Professional radio astronomy dishes are engineered for electrical reflectivity, structural rigidity, thermal stability, and low weight. The exact construction depends on frequency range (long-wavelength vs millimetre work), but most large instruments share similar materials and design principles.
Main Reflecting Surface
1️⃣ Aluminium panels
Used on many large centimetre–millimetre telescopes.
- High electrical conductivity
- Lightweight
- Corrosion resistant
- Easy to machine to precise curvature
Examples:
- Very Large Array
- Effelsberg 100-m Radio Telescope
Panels are typically bolted to a backup structure and individually adjustable for surface accuracy.
2️⃣ Steel panels
Heavier but strong and cost-effective.
- Often galvanized or coated
- Common in older large dishes
- Suitable for longer wavelengths
Example:
- Green Bank Telescope
3️⃣ Aluminium mesh (wire mesh surface)
Used when observing long wavelengths (e.g., 21 cm hydrogen line and longer).
- Much lighter than solid sheet
- Wind passes through
- Electrically reflective if mesh spacing ≪ wavelength
For 21 cm (1420 MHz), mesh spacing under ~2 cm works well — ideal for amateur builds.
4️⃣ Carbon fibre reinforced polymer (CFRP)
Used in high-frequency or precision telescopes.
- Very stiff
- Low thermal expansion
- Lightweight
Common in modern millimetre/sub-millimetre instruments.
Example:
- Atacama Large Millimeter/submillimeter Array
Backup Structure (Dish Frame)
Usually:
- Welded steel truss
- Sometimes aluminium space frame
- Increasingly CFRP structures for precision arrays
The frame maintains the parabolic shape under gravity and wind loading.
Surface Accuracy Matters
Required surface precision depends on wavelength:
- 21 cm hydrogen line → millimetre accuracy is plenty
- 3 mm (100 GHz) → surface must be accurate to ~0.1 mm
Rule of thumb:
Surface RMS error ≲ λ / 16
Protective Coatings
- Anodized aluminium
- Galvanized steel
- White thermal paint (to reduce solar heating distortion)
Special Case: Non-dish Telescopes
Some professional instruments are not dishes at all:
- Arecibo Observatory — was a fixed spherical reflector built from perforated aluminium panels when working
- LOFAR — phased dipole arrays (no dish)
In Summary
Professional radio astronomy dishes are typically made from:
- Reflector: Aluminium panels or mesh
- Structure: Steel or aluminium truss
- Precision builds: Carbon fibre composites
For amateur 1420 MHz hydrogen work, aluminium sheet or fine aluminium mesh over a rigid frame is entirely appropriate and very close in principle to professional systems.