Waveguide transitions and waveguide-to-coaxial adapters that join different waveguide sizes or connect waveguide to coaxial cable · Waveguide sizes, frequency band, VSWR and insertion loss, flange types, connector, geometry (in-line, end-launch, right-angle), material and dimensions
A waveguide transition joins two different waveguide sizes or shapes, and a waveguide-to-coaxial adapter connects a waveguide run to coaxial cable or instruments. Both must pass the band with little reflection and loss. Ask three things first: which waveguide sizes, flanges and connector the part must join, what frequency band it must cover, and what VSWR, insertion loss and power the system can accept.
Rectangular, square and circular waveguide transitions and waveguide-to-coaxial adapters (in-line, end-launch and right-angle) for microwave and millimetre-wave systems. Straight waveguide sections, waveguide filters and couplers, band-pass filters (see band-pass filter), coaxial adapters between connector types and RF switches (see RF switch) are outside this page.
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01
XEXA Tech lists a WR28 (BJ320) to WR22 (BJ400) rectangular transition for 30.0–40.0 GHz, 25.4 mm long, with an FBP320 (UBR320) flange on the WR28 side and an FUGP400 (UG-383/U) flange on the WR22 side, in aluminium with precisely fabricated tapers. It states: "The operating frequency is generally the overlapping frequency region of adjacent waveguides, or determined according to the frequency range of high-frequency waveguides." It also offers rectangle-to-square and circle-to-rectangle types. [1]
HengDa lists right-angle waveguide-to-coaxial adapters from 0.32–0.49 GHz (R3/WR2300) to 0.64–0.98 GHz (R8/WR1150) with FDP/FDM flanges, N, SMA or TNC connectors and aluminium bodies. Advanced Microwave lists end-launch adapters from 1.72–2.61 GHz (WR430) to 3.94–5.99 GHz (WR187) with N or SMA connectors, FDP/FDM flanges and aluminium or copper bodies. [2] [3]
Give the supplier both port definitions (waveguide size and flange, or connector type and gender), frequency band, maximum VSWR and insertion loss, average and peak power, geometry (in-line, end-launch, right-angle, taper length limit), material and finish, pressurisation or sealing, and operating environment.
02
The listed maximum VSWR is 1.1 for the WR28-WR22 transition, 1.25 for the end-launch adapters, and 1.3 for the lower-frequency right-angle adapters (1.25 at WR1150); the transition also lists insertion loss of 0.1 dB maximum. [1] [3] [2]
Editorial calculation: VSWR converts to return loss as −20·log10((VSWR−1)/(VSWR+1)), so VSWR 1.1, 1.25 and 1.3 correspond to about 26.4 dB, 19.1 dB and 17.7 dB return loss. [1] [3] [2]
Size scales with wavelength: the WR2300 right-angle adapter is listed at 400 × 384 × 676 mm, while the WR187 end-launch adapter is 74.7 × 63 × 89 mm and the WR28-WR22 transition is 25.4 mm long. [2] [3] [1]
03
RF Essentials' waveguide reference explains that the WR number is the broad-wall dimension in hundredths of an inch, that the dominant TE₁₀ mode has a cutoff fc = c / (2a) with a the broad wall, and that the recommended band of each size sits between the TE₁₀ cutoff and the next higher mode so that only one mode propagates. Its table lists, for example, WR-187 (47.549 × 22.149 mm, 3.95–5.85 GHz, cutoff 3.153 GHz), WR-28 (7.112 × 3.556 mm, 26.50–40.00 GHz, cutoff 21.077 GHz, TE₂₀ cutoff 42.154 GHz) and WR-22 (5.690 × 2.845 mm, 33.00–50.00 GHz, cutoff 26.346 GHz). [4]
Editorial calculation: c / (2 × 7.112 mm) = 299,792,458 / 0.014224 ≈ 21.08 GHz, matching the WR-28 table value, and c / (2 × 5.690 mm) ≈ 26.34 GHz for WR-22. The 30–40 GHz WR28-WR22 transition above therefore runs above both cutoffs, but its lower edge sits below WR-22's 33 GHz recommended band, so confirm VSWR and loss at the band edges you will use. The WR-187 end-launch adapter's 3.94–5.99 GHz listing likewise extends beyond the 3.95–5.85 GHz recommended band in this table. [4] [1] [3]
| Size | Inside a × b (mm) | Recommended band (GHz) | TE₁₀ cutoff (GHz) |
|---|---|---|---|
| WR-187 | 47.549 × 22.149 | 3.95–5.85 | 3.153 |
| WR-90 | 22.860 × 10.160 | 8.20–12.40 | 6.557 |
| WR-42 | 10.668 × 4.318 | 18.00–26.50 | 14.051 |
| WR-28 | 7.112 × 3.556 | 26.50–40.00 | 21.077 |
| WR-22 | 5.690 × 2.845 | 33.00–50.00 | 26.346 |
State the operating band for each port, confirm it lies inside each waveguide's single-mode range, and ask for measured VSWR and insertion loss at the band edges.
04
This is a functional reference built from the sources cited; it is not one maker's design.
| Part | Role | Fix in the order |
|---|---|---|
| Taper or step section | Match one waveguide size to another. [1] | Length; profile. |
| Coaxial probe or launch | Couple coax to the waveguide mode. [2] [3] | Geometry; connector. |
| Flanges | Join to the waveguide run. [1] [2] [3] | Flange type each end. |
| Connector | Join to coaxial cable. [2] [3] | N, SMA, TNC or other. |
| Body | Carry the waveguide and set dimensions. [1] [3] | Aluminium or copper; finish. |
05
A waveguide transition selection needs values for your system. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.
| Field | What it means and published values | Ask the supplier for |
|---|---|---|
| Frequency Range | E.g. 30–40 GHz; 0.32–0.49 GHz; 3.94–5.99 GHz. [1] [2] [3] | Band. |
| Waveguide size | WR number = broad wall in hundredths of an inch; TE₁₀ cutoff c / (2a). [4] | WR size each port. |
| Insertion Loss | E.g. 0.1 dB max. [1] | Max across band. |
| Return Loss | From VSWR 1.1–1.3 max, about 26.4–17.7 dB. [1] [2] [3] | VSWR or return loss max. |
| Impedance | Coaxial side impedance. | Value. |
| Power Handling | Average and peak power. | Values; pressurisation. |
| Operating Temperature | Service temperature range. | Range. |
| Flange Type | E.g. FBP320, UG-383/U, FDP/FDM. [1] [2] [3] | Flange each end. |
| Material | E.g. aluminium; copper. [1] [3] | Material. |
| Surface Finish | Plating or paint. | Finish. |
| Weight | Part mass. | Value. |
06
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Port 1: [waveguide size; flange] Port 2: [waveguide size and flange, or connector] Band: [GHz] Performance: [VSWR max; insertion loss max] Power: [average; peak] Geometry: [in-line, end-launch, right-angle; length limit] Material: [body; finish] Volume: [quantity]
These companies list waveguide transitions or waveguide-to-coaxial adapters.
Lists rectangular, square and circular waveguide transitions, such as WR28 to WR22 for 30–40 GHz, and waveguide-coaxial adapters.
Product scope checked 2026-10-11
Lists right-angle waveguide-to-coaxial adapters with N, SMA and TNC connectors.
Product scope checked 2026-10-11
Lists end-launch waveguide-to-coaxial adapters and waveguide-to-microstrip adapters.
Product scope checked 2026-10-11
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
XEXA Tech states: "The operating frequency is generally the overlapping frequency region of adjacent waveguides, or determined according to the frequency range of high-frequency waveguides"; a WR28-WR22 transition is listed for 30–40 GHz. [1]
Published adapters list VSWR of 1.25 to 1.3 maximum, about 19 dB to 18 dB return loss by editorial calculation. [2] [3]
Published lower-frequency adapters offer N, SMA or TNC connectors. [2] [3]
It is the broad-wall inside dimension in hundredths of an inch; WR-28 has a 0.280-inch (7.112 mm) broad wall. [4]
21.077 GHz for the TE₁₀ mode, with a recommended band of 26.5–40 GHz. [4]
Sources checked 2026-10-12. Sources are three makers' product tables for specific transition and adapter series, cited as examples of the parameters a waveguide transition specification covers, not endorsements.
Ask for use case, specification boundaries, supplier type, and RFQ preparation information for this product.
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