Tri-Channel Rotary Joint with a 14 Channel Slip Ring 

Rotary joints for military applications are among the most demanding rotary joints in terms of durability, reliability and low maintenance.

At MDL, we engineer and manufacture rotary joints for a large number of satcom and radar applications. Our newly developed Tri-Channel Rotary Joint with a 14 Channel Slip Ring has been custom-designed for weapon radar systems. It features 2 waveguide channels, 14 channel slip ring, and 1 coax seal channel.

With over 65 years in the microwave industry, high reliability is MDL’s trademark. Meeting strict military standards in precision and reliability, all our products undergo 100% functional performance verification, complete inspection and testing.

Contact our Engineering team for your next demanding application. We look forward to collaborating with you every step of the way.

Microwave Development Labs, Inc.
135 Crescent Road, Needham Heights, MA 02494

Contact via:
Telephone: (781) 292-6684
FAX: (781) 453-8629


September 14, 2016 – Microwave Development Laboratories (MDL) will be exhibiting at EDI CON USA (September 20-22) at the Hynes Convention Center in Boston (Booth # 329) and will also be making a technical presentation as part of the conference sessions.

Long recognized for its expertise in developing and supplying high-performance waveguide products, MDL will be exhibiting its waveguide and coaxial rotary joints and rotary switches at EDI CON 2016. MDL custom designs rotary joints and switches in different models that meet or exceed specified electrical and mechanical requirements. Rotary joints based on rigid waveguide provide high-performance and dependable connections in many commercial and military RF/microwave systems.

On Wednesday, September 21st at 3:00 (Room 209) MDL will speak on the subject of “Additive Manufacturing Techniques for the Production of RF Components.” This presentation, to be given by MDL’s Tom WcWalters, will showcase different additive manufacturing (AM) techniques used for the production of passive RF components, specifically waveguide components.

Tom will discuss Multi-Jet and Laser Beam Melting approaches and present examples of MDL products manufactured using AM technology. These AM techniques can save customers production cost and increase deliverability while maintaining good accuracy and reproducibility of RF components.


About MDL

Founded in 1948, MDL is the largest independent producer of waveguide and waveguide assemblies in the microwave industry. MDL’s products are used extensively in defense applications and in satellite and mobile TV communications.


Microwave Development Labs, Inc.

135 Crescent Road, Needham Heights, MA 02494


Contact via:

Telephone: (781) 292-6684

FAX: (781) 453-8629




-Company to Show Its Waveguide-Based Products & Online Tools-

Needham Heights, MA, May 17, 2016 – Microwave Development Laboratories, Inc. ( will offer a sampling of its extensive expertise and product lines based on high-performance waveguide technology at the upcoming 2016 IEEE International Microwave Symposium (IMS, and Exhibition scheduled for May 22-27, 2016 in San Francisco, CA. MDL will be exhibiting within the Moscone Center at Booth #2432.

As part of the 2016 IMS Exhibition, Microwave Development Laboratories will welcome visitors to its booth with details and advice on the use of its comprehensive waveguide-based product lines, and how to match different sizes of waveguide products to different frequency bands and applications.

Products on display will include waveguide bends and twists, waveguide-to-coax adapters, power dividers, phase shifters, rotary joints, variable attenuators, and rotary switches. For applications requiring higher frequencies and higher power-handling capabilities, waveguide is still a preferred format over various other component formats, including surface-mount and coaxial components.

Rotary joints based on rigid waveguide can provide high-performance and dependable connections in many commercial and military RF/microwave systems. As long-time, highly experienced developers of waveguide and coaxial rotary joints, MDL can provide standard models of both waveguide and coaxial rotary joints, and provide guidance on performance differences in between the two types in terms of insertion loss, VSWR and power-handling capabilities,

In addition, visitors to the 2016 IEEE IMS Exhibition can learn more about Microwave Development Laboratories’ handy online tools, including their new Reflectometer Calculator, Rigid Waveguide Sliderule app and Rigid Waveguide Tool. These free-of-charge, downloadable programs help simplify and speed the process of finding the right performance for a particular size waveguide or waveguide component. Also online at MDL’s website are a CAD database for MDL Cast 90 degree Bends and the company’s full product catalog. Stop by MDL’s Booth (#2432) to talk about special shaped Bends based on MDL’s Additive Manufacturing Process.


Microwave Development Labs, Inc.

135 Crescent Road, Needham Heights, MA 02494

Contact via:

Telephone: (781) 292-6684

FAX: (781) 453-8629




MDL’s Aluminum Casting Material Offerings and the Rational for Choices for Microwave Castings for RF Applications.

By John Kane, Design and Manufacturing Engineer, @MDLlab

MDL has been producing Microwave Waveguide Castings for well over 50 years. During that time, one could say we “know a thing or two” about the fabrication process of Castings and what materials are best suited and mostly used in the Waveguide RF Industry.                                                                                                                                                                
MDL offers two choices of Aluminum materials D712 and A356.

The Aluminum materials can be separated into two categories;
a.) Aluminum that can be Brazed with other Aluminum Alloys (D712 material).
b.) Aluminum that cannot be Brazed with other Aluminum Alloys (A356 material).

The descriptions below provide just some of the beneficial characteristics of each of the Aluminum materials MDL offers.                                                                                                                     

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Alloy 712 is employed when a combination of good mechanical properties without heat treatment is needed. It also shows good shock, corrosion resistance, machinability and dimensional stability. No distortion is exhibited when D712 is heated. After brazing, the D712 alloy will regain its original strength by natural aging. (** D712 will age harden to T6 Temper over time.**)                                                                                                                                   
Ability to Cast —Alloy D712 has fair to good cast-ability. Although its pressure tightness and resistance to hot cracking are only fair, the alloy’s fluidity and solidification shrinkage tendency are rated as good.
Machinability—the machining characteristics of the D712 alloy are excellent. Fast speeds and feeds and wear-resistant tools correctly ground for cutting aluminum are recommended.
Finishing—Polished finishes are good. The anodized finish is good, and the color is medium golden yellow. Ability to Weld —Welding characteristics are fair for most common methods. The D712 alloy is NECESSARY for brazing.
Corrosion Resistance—the D712 alloy has good natural resistance to corrosion, and good additional protection is received from chemical conversion coatings.                                                  

Screen Shot 2016-03-28 at 10.37.35 AM

 Alloy A356 has greater elongation, higher strength and considerably higher ductility than D712. It has these improved mechanical properties because impurities are lower in A356 than in D712. Typical applications are airframe castings, machine parts, truck chassis parts, aircraft and missile components, and structural parts requiring high strength.

 Ability to Cast—all casting characteristics are excellent for this alloy.
Machinability—Alloy A356 has good machinability. Abrasiveness can be overcome and high tool wear can be minimized by using sharp, carbide-tipped tools with high rakes and clearances. Moderate to fast speeds are recommended.
Finishing—Electroplated finishes are good. Chemical conversion coatings give good protection, but anodized appearance is only fair. Mechanical finishes on A356 are good.
Ability to Weld—all common welding methods are excellent for joining this alloy. Brazing is not performed for this Alloy.
Corrosion Resistance—the A356 alloy has good resistance to most forms of corrosion.The following Tables list the compositions and the typical properties of the D712, A356 and A380 Aluminum Alloys. A380 is the most common and most cost effective Aluminum Alloy used in Die Casting.

Screen Shot 2016-03-28 at 10.40.56 AMScreen Shot 2016-03-28 at 10.41.30 AM.pngScreen Shot 2016-03-28 at 10.41.55 AM.png

Pictures of Aluminum Die Cast parts courtesy of Viking SATCOM.

When choosing Casting for your Microwave Waveguide system, please consult MDL on your Casting material choice. MDL’s 50+ years of experience will guide you to the appropriate choice. Future considerations should include your rate of production. D712 and A356 Castings are typically produced in low to moderate volumes. Castings produced with Die’s should only be considered in High Volume production rates (due to the expense of the Die).

Visit our website at or call 1-781-292-6684 for your casting needs.

Microwave Development Labs Shows Sampling of Waveguide at 2015 IMS in Phoenix, AZ

Microwave Development Laboratories, Inc. ( will offer a sampling of its extensive expertise and product lines based on high-performance waveguide technology at the upcoming 2015 IEEE International Microwave Symposium (IMS, and Exhibition scheduled for May 17-22, 2015 in Phoenix, AZ. As part of the 2015 IMS Exhibition, Microwave Development Laboratories will welcome visitors to its booth (Booth 621) with details and advice on the use of its comprehensive waveguide-based product lines, and how to match different sizes of waveguide products to different frequency bands and applications. Products on display will include waveguide bends and twists, waveguide-to-coax adapters, power dividers, phase shifters, rotary joints, variable attenuators, and rotary switches. For applications requiring higher frequencies and higher power-handling capabilities, waveguide is still a preferred format over various other component formats, including surface-mount and coaxial components.

In addition, visits to Booth 621 at the 2015 IEEE IMS Exhibition can learn more about Microwave Development Laboratories’ handy online tools, including their online Reflectometer Calculator and their Rigid Waveguide Sliderule application. These are free-of-charge, downloadable programs that help simplify and speed the process of finding the right performance for a particular size waveguide or waveguide component. For all your waveguide needs, visit Microwave Development Laboratories at Booth 621 at the upcoming 2015 IEEE IMS Exhibition in Phoenix, AZ this May 17-22,2015.

Microwave Development Labs, Inc.
135 Crescent Road, Needham Heights, MA 02494
Telephone: (781) 292-6684
FAX: (781) 453-8629

Celebrating National Engineers Week

By John Kane

The Management and Engineers at MDL thought we might have a little fun with this months’ BLOG, which is written to commemorate National Engineers Week. (February 22 – 28)

Rather than exchange our usual, yearly, Engineer’s Week Cards and custom pocket protectors “bling”, we thought it might be nice, to actually interview one of our Engineers and ask what attracted them into the Engineering field.

The topic was good; the “interview idea” seemed appropriate; OK who should be interviewed? The room fell silent.

CRICKETS! (They always appear in this situation!)

“Dr. Riblet (President and CEO of MDL), I think an interview with you would be, very enlightening!” someone finally offered.

“No, No, I think someone else may be better suited for this one!” he replied.

AGAIN, CRICKETS! Damn! One down, two to go!

Finally after a short pause, Dr. Riblet turned to me and said,” Why don’t you interview yourself?”

Case closed, send everyone home!

Katie; “Bar the door!”

And so, here I sit, staring at the screen…

OK, let’s begin…

Interviewer – (John) – How did you decide to study Engineering?

Engineer – (me) – “Well, I seemed to excel in Math and Science in High School.”

Interviewer – (John) – How did you get into the RF side of Engineering?

Engineer – (me) – “I had a wonderful Professor in College, Dr. Peter Rizzi, who taught a course in Electromagnetic Theory. He was someone that turned on the Engineering can be exciting switch, for me.”

Interviewer – (John) – Does this sound boring to you?

Engineer – (me) – “Yes!”

Interviewer – (John) – How do we make it better?

Engineer – (me) – “Should we throw in a couple, cool, HFSS Electromagnetic simulations?”

Interviewer – (John) – “Nope, we’ll just keep it short, simple and honest!….”

Engineer – (me) – “Three words can’t be considered a BLOG!”

Interviewer – (John) – “What does being an Engineer mean to you?”

Engineer – (me) – “OK, OK…here’s what I have figured out in my 30+ years of Engineering…when in doubt; turn to Wikipedia!

Wikipedia’s definition of Engineering is:

Engineering (from Latin ingenium, meaning “cleverness” and ingeniare, meaning “to contrive, devise”) is the application of scientific, economic, social, and practical knowledge in order to invent, design, build, maintain, research, and improve structures, machines, devices, systems, materials and processes.

Engineering and Engineers are about SOLVING PROBLEMS!

So, be inquisitive, inventive, clever and even ingenious…..

Don’t be timid or unsure!

Love what you do!

Enjoy…30+ years, goes fast!”


(Nobody else knows about it!)

Why Use a Waveguide Variable Attenuator?

Waveguide-based high-frequency systems often require some control of amplitude or signal level. Waveguide attenuators can deliver that means of control, with fixed attenuators providing a single value attenuation setting and variable attenuators providing a range of attenuation control across a desired frequency range.

AttenuatorWaveguide variable attenuators can be especially useful in test-and-measurement systems and in applications where the final desired level may not be precisely known or may fall within a range of levels. But selecting a waveguide variable attenuator for an application is not a trivial task, and it can be helpful to know a bit about some of the main attributes of these components and some key performance parameters. Since there are several kinds of waveguide variable attenuators, it can also be helpful to know about the different ways in which the attenuation can be controlled. Typical options to control attenuation include; either a manual controlled version or a motor controlled version. The motor controlled version uses voltage to adjust the attenuator and attenuation value. Knowing what options are available allows the customer to pick the best waveguide variable attenuator for their particular application. Waveguide variable attenuators are available with a wide range of attenuation values, some capable of adjusting attenuation settings from 0 to 30 dB or more with impressive stability and reliability across waveguide frequency bands.

As with other waveguide components, the size of the waveguide in a variable attenuator will determine the usable frequency range. Within a given Waveguide sizes’ frequency range, two different constructions of variable attenuators will offer various attenuation ranges. Sidewall Variable Attenuators have an attenuation range of up to 40dB, whereas Topwall Variable Attenuators typically have an attenuation range from 0 to 15-20dB. As mentioned before, there are typically two different ways to control the attenuation range. Often, some form of movable structural element within the waveguide, such as a rotary vane or moving resistive card will cause the attenuation variation. The attenuation element may be moved manually or under motorized power. Manual variable attenuators typically employ an adjustable screw control to adjust the level of attenuation, while motor-driven waveguide variable attenuators may provide continuously variable control of the attenuator using voltage-tuned motors or they may tune in steps using, for example, a stepper motor for control of the attenuation element and attenuation. Many suppliers of mechanically tuned waveguide variable attenuators will offer a choice of the number of turns required by the tuning element to achieve the full attenuation setting.

Additionally, waveguide variable attenuators are available with fully electronic control of attenuation, for example, using PIN diodes to tune the attenuation level of the component. Manually tuned waveguide variable attenuators offer the benefits of simplicity and straightforward control. Motor- or diode-controlled electronically adjusted waveguide variable attenuators offer the option of remote control and rapid resetting of attenuation level, as needed.

Various methods can be employed to display the attenuation level set on one of these components, from simple mechanical dials to more sophisticated electronic readouts. The choice of attenuation display will typically be determined by the needs of a particular application. Depending upon the need for accuracy, waveguide variable attenuators are available as calibrated or uncalibrated models. Calibrated attenuators are typically verified by a supplier at different spot frequencies and attenuation settings; although these frequencies and attenuation settings can be chosen by a customer to best match the needs of an application.

Once such basic requirements as frequency range/waveguide size, attenuation range, and manual or electronic control of attenuation have been decided, specifying a waveguide variable attenuator is a matter of comparing key electrical and mechanical parameters for different available models. The electrical performance of different attenuators can be compared in terms of insertion loss, voltage standing-wave ratio (VSWR), and power-handling capability.

For many applications, stability is an important characteristic: How much will the attenuation and/or the phase response of the waveguide variable attenuator vary with frequency, or with attenuation setting, or even with temperature. In other applications, the attenuation flatness versus frequency might be of interest. Variations of ±1dB or ±2dB in attenuation can be typical across the full waveguide frequency range. (I.e. -10 to 15 GHz for a WR75) These variations, in attenuation, can also be impacted by the amount of total attenuation offered by a component. A waveguide variable attenuator offering an attenuation adjustment range of 0 to 15dB can be expected to provide less variation with frequency than a unit with an attenuation adjustment range of 0 to 40dB.

Most waveguide variable attenuators are somewhat limited in RF/microwave power-handling capability compared to fixed waveguide attenuators operating near or within the same frequency range. A wide range of waveguide variable attenuators are designed for input power levels in the 1-W or less continuous-wave (CW) power range, with higher-power units designed for input power levels of typically 4 to 5 W. In contrast, high-power waveguide fixed attenuators covering similar frequencies may be rated for 40 W or more of CW power.

The power-handling capability can be influenced by a number of factors, including the type of attenuation element used in the attenuator, the types of materials (I.e. -aluminum or brass) used in the construction of the attenuator or even the type of finish applied (such as a corrosion-resistant finish or silver plating).

The mechanical construction of a waveguide variable attenuator may be critical, for some applications. Waveguide size is a function of the wavelength of a frequency of interest, the physical size of most waveguide variable attenuators (such as the length) will be mostly determined by the operating frequency, with lower-frequency attenuators being considerably larger than higher-frequency attenuators, even though they may typically be rated for the same power-handling capabilities. The type of flanges used on the waveguide input and output ports may be of significance or the drive mechanisms’ construction.

Contact MDL for your waveguide variable-attenuator questions or requirements at 1-781-292-6684 or visit our website at

Importance of In-House Manufacturing at MDL

In honor of this year’s Manufacturing Day, we decided to tackle a topic that is very important to us…in-house manufacturing.


In-house manufacturing is vital to product development at Microwave Development Laboratories (MDL). With in-house manufacturing, our engineers cannot only watch their designs come to life, but can control every aspect of its development to perfection! This allows you, the customer to collaborate with us every step of the way. In-house manufacturing also allows us to ensure high-reliability and quality in all of our microwave components, sub-systems and assemblies.

Our facility in Needham, Massachusetts encompasses CNC machining centers, aluminum dip brazing (watch it in action here), EDM facilities, cleaning, impregnation, iridite, heat-treating, RF testing, and finishing. MDL also offers off the shelf items, as well as custom pieces that require special tolerances, complicated configurations, multiple formed bends, twists, or offsets which are all manufactured with precision and are subjected to complete inspection and testing.

Find a Coax Fit for Waveguide

Waveguide can provide outstanding electrical performance in terms of low insertion loss and low VSWR at microwave and millimeter-wave frequencies, but it may often be necessary to transition between waveguide and coaxial components. Doing so requires the right Waveguide-to-coaxial adapter and knowledge of how to integrate it into a design without introducing un-wanted chaos. The right adapter can provide convenience as well as performance.

WaveguideCoaxWaveguide-to-coaxial adapters allow power to be propagated in either direction, with each side of the adapter providing the full frequency range of its waveguide size. Although the coaxial connector side of the adapter theoretically works broadband, the frequency band is limited by the waveguide structure on the other side of the adapter.

A general procedure when connecting an adapter to a waveguide should involve making certain that the rectangular waveguide ports are oriented the same. The ports should be carefully aligned with respect to the waveguide opening in order to minimize reflections. Then the flanges should be bolted or clamped securely together to evenly distribute pressure over the contacting surfaces of the waveguide portions. A tight fit provides a good impedance match between the waveguide sections, whereas a loose fit can result in mismatches, leakage, and distortion.

When considering a waveguide-to-coaxial adapter for an application, the waveguide side of the adapter is selected to fit a given waveguide and flange size, while the coaxial side of the adapter needs to match the connector type (SMA, Type-N, etc.) of the mating component (antenna, coaxial cable, etc.) to be linked in a system. Again, although the coaxial interface is a broadband connection, the waveguide and flange size on the other end of the adapter will determine the frequency range of the adapter. (Example: a WR-75 rectangular waveguide interface has a frequency range of 10 to 15 GHz.) The overall performance of the adapter depends on the transition between the waveguide and coaxial component. How well this transition is accomplished translates to the performance parameters, such as insertion loss and VSWR. These performance parameters should be used to compare the quality of different adapters. (I.e., Low VSWR and insertion loss adapters have a very good transition design.)

Ideally, a waveguide-to-coaxial adapter should not degrade the performance of the transmission line in which it is inserted while making the link between the two different transmission-line topologies. Over its operating frequency range, a good waveguide-to-coaxial adapter will typically introduce additional insertion loss of less than 0.5 dB below 18 GHz and often typically around 0.2 dB or less for frequencies below 10 GHz.

An adapter’s voltage standing wave ratio (VSWR) specification is an indication of the impedance match or mismatch that a waveguide-to-coaxial adapter will introduce into a circuit or system. Ideally, the adapter’s VSWR should be as low as possible, so that minimal reflections occur at that point in the circuit or system with the addition of the adapter. As an example, rectangular-waveguide-to-Type N coaxial adapters machined by MDL ( exhibit maximum VSWR of 1.25:1 with pressurized versions offering a maximum VSWR of 1.10:1. These Type N standard adapters cover a total frequency range of WR-650 (1.12 to 1.70 GHz) through WR-75 (10 to 15 GHz), maintaining low VSWR.

At higher frequencies, standard rectangular waveguide to SMA coaxial adapters exhibit a maximum VSWR of 1.25:1 from 2.6 to 40.0 GHz, with some showing typical values of 1.14:1 over that frequency range. For frequencies to 40 GHz using 2.9-mm coaxial connectors, some double-ridge-waveguide-to-coaxial adapters are capable of maximum VSWRs of only 1.30:1. Again, the adapter’s goal is to provide a mechanical link between a waveguide portion of a system and a coaxial component or portion, while remaining electrically “invisible.” Adapters with a low VSWR can electrically disappear once installed.

In many applications, waveguide-to-coaxial adapter will be used as part of a test system, to introduce and detect signals for analysis to a coaxial test port from a waveguide transmission line or component. Such applications will generally be at relatively low power levels, of +10 dBm or less. But often, waveguide-to-coaxial adapters are used as part of a radar system, typically with high-power pulsed signals, and the power rating of an adapter may prove to be a specification of interest. Many commercial standard waveguide-to-coaxial adapters and double-ridge-waveguide-to-coaxial adapters, depending on the coaxial connector type and are rated for continuous-wave (CW) power levels as high as 1 kW and peak power levels to 5 kW when using rugged Type N connectors on the coaxial side.

Traditional waveguide-to-coaxial adapters mount a waveguide flange at one end and a coaxial connector on the topside of the assembly, typically at a right angle to the waveguide flange, for ease of access. But various other adapter configurations are available, including end launch adapters, which essentially mount the waveguide and coaxial connectors in a straight line, so that the adapter can be installed as part of an in-line addition, such as to run a coaxial cable from a waveguide fixture. These types of adapters are available with similar waveguide sizes and connector types as traditional waveguide-to-coaxial adapters, and offer comparable electrical performance in terms of loss and VSWR, with the added convenience (where needed) of in-line installation.

Although this blog has detailed various types of waveguide-to-coaxial adapters, it should be noted that it may at times be necessary to mount together two different waveguide components within a system, in which case, a waveguide-to-waveguide adapter (Transformer) will be needed. Such adapters are specified by two different waveguide sizes, larger and smaller sizes, and they exhibit an optimum frequency range, typically the frequency range midband between the two waveguide bands. Waveguide-to-waveguide adapters (Transformers) are also specified by the usual electrical parameters, such as insertion loss, maximum RF/microwave power, and VSWR.

Waveguide is a viable transmission-line configuration that is still very much in use in high-frequency applications from RF through millimeter-wave frequencies. The adapters described herein are just a sampling of the different products available, for waveguide-to-coaxial or waveguide-to-waveguide transformations. Practical solutions can be found throughout the MDL website at

Contact MDL for your waveguide-to-coaxial adapter questions or requirements at 1-781-292-6684, visit our website at, or send us a tweet @MDLlab!

Stop Spinning Your Wheels When Selecting Rotary Joints

Rotary joints based on rigid waveguide can provide high-performance, dependable connections in many commercial and military RF/microwave systems. But matching the right waveguide rotary joint to a particular application can call for a bit of “rotary joint know-how” beyond simply selecting proper waveguide sizes. These are precision components that can help keep high-frequency signals connected under a variety of conditions, and are available in different waveguide sizes as well as compact, coaxial versions as needed.

Rotary joints, whether waveguide or coaxial types, allow the connection of high-frequency analog and high-speed digital signals in setups where at least one of the transmission lines must rotate, such as when connected to an antenna. Ideally, a rotary joint provides an electrical connection that remains consistent over time and with movement of the joint, with low insertion loss and with power-handling capabilities that exceed the maximum limits of the system. Rotary joints in both waveguide and coaxial forms have been used in many different types of high-frequency systems, including in air-traffic-control (ATC), radar, satellite-communications (satcom), and surveillance systems.

RotaryJointsComparing and Specifying Rotary Joints

Specifying a rigid waveguide rotary joint or other waveguide component usually starts with a required frequency range. For a rigid rectangular waveguide (WR) component, the frequency range is indicated by the WR waveguide size, such as a WR28 rotary joint with a frequency range of 26.5 to 40.0 GHz or a WR75 rotary joint, with a frequency range of 10.0 to 15.0 GHz. Lower WR numbers indicate smaller rigid waveguide dimensions and higher operating frequencies for the waveguide components.

A rotary joint will also have a power rating associated with it, whether the rotary joint is maintained in dry air or in nitrogen or other controlled atmosphere. High-power applications, such as transmitters, may require excellent power-handling capabilities, and these can be compared for different waveguide rotary joints in terms of continuous-wave (CW) power or peak power levels. When comparing peak power levels for different joints, the measured power should refer to test signals for the same pulse length. The power-handling capabilities of a waveguide rotary joint are tied to its composite materials, which are typically copper, brass, or aluminum, and with silver-plated or painted finishes; these construction materials, including additional mounting flanges and terminations, also impact the weight of a rigid waveguide rotary joint for a given WR size as well as its insertion-loss performance.

Waveguide rotary joints are typically produced in a number of different mechanical configurations in support of different transmission-line interconnections in both single-channel and multiple-channel applications, for use with analog, digital, or even fiber-optic signals. Some configurations may even combine waveguide and coaxial transmission lines within the same rotary joint for efficiency. Examples of different waveguide rotary joint mechanical configurations include I, L, U, and F formats, with one arm of the rotary joint fixed to a system housing or enclosure and the other arm free to rotate. In an I style rotary joint, for example, two transmission arms are in line, while in an L style rotary joint, one of the transmission arms is at a right angle to the other transmission arm. In an F style rotary joint, an in-line transmission arm is fixed to the housing, while one right-angle transmission arm is free to rotate. In a U style rotary joint, two transmission arms are at right angles to the center of rotation, with one fixed to the housing or enclosure and one free to rotate.

Rotary joints can be characterized and compared in terms of how well they rotate, such as their electrical performance with rotation, their maximum rotational speeds, and even their operating lifetimes, which are usually indicated as an expected number of rotations for the rotary joint. Rotary joints are rated for maximum rotational speeds, such as 500 rpm, and the operating lifetime—usually expressed as the total number of expected rotations—assumes operating a rotary joint within its rated speed limits. The operating lifetime of a rotary joint depends upon a number of other factors, including mechanical loading, input power levels, and operating temperatures.

The electrical performance of a rotary joint can change with its rotation, and such parameters as insertion loss, phase, and voltage standing wave ratio (VSWR) are typically characterized dynamically as a function of rotation and documented as phase WOW, or insertion loss WOW, or VSWR WOW. This is typically a ratio of the maximum to minimum deviations of a performance parameter with rotation, such as VSWR WOW = (maximum VSWR)/(minimum VSWR) for the effects of rotary joint rotation on VSWR.

Waveguide rotary joints can be compared in terms of many fundamental performance specifications, such as insertion loss and VSWR with frequency, in addition to some parameters that are somewhat unique to waveguide rotary joints, such as leak rate and torque. Most rotary joints are equipped with seals to allow pressurization, and are tested for leak rate, for use in different environments. The leak rate provides an estimation of a component’s expected behavior in a controlled environment, such as a nitrogen environment. The torque specification for a rotary joint is a measure of the mechanical resistance during startup or turning of the joint, usually in Newton-meters (Nm). It provides a means of comparing the different levels of force needed for working with different rotary joints in a given application.

Of course, the use of transmission-line transitions, such as a coaxial-to-waveguide transition, enables the incorporation of different types of transmission lines within a single-channel or multiple-channel rotary joint. Whereas waveguide rotary joints are interconnected according to their frequencies and waveguide sizes, coaxial rotary joints are capable of broader potential frequency bandwidths and interconnections according to broadband coaxial connectors, such as Type N, TNC, and even SMA connectors with bandwidths as wide as DC to 40 GHz. Coaxial rotary joints are often employed for combination functions within RF/microwave systems, including as couplers and rotary joints.

As developers of waveguide and coaxial rotary joints, we typically provide standard models of both types of rotary joints and can detail some of the performance differences, in terms of insertion loss, VSWR, and power-handling capabilities, between the two types of rotary joints. And in some cases, the different transmission-line types can be combined within a single rotary-joint solution that provides both waveguide and coaxial interconnections. In most cases, these are unique RF/microwave components that perform unique roles in high-frequency systems.

Contact MDL for your Rotary Joint questions or requirements at 1-781-292-6684 or visit our website at