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mcnanovna

Antenna Analysis

This tutorial covers common antenna analysis tasks using mcnanovna.

Basic SWR and Impedance

The most common antenna measurement is SWR (Standing Wave Ratio) and impedance at the feedpoint.

Ask Claude: “Analyze my antenna from 144 to 148 MHz”

Claude will:

  1. Run a sweep across the band
  2. Find the resonant frequency (minimum SWR)
  3. Calculate impedance at resonance
  4. Report bandwidth where SWR < 2:1

Example output:

Resonant frequency: 145.2 MHz
SWR at resonance: 1.15:1
Impedance at resonance: 48.5 + j2.3 Ω
Bandwidth (SWR < 2:1): 143.8 - 146.9 MHz (3.1 MHz)
Return loss at resonance: -23.4 dB

Finding Resonance

For antennas with multiple resonances (like a multi-band antenna):

Ask Claude: “Find all resonances from 1 to 30 MHz”

Claude uses analyze_s11_resonance to find all points where the antenna is resonant.

Impedance Matching

If your antenna doesn’t match 50Ω, design a matching network:

Ask Claude: “Design a matching network for 35+j25 ohms at 145 MHz”

Claude uses analyze_lc_match to compute L-network solutions:

Solution 1: Series L (27 nH) + Shunt C (18 pF)
Solution 2: Shunt C (12 pF) + Series L (42 nH)

Antenna Types

Expected characteristics:

  • Resonant impedance: ~73Ω
  • Narrow bandwidth
  • Figure-8 radiation pattern

Ask Claude: “Analyze my dipole on 20m”

Troubleshooting Antennas

High SWR everywhere

Possible causes:

  • Feedline not connected properly
  • Antenna not resonant in measurement range
  • Major construction problem

What to check:

  • Verify feedline continuity
  • Widen the measurement range
  • Check physical dimensions

SWR dip but wrong frequency

The antenna is resonant but not where you want it.

  • Too low: Antenna is electrically long → shorten
  • Too high: Antenna is electrically short → lengthen

Good SWR but high reactance

The antenna is resonant but not at 50Ω.

Ask Claude: “Design a matching network for my measured impedance”

Narrow bandwidth

High-Q antennas (small loops, loaded verticals) have narrow bandwidth. Options:

  • Accept it (tune for the portion of band you use)
  • Add loading to lower Q
  • Use an antenna tuner

Radiation Patterns

For a quick analytical pattern based on antenna type:

Ask Claude: “Show the radiation pattern for my dipole”

This uses the S11 data to determine resonance and impedance, then generates an idealized 3D pattern.

For measured patterns, see 3D Pattern Measurement.