Precision Validation of Radar System Performance in the Field
By Wilkie Yu, Keysight Technologies, Inc*
* Keysight Technologies Inc., formerly Agilent’s electronic measurement business
Modern radar systems are used in a multitude of application, from traffic enforcement to weather prediction. Some of these applications are considered mission critical, meaning that any system malfunction or failure puts lives at risk. To prevent such a scenario from occurring, routine maintenance and occasional troubleshooting and repair are essential, all of which must be done quickly, accurately and in any weather condition to assure the highest system uptime. Unfortunately, the realities of modern radar installation and maintenance don’t always make this possible. Mission critical systems are often highly complex and making accurate measurements in the field using benchtop equipment is no easy task. Luckily, breakthrough technologies available in handheld combination analyzers are now transforming the way maintainers test mission-critical radar systems in the field.
Radar System Maintenance and Troubleshooting:
Radar systems fall into a number of different categories with applications covering civilian air traffic control, ground-based and airborne military air defense and meteorological, just to name a few. A prime example of a mission critical radar system used worldwide is a commercial air traffic control system. Essentially, these radar systems transmit and receive waveforms (e.g., pulsed, unmodulated continuous waves (CW) and FM-CW) that when processed produce important information regarding target range, size and shape; velocity; trajectory; azimuth angle; elevation angle and aircraft identification.
When characterizing and troubleshooting radar systems and components in the field, it is often necessary to measure both the time- and frequency–domain performance over a variety of test conditions. Complicating this process is the complexity of modern radar systems, which means that maintainers must also coordinate and compare waveforms in both the time and frequency domains. Maintainers may even need to field test and tune the numerous functional blocks or Line Replaceable Units (LRUs) that make up the radar system.
Traditionally such testing is accomplished using multiple benchtop instruments. This is especially true for field testing at the LRU level. In this case, there is typically a set of basic measurements in both the time and frequency domains (e.g., absolute and relative amplitude and phase) and various combinations of those measurements that must be made. Covering all of the various measurement modes requires at least three to four different instruments. For example, a peak power meter can be used to measure the absolute amplitude of a transmitter as a function of time, but a spectrum analyzer would be needed to measure the absolute amplitude as a function of frequency. When performing relative measurements, the peak power meter could measure the relative time and amplitude of a waveform, but a Vector Network Analyzer (VNA) or vector voltmeter would be needed to measure the amplitude and phase as a function of frequency.
Figure 1 shows the typical set of instruments used to field test a commercial aviation radar system over the past several decades. Each instrument measures a specific function such as power, spectrum or frequency response. Since most benchtop equipment is designed for indoor operation, the test site must have adequate weather protection to guarantee its safety against harsh weather conditions. Additionally, the instruments generally require a warm-up time as specified by each individual instrument’s manufacturer.
There are a number of obvious issues with this traditional field testing approach. To begin with, the accuracy of benchtop instruments is generally only specified by the manufacturer when operated at a set temperature (e.g., 23 +/-5 degrees C). In the field, however, testing may occur over a wide range of environmental conditions, causing uncertainty in the measured data. Worse yet, older benchtop equipment is often used for field testing, much of which is well beyond its service life and therefore, unrepairable by the manufacturer. Replacing obsolete equipment with newer options does have some benefit in terms of reducing the overall cost-of-test since the newer instruments typically have 3-year warranties and lower overall calibration and repair costs. Newer instruments also generally have higher performance, improved accuracy, and functions that are specifically designed for field testing. However, a one for one instrument replacement is not optimum.
The All-In-One Analyzer
While the traditional method of validating radar system performance in the field has sufficed in the past, modern “all-in-one” or combination analyzers with the capability of multiple instruments now provide the most convenient and economical solution to field testing radar systems. The trick to getting successful and accurate results of course, is selecting the appropriate instrument.
Keysight Technologies’ FieldFox combination analyzers provide all the measurement capability of the four benchtop instruments shown in Figure 1. With the addition of a peak power sensor, they provide a solution that can easily be carried to a test site for measuring the time and frequency performance of a radar system in the field (Figure 2). The FieldFox combination analyzers have all of the instrument functionality needed to test to the LRU level in the field. Specific measurements supported include a full pulse analysis capability to 40 GHz with a USB peak power sensor, and a relative timing measurement of the transmitter main to auxiliary pulses. FieldFox combination analyzers also support Stable Local Oscillator (STALO) phase alignment via their vector voltmeter mode.
Combination analyzers offer a variety of test modes for characterizing and troubleshooting LRUs. For example, FieldFox can be used when examining the beacon system of air traffic control radar. Mode S radar essentially interrogates an individual aircraft transponder and is very useful in dense-traffic conditions. In VNA mode, the handheld analyzer can be used to characterize the insertion loss and phase characteristic of rotary joints, which provide RF continuity to a continuously rotating antenna system. During periodic maintenance of radar systems, it is important to verify that rotational variations in the amplitude and phase through the rotary joint will not reduce system performance. The VNA is configured with limit lines to quickly identify when transmission characteristics exceed specifications as the joint is physically rotated. The VNA is also configured with a Pass/Fail indicator that highlights the portion of the frequency response that exceeds the limits.
FieldFox combination analyzers are specifically designed for field testing with a 3.5 hour battery life, built-in GPS and a rugged, fully sealed (no fans or vents) enclosure that is compliant with U.S. MIL-PRF-28800F Class 2 requirements and MIL-STD-810G Method 511.5, Procedure 1 requirements for operation in explosive environments. They also meet IEC/EN 60529 IP53 requirements for protection from dust and water. This weather resistant construction ensures their durability in even the harshest environments. And, weighing in at just 6.6 pounds, the analyzers are easy to transport over any distance. As an added benefit, FieldFox combination analyzers feature remote operation through an application that runs on an Apple iOS device—an ideal feature for test environments where it may be difficult to control and observe the analyzer while simultaneously operating some part of the radar system.
Unlike comparable benchtop instruments that are specified to operate at a set temperature and require a lengthy warm-up time, FieldFox combination analyzers feature an automatic internal alignment function in spectrum analyzer mode that compensates for temperature changes over a range of -10°C to +55°C. With this InstAlign feature, the spectrum analyzer is ready to make highly accuracy measurements immediately at turn on and through any temperature changes over the specified range.
Just as critically, time- and frequency-domain measurements made using combination analyzers have been shown to correlate with benchmark data taken in the development lab using benchtop instruments, and at system installation (Figures 3 and 4). In fact, FieldFox achieves S-parameter results that track the world’s highest performance VNA within a few hundredths of a dB, and the world’s highest performance spectrum analyzer within 10ths of a dB. FieldFox data correlation increases both the engineer’s confidence in measured results and reduces the risk of passing bad LRUs or failing good ones, ensuring optimum system performance. Because FieldFox offers comparable measurement performance and functionality to that provided by conventional benchtop instruments, it is the ideal solution for radar maintainers performing radar ground station installation and maintenance measurements in the field.
A key benefit of using modern, field-ready technology like the combination analyzers for field testing radar systems is a reduction in the overall capital and operating expenditure. A single combination analyzer can replace all four RF instruments traditionally used for civilian radar test in the field. Moreover, it is less expensive than comparable benchtop instruments (typically just one-third the cost) and requires just a single yearly calibration, which reduces the annual calibration cost by a factor of up to 5. In contrast, the traditional four-benchtop instrument approach requires four calibrations per year plus calibrations for spares.
ieldFox also has the lowest failure rate of any complex microwave instrument from Keysight Technologies and a much lower failure rate than any other handheld on the market today. In fact, FieldFox offers the highest reliability of any complex RF and microwave instrument, which reduces the overall test cost by at least 50% over comparable benchtops. And, unlike benchtops or other handhelds, FieldFox spectrum analyzers reach full amplitude accuracy immediately at power on. With its CalReady feature, the VNA is already calibrated and ready to make measurements without having to use a cal kit—which significantly increases system uptime. The low failure rate and high instrument uptime translates into a dramatic reduction in the cost-of-test.
The small size of combination analyzers speeds the maintainer’s time to the radar test site and the time to first measurement, which makes troubleshooting and repair easier and faster. A standard 3-year warranty on the analyzers reduces the overall repair cost. And, since combination analyzers are not outdated or anywhere near the end of their support life, there is no need to maintain spare parts or even a spare instrument inventory, both of which significantly add to the overall cost-of-test. Finally, because engineers need only use one FieldFox versus multiple other instruments, the combination analyzers are easier to learn, which minimizes any training cost.
Maintaining complex mission critical systems like civil air control radar has traditionally required maintainers to use decades-old benchtop equipment, some of which was beyond its service life. This was the only way to assure accurate and repeatable radar measurements. Thanks to the accuracy and functionality of Keysight’s FieldFox combination analyzers, radar maintainers now have an easier, more cost-effective option for performing precision radar system performance validation, maintenance and repair in the field. The solution not only dramatically reduces their cost-of-test, but also increases the uptime of their mission critical systems as well.
Watch a video, download application notes and learn more about performing precise validation of radar system performance in the field with FieldFox at:
this article to a friend!