Packing a traveling-wave-tube amplifier (TWTA) into a 19-in. rack-mount enclosure is certainly nothing new. But equipping such a high-power amplifier (HPA) with a front-panel touch-screen user interface is a new slant on an old product, and the approach taken in bringing ease of use to the new model XTRM-400K Ku-band TWTA from Comtech Xicom Technology. The enclosure houses a traveling-wave tube (TWT) with dual-stage collector and supporting components. The tube is capable of 400 W continuous output power, with at least 350 W output power from 13.75 to 14.50 GHz at the amplifier’s waveguide output flange.

With its robust output power, model XTRM-400K (Fig. 1) is ideal for satellite-communications uplinks. The on-board liquid-crystal-display (LCD) touchscreen provides a measure of simplicity to operators. The touchscreen shows the status of the amplifier and allows operators to perform parameter trend analysis, in addition to logging specific performance events. It provides a quick summary of faults, including high VSWR, high voltage, and excessive TWT temperature. It provides details on output power, reflected power, heater hours, and even uplink power (as an option). The display can also show and control waveguide switches or a power combiner, greatly reducing system-level requirements for separate controllers in common architectures. In addition, the XTRM-400K TWTA also provides an Ethernet interface as well as RS-232 and combination RS-422/RS-485 ports for remote control and diagnostics.

Model XTRM-400K provides at least 70 dB large-signal gain and at least 75 dB small-signal gain. It also includes an attenuator with continuously adjustable 25-dB range for setting output levels. The gain is flat within a maximum window of 1 dB for any 80-MHz segment of the total bandwidth and within 2.5 dB across the full 750-MHz bandwidth. The gain slope is specified as ±0.04 dB/MHz with worst-case gain stability of ±0.25 dB for any 24-hour test period. The stability over temperature is specified as ±1 dB at any frequency for the full -40 to +50°C operating temperature range of the amplifier.

The model XTRM-400K amplifier is actually a subsystem, with a pair of isolators providing reflected-power protection for a first-stage solid-state amplifier (SSA) and the TWT (Fig. 2). Additional components in the subsystem include receive-band and harmonic filtering and couplers for monitoring the direct and reflected output-power levels. Input signals are fed via a Type N female connector while outputs are available at a WR-75 rectangular waveguide flange. Model XTRM-400K occupies three rack units (RUs) and weighs 56 lbs.

In spite of its high power rating, the amplifier maintains low noise levels. Harmonic output levels are held to -60 dBc or better while maximum intermodulation distortion (IMD) is -18 dBc when the amplifier is backed off 4 dB from its rated output-power level. Transmit-band noise is -70 dBW in a 4-kHz bandwidth while receive-band noise is -150 dBW in a 4-kHz bandwidth from 10.95 to 12.75 GHz. Residual AM noise is -50 dBc or better at offsets to 10 kHz while maximum phase noise is 12 dB below the IESS phase noise profile. AC fundamental levels are down -50 dBc while the sum of all spurious levels is -47 dBc or better. The linear group delay in any 80-MHz bandwidth is within ±0.01 ns/MHz. The amplifier has maximum input and output VSWR of 1.30:1.

The company also offers its model XTD-400K TWTA with essentially the same electrical performance, at least 350 W output power at the amplifier, and 400 W from the tube from 13.75 to 14.50 GHz, but in a more compact antenna-mountable housing measuring 10.25 x 20.50 x 11.00 in.
Comtech Xicom Technology, 3550 Bassett Street, Santa Clara, CA 95054; (408) 213-3000, FAX: (408) 213-3001, e-mail: sales@xicomtech.com, Internet: www.xicomtech.com.