3D Pattern Measurement

This tutorial walks through measuring a complete 3D antenna radiation pattern using mcpositioner and mcnanovna together.

Prerequisites

• NanoVNA-H connected via USB
• ESP32 positioner built and on WiFi
• Both MCP servers added to Claude Code:

  claude mcp add mcnanovna -- uvx mcnanovna
  claude mcp add mcpositioner -- uvx mcpositioner

Setup

Physical Arrangement

                    Transmit Antenna
                    (on VNA Port 1)
                          │
                          │  Line of sight
                          ▼
    ┌─────────────────────────────────────────┐
    │                                         │
    │              Positioner                 │
    │         ┌─────────────────┐             │
    │         │    Antenna      │             │
    │         │  Under Test     │◄── VNA Port 2
    │         │   (rotates)     │             │
    │         └────────┬────────┘             │
    │                  │                      │
    │              θ axis                     │
    │                  │                      │
    │         ────────────────                │
    │              φ axis                     │
    └─────────────────────────────────────────┘

• Transmit antenna: Fixed, connected to VNA Port 1
• Antenna under test: Mounted on positioner, connected to VNA Port 2
• Distance: Far-field (at least 2λ, preferably 10λ+)

Tip

For accurate patterns, the transmit antenna should have a known, broad pattern (like a dipole) so it illuminates the AUT evenly across all angles.

Measurement Procedure

1. Verify both servers are connected

   Ask Claude: “Check positioner status and VNA info”

   Claude will call positioner_status and info to verify both devices respond.

2. Home the positioner

   Ask Claude: “Home the positioner on both axes”

   This establishes the reference position (theta=0, phi=0).

3. Calibrate the VNA

   Ask Claude: “Calibrate for the 2m band”

   Follow the SOLT calibration procedure. This is critical for accurate S21 measurements.

4. Run the pattern measurement

   Ask Claude: “Measure a 3D radiation pattern for my dipole antenna on 2m”

   Claude uses the measure_pattern_grid prompt to guide the measurement:

   • Confirms grid resolution (default: 5° theta × 10° phi)
   • Moves through each grid point in serpentine order
   • Measures S21 at each position
   • Assembles the pattern data

5. View the results

   If the mcnanovna web UI is running (MCNANOVNA_WEB_PORT=8080), the pattern renders in 3D automatically.

   Or ask Claude: “Show the pattern statistics”

Resolution Tradeoffs

Step Size	Grid Points	Time	Use Case
10° × 20°	342	~9 min	Quick survey, verify setup
5° × 10°	1332	~33 min	Standard measurement
2° × 5°	6552	~2.7 hr	Publication-quality

Pattern Normalization

By default, patterns are relative—the peak is set to 0 dBi. This shows the pattern shape but not absolute gain.

For absolute gain, measure a reference antenna first:

1. Mount a known-gain antenna (e.g., calibrated dipole at 2.15 dBi)
2. Measure S21 at bore-sight
3. Note the reference S21 value
4. Measure your antenna under test
5. Offset all measurements: gain_dBi = S21_dB - reference_S21_dB + reference_gain_dBi

Troubleshooting

Pattern looks wrong

• Check that the transmit antenna is properly aimed
• Verify far-field distance (reflections cause errors)
• Recalibrate VNA if temperature changed significantly

Measurement is noisy

• Increase VNA averaging (use more points)
• Reduce IF bandwidth
• Check cable connections

Positioner loses position

• Motors may be missing steps—reduce speed
• Check mechanical coupling for slippage
• Increase motor current in firmware

Web UI not updating

• Check MCNANOVNA_WEB_PORT is set
• Verify browser can reach the port
• Check for WebSocket connection errors in browser console