan unit. Additional licenses can also be purchased or leased.

The user interface for Data Display, like that for RadarMan, is very intuitive to use. The processing setup screen contains a section for selecting data files, and a section for selecting plot types, processing functions and plotting parameters. An error check feature assures that all selections can be logically processed and displayed. The processing setup can be saved as a named file for later use. Once the processing setup is complete, the setup page is exited and the plot windows open. Pressing the Begin Processing button starts the processing engine to create the data plots.

The software allows re-plotting of RadarMan data in all formats available in its real-time plotting, with the additional capability of navigating through files to any point based on block number, time stamp, or target/antenna position. In addition, the software can simultaneously plot data from multiple files or multiple waveform entries, either as overplots in a single window, or individually. Markers on line plots display the X and Y values at the location of the marker, and plots can be easily zoomed to any scale.

ISAR images can be created at any requested angle, or continuously updated at requested angle increments. These image sequences can be saved to .AVI files as movies at selectable frame rates. In addition to ISAR images, the software can create SAR images from data collected on a rail-mounted antenna connected to RadarMan.

Displayed images can be measured on individual pixels using a cursor tip tool, or regions of the image can be selected using a rectangle drawing tool to display the RSS value of the included pixels. The software also performs image edit and reconstruct (IER) for ISAR images, as well as sector statistics for line plots.

QuarterBranch’s policy for adding processing functionality to Data Display is that if the requested feature is added to the standard product for release to the entire user population, the new feature is added at no charge. If the feature is to be proprietary, then standard time-and-materials charges apply. All requests for additions are placed into the release schedule to ensure timely availability for all customers who are under warranty or paid support. Added features that are proprietary to a user are not made available in the standard product and are not released to the general user population. In short, if Data Display does not have a required tool, just ask.

Supportability

The incredibly small size and relatively low price of the RadarMan core product allows it to be supported in its entirety through the deployment of an on-site spare unit. For critical operations where down time cannot be tolerated, this approach ensures virtually 100 percent system availability by direct replacement of the entire RadarMan core unit in the event of a failure, which can be completed in less than 10 minutes. With this level of support, the original system can be sent for repair while operations continue using the spare unit.

For less critical applications that cannot justify the purchase of a spare core unit, quick-reaction return-to-operation support can still be obtained through short-term spare rentals, which can be shipped overnight for immediate installation.

Unit-level support also makes system upgrades more tolerable as technology progresses. For this effort, a spare unit would be deployed while the original is updated with the new version, thus eliminating down time during the upgrade process.

Flexibility

RadarMan is adaptable to virtually any required measurement configuration including multiple antenna bands, full-polarization matrix switching and dual receive channels. It is designed to interface to any appropriate transmitter device as required for the application, from solid-state milliwatts to kilowatts from TWTAs. Its features and specifications make it fully capable of instrumenting large, fixed ranges, while its size makes it ideal for portable field measurements, from ground-based operations such as flight-line or production-environment measurements, to airborne applications.

Conclusion

Though it comes in a remarkably small package, RadarMan is just as remarkably capable. Smart design decisions left out seldom-used legacy features, such as multi-decade video bandwidth selection and million-step-deep waveform tables that are typical in competing products, enabling the system to be small and relatively easy to use, while supporting the vast majority of measurement requirements.

QuarterBranch Technologies Inc.
Lovettsville, VA
(540) 822-4634
www.quarterbranch.com