Spectrum and Network Analyzers
Separate sensitivity, large-signal range, phase noise, and calibration-plane requirements.
RF Spectral and Vector-Response Measurement Chains
A spectrum analyzer converts an input through attenuation, gain, mixing, and filtering before digitization and spectral analysis. Sensitivity is limited by internal noise; a strong carrier can instead expose compression, distortion, or oscillator phase noise. The appropriate front-end setting depends on the weak signal and nearby interferers that must be resolved together.
A vector network analyzer uses a coherent source and receiver paths to measure amplitude and phase, commonly as S-parameters. Calibration corrects systematic errors at a defined reference plane. If a board launch, cable, probe, or fixture lies between that plane and the DUT, its behavior must be included in the calibration plan or characterized for de-embedding.
Define the measurement before selecting RF and timing parts: frequency range, signal level, separation from blockers or carrier, modulation or analysis bandwidth, phase-noise offsets, port count, fixture, and required uncertainty. Frequency coverage alone does not establish sensitivity, dynamic range, or vector accuracy.
Component Requirements
Typical functions, devices, and parameters in Spectrum & Network Analyzers.
| System function | Typical devices | Key parameters | Browse |
|---|---|---|---|
| RF input and preselection Routes, protects, and filters the input signal ahead of frequency conversion. | RF switches, attenuators, filters, LNAs, limiters | Frequency, noise figure, linearity, loss, isolation, power handling | View category |
| Local oscillator and synthesizer Supplies coherent conversion signals for spectrum analysis and VNA receiver channels. | PLLs, VCOs, clock references, frequency dividers | Phase noise by offset, spurs, tuning range, settling, reference input | View category |
| IF and digitizer Amplifies and digitizes converted signals for spectral or vector processing. | IF amplifiers, filters, ADCs, clock buffers | IF bandwidth, noise, linearity, SFDR, sample clock quality | View category |
| Vector source and receiver ports Drives calibrated test signals and measures reflected or transmitted response at instrument ports. | RF synthesizers, directional couplers, receivers, interface switches | Port count, output level, directivity, tracking, phase coherence | View category |
Design & Selection Considerations
Weak-signal and blocker conditions
State the smallest signal, nearby or in-band blockers, carrier level, offset spacing, resolution bandwidth, sweep time, and required measurement uncertainty.
LO, reference, and phase-noise offsets
Specify frequency span, close-in and far-out offsets of interest, internal or external reference, settling, and synchronization with other sources.
Vector receiver and calibration plane
Define port count, frequency span, amplitude and phase uncertainty, connector system, calibration standards, cable state, fixture and any de-embedding data.
Conversion and digitizer range
Check mixer level, gain and attenuation range, IF bandwidth, converter performance, spurious responses, and overload recovery for the expected input.
Supply Chain Considerations
RF performance depends on frequency and level
Compare noise, phase noise, gain, compression, and distortion at the frequency and input level of interest; a broad frequency-range match alone is not equivalent.
Calibration accessories are part of the measurement
Keep calibration kit, connector type, torque or handling requirements, cable set, and fixture characterization associated with VNA boards and service spares.
Coherent channels need shared-reference context
List which sources and receivers must share a reference or phase relationship. A clock or synthesizer alternate can preserve nominal frequency while changing phase-noise or synchronization behavior.
Supply Chain Support
RF path BOM by receiver and source
Separate input attenuation, mixer and LO, IF gain and filtering, digitizer, reference distribution, and VNA source/receiver ports.
Measurement setup with each RF request
Include frequency, level, spacing or offset, analysis bandwidth, port configuration, calibration plane, cables, and fixture information.
RF alternate review
Compare the operating band and the relevant noise, phase, linearity, isolation, gain, and configuration limits at the actual operating point.
Frequently Asked Questions
The displayed average noise level describes the analyzer's broadband noise under specified conditions and is relevant to weak-signal visibility. Dynamic range describes the usable separation between signals under a particular measurement and can also be limited by input-mixer distortion or local-oscillator phase noise. For a two-tone or close-in measurement, compare the relevant limits at the stated input level, offset, attenuation, and resolution bandwidth.
The analyzer's local oscillator participates in frequency conversion, so its phase fluctuations can appear around a strong displayed signal and mask nearby components. The required performance depends on carrier level and offset frequency; a distant noise-floor figure does not describe close-in resolution. Include the offset range, carrier conditions, and reference-lock configuration when reviewing the synthesizer and reference path.
Choose the reference plane at the electrical boundary where the DUT behavior must be known. A calibration at the cable ends corrects to those connectors; a fixture beyond that plane can remain in the result unless it is characterized and removed through an appropriate fixture or de-embedding method. Keep the standards, cable state, connector, and fixture model tied to the measurement setup.