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

MDL Excited for Largest Microwave Exhibit

For this year’s Microwave Week (June 1-6), the MDL team will be in Tampa Bay, Florida for the IEEE MTT International Microwave Symposium (IMS). The IMS is one of the largest exhibitions in the microwave industry hosting over 500 companies.  Attending this weeklong event is a great opportunity to participate in technical sessions, interactive forums, workshops, industrial exhibits, application seminars, and more!

If you plan on attending, visit MDL at booth 1715 to learn more about microwave components, sub-systems and assemblies including custom waveguide rotary joints and rotary switches, power combiners and dividers, and monopulse comparators just to name a few. Need help locating the MDL booth? Use IEEE’s interactive exhibitor list!


Won’t be able to attend IMS? Visit MDL’s website to learn more about our components, sub-systems and assemblies. Stay connected with MDL on Twitter, LinkedIN, YouTube and here on our blog for more news and events.

The 2014 Satellite Show Recap

The MDL team had a great time in Washington, DC for this year’s Satellite Show. This year’s event spanned three days and brought in approximately 12,000 satellite professionals from all segments of the satellite industry! It served as an excellent event to network with fellow industry professionals and to educate attendees on the advantages of using MDL’s components, sub-systems and assemblies.

Visitors to the booth could view numerous satellite materials from MDL including custom waveguide assemblies, rotary switches, and coaxial rotary joints (as shown below). Videos on MDL’s robotic brazing and cleaning processes were also on display and can be viewed here.


Didn’t get a chance to visit us? Stop by MDL’s website to learn more about our components, sub-systems and assemblies. For more MDL news and updates, connect with us on Twitter, LinkedIN, YouTube and here on our blog.

MDL Exhibits at Satellite 2014

After months of preparation, the MDL team is ready for next week’s Satellite Show in Washington, DC. Stop by booth 3131 from March 11-13 at the Walter E. Washington Convention Center to learn more about MDL products, special online tools, and more!


With 350+ exhibitors at this year’s show, finding booths can feel like a scavenger hunt! We recommend using the Satellite Show Exhibitor tool to make finding the booths easier. You can find MDL’s exact booth location by entering number 3131 in the Satellite Show tool and clicking on Microwave Development Labs. (see image below).

ExpoLayoutOnce you arrive at our booth, you’ll be able to experiment with the Rigid Waveguide Slide Rule and Reflectometer tools. If you have questions about our online tools or how MDL can assist with your satellite needs don’t hesitate to ask in person, on Twitter @MDLlab or by phone at 781-292-6684!

We hope to see you there!

Stop Looking for Your Old HP Slide-Tool…

The days of searching through desk drawers for your old HP Slide-chart tool are finally a thing of the past with the launch of MDL’s newest tool online – the Reflectometer Calculator (as shown below).  This has always been a vital tool for correlating/converting VSWR to Return Loss or Reflection Coefficient. The Reflectometer Calculator also shows the contribution to overall Loss due to the Reflections (Mismatch Loss)!

Reflectometer Tool

The Reflectometer Calculator allows engineers to input any one of three known values, (Reflection Coefficient (p), VSWR or Return Loss), to quickly convert to the other unknown values. This tool allows the user to put their System or Component’s performance in perspective. Users can quickly convert to numbers they are comfortable using to determine the System or Component’s RF efficiency. The calculator will even provide engineers with a window of uncertainty for measurements taken with less than perfect systems (Coupler Directivity).

The tool will help you to answer these questions:

  1. What is the dB value for a 1.2:1 VSWR? Answer: (20.8dB)
  2. What portion of my Loss measurement is due to my device measuring a 1.5:1 VSWR? Answer: (0.175dB)
  3. What is the reflective coefficient of a product measuring a 1.3:1 VSWR? Answer: (0.13)

Looking for other tools to help you get the job done? Check out another popular tool from MDL – the Rigid Waveguide Slide Rule. It is available for download on your Android, Blackberry or OS devices. Download here.