One of the methods for radar testing is the simulation of an environment where there are dynamic or static objects that are scanned by the radar under test. In particular, simulation implemented by MPG Instruments (Rome, Italy) generates skin-echo pulses coming from radar that transmits a defined pattern stream. The system simulates an object in the scanning area of the radar and is hit by a pulse pattern stream. The X-band radar must be tested at a frequency from 7 GHz to 12.5 GHz, and K-band between 12 GHz and 40 GHz.
Since the pulse pattern streams of radar can be extremely different from each other in terms of pulse width, PRI, modulation on the pulse, and frequency of transmission, the simulation system must generate a scenario and transmit skin-echo pulses that are customizable by operators.
The system simulates the presence of an object within the coverage area of the radar under test. It can simulate either a static object or a dynamic object. If a static object is selected, the operator can set the distance of the object from the radar. The system hangs up the synchronization of the radar under test through the radar trigger output, which indicates the time when the pulses stream is transmitted, calculates the flight time of pulses, and transmits the skin-echo pulse back at the correct time to simulate the presence of an object at the distance specified by the operator. If a moving object has to be simulated, the operator can insert a completely customized trajectory of the object. The system can accept a trajectory pattern composed by the distance from the radar and time of the simulation. That means the system will be able to simulate objects either at constant or variable speed, with accelerations and decelerations during the simulated trajectory. Once hooked on the trigger of the radar under test, the system will calculate the flight time, apply the appropriate manipulation, and transmit the skin-echo pulse back.
In developing this test system, critical points were encountered. Performance of radar under analysis is characterized by high operating frequencies, combined with considerable bandwidths, and highly reduced frequency switching time. To cover a wide range of applications, the testing system can operate at a frequency between 10 MHz and 15 GHz, and transmit pulses of 500 ns to 10 μs, inside which the carrier can be further modulated in accordance to a defined pattern, with a repetition frequency of 10 Hz to 1 kHz.
Mp>To achieve this target, the system uses an NI PXIe-5646R vector signal transceiver (VST) from National Instruments (Austin, TX) to generate and process signals in the intermediate frequency (IF) band. The modulated signals are then sent to a range extender that executes up-conversion of the IF signal at higher frequencies, manages the frequency agility, and controls the phase coherency if required (for example, in beam forming applications). The range extender also has the task of generating a reference frequency at 1200 MHz characterized by extremely low phase noise. The VST modulates it and sends it back to the range extender.
The system features a LabVIEW interface that manages the simulation and can configure the pulse stream (pulse width and PRI – Pulse Repetition Interval) and the configuration of the trigger generator (if there is no way to access the radar trigger). The pulse is fully characterized by loading an I/Q data table that is then processed by the I/Q modulator; the software interface will also show the modulation in the time domain. The operator can choose between a static or dynamic object, and can load a customizable trajectory to run.
During simulation, the trigger and the skin-echo pulses are depicted on the lower graph of the interface that moves according to time. If a dynamic object has been selected, a graph of the distance against time will show the trajectory loaded by the user, and a red pin on the trajectory will indicate the precise position of the object and its behavior (distance from radar and time from the beginning of the simulation). The user will then be able to pause the simulation to stop a moving object in real time while the simulation is still in progress.
The result is a system capable of generating radio pulses with a resolution of 8 ns, based on the sampling of the I/Q modulator. It can then accurately characterize the flight time with a sampling rate of 125 MS/s that results in a spatial resolution of 2.4 meters. The system can simulate a maximum radar coverage area of 400 km.
This article was written by Mauro Cortese of MPG Instruments. For more information on NI equipment used in this application, visit http://info.hotims.com/55592-542 .