Stellant Systems, a premier manufacturer of critical spectrum and power amplification systems for defense, space, medical, scientific, and industrial customers worldwide, has shipped a set of spaceflight-qualified 35-W Q-band linearized channelized traveling-wave tube amplifiers (LCTWTAs) in a conduction-cooled package that operate from 40 - 42 GHz.
The model 2000HDA-A16 linearized channel amplifier traveling-wave tube amplifier (LCTWTA), designed and manufactured by Stellant Systems, consists of a linearized channel amplifier (LCAMP), a traveling-wave tube (TWT), and an electronic power conditioner (EPC). The TWT and LCAMP completed flight qualification testing in 2018. This particular model LCTWTA produces a minimum of 35 W of RF power at end-of-life (EOL) across the frequency band of 40 – 42 GHz.
A flight set of 31 units was delivered in support of a commercial HTS spacecraft, shown in Figure 1. The TWT itself is qualified for operation up to 200 W over the full 37.5 to 42.5 GHz Q-band allocation, representing the highest CW power helix TWT qualified for space applications at Q-band. These LCTWTAs enable gigabits per second (Gbps) data rates by providing unprecedented power, efficiency, and linearity for a Q-band downlink. This model LCTWTA was awarded an R&D 100 award in 2019.
Figure 2. shows the model 2000HDA-A16 EPC with the model 9922HA conduction-cooled TWT next to the linearizer and channel amplifier (LCAMP). The TWT model 9922HA employs a helical RF circuit with periodic, permanent magnet (PPM) focusing packaged for conduction cooling. The electron gun is a dual-anode, isolated-focus-electrode design and is designed for greater than 15 years of mission life. The helix circuit is designed to provide CW-saturated RF output at 35 W RF over the 40 to 42 GHz Q-band frequency range. The 9922HA was designed primarily using the Naval Research Laboratory codes CHRISTINE 3D and MICHELLE.
TWT Qualification
The model 9922HA TWT is part of the 9922H TWT family, which completed flight qualification in 2018. The TWT body current at saturated drive level is below 0.5 mA (flight set average), while the output power exceeds 37 W (beginning of life) across 40.0 to 42.0 GHz with an average efficiency of 49%.
Electronic Power Conditioner (EPC)
The electronic power conditioner (EPC) shown in Fig. 2 is the 7-kV model 2000HDA, first launched in 2003, now with over 2400 units in orbit and a cumulative 170 million operating hours. It is capable of processing over 300 W of DC power. The EPC can be configured to accept either regulated or unregulated spacecraft bus voltages of up to 100 volts. The EPC efficiency ranges between 91% and 95%, depending on the spacecraft bus voltage interface and the extremes of the environmental requirements.
LCTWTA Performance
The stellar LCAMP is shown in the middle of Fig. 2. An LCAMP consists of a channel amplifier (CAMP) and linearizer. The LCTWTA has an input dynamic range of -49 dBm to -13 dBm with 36 gain steps in 1.0 ± 0.3 dB increments in Fixed Gain Mode (FGM). In ALC mode, this LCTWTA has a minimum control range of +2 to -13 dB relative to saturation with 36 gain steps in 0.5 dB ± 0.25 dB increments, and the linearizer provides 5 dB gain expansion and 40° phase expansion over swept power with 20° intentional phase expansion variation across frequency to match TWTA characteristics.
Thirty-one (31) integrated LCTWTAs were delivered for this program. They were tested over a temperature range of approximately 0 oC to 60 oC. The efficiency of the entire LCTWTA, along with the noise power ratio (NPR), plotted vs. output power, is shown in Fig. 3. The range across units, frequency, and temperature is shown by the dotted curves, with the heavy curves showing the average. The 0 dB point on the horizontal axis corresponds to ~39 W output power.
Fig. 4The output power and phase versus drive for the flight set are shown in Fig. 4. Again, the heavy curves show the average of the flight set across units, frequency, and temperature, and the dotted curves show the range. The LCAMP was able to compensate to keep the phase shift at an average of 10 degrees at saturation.
This solution will enable Gbps-level total data transfers via downlink for a high-throughput satellite (HTS) application.
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