It seems that everything is going digital, and radar systems are no exception. Designers of radar equipment are increasingly relying on transmit/receive modules with high dynamic range for the detection of extremely low-level signals. The coming generation of these modules will contain digital I/Q or digital IF capabilities as well as very high-speed digital buses. This in turn is driving a need for updated test equipment that supports the move from analog to digital radar systems.
With its M8190A arbitrary waveform generator (AWG), Agilent delivers spurious-free dynamic range of up to 80 dBc at 14-bit resolution (see the figure). The instrument offers switchable resolution; the digital-to-analog converter (DAC) operates at 8 Gsamples/s at 14-bit resolution and at 12 Gsamples/s at 12-bit resolution. Thus, users can decide if they need higher bandwidth or higher resolution for a given measurement.
In traditional I/Q modulation schemes used to generate high-frequency signals, a pair of DACs generates the baseband signal for subsequent modulation up to RF. This generally works well but the output may be plagued by spurious signals. These glitches do not affect the final settled value of the signal, but they do corrupt the spectral content of the output signal.
The risk is misinterpreting these glitches as analog output. Modulation adjustment tames the spurs, but this tends not to hold over time and temperature. In the M8190A, Agilent’s proprietary DACs deliver intermodulation that is down about 70 dB; you can use the output directly if it’s high enough in frequency for your measurement, or it can be mixed up to RF.
The secret to removing the DAC output glitches lies in the use of a resampling switch on each of the 26 current sources that comprise the DAC. Each of these switches handles only one value of current, on or off, making the process extremely linear. The values are then added in the resistor termination to achieve the final output.
Resolution and bandwidth are important, but for realistic test scenarios, an AWG needs a lot of memory for long play times. The M8190A contains up to 2 Gsamples of waveform memory, yielding 1/6 seconds of play time at the highest sampling rate. That memory is put to its best possible use through sequencing.
The memory is divisible into as many as 256,000 segments, each of which can be looped up to 4 billion times. Additionally, there are three levels of sequencing available; the advanced mode permits setup of very complex waveforms. There is also the option of real-time memory access.
The M8190A boasts three user-selectable amplifiers, each of which is optimized for different signal characteristics. The first is for I/Q signal generation, the second for high-bandwidth IF/RF applications at bandwidths up to 5 GHz, and the third for time-domain applications requiring low jitter and low overshoot.
Configurations for the instrument include a five-slot AXIe chassis, which fits up to two M8190A arbs with a system controller and ESM module for PCI Express connectivity. This configuration requires only the addition of a monitor to form a complete instrument. Alternately, a two-slot AXIe chassis can be fitted with a single arb and the ESM module. This configuration would require a PC or laptop with a PCI Express card.
When it comes to generating signal waveforms, users have various options including Matlab, LabVIEW, or home-brewed software created with Microsoft Visual Studio. Pricing for the M8190A starts at $79,000.