Vacuum tubes still rule the roost in high-performance radar

Citation

(2008), "Vacuum tubes still rule the roost in high-performance radar", Aircraft Engineering and Aerospace Technology, Vol. 80 No. 6. https://doi.org/10.1108/aeat.2008.12780faf.004

Vacuum tubes still rule the roost in high-performance radar

Article Type: Mini features From: Aircraft Engineering and Aerospace Technology: An International Journal, Volume 80, Issue 6

Since the invention of the transistor in 1947, solid-state electronics have gradually displaced vacuum tube designs in most electronic applications. However, one area where vacuum technology remains unsurpassed is in the generation of microwaves – from microwave ovens to high-power radars.

High-power, high-frequency radar transmitters use travelling wave tubes (TWTs) to amplify the radio frequency signals in today’s high-performance radar systems and satellite communications, where they are said to be unequalled for reliability and efficiency.

Invented in the same decade as the transistor, TWTs have steadily become increasingly sophisticated. They can now reportedly achieve efficiencies of over 40 per cent in S-band radars, compared with less than 20 per cent for solid state transmitters. In X band, the difference is said to be even more marked, with TWTs claiming to be nearly three times as efficient as solid state systems!

The performance of modern TWTs, in terms of pulse fidelity, reliability and durability, has led them to populate the world’s satellite communications networks, and they are reported to be at the heart of practically every state-of-the-art military radar, electronic warfare and complex weapon system in service today.

According to Howard Smith, Engineering Director at UK microwave technology specialists TMD Technologies: “At any serious power and/or frequency, TWT systems can always outperform solid state systems.”

According to TMD Technologies, the key weakness with solid state transistors in high-power microwave generation is the poor efficiency, which causes high-thermal dissipation, and thus high-junction temperature. The high-junction temperature degrades the reliability, and variation in junction temperature degrades the RF performance.

However, these limitations with solid state radar transmitters are not always recognised. According to TMD Technologies Chairman Peter Butcher: “We are not opposed to solid state in microwave; in fact we have designed a number of solid state amplifiers which are operating satisfactorily around the world. But for high power, and frequencies above 3 GHz, the benefits of TWT systems in terms of performance and reliability far outweigh solid state alternatives.”

“Our task now is to demonstrate this to the marketplace, which over the years has been misled into believing the opposite is true.”

TMD Technologies believes that in the high efficiency of TWT systems is not just an advantage in its own right, but also leads to higher reliability and longevity. The energy saving also has the increasingly important advantage of having a lower carbon footprint, where the difference in efficiency is as significant as between a conventional incandescent lamp and a modern low-energy light bulb.

Details available from: TMD Technologies, Tel.: +44 (0)20 8581 5002, Fax: +44 (0)20 8581 5012, E-mail: heather.skinner@tmd.co.uk, web site: www.tmd.co.uk