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vor 7 Jahren

10-2016

  • Text
  • Komponenten
  • Technik
  • Radio
  • Filter
  • Oszillatoren
  • Quarze
  • Emv
  • Messtechnik
  • Bauelemente
  • Software
  • Frequency
  • Wireless
  • Antenna
  • Anwendungen
  • Antenne
  • Frequenzbereich
  • Circuit
Fachzeitschrift für Hochfrequenz- und Mikrowellentechnik

RF & Wireless Figure 3:

RF & Wireless Figure 3: The popup window for SA setup enables selection of key parameters for multiple measurement channels The core instrument is a Keysight PNA microwave network analyzer. These solutions can be configured in two ways: one supports single-sweep measurements through 1.0 mm coaxial connections; the other supports a variety of banded measurements via waveguide. The single-sweep configuration is based on a 67 GHz PNA and includes a pair of companion mmWave controllers that support two- or four-port measurements (Keysight N5261A or N5262A, respectively). These connect to broadband frequency extenders, providing the interface between the mmWave test-head modules and the network analyzer (Figure 1). The extenders provide a 1.0 mm coaxial interface to the DUT up to 110 GHz, and waveguide is used above 110 GHz. The banded configuration supports a variety of frequency extenders from OML, Inc. and Virginia Diodes, Inc. (VDI). These use waveguide for frequencies above 110 GHz and in some frequency bands between 67 and 110 GHz. Figure 2 shows an example configuration using frequency extenders from OML. The latest version of Keysight’s optional “SA on VNA” capability now supports all of these configurations, enabling integrated spectrum analysis into the terahertz range on the PNA and PNA-X network analyzers. The optional spectrum analyzer mode includes a user interface that presents the typical array of setup parameters: center frequency and span; start and stop frequencies; step size; resolution bandwidth (RBW); detector shape; averaging; and receiver attenuation (Figure 3). One important note about using SA in the distributed configuration: because the internal receiver attenuators are bypassed, external attenuators may be required when testing high-power DUTs. The integration of SA capabilities enables quick handoffs from the VNA mode without changing the physical test setup. For example, if an anomaly crops up in a VNA trace, the user can place a marker at that point and press “Marker to SA” to initiate a spectrum measurement. The measurement appears in a new window, enabling further observation and analysis of spectral content and behavior. The PNA and PNA-X also include a calibrated stimulus that can be directed to any and all DUT ports. Through tight control of frequency, amplitude and DC offset, this provides a very accurate test solution for the characterization of harmonics and intermodulation products. In addition, internal pulse generators and modulators enable characterization of DUTs with pulsed-RF stimuli. The net result is the ability to evaluate DUT behavior under a wide operating range and in a variety of operating conditions. Implementing SA functionality The Keysight implementation of spectrum analysis is built on its existing VNA architecture. A typical spectrum analyzer includes a microwave pre-selector (i.e., a filter) that blocks highlevel signals while measuring low-level signals as well as unwanted mixing products; this removes receiver harmonics and image responses. The SA-on- VNA design uses a powerful software-based technology to virtually eliminate images and internal spurious signals. The same techniques can be utilized in the distributed-architecture VNA configuration used for mmWave measurements. The only additional consideration is a special calibration of the SA receivers to ensure accurate measurements. This calibration must include the frequency-extender heads as well as all associated hardware, cabling and fixturing. Because the user may change Figure 4: The single-connection, multi-channel SA capability provides accurate, simultaneous measurements on all DUT ports 58 hf-praxis 10/2016

RF & Wireless Figure 5: As span increases, the integrated SA capability provides a significant speed advantage over standalone spectrum or signal analyzers one or more of those elements to suit a specific frequency range or setup, two types of calibrations must be performed any time the test configuration changes: power level and IF receiver. To simplify these situations, the new high-frequency SA options include functionality that automates the calibration processes and guides the user. Applying the advantages of integrated SA The integration of SA capabilities into a VNA offers two key advantages over the multi-instrument approach: multiple simultaneous measurements and calibrated accuracy. Through its multiple test ports, a VNA enables multi-channel spectrum analysis that is synchronized with the internal swept signal generators. In addition, a PNA or PNA-X, through a single connection, provides simultaneous measurements on all DUT ports. The range of possible measurements includes input spectra, output spectra, channel power, gain compression, feedthrough, reflections, conversion gain, harmonics, and intermodulation (Figure 4). This simplifies characterization of devices such as mixers, frequency converters and amplifiers as well as high-frequency modules and subsystems. VNA calibration and de-embedding techniques are essential to the accuracy of in-fixture and onwafer measurements. The process corrects for the instrument’s systematic errors, and it removes cable and fixture effects. It can be used with frequency extenders, and it’s also applicable to the SA-on-VNA capability. In addition, the power-compensation features can be used to deliver a stimulus of known power to the DUT, thereby compensating for known loss in the fixture or probes. The resulting improvement in measurement accuracy enables a deeper understanding of a DUT’s true performance. Accelerating searches for spurious signals Spurious are unwanted signals - harmonic or nonharmonic - that may cause interference from transmitters, false responses in radar systems, or reduced dynamic range in communications receivers. As a result, spurs must be identified and measured before a designer takes action to reduce them to sufficiently low levels as defined by a system or device specification. The search for spurs presents two challenges: time and complexity. The process of checking spurious performance is time-consuming, especially when searching for low-level signals over a broad frequency range. Characterizing spurs over the operating range of typical mixers and frequencyconversion devices tends to be tedious and complicated, and it often requires external control software. With the integrated high-performance SA capability, a PNA or PNA-X can perform fast spurious searches across a broad frequency band, improving test time compared to a standalone signal analyzer (Figure 5). Speed does not degrade accuracy: measurements results are comparable to those obtained with today’s most sophisticated spectrum or signal analyzers. Conclusion Author biography Working at mmWave and submmWave frequencies can be challenging. As implemented in the Keysight PNA and PNA-X microwave network analyzers, the optional addition of integrated SA capabilities to a distributed VNA architecture makes it possible to characterize component performance and behavior into the terahertz range in a single test setup. The integrated stimulus, along with the ability to perform spectrum analyzer measurements on multiple channels simultaneously, offers researches and design engineers new insights in much less time and with excellent accuracy. For more information, please visit www.keysight.com/find/thz. ◄ Suren Singh is an industry application specialist for Keysight Technologies, focusing on terahertz measurement solutions. He earned a BSEE from the University of Durban-Westville, Durban, South Africa, in 1985, and received his Graduate Diploma (1992) and MSEE (1995) from the University of Witwatersrand, Johannesburg. Since 1986, Suren has been with the Hewlett-Packard Company, Agilent Technologies and now Keysight Technologies. His experience includes application engineering, product design, manufacturing, and test-process development for microwave hybrid microcircuits. Suren is a current member of IEEE and has presented at several conference, covering mmWave and terahertz applications. hf-praxis 10/2016 59

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