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Broadband TWTAs Power 6 To 40 GHz

Airborne platforms that rely on broadband amplifi cation, such as electronic-warfare (EW) and electronic-countermeasures (ECM) systems, need amplifi ers that are rugged but compact enough to meet tight weight limits. The MT 2100 series of traveling-wave-tube amplifiers (TWTAs) from MCL, Inc. are designed and built for these requirements. With models covering 6 to 18 GHz and 18 to 40 GHz, MT 2100 high-power amplifi ers (HPAs) are ideal for military aircraft environments as well as general outdoor environments where they are mounted to the same tower as an antenna.

MT 2100 TWTAs cover wide instantaneous bandwidths with as much as 100 W continuous-wave (CW) output power from 6 to 18 GHz and 50 W CW power from 18 to 40 GHz. A 6-to-18-GHz MT 2100 TWTA, for example, is built around a 125-W traveling wave tube (TWT) and a highvoltage power supply. It delivers 100 W output power at its waveguide fl ange, in a compact but rugged metal housing weighing only 25 lbs. (see figure). It achieves 50 dB gain with less than 6-dB gain variation (with equalization) across the 6-to-18-GHz range. The gain also remains stable within 1.2 dB for a 10C rise in temperature (the HPA is designed for operating baseplate temperatures to +70C). In spite of its high output-power levels, the 6-to-18- GHz MT 2100 has low noise levels, with -8 dBc harmonics and maximum residual frequency modulation (FM) of -57 dBm/Hz for offsets more than 500 kHz from the carrier.

At higher frequencies, the 18-to- 40-GHz MT 2100 generates at least 50 W output power across the full frequency range, with at least 40 W output power at the band edges. The minimum rated power gain is 46 dB, with minimum small-signal gain of 50 dB. The TWTA is designed for stable gain performance over time. After a 30-minute warm-up, and assuming constant input drive level, the TWTA is rated for no more than 0.25 dB variation in gain over a 24-hour period, operating at its full-rated output-power level or any level to 10 dB less than the full-rated output-power level. Harmonic levels are typically -13 dBc or less from 18 to 40 GHz.

The 50-W, 18-to-40-GHz MT 2100 incorporates fi eld-replaceable units (FRUs) for ease of maintenance. The 50-W, 18-to-40-GHz model measures 20.5 x 11.80 x 9.60 in. (520.7 x 299.7 x 243.8 mm) and weighs about 47 lbs. (24.5 kg or less) in a weather-resistant enclosure. It features integral DC blowers to dissipate heat generated by the TWT and power electronics.

Each MT 2100 HPA can be equipped with an optional GaAs driver amplifi er from MITEQ in front of the TWT as well as an optional variable attenuator for control of signal levels to the TWT. The HPA subsystems include protective circuitry for the amplifi ers, including isolators and high-directivity couplers to continuously monitor power in the forward and reverse directions. Optional fi ltering is available to reduce harmonic levels.

The rugged MT 2100 TWTAs can operate without damage into an 2.0:1 VSWR output load at any phase. They include an output power switch with on/off isolation of 30 dB and MIL-C-5015 DDK connectors for DC inputs. High-frequency inputs can be fed via waveguide fl anges or coaxial connectors. A MS3116-20- 41S connector is used for monitoring and control, allowing operators to check performance levels as part of regular monitoring or maintenance routines. Using an external computer, for example, an operator can view displays of RF forward power, RF refl ected power, tube drive power, helix current, tube temperature, and other key parameters in order to ensure long tube and amplifi er operating lifetimes. The MT 2100 TWTAs also feature programmable alarms for over-limit tube temperature, tube overdrive conditions, and RF refl ected power.

In addition to EW and ECM applications, the MT 2100 TWTAs are suited for electromagneticcompatibility (EMC) and electromagnetic-interference (EMI) testing. For applications requiring higher power levels over the 2-to- 40-GHz frequency range, the fi rm also offers the slightly larger TWTAs of the MT 3100 series.

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