S21 Series/Shunt Analysis

S21 analysis modes extract component parameters from transmission measurements. Connect components between CH0 and CH1 ports using series or shunt configurations to measure L, C, R, and Q values.

Analysis Modes

Access via DISPLAY > MEASURE:

Mode	Configuration	Use Case
LC SERIES	Component in series	Low impedance components
LC SHUNT	Component in parallel	High impedance components

LC Series Mode

For measuring low-impedance components (< 100 ohms):

Connection

CH0 ----[Component]---- CH1
          (series)

Connect the component directly between the center pins of CH0 and CH1.

Enable LC Series

1. Connect component in series between ports
2. Go to DISPLAY > MEASURE
3. Tap LC SERIES
4. The display shows extracted parameters

Display Shows

LC-SERIES
Fs = 10.000000 MHz
Lm = 2.53 uH  Cm = 100.5 pF  Rm = 2.3 ohm
Q = 68.5

• Fs: Series resonant frequency (peak transmission)
• Lm: Motional/series inductance
• Cm: Motional/series capacitance
• Rm: Series resistance (ESR)
• Q: Quality factor

LC Shunt Mode

For measuring high-impedance components (> 100 ohms):

Connection

CH0 ----+-------- CH1
        |
    [Component]
        |
       GND

Connect the component between the signal path and ground (shunt configuration).

Enable LC Shunt

1. Connect component in shunt between signal and ground
2. Go to DISPLAY > MEASURE
3. Tap LC SHUNT
4. The display shows extracted parameters

Display Shows

LC-SHUNT
Fs = 5.000000 MHz
Lm = 10.1 uH  Cm = 100.2 pF  Rm = 5.6 ohm
Q = 56.2

Measurement Principle

Series Mode

The firmware finds:

1. Peak transmission (minimum loss) = series resonance
2. -45 degree phase points on either side
3. From these, calculates bandwidth and Q
4. Derives L, C, R from frequency and Q

Shunt Mode

The firmware finds:

1. Minimum transmission (maximum loss) = parallel resonance
2. +/-45 degree phase points on either side
3. From these, calculates bandwidth and Q
4. Derives L, C, R from frequency and Q

Note

The analysis automatically places markers at the resonant frequency and -45/+45 degree points.

Shell Commands

# Enable analysis modes
measure lcseries    # LC series mode
measure lcshunt     # LC shunt mode
measure none        # Disable

# Set measurement resistance (fixture impedance)
# Default is 50 ohms from config._measure_r

Practical Examples

Measure an Inductor

1. Connect inductor in shunt configuration (to ground)
2. Set sweep from 1 MHz to 100 MHz
3. Enable LC SHUNT mode
4. Read inductance and Q from display

For series connection (between ports):

1. Connect inductor between CH0 and CH1
2. Enable LC SERIES mode
3. Read inductance and Q

Measure a Capacitor

1. Connect capacitor in series between ports
2. Set sweep to cover expected resonance
3. Enable LC SERIES mode
4. Read capacitance and ESR

Tip

Capacitors are best measured in series mode; inductors often work better in shunt mode, depending on their impedance.

Verify Component Values

1. Set sweep range based on expected values:
   • Higher L/C = lower resonant frequency
   • Lower L/C = higher resonant frequency
2. Connect component in appropriate configuration
3. Run measurement
4. Compare measured values to specifications

Frequency Range Guidelines

Component Value	Series Mode Range	Shunt Mode Range
1 nH - 10 nH	100 MHz - 1 GHz	500 MHz+
10 nH - 100 nH	30 MHz - 300 MHz	100 MHz - 500 MHz
100 nH - 1 uH	10 MHz - 100 MHz	30 MHz - 200 MHz
1 uH - 10 uH	1 MHz - 30 MHz	5 MHz - 50 MHz
1 pF - 10 pF	100 MHz - 1 GHz	Use series mode
10 pF - 100 pF	30 MHz - 300 MHz	100 MHz+
100 pF - 1 nF	10 MHz - 100 MHz	30 MHz - 200 MHz

Tips for Accurate Measurements

Tip

• Short leads: Keep component leads as short as possible
• Calibration: Perform SOLT calibration with the test fixture
• Multiple readings: Average several measurements
• Temperature: Component values change with temperature

Caution

Very low Q components (< 10) may not produce accurate results as the phase transition is too gradual for precise detection.