Question E9C11:
How is the far-field elevation pattern of a vertically polarized antenna affected by being mounted over seawater versus soil?  

Choices:  
A: Radiation at low angles decreases  
B: Additional lobes appear at higher elevation angles  
C: Separate elevation lobes will combine into a single lobe  
D: Radiation at low angles increases    

Correct Answer is  D: Radiation at low angles increases  

Correct answer: D — Radiation at low angles increases

Why D is correct:
- Seawater has very high conductivity and permittivity ($\sigma \approx 4$–5 S/m, $\epsilon_r \approx 80$), making it behave like an excellent ground plane.
- For a vertical, the far-field elevation pattern is the vector sum of the direct ray and the ground-reflected ray. Over seawater the vertical-polarization reflection coefficient at low elevation angles has magnitude near 1 (low loss), so the two rays add strongly near the horizon, boosting low-angle radiation.
- In effect, the “image” of the vertical in the highly conductive surface is strong, increasing the field at small elevation angles that are most useful for DX.

Why the other choices are incorrect:
- A: Radiation at low angles decreases — Opposite of what happens. Poor soil decreases low-angle radiation; seawater increases it.
- B: Additional lobes at higher elevation angles — The number and placement of lobes are mainly set by antenna height (in wavelengths) and geometry, not improved ground conductivity. Seawater primarily strengthens low angles rather than creating extra high-angle lobes.
- C: Separate elevation lobes will combine into a single lobe — Ground quality doesn’t merge lobes; it changes relative lobe strengths. The multi-lobe structure is governed by height and array configuration.

Useful formulas and rules of thumb:
- Two-ray (direct + ground-reflected) model for elevation pattern:
  $$E(\theta) \propto \left| 1 + \Gamma_v(\theta)\, e^{j\,2kh\sin\theta} \right|$$
  where $k = 2\pi/\lambda$, $h$ is antenna height, and $\Gamma_v(\theta)$ is the vertical-polarization reflection coefficient.
- Over seawater at low elevation angles: $|\Gamma_v| \approx 1$ (strong, low-loss reflection), giving constructive interference near the horizon.
- Over average/dry soil: $|\Gamma_v| \ll 1$ and lossy, so the low-angle lobe is much weaker.
- Practical rule of thumb: A vertically polarized antenna over seawater can be several dB (often 3–10 dB) stronger at 1–10 degrees elevation than the same antenna over average soil, dramatically improving DX performance.