A proposed microstrip Yagi antenna would operate at a frequency of 8.4 GHz (which is in the X band) and would feature a mechanically simpler, more elegant design, relative to a prior L-band microstrip Yagi antenna. In general, the purpose of designing a microstrip Yagi antenna is to combine features of a Yagi antenna with those of a microstrip patch to obtain an antenna that can be manufactured at low cost, has a low profile, and radiates a directive beam that, as plotted on an elevation plane perpendicular to the antenna plane, appears tilted away from the broadside. Such antennas are suitable for flush mounting on surfaces of diverse objects, including spacecraft, aircraft, land vehicles, and computers.

This Simplified Exploded View depicts the main components of the three-element microstrip Yagiantenna featuring dual offset aperture-coupled feed for each patch.
The design of the original version of the prior L-band microstrip Yagi antenna utilized a dual coaxial probe feed to generate circularly polarized radiation. (In some other versions of the prior antenna, a single aperture-coupled feed has been used to obtain linear polarization, but this would be of no help in contemplated applications in which circular polarization would be required.) The coaxial feed in the original circularpolarization version introduces electrical and mechanical complexities and difficulties. Electrically, it is difficult to match the impedance of the coaxial cable to that of the antenna because of the parasitics involved in the coaxial through-feed connections. Mechanically, the geometry of the coaxial feed makes it difficult to impart a low profile and predominantly planar character to both the antenna and its feed structure. In contrast, in the proposed X-band microstrip Yagi antenna, a dual aperture-coupled feed would be used to obtain circular polarization, simplifying both the electrical and mechanical aspects of design and imparting a predominantly planar character to the overall shape.

Stated somewhat more precisely, what has been proposed is a microstrip antenna comprising an array of three Yagi elements. Each element would include four microstrip-patch Yagi subelements: one reflector patch, one driven patch, and two director patches. To obtain circular polarization, each driven patch would be fed by use of a dual offset aperture-coupled feed featuring bow-tie-shaped apertures (see figure). The selection of the dual offset bow-tie aperture geometry is supported by results found in published literature that show that this geometry would enable matching of the impedances of the driven patches to the 50-Ω impedance of the microstrip feedline while maintaining a desirably large front-to-back lobe ratio.

This work was done by Ronald Pogorzelski and Jaikrishna Venkatesan 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

(818) 354-2240

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Refer to NPO-41791, volume and number of this NASA Tech Briefs issue, and the page number.

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This Brief includes a Technical Support Package (TSP).
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Microstrip Yagi Antenna With Dual Aperture-Coupled Feed

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NASA Tech Briefs Magazine

This article first appeared in the January, 2008 issue of NASA Tech Briefs Magazine (Vol. 32 No. 1).

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Overview

The document discusses the development of a Microstrip Yagi Antenna with a Dual Aperture-Coupled Feed, originally designed at NASA's Jet Propulsion Laboratory (JPL) by Dr. John Huang. This innovative antenna is specifically tailored for X-band operation at 8.4 GHz and aims to achieve circular polarization, which is essential for various aerospace applications.

The original design utilized a coaxial probe feed, which posed significant electrical and mechanical challenges, particularly in matching the coaxial line to the antenna due to parasitic effects. Additionally, the coaxial feed required complex integration through multiple substrates, complicating the overall design. To address these issues, the new design employs a dual offset aperture-coupled feed, which allows for a more elegant and planar implementation of the antenna and its associated feed electronics.

The microstrip Yagi array consists of three elements, each featuring one reflector patch, one driven patch, and two director patches. The dual bow-tie shaped aperture-coupled feed enhances coupling between the microstrip feedline and the driven patch element, facilitating a better match to a 50-Ohm microstrip feedline while maintaining a low front-to-back lobe ratio. This design choice is crucial for optimizing antenna performance and reducing cross-polarized radiation, which can be problematic in other feeding techniques.

The document highlights the novelty of this design, emphasizing its potential for integration into landed assets' panels, making it suitable for various applications in aerospace technology. The use of a bow-tie shaped aperture is particularly noted for its ability to balance coupling efficiency and radiation pattern quality.

Overall, the Microstrip Yagi Antenna with Dual Aperture-Coupled Feed represents a significant advancement in antenna technology, addressing the limitations of previous designs while providing a solution that is both efficient and practical for modern aerospace applications. The document serves as a technical support package under NASA's Commercial Technology Program, aiming to disseminate aerospace-related developments with broader technological, scientific, and commercial implications.