The figure shows a prototype radial power-combining waveguide structure, capable of operation at frequencies from 31 to 36 GHz, that features an unusually large number (N = 24) of combining (input) ports. The combination of wide-band operation and large N is achieved by incorporating several enhancements over a basic radial power-combiner design. In addition, the structure can be operated as a power divider by reversing the roles of the input and output ports.
In this structure, full-height waveguides at the combining ports are matched in impedance to reduced-height radial waveguides inside the combiner base. This match is effected by impedance-transforming stepped waveguide sections. This matching scheme is essential to achievement of large N because N is limited by the height of the waveguides in the base.
Power is coupled from the 24 reduced-height radial waveguides into the TE01 mode of a circular waveguide in the base with the help of a matching post at the bottom of the base. (“TE” signifies “transverse electric,” the first subscript is the azimuthal mode number, and the second subscript is the radial mode number.) More specifically, the matching post matches the reflections from the walls of the 24 reduced-height waveguides and enables the base design to exceed the bandwidth requirement.
After propagating along the circular waveguide, the combined power is coupled, via a mode transducer, to a rectangular waveguide output port. The mode transducer is divided into three sections, each sized and shaped as part of an overall design to satisfy the mode-conversion and output-coupling requirements while enabling the circular waveguide to be wide enough for combining the 24 inputs over the frequency range of 31 to 36 GHz. During the design process, it was found that two different rectangular waveguide outputs could be accommodated through modification of only the first section of the mode converter, thereby enabling operation in multiple frequency ranges.
This work was done by Larry Epp, Daniel Hoppe, Abdur Khan, and Daniel Kelley of Caltech for NASA’s Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Innovative Technology Assets Management
JPL
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109-8099
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Refer to NPO-41511, volume and number of this NASA Tech Briefs issue, and the page number.
This Brief includes a Technical Support Package (TSP).
24-Way Radial Power Combiner/Divider for 31 to 36 GHz
(reference NPO-41511) is currently available for download from the TSP library.
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Overview
The document discusses the development of a 24-way radial power combiner/divider designed for operation in the Ka-band frequency range of 31 to 36 GHz. This innovation addresses a significant challenge in solid-state power amplifier (SSPA) technology, where individual Monolithic Microwave Integrated Circuits (MMICs) produce less power and operate at lower efficiency compared to traditional tube devices like Traveling Wave Tube Amplifiers (TWTAs). To enhance the output power capabilities of SSPAs, it is essential to efficiently combine multiple MMICs, which necessitates a combining circuit that minimizes power loss.
The prototype combiner, referred to as N=24, was designed to improve efficiency by eliminating the use of resistive cards in the radial base, which typically introduce insertion loss and complicate tolerance issues. Instead, the design focuses on achieving high isolation externally while maintaining low insertion loss, which is reported to be less than 0.6 dB. The combiner features an input match of less than -20 dB and an output match of less than -24 dB at the rectangular waveguide port of the Marie Transducer, indicating effective performance across the specified frequency range.
The design incorporates a radial base with rectangular waveguide inputs and a circular waveguide output, utilizing impedance transforming sections to facilitate the combination of signals from the 24 inputs. This approach allows for a functional bandwidth that exceeds the initial design specifications, making it suitable for various applications in space telecommunications and other fields where high efficiency and power output are critical.
The document also highlights the innovative mode transducer designed to convert the circular waveguide output back to rectangular waveguide, which is essential for integrating the combiner into existing systems. The transducer design is based on previous work but has been adapted to meet the specific requirements of this project, ensuring compatibility with multiple frequency ranges.
Overall, this technical support package outlines the advancements made in the design and functionality of the 24-way radial power combiner/divider, emphasizing its potential to enhance the performance of solid-state power amplifiers in high-frequency applications while addressing the limitations of current technologies.
