RF power amplifier testing
RF power amplifiers are an essential part of any RF design. These crucial components take a low-level RF signal and boosts its power, without adding any change to format, modulation, or other factors. Due to the signal amplification characteristic of this rf power amplifier type, solid state RF amplifiers are often used in most RF, microwave, and millimeter-wave sensing, communications, electronic warfare, and directed energy weapons.
There are a variety of different types of high power rf amplifiers, with a wide range of frequencies, output power, and power gain. Given the large signal power levels of PAs and the importance of efficiency and linearity at these power levels, there are several test techniques and methods specifically dedicated to effectively characterizing and testing PA performance at the device and system level.
Important RF Power Amplifier Performance Parameters
l Operational bandwidth/frequency range
l Small signal gain
l Efficiency/power added efficiency (PAE)
l Gain flatness
l Input power
l Noise figure
l Input voltage standing wave ratio (VSWR)
l Stability
l Input and output impedance
l Output 1dB compression point (P1dB)
l Output third-order intercept point (IP3)
l Saturation Power (Psat)
l Peak power handling (pulsed operation)
l Reverse isolation
l Harmonics
l Spurious suppression
l Operating temperature range and thermal management system/requirements
l Supply voltage & bias conditions
Obviously, RF power amplifiers require a substantial amount of technical testing, beyond that of many other RF devices. To make sure the RF amplifier remains stable under stress conditions and has a long lifetime, the RF performance is verified while the device is driven up to and beyond maximum input power.
Power amplifiers are typically tested in a small signal sense, for linearity, and under varying load impedance over wide operating parameters. Most of this testing is done during characterization and quality control testing, but power amplifiers must often also be regularly testing to ensure they still meet specification over certain intervals depending on how they are operated. The reason for this is that the power levels and thermal dynamics of operating a power amplifier lead to high sustained temperatures while being energized, which can result in rapid degradation of the amplifier materials and structures.
Many of the small signal parameters, such as gain, bandwidth, gain flatness, VSWR, impedance, etc. can be tested using traditional VNA and S-parameter measurements. However, many of the nonlinear aspects of power amplifiers require additional measurements and techniques, possibly including X-parameters as an extension of S-parameters to account for non-linearity. Load-pull testing is also performed on power amplifiers to better determine the output behavior of the power amplifier facing various load conditions. Harmonic and spurious testing using signal generators and power meters/spectrum analyzers (often protected by couplers and attenuators) is also often performed. To better determine pulsed power performance of a power amplifier, peak power meters may be used with adequate bandwidth to capture the signal envelope of amplifiers output.
Learn more about KeyLink Microwave’s line of RF power amplifiers (PAs)
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