Somewhere on a dusty desert road, troops patrolling to maintain peace or advancing toward an increasingly illusive enemy are keeping a sharp eye out for radio controlled improvised explosive devices (RCIEDs). These concealed threats buried in the road, plugged into streetlights or hidden by other decoys, have cost the lives of many soldiers and countless civilians.
Threats like these have come closer to home and law enforcement have been tasked to protect key government buildings, residences and vehicles of important officials.
Jamming the trigger
Counter-RCIED devices used by the military and law enforcement rely on jamming wireless trigger signals. They can be vehicle-mounted, transportable or man-carried, but they all use one of three common jamming techniques – swept continuous wave (CW), spot and barrage.
In swept CW, the carrier frequency is “swept” over various suspect frequency ranges. The sweep frequency must be high enough to deny trigger signals the time to detonate, yet slow enough to give the RCIED receiver time to respond to the jamming signal. An acceptable tradeoff between those challenges requires significant power.
Spot jamming works by targeting a known frequency and therein lies the challenge because that frequency is usually unknown. The jammer therefore must not only be able to detect and determine the trigger frequency, often in the presence of interference from legitimate signals, but also tune the jammer to that frequency, and do it all very quickly.
The barrage technique overcomes the problem of not knowing the frequency by using a wide bandwidth for the noise-modulated jamming signal such that it covers an entire communication band instead of just one channel. Since the noise is spread over a large bandwidth, it requires high RF power to be effective.
Irrespective of the jamming technique and other features, such as networking and in-field programmability, all counter-RCIED jammers must meet the following requirements:
- High RF transmitted power over a wide bandwidth for effective jamming
- Consistently high gain and efficiency over a wide bandwidth to support operation using battery power
- Small size and low weight for easy transportability
Enabling technologies: GaN on Silicon Carbide (SiC)
Gallium Nitride (GaN) is the predominant technology used to build RF power amplifiers (PAs) in jammers. GaN offers unique electrical characteristics – a bandgap of 3.4 eV gives GaN a breakdown field that is 20 times higher than other RF semiconductor technologies. This is responsible not only for GaN’s high-temperature reliability, but also power density capability. GaN, therefore, enables jammer equipment to meet all of the previously mentioned requirements.
The best of the best technology
Not all GaN devices are equal, however. On a substrate of another wide bandgap semiconductor, Silicon Carbide (SiC), Wolfspeed’s GaN on SiC devices are the fruition of more than two decades of experience since creating the industry’s first GaN on SiC high electron mobility transistor (HEMT).
Wolfspeed uses SiC instead of Si as a substrate both because of a better lattice structure match with GaN’s as well as SiC’s thermal conductivity that is nearly three times higher than that of Si. This builds on GaN’s strengths to achieve exceptional power densities.
The CG2H30070F is such a device that features an input match to deliver the highest possible instantaneous broadband performance over a wide 500 MHz-to-3 GHz range. It is available in a 2-lead metal/ceramic flanged package for optimal electrical and thermal performance.
In CW mode and with VDD 28 V, IDQ 1 A and PIN = 38 dBm, the device has a typical power gain of 12 dB, output power of 50 W and drain efficiency 71 percent. The HEMT is rugged enough to withstand an output mismatch stress (VSWR) of 5:1, an important parameter since jammer equipment must be robust against signal interference.
The CG2H30070F-AMP2 reference board (figure 1) combines two of these HEMTs to achieve 100 W CW over the entire bandwidth instantaneously. It offers high efficiency and nearly flat gain over the entire specified frequency range (figure 2).
For its reference designs, Wolfspeed uses its highly accurate large signal transistor models – available on request – and takes pad parasitic effects into account by modeling passive components. This makes it easier to achieve first pass success.
Visit the CG2H30070F page for more information or to request all of the CG2H30070F-AMP2 design files to get going on your counter-RCIED solution.