The Advantages of Rivendell’s Magnetron Technology over Solid State and Traditional Magnetrons

Written By: Mark Robertson, CTO

Published: 16^th December, 2025

Magnetrons have long served as the reliable workhorses of industrial heating. Powering applications from cooking bacon and tempering food products to advanced plasma processes and more. Known for their cost-effectiveness and energy efficiency, magnetrons also provide a compelling alternative to fossil fuel-based heating methods. A distinct advantage lies in their ability to heat materials from the inside out— contrasting with convection heating, which warms from the outside in. They are perfectly suited for new-age industrial demands.

The last decade has ushered in a new era of industrial demands, with applications requiring higher power levels, greater performance, and precise control. Magnetrons, while economical, have traditionally struggled to deliver the frequency stability, phase coherence, and consistent output power that these advanced systems require. In such cases, solid-state RF technology has dominated, albeit with significantly higher capital (CAPEX) and operating (OPEX) costs.

Rivendell Technologies is here to change that. By introducing a new generation of magnetron-based systems, we’re bridging the gap—delivering the precision, stability, and power output which today's applications demand, all while maintaining the cost advantages and familiarity the industry has relied on for decades. Our technology combines the best of both worlds: the cost and efficiencies of magnetrons, combined and redesigned to meet tomorrow's performance standards.

Magnetron Instability – Changing the Narrative

Magnetrons have had the reputation of being unstable or imprecise in terms of their frequency, phase and power output. This has primarily been a function of the power supplies used to drive them. To boil it down, three primary power supply factors influence the output of the magnetron: the high voltage supply to the cathode, the current supply to the filament, and the current supply to the electromagnet surrounding the tube.

Unstable inputs result in an unstable output.

Any variation in these inputs will manifest as a change in the power output of the tube, resulting in a corresponding change in frequency and phase. There are numerous white papers on these phenomena, and as such, this article will not delve into the physics behind magnetron operation. If you precisely control these inputs (cost-effectively), then you are one giant leap closer to replicating what solid-state technology can do. This is precisely what Rivendell Technologies is doing.

Power supply and control electronics have evolved since the standard magnetron power supply was invented. These power supplies, or transmitters as they are commonly referred to, typically include an SCR-driven AC filament circuit, a rudimentary solenoid/electromagnet supply (typically a simple single-phase, full-bridge rectified DC supply) and a 6 or 12 pulse high voltage rectifier design.

In order to understand the influence these circuits have on magnetron performance, you need only look at the power and spectral output of the tube with respect to time.

Figure 1: Standard Magnetron Power Ripple at 100kW

In Figure 1 above, the following power supply influences can be seen:

• The 12-pulse rectifier shape from the anode supply and;

  
  

• The 60Hz AC filament shape can be seen (albeit harder to point out);

  
  

Combined together, they account for a nominal ripple of about 13kW. On a longer timescale, the precision of solenoid control comes into play, increasing that variation even further. To be clear, the above are only the major factors impacting power stability and frequency stability and other minor factors exist such as magnetron temperature and the match seen by the tube among others. Rivendell Technologies has designed a cost-effective solution to address these major factors, and the improvement is evident.

To single out the effect of each primary power supply factor, we can improve them one at a time. Starting with the high voltage (HV) ripple, a passive network can be added to the HV circuit and the result is shown in the figure below.

Figure 2: Magnetron Power Ripple at 100kW with HV Smoothing

As shown in Figure 2 above, the overall power ripple has been reduced from approximately 13kW down to approximately 4.8kW. The large spikes still present are a direct result of the SCR-driven AC-filament. This can be rectified (pun intended) by either moving to a true-sinusoid power supply, or by going to a DC-filament. In this case, the improvement with a DC filament is shown in the figure below.

Figure 3: Magnetron Power Ripple with HV Smoothing and a DC Filament

This improvement has reduced the overall ripple from approximately 4.8kW down to approximately 1.6kW. As a note, moving to a true-sinusoid power supply can, in our experience, reduce the power ripple to around 2 - 3kW on average.

The final improvement lies in the control of the solenoid. This is not a trivial task as controlling a large inductive component effectively requires somewhat advanced power supplies and fast control schemes. Rivendell Technologies has implemented these items, and as shown in the figure below, successfully.

Figure 4: 4kW Step in Magnetron Output Power

As seen in the figure above, we are able to execute a 4kW step of the output power in approximately 70ms solely with solenoid control. This also means that we are able to effectively respond to regular changes in the mains input to the power supply. However, very large deviations in the mains input can take up to 300ms to correct and result in a large deviation from the average. However, we continue to pursue development on improving this particular feature even further.

By modifying the transmitter with modern technology, including off-the-shelf power supplies and custom high-speed controls, a nominal power output stability of +/-1% (max) has been realized, all while maintaining the level of simplicity and industrial reliability our customers depend on.

Another distinct benefit of stabilizing magnetron output power is that the frequency and phase stability also improve. In other words, the frequency and phase output of the magnetron are intimately linked to the same power supply factors which affect magnetron output power. In the comparison below, the frequency stability of the magnetron is shown before and after implementing our improvements.

Video 1: Magnetron Output Spectrum at 100kW without Power Smoothing Improvements

Video 2: Magnetron Output Spectrum at 100kW with Power Smoothing Improvements

Frequency & Phase Agility – Locking-In

Despite solving the power stability issues with a meticulously engineered magnetron power supply designed to maintain relatively stable frequency and phase characteristics. Such configurations inherently lack the capability for actual frequency and phase agility. Addressing this critical shortcoming is another area where the Rivendell Technologies Narya product line distinguishes itself.

At the heart of Narya’s innovation is the strategic integration of solid-state technology, specifically through the use of injection locking. By injecting a stable, low-power reference signal from a solid-state oscillator into the magnetron, Narya effectively synchronizes the magnetron's output to the desired frequency and phase. This technique enables dynamic control, allowing the magnetron to respond in real time to changes in operational requirements. The result is a hybrid system that combines the high-power efficiency of traditional magnetrons with the precision, agility, and responsiveness typically associated with solid-state RF sources.

To demonstrate this improvement, let’s compare the spectrum of a standard magnetron in a common transmitter with a transition from an unlocked state to a frequency locked state.

Video 3: Magnetron Output Spectrum before and after Frequency Locking

The result is clear: the frequency stability in vastly improved. Furthermore, we can also demonstrate frequency agility, as shown in the short video below, on a magnetron operating at 100 kW in a standard transmitter.

Video 4: 2MHz Sweep of Magnetron Output Frequency at 100kW Output Power

With respect to phase agility, the best demonstration of this control is achieved through the combination of high-power magnetrons.

Combination – The Next Step Forward

An efficient combination of RF signals with the simple intent of doubling output power hinges on precise control of frequency and phase (and to some minor extent, power). Whether the combination technology is a magic-tee, hybrid-90, or other device, the core principles remain the same.

Enter Narya-I, a solution which efficiently combines two industrial L-Band, 100kW magnetrons together.

Figure 5: Narya-I Demonstration System Located in Carleton Place, Ontario

This solution achieves a combining efficiency of at least 99% using off-the-shelf waveguide and transmitter components with zero special tuning. The secret sauce lies in the custom, high-speed control system, which enables real-time control and monitoring of every critical system parameter. Check out our 200kW system demonstration video below!

Video 5: 200kW Demonstration

Scalable by design, this technology can be easily expanded to reach output powers of 400kW, 800kW and beyond, where the only practical limitation is the waveguide itself.

Stay tuned for further features and improvements to this technology as we continue to master frequency and phase control!

For additional details, visit our website to learn more at https://www.rivendelltechnologies.com

We would love to hear from you anytime via email at info@rivtechrf.com

Our doors are also open for demonstrations. Contact us to schedule your visit to our Carleton Place, Ontario facility.