TEST & MEASUREMENT FEATURE


Navigation radars must be able to safely recognise other ships despite the numerous disruptive echoes caused by high seas


Testing times for radar systems


Dr Rainer Lenz of Rohde & Schwarz discusses an innovative solution that allows users to test radar systems


R


adar systems provide images of the surroundings. They use


electromagnetic signals to illuminate their surroundings and then generate an image of the environment from the echoes returned by reflecting objects. Unlike optical systems, radars can also produce a situational image in the dark or where visibility is poor. Radars consist of several subsystems,


including a transmitter, receiver and the radar processor, which calculates the situational image from the data received. The radar is set in the appropriate operating mode for the specific task and the radar processor sets the required parameters, such as the pulse duration and pulse repetition rate. One of the typical requirements for


navigation radars is to reliably detect the signal echo reflected by another ship from among the numerous


disruptive echoes caused by waves. Since radar images are essential for navigation and reconnaissance, the systems must be extremely reliable, which often requires extensive field tests and standard laboratory tests – and these have to be repeated in every operating mode. Navigation radars, for example, have two separate modes for detecting close and faraway objects. All these tests take time and tie up resources, which is why manufacturers and operators always strive to minimise the effort involved.


SIMULATION SOFTWARE REDUCES TESTING EFFORT The R&S SMW-K78 radar echo generation software option for the company’s SMW200A vector signal generator enables users to artificially generate radar echoes. The R&S FSW signal and spectrum analyser is also


TYPICAL TEST SCENARIO AT SEA


For certification tests, maritime radars are mounted on a ship and put into operation. The ship operates in a defined sea area in which objects with defined backscatter properties and backscatter power (mainly buoys) are placed. These are arranged so that it is possible to determine the most important radar properties such as the range resolution and the azimuth resolution. The range resolution of a radar is its ability to recognise that two


objects positioned behind each other at the same azimuth angle to the radar are separate objects. The radar under test transmits a pulsed signal and receives the echo signals from the two test buoys. The difference in the delay times of both echoes is a measure for the geometric spacing of the two objects. If the system can separate the two echo signals from each other, the two objects will be displayed on the radar screen. If the


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needed as a radar receiver, which makes field tests largely unnecessary. The option can generate radar signal echoes in a realistic manner and provides all the prerequisites for conducted and over- the-air (OTA) tests. The generator controls the spectrum analyser and configures it so that both devices appear to the user as a single system that is operated via the generator. For pure receiver tests, the SMW200A can be used as an echo generator even without the spectrum analyser. It generates the transmit signals in the digital baseband, e.g. using the R&S Pulse Sequencer software.


REALISTIC SIMULATION OF RADAR ECHOES The SMW200A generates radar echoes of static and moving objects at user- configurable ranges. It automatically sets the delay, the Doppler frequency and the RF output level for each object. For moving objects, the generator constantly updates the delay and the output level of the echo signal. This means, for instance,


range resolution is too low, only one object will be seen on the screen. Determination of the azimuth resolution is similar. In this case, a check is made to see if the system can distinguish between two objects that are positioned at the same range, but at different azimuth angles to the direction the ship is traveling. This ability is mainly determined by the antenna characteristic.


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