What is analysis bandwidth on a spectrum analyzer?

Analysis bandwidth (also called demodulation bandwidth or instantaneous bandwidth) is the maximum signal bandwidth a spectrum analyzer can capture simultaneously for vector (I/Q) analysis. Unlike RBW, which is the filter bandwidth used for swept spectrum display, analysis bandwidth determines the widest modulated signal that can be demodulated, measured for EVM, or analyzed for ACLR in a single acquisition. Modern signal analyzers achieve 510 MHz to 2 GHz analysis bandwidth. For 5G NR 100 MHz carriers, minimum 120 MHz analysis bandwidth is needed (100 MHz signal + guard bands).

How does oscilloscope bandwidth affect RF measurements?

Oscilloscope bandwidth is the frequency at which the analog front-end attenuates a sine wave by 3 dB. For accurate time-domain RF measurements, the oscilloscope bandwidth must be at least 2-3x the highest frequency component. Modern real-time oscilloscopes achieve 70+ GHz bandwidth with 256 GSa/s sampling rate, enabling direct capture of mmWave 5G signals. The rule of thumb for digital signals is: BW ≥ 0.35/rise_time. For a 100 ps rise time, BW ≥ 3.5 GHz. Oscilloscope-based RF analysis trades measurement speed for bandwidth compared to dedicated spectrum analyzers.

What is VNA IF bandwidth and how does it affect measurements?

VNA IF bandwidth is the detection bandwidth of the receiver after downconversion. Wider IF bandwidth enables faster sweeps but increases noise floor. Narrower IF bandwidth reduces noise floor by 10×log10(BW_wide/BW_narrow) dB but proportionally increases measurement time. Typical range: 1 Hz to 1 MHz. For a 70 dB dynamic range measurement: 100 Hz IFBW provides ~95 dB receiver dynamic range. At 100 kHz IFBW: ~65 dB dynamic range. The trade-off is: every 10x reduction in IFBW improves noise floor by 10 dB but increases sweep time by 10x.

RF Test & Measurement

Test Bandwidth

/test BAND-width/

The effective measurement bandwidth of an RF test instrument, determining the maximum signal bandwidth that can be accurately captured and analyzed. For spectrum analyzers, this is the analysis (demodulation) bandwidth. For oscilloscopes, it is the analog front-end bandwidth. For VNAs, it is the IF bandwidth that trades speed against noise floor. Modern wideband signal analyzers achieve 2+ GHz analysis bandwidth for 5G NR and radar testing.

Signal Analyzer: Up to 2 GHz

Oscilloscope: Up to 70+ GHz

VNA IFBW: 1 Hz to 1 MHz

Understanding Test Bandwidth

Every RF measurement instrument has a finite bandwidth that limits what signals it can accurately measure. The term "test bandwidth" encompasses several distinct concepts depending on the instrument type. For swept spectrum analyzers, the resolution bandwidth (RBW) determines spectral resolution, while the analysis bandwidth determines the widest signal that can be demodulated in one capture. For real-time oscilloscopes, the analog bandwidth limits the highest frequency component visible.

Matching instrument bandwidth to the signal under test is critical. Insufficient bandwidth causes measurement errors: underestimated peak power, incorrect EVM readings, and missed spectral components. The general rule is that analysis bandwidth should be at least 1.2 times the signal bandwidth to capture the full occupied spectrum including roll-off regions.

Instrument Bandwidth Specs

Signal Analyzer Analysis BW:
5G NR 100 MHz: need ≥ 120 MHz analysis BW
5G NR FR2 (400 MHz): need ≥ 500 MHz
Radar pulse: need ≥ 2/pulse_width

Oscilloscope Rule of Thumb:
BW ≥ 0.35 / t_rise
100 ps rise time: BW ≥ 3.5 GHz
10 ps rise time: BW ≥ 35 GHz

VNA IFBW vs. Dynamic Range:
DR ≅ Noise Floor − 10 × log₁₀(IFBW)
1 Hz IFBW: +30 dB vs. 1 kHz IFBW

Instrument Bandwidth Comparison

Instrument	Bandwidth Type	Typical Range	Trade-off
Signal Analyzer	Analysis BW	25 MHz – 2 GHz	Cost vs. capture BW
Oscilloscope	Analog BW	500 MHz – 70 GHz	BW vs. noise/cost
VNA	IF BW	1 Hz – 1 MHz	Speed vs. DR
EMI Receiver	RBW	200 Hz – 1 MHz	Standard-defined

Common Questions

Frequently Asked Questions

What is analysis bandwidth?

Maximum signal bandwidth captured simultaneously for I/Q analysis. Unlike RBW (swept display). Modern analyzers: 510 MHz to 2 GHz. 5G NR 100 MHz needs ≥120 MHz analysis BW. Determines widest signal for EVM/ACLR measurement.

How does oscilloscope BW affect RF?

Analog front-end −3 dB point. Need 2 to 3x highest frequency component. Rule: BW ≥ 0.35/rise_time. Modern: 70+ GHz, 256 GSa/s for mmWave. Trades speed for bandwidth vs. dedicated spectrum analyzers.

What is VNA IF bandwidth?

Detection BW after downconversion. Wider = faster, more noise. Narrower = slower, lower noise floor. Every 10x reduction: +10 dB DR, 10x slower. 100 Hz: ~95 dB DR. 100 kHz: ~65 dB DR. Critical for filter and component characterization.

Related Terms

← Bandwidth (Satellite) Variable Transponder →

Test Equipment

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