---
title: Antenna Analysis
description: Using mcnanovna to analyze antenna performance
---

import { Tabs, TabItem, Aside } from '@astrojs/starlight/components';
import HardwareCards from '../../../components/HardwareCards.astro';

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.

Say: "Analyze my antenna from 144 to 148 MHz"

Your assistant 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):

Say: "Find all resonances from 1 to 30 MHz"

This 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:

Say: "Design a matching network for 35+j25 ohms at 145 MHz"

This 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

<Tabs>
  <TabItem label="Dipole">
    **Expected characteristics:**
    - Resonant impedance: ~73Ω
    - Narrow bandwidth
    - Figure-8 radiation pattern

    Say: "Analyze my dipole on 20m"
  </TabItem>
  <TabItem label="Vertical">
    **Expected characteristics:**
    - Resonant impedance: ~36Ω (ground-mounted)
    - Needs matching network or radials
    - Omnidirectional pattern

    Say: "Analyze my vertical on 40m"
  </TabItem>
  <TabItem label="Yagi">
    **Expected characteristics:**
    - Low impedance at feedpoint (~25Ω)
    - Narrow bandwidth
    - Directional pattern

    Say: "Analyze my Yagi from 144 to 148 MHz"
  </TabItem>
  <TabItem label="Loop">
    **Expected characteristics:**
    - Variable impedance based on size
    - High Q (narrow bandwidth)
    - Figure-8 pattern (small loop)

    Say: "Analyze my magnetic loop on 40m"
  </TabItem>
</Tabs>

## 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

<Aside type="tip">
For a dipole, each side is approximately λ/4 in length. At 145 MHz, that's about 51 cm per side.
</Aside>

### Good SWR but high reactance

The antenna is resonant but not at 50Ω.

Say: "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:

Say: "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](/tutorials/pattern-measurement/).

<HardwareCards show="h" heading={false} />