JED - March 2010 - (Page 41)

TECHNOLOGY SURVEY TWTs and MPMs By Ollie Holt ED’s last survey on power amplifiers, which included traveling wave tubes (TWTs) and microwave power modules (MPM)s, appeared in April 2008. In this month’s issue, JED chose to review the current state of power amplifiers with a focus on TWTs and MPMs used for EW applications and look at their capabilities and limitations. The April 2008 survey focused mostly on solid state power amplifiers. Since the April 2008 survey, very little has changed in TWT and MPM amplifier technology other than some improvements in efficiencies, reliability and increased power output levels. Most of the TWT power amplifiers listed in this survey were developed for radar, radar jamming or communication applications. The TWT was originally developed by British scientists in 1942-43 in support of creating higher power radar systems for use by the military in World War II. The TWT enabled the radars to transmit at higher RF power levels, enabling the radars to achieve longer detection ranges. The British passed this TWT technology to its US ally. J The Journal of Electronic Defense | March 2010 The Journal of Electronic Defense | March 2010 Figure 1: Helix TWT Block Diagram Figure 1 is a crude block diagram of a Helix TWT. A Helix TWT looks like a long vacuum tube. The electron gun on the left, which is similar to the cathode of a vacuum tube, emits electrons down through the helix wire directed towards the collector. The magnets (yellow tube in Figure 1) form a containment field focusing the electron beam down through the helix coil at the collector. The helix coil extends from the RF input to the RF output couplers. The RF input device is a directional coupler, which is used to induce the RF signal to be amplified into the helix coil. It is a directional coupler used in order to direct the input signal toward the collector, not toward the electron gun. As the RF signal travels along the helix coil toward the collector, the electromagnetic field created by the RF current in the helix interacts with the electron beam traveling through the center of the helix, causing a phenomenon called velocity modulation. The electron beam induces more current into the helix as the signal flows through the helix toward the collector causing amplification of the RF signal. The RF output is another directional coupler positioned near the collector. The coupler removes the amplified RF signal from the TWT. The attenuators are

Table of Contents for the Digital Edition of JED - March 2010

JED - March 2010
Contents
The View From Here
Calendar
From the President
Letters
The Monitor
Washington Report
World Report
Modernizing EW Ranges
Shooting Down the Good Guys
USAF EW Sustainment
Technology Survey: TWTs and MPMs
EW 101
AOC News
Industry/Institute/University Members
JED Sales Offices
Index of Advertisers
JED Quick Look

JED - March 2010

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