Radiating interrupted boundary slot antenna

Cavity backed slot antenna systems and methods are provided. The systems include a frequency selective surface, a housing containing a cavity, and a feed structure between at least portions of the frequency selective surface and the cavity. The frequency selective surface can be embedded in a non-conductive slot in a first ground plane. The cavity can contain a space filler. Embodiments of the present disclosure provide an antenna with a relatively wide bandwidth and a relatively small antenna element.

FIELD

The present disclosure provides systems and methods to broadband a cavity backed slot antenna.

BACKGROUND

The installation of antennas and antenna arrays in volume constrained platforms is a consistent and challenging problem for both commercial and military organizations. Applications requiring the use of conformal antennas (confined to the surface of an associated platform) are particularly demanding. Many attempts at solving this problem have been made with some success principally in the area of single antenna apertures. There has been little improvement, however, in the development of antenna elements that can be used both singularly and in arrays for these difficult situations.

In addition to needing to comply with physical space limitations, antennas are increasingly required to provide support over a wide range of frequencies. However, providing such broadband performance is challenging, particularly where space is limited. Moreover, in at least some antenna configurations there is a trade between the size of the antenna and the available bandwidth.

A cavity-backed slot antenna can provide an antenna having a size that is relatively small as compared to alternate designs, such as dipole antennas. Moreover, cavity-backed slot antennas can be mounted on or can form the surface of an associated structure, such as the surface of an aircraft or other vehicle. However, the bandwidth ratio of cavity-backed slot antennas is usually limited to no more than 3:1. In addition, conventional techniques for increasing the bandwidth of a cavity-backed slot antenna often require an increase in the volume of the antenna cavity.

SUMMARY

Embodiments of the present disclosure provide cavity backed slot antennas with broadband characteristics, and methods to broadband cavity backed slot antennas. Embodiments of the present disclosure can provide an antenna element design that is small enough to be used as an individual radiator or as one of many radiators in an array for conformal, volume constrained applications. The present disclosure enables a reduction in element size, allowing for elements to be placed at less than half-wavelength spacing at the highest frequency of operation while maintaining broad bandwidth. The broad bandwidth allows the use of fewer antennas to cover the full frequency range resulting in less volume use of the platform. The small element size for half-wavelength spacing allows the use of the element in an array without the unintended result of radiation in grating lobes (high gain levels in unintended directions due to large spacing between array apertures).

Typical cavity backed slot antennas have a bandwidth of ˜8-10% BW and typical methods of increasing this bandwidth may lead to a 3:1 bandwidth. Embodiments of the present disclosure allow bandwidths of 9:1 or greater while significantly reducing the size of the antenna element. For example, while a conventional cavity backed slot antenna has a cavity with a depth of a quarter λ, a cavity backed slot antenna element in accordance with embodiments of the present disclosure may have dimensions of, for example, 0.169λ×0.051λ×0.034λ at the lowest frequency.

An antenna in accordance with embodiments of the present disclosure can feature a distributed resistor, inductor, and capacitor (RLC) network that is placed directly into the antenna aperture or slot in the form of an integrated frequency selective surface (FSS). Moreover, the manner in which these FSS components have been integrated directly into the aperture allows the radiating portion of the aperture to scale over frequency, maintaining the shape of the radiation pattern over the full operating band, while avoiding distortions in the shape of the radiation pattern that can be caused by over-moding in a conventional configuration. Further improvements to the bandwidth of the antenna can be made with the application of frequency dependent magnetic materials over the aperture. Embodiments of the present disclosure provide an antenna element that can be used as a single antenna or in an array.

An antenna in accordance with further embodiments of the present disclosure can include a feed structure or element that extends across the slot. In accordance with at least some embodiments of the present disclosure, the feed element comprises a fan shaped structure. The fan shaped feed can include a first portion defined by sides that extend from a feed point at or adjacent a first side of the slot to a line at or adjacent a second side of the slot. Accordingly, all or a majority of the first portion of the feed overlies the slot. The fan shaped feed can additionally include a second portion defined at least in part by a curved edge that extends between the sides such that all or a majority of the second portion of the feed overlies a portion of a ground plane in which the slot is formed.

Additional features and advantages of embodiments of the disclosed systems and methods will become more readily apparent from the following description, particularly when taken together with the accompanying drawings.

DETAILED DESCRIPTION

Embodiments of the present disclosure are generally directed to an antenna that can be conformally mounted, and that provides a relatively high bandwidth.FIG. 1Aillustrates a partial cross section of an area of a vehicle or platform104that incorporates an antenna system108having a number of cavity backed slot antenna elements112in accordance with embodiments of the present disclosure disposed in an array116.FIG. 1Bdepicts the antenna system108ofFIG. 1Ain a plan view. As shown inFIG. 1A, the antenna system108can be conformally mounted, such that a portion of the vehicle104surface is formed by, or is immediately adjacent, a surface of the antenna system108. The cavity backed slot antenna elements112can be configured each have the same or different operating bandwidths. Although the example antenna system108illustrated inFIGS. 1A-Bis configured as an array116having a plurality of closely spaced cavity backed slot antenna elements112, embodiments of the present invention are not so limited. For example, an antenna system108in accordance with embodiments of the present disclosure can include a single cavity backed slot antenna element112. As yet another example, an antenna system108in accordance with embodiments of the present disclosure can include an array116in which the included cavity backed slot antenna elements112are located directly adjacent one another. For example, adjacent cavity backed slot antenna elements112can be separated by a distance of less than half the wavelength of the highest frequency of operation of either of the adjacent cavity backed slot antenna elements112. Moreover, an antenna system108in accordance with embodiments of the present disclosure can include an array in which the included cavity backed slot antenna elements112are disposed at the same or various angles, orientations, or positions relative to a reference line. For example, as shown inFIG. 1B, the individual cavity backed slot antennas112can be arranged such that they are each intersected by a line X-X′, and moreover can be at an angle greater than 0 and less than 90 degrees relative to the reference line X-X′.

FIG. 2illustrates a cavity backed slot antenna element112, and in particular depicts components that can be included in a broadband, cavity backed slot antenna element112in accordance with embodiments of the present disclosure in an exploded perspective view. The cavity backed slot antenna element112includes a first ground plane204having a planar conductive surface, with a non-conductive slot208formed therein. As can be appreciated by one of skill in the art after consideration of the present disclosure, the non-conductive slot208is defined by an aperture210formed in the first ground plane204. In accordance with an exemplary embodiment of the present disclosure, the first ground plane204is formed from a sheet of metal, such as aluminum or copper. As can be appreciated by one of skill in the art after consideration of the present disclosure, a first surface212of the first ground plane204may form an outside surface of the antenna element112. Moreover, where the antenna system108including the cavity backed slot antenna element112is mounted to a vehicle or platform104, the first surface212of the first ground plane can, for example, comprise a portion of a surface of that vehicle or platform104, or can be located directly underneath a surface of the vehicle or platform104.

An embedded frequency selective surface (FSS)216is contained within or adjacent the slot208. For example, the FSS216can coincide with a plane that also coincides with or that is parallel to a plane of the ground plane204. The FSS216of a cavity backed slot antenna element112in accordance with embodiments of the present disclosure provides capacitive, inductive, and/or resistive loading of the cavity256, increasing the effective depth of the cavity256. For example, the FSS216may comprise one or more components that extend from one or more edges of the slot208, in a plane corresponding to the plane of the first ground plane204. Moreover, the FSS216may comprise electrically conductive lines, such as metallic lines, that extend from one or more edges of the slot208. In certain embodiments the FSS216may include conductive, resistive, inductive, and/or capacitive components, thereby forming an RLC network. A second surface220of the first ground plane204, and features or components of the FSS216, may be supported by or connected to a first dielectric layer224. The first dielectric layer224can span the slot208. In addition, the first dielectric layer224can extend across all or portions of the second surface220of the first ground plane204. The first dielectric layer224may comprise, for example, a thin dielectric sheet comprising ceramic and Teflon based circuit board materials, or other dielectric materials.

The cavity backed slot antenna element112can also include a conductive feed structure or element228. The feed element228can be located between the first dielectric layer224and a second dielectric layer232. In accordance with at least some embodiments of the present disclosure, the feed element228includes a flared feed section236and a strip line feed240. The flared feed section236as shown is shaped as a fan, but may take on many other shapes in order to tailor the bandwidth and gain to specific applications. The feed element228can therefore be configured so that it contributes to the broad bandwidth of the cavity backed slot antenna element112. In accordance with alternate embodiments of the present disclosure, the feed element228comprises another configuration, such as a monopole. The strip line feed240portion of the feed element228can in turn be connected to transmit/receive components. The second dielectric layer232may be connected to the first dielectric layer224, at least in portions surrounding the feed element, using adhesive or fusion bonding. Alternatively, the second dielectric layer232may be formed from the same piece of material as is the first dielectric layer224, for example as a single piece of folded material encapsulating the flared feed236and at least portions of the strip line feed240.

In at least some embodiments, the cavity backed slot antenna element112can additionally include a second ground plane244. If provided, the second ground plane244is separated from the feed structure228by the second layer of dielectric material232. This second ground plane244can include a non-conductive slot or region248formed therein. In general, the location of the non-conductive region248is in an area corresponding to the cavity256, described in greater detail elsewhere herein. The second ground plane244can be formed from a sheet of conductive material, such as but not limited to aluminum or copper.

The cavity backed slot antenna element112additionally includes a housing252that is made of an electrically conductive material, and that has a cavity256formed therein. The cavity is sized according to the designed bandwidth of the cavity backed slot antenna element112. However, the unique loading of the cavity by the FSS216as described herein allows the cavity to be smaller than it would otherwise be for a given bandwidth. For example, the cavity256of a cavity backed slot antenna element112in accordance with embodiments of the present disclosure may be sized at 0.169λ×0.051λ×0.034λ, where λ, is the wavelength of the lowest operating frequency. The cavity256can contain a space filler260. Examples of a suitable space filler260include, but are not limited to, air, a dielectric, an absorber, a radar absorbing material (RAM), a metamaterial, an artificial magnetic conductor, or other materials. In addition, different space filler260materials having different properties can be disposed in different areas of the cavity256. The space filler260may be selected as a material or combination of materials that changes or affects the propagation of electromagnetic waves through the cavity256in a way that selectively loads the FSS216. More particularly, the composition of the space filler260can be selected depending upon the desired bandwidth and gain of the cavity256.

FIG. 3illustrates the cavity backed slot antenna element112in a plan view, and in particular depicts the relative locations of the non-conductive slot208formed in the first ground plane204, the FSS216located within or adjacent the non-conductive slot208, the flared feed section236and the strip line feed240of the feed structure element228, and the boundary of the slot248, which corresponds to or lies within the boundary of the cavity256, and the space filler260, in the plan view.

FIG. 4illustrates the cavity backed slot antenna element112in a side elevation, and in particular depicts the relative locations of the first ground plane204, first dielectric sheet224, feed structure element228, second dielectric sheet232, and housing252in an elevation view. Also, the cavity256formed within the housing252and the space filler260are depicted.

In accordance with at least some embodiments of the present disclosure, and as depicted inFIG. 5, the FSS216includes a plurality of elements504that include electrically conductive areas or lines508that are each connected to the first ground plane204by at least one of a resistive512, conductive516, or capacitive520component. The elements504can be configured to alternately extend from opposite sides of the slot208. Moreover, the elements504can be arranged in pairs of like types. In accordance with still other embodiments of the present disclosure, elements504comprising resistive512, conductive516, and/or capacitive520components can be arranged in any order.

As can be appreciated by one of skill in the art after consideration of the present disclosure, the values of the components512,516, and520, such as their resistance, inductance, or capacitance, and/or the configuration of the areas or lines508, can be selected, alone or in combination, to obtain a desired FSS216characteristic or set of characteristics. For example, the FSS216can be tuned to filter out higher order harmonics that might otherwise be present in the slot208. The one or more resistive512, conductive516, and/or capacitive520components can be formed by a printing process. In accordance with at least some embodiments of the present disclosure, the FSS216elements504may include an array of electrically conductive lines comprising a dipole array. Alternatively or in addition, the FSS216may include or be associated with a magnetic material, including by not limited to a frequency dependent magnetic material, that is also located in the slot208.

With reference now toFIG. 6, a portion of a slot208in a first ground plane204in relation to a feed structure or element228in accordance with embodiments of the present disclosure is illustrated in a top plan view. As shown, the feed element228generally includes a flared feed section236and a strip line feed240. The strip line feed240can extend towards the slot208, and can intersect with the flared feed section236along a line that is near an edge of the aperture210defining the slot208. For example, the intersection between the strip line feed240and the flared feed section236can be a distance that is less than one tenth of the distance D corresponding to the width of the slot208. Moreover, the intersection between the strip line feed240and the flared feed section236can overlay the slot208. The flared feed section236can be configured in the shape of a fan, with straight side portions604that extend away from each other with distance from the intersection of the flared feed section236and the strip line feed240, and with a curved or arched portion608connecting the ends of the side portions604opposite the intersection with the strip line feed240. In accordance with at least some embodiments of the present disclosure, the portion of the flared feed section236that includes the straight side portions604can overlay the slot208. In accordance with further embodiments of the present disclosure, the area of the flared feed section228defined by a line extending between the ends of the straight side portions604opposite their intersection with the strip line feed240and the curved portion608overlays a portion of the first ground plane204adjacent or near the slot208.

The feed element228generally operates to transfer radio frequency energy between the slot208and a transceiver (not shown) in transmit or receive modes of operation. In accordance with embodiments of the present disclosure, the sides604of the feed element228are angled relative to the adjacent edge of the slot208to create a tapered transition that promotes the transition of different, relatively high frequencies (i.e. frequencies with wavelengths that are shorter than the length of the slot) across the slot208. In accordance with further embodiments of the present disclosure, the portion of the flared feed section236that overlays a portion of the first ground plane204cooperates with the first ground plane204to form a parallel plate capacitor. The capacitance thus introduced by the flared feed section236assists in matching the impedance of the antenna element112at frequencies with wavelengths that are longer than the slot208, by cancelling the inductance presented to such frequencies by the slot208.

In the cavity backed slot antenna element112as disclosed herein, the FSS216allows for control of the illumination of the slot208aperture and prevents the antenna element112from over-moding at higher frequencies. The FSS216can also contribute to the match of the cavity backed slot antenna element112, improving the broadband gain, the return loss, and the voltage standing wave ratio, and providing a stable radiation pattern. These attributes are depicted inFIGS. 7-10. In particular,FIG. 7depicts the broadband gain of an example antenna element112in accordance with embodiments of the present invention,FIG. 8depicts the return loss of an example antenna element112in accordance with embodiments of the present disclosure,FIG. 9depicts the voltage standing wave ratio of an example antenna element112in accordance with embodiments of the present disclosure, andFIG. 10depicts the radiation pattern of an example antenna element112in accordance with embodiments of the present disclosure at different operating frequencies. From these figures, it can be appreciated that a cavity backed slot antenna element112as described herein can provide excellent performance over a surprisingly wide bandwidth. Moreover, although these examples are within a range of 2-18 GHz (providing a bandwidth ratio of 1:9), a cavity backed slot antenna element112in accordance with embodiments of the present disclosure can be scaled to cover other frequency ranges.

Accordingly, embodiments of the present disclosure provide a cavity backed slot antenna element112that features an FSS216disposed within the slot208. Moreover, embodiments of the disclosed cavity backed slot antenna element112provide the surprising result of a broadened effective bandwidth as compared to a conventional cavity type antenna. Moreover, such performance can be provided in a relatively compact format that can be mounted to a platform conformally.

A cavity backed slot antenna element112as described herein includes a cavity256that is electrically loaded by an FSS216. The result is an increase in the effective electrical depth of the cavity256, and a broadening of the operative bandwidth. In particular, the resulting bandwidth can extend from a frequency related to an expected operating frequency determined from the cavity configuration in the absence of the FSS, to a frequency related to an expected passband of the FSS, including any gaps between those frequencies. In addition, embodiments of the present disclosure can enable a reduction in the size of the antenna as compared to one employing conventional techniques. In particular, by increasing the effective electrical depth of the cavity256, a cavity backed slot antenna element112as described herein can have dimensions of 0.169λ×0.051λ×0.034λ, at the lowest operating frequency.

The present invention relates to a broadband cavity-backed slot antenna. The antenna includes a slot aperture with an integrated FSS (Frequency Selective Surface), a flared feed that can take on a multitude of shapes in different embodiments, and a cavity that can be filled with one or a combination of air, dielectric, absorber, and RAM (Radar Absorbing Material) depending upon the application requirements. Embodiments of antennas as disclosed herein may achieve a bandwidth of 9:1 in certain configurations, covering a range of 2-18 GHz for example, but may be scaled to operate in other frequency ranges as well.

The foregoing description has been presented for purposes of illustration and description. Further, the description is not intended to limit the disclosed systems and methods to the forms disclosed herein. Consequently, variations and modifications commensurate with the above teachings, within the skill or knowledge of the relevant art, are within the scope of the present disclosure. The embodiments described hereinabove are further intended to explain the best mode presently known of practicing the disclosed systems and methods, and to enable others skilled in the art to utilize the disclosed systems and methods in such or in other embodiments and with various modifications required by the particular application or use. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.