Flange
Understanding Waveguide Flanges
Waveguide flanges serve the same function as coaxial connectors: they provide a repeatable, standardized interface between components. However, because waveguide operates at the wavelength scale, flange alignment must be very precise. Even small misalignment creates impedance discontinuities and increases insertion loss and VSWR.
Flange Types
- Cover (flat) flanges: Flat mating surface. Both flanges make direct metal-to-metal contact. Requires very clean, flat surfaces. Examples: UG-cover series.
- Choke flanges: Have a circular groove that acts as a quarter-wave short circuit, creating an effective electrical contact without requiring perfect metal-to-metal contact. Reduce sensitivity to surface flatness and contamination.
- Precision flanges: Use alignment pins and holes for repeatable positioning. IEEE standard or manufacturer-specific (like CMR, CBR, CPR).
Flange Standards
Flanges are standardized by waveguide size. Common designations include UG-series (military) and IEEE/IEC series. For WR-90 (X-band), common flanges are UG-39/U (cover) and UG-40/U (choke). For Ka-band WR-28, the CMR-28 precision flange is widely used.
| WR Size | Cover Flange | Choke Flange | Precision |
|---|---|---|---|
| WR-284 | UG-584/U | UG-585/U | CPR-284 |
| WR-90 | UG-39/U | UG-40/U | CMR-90 |
| WR-42 | UG-595/U | UG-596/U | CMR-42 |
| WR-28 | UG-599/U | UG-600/U | CMR-28 |
| WR-10 | UG-387/U | UG-388/U | CMR-10 |
Frequently Asked Questions
What is a waveguide flange?
A waveguide flange is a standardized metal plate that connects waveguide sections together. It ensures precise alignment of the waveguide apertures and provides electrical continuity of the internal conducting walls. Different flange types are used for different precision requirements.
What is the difference between a cover and choke flange?
A cover flange has a flat mating surface requiring direct metal-to-metal contact. A choke flange has an annular groove that creates an electrical short through a quarter-wave transformer effect, reducing sensitivity to surface imperfections. Best practice is to mate one cover flange with one choke flange.
Do all waveguide flanges mate together?
Flanges for the same waveguide size (WR number) are generally compatible. UG-series flanges use standard bolt patterns, and cover-to-choke mating is the standard configuration. Precision flanges (CMR/CPR) require matching alignment pin/hole configurations.