TE11 Circular
Waveguide
Complete TE11 circular waveguide reference for antenna feed applications. Pipe inner diameters, frequency bands, and mating flange dimensions for 35 standard sizes from Ku-band (12.4 GHz) through G-band (220 GHz).
TE11 Flange Geometry
Standard round contact flange interface for circular waveguide antenna feeds. Four-hole bolt pattern with two alignment pins for repeatable orientation. The circular pipe bore is concentric with the flange body.
bolt circle (N BSC), and alignment pins (P), 4 holes at 45°
overall depth (X), and alignment pin pocket detail
• Pipe bore is circular; I.D. per the pipe size table below
• Bolt holes: .112-40 UNC .2B THD, 4 holes equally spaced at 45° from reference
• Alignment pin holes: .140 (3.50) DIA, .028 (.71) deep, 2 places
• Alignment pins: .0615 (1.56) / .0610 (1.55) DIA, 2 each
• Flatness: .0005 (.013) maximum across mating face
• True position: X .001 at .004 DIA (.10)
• All dimensions in inches (millimeters)
TE11 Circular Waveguide Pipe Sizes
All standard TE11 antenna feed circular waveguide pipe inner diameters and their operating frequency bands. These are specifically for TE11 mode antenna feed applications, not to be confused with standard circular waveguide sizes. Where two pipe sizes cover the same frequency range, the smaller pipe provides better single-mode operation while the larger pipe has lower insertion loss.
| Designation | Band | Pipe I.D. inches (mm) |
Frequency Band (GHz) |
TE11 Cutoff (GHz) |
Mating Flange |
|---|
TE11 Flange Dimensions
Mating flange dimensions for each band group. Multiple pipe sizes share the same flange interface within a band. Dimensions reference the technical drawing above.
| Band | Frequency Range (GHz) |
M Flange OD |
N Bolt Circle BSC |
P Pin Spacing |
R Plate Thickness |
Flange Designation |
Pipe Sizes Covered |
|---|
TE11 Mode in Circular Waveguide
The TE11 mode is the dominant (lowest-order) propagating mode in circular waveguide. Unlike rectangular waveguide where the TE10 mode is dominant, circular waveguide supports the TE11 mode first, which has an electric field pattern that is well-suited for antenna feed applications.
Cutoff Frequency
The TE11 cutoff frequency for a circular waveguide of inner diameter D is:
Where: c = speed of light (11.803 in/ns), D = inner diameter (inches)
Simplified: fc (GHz) ≈ 6.918 / D (inches)
The waveguide operates between the TE11 cutoff and the next higher mode (TM01) cutoff, which is 1.3065 times the TE11 cutoff. This gives a usable single-mode bandwidth ratio of approximately 1.31:1.
Why Circular Waveguide for Antenna Feeds?
- Pattern symmetry: The circular cross-section produces balanced E and H-plane radiation patterns, which is critical for achieving low cross-polarization in reflector antenna systems.
- Dual polarization: Circular waveguide supports two orthogonal TE11 modes simultaneously at the same frequency, enabling dual-linear or circular polarization through a single waveguide. An orthomode transducer (OMT) separates the two polarizations into individual rectangular waveguide ports.
- Lower loss: For the same cutoff frequency, circular waveguide has a larger cross-sectional area than rectangular waveguide, resulting in lower attenuation per unit length.
- Mechanical fit: The circular bore interfaces cleanly with conical feedhorns, scalar rings, and corrugated horn antennas used in dish feed assemblies.
Pipe Size Selection
The table above lists multiple pipe sizes for many frequency bands (e.g., V-0 and V-1 both cover V-band frequencies). The selection guideline is:
- Below 100 GHz: Choose the smaller pipe. This keeps the operating frequency closer to the TM01 cutoff, reducing the risk of higher-order mode propagation that degrades polarization purity.
- 100 GHz and above: Choose the larger pipe. At these frequencies, conductor losses dominate, and the larger bore provides a meaningful reduction in attenuation.
Rectangular-to-Circular Transitions
Most RF systems use rectangular waveguide for the majority of the transmission path and transition to circular waveguide only at the antenna feed. Standard transitions (WR-xx to circular) are available for all common band/pipe size combinations. The transition converts the TE10 rectangular mode to the TE11 circular mode with minimal VSWR and insertion loss.
Frequently Asked Questions
What is TE11 mode in circular waveguide?
TE11 is the dominant propagating mode in circular waveguide. The cutoff frequency is fc = 6.918 / D (GHz), where D is the pipe inner diameter in inches. It produces a symmetric field pattern ideal for antenna feed applications and supports dual-polarization operation.
Why use circular waveguide for antenna feeds?
Circular waveguide matches the symmetry of parabolic dish antennas, supports dual-polarization through a single pipe, produces balanced radiation patterns with low cross-polarization, and interfaces cleanly with conical feedhorns. For these reasons, virtually all satellite earth station and radar antenna feeds use circular waveguide at the feed aperture.
How do I choose between two pipe sizes for the same band?
Below 100 GHz, use the smaller pipe for better single-mode operation and polarization purity. Above 100 GHz, use the larger pipe to reduce conductor losses, which become dominant at millimeter-wave frequencies. The trade-off is between mode purity (smaller pipe) and lower attenuation (larger pipe).
Are these flanges the same as rectangular waveguide flanges?
Yes. Circular waveguide for antenna feeds uses the same UG-series round contact flanges (UG-425/U, UG-381/U, UG-383/U, UG-385/U, UG-387/U) as rectangular waveguide. The flange interface is identical; only the bore is circular instead of rectangular. This ensures mechanical compatibility with rectangular-to-circular transitions, OMTs, and feedhorns.
What material is used for circular waveguide?
Brass (CDA 360) is standard for most sizes. Aluminum (6061-T6) is used for lightweight applications, particularly in airborne and portable systems. The bore surface is typically gold-plated or silver-plated for minimum conductivity loss. Precision pipe I.D. tolerance is typically ±.001 (.03mm) for standard grades and ±.0005 (.013mm) for high-performance grades.