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GaN or GaAs, TWT or Klystron-Testing High Power Amplifiers for RADAR Signals using Peak Power Meters

Measuring and characterizing pulsed RF signals used in radar applications present unique challenges. Unlike communication signals, pulsed radar signals are "on" for a short time followed by a long "off" period, during "on" time the system transmits anywhere from kilowatts to megawatts of power. The high power pulsing can stress the power amplifier (PA) in a number of ways both during the on/off transitions and during prolonged "on" periods. As new PA device technologies are introduced, latest one being GaN, the behavior of the amplifier needs to be thoroughly tested and evaluated. Given the time domain nature of the pulsed RF signal, the best way to observe the performance of the amplifier is through time domain signal analysis. This article explains why the peak power meter is a must have test instrument for characterizing the behavior of pulsed RF power amplifiers (PA) used in radar systems

Using RF Power Meters for EMC Testing

The complexity of modern digital equipment has caused EMI/EMC susceptibility testing to become increasingly important. Many EMC standards have been created including MILSTD- 461, IEC 61000, ISO 11451 Automotive, EN 50, and FCC part 15 that provide specific guidelines for EMC and EMI test methodologies. Early standards required a CW carrier, or single tone with constant modulation as the disturbance test signal. In January of 2010, the International Electrotechnical Commission, or IEC approved the 61000-4-4-am1 (ed. 2) amendment allowing the use of burst testing on devices. Amendment 1 defines an impulse (spike frequency) of 100kHz and Edition 2 requires burst testing with either the traditional 5kHz spike or the new 100kHz spike frequency. The burst test emulates real world RF interference emitted by base station communication amplifiers and ground based RADAR antennas. This article will discuss how a peak power sensor can replace an average diode detector in a field probe to measure pulse power, improve repeatability and increase dynamic range of the power measurement.

Statistical Analysis of Modern Communication Signals

The latest wireless communication formats like DVB, DAB, WiMax, WLAN, and LTE cellular use OFDM modulation with multiple carriers to transmit digital information. OFDM is a multi-carrier modulation scheme with a large dynamic range requirement due to the high crest factor signal. The introduction of this digital transmission technology has made it necessary to deal with peak power levels up to 20 dB above the average value. All of the RF power components must be capable of handling these high voltage peaks to avoid break down, or flash over. The peak power of several interconnected transmitters can reach more than one hundred times the thermal or average power level and RF component selection should not be based solely on these average values. Short voltage spikes that rarely occur are critical when determining the power handling capability of the transmission system components. The crest factor, i.e. the ratio of the peak value to the average or RMS value, must be correctly determined in order to specify these components. Signals with these high peak-to-average ratios should be measured using a statistical approach rather than a single measurement because it is unlikely to capture one of these rare events with a single peak power acquisition.

Time Matters — How Power Meters Measure Fast Signals

Modern wireless and cable transmission technologies, as well as radar systems, present demanding challenges for device and system developers. Manufacturers of test and measurement equipment are driven to offer products that fully support today’s needs, while anticipating the requirements of future technologies. Accuracy has always been a critical requirement in the test and measurement world, but modern technologies demand another must-have - highest data acquisition and processing speeds to allow accurate measurements of complex signal waveforms. This paper describes the different techniques RF peak power meters employ to meet these challenges.

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