Edwin G. Wintucky

Advances in Space Traveling-Wave Tubes for NASA Missions

Significant advances in the performance and reliability of traveling-wave tubes (TWTs) utilized in amplifying space communication signals for NASA missions have been achieved over the last three decades through collaborative efforts between NASA and primarily L-3 Communications Electron Technologies, Inc. (L-3 ETI). This paper summarizes some of the key milestones during this period and includes development of TWTs for the Communications Technology Satellite, Cassini, and Lunar Reconnaissance Orbiter missions. Technical advances in computer modeling, design techniques, materials, and fabrication have enabled power efficiency to increase by almost 40% and the output power/mass figure-of-merit to increase by an order of magnitude during this period.

Ultra-High Power and Efficiency Space Traveling-Wave Tube Amplifier Power Combiner With Reduced Size and Mass for NASA Missions

In the 2008 IEEE Microwave Theory and Techniques Society International Microwave Symposium Digest version of our paper, recent advances in high power and efficiency space traveling-wave tube amplifiers for NASAs space-to-Earth communications are presented. The RF power and efficiency of a new K-band amplifier are 40 W and 50% and that of a new K-band amplifier are 200 W and 60%. An important figure-of-merit, which is defined as the ratio of the RF power output to the mass (W/kg) of a traveling-wave tube (TWT), has improved by a factor of 10 over the previous generation Ka-band devices. In this paper, a high power high efficiency Ka -band combiner for multiple TWTs, based on a novel hybrid magic-T waveguide circuit design, is presented. The measured combiner efficiency is as high as 90%. In addition, at the design frequency of 32.05 GHz, error-free uncoded binary phase-shift keying/quadrature phase-shift keying (QPSK) data transmission at 8 Mb/s, which is typical for deep-space communications, is demonstrated. Furthermore, QPSK data transmission at 622 Mb/s is demonstrated with a low bit error rate of 2.4 times10-8, which exceeds the deep-space state-of-the-art data rate transmission capability by more than two orders of magnitude. A potential application of the TWT combiner is in deep-space communication systems for planetary exploration requiring transmitter power on the order of a kilowatt or higher.

Traveling-wave tube cold-test circuit optimization using CST MICROWAVE STUDIO

The internal optimizer of CST MICROWAVE STUDIO (MWS) was used along with an application-specific Visual Basic for Applications (VBA) script to develop a method to optimize traveling-wave tube (TWT) cold-test circuit performance. The optimization procedure allows simultaneous optimization of circuit specifications including on-axis interaction impedance, bandwidth or geometric limitations. The application of MWS to TWT cold-test circuit optimization is described below.

Waveguide power combiner demonstration for multiple high power millimeter wave TWTAs

Summary form only given. The work presented here is the results of a proof-of-concept demonstration of the power combining Ka-band waveguide circuit design and test procedure using two Ka-band TWTAs (Varian model VZA6902V3 and Logimetrics model A440/KA-1066), both of which were previously employed in data uplink evaluation terminals at 29.36 GHz for the NASA Advanced Communications Technology Satellite (ACTS) program. The characterization of the individual TWTAs and power combining demonstration were carried out over a 500 MHz bandwidth from 29.1 to 29.6 GHz to simulate the deep space network (DSN) bandwidth of 31.8 to 32.3 GHz. The input and output powers were corrected for circuit insertion losses due to the waveguide components. The RF saturated powers of both ACTS TWTAs were in the order of 120 W.

High Power Combining of Ka-Band TWTs for Deep Space Communications

This paper presents the results of a high efficiency power combining demonstration of two 100 W Ka-band space TWTs using a 4-port magic-T hybrid junction-based waveguide circuit. Power combining efficiencies of about 90% over a 1 GHz frequency band centered at 32.05 GHz and a high data transmission rate of 622 Mbps were successfully demonstrated

Q-band (37–41 GHz) satellite beacon architecture for RF propagation experiments

In this paper, the design of a beacon transmitter that will be flown as a hosted payload on a geostationary satellite to enable propagation experiments at Q-band (37-41 GHz) frequencies is presented. The beacon uses a phased locked loop stabilized dielectric resonator oscillator and a solid-state power amplifier to achieve the desired output power. The satellite beacon antenna is configured as an offset-fed cut-paraboloidal reflector.

Demonstration of multi-Gbps data rates at Ka-band using software-defined modem and broadband high power amplifier for space communications

The paper presents the first ever research and experimental results regarding the combination of a software-defined multi-Gbps modem and a broadband high power space amplifier when tested with an extended form of the industry standard DVB-S2 and LDPC rate 9/10 FEC codec. The modem supports waveforms including QPSK, 8-PSK, 16-APSK, 32-APSK, 64-APSK, and 128-QAM. The broadband high power amplifier is a space qualified traveling-wave tube (TWT), which has a passband greater than 3 GHz at 33 GHz, output power of 200 watts and efficiency greater than 60%. The modem and the TWTA together enabled an unprecedented data rate at 20 Gbps with low BER of 10−9. The presented results include a plot of the received waveform constellation, BER vs. Eb/N0 and implementation loss for each of the modulation types tested. The above results when included in an RF link budget analysis show that NASAs payload data rate can be increased by an order of magnitude (>10X) over current state-of-practice, limited only by the spacecraft EIRP, ground receiver G/T, range, and available spectrum or bandwidth.

Ka-band waveguide hybrid combiner for MMIC amplifiers with unequal and arbitrary power output ratio

The design, simulation and characterization of a novel Ka-band (32.05±0.25 GHz) rectangular waveguide branch-line hybrid unequal power combiner is presented. The manufactured combiner was designed to combine input signals, which are in phase and with an amplitude ratio of two. The measured return loss and isolation of the branch-line hybrid are better than 22 and 27 dB, respectively. The application of the branch-line hybrid for combining two MMIC power amplifiers with output power ratio of two is demonstrated. The measured combining efficiency is 92.9% at the center frequency of 32.05 GHz.

Peak satellite-to-earth data rates derived from measurements of a 20 Gbps bread-board modem

A prototype data link using a Ka-band space qualified, high efficiency 200 W TWT amplifier and a bread-board modem emulator were created to explore the feasibility of very high speed communications in satellite-to-earth applications. Experiments were conducted using a DVB-S2-like waveform with modifications to support up to 20 Gbps through the addition of 128 Quadrature Amplitude Modulation (QAM). Limited by the bandwidth of the amplifier, a constant peak symbol rate of 3.2 Giga-symbols/sec was selected and the modulation order was varied to explore what peak data rate might be supported by an RF link through this amplifier. Using 128-QAM, an implementation loss of 3 dB was observed at 20 Gbps, and the loss decreased as data rate or bandwidth were reduced. Building on this measured data, realistic link budget calculations were completed. Low-earth orbit (LEO) missions based on this TWTA with reasonable hardware assumptions and antenna sizing are found to be bandwidth-limited, rather than power-limited, making the spectral efficiency of 9/10-rate encoded 128-QAM very attractive. Assuming a bandwidth allocation of 1 GHz, these computations indicate that low earth orbit vehicles could achieve data rates up to 5 Gbps—an order of magnitude beyond the current state-of-practice, yet still within the processing power of a current FPGA-based software-defined modem. The measured performance results and a description of the experimental setup are presented to support these conclusions.

HIGH EFFICIENCY KA-BAND MMIC SSPA POWER COMBINER FOR NASA'S SPACE COMMUNICATIONS

In this paper, we will review the design, construction and performance of the two-way Ka-band waveguide branch-line and asymmetric magic-T based unequal power combiners. The manufactured combiners were designed to combine input signals that are equal in phase and with an amplitude ratio of two. Next, the design, construction and performance of a three-way branch-line unequal power combiner, achieved by serially interconnecting two 2-way branch-line hybrids and optimizing the dimensions using software tools, is presented. The application of the two-way and three-way combiners for combining the output from two or three MMIC PAs was demonstrated. The observed efficiencies for all three power combining configurations are 90 percent or greater at Ka-band (31.8 to 32.3 GHz).