Patent Grant
6897809
The present invention is generally directed to an antenna for communicating electromagnetic signals, and relates more particularly to a planar array antenna having patch radiators disposed within a compact volume for increasing RF bandwidth and beamwidth.
Antenna designers are often forced to design antennas in a backward fashion. For example, because of the increasing public concern over aesthetics and the “environment” , antenna designers are typically required to build an antenna in accordance with a radome that has been approved by the general public, land owners, government organizations, or neighborhood associations that will reside in close proximity to the antenna. Radomes are typically enclosures that protect antennas from environmental conditions such as rain, sleet, snow, dirt, wind, etc. Requiring antenna designers to build an antenna to fit within a radome as opposed to designing or sizing a radome after an antenna is constructed creates many problems for antenna designers. Stated differently, the antenna designer must build an antenna with enhanced functionality within spatial limits that define an antenna volume within a radome. Such a requirement is counterproductive to antenna design since antenna designers recognize that the size of antennas are typically a function of their operating frequency. Therefore, antenna designers need to develop high performance antennas that must fit within volumes that cut against the ability to size antenna structures relative to their operating frequency.
Conventional antenna systems confined within predefined volumes, such as radomes, usually cannot provide for large beamwidths in addition to large bandwidths. In other words, the conventional art typically requires costly and bulky hardware in order to provide for a wide beamwidths and bandwidths, where beamwidth is measured from the half-power points (−3 dB to −3 dB) of a respective RF beam. Such bulky and costly hardware usually cannot fit within very small, predefined volumes.
Another drawback of the conventional art relates to the manufacturing of an antenna system and the potential for passive intermodulation (PIM) that can result because of the material used in conventional manufacturing techniques. More specifically, with conventional antenna systems, dissimilar materials, ferrous materials, metal-to-metal contacts, and deformed or soldered junctions are used in order to assemble a respective antenna system. Such manufacturing techniques can make an antenna system more susceptible to PIM and therefore, performance of a conventional antenna system can be substantially reduced.
Accordingly, there is a need in the art for a substantially compact antenna system that can fit within a predefined volume and that can generate relatively wide RF radiation patterns and increased RF bandwidth. Further, there is another need in the art for a compact antenna system that can be manufactured with ease and that can utilize manufacturing techniques which substantially reduce passive intermodulation. There is an additional need in the art for a substantially compact antenna system that can handle the power characteristics of conventional antenna systems without degrading the performance of the antenna system.
The present invention solves the aforementioned problems with an antenna system that can generate large and wide RF radiation fields in addition to providing increased bandwidth. This enhanced functionality can be achieved with a compact antenna system, where the antenna system without a radome can typically have a height of less than one seventh ({fraction (1/7)}) of a wavelength and a width that is less than or equal to six-tenths (0.6) of a wavelength. With an antenna radome, the antenna system can have a height that is less than or equal to one-fifth (⅕) of a wavelength. The antenna system can comprise one or more patch radiators separated from each other by an air dielectric and by relatively small spacer elements. The patch radiators can have predefined shapes for increasing beamwidths.
In one exemplary embodiment, the patch radiators can have a substantially rectangular shape. One or more lower patch radiators can be mounted to a printed circuit board that can comprise an RF feed network and a ground plane which defines a plurality of symmetrically, shaped slots. In one exemplary embodiment, the slots can comprise a “dog-bone” or “dumbell” shape that has an electrical path length that is less than or equal to a half wavelength.
The slots within the ground plane of the printed circuit board can be excited by stubs that are part of the feed network of the printed circuit board. The slots, in turn, can establish a transverse magnetic mode of RF radiation in a cavity which is disposed adjacent to the ground plane of the printed circuit board and a ground plane of the antenna system.
The cavity can be concentrically aligned with geometric centers of the patch radiators. The feed network of the printed circuit board can be aligned with portions of the cavity such that the portions of the cavity function as a heat sink for absorbing or receiving thermal energy produced by the feed network. Because of this efficient heat transfer function, the printed circuit board can comprise a relatively thin dielectric material that is typically inexpensive.
The cavity disposed between the printed circuit board and the ground plane of the antenna system can function electrically as a closed boundary when mechanically, the cavity has open corners. The open corner design facilitates ease in manufacturing the cavity. The open corners of the cavity can also have dimensions that permit resonance while substantially reducing Passive Intermodulation (PIM).
PIM can be further reduced by planar fasteners used to attach respective flanges and a planar center of a respective cavity to the ground plane of the printed circuit board and the ground plane of the antenna system. The planar fasteners can comprise a dielectric adhesive. In addition to the dielectric adhesive, the present invention can also employ other types of fasteners that reduce the use of dissimilar materials, ferrous materials, metal to metal contacts, deformed or soldered junctions and other similar materials in order to reduce PIM.
For example, the patch radiators can be spaced apart by plastic fasteners that permanently “snap” into place. Such fasteners not only reduce PIM, but also such fasteners substantially reduce labor and material costs associated with the manufacturing of the antenna system.
In one exemplary embodiment, a radome is placed over the patch radiators. Radomes are typically designed to be electrically transparent to the radiators of a antenna system. However, for the present invention, when a radome is placed over the patch radiators, an unexpected result occurs: the performance of the patch radiators is increased. More specifically, return loss is improved and peak gain is higher relative to an antenna without a radome. Further, upper side lobe suppression is improved compared to an antenna without a radome.
While providing a product that can be manufactured efficiently, the present invention also provides an efficient RF antenna system. The RF energy produced by the cavity, slots, and stubs can then be coupled to one or more patch radiators. The patch radiators can then resonate and propagate RF energy with relatively wide beamwidths and increased bandwidth.
The antenna of the present invention can solve the aforementioned problems and is useful for wireless communications applications, such as personal communication services (PCS) and cellular mobile radio telephone (CMR) service. The antenna system can include one or more patch radiators, a printed circuit board disposed adjacent to the one or more patch radiators, and plurality of slots disposed within a ground plane of the printed circuit board. The antenna further includes a cavity disposed adjacent to the ground plane of the printed circuit board and a second ground plane disposed adjacent to the cavity. The antenna system radiates RF energy with relatively wide beamwidth and bandwidth.
Turning now to the drawings, in which like reference numerals refer to like elements,
The antenna system 100, which can transmit and receive electromagnetic signals, includes radiating elements 110, 140, a ground plane 120, and a feed network 130. The antenna system 100 further includes a printed circuit board 150, and a port 160.
Referring now to
Referring now to
A second radiating element 140 is spaced from a first radiating element 110 by a spacing S1. Spacing S1 is typically a resonant dimension. That is, the parameter S1 size is typically a resonant dimension or a dimension that promotes resonance of the second radiating element 140. The second radiating element 140 in one exemplary embodiment can have a length L1 of 0.364 wavelengths and a width W1 of 0.144 wavelengths. However, the present invention is not limited to these values. Other resonant dimensions are not beyond the scope of the present invention. Further, the present invention is not limited to a plurality of radiating elements 110, 140. A single radiating element can be employed with out departing from the scope and spirit of the invention.
The first radiating antenna element 110 can be spaced from the printed circuit board 150 by a spacing parameter S2 which is also typically a resonant value. In other words, the parameter S2 is one that typically promotes resonance of the radiating patch element 110. In terms of wavelength, the parameter S2 is typically between 0.03 to 0.05 wavelengths (or 0.42 to 0.83 inches at the exemplary operating frequency range). The first radiating element 110 in one exemplary embodiment can have a length L2 of 0.364 wavelengths and a width W2 of 0.224 wavelengths. However, the present invention is not limited to these values. Other resonant dimensions are not beyond the scope of the present invention.
The second radiating element 140 is typically held in place relative to the first radiating element 110 by spacer elements/fasteners 500 which can comprise dielectric stand-offs. The first radiating element 110 is similarly positioned from the printed circuit board 150 by a plurality of spacers/fasteners 500. The spacers/fasteners 500 are typically designed to permanently “snap” into place in order to eliminate or reduce the use of soldering points of the present invention. This, in turn, also substantially reduces work in the manufacturing process of the Antenna System 100. Further, by using such spacers/fasteners passive intermodulation (PIM) can also be substantially reduced or eliminated. However, the present invention is not limited to “snap” type fasteners. Other fasteners or dielectric supports that can reduce PIM are not beyond the scope of the present invention. For example, slim or narrow blocks of dielectric foams could be used to support the radiating elements 110, 140.
As illustrated in
In one preferred exemplary embodiment, both the second radiating element 140 and first radiating element 110 are substantially rectangular in shape. The rectangular shape of the patches 140, 110 in combination with the apertures or slots 700 (as will be discussed below) and resonating cavity 200 increase bandwidth and beamwidth produced by the antenna system 100. However, the present invention is not limited to rectangular shaped patch elements. Other shapes include, but are not limited to, square, circular, and other similar shapes that maximize the beamwidth and bandwidth of a compact antenna system.
The present invention is also not limited to the number of radiating elements 110, 140 within a stacked arrangement or the number of stacked arrangements illustrated in the drawings. Additional or fewer radiating elements 110, 140 of stacked arrangements are not beyond the scope of the present invention. For example, more radiating elements 110, 140 could be employed in respective stacked arrangements in order to increase bandwidth.
By using portions of the resonating 200 cavity as a heat sink, a relatively thin printed circuit board 150 can be used. The cavity 200 can be fastened to the printed circuit board 150 (and more specifically, the ground plane 530 of the printed circuit board 150) by using a planar fastener 540 such as a dielectric adhesive. This planar fastener 540 can then reduce the thermal resistance between the feed network 130 and the flange 520.
The cavity 200 can also be attached to the ground plane 120 with a similar planar fastener 540 such as a dielectric adhesive discussed above. Using such fasteners not only reduces the thermal resistance between the feed network 130 and the cavity, it also substantially reduces passive intermodulation (PIM). With portions of the cavity 200 functioning as a heat sink for the feed network 130 exposed upon a printed circuit board 150, a relatively thin substrate of material can be used as the printed circuit board 150. The cavity 200 is attached to the ground plane 530 of the printed circuit board 150 with a planar fastener 540. Similarly, the cavity 200 is attached to the radome supporting ground plane 120 by a planar fastener 540.
The cavity 200 typically propagates a single transverse magnetic (TM01) mode of RF energy for the single polarization supported by the antenna system 100. Since cavity 200 resonates, the height or spacing S3 of the cavity has a resonant dimension of 0.027 wavelengths (or a dimension of 0.375 inches at the exemplary operating frequency). The length L3 and width W3 of the resonant cavity 200 each can have a resonant dimension of 0.433 wavelengths. However, the present invention is not limited to these values. Other resonant dimensions are not beyond the scope of the present invention. While propagating a transverse magnetic mode of RF energy, cavity 200 can also substantially increase the front to back ratio of the antenna system 100. The cavity 200 is excited by a slot 700 as will be discussed in further detail below.
Referring now to
Referring now to
Referring now to
In the exemplary embodiment illustrated in
When radome 800 is positioned over the radiating elements 110, 140, performance of the antenna system 100 is unexpectedly enhanced. In other words, while radomes are usually designed to be transparent and to have little or no effect on RF energy being generated or received by an antenna, radome 800 provides for some unexpected results for the present invention. More specifically, Table 1 illustrates some increased performance in peak gain, upper side lobe suppression, and in return loss when radome 800 is encloses the inventive antenna.
The printed circuit board 150 is a relatively thin sheet of dielectric material and can be one of many low-loss dielectric materials used for the purpose of radio circuitry. In one preferred and exemplary embodiment, the material used has a relative dielectric constant value of dk=3.38 (and ∈r=2.7 —when substrate is used as microstrip). In the preferred exemplary environment, TEFLON-based substrate materials are typically not used in order reduce cost. However, TEFLON-based substrate materials and other dielectric materials are not beyond the scope of the
Referring now to
Referring now to
Referring now to
For example, in addition to the open corners of the cavity 200, the present invention employs (as discussed above) planar fasteners 540 to attach the Flanges 520 of the cavity 200 to the ground plane 530 of the printed circuit board 120. Meanwhile, the base of the cavity 200 can be attached to the radome-supporting ground plane 120 by another dielectric planar fastener. Similarly, the first radiating element 110 is supported by non-soldered spacers/fasteners 500, and also supports additional spacers/fasteners 500 to support the second radiating element 140.
Referring now to
Step 1210 is the first step of the inventive process 1200 in which the antenna system 100 is assembled without metal-to-metal contacts and soldering. More specifically, in this step, the antenna system 100 can be manufactured in a way to substantially reduce passive intermodulation (PIM). Dissimilar materials, ferrous materials, metal-to-metal contacts, and deformed or soldered junctions are typically not employed or are limited in the antenna system 100 in order to substantially reduce or eliminate PIM. One way in which PIM is substantially reduced or eliminated is the use of dielectric planar fasteners 540 in order to connect portions of the cavity 200 to the slotted ground plane 530 and the ground plane 120. Another way in which PIM is reduced or substantially eliminated is by employing open corners in the cavity 200 where respective walls, such as walls 1000C and 1000D of
Next, in step 1220 RF energy is propagated along the feed network 130 of the printed circuit board 150. In step 1230, heat is dissipated from the feed network 130 into flanges 520 of the cavity 200.
In step 1240, the slots 700 are symmetrically shaped and sized such that each slot has an effective electrical length of less than or equal to a half wavelength. Such shape and size of the slots 700 promotes efficient RF coupling between the slots 700 and the stubs 710 and between the slots 700 and the resonant cavities 200.
In step 1250, the slots 700 disposed in ground plane 530 set up or establish a transverse magnetic (TM) mode of RF energy in the cavity 200. Next, in step 1260, the radiating elements such as the first and second patch radiators 110, 140 are excited with RF energy emitted from the slot 700 or the stubs 710 or both. Next, in step 1270, RF radiation is produced with increased RF beamwidth and bandwidth.
The present invention provides cavity-backed, aperture or slot coupled patch elements that produce RF energy with increased beamwidths and bandwidths. The present invention also provides a compact antenna system that has a height (without a radome) of less than one seventh ({fraction (1/7)}) of a wavelength and a width that is less than or equal to six-tenths (0.6) of a wavelength. With a radome, the height can be one-fifth (⅕) of a wavelength. While being compact, the present invention is power efficient. The present invention incorporates an efficient heat transfer design such that a feed network transfers its heat to a resonating cavity used to set up desired transverse magnetic modes of RF energy. The efficient heat transfer permits the present invention to utilize relatively thin dielectric materials for the printed circuit board supporting the feed network.
The present invention further incorporates a low PIM design approach by utilizing capacitive coupling of all potential metal-to-metal junctions through employing non-conductive planar fasteners and open corners for the resonant cavity 200. The low PIM design approach also yields efficient and low cost manufacturing methods. For example, the planar fasteners 540 eliminate any need for soldering the resonant cavity 200 to the ground plane 530. The use of dielectric spacers 500 further eliminates any need for costly dielectric spacer sheets while also reducing assembly time.
The radome 800 yields some unexpected results for the present invention. While designed to be electrically transparent to the radiating elements 110, 140, the radome 800 actually increases the performance of the antenna system 100.
Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Thus, although this invention has been described in exemplary form with a certain degree of particularity, it should be understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description.
This application is a continuation of U.S. application Ser. No. 09/785,032, filed Feb. 16, 2001, now U.S. Pat. No. 6,392,600, entitled, “Method and Shystem for Increasing RF Bandwidth and Beamwidth in a Compact Volume”, the entire contents of which are hereby incorporated by reference.
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| Number | Date | Country | |
|---|---|---|---|
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| Number | Date | Country | |
|---|---|---|---|
| Parent | 09785032 | Feb 2001 | US |
| Child | 10091186 | US |
