The announcement of ABI Research’s recent study “ Microwave and Millimeter Wave High-Power Vacuum Electron Devices: Successfully Holding Off the Gallium Nitride Threat ” got covered by a number of media outlets including Microwave Journal this past week (August 30th). Analysts examining this $1 billion+ market segment for microwave and millimeter-wave power devices used mostly in specialized military (electronic warfare), scientific/medical and space communications applications, concluded that tube technology such as TWTA would maintain its market leadership role despite the aggressive attempts by solid-state technology such as Gallium Nitride to replace it. The press release discussed how after several rounds of consolidation in recent years, the tube industry is relatively stable, quoting ABI Research director Lance Wilson who stated that, “There is potential for some further consolidation, but there are no signs of that happening yet. One new RF semiconductor technology - gallium nitride (GaN) – may change the landscape but has not yet done so to any meaningful degree. While it is not yet monopolizing the microwave RF power industry, GaN is advancing steadily and is a technology that should be closely watched, as it will continue to be a threat to some aspects of the microwave and millimeter wave VED marketplace.”

This conclusion is not exactly new to those people who have been following the microwave tube business for years. One interesting report that I found online was presented by David Zavadil of Teledyne MEC to the Dixie Crow’s Chapter of the Association of Old Crows back in March 2008. Zavadil pointed out many of the technical and economical reasons why the tube business would be secure from any GaN challenges in his presentation, “The Role of Microwave Tubes in the Digital World or Can TWTs Survive the Solid State Challenge?”, at least for the EW market.

Breaking the tube market down by application, Zavadil estimates that 43% of the tube market is Radar, 27% communications, 15% EW and the remaining 15% is for miscellaneous niche applications. The consolidation of US domestic tube suppliers mentioned in the ABI Report is also presented by Zavadil’s with CPI (formerly Varian) and L3 as market leaders (each with ~42%) followed by MEC at 12%. Zavadil’s presents a timeline graph showing how this consolidation occurred between the 1960’s and today’s current state; indicating the acquisitions that marked Raytheon’s, Litton’s, Hughes’ and ITT’s departure from the market. Note - significant non-US suppliers include Thales and e2v are not part of this chart.

image courtesy of Teledyne MEC

Looking closer at the EW market (estimated at $85 M/yr in 2008), the trend is for system modernization (smaller/lighter/cheaper), off-board jamming, and active arrays, multi-beam (CCJ & NGP). These goals can all be achieved with today’s crop of TWT technology. Whereas, Solid state really only competes in applications that are less than 5 watts or below 1GHz. While they are not cheap, tubes maintain a price advantage over solid state where a commercial solid-state amp (SSA) with equivalent octave bandwidth would cost 6 times the price of a tube based on a $/watt basis. While the TWT does have a wear-out mechanism that is not an issue for a SSA, tube cathodes now outlive EW systems and past leakage problems can easily be sorted out early in post-production life testing. The problem that tubes need high voltage has been mitigated by a robust high-voltage power supply industry which has made considerable advances in past decades, using COTS components. While tube manufacturers may tout a reliability advantage that may or may not be true, tubes do have the advantages that come with the legacy and maturity of a proven technology.

Suppliers have also developed stress testing and screening procedure during production that have allowed tubes to achieve adequate life and reliability performance, further gaining the trust of their customers. These are among the factors that tube manufacturers have used to successfully fend off the solid state challenge. But as GaN continues to be developed and tested, these advantages may erode over time, especially if the rates of development and cost reduction are greater than those for tubes. It that case, tube replacement by SSA will just be a matter of time and gained trust.