WR650 Waveguide for hydrogen line radio astronomy

If you want a rectangular waveguide that works well around 1.4 GHz, a common standard choice is WR650.

✅ Why WR650 at ~1.4 GHz

• WR650 is specified for roughly 1.1 GHz to 1.7 GHz — comfortably covering 1.4 GHz.
• Its internal cross‑section: about 165.1 mm × 82.55 mm.
• Using a waveguide sized for a lower cutoff than your operating frequency ensures proper propagation (i.e. avoids cutoff losses).

⚠️ What you lose by going too small or too large

• A waveguide too small will have a cutoff higher than 1.4 GHz → signal will be strongly attenuated or not propagate.
• Oversized waveguides may support multiple modes (higher‑order modes), complicating field patterns, impedance matching, and possibly increasing losses or instability.