Use the chart below to shortlist a WR size whose specified operating band covers your full frequency range. Then check the actual component’s flange, insertion loss, return loss, peak and average power, and environmental limits. Being above cutoff does not establish acceptable performance.
WR Sizes
Table of Contents
WR Designation Meaning
WR identifies rectangular waveguide. Its number approximately tracks the internal broad-wall width in hundredths of an inch: WR90 is 0.900 inch wide, while WR62 is 0.622 inch. Use the drawing dimensions rather than deriving a precision dimension from the rounded designation.
The broad wall is conventionally labeled a, and the narrow wall b. The chart applies to ordinary, full-height, hollow rectangular waveguide with an approximately air-filled interior. Ridged, dielectric-loaded and other custom guides need their own mode and bandwidth data.
Common WR Size Chart
These are common reference bands, not universal guaranteed bands for every component. Historical NBS/NIST calibration publications document the familiar WR90, WR75 and WR62 ranges, and the WR42, WR28 and WR22 ranges shown here. Those publications are reference evidence, not a statement of current calibration-service availability.[1][2]
| WR size and nominal aperture | Common band; calculated TE10 cutoff |
|---|---|
| WR90 0.900 × 0.400 in 22.860 × 10.160 mm |
8.2–12.4 GHz Cutoff: 6.56 GHz |
| WR75 0.750 × 0.375 in 19.050 × 9.525 mm |
10–15 GHz Cutoff: 7.87 GHz |
| WR62 0.622 × 0.311 in 15.799 × 7.899 mm |
12.4–18 GHz Cutoff: 9.49 GHz |
| WR51 0.510 × 0.255 in 12.954 × 6.477 mm |
15–22 GHz Cutoff: 11.57 GHz |
| WR42 0.420 × 0.170 in 10.668 × 4.318 mm |
18–26.5 GHz Cutoff: 14.05 GHz |
| WR34 0.340 × 0.170 in 8.636 × 4.318 mm |
22–33 GHz Cutoff: 17.36 GHz |
| WR28 0.280 × 0.140 in 7.112 × 3.556 mm |
26.5–40 GHz Cutoff: 21.08 GHz |
| WR22 0.224 × 0.112 in 5.690 × 2.845 mm |
33–50 GHz Cutoff: 26.35 GHz |
Metric dimensions are rounded for display; the cutoff calculations use the inch dimensions converted at 25.4 mm per inch and c = 299,792,458 m/s. They are theoretical values, not measurements of a supplied assembly.
Dolph’s WR/R and flange reference publishes some different band edges, including 8.2–12.5 GHz for WR90 and 11.9–18 GHz for WR62. Use the ordered component’s approved frequency range and test data when a requirement extends beyond the common chart.
Waveguide Flange Matching
A WR size specifies the guide opening, not the complete mating interface. Compare both flange drawings for aperture height and orientation, bolt pattern, alignment pins, face geometry and any gasket groove. The flange size guide separates those checks from the WR/R designation.
Record the exact flange at each end of an adapter or transition. “WR28 both ends” does not identify whether the faces, pins or seal arrangements match the existing equipment.
Frequency Ranges
Operating Band Range
The complete RF path must meet its specifications over the required band. A straight section’s range does not extend the rating of an attached window, filter, switch, adapter or antenna. Include tuning, temperature and manufacturing variation in the agreed acceptance conditions.
State frequencies numerically. Labels such as X, Ku, K, Ka and Q are useful shorthand, but a WR range can cross a named-band boundary. For example, the 22–33 GHz WR34 reference band should not be described as exclusively Ka-band.
Cutoff Frequency
For an ideal air-filled rectangular guide with a > b, the dominant TE10 cutoff is fc = c / (2a). With a in millimeters, fc in GHz = 149.896229 / a; 150 / a is a quick approximation. MIT’s waveguide notes derive the cutoff relations and distinguish propagating from evanescent modes.[3]
For WR90, a = 22.86 mm gives fc ≈ 6.56 GHz. The next possible higher-order cutoffs are TE20 at c/a ≈ 13.11 GHz and TE01 at c/(2b) ≈ 14.75 GHz. The lower of those two sets the next mode threshold for this ideal guide.
Below cutoff, the TE10 field is evanescent. Just above cutoff, dispersion and conductor attenuation make the theoretical threshold a poor operating-band recommendation. The common 8.2–12.4 GHz WR90 band leaves margin on both sides.
Band Overlap
At 14 GHz, both WR75 and WR62 fall within the chart’s common bands. That gives two candidates, not interchangeable parts. Compare measured loss, power limits, available components and the interfaces already installed.
A larger guide may reduce conductor loss or increase power capacity under suitable conditions, but size alone does not establish either result. Near-cutoff operation, mismatches, surface finish, pressure and local field concentrations can change the comparison.
A transition can connect different apertures but cannot make a below-cutoff section support ordinary propagation. Specify the transition’s full operating band and include its insertion loss and return loss in the assembly budget.
Applications
Radar Systems
Specify pulse-envelope peak power, pulse width, repetition rate and average power separately. For rectangular pulses, average power equals peak power multiplied by duty cycle. A calculated example of 50 kW, 0.5 μs pulses at 1 kHz has a 0.05% duty cycle and 25 W average power; the peak field still corresponds to the 50 kW pulse.
Use the waveguide power-handling checks to define pressure, temperature, mismatch and cooling conditions. For phase-sensitive paths, also specify electrical length and permitted phase change across temperature.
Satellite Communications
List the actual transmit and receive bands before selecting a feed path. A component that covers one direction may not cover the other. Specify polarization, port isolation where applicable, and the flange at each feed, OMT, filter and transceiver connection.
A pressure window can establish a sealed boundary while passing RF, but its usable band and power limit depend on its design. NASA describes a specific WR28 window developed for a 32 GHz Deep Space Network application; that example does not qualify every WR28 window for the same service.[4]
Test and Measurement
Match the VNA extender, calibration standards and test fixture to the required frequency range and flange. Define the measurement reference planes and whether adapters are included in the result or removed through calibration or de-embedding.
Inspect and clean the mating faces, use the specified alignment hardware and fastening procedure, and record reconnection repeatability. NIST has shown that aperture errors and flange misalignment can affect waveguide calibration results.[5]
Selection Pitfalls
- Frequency barely above cutoff: request supported operating-band data instead of accepting propagation as proof of low loss.
- Matching WR labels only: check the complete flange drawing and aperture height.
- Choosing by average power alone: verify peak-field and thermal limits separately.
- Using a straight-section chart for the whole path: check each component and the assembled response.
- Comparing unexplained loss values: specify frequency, length, reference planes, temperature and whether adapters are included.
For a custom waveguide assembly, supply the frequency span, selected WR size, both flange drawings, maximum loss and VSWR, power waveform, pressure and temperature limits, and installation envelope. Agree the dimensional and RF records required in the acceptance report before production.
