Interview with Diane Kees from Micro Harmonics Corporation

everything RF recently interviewed Diane Kees, the CEO of Micro Harmonics Corporation. Diane is a microwave engineer with deep expertise in ferrite devices for millimeter-wave applications, supported by advanced study in microwave engineering at the University of Virginia and specialized research on Faraday-rotation isolators and waveguide circulators. Since joining Micro Harmonics, she has played a leading role in the development and commercialization of high-frequency ferrite components, bringing to that work a broad engineering background spanning process automation, plant engineering, and technical instruction.

Q. Can you give us an overview of Micro Harmonics, including when the company was founded, how it started, and how it evolved from a research and design consultancy into a manufacturer of millimeter-wave RF components?

Diane Kees: Micro Harmonics was founded in 2008 as a research and design consultancy focused on advanced microwave, millimeter-wave, and sub-THz components. The company initially worked on solving difficult high-frequency design challenges for customers and research programs, which helped build deep expertise in waveguide structures and low-loss component design. 

A major turning point came in 2015, when we began developing a new class of high-performance Faraday rotation isolators under a NASA SBIR contract. That work laid the foundation for the company’s move from consulting into manufacturing. Rather than producing standard catalog copies, Micro Harmonics focused on creating components that addressed real performance gaps in the market, especially at higher frequencies where insertion loss, bandwidth, and integration become more challenging.

Today, Micro Harmonics may be best known for our low-loss millimeter-wave isolators, with products available across every standard waveguide band from WR-28 (26 to 40 GHz) through WR-2.8 (260 to 400 GHz). However, we continue to expand our portfolio and the frequency ranges for our product lines.  

Q. Can you provide an overview of Micro Harmonics’ product portfolio and the frequency ranges your components support?

Diane Kees: Our portfolio includes our isolators, hybrid circulators, ferrite-based voltage-variable attenuators, cryogenic isolators, and orthomode transducers. Here are our currently available frequency ranges.  

Q. Isolators are one of Micro Harmonics’ flagship products. What key performance parameters, such as insertion loss, isolation, and power handling, are most critical when designing mmWave isolators?

Diane Kees: For millimeter-wave isolators, the two most critical design priorities are low insertion loss and high power handling. At these frequencies, even small losses can have a major impact on overall system performance, so insertion loss is usually the first parameter engineers care about. If the isolator introduces too much loss, it can reduce available signal power, hurt noise performance, and make the rest of the RF chain harder to optimize.

Power handling is also very important, particularly in applications where higher drive levels are needed or where reliability under real operating conditions matters. An isolator has to do more than provide protection on paper. It has to maintain that performance while handling the power levels the system demands. 

Of course, isolation remains essential as well, since the isolator’s core job is to protect sensitive upstream components from reflected signals. But in many MMW systems, the real challenge is achieving strong isolation without sacrificing insertion loss.

Beyond the core specifications, we also think two practical factors matter to customers: full-band measured test data and direct engineering support. At mmWave frequencies, designers want to see how a component performs across the entire band, not just at a single point. Additionally, because these systems are often highly specialized, access to engineering support can be just as valuable as the datasheet itself.

Q. Your components operate at millimeter-wave frequencies from roughly 25 GHz to over 400 GHz. What engineering challenges arise when designing components at these extremely high frequencies? 

Diane Kees: Designing components at millimeter-wave frequencies becomes much more demanding because everything gets smaller, more sensitive, and less forgiving.  

The first challenge is simply scale. As frequency increases, wavelength decreases dramatically. At 10 GHz, the wavelength is about 3 centimeters. At 100 GHz, it is about 3 millimeters. That means the physical dimensions of the waveguide and internal component features become extremely small, so machining tolerances, alignment, surface quality, and assembly precision all become much more critical. In many cases, parts must be inspected and assembled under magnification because even very small dimensional errors can affect electrical performance.

The second major challenge is loss. As frequency rises, conductor losses increase, so maintaining low insertion loss becomes much harder. That is one reason thermal considerations also become more important at higher frequencies, since components can generate more heat as losses increase.

Measurement and validation are another major challenge. Millimeter-wave testing requires specialized and expensive equipment, including vector network analyzers with high-frequency extenders, along with careful calibration and precise measurement techniques. At these frequencies, performance cannot be assumed from the design alone. It has to be verified carefully through testing.

Finally, development is highly iterative. Designing successful millimeter-wave components usually requires a closed loop between electromagnetic simulation, precision fabrication, and measured test results. In other words, it is not just a design exercise. It is a process of refining the component until real-world performance matches the intended electrical behavior. 

Q. Who are the typical customers for Micro Harmonics’ components, and what are the primary applications where they are used?  

Diane Kees: Most of Micro Harmonics’ components end up in test and measurement applications. That is really the biggest area for us, since engineers and researchers working at millimeter-wave frequencies need components that are precise, low-loss, fully characterized, and cover the full waveguide bandwidth. After that, we see strong use in telecommunications and other millimeter-wave systems, where performance at these frequencies becomes critical. Our components are also used in areas like remote sensing, radio astronomy, and radar.

So while the end markets vary, the typical customer is usually working on a high-frequency system where performance, accuracy, and dependable measured data really matter. 

Q. Micro Harmonics has developed a patented hybrid circulator architecture. What limitations of traditional circulator designs were you trying to overcome with this technology? 

Diane Kees: The main issue we were trying to address was the growing set of limitations that come with traditional Y-junction circulator designs at millimeter-wave frequencies. Bandwidth was a big part of that, but more broadly, Y-junction circulators begin to reach their practical limits as frequency increases. At higher millimeter-wave bands, especially above about 150 GHz, it becomes extremely difficult to get the level of performance newer systems require using the traditional Y-junction approach. 

We pushed the Y-junction approach as far as we could using advanced impedance-matching techniques, but eventually we ran into fundamental limits tied to the ferrite material itself. At that point, there was only so much more performance the traditional design could deliver. So instead of continuing to work around those limitations, we developed a new hybrid circulator architecture. 

Micro Harmonic's Patented High Isolation Hybrid Coupler ArchitectureThe result is a patented circulator technology that offers much wider bandwidth than a conventional Y-junction design, while remaining a compact passive device. In bands from WR-15 through WR-3.4, the hybrid circulator delivers about 24% fractional bandwidth. That is roughly three times the bandwidth of a W-band Y-junction circulator and more than 10 times the bandwidth of a Y-junction circulator in WR-5.1. We have also developed full-waveguide-band hybrid circulators in WR-15 and WR-6.5. 

Q. Your components use ferrite-based designs and unique thermal management techniques such as diamond heatsinks. How do these design approaches improve performance and reliability in high-frequency systems? 

Diane Kees: These design approaches improve performance in two key areas that matter a lot at MMW frequencies: loss and heat.

In traditional Faraday rotation isolators, the ferrite section is often relatively long. That design has been used for many years, but as you move higher in frequency, ferrite materials become more lossy, which increases insertion loss. At millimeter-wave frequencies, that is a major issue.

We addressed that by redesigning the isolator from the ground up. The changes minimize insertion loss, maximize stability by making the isolator insensitive to external magnetic fields, and make the device more compact.

The other big issue is thermal management. Conventional isolators often do not have a very effective path for heat dissipation, which can limit power handling and increase thermal stress.

Our isolators use an optical CVD diamond support disc to conduct heat into the block. Because diamonds are such an effective thermal conductor, the device runs cooler, handles reverse power better, and sees less stress on critical internal materials and joints. 

Insertion loss of traditional style “legacy” isolators and Micro Harmonics isolatorThat combination of lower loss and better heat dissipation is what helps improve both performance and reliability in high-frequency systems. 

Q. Micro Harmonics offers isolators designed for cryogenic operation. What are the key challenges in designing RF components for extremely low temperatures, and what applications require these cryogenic microwave solutions? 

Diane Kees: Designing RF components for cryogenic operation is challenging because a device that performs well at room temperature can behave very differently once it is cooled. In the case of a Faraday rotation isolator, one of the main issues is that the ferrite material is temperature-dependent. As the temperature drops, the ferrite rod’s properties change, and that can have a major effect on performance. For example, an isolator that delivers about 30 dB of isolation at room temperature may degrade to around 12 dB at 80 K if it was not specifically designed for cryogenic operation. 

Micro Harmonics WR-28 Cryogenic Isolator

A second challenge is the magnetic bias field. Faraday rotation isolators rely on an external magnetic field, and the strength of that field can also change at low temperatures. On top of that, any component made from multiple precisely fitted parts will experience mechanical stress as materials contract during cooling, which can further affect performance. As your article also points out, some materials used in millimeter-wave components can begin to superconduct at cryogenic temperatures, which can create unpredictable behavior such as resonances, leakage paths, and reflected power instead of absorbed power.

As for applications, cryogenic microwave solutions are needed anywhere engineers are trying to lower system noise and improve sensitivity or performance. A good example comes from Plymouth Rock Technologies, which was working under a Navy SBIR program to reduce the size and weight of large satcom antenna systems on aircraft carriers so they could be mounted higher on the ship’s superstructure without losing performance. Their solution involved cryogenically cooling the low-noise amplifier, but that created a new challenge: finding an isolator that could still perform properly at those very low temperatures. In that case, the cryogenic isolator helped reduce noise and improve the gain ratio in a harsh mil-spec environment.

More broadly, these kinds of cryogenic components are becoming important in ultra-high-frequency wireless systems, including 5G and 6G communications, stand-off security scanning, and military defense applications, where lowering the noise floor can make a meaningful difference in overall system performance. 

Q. When developing RF components for space applications, what design, testing, and quality assurance processes are required to ensure reliability in the space environment? 

Diane Kees: For space-related RF components, reliability starts with the basics: material selection, design discipline, and environmental testing. Materials have to be chosen carefully, including for compliance with NASA outgassing requirements, and the component design has to account for the extreme conditions these systems may face. 

From our perspective, one of the key reliability challenges is low-temperature operation. Standard isolators do not perform well, and in some cases may not function at all, in cryogenic environments. That is why we worked with NASA to develop a line of cryogenic millimeter-wave components, including cryogenic Faraday rotation isolators. 

Testing is a critical part of that process. Our cryogenic isolators are routinely tested at 25 K in our cryostat, and we use a resistive thin film for isolation that is not in the class of superconductors. Performance has also been independently verified down to 1 K by researchers at the University of Chicago and the Smithsonian Astrophysical Observatory. 

More recently, when a customer requested a WR-10 cryogenic circulator in 2024, we combined our work in cryogenic isolators with our patented hybrid circulator technology to develop a WR-10 cryogenic hybrid circulator in a very short time. That kind of work reflects the overall process: careful design, appropriate materials, low-temperature testing, and validation that the component will perform reliably in demanding environments. 

Q. Micro Harmonics provides full RF test data for every component shipped. Why is detailed characterization important for millimeter-wave components, and what measurement techniques and test equipment are used to verify performance at these frequencies? 

Diane Kees: Detailed characterization is especially important at millimeter-wave frequencies because small physical variations can have a real impact on electrical performance. At these frequencies, components are extremely small, assembly is often done by hand, and even slight differences in alignment, materials, or internal geometry can affect performance across the band. 

That is true not just for isolators, but for circulators, attenuators, orthomode transducers, and other millimeter-wave components as well. No two mm-wave components have exactly the same frequency response. Each one has its own measured signature, and the differences can sometimes be significant enough that relying only on catalog specs is not enough. 

Specifications like bandwidth, insertion loss, isolation, return loss, power handling, and size are all important, but what customers really need to see is the actual measured performance of the specific component they are buying. That is why Micro Harmonics tests every component across the full waveguide band and provides the RF test data to the customer at no additional cost. 

The key test instrument for this work is the vector network analyzer, or VNA. VNAs are essential for millimeter-wave measurement because they allow us to characterize component performance across frequency and verify that the device is meeting its intended specifications. At these frequencies, full-band measured data is one of the best ways to give engineers confidence that the component will perform as expected once it is integrated into a system. 

Q. With increasing interest in mmWave and sub-THz systems, what technology trends do you believe will drive demand for high-performance millimeter-wave components in the coming years? 

Diane Kees: We think demand will be driven first by the continued push toward 6G and beyond, especially as more development moves into higher mmWave and sub-THz bands. Those frequency ranges offer much wider available spectrum and are being explored not only for higher data rates, but also for functions like sensing and communication, which will place even greater demands on front-end component performance. 

A second driver is that as systems move higher in frequency, the component challenges become more difficult. Loss, bandwidth, power handling, packaging, and characterization all become more critical, so there is a growing need for components that are not just theoretically possible but that also deliver high performance in real-world systems. 

We also expect continued demand from test and measurement, because every step forward in mmWave and sub-THz development depends on having components that engineers can trust while they design, validate, and refine those systems.

At Micro Harmonics, we tend to follow customer demand and customer need very closely. As customers push toward higher frequencies and higher power levels, we expect demand for high-performance millimeter-wave components to keep growing.

Micro Harmonics Corporation:

Micro Harmonics specializes in the design and manufacture of advanced millimeter wave components, including Faraday rotation isolators operating from 25-400 GHz, hybrid circulators, voltage variable attenuators, orthomode transducers, and cryogenic isolators. Our products cover every standard waveguide band from WR-28 (26-40 GHz) through WR-2.8 (260-400 GHz). These are the most technologically advanced millimeter wave products on the market today. They are optimized for extended bandwidth and the industry’s lowest insertion loss. We test every single component we make across the full waveguide band on a vector network analyzer to ensure compliance, and we send the test data with every unit we ship. Don’t settle for anything less.