FEATURE TEST & MEASUREMENT
other measuring equipment to perform all the tests. Unlike standard approaches, the SMW200A vector generator equipped with the SMW-K78 option can be used to perform a variety of tests and without a lot of equipment.
CONDUCTED TESTS AND OTA TESTS For conducted tests, the radar signal is fed to the FSW via a cable. It is then down-converted, digitised in real-time and fed to the SMW200A. The generator uses this signal to generate echo signals that are indistinguishable from real echoes. For OTA tests, the signals are received and transmitted by antennas that are connected to the input port of the analyser and to the output port of the generator. Conducted tests are ideal for
that the signal level of the echo of an object that is radially approaching the radar increases after each update. The algorithm is based on the radar equation and the propagation loss in free space. The generator can simultaneously produce up to a total of 24 static and moving objects. The top section of Fig. 1 shows the
menu for defining the objects used to create the echo signal with static objects assigned a specific range. Their size can be defined via the radar cross section (RCS). The R&S SMW-K78 option models the point objects with a constant RCS, which is often called ‘Swerling 0’ after the underlying RCS statistic. For moving objects, the velocity and the start and end range to the radar can be specified (Fig. 1, bottom). The objects can be assigned a movement pattern, e.g. a one-way path from the start to the end location or continuous movement between the start and end location. Superposition of echoes can easily be simulated by mixing static and moving objects.
HANDLING DIFFERENT TEST CASES Radar engineers have to cope with numerous test cases and types. Typical system tests include confirming fixed target suppression performance for moving target indicator (MTI) radars and testing the minimum threshold for detecting an object. For a test system to be able to test whether a radar system can detect small objects near a large object, it must have a sufficiently large spurious-free dynamic range. By generating multiple echoes and several objects with different velocities, it can be demonstrated how well radars can simultaneously track, resolve and display these objects. Standard test approaches only partially solve these issues. They are often not flexible, generally need intensive maintenance and also require
32 DECEMBER/JANUARY 2017 | INSTRUMENTATION
Fig. 1: Configuration of a static (top) and a moving object (bottom) on the SMW200A vector signal generator
development and final testing before radars are permanently installed on a platform. They significantly reduce the overall effort since tests that would only be possible fairly late, such as certification runs for navigation radar, can be carried out during development. The software offers the option
of manually configuring the radar receive level or using the radar equation to automatically calculate it based on the radar scenario. If radars are already in operation and
Fig. 2: Preview of the configured scenario containing a static and a moving object (top). Bottom: Calculated echo signal level versus time
installed on a ship, for instance, then the effort to set up tests in the lab is excessively high. In such cases, functional tests have to be performed at sea. However, these take time and during this time the ship cannot be used. The Rohde & Schwarz solution makes it possible to perform comprehensive tests during normal port layovers. The setup consists of the FSW and SMW200A with antennas at the RF inputs and outputs. The generator and the analyser are installed
in a stationary test system that receives the radar signals via a test antenna with known properties and returns the echoes to the radar under test. This test setup can be completely configured on the SMW200A if all relevant transmission path parameters are known (e.g. radar and test setup antenna gains and radar transmit power). For this test case it is possible to
manually configure the radar receive level or use the radar equation to automatically calculate it based on the radar scenario. The required RF output power at the generator is automatically determined from the configured parameters so that the right echo level reaches the input of the radar receiver.
EXAMPLE OF A TEST SCENARIO A typical test scenario consists of two objects. Such scenarios can be easily simulated in the lab with the SMW200A. The parameters can be changed for variants. The top section of Fig. 2 shows a preview in the range/ velocity view displaying the overall result of all configured reflecting object parameters. Object 2 (orange) is stationary at a range of 3.75km from the radar. Object 1 (blue) moves a few kilometers away from the radar at a velocity of 750 m/s and returns. Before the tests are carried out, the user can check whether the scenario is properly configured. The bottom section of Fig. 2 shows
the level of the echo signal versus time calculated by the SMW200A. Echo 2 (caused by object 2) has a constant level and a constant time delay to the transmission pulses. Both the level of echo 1 (caused by object 1) as well as the time delay to the transmission pulses vary based on the range.
SAVING TIME WHILE TESTING The SMW-K78 option for radar echo generation saves time when testing prototypes in development as well as when servicing operational radar systems. In addition, the SMW200A signal generator together with the FSW signal and spectrum analyser make it possible to perform conclusive radar tests that previously could only be made in time-consuming field tests after development was complete. The user does not have to invest in special solutions and the cost of lab equipment is reduced since the spectrum analyser and vector signal generator are already on hand and can be used for other measuring tasks.
Rohde & Schwarz T: 01252 818888
www.rohde-schwarz.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60
