Record GaN HEMT PA tackles radar tubes
Fujitsu has combined two GaN HEMTs into the world s highest power output C-band solid-state PA module, which it hopes will replace vacuum tubes in radar.
Hisao Shigematsu reported the 320 W record amplifier on October 15 at the Compound Semiconductor IC Symposium in Monterey, California, plus a second, more efficient module.
The high-output device operates with 57 percent efficiency, while the second 250 W amplifier claims 60 efficiency, both using the same GaN technology that Fujitsu sells in mobile base stations.
“We believe our GaN HEMT has higher efficiency than that of any other company,” Shigematsu told compoundsemiconductor.net.
“As the chip technology has already been developed, Fujitsu Laboratories does not foresee that a great length of time will be required until the production stage is reached for these types of amplifiers.”
To date only traveling wave tubes have generally been able to deliver the power needed for C-band radar, but GaN transistors are the first serious solid-state challengers.
Single GaAs chips have insufficient breakdown voltages to match the powers provided by vacuum tubes. Stringing them together doesn't help, because this reduces efficiency due to losses in interconnecting circuitry. This limits efficiency to values far below that of Fujitsu s GaN amplifiers.
“Poor efficiency causes self-heating and degrades the output power,” Shigematsu pointed out.
To avoid any such heating effects, the amplifier was specially designed to optimize the distance between the two GaN HEMTs, within the module's specific dimensions.
Traveling wave tubes power comes at the cost of low efficiency, and the tubes themselves are bulky, fragile and have a short lifespan. Fujitsu believes it can now overcome these failings with GaN transistors.
As well as benefiting radar, the Japanese conglomerate believes the amplifers will find application in satellite communications and next-generation mobile base stations.
