Low-loss dual polarized antenna for satcom and polarimetric weather radar

The present invention is a low-loss polarized antenna for satellite communications and polarimetric weather radar. The antenna may comprise: (a) a microstrip patch antenna, (b) a waveguide, and (c) a coupling interface between the antenna and waveguide. The microstrip patch antennas may individually comprise: (i) a patch radiator having a defined area, and (ii) an associated microstrip.In a further embodiment of the invention, an antenna array is presented. The antenna array may comprise: (a) a plurality of microstrip antennas, and (b) a plurality of waveguides. The antenna array may further comprise: (c) a waveguide combiner. The microstrip patch antennas may individually comprise: (i) a patch radiator having a defined area, and (ii) an associated microstrip.In still a further embodiment of the invention, a method for the manufacturing of an antenna is presented. The method may comprise the step: (a) operably coupling a microstrip patch antenna to a waveguide.

FIELD OF THE INVENTION

This invention relates generally to the transmission and reception of radio frequency signals and, more particularly to a low-profile, low-loss antenna apparatus.

BACKGROUND OF THE INVENTION

In many telecommunications applications, microstrip antennas are employed. There are several types of microstrip antennas (also known as printed antennas), the most common of which is the microstrip patch antenna. A microstrip patch antenna is a narrowband, wide-beam antenna fabricated by etching an antenna element pattern in metal trace bonded to an insulating substrate. Because such antennas may be low profile, mechanically rugged and conformable, they are often employed on aircraft and spacecraft, or are incorporated into mobile radio communications devices.

Microstrip antennas are also relatively inexpensive to manufacture and design because of the simple 2-dimensional physical geometry. An advantage inherent to patch antennas is the ability to either transmit or receive (i.e. transceive) electromagnetic signals having polarization diversity. Patch antennas can easily be designed to have Vertical, Horizontal, Right Hand Circular (RHCP) or Left Hand Circular (LHCP) Polarizations with a single antenna feedpoint. This unique property allows patch antennas to be used in many types of communications links that may have varied requirements.

Another potential improvement for modern communications devices is the incorporation of waveguide architectures. Waveguides represent an effective mechanism for conveying signals with very little degradation or loss. Waveguides are commonly used in microwave communications, broadcasting, and radar installations. A waveguide consists of a rectangular or cylindrical metal tube or pipe. The electromagnetic field propagates lengthwise.

To function properly, a waveguide must have a certain minimum cross-sectional dimensions relative to the wavelength of the desired signal. If the waveguide is too narrow or the frequency is too low (i.e. the wavelength is too long), the electromagnetic fields cannot propagate. At any frequency above the cutoff (the lowest frequency at which the waveguide is large enough), the feed line will work well, although certain operating characteristics vary depending on the number of wavelengths in the cross section.

Mobility is a prime concern in the design of modern communications systems. Users are more likely than ever to require information in a variety of locales, thereby necessitating efficient mechanisms for ensuring the integrity of communicated data while minimizing the physical dimensions of individual communication system devices. Airborne TV antenna systems present a unique design challenge. Such antennas must be light weight, inexpensive, and capable of receiving dual circular-polarization (CP) radio frequency (RF) signals. Additionally, in order to be tail-mount compatible with medium size aircraft, the antennas must be able to fit in a package on the order of a 9″ swept volume.

Additionally, many current weather radars, including NEXRAD, transmit and receive radio waves with a single, horizontal polarization. However, the next generation of functionality in radar systems, such as polarimetric radar, may require a dual linear-polarization (LP) aperture.

As such it would be desirable to provide a low cost, light weight, high efficiency radiating antenna architecture capable of dual CP operation in an aircraft tail-mount compatible footprint or dual LP operation in weather radar.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a low-loss, dual polarized antenna. In general, the invention applies to systems where a microstrip patch antenna is combined with a waveguide for the transmission or reception of electromagnetic signals.

In an embodiment of the invention, a low-loss, dual polarized antenna is presented. The antenna may comprise: (a) a microstrip patch antenna, (b) a waveguide, and (c) a coupling interface between the antenna and waveguide. The microstrip patch antennas in the array may individually comprise: (i) a patch radiator having a defined area, and (ii) an associated microstrip. The configuration of the microstrip may dictate the polarity and phase of the signal that is either transmitted or received by the microstrip patch antenna. The polarity may be dual linearly-polarized or dual circularly polarized.

In a further embodiment of the invention, an antenna array is presented. The antenna array may comprise: (a) a plurality of microstrip antennas, and (b) a plurality of waveguides. The antenna array may further comprise: (c) a waveguide combiner.

In still a further embodiment of the invention, a method for the manufacturing of an antenna is presented. The method may comprise the step: (a) operably coupling a microstrip patch antenna to a waveguide.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, a cross-sectional representation of a microstrip patch antenna100in accordance with an embodiment of the present invention is presented. The antenna comprises a microstrip patch antenna101and a waveguide102disposed substantially adjacent the microstrip patch antenna. The microstrip patch antenna is comprised of a patch element103, a stripline104, a first dielectric layer105, a second dielectric layer106, a third dielectric layer107, a first ground plane108, a second ground plane109, and coupling mechanisms for transferring signals between the patch element103and stripline104and between the stripline104and waveguide102.

The patch element103can be a relatively thin sheet of metal or other material having metallic properties capable of emitting or receiving electromagnetic signals. The patch element103is disposed on a first side of the first dielectric layer105.

The first ground plane108is disposed on the second side of the first dielectric layer105. The second dielectric layer106and third dielectric layer107are disposed between the first ground plane108and the second ground plane109.

The stripline104is disposed between the second dielectric layer106and third dielectric layer107. The stripline104may be configured so that the antenna receives or emits polarized electromagnetic signals, as will be further discussed.

The waveguide102is used as a low-loss conduit between the microstrip patch antenna and an external device capable of generating and/or processing electromagnetic signals (not pictured). The waveguide102may comprise a substantially rectangular raised ridge110disposed along the length of the waveguide.

Referring toFIG. 2, an axonometric representation200of a microstrip patch antenna and waveguide in accordance with an embodiment of the present invention is presented. A patch element201is disposed on a first surface of a first dielectric layer202and a stripline203is disposed between a second dielectric layer204and a third dielectric layer205. The respective couplings between a waveguide206and stripline203, and stripline203and patch element201can be accomplished in any number of standard ways. In the depicted embodiment, a first open-space slot207is disposed in a first ground plate208presenting a conduit between the patch element201and the stripline203. A second open-space slot209is disposed in a second ground plate210presenting a conduit between the stripline203and the waveguide206. In further embodiments, the respective couplings between the waveguide206and stripline203, and stripline203and patch element201may be selected from the group comprising: probe coupling, proximity coupling, or edge feeding.

The microstrip patch antenna may also comprise a plurality of circuit board vias211disposed within the second dielectric layer204and the third dielectric layer205and linking the first ground plate208and the second ground plate210. The board vias may comprise generally cylindrical holes through the second dielectric layer204and third dielectric layer205which are plated with a conducting material. The circuit board vias serve to extinguish “parallel plate” modes within the stripline structure. The vias tie the ground layers207and208together and so as to extinguish potential differences to exist across them. The stripline is thus permitted to act as the conductor while the top and bottom layers are at “ground” potential.

Referring toFIG. 3, an antenna array comprising a plurality of microstrip patch antennas300in accordance with an embodiment of the present invention is presented. The plurality of microstrip patch antennas300may be arranged in a rectangular or other close-packed geometric pattern. The striplines301of each of the plurality of microstrip patch antennas300may be individually configured for vertical, horizontal, dual linear or circular polarity in a transceived signal. In the presently depicted embodiment, antenna sub-arrays302configured for vertical polarity and antenna sub-arrays303configured for horizontal polarity are combined to form an array so as to jointly result in dual linear polarity. In a further embodiment, the sub arrays302and303may comprise 90°-hybrid microstrip patch antennas, such as those commonly found in the art, so as to result in circular polarity. The antenna array may be operably connected to a plurality of waveguides (not pictured) via any number of methods including chemical adhesion, solder, mechanical clamps, rivets or screws. In the depicted embodiment, board-compression screw holes304are provided.

Referring toFIG. 4, a plurality of waveguides400in accordance with the present invention is presented. A waveguide401may comprise a linear structure having a substantially hollow rectangular cross-section and being disposed substantially adjacent to a microstrip sub-array such as that ofFIG. 3. The waveguide may be manufactured from any number of electromagnetically conductive materials including brass, copper, silver, aluminum, or any other metal that has low bulk resistivity.

The waveguide401may also comprise a ridge402disposed along the center length of the individual waveguides so as to compress the lateral dimensions of a signal and ensure very low signal degradation or loss. The waveguide design dimensions are a function of the designated frequencies of operation. The significant dimension is the width of the ridge waveguide. In a particular embodiment of the invention, adjacent ridged waveguides401feed opposite polarizations (i.e. horizontal and vertical). As such, the effective spacing402for each waveguide (and thus microstrip each patch antenna sub-array) is twice the waveguide width. In order to maintain high operating performance and avoid grating lobes, the spacing must be less than a free-space wavelength. Regular non-ridged waveguides may not support array spacing this small. As such, a ridge waveguide may be used.

Each waveguide may further comprise a coupling mechanism providing a conduit for signal transfer from the waveguide401to a waveguide combiner (not pictured). The coupling mechanism may be may be selected from slot coupling probe coupling, proximity coupling, or edge feeding. In the presently depicted embodiment, a slot couple403is utilized.

The waveguide may be operably connected to the waveguide combiner via any number of methods including chemical adhesion, solder, mechanical clamps, rivets or screws. In the depicted embodiment, board-compression screw holes404are provided.

The waveguide may be operably connected to a microstrip patch antenna array (not pictured) via any number of methods including chemical adhesion, solder, mechanical clamps, rivets or screws. In the depicted embodiment, board-compression screw holes405are provided.

Referring toFIG. 5, an axonometric view of a waveguide500in accordance with the present invention is presented. The waveguide500may comprise a ridge501disposed along the center length of the waveguide so as to compress the lateral dimensions of a signal and ensure very low signal degradation or loss. In a particular embodiment, the waveguide500and ridge501may have dimensions such that the waveguide structure is capable of transceiving direct broadcast satellite (DBS) signals such as DirecTV™. Such DBS signals are on the order of 12.2-12.7 GHz. In a further embodiment, the waveguide500and ridge501may have dimensions such that it is capable of transceiving polarimetric radar signals. Such polarimetric radar signals are on the order of 9.3-9.4 GHz. In still a further embodiment, the waveguide may have a height503of from 2.8 mm to 19.0 mm and a width504of from 5.7 mm to 38.1 mm. In still a further embodiment, the waveguide may have a height503of 12.5 mm and a width504of 25.0 mm.

In still a further embodiment, the waveguide ridge501may have a height505of from 1.75 mm to 11.9 mm and a width506of from 2.28 to 15.24 mm. In still a further embodiment, the waveguide ridge may have a height505of 7.8 mm and a width506of 10.0 mm.

The waveguide may be operably connected to a microstrip patch antenna array via any number of methods including chemical adhesion, solder, mechanical clamps, rivets or screws. In the depicted embodiment, board-compression screw holes507are provided.

Referring toFIG. 6, a waveguide combiner600in accordance with the present invention is presented. The combiner is capable of receiving multiple instances of a common signal from a series of inputs and combining them to increase the overall signal strength. The combiner600may comprise a plurality of inputs601which are combined to sum to a single output602. The inputs may comprise a coupling mechanism for the transfer of signals from a plurality of waveguides. The coupling mechanism may be may be selected from slot coupling, probe coupling, proximity coupling, or edge feeding. In the presently depicted embodiment, a slot couple601is presented.

The waveguide combiner600may be operably connected to a plurality of waveguides (not pictured) via any number of methods including chemical adhesion, solder, mechanical clamps, rivets or screws. In the depicted embodiment, board-compression screw holes603are provided.