Is it beneficial to have full wavelength sized antennas rather than half wavelength?
In most practical radio-astronomy and communication setups, a full-wavelength antenna is not inherently “better” than a half-wavelength one—they simply behave differently, and the choice depends on what pattern, impedance, and physical size you want.
Here’s the key comparison:
Half-Wavelength Dipole (λ/2)
Pros
- Predictable, broad radiation pattern with a single main lobe and no strong nulls off the ends.
- Feedpoint impedance ~73 Ω, which is easy to match to 50–75 Ω coax.
- Physically manageable size for most bands.
- Excellent efficiency because it’s resonant.
Cons
- Narrower overall physical aperture compared with larger antennas.
Full-Wavelength Dipole (λ)
A full-wavelength dipole does not behave like a larger version of the λ/2 dipole.
Pros
- Higher directivity in the broadside direction.
- Narrower beamwidth, which can slightly increase gain (typically ~1–2 dB above a half-wave).
Cons
- Very high feedpoint impedance (typically ~1000–3000 Ω), requiring a matching network or a high-ratio balun.
- Multiple lobes and nulls. The radiation pattern breaks into several lobes, which may or may not suit your application.
- More sensitive to height above ground due to current distribution differences.
- Physically large.
For radio astronomy (especially L-band, 1420 MHz):
- Antennas are often part of arrays or used for controlled beam shapes.
- Predictability and impedance matching are usually more important than raw size, which is why λ/2 and shorter driven elements (e.g., in Yagis or log-periodics) are standard.
- A full-wave dipole’s complex multi-lobe pattern is often undesirable unless used intentionally in an array.
Bottom line
- λ/2 dipoles are used because they are resonant, efficient, easy to match, and have a clean pattern.
- λ dipoles offer slightly more gain but introduce impedance issues and more complex patterns.
- Bigger is not automatically better.