Mahesh Kumar, Vijay Raj
The Challenge
To develop a Portable Radar Echo Simulation System using COTS products to evaluate Radars as close to its field conditions at ground itself.
The Solution
Designing & Developing a DRFM based Radar Simulation System by utilizing the PXIe hardware architecture & LabVIEW FPGA software.
Description
Development of today’s sophisticated radar systems requires advanced simulation and measurement techniques in order to evaluate performance under all operating modes and to ensure performance specifications are met and fully characterized. To achieve this, more realistic testing with RF signals representing the field environment conditions are required. Hence, radar designers are looking for a portable real-time radar simulation system on which they can generate the Radar RF signals as close to the required field conditions. These field conditions will include multiple targets, terrains, clutters, noise jamming, RCS models.
The most widely used method of radar echo simulation is to employ a DRFM or digital RF memory. Digital Radio Frequency Memory (DRFM) is an electronic method for digitally capturing and retransmitting the RF signals. The DRFM allows the indefinite storage (delay) of radio frequency signals in digital form. Signals can be played back in exact replication of the original coherent signal or with the signal altered for the user’s purpose.
System Design
As lot of real-time signal processing is required for these kinds of simulations, we developed this system around NI PXIe 5646R VST on a PXIe 1085 Chassis. For digital storage of RF signals, we have configured a NI 8265, 24 TB RAID Storage. NI PXIe 5646R module provides us with the required DRFM concept implementation.
Our solution has the following hardware components
NI PXIe 1085 Chassis – For housing of PXIe modules & for routing of data between the modules to achieve DRFM concept
NI PXIe 5646R – Vector Signal Transceiver with on-board FPGA which receives the Radar signal, incorporates all the desired echo characteristics through DRFM concept & retransmits as RF output
NI 8265, 24 TB RAID – Stores the RF signals for future simulations
NI PXIe 5673E & NI PXIe 5663E – Simulates & Analyses Radar signals during the non-availability of Radar during testing of this simulation system
Application Flow
The overall application flow for our DRFM based Radar Echo Simulation System is as follows:
- Acquiring the Radar signal in the band of 65MHz-6GHz by continuously scanning the band.
- Downconverting the RF signals to Baseband IQ data.
- Measuring the signal characteristics like center frequency, power, bandwidth, pulse width and pulse repetition time for user analysis.
- Incorporating the desired Echo Characteristics into the acquired signal.
- Upconverting the IQ data with Echo Characteristics to RF frequency & retransmit as RF signal output.
This complete process starting from receiving RF signal to retransmitting the echo RF signal will work with a timing latency of 2.4 microseconds (Min time delay between receiving & retransmitting RF signal is 400 meters) and resolution which we are able to achieve in our system is approximately 3 meters.
Our application can be broadly classified into three modes of operation; first will be Acquisition Mode where the system will scan for presence of RF signals starting from 65 MHz to 6 GHz. RF List Mode feature of VST is used to sweep the spectrum at faster rate. In RF list mode, the device deterministically steps through a predetermined set of RF configurations. In this mode, start frequency, stop frequency, bandwidth and bin size are pre-defined as sub-span information. Once the system detects the presence of RF signals in certain frequency range, user will be intimated about the signals presence. Then, the user can tune the system to operate for that particular frequency range with 200 MHz instantaneous bandwidth.
The second mode of operation is DRFM mode. In this mode, the VST will be tuned to the frequency which is obtained in acquisition mode. Using LabVIEW FPGA, VST is programmed to incorporate the desired echo characteristics into the received signal. The radar echo parameters that can be configured include Range, Doppler, RCS & Noise Jamming. Modified signal will then be re-transmitted through the RF output port of NI PXIe 5646R module.
In the third mode of operation, we operate NI PXIe 5646R module only as a RF Receiver. The module will be tuned to receive a maximum of 200MHz instantaneous bandwidth at the frequency that is detected in acquisition mode. The signal captured in time domain will then be transformed into spectral domain using FFT. From time domain data, pulse parameters such as PW and PRT and type of signal are measured. From spectral domain data, signal parameters such as frequency, power level and bandwidth are measured. In addition to this, we also do recording of the IQ data into the NI 8265 RAID storage for future offline simulations.
We got three advantages on choosing NI’s technology for this simulation system.
Availability of RF Transceiver with on-board FPGA: As any DRFM system will have one channel for receiver and one channel for transmitter, the availability of the same on NI PXIe 5646R VST Transceiver module reduced the physical size of the solution enormously. In the absence of this module, we would require to either choose a stand-alone instrument which is bulky in size as well as cost. Availability NI PXIe 5646R module made a major contribution in making our solution a portable one.
Power of LabVIEW FPGA tool: FPGA forms a major part of any DRFM based system. If we need to do the FPGA programming on VHDL/Verilog for the scale of application software we are addressing, it would have taken us a very long time to realize this solution. Whereas LabVIEW FPGA allowed us a seamless integration of our software algorithms with the FPGA present in PXIe 5646R module and fastened our software development efforts.
High Data Streaming technology of PXIe platform: The Peer-to-Peer Streaming capability of the NI PXIe 1085 chassis enabled us to handle the signal processing between the FPGAs present in NI PXIe 5646R & NI PXIe 7975R FlexRIO FPGA modules. The data streaming feature also helped us in performing the recording of the RF signals as Baseband I & Q on NI 8265 RAID drive.
Features of DRFM based Radar Simulation System
- Completely based on PXIe COTS Hardware
- Easy to use Software GUIs for Radar Echo Simulation functionalities of Range, Doppler, RCS, Noise Jamming
- Scalable & Upgradable hardware & software platform
- Portable Benchtop System
- Includes RF Signal Recording for offline simulations
Conclusion
By choosing PXIe COTS hardware and LabVIEW software platform for this solution, we were successfully able to design & develop such a complicated simulation system within 4 months. To address requirements in X/Ku/Ka Bands, we just need to include an RF Up/Down converter to the NI PXIe 5646R module. System can be easily upgraded to include features like RGPO, VGPO (ECM features) as application software is written in LabVIEW & LabVIEW FPGA. Hence, we feel the system can be scalable to address any future add-ons easily without too much R&D efforts.
