Magnetrons are high-power, high-frequency transmitter tubes that have been key to making radar work. We tend to think primarily about magnetrons, but klystrons, traveling-wave-tubes (TWTs) and crossfield amplifiers (CFAs) are also used, although not generally on commercial shipboard radar. They were then the only viable technologies able to achieve the necessary high levels of RF power at a sufficiently high operating efficiency. They performed well if
all you wanted to know is what, if anything, is out there, or how long it’s going to take to heat
up my soup in the microwave oven.
However, magnetrons have their drawbacks: size, weight, space, power consumption and
cost. Also, their life expectancy is only a few thousand hours and have unstable frequency and
phase of their output signals. Hence, the trend is to solid-state devices. But magnetrons still have
their place, according to Anthony Battaglia, Senior Business Unit Manager at Richardson Electronics. He says they will probably continue to be used in the very high power, longer-range
radar applications (see sidebar, page 40).
Furuno Senior Product Manager Eric Kunz agrees. The company makes both solid-state and
magnetron radars. He says they’ve made solid-state radars in their S-band commercial radar line
for at least seven years and now offer it in many recreational models as well. He adds that
Furuno has also introduced a new line of magnetron X-band radars. “Long-range detection is
something magnetron radars do very well.” He says they’re still superior to solid-state radars for
detecting weak targets and birds.
Solid state arrives
Solid-state devices offer many advantages such as lighter weight, smaller size, lower power
consumption, longer lifespan, instant turn-on, and wideband capabilities. However, the available options—laterally diffused metal oxide silicon (LDMOS) and gallium arsenide (GaAs)—are
not capable of sufficient power output at high frequencies due to limitations in breakdown voltage, power density and thermal conduction capabilities.
LDMOS is currently commonly used in RF power amplifiers in a number of
industries. However, it is generally limited to applications below about 3 GHz. GaAs
is widely used in very high-frequency amplifier circuits due to its ability to function
at frequencies in the range of 150 GHz. But with power levels limited to about 5
watts, and since they cannot withstand the high voltages, currents, and operating
temperatures, manufacturers have had to use multiple numbers of these devices in
push-pull or parallel, combining amplifier outputs to get up to about 20 to 40
Solid-state transceivers were used in radar sets in the mid- to late 2000s. This
was done using multiple devices using power splitters and adders/combiners and
their output powers summed up in-phase to the required output power, if necessary.
Studies had shown that failure of one or more such power modules did not cause the complete loss of the transmitter but rather only a slight reduction in range, typically on
the order of a few percent per failed module. Mark Bown, Marketing Manager at
Kelvin Hughes, describes their use of this technique in their early SharpEye series
introduced in 2006: “We started to move to GaN (gallium nitride) in 2013. Prior to
that LDMOS and GaAs were used depending on the frequency band where LDMOS
Navico’s BR- 24 solid-state radar, introduced in 2009, utilized a similar approach. These were
later to be followed by JRC’s JMA 9172-SA, Simrad’s HALO, Furuno’s DRS4D-NXT, Raymarine’s
A venerable technology looks toward semi-retirement
New Japan Radio Co.’s Electronic Frequency Tuning
Magnetron can be frequency modulated, allowing the
radar designer to use pulse compression technology.
Richardson Electronics’ Anthony Battaglia says it
“bridges the performance of solid-state technology along with the advantages of high-power magnetron technology, so the
radar manufacturer can have the
best of both worlds.”
Courtesy of Richardson Electronics
They’ve served us well over the past 60
or 70 years. They’ve been around since
WWII, and it’s anybody’s guess how
many collisions they’ve averted or how
many lives they’ve saved. But magnetrons are an old technology and
newcomers are vying to fill the vacuum
left by the transmitter tube.