JED - August 2016 - (Page 35)

TECHNOLOGY SURVEY A SAMPLING OF SOLID STATE POWER AMPLIFIERS By Ollie Holt Output Power (Watts) 104 103 SiC 102 GaN 101 1 GaAs 10-1 SiBJT 1 100 10 Frequency (GHz) Many different solid-state technologies can be used to build SSPAs. The different technologies have varying output powers and operational frequency ranges, which are shown in the figure to the right. For example, Silicon Carbide (SiC) provides the highest power possible, but is only able to perform up to approximately 5 GHz. Gallium Arsenide (GaAs) and Gallium Nitride (GaN) provide much higher operating frequencies. GaN has become the "go to" technology for high-frequency SSPAs. Note that Silicon Bipolar Transistor (SiBJT) is still used in some low-power, low-frequency applications. GaN was originally used in Light Emitted Diodes (LEDs). It has a wide bandgap of 3.4 eV, making it suitable for applications in optoelectronics, as well as high-power and high-frequency devices (i.e., EW SSPAs). GaN has a low sensitivity to ionizing radia- tion, which makes it an appropriate material for military and space applications that require high stability in radiation environments. GaN transistors also operate at much higher temperatures and higher voltages than other solid-state transistors. This survey requested information on parameters that impact the performance of SSPAs. First, the survey lists the operational frequency range of the SSPA. This defines the lower to upper frequency range of the SSPA listed. The next column in the table, "gain," defines the increase in power that can be achieved from input to output. Multiplying the input power by the gain equals the output power, as long as the amplifier operates in the linear region. Typically, a power amplifier is in the linear operating mode if the maximum input power limit is not exceeded. In the next column of the table, dBc relative to the carrier is a measure of how much higher the carrier signal is with respect to harmonics or spurious signals created within the device. For most applications, the larger this value, the better the SSPA's performance. Also, note that when the input power exceeds the maximum, the amplifier will start operating in non-linear mode. In this mode, the harmonics and spurious signals will continue to increase in output power, but the signal will not, until the signal's output power and the spurious output power are equivalent. Efficiency is defined as the power-added efficiency (PAE). This is the output power (RF) minus the input power (RF) divided by the DC power. In high-gain systems, the results are almost the same as efficiency (output power divided by input power), but in low-gain systems, the efficiency can be very different. In this survey, the input power (DC power) is the average input power. For a pulsed system, the PAE is calculated using input power (DC) when the pulse is created as opposed to the average. The next item is reliability. Reliability is a probabilistic value of how many hours the product may operate before failure. In this case, the reliability value is the manufacturer's derived length of time the typical SSPA will operate under stated conditions. Next month, we will look at manpack COMINT and DF systems. The Journal of Electronic Defense | August 2016 I n JED's March issue, the product survey focused on traveling wave tube (TWT) and microwave power module (MPM) amplifiers. This month's survey continues to look at power amplifiers, but focuses on solid state power amplifiers (SSPAs) for the defense market. SSPAs have advantages over other power amplifiers including lower operating voltages and higher reliability. 35

Table of Contents for the Digital Edition of JED - August 2016

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
World Report
Cyber Blitz: US Army Gains New Insight for EW/Cyber Operational Integration
Technology Survey: Solid State Power Amplifiers for EW, Radar and Communications Applications
EW 101
Threat Monitor
AOC Election
Index of Advertisers
JED Quick Look

JED - August 2016

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