Qualification of Multi-Channel Direction Finding Radar Receivers in The Lab
Kongsberg Defence & Aerospace selected a radar test setup from Rohde & Schwarz based on the R&S SMW200A vector signal generator for multi-channel phase-coherent radar signal generation. Kongsberg is Norway’s premier supplier of defense and aerospace-related technologies. The joint strike missile (JSM) is a fifth generation long range precision strike missile. Using advanced sensors, the JSM can locate targets based on their electronic signature. Qualification of the JSM is under way with the Royal Norwegian Air Force (RNoAF).
Kongsberg’s JSM must operate autonomously in highly contested environments. To increase mission success, the missile has a passive RF sensor that can locate and identify radio frequency emitters. To test and verify this RF direction finding capability in a laboratory, Kongsberg required a multi-channel phase coherent vector signal generator that could be linked to existing test environments.
The Rohde & Schwarz test system that they selected can simulate multiple emitters in a dynamic environment in real time, enabling Kongsberg to perform closed loop testing of the missile system with the passive RF sensor and enabling massive amounts of integrated system testing on the host hardware, without costly flight tests and with a high level of repeatability.
Test Tasks, Challenges and Requirements
To test direction finding receivers effectively and efficiently, the test system must meet the following requirements:
Test system RF outputs must be connected to the receiver antenna inputs; a separate signal must be provided for each input, so the test system has an independent signal source for each simulated antenna.
The test system must be calibrated at the RF interface for exact adherence to the relative amplitudes and phases between the channels.
The phase relationships between the simulated signals must remain stable during simulation (phase coherence).
Test systems for multichannel applications are often operated in a hardware-in-the-loop (HIL) environment; high update rates and low latencies are essential, because a computer feeds signal data into the test system at high speeds.
The Test System
The test system includes a scenario simulator that generates pulse descriptor words (PDWs). The PDWs are the basis for generating corresponding RF signals that are then fed to the device under test (DUT).
Kongsberg developed an in-house real-time simulation environment that can accurately replicate all aspects of a missile flight. The simulator can generate PDWs for a large number of simultaneous emitters, taking into account positions, attitudes, antenna patterns and propagation. Integration of the Rohde & Schwarz test system closes the loop by generating accurate RF incident signals identical to those at the receiver inputs.
Time-synchronized PDWs are sent to the Rohde & Schwarz test system. The PDWs include the phase and amplitude response of the antennas along with other parameters.
The main components of the Rohde & Schwarz test system include two coupled R&S SMW200A vector signal generators (VSG) and an analog R&S SMA100B signal generator for the local oscillator (LO) signal. Using a common LO source together with the advanced clock distribution concept of the VSGs ensures accurate, stable and repeatable simulations of relative amplitude, phase and group delay offsets between the RF ports at the reference plane for the DUT input, as required for precise AOA simulations.
R&S RF Ports Alignment Software runs predefined and optimized alignment routines for RF signals at the reference plane. RF frequencies, used bandwidth, and level range for alignment are configured for the test case. Together with a network analyzer, the software automatically determines the correction coefficients for all RF ports and loads the data to the Rohde & Schwarz test system. The DUT may be the RF sensor or a portion of the subsystem running true operational software on real flight hardware.
The multi-channel radar test system used by Kongsberg is a four RF channel system. It has two general-purpose, high-end R&S SMW200A vector signal generators providing radar signals to the DUT, an analog R&S SMA100B signal generator for LO distribution and a Rohde & Schwarz vector network analyzer (VNA) for measuring the required corrections for the RF port alignment process. All instruments are integrated into a rack for a compact and transportable advanced testing solution when phase-coherent radar signals are required.
Additional RF channels or simulation features can easily be retrofitted with purchased hardware components or software licenses. Thanks to the advanced clock distribution and LO coupling mechanism, the relative phase between multiple RF ports remains stable not just for hours, but days. Predefined, optimized and automated calibration routines ensure highly repeatable scenarios independent of frequency bands, signal power levels and bandwidths.
Since the RF hardware is based on general purpose vector signal generators, users have fast delivery times and worldwide service support. The equipment is commercial off-the-shelf, all instruments can be used for other applications, testing and projects by extending their signal generation capabilities with application-specific software licenses.
“Rohde & Schwarz was able to offer a system that not only has excellent phase coherence, but also provided a flexible and scalable solution where Kongsberg was able to integrate the signal generator in an existing closed-loop simulation environment,” said Erik Narverud, Team Manager for Passive RF Sensor System Integration at Kongsberg.
This article was written by Markus Irsigler, Product Manager Signal Generators, A&D at Rohde & Schwarz. For more information, visit here .