New-Tech Europe | March 2017 | Digital Edition

equipment can generate radar targets using similar methods to those of DRFMs: RF down- conversion, digital manipulation in baseband and RF up-conversion. It does so by combining an RF signal analyser as the receiver with a signal generator for the transmitter. Typical systems operate from 100 kHz to 40 GHz and receive any kind of RF radar signal in the specified frequency band with up to 160 MHz bandwidth, then converting the signal to in- phase and quadrature-phase data (I/Q data). I/Q data are applied to the baseband input of the signal generator where time delay, Doppler frequency shift and attenuation are applied to the specified user values. The radar echo signal is then retransmitted to the radar by the signal generator. One advantage of this measuring equipment is its exceptional RF performance, which is suitable for additional parametric radar tests during research and development or production. The flexible and modular approach allows the vector signal generator or the signal and spectrum analyser to be used in other setups as well – and in their dedicated field installation. The Fig. 4 above shows the Fast Fourier Transform (FFT) spectrum, range-Doppler plot and target list of a radar under test (RUT). The COTS target generator was setup to generate a single target with a range of 2000 m and radial velocity of -25 m/s. As depicted in the figure above, the radar, which operates with a signal bandwidth (fsw) of 20 MHz and a coherent processing interval (Tcpi) of 500 µs measures the range and radial velocity accordingly. The COTS radar target generator is able to generate up to 20 different

Fig. 3: Representation of a COTS real-time radar target generator (R&S®SMW200A vector signal generator and R&S®FSW signal and spectrum analyser)

signal fidelity. In addition, spurious- free dynamic range (SFDR) may limit the radar’s ability to distinguish real targets from electronic countermeasure signals. With high signal fidelity, DRFMs having coherent target echo returns are well suited to specific radar tests, but are unsuited to handling a broad variety of signal conditions and scene effects. Cost as well as limited flexibility means they are ill-suited to test the functional parameters of the radar. Commercial off-the-shelf test and measurement equipment Today, COTS test and measurement

digitisation capability. Furthermore, these specialised target generators come at a high cost. According to the US Department of Defense (DoD), the price of a single DRFM module ranges from USD 150,000 to USD 700,000 [1]. The minimum delay introduced by a DRFM is mainly limited by its ADC and DAC. In addition, signal processing adds a number of processing cycles to the radar echo signal. Typical minimum range delays range from below 100 ns to below 1 µs. A further consideration is how the analogue RF signal is represented in the digital domain (amplitude, phase, I/Q) and the number of bits, because this is what mainly determines the DRFM’s

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