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Military Microwaves Supplement
Recent Advances in Radar Technology
Using Calibration to Optimize Performance in Crucial Measurements
The initial GaN high electron mobility transistors (HEMT) adoption started with ultra broadband applications and S-, C- and X-Band radar applications. In recent years, telecom applications have ramped up GaN HEMT production volumes. Cree recently reported that it has shipped more than 2 million transistors to the telecom market, which is accelerating the adoption of GaN HEMT technology. These increased volumes have enabled the GaN cost platform to be competitive with Si or GaAs solid-state FETs, independent of frequency.
At L-Band frequencies, Cree has developed two new GaN HEMTs optimized for use in 1.2 to 1.4 GHz radar amplifier systems: the 250 W CGHV14250 and the 500 W CGHV14500. These L-Band high power transistors feature ultra-high efficiency performance (Class A/B operation in the 65 to 70 percent range), high power gain performance (20 dB range) and wide bandwidth capabilities. The new transistors are also input matched and unmatched on the output, allowing for utilization in HPA applications ranging from UHF to 1800 MHz, including tactical air navigation systems (TACAN), identification friend or foe (IFF) systems and other military telemetry systems.
Manufactured using Cree’s latest generation 0.4 um, 50 V process, the CGHV14250 and CGHV14500 offer superior GaN HEMT performance, efficiency and bandwidth at an affordable price. Cree’s GaN HEMT technology also delivers proven reliability of 2.5 million hours of MTTF life (285 years) at peak junction temperature of 225°C. Cree GaN processes are reliable, stable and proven, with a fielded FIT rate of less than 10. As one of the pioneers in commercializing GaN technology, Cree has demonstrated volume production and the reliability experiences to support pulsed, CW and modulated waveform applications.
GaN’s high efficiency and gain characteristics provide system designers with a number of advantages, including economies in heat sinks and thermal management. GaN high power density packages provide the potential benefits of smaller amplifier size/footprint and reduced drive power, resulting in lighter system weight, which can be important for mobile, outdoor and airborne applications. Further, GaN’s efficiency advantage helps reduce load requirements for the power distribution system and the wider bandwidth potential offers system designers the option to employ a single antenna approach based on a multi-band high power amplifier (HPA) capability.
Full Specifications and Features
Under typical operation at 25°C case temperature, the 250 W CGHV14250’s output power reaches 330 W, 18 dB power gain with 77 percent typical drain efficiency (see Figure 1). The 500 W CGHV14500 is rated for 500 W typical output power, 17 dB power gain, and 70 percent typical drain efficiency at 25°C. These specifications are measured at 500 µsec, 10 percent duty cycle operating conditions. For both the 250 and 500 W GaN HEMTs, the pulsed amplitude droop is < 0.3 dB.
Although the device part numbers indicate 250 and 500 W, a closer look at the data sheet reveals they are rated at a case temperature of 85°C (see Figure 2). In examining Figures 1 and 2 to compare the devices’ performance at 25° versus 85°C, note that the efficiency of the transistors remains above 70 percent from 25° up to 85°C. In demonstration of the robustness of the device, the power dissipation is also shown for running the parts in continuous wave (CW) mode (see Figure 3).
Targeted applications for the new L-Band GaN HEMTs include TACAN, IFF systems and other military telemetry systems. Cree provides RF design engineers with Cree’s industry-leading large signal models, now available for Agilent’s ADS and AWR’s Microwave Office simulators. S-parameter files are also available. The demonstrator circuits for the CGHV14250 and CGHV14500 were designed with their respective proprietary large signal models and achieved first-pass success for both the 1.2 to 1.4 GHz circuits and the 960 to 1250 MHz circuits (see Figure 4).
Demonstration test fixtures for 1.2 to 1.4 GHz radar are available from Digi-Key, as well as directly from Cree. Additionally, an application circuit for IFF and TACAN performance will be available shortly.
Research Triangle Park, NC
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