War is known for bringing pain and suffering, as it seldom brings anything good to humanity. Even if something positive comes from it, the benefits are often meager at best. However, one war drastically changed not just the art of warfare but also the way people live their lives.
World War II (WWII), which lasted from 1939 to 1945, led to the development of several technologies and products that have now become an irreplaceable part of our lives. Synthetic rubber, duct tape, flu vaccines, penicillin, electronic computers and radar all were developed or gained significant traction because of the war effort. In addition, the cavity magnetron that still powers microwave ovens in addition to providing high RF transmit power, was invented in the early part of WWII and became a mainstay of radar systems used by the Allied forces.
Though the name cavity magnetron implies that we are going to talk about some infamous leader of the Decepticon Army; it was one of the functional blocks that saw its first application in radar systems during WWII and proved to be crucial in enhancing the effectiveness of radar systems. The contribution was so significant that many experts consider it one of the major reasons behind the Allied forces winning the war.
Though originally designed for the generation of electromagnetic signals to be used in high frequency military applications, the cavity magnetron and other similar vacuum tubes gained more popularity after they found application in American households as microwave ovens. Currently, their applications stretch far beyond the defense domain to sectors including medical, household, space and many more. Figure 1 shows some common applications that use tube-based transmitters, along with where they operate in the frequency spectrum.
Figure 1 The microwave spectrum and some common applications.
From devices that cook food, to devices that jam military communications with a frequency band ranging from 1 to 1000 GHz, microwave tubes offer different solutions at different frequency ranges. If we consider the entire microwave band, the consumer microwave oven emerges as the biggest application of microwave tubes. According to the Residential Energy Consumption Survey 2020, more than 95 percent of U.S. households had at least one microwave. This equates to approximately 126 million microwave ovens being used in household applications in the U.S. alone.1 Considering just the high frequency or high-power applications, the defense industry becomes the largest user, accounting for more than 30 percent of the high-power microwave tube market, according to a report from Stratview Research.2
Microwave Tubes on the Battlefield
Defense applications for microwave tubes are very diverse. Radar systems, remote-sensing, electronic warfare (EW), satellite communications, improvised explosive device (IED) and infrared (IR) countermeasures are some of the most popular defense applications using microwave tubes. Of these applications, radars and satellite communication links were among the first applications to use microwave tubes.
The advent and growth of solid-state power amplifiers (SSPAs) are diminishing the market share of microwave tubes in all but the highest power applications. Recently, the industry has shifted focus toward utilizing tubes in high-power EW applications and innovations in microwave tube-based directed energy (DE) weapons. DE weapons use concentrated electromagnetic energy, rather than kinetic energy, to sabotage, damage or disable various electronic systems used by enemy forces. DE weapons are emerging as a popular EW option because of their ability to render enemy systems useless without the need to fire a bullet or cause any physical explosions.
Both lasers and microwave tubes can be used to launch a DE attack but tubes are preferred for wider attacks given the distance from the target is the same. DE systems based on microwaves are classified as high-power microwave (HPM) weapons and countries like Russia, China, France and the U.S. have been working on HPMs for more than a decade. However, only a few HPMs have seen field operations. Table 1 shows some popular HPM systems.
Like any device that transmits RF power, HPMs require a source to convert the electromagnetic pulses to higher power signals with frequencies well into the GHz range. The output power and frequency capabilities of microwave generators are fairly broad. That allows almost every common microwave tube variant to be used for HPMs and the same flexibility makes tubes broadly applicable to a wide variety of defense applications. Table 2 presents a high-level comparison of the common microwave tube types and indicates their suitability in HPM applications.
While each microwave generator is suitable to be used in a wide variety of defense applications, they each have disadvantages. For instance, Klystrons can provide the highest power outputs but they may be less preferred because of their complex operation. Similarly, BWOs, though extensively explored by the industry, become limited in high frequency applications because high frequency implies smaller sources.
Macro Opportunities for Microwave Tubes in the Defense Industry
Since defense is fundamental to national sovereignty, funding for procurement and innovation in the defense industry is often a large portion of a country’s budget. The goals and strategies may be different, but defense spending is a critical part of the budget for developed and developing countries. Global defense expenditures have risen continuously since 2015 and from 2013 to 2022, expenditures grew by 19 percent, according to SIPRI.3
The U.S. has the largest defense budget, by far, so it is not surprising that they are also the biggest consumer of microwave tubes. This is a numbers game with the U.S., given the growth in combat aircraft, warships, missiles and electronic countermeasures (ECM)/electronic counter-countermeasures (ECCM) equipment. We estimate that more than 40 percent of the microwave tubes shipped in the defense industry go to U.S. equipment.
While SSPA solutions, particularly GaN, are making fast inroads into the RF power market, some of the very highest power applications require power levels best served by tube-based amplifiers. Naval applications, with long-range search radars, are a prime example of the need for high-power transmitters. Despite their expense, the number of ships is growing quickly. The Chinese Navy, the largest in the world, currently stands at approximately 350 ships, but they are planning to expand to 400 ships as soon as 2025.4 Most of these ships will be surface combatants likely employing several different types of radars. The U.S. Navy has announced another major expansion that will see it acquire between 282 and 340 ships over the 2023 to 2052 period.5
Despite the threat from solid-state power technology, microwave tubes will continue to occupy a niche and play a vital role in defense applications. Their versatility and innovation potential make them an integral part of the ever-evolving defense industry. As technologies advance and new challenges emerge, microwave tubes are poised to keep contributing significantly to future defense capabilities.
References
- “U.S. Household Growth Over Last Decade was the Lowest Ever Recorded,“ Pew Research Center, October 2021, Web: www.pewresearch.org/short-reads/2021/10/12/u-s-household-growth-over-last-decade-was-the-lowest-ever-recorded/.
- “Microwave Tubes Market Size, Share, Trend, Forecast, Competitive Analysis, and Growth Opporunity: 2022-2027,” Stratview Research, February 2023, Web: www.stratviewresearch.com/2981/microwave-tubes-market.html.
- “Trends in Military Expenditure, 2022” SIPRI, April 2023, Web: www.sipri.org/sites/default/files/2023-04/2304_fs_milex_2022.pdf.
- “Pentagon: Chinese Navy to Expand to 400 Ships by 2025, Growth Focused on Surface Combatants,” USNI News, November 2022, Web: news.usni.org/2022/11/29/pentagon-chinese-navy-to-expand-to-400-ships-by-2025-growth-focused-on-surface-combatants.
- “An Analysis of the Navy’s Fiscal Year 2023 Shipbuilding Plan,” Congressional Budget Office, November 2022, Web: www.cbo.gov/publication/58745.
