By COURTNEY E. HOWARD
Not all waveform analyzers are the same, and so professionals should carefully consider the specifications and capabilities of the models available and weigh them against the specific needs of their military and aerospace application.
First, it is important to understand the relationship between the waveform to be analyzed and the specifications of the equipment performing the signal analysis, explains Darren McCarthy, RF technical marketing manager at Tektronix in Beaverton, Ore. The most common method of analyzing modern waveforms is the use of vector signal analyzers, or fast Fourier transform (FFT)- based analysis techniques. "It is important that all the waveform information is captured within the communication channel for a finite period of time; however, most dynamic range specifications on spectrum analyzers are represented by swept analysis techniques and have no correlation to the vector analysis applications," McCarthy describes.
The system's ability to capture and analyze not only repetitive signals, but also intermittent or time-varying signals is another major consideration when selecting the optimal waveform analyzer. "The true power of a waveform analyzer comes with its ability not only to analyze what signals are supposed to be present, but also to analyze the signals that are not supposed to be there," says Sue Guzman, Aeroflex Cupertino general manager and vice president of Aeroflex Test Solutions in Cupertino, Calif. "Critical to this ability is the need for simultaneously displaying the captured waveform in all three domains: time, frequency, and modulation."
When selecting a signal analyzer to evaluate waveforms, consider RF frequency, information or acquisition bandwidth, and signal fidelity (dynamic range) within the acquisition bandwidth and at the frequency of interest, McCarthy advises. "You need to be able to tune to the frequency of interest," he says. Information bandwidth relates to the instantaneous FFT bandwidth that can be continually processed for analysis. "If your waveform hops over multiple channels, and you are interested in the analysis of the waveform during the hopping transitions, the information bandwidth of your signal analyzer must be able to capture the entire hopping transitions over multiple channels."
Signal fidelity also needs to be considered under the representative waveform conditions. "At microwave frequencies, in order to enable wide instantaneous bandwidths, many spectrum analyzers need to remove preselection filters that limit bandwidth and distort the incoming signal," McCarthy advises. "During these conditions, the analyzer specifications no longer apply."
Today's technologies provide a much more capable platform for waveform analyzers, including wider instantaneous bandwidths, much higher speed, much deeper signal memory, and many more software analysis features that, at one time, only were available as post-processing capabilities on computers separate from the waveform analyzer itself, " Guzman admits. "The instantaneous bandwidth available determines the fastest pulses that can be analyzed or determines the widest frequency signal which can be measured," she describes.
The system should offer modularity, enabling upgrades as better performing analog-to-digital converters (ADCs) and faster processors become available, without causing the user to purchase an entirely new system each time, Guzman adds. The breadth of analysis capability present in the software/firmware of the system, especially the variety of data visualization options and the number of different demodulation types supported, is key, she says.
"Software option flexibility enables the analyzer to be used for multiple purposes: phase noise testing, signal source tester, peak/channel power meter, modulation analyzer, oscilloscopes, and frequency counter," McCarthy explains, describing the new Tektronix RSA6120A. As a result, such systems–capable of many different automated scalar and vector pulse analysis parameters, for example–can replace several instruments usually required for accurate pulse performance characterization.
The depth and speed of the signal memory available, which determines how long of a waveform recording can be taken or determines how well intermittent signals can be captured, is another important consideration, Guzman describes. "Longer waveform recordings capture a more complete picture of the signal or environment being tested."
The measurement utility and performance can give you the confidence to design the most advanced radio and radar applications, says McCarthy. "Read the specifications, and ask how they apply to your waveform analysis needs."
Do not lock yourself into a corner, Guzman cautions. "Select one with the hardware modularity to adapt to newer ADC and processing capability, and with a software/firmware architecture that allows the system to add new demodulation or analysis functions. Invest in a test solution that can grow with you, not one that traps you in the past."
More Military & Aerospace Electronics Current Issue Articles
More Military & Aerospace Electronics Archives Issue Articles