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Radar systems and technologies serve many different purposes in commercial, industrial, and military applications. In the automotive industry, for example, radar systems have improved vehicular safety by providing collision avoidance, blind spot detection, and automatic cruise control. Military radar systems have long been used for tracking enemy vehicles and missiles and for detecting threats from the land, sea, and the air.

Each radar was developed for a specific application, resulting in a wide range of radar systems with different operating frequencies, waveforms, transmit power, antenna aperture, and other parameters. Such systems must be tested, often with commercial test equipment.

Radar target generator system

For example, spectrum analyzers and vector signal analyzers help evaluate radar transmitters, vector signal generators can be used to check receiver performance, and vector network analyzers are often used to characterize the components used in radar systems. Quality measurement solutions for these radar systems and components can often be found in the form of commercial-off-the-shelf (COTS) test gear.

Radar system operators are often interested in quick measurements and an overview covering the main functions of a radar system: target detection and tracking. Exercising a radar system requires the generation of signals that represent targets or the reflection of signals from targets. These target signals must be produced over the entire unambiguous operating range of the radar system, including the unambiguous radial velocity interval and azimuth/elevation coverage.

The target signals should have adjustable properties, such as different radar cross sections (RCSs), so that a radar under test (RUT) is properly evaluated for acceptable detection and false alarm rates. Another important performance factor is radar accuracy, which must be measured periodically as components age and radar system performance parameters (e.g., signal generation and detection) may fluctuate.

This is especially true of older radar systems that may still employ high-powered traveling-wave-tube (TWT) technologies, where performance levels can degrade with age. Ditto for electromagnetic (EM) components such as yttrium-iron-garnet (YIG) tuned oscillators and filters.

Field testing of radar systems has the potential to be expensive, as it can be difficult to configure repeatable test conditions. As an example, airborne radars might be tested under controlled conditions with nearby flying jets and artificial targets deployed, detected, and tracked by the radar under test. The Global Positioning System (GPS) coordinates of a target can then be compared with the radar test data to check radar system performance.

Although such tests can be complex, time-consuming, and expensive, they are necessary to ensure the proper functionality of the radar system and to build confidence in its performance, from the hardware through the detection software algorithms. Fortunately, such testing is possible with COTS test equipment and a radar target generation application from Rohde & Schwarz.

Radar Target Generator

The radar target generator (Fig. 1) captures a transmitted radar signal from the RUT; generates a target range by delaying the received radar signal and introducing a desired radial velocity, owing to Doppler frequency shift; then retransmits the manipulated signal back to the radar. In addition, the generator can set RCS via attenuation of the transmitted signal. The system does not need to know which kind of radar waveform has been transmitted.

COTS instruments

The radar target generator essentially acts like a digital radio-frequency memory (DRFM) comprised of COTS test-and-measurement equipment. This allows some of the equipment to function also for its initial purposes, such as a signal analyzer being used for signal analysis and a vector signal generator being used to create test signals for high-frequency component testing. But when the analyzer and generator are used together (Fig. 2), they form a flexible radar target generator capable bring laboratory test quality to the field.

Functioning of the radar target generator system relies on the real-time digital in-phase/quadrature (I/Q) link from the FSW signal and spectrum analyzer and the fading simulator extension offered on the SMW200A vector signal generator. This option for the signal generator was originally aimed at mobile communications testing, but the software offers enough flexibility to manipulate I/Q data within the signal processing chain for use in radar system testing.

The radar target generator system can produce as many as 20 signal fading paths (as many as 40 with a second fading simulator) to mimic as many as 20 targets (40 targets with the second fading simulator) in arbitrary range Doppler cells. The test system provides digital I/Q signal and fading bandwidths to 160 MHz. It can command very high Doppler frequency shifts (to ±4 kHz in the fading simulator).

The transmitter carrier frequency can be tuned from 100 kHz to 20 GHz, while the test receiver is locked to the frequency of the RUT. The test system can control maximum time delays to 0.5 s, adjustable in 10-ps steps (an equivalent range of 75,000 km).

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