Spectrum analyzers measure faster and more accurately

-- EDN, 11/23/2000

The first member of a new PSA (performance-spectrum-analyzer) family from Agilent Technologies uses more digital technology than did earlier generations of the RF instruments. The improved architecture makes possible faster, more accurate measurements and, says Agilent, provides more setup flexibility than do competitive products, thereby simplifying the task of obtaining the information you need. You can get the 30-Hz to 26.5-GHz E4440A's speed, accuracy, and flexibility for $48,000, a cost lower than that of several competitive products (Picture).

The E4440A provides better performance than do competitive units in several areas. The DANL (displayed average noise level) is -153 dBm, 5 dBm lower than that of several competitive units. The phase noise at 1 GHz with a 1-MHz offset is -140 dBc/Hz, 5 dBc/Hz lower than that of the best competitive unit, and the amplitude inaccuracy at 3 GHz is ±0.35 dB versus ±1.5 dB for the competitive units.

The DSP-based RBW (resolution-bandwidth) filters are adjustable in 160 steps, whereas competitive units offer only a few steps in a 1-3-10 or 1-2-5-10 sequence. Moreover, the added setup flexibility does not force you to take extra steps to find the optimum bandwidth; you can adjust RBW in the customary way until you find a pair of settings that bracket the setting you need. Only then do you invoke the more closely spaced settings.

The DSP-based filters also provide much steeper skirts than do conventional filters. The shape factor (ratio of -60-dB to -3-dB bandwidth) is 5-to-1 versus approximately 12-to-1 for analog filters. The use of DSP also enables much faster sweeps than spectrum analyzers have traditionally allowed. Fast sweeps at narrow RBW produce filter outputs that are too low. The choice of sweep speed has thus represented a compromise between accuracy and measurement time. The use of DSP techniques enables correcting the filter's output amplitude, however, allowing higher sweep speeds at low values of RBW.

Agilent says that the E4440A is the first in a family of spectrum analyzers that will share the same DSP-based architecture. Future family members will offer narrower frequency ranges at lower prices.

Agilent Technologies, 1-800-452-4844. www.agilent.com.

at www.rscahners.ims.ca/ednmag.

-by Dan Strassberg