Electronic Design

Spectrum Analyzer Delivers Unprecedented Ku-Band Performance

Designers of high-frequency RF equipment and systems are finding that performance is everything when it comes to spectrum analysis. They need to be able to see small signals in the presence of large ones. Working with digital RF requires analysis with a combination of dynamic range and image rejection at very wide bandwidths.

All of the above and more are manifested in the Tektronix RSA6120A spectrum analyzer (see the figure), which incorporates a feature set that’s targeted directly at digital-RF designers working in the Ku-band frequencies (12 to 18 GHz). The instrument offers extremely high spurious-free dynamic range of 75 dB in the Ku-band, an enhanced set of radar measurements, and switched-filter preselection that overcomes the limitations of earlier spectrum analyzers.

Sporting a full 110 MHz of real-time bandwidth, the RSA6120A offers the industry’s best dynamic range in both wideband and narrowband measurements, according to the company. “One benchmark for narrowband performance is the third-order intercept spec (TOI),” says Darren McCarthy, Tektronix’s technical marketing manager for RF test. McCarthy also says that the analyzer has a TOI spec that’s 3 to 8 dB better than competing instruments. The RSA6120A is specified for a TOI of +19 dB above 6 GHz. On the wideband side, it delivers impressive signal fidelity in the Ku-band.

The instrument’s roster of radar measurements includes new pulse statistics and histograms. It also features new pulse measurements, including overshoot, ripple, and droop. A total of 27 different automatic scalar and vector measurements is available on each radar pulse, all at the push of a single button. An important addition is impulse-response measurement, which provides automatic measurement of radar chirp quality. “This gives users qualitative measurement of impedance-mismatch problems in the signal chain,” says McCarthy.

A key to the RSA6120A analyzer’s performance is its application of microwave preselection in the signal-downconversion chain to narrow down to a band of interest from within a wideband window. While traditional preselector approaches use YIG-based (yttrium-iron-garnet) technology, this approach can cause phase and amplitude distortion through alteration of magnetic fields. It also can introduce hysteresis when tuning across frequencies. Moreover, because YIG preselectors are inherently narrowband devices, wideband measurements cannot be made with the preselector inline. As a result, the instrument’s acquisition window is thrown open to images and other artifacts of upstream mixers.

Instead, the RSA6120A uses a switched-filter preselector, which offers wide frequency coverage and is always inline. Flatness across 100 MHz is specified at ±0.7 dB RMS and ±1.5° RMS. While it’s true that switched-filter preselectors also introduce amplitude and phase errors, as do YIG filters, the errors introduced by a switched-filter preselector are stable over time and temperature and can be characterized and compensated for in software. So unlike the YIG preselector, the switched-filter preselector can be used for wideband signals. And because the preselector in the RSA6120A analyzer is always inline, radiation from its local oscillator (LO) into the RF signal chain is virtually eliminated.

Pricing for the RSA6120A spectrum analyzer starts at $96,400. The instrument is available now.

Tektronix Inc.


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