In this innovation, the three-way combiner consists internally of two branchline hybrids that are connected in series by a short length of waveguide. Each branch-line hybrid is designed to combine input signals that are in phase with an amplitude ratio of two. The combiner is constructed in an E-plane splitblock arrangement and is precision machined from blocks of aluminum with standard WR-28 waveguide ports. The port impedances of the combiner are matched to that of a standard WR-28 waveguide. The component parts include the power combiner and the MMIC (monolithic microwave integrated circuit) power amplifiers (PAs). The three-way series power combiner is a sixport device. For basic operation, power that enters ports 3, 5, and 6 is combined in phase and appears at port 1. Ports 2 and 4 are isolated ports. The application of the three-way combiner for combining three PAs with unequal output powers was demonstrated.

This photo of the fabricated Serial Combiner shows the split-block construction arrangement.
NASA requires narrow-band solidstate power amplifiers (SSPAs) at Kaband frequencies with output power in the range of 3 to 5 W for radio or gravity science experiments. In addition, NASA also requires wideband, high-efficiency SSPAs at Ka-band frequencies with output power in the range of 5 to 15 W for high-data-rate communications from deep space to Earth. The three-way power combiner is designed to operate over the frequency band of 31.8 to 32.3 GHz, which is NASA’s deep-space frequency band.

For the proof-of-concept demonstration of this innovation, three available PAs were selected with output powers of 0.1, 0.2, and 0.6 W to meet the amplitude ratio of two. The 0.1- and 0.2-W PAs, which are in the 1:2 power ratio, are initially combined in a branch-line hybrid that has a coupling value of 4.77 dB. Likewise, the combined output of the first branch-line hybrid is combined with the output from the third PA in a second branchline hybrid, also with a coupling value of 4.77 dB. The measured combining efficiency at the center frequency of 32.05 GHz is greater than 90% for a wide range of power ratios both below and above two. The measured return loss at the output port 1 and the isolation among the input ports 3, 5, and 6 of the three-way combiner are greater than 16 and 22 dB, respectively.

Edwin G. Wintucky, and Jon C. Freeman of Glenn Research Center; and Christine T. Chevalier of QinetiQ North America Corp.

Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steven Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. LEW-18688-1

NASA Tech Briefs Magazine

This article first appeared in the October, 2012 issue of NASA Tech Briefs Magazine.

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