Unit 1 — Theory of Operation

TM-TOOL-002 — Open Handout TM Chapter: Chapter 2 ELOs: Understand the operating principle of the ANTENNA ANALYZER — VECTOR IMPEDANCE MEASUREMENT; identify key specifications Estimated time: 20 minutes

Step 1: Read the TM

Open TM-TOOL-002. Read Chapter 2 — Theory of Operation completely.

Then come back here.

Chapter 2 Content

2-1 AD8302 Gain/Phase Detector

The AD8302 accepts two RF signals on INPA and INPB (50Ω each) and produces two DC outputs:

• VMAG: Proportional to |V_A / V_B| in dB (30 mV/dB, range −30 to 0 dBm per input).
• VPHS: Proportional to phase difference (10 mV/°, 0° to 180° range).

INPA receives the reference (forward-coupled) signal; INPB receives the reflected signal. The ratio VREFL/VFWD and the phase shift Δφ together yield the complex reflection coefficient Γ:

Γ = |V_refl / V_fwd| ∠ Δφ Z_ant = Z0 × (1 + Γ) / (1 − Γ) (Z0 = 50 Ω)

2-2 Directional Coupler A multiband RF coupler (TM-TOOL-002-SCH-004) separates the forward and reflected waves on the transmission line to the DUT (antenna). Coupling factor is −20 dB on the HF section and −20 dB on the VHF/UHF section. Directivity must be ≥20 dB across the band to keep reflected signal isolation adequate for accurate Γ measurement.

2-3 Frequency Sources

AD9851 DDS (HF, 0.1–30 MHz): 125 MHz reference clock, 32-bit frequency word, phase noise −100 dBc/Hz at 1 kHz offset. Controlled via 3-wire SPI from ESP32. Sweep rate: ~1000 points/second.

ADF4351 PLL (VHF/UHF, 30 MHz–1.3 GHz): Fractional-N synthesizer, 32.768 MHz TCXO reference, phase noise −90 dBc/Hz at 10 kHz. Integer-boundary spurs require spur-avoidance in sweep software when crossing integer multiples of the PFD reference frequency.

Why Theory Matters

You cannot use a measurement tool correctly without understanding how it works. Theory tells you: - What the tool measures and how it converts the quantity to a readable output - What the sources of error are — so you can recognize and minimize them - What the valid operating range is — so you stay within its specifications - How to interpret results that don't match expectations

If a measurement looks wrong, theory is where you look first.

Self-Check Questions

SC1-1. In one sentence, state the operating principle of the ANTENNA ANALYZER — VECTOR IMPEDANCE MEASUREMENT as described in Chapter 2.

SC1-2. What does Chapter 2 identify as the primary source(s) of measurement error or uncertainty?

SC1-3. What key specification(s) (accuracy, range, frequency coverage) does the TM state?

SC1-4. What does Chapter 2 say the ANTENNA ANALYZER — VECTOR IMPEDANCE MEASUREMENT cannot do — what are its limitations?

SC1-5. List two formulas or relationships from Chapter 2 that govern the tool's operation.

Answer Key

SC1-1. See TM §2-1. Compare your sentence to the first substantive paragraph of Chapter 2.

SC1-2. See Chapter 2. Look for language about error sources, accuracy limits, parasitic effects, or frequency dependence.

SC1-3. See Chapter 2. Look for numbers with units: %, ppm, Hz, Ω, dB, W.

SC1-4. See Chapter 2 and Chapter 1. Limitations are often stated as frequency range, power limits, or accuracy bounds.

SC1-5. See Chapter 2. Equations or proportionality statements are the relationships that govern the tool.

Checkpoint

Before proceeding, state without looking: - The operating principle of the ANTENNA ANALYZER — VECTOR IMPEDANCE MEASUREMENT - The primary error source(s) - At least one key specification with its value

→ Proceed to Unit 2