WAVEGUIDE-TO-COAX ENGINEERING NOTE
HOW TO CHOOSE A
WAVEGUIDE TO
COAX ADAPTER
A waveguide-to-coax adapter is not selected by connector alone. The operating band determines the rectangular waveguide size, while flange type, coax connector, insertion loss, VSWR, RF power and mechanical orientation determine whether the transition will work in the actual RF system.
SELECTION ORDER
START WITH
FREQUENCY.
Rectangular waveguide is band-specific. The first selection question is therefore the operating frequency, not the coax connector. Once the frequency places the design in a WR band, choose the flange and coax interface that match the rest of the system.
WR650–WR159
1.12–7.05 GHz coverage with Type N and SMA configurations available by model.
WR137–WR75
5.85–15.0 GHz coverage with CPRF or Cover flanges and Type N / SMA options by band.
WR62–WR51
12.4–22.0 GHz coverage using Cover flanges and SMA-F standard configurations.
WR42–WR28
18.0–40.0 GHz coverage using Cover flanges and 2.92 mm female coaxial interfaces.
INTERACTIVE ENGINEERING TOOL
FIND THE
WAVEGUIDE BAND.
Enter a frequency and optional connector preference. The selector checks the current Impulse in-house waveguide-to-coax adapter families and returns compatible WR bands and standard catalog configurations that contain that frequency.
Band overlap is normal near some waveguide boundaries. The selector uses the current Impulse model table for frequency range, WR size, flange, connector and VSWR. Power is shown from the current general product-line specification; use the exact model datasheet or factory confirmation for release.
MECHANICAL INTERFACES
THE FLANGE AND
CONNECTOR BOTH MATTER.
The adapter has two independent interfaces. The waveguide side must mate mechanically and electrically to the correct flange, while the coax side must use a connector appropriate for frequency, power, cable system and existing test or system hardware.
CPRF flange
Current Impulse catalog models use CPRF flanges on several lower-frequency waveguide families including WR650, WR430, WR340, WR229, WR159 and WR137.
VERIFY EXACT MODEL FLANGECover flange
Cover flanges are standard on many bands including WR284, WR187 and the higher-frequency WR112 through WR28 families.
VERIFY BOLT PATTERN + ORIENTATIONType N female
Used on many lower- and mid-microwave models where robust coaxial interfacing and higher average power capability are useful.
MODEL / BAND DEPENDENTSMA female
Available across a broad portion of the Impulse range, including many WR650 through WR51 models, depending on waveguide size.
MODEL / BAND DEPENDENT2.92 mm female
Used on the current WR42, WR34 and WR28 adapter families covering 18.0–40.0 GHz.
UPPER MICROWAVE / mmWAVEConnector direction
Impulse standard products are right-angle transitions. Confirm coax port direction, flange orientation and surrounding clearance before releasing the mechanical design.
CHECK ENVELOPE DRAWINGELECTRICAL PERFORMANCE
DON'T STOP AT
THE FREQUENCY BAND.
Two adapters that cover the same frequency range can still differ in match, insertion loss, connector, flange and power handling. Those values determine how much the transition contributes to system loss, reflection and RF stress.
Forward loss adds directly to the RF budget.
Adapter insertion loss reduces power delivered through the transition. At high power, even small loss also creates local heat that must be carried by the structure.
The transition must preserve the impedance match.
VSWR or return loss describes reflection at the defined measurement plane. Poor match can distort measurements, reduce delivered power and increase standing-wave stress.
Average heating sets one limit.
Current Impulse catalog ratings vary by band and connector. Lower-frequency Type N configurations can support higher CW levels than the smallest mmWave families.
Peak electric-field stress is a separate check.
Peak power cannot be inferred from CW rating alone. Connector geometry, field concentration, pulse conditions and mismatch must remain within the controlled model rating.
WORKED IMPULSE EXAMPLE
10 GHz.
WR90.
SMA-F.
For a 10 GHz system that requires a right-angle waveguide-to-SMA transition, WR90 is one current Impulse option because the WGC90A-F6-C1-ITI covers 8.20–12.4 GHz. The current Impulse product page lists a Cover flange, SMA-F connector and 1.15 maximum VSWR for this model. Impulse's current general specifications list SMA-F and 2.92 mm-F configurations at 50 W typical RF power with 1–3 kW peak capability across the product line, subject to the exact model specification.
VIEW IMPULSE WG-COAX ADAPTERS→Use the current model datasheet or controlled catalog for final acceptance. Frequency, connector, flange, insertion loss, VSWR and power limits are model-specific and may change as products are revised.
MECHANICAL INTEGRATION
AN RF MATCH CAN STILL
FAIL THE MECHANICAL DESIGN.
A correct WR band does not guarantee that the adapter physically fits. Waveguide flange geometry, bolt access, connector direction, cable bend radius, nearby hardware and assembly sequence all have to close before the part is released.
Match the actual waveguide interface.
Confirm CPRF versus Cover, bolt pattern, flange thickness, alignment features and any gasket or pressure requirement.
Decide where the coax port must point.
Check the assembly drawing, adjacent components and service access. Rotating a waveguide component can change the mechanical arrangement even when the electrical band is correct.
Leave room for torque and cable routing.
Connector tools, cable bend radius and strain relief need real clearance. A technically compatible SMA or Type N interface can still be unusable if the surrounding structure blocks installation.
Material and finish belong in the installation review.
Temperature, corrosion exposure, vibration, mounting stiffness and conductive contact can affect both mechanical reliability and RF repeatability.
ADAPTER REQUIREMENT CHECKLIST
SPECIFY BOTH
SIDES OF THE
TRANSITION.
A useful RFQ defines the complete interface instead of requesting only “a waveguide adapter.”
Full operating band, center frequency, any harmonics or out-of-band power and the required margin to waveguide band edges.
WR size if already fixed by the system, plus flange type and any mating hardware requirement.
Type N, SMA, 2.92 mm or another required interface, including gender and cable/test-system compatibility.
Maximum acceptable forward loss across the full operating band.
Required match limit and the reference planes used for acceptance.
CW power, peak power, duty cycle, pulse width, repetition rate and any fault mismatch condition.
Right-angle geometry, required connector direction, flange clocking and mechanical envelope.
Temperature range, pressure/altitude, vibration, material/finish restrictions and any military or aerospace requirement.
Required quantity, prototype versus production status, desired delivery date and whether immediate stock is important.
IMPULSE / IN-HOUSE RF HARDWARE
WR650 TO WR28.
1.12 TO 40 GHz.
Impulse Technologies manufactures right-angle waveguide-to-coax adapters covering WR650 through WR28. Current standard configurations use CPRF or Cover flanges and Type N-F, SMA-F or 2.92 mm-F connectors depending on waveguide size.
Waveguide-to-Coax Adapters
Browse current models by WR size, operating frequency, flange, connector, VSWR, insertion loss and power.
VIEW WG-COAX ADAPTERS → INTERFACE FUNDAMENTALSWhat Is a Waveguide-Coax Adapter?
Review the purpose of the transition, waveguide/coax field conversion and common RF system applications.
READ FUNDAMENTALS →WAVEGUIDE-TO-COAX FAQ
COMMON ADAPTER
SELECTION QUESTIONS.
How do I choose the correct waveguide size?+
Start with the operating frequency and identify the WR band that contains the required range. Then verify that the existing system uses the same waveguide size and flange.
Can the same frequency fit more than one WR band?+
Yes. Adjacent standard waveguide bands can overlap. The existing mechanical interface, bandwidth, required margin, flange and system design determine which band is appropriate.
Should I choose SMA, Type N or 2.92 mm first?+
No. First establish the frequency and waveguide band. Then choose among the connector configurations available for that band while checking power, cable/test-system compatibility and mechanical clearance.
Why do insertion loss and VSWR both matter?+
Insertion loss describes forward transmission loss. VSWR describes mismatch and reflected energy. A complete transition specification normally controls both.
Is CW power the same as peak power?+
No. CW power is primarily tied to continuous heating, while peak power can be limited by electric-field stress, connector geometry, pulse conditions and mismatch. Check both ratings separately.
RF COMPONENT SELECTION
NEED A WG-COAX
ADAPTER MATCH?
Send the frequency range, waveguide size, flange, connector, insertion-loss and VSWR limits, RF power, orientation, quantity and timing. Impulse can review the in-house adapter families against the actual requirement.
