10 Spectrum Analyzer basis of

Technical Note

The Basis of Spectrum Analyzers

Slide 1 SpectrumAnalyzer-E-E-

The Basis of Spectrum Analyzers

Anritsu Corporation Ver. Slide 2 SpectrumAnalyzer-E-E-

Contents

1. What is a Spectrum Analyzer?
2. Measurement Categories
3. Principals of a Spectrum Analyzer
4. Characteristics 4 Suitable Input Level 4 Maximum Input Level 4 Measurement Frequency Range 4 Sideband Noise 4 Resolution bandwidth for frequency (RBW) 4 RBW and Sweep Time 4 Detection method 4 Video filter (VBW) 4 Dynamic Range (Average Noise Level, Residual response, Distortion)
5. Application Areas

Slide 5 SpectrumAnalyzer-E-E- Frequency Power (dBm) (W) f 0 -10dBm 0 2f 0 -20dBm 0 3f 0 -54dBm 4 (Sum) 0

Describing Electrical Signals

Power 0 (-9) Oscilloscope waveforms Spectrum analyzer waveforms Slide 6 SpectrumAnalyzer-E-E-

Measurement Categories

Level (amplitude) Frequency Time

Time vs. Level

Oscilloscope (Time domain)

Frequency vs. Level

Spectrum analyzer (Frequency domain)

Frequency vs. Time

Modulation analyzer

(Modulation domain)

Slide 7 SpectrumAnalyzer-E-E-

Time Domain

• Changes in time can be seen. • If a signal has many frequency elements, the analysis is difficult.

Frequency Domain

• Each element of a complex signal can be separated easily. • Low-level distortion signals can be detected. • Spurious elements can be measured.

Modulation Domain

• Changes in frequency can be seen. • The modulation accuracy can be analyzed. • Changes in amplitude cannot be seen.

Analysis of Electrical Signals

Slide 8 SpectrumAnalyzer-E-E-

Time

domain

Frequency

domain

Modulation

domain

Slide 11 SpectrumAnalyzer-E-E- When the signal and local oscillator are added at the mixer input, the suitable input level is the distortion level specification that doesn't influence the measurement. The level relationship between the input signal and the distortion is specified at the mixer input level, not at the input connector. Therefore, the RF attenuator attenuates the input signal to a suitable mixer input level. 2nd harmonic distortion ≤ -90dBc at MIX input level -10dBm ATT MIX Local OSC. This Level Input Signal

4 Suitable Input Level

e The specification of MS8609A. Slide 12 SpectrumAnalyzer-E-E-

The maximum input level prevents damage to the input

circuit. It is based on the input levels to the Attenuator and

Mixer.

Maximum input level: +20dBm (Op-32: +30dBm) ATT MIX Local OSC. Damage Level

4 Maximum Input Level

Input Signal e The specification of MS8609A

Slide 13 SpectrumAnalyzer-E-E-

The measurement frequency range is determined by the

center frequency of the IF filter and the local oscillator

frequency range.

Input Signal Freq. = Local Signal Freq. – IF Freq.

The input signal and the local signal are mixed by the mixer.

The mixer output is filtered by the IF filter with center

frequency fc and displayed on the screen.

4 Measurement Frequency Range

Input Signal IF Filter (0 to 300MHz) Local OSC. (200 to 500MHz) (fc=200MHz) (200MHz) f Slide 14 SpectrumAnalyzer-E-E- It appears in the base of the spectrum because of noise in the internal local signal source. Sideband noise shows the signal purity, and the performance of nearby signal analysis is determined by this characteristic. It is specified by how many dB down from the center at an offset of 10kHz (or 100kHz) when the resolution bandwidth (RBW) is narrow enough, and a high purity signal is input.

4 Sideband Noise

For the local signal source, the dotted line spectrum is the ideal. However, it actually has sideband noise like the solid line. Masking occurs by the sideband noise when there is a nearby A or B signal and it is not possible to detect it. Ideal

Slide 17 SpectrumAnalyzer-E-E- e The specification of MS8609A: Selectivity <15 : 1

When a narrow RBW is selected, the 3dB bandwidth and

60dB bandwidth become small, the frequency resolution is

greater, the average noise level falls, and you can see low-

level signals.

60dB Bandwidth

Selectivity =

3dB Bandwidth

4 Resolution bandwidth for frequency (RBW)

Slide 18 SpectrumAnalyzer-E-E-

4 RBW and Sweep Time

A signal displayed with the proper sweep time is shown in the 1st wave. The amplitude in the display decreases in the 2nd and 3rd waves when the sweep is made too early, and the frequency shifts. When the sweep speed is not proper, UNCAL is displayed in the screen.

Proper

sweep time = K ×

(RBW ≥ VBW)

Frequency span

RBW × VBW K=

Slide 19 SpectrumAnalyzer-E-E-

Normal: Displays both the maximum level and the minimum level

present between the current sample point and the next sample point.

Pos Peak: Displays the maximum level present between the current

sample point and the next sample point. Pos Peak is used to measure the peak value of signals near the noise level.

Sample: Displays the instantaneous signal level at each sample point.

Sample is used for noise level measurement and time domain measurement.

Neg Peak: Displays the minimum level present between the current

sample point and the next sample point.

RMS: Displays the root-mean-square (effective) value of the signal

input between the current sample point and the next sample point.

4 Detection methods

Slide 20 SpectrumAnalyzer-E-E- Pos Peak is used for Normal signal measurement, Occupied bandwidth measurement, and Adjacent channel leakage power ratio measurement as a Digital method. Sample is used for Random noise measurement, Occupied bandwidth measurement, and Adjacent channel leakage power ratio measurement as an Analog method.

4 Detection methods

Slide 23 SpectrumAnalyzer-E-E-

It is the range that can be measured without making it

suffer in the noise level, residual responses, and

distortion.

However, there is no definition common to all

manufacturers, and the value is different depending on

what it is based on.

(1) Average Noise Level

(2) Residual response

(3) Distortion: 2nd harmonic Distortion

Two-tone 3rd order Distortion

4 Dynamic Range

Slide 24 SpectrumAnalyzer-E-E-

(1) Average Noise Level

e The specification of MS8609A Average Noise Level ≤ -121dBm (f 0 =2GHz, RBW 300Hz, ATT 0dB) For noise generated internally, a key factor is thermal noise and the noise generated from active elements such as transistors and ICs. Therefore, the average noise level becomes the lower limit of the input signal level that can be measured. The method of stating the average noise level varies according to the manufacturer. For example, it may be stated in the measurement specification, or the value in change per Hz. Pn (average level) = 10 log 10 (kTB) + No k: Boltzmann constant (1× 10 -23J/K), T: Absolute temperature (k), B: IF bandwidth, N 0 : Noise figure (active element)

Slide 25 SpectrumAnalyzer-E-E-

The average noise level changes with RBW and ATT

RBW 30kHz 10kHz 3kHz 1kHz ATT 60dB 50dB 40dB 30dB 20dB 10dB Changing RBW Changing ATT The average noise level increases 10dB when RBW value is changed from 1kHz to 10kHz. The average noise level changes by 10dB when ATT value is changed by 10dB. Slide 26 SpectrumAnalyzer-E-E-

(2) Residual response

Residual response is a phenomenon that appears as an

input signal on the screen even though there is no real

input signal.

Various local oscillators are used internally in spectrum

analyzers. Residual response appears when the basic

waveform and the harmonic components are mixed,

producing the IF frequency.

Residual responses appear in a specific frequency band,

and the average noise level relates to all frequency bands.

Residual response ≤ -100dBm (f 0 =2GHz band) e The specification of MS8609A

Slide 29 SpectrumAnalyzer-E-E-

(4) Two-tone 3rd Order Distortion

When two high-level signals with nearby frequencies are

input to the mixer, the two signals influence each other.

As a result, a frequency not contained in the input signal

appears. These phenomena are called Two-tone 3rd Order

Distortion.

2f 1 -f 2 f 1 f 2 2f 2 -f 1 -30dBm -85dBc e The specification of MS8609A Two-tone 3rd order distotion ≤ -85dBc (f 0 =2GHz, Offset 50kHz, MIX input -30dBm) Slide 30 SpectrumAnalyzer-E-E- 1dB 1dB 1dB 3dB TOI b a y1 = x + a y2 = 3x + b For MS8609A

1. Two-tone 3rd order distortion: <-85dBc (0 to 3) Mixer input: -30dBm They mean that the absolute value of 3 rd order distortion is –115dBm when Mixer input level is –30dBm. TOI = (a – b)/2 + a = (-30+115)/2 –30 = +12
2. Two-tone 3rd order distortion: <-80dBc (3 to 7) Mixer input: -30dBm TOI = (a – b)/2 + a = (-30+110)/2 –30 = +10dBm
3. Two-tone 3rd order distortion: <-75dBc (7 to 13) Mixer input: -30dBm TOI = (a – b)/2 + a = (-30+105)/2 –30 = +7 x(Input level) y(Output level)

What is Third Order Intercept point(TOI)?

-85dBc MIX. input -30dBm (-115dBm) e MS9609A Spec. at 2GHz y1 is 1st tone and y2 is 3rd order distortion. y1 = x + a (1) y2 =3 x + b (2) The intersection between (1) and (2) is TOI. x + a = 3x + b Æ x = (a – b)/ y = (a – b)/2 + a

Slide 31 SpectrumAnalyzer-E-E-

4 Dynamic Range

A B C -30dBm A: Average noise ≤ -121dBm (f 0 =2GHz, RBW300Hz) B: Residual response ≤ -100dBm (2GHz band) C: 2nd harmonic distortion ≤ -90dBc at MIX input -10dBm A: Average noise -30dBm –(-121dBm) = 91dB / RBW300Hz Æ 116dB / RBW1Hz B: Residual response -30dBm –(-100dBm) = 70dB C: 2nd harmonic distortion 20dB + 90dBc = 110dB Signal e The specification of MS8609A e Input level is -30dBm Slide 32 SpectrumAnalyzer-E-E-

5. Application Areas

####### IEC, EN (Europe), FCC (America), JIS

####### (Japan)

####### 5. EMI

####### CATV, Analog/Digital TV,

####### Broadcasting, Transmitter Amplifiers,

####### Distributors

####### 4. CATV

####### 3. Satellite BS, CS, Digital Broadcasting

####### broadcasting

####### VCOs, Synthesizers, Mixers, Filters,

####### Amplifiers, Antennas

####### 2. Devices

####### 1. Mobile Mobile phones, Wireless LANs

####### communications