A multilayer patch antenna, similar to a Yagi antenna, surrounded by a metallic wall has been devised to satisfy requirements to fit within a specified size and shape and to generate a beam with a half-power angular width of ≤40°. This antenna provides a gain of about 14 dB; in contrast, the gain of a typical single-patch antenna lies between 5 and 6 dB.

This antenna can be considered an alternative to a two-dimensional array of patch antenna elements, or to a horn or helical antenna. Unlike a two-dimensional array of patches, this antenna can function without need for a power-division network (unless circular polarization is needed). The profile of this antenna is lower than that of a horn or a helical antenna designed for the same frequency. The primary disadvantage of this antenna, relative to a horn or a helical antenna, is that its footprint is slightly larger.

This antenna (see figure) includes four dielectric substrate layers of polytetrafluoroethylene (PTFE) [which has a relative permittivity of 2.2], on which metallic patch antenna elements are formed. It also includes two thick spacer layers of a foam that has a relative permittivity of 1.08. A metallic wall surrounds the aforementioned components on four sides, forming an open cavity suggestive of a shallow, boxlike feed horn. The length of each side is about two wavelengths and the total height is about one wavelength. Without this cavity, the antenna gain achieved was 2 dB lower.

A microstrip feed line is etched on the upper side of PTFE dielectric layer 1 and is proximity-coupled to a driven patch element located on the upper side of PTFE dielectric layer 2. A ground plane is located on the bottom of PTFE dielectric layer 1 and is electrically connected to the metallic wall. The foam layers support PTFE dielectric layers 3 and 4, on which are located two additional patches that function as "parasitic" antenna elements in that they are electromagnetically coupled to the driven element.

The use of proximity coupling by a microstrip feed line assists mainly in matching to the high input impedance attributable to the three-layer configuration of patch antenna elements. Some fine tuning of the proximity coupling is effected by widening of the microstrip under the driven patch. By enabling the driven patch to exist on a substrate thicker than that of the microstrip feed line, the proximity coupling likely increases the bandwidth of the antenna moderately. One can provide for circular polarization by introducing a microstrip power divider with a 90° phase delay in the microstrip feed line to one of two proximity couplings.

This Multilayer Patch Antenna protrudes less than does a horn or a helical antenna. For clarity, the layers of foam that support PTFE dielectric layers 3 and 4 are not shown in this view

This work was done by Mark Zawadzki and John Huang of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Computers/Electronics category.

NPO-21242

Topics:
Antennas Electronic equipment Electronics & Computers Foams Forming Logistics Manufacturing processes
This Brief includes a Technical Support Package (TSP).
Document cover
Multilayer Patch Antenna Surrounded by a Metallic Wall

(reference NPO-21242) is currently available for download from the TSP library.

Don't have an account?

More From SAE Media Group

    Magazine cover
    NASA Tech Briefs Magazine

    This article first appeared in the July, 2003 issue of NASA Tech Briefs Magazine (Vol. 27 No. 7).

    Read more articles from the archives here.

    Overview

    The document presents a technical overview of a novel multilayer patch antenna developed at NASA's Jet Propulsion Laboratory (JPL). This antenna is designed to meet specific requirements for size, shape, and performance, particularly for applications that necessitate a half-power beamwidth of 40 degrees or less.

    The antenna features a unique configuration consisting of four layers of polytetrafluoroethylene (PTFE) dielectric substrate, which has a relative permittivity of 2.2, and two thick layers of foam with a lower dielectric constant (ε_r = 1.08). The overall footprint of the antenna is approximately two wavelengths by two wavelengths, with a total height of about one wavelength. A metallic wall surrounds the antenna, forming a cavity that enhances its performance. This design allows the antenna to achieve a gain of about 14 dB, significantly higher than the typical gain of 5-6 dB found in single patch antennas.

    The feeding mechanism employs proximity coupling via a microstrip feed line, which is etched on the upper side of the first dielectric layer. This method not only matches the high input impedance of the multilayer configuration but also contributes to a slight improvement in bandwidth. The driven patch element is located on the second dielectric layer, while additional parasitic patches are etched on the third and fourth layers, electromagnetically coupling to the driven element to enhance performance.

    One of the key advantages of this multilayer patch antenna is its ability to function without the need for a power-division network, unless circular polarization is required. This simplifies the design compared to traditional two-dimensional arrays. However, the footprint of this antenna is slightly larger than that of a horn or helical antenna, which are typically used for similar applications.

    The document emphasizes the novelty of the design, particularly the combination of the metallic wall and proximity coupling, which distinguishes it from prior art. The antenna's development addresses specific challenges in array applications, providing a solution that meets stringent performance criteria while maintaining a compact profile.

    Overall, this multilayer patch antenna represents a significant advancement in antenna technology, offering improved gain and efficiency for various aerospace applications.