Patent Application
20090058731
The subject matter described herein generally relates to patch antennas, and more particularly relates to an integrated dual band stacked patch antenna that is suitable for use with both global positioning system (GPS) signals and satellite digital audio radio service (SDARS) signals.
The prior art is replete with radio frequency (RF) and microwave antenna designs, structures, and configurations. Such antennas are utilized in many different applications to wirelessly transmit and receive signals that convey information or data. For example, modern automobiles (and other vehicles) might utilize a number of antennas that receive signals throughout the RF spectrum. Indeed, a vehicle may include one or more of the following systems: an AM/FM radio; a satellite radio; a GPS based navigation system; and a mobile telecommunication system. Some vehicles may include antennas to receive SDARS signals and/or GPS signals. In this context, L1 GPS signals are used for commercial navigation and mapping systems. By definition, SDARS signals that originate from satellites are left hand circularly polarized (LHCP) signals in the frequency band of 2.320 GHz to 2.345 GHz, and L1 GPS signals that originate from satellites are right hand circularly polarized (RHCP) signals in the frequency band of 1.57442 GHz to 1.57642 GHz. Some satellite radio systems also utilize terrestrial repeaters that transmit SDARS signals with vertical linear polarization (VLP) in the frequency band of 2.320 GHz to 2.345 GHz. These repeaters are employed to improve terrestrial signal reception by transmitting the SDARS signals at low elevation angles.
The traditional approach for achieving both GPS and SDARS reception in a vehicle is to place two individual patch antennas on the roof of the vehicle, where one antenna is devoted to the GPS band and the other antenna is devoted to the SDARS band. The distinct GPS antenna is individually designed for enhanced gain of RHCP signals in the GPS band, while the separate and distinct SDARS antenna is individually designed for enhanced gain of LHCP signals (and terrestrial VLP signals) in the SDARS band. Unfortunately, undesirable coupling often occurs between the two antennas when they are placed close to one another, which is often the case in vehicle installations that strive to achieve a streamlined and clean appearance. Such coupling degrades the overall performance of each antenna, particularly the VLP terrestrial gain in the SDARS frequency band (in addition, typical standalone SDARS patch antennas do not provide adequate VLP gain for reliable quality of service).
Two types of integrated GPS/SDARS patch antennas are described in United States Patent Application Publication No. 2006/0097924 A1. A first design employs a single layer structure with both radiating elements residing on the same dielectric layer. This first design may not provide a desirable amount of VLP gain for terrestrial SDARS signals. A second design employs a stacked structure having two feeds—one for the GPS signals and one for the SDARS signals. In addition, this second design uses a shorting pin connected between one radiating element and the ground plane. This second design has the disadvantage of having a relatively complex configuration, and the further disadvantage of requiring two distinct feed elements, which increases the complexity and cost of final assembly onto a vehicle.
A dual band patch antenna as described herein includes a stacked arrangement of two radiating elements separated by dielectric material. Both radiating elements share the same conductive feed, which may simplify the construction, reduces manufacturing cost, and reduces final assembly time. In one embodiment suitable for use in vehicular deployments, the dual band patch antenna can be configured and tuned to receive RHCP GPS signals simultaneously with LHCP SDARS signals. This particular dual band patch antenna is at the same time also configured and tuned to provide enhanced gain for terrestrial VLP SDARS signals.
The above and other features can be provided by an embodiment of a dual band patch antenna that includes: a first patch antenna arrangement configured to receive signals in a first frequency band; a second patch antenna arrangement coupled to, and stacked on, the first patch antenna arrangement, the second patch antenna arrangement being configured to receive signals in a second frequency band; and only one signal feed shared by both the first patch antenna arrangement and the second patch antenna arrangement.
The above and other features can also be provided by an embodiment of a dual band patch antenna that includes: a first antenna arrangement comprising a ground plane element, a first radiating element, and a first dielectric layer coupled between ground plane element and the first radiating element; a second antenna arrangement coupled to the first antenna arrangement, the second antenna arrangement comprising a second radiating element and a second dielectric layer coupled to the second radiating element, and the second antenna arrangement being coupled to the first antenna arrangement such that the first radiating element is located between the first dielectric layer and the second dielectric layer; and a signal feed shared by both the first antenna arrangement and the second antenna arrangement.
The above and other features can also be provided by an embodiment of a dual band patch antenna that includes: a ground plane element having a signal port formed therein; an upper radiating element; dielectric material between the ground plane element and the upper radiating element; a lower radiating element located within the dielectric material, the lower radiating element comprising an aperture formed therein; and only one signal feed for both the upper radiating element and the lower radiating element, the signal feed being connected to the upper radiating element, and the signal feed extending through the dielectric material, through the aperture without contacting the lower radiating element, and through the signal port without contacting the ground plane element. The lower radiating element, the dielectric material, and the ground plane element cooperate to receive signals in a first frequency band, while the upper radiating element, the dielectric material, and the ground plane element cooperate to receive signals in a second frequency band.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
One or more embodiments of the invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and
The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.
For the sake of brevity, conventional techniques and aspects related to GPS systems, SDARS systems, RF/microwave antenna design, and RF/microwave signal propagation may not be described in detail herein. In addition, those skilled in the art will appreciate that embodiments of the dual band patch antennas described herein may be practiced in conjunction with any number of applications and installations at any set of two or more frequency bands, and that the vehicular deployment described herein is merely one suitable example.
The following description refers to elements or nodes or features being “connected” or “coupled” together. As used herein, unless expressly stated otherwise, “connected” means that one element/node/feature is directly joined to (or directly communicates with) another element/node/feature, and not necessarily mechanically. Likewise, unless expressly stated otherwise, “coupled” means that one element/node/feature is directly or indirectly joined to (or directly or indirectly communicates with) another element/node/feature, and not necessarily mechanically.
A dual band patch antenna configured in the manner described herein can be used to receive signals in a first frequency band and to receive signals in a second frequency band. In practice, the antenna has a reciprocal operating nature, and the same antenna structure may be used both in receive mode and in transmit mode. In certain embodiments, the first frequency band and the second frequency band are non-overlapping, i.e., there are no shared frequencies in the two bands. The reception of the different signals may occur simultaneously, concurrently, or at different times. Although an antenna as described herein can be suitably configured and tuned to receive signals in any two frequency bands (within practical and economical limits), the following non-limiting examples relate to a vehicular implementation that is intended to support the L1 GPS band and the SDARS band, where the L1 GPS band is normally utilized for navigation messages, coarse-acquisition data, and encrypted precision code. More specifically, the antenna embodiments described herein are suitably configured to receive right hand circularly polarized L1 GPS signals in the 1.57442 GHz to 1.57642 GHz frequency band, to receive left hand circularly polarized SDARS signals in the 2.320 GHz to 2.345 GHz frequency band, and to receive vertical linear polarized SDARS signals in the 2.320 GHz to 2.345 GHz frequency band. This allows the antenna embodiments to be used with common satellite radio and GPS-based onboard navigation systems.
Again, the dual band capability of the embodiments described herein is not limited to GPS and SDARS frequency bands. Generally, such antenna embodiments can be configured and tuned to support any two bands, thus providing a compact, low cost, high performance, single feed, stacked patch antenna, regardless of polarization or gain pattern dependence.
In operation, the radiating element for the first (lower) patch antenna arrangement will have some effect on the performance of the second (upper) patch antenna arrangement and, analogously, the radiating element for the second (upper) patch antenna arrangement will have some impact on the performance of the first (lower) patch antenna arrangement. In practice, a complex RF coupling interaction takes place with antenna 100 to obtain the desired overall performance for both frequency bands of interest.
The illustrated embodiment of antenna 100 includes a ground plane element 102, a first dielectric layer 104 (obscured from view in
In practice, the first antenna arrangement may be fabricated by forming thin metal layers on the top and bottom exposed surfaces of dielectric layer 104. The thickness of the metal layers will depend upon the particular dielectric material, the type of metal used, the substrate fabrication technique, and desired performance characteristics. For example, the thickness of the metal layers in practical embodiments may within the range of about 8 to 35 micrometers. Thereafter, the metal layers can be selectively removed or patterned using well known techniques (such as masking, photolithography, and etching) to create the desired size, shape, and features of ground plane element 102, first radiating element 106, and aperture 120 (described below). Likewise, the second antenna arrangement may be fabricated by forming a thin metal layer on the top exposed surface of dielectric layer 108, followed by selective removal of the metal to create the desired size, shape, and features of second radiating element 110. The thickness of the metal layers for the second antenna arrangement will depend upon the particular dielectric material, the type of metal used, the substrate fabrication technique, and desired performance characteristics. For example, the thickness of the metal layers in practical embodiments may be within the range of about 8 to 35 micrometers.
In preferred embodiments, the same dielectric material is used to form both dielectric layers 104/108. In one exemplary embodiment, dielectric layers 104/108 are formed from a ceramic material such as alumina, and the metallization on dielectric layers 104/108 is formed from copper cladding, gold coated copper cladding, using commercial thin film processes, typically specified as 100-150 microinches, or the like. For such an embodiment, the antenna arrangements are suitably configured to cooperate with the dielectric constant (approximately nineteen in this particular embodiment) exhibited by the ceramic dielectric material. In another exemplary embodiment, dielectric layers 104/108 are formed from a dielectric material that is commonly used in printed circuit boards, such as FR-4 or other laminates, and the metallization on dielectric layers 104/108 is formed from copper, aluminum, or the like. The dielectric layers in such an embodiment can be formed from a class of materials including a composite polytetrafluoroethylene (PTFE) with glass or ceramic, and a composite hydrocarbon with ceramic (such as the TMM materials available from Rogers Corp.), with dielectric constants in the range of approximately 2.8 to 10.2. An embodiment that leverages printed circuit board techniques and technologies represents a relatively low cost alternative. For such an embodiment, the antenna arrangements are suitably configured to cooperate with the relatively low dielectric constant (approximately ten or less) exhibited by the laminate dielectric material. Of course, a dual band patch antenna as described herein can be realized using other dielectric materials and metallization materials.
Ground plane element 102 functions as the ground plane for both first radiating element 106 and second radiating element 110. In a typical vehicle installation, ground plane element 102 can be electrically coupled to a conductive sheet or component of the vehicle, such as the roof, a fender, or the trunk lid. In practice, ground plane element 102 may terminate at the boundary of dielectric layer 104 or it may extend beyond the boundary as depicted in
Signal port 114 enables the received GPS and SDARS signals to be propagated from dual band patch antenna 100 to the system or systems of interest. In this regard, signal port 114 may include, accommodate, or cooperate with a suitably configured connector 116 for signal feed 112. Connector 116 isolates signal feed 112 from ground plane element 102 using well known principles. Connector 116 may be, for example, a male or female SMA connector or any RF/microwave component. Antenna 100 may also include or be coupled to a system connection cable 118 via connector 116, where system connection cable 118 is configured to propagate signals having frequencies in either of the two bands supported by antenna 100. Notably, antenna 100 utilizes only one connector 116 and only one system connection cable 118 to propagate the dual band signals; this simplifies the installation of antenna 100 and reduces cost.
As shown in
Dual band patch antenna 100 utilizes only one signal feed 112, which is shared by both patch antenna arrangements. In other words, signal feed 112 is used for first radiating element 106 and for second radiating element 110. Signal feed 112 may be realized as a solid conductor, a conductive post or wire, a standard sized RF connector pin, or a conductive tube. Notably, signal feed 112 physically contacts only one of the two radiating elements; in the exemplary embodiment signal feed 112 is in electrical contact with second radiating element 110, and signal feed 112 has no direct physical contact with first radiating element 106. Here, signal feed 112 is connected to the lower surface of second radiating element 110, signal feed 112 extends through dielectric layers 104/108, and signal feed 112 extends through signal port 114.
To accommodate signal feed 112, first radiating element 106 includes an aperture 120 formed therein. Aperture 120 may be realized as a hole, a slot, or an opening formed in first radiating element 106, and aperture 120 is configured to receive signal feed 112 such that signal feed 112 does not contact first radiating element 106. During fabrication, a properly sized hole can be drilled through the dielectric material, either stopping at second radiating element 110 or through second radiating element 110. This drilled hole may or may not be plated with metal. Thereafter, signal feed 112 (which may be realized as a standard SMA pin) can be inserted into the hole into contact with second radiating element 110. After installation, signal feed 112 is preferably flush against the dielectric material although a slight gap may exist between the dielectric material and the outer surface of signal feed 112. In practice, signal feed 112 may be soldered or otherwise affixed to second radiating element 110.
Signal feed 112, the dielectric material, and aperture 120 cooperate to function as an aperture coupler for first radiating element 106. In other words, signal feed 112 is coupled to first radiating element 106 via aperture coupling, and absent any physical contact with first radiating element 106 itself. For the illustrated embodiment, the diameter of aperture 120 is influenced by the diameter of signal feed 112, the type of dielectric material, the output impedance of antenna 100, the desired amount of coupling, and the frequencies of the signals to be coupled. Thus, signals received by first radiating element 106 are aperture coupled to signal feed 112, while signals received by second radiating element 110 are directly coupled to signal feed 112. Accordingly, first radiating element 106, the dielectric material, signal feed 112, and ground plane element 102 cooperate to receive signals in the L1 GPS band, while second radiating element 110, the dielectric material, signal feed 112, and ground plane element 102 cooperate to receive signals in the SDARS band.
In practice, the aperture coupling mechanism is arranged to minimize sensitivity to manufacturing and assembly inconsistencies. In particular, large aperture diameters tend to be less sensitive to both the exact feed placement within the aperture and to variations in the dimensions of the feed.
Moreover, antenna 100 lacks any intervening interconnects or shorting pins between ground plane element 102, first radiating element 106, and second radiating element 110. As illustrated in
The actual size, shape, and arrangement of elements in dual band patch antenna 100 will vary depending upon the particular application, packaging constraints, desired materials, manufacturing considerations, and other practical influences. The embodiment described below with reference to
Referring to
Signal feed 112 may also be offset relative to second radiating element 110. In this regard, the central longitudinal axis of signal feed 112 is positioned about 3.7 mm from the right edges of first radiating element 106 and second radiating element 110. For this embodiment, aperture 120, which is formed in first radiating element 106 and is concentric with signal feed 112, has a radius of approximately 1.7 mm.
Given the physical dimensions of first radiating element 106 and second radiating element 110, the dielectric material for dielectric layers 104/108 is selected to obtain the appropriate center frequencies of operation. Conversely, given the dielectric constants of the materials chosen for dielectric layers 104/108, the physical dimensions could then be selected to obtain the appropriate center frequencies of operation. As mentioned previously, the same dielectric material may, but need not, be chosen for both dielectric layers 104/108. The physical dimensions described above are suitable for ceramic substrates where the dielectric constant for both dielectric layers 104/108 is 19.0. The selection of the same dielectric material is desirable to minimize material costs and to simplify the manufacturing process. This design also uses a particularly wide aperture coupler for the feeding mechanism for first radiating element 106 in an effort to minimize the sensitivity of the structure to feed pin placement. Of course, fine tuning of the various physical parameters (such as the corner truncation dimensions, overall size of the metallization areas, overall size of dielectric layers 104/108, the offset of radiation elements 106/110 relative to signal feed 112, and the dimensions of aperture 120) may be employed to achieve the desired performance for the designated frequency bands.
For the vehicular application described herein, the first patch antenna arrangement is configured to receive signals in a GPS frequency band (e.g., the L1 GPS frequency band of 1.57442 GHz to 1.57642 GHz), while the second patch antenna arrangement is configured to receive signals in the SDARS frequency band (i.e., the 2.320 GHz to 2.345 GHz band). As mentioned previously, the first patch antenna arrangement is suitably configured to receive RHCP signals (such as L1 GPS signals), while the second patch antenna arrangement is suitably configured to receive LHCP signals (such as SDARS signals that originate from satellites). Notably, the second patch antenna arrangement is also configured to effectively receive VLP SDARS signals in the 2.320 GHz to 2.345 GHz frequency band—such signals originate from terrestrial repeaters used by some satellite radio providers. The placement of the SDARS patch antenna arrangement above the GPS patch antenna arrangement results in improved low angle performance for SDARS signals. Moreover, the physical configuration of antenna 100 (e.g., the type and thickness of dielectric material, type and the thickness of the metallization layers) may be designed to increase or reduce the overall height of the SDARS patch antenna, according to the desired gain characteristics for terrestrial VLP SDARS signals.
A dual band stacked patch antenna having the dimensions and characteristics described above was validated using an electromagnetic modeling application. The simulations assumed an infinite ground plane. The return loss (S11) is depicted in
For comparison,
Antenna 300 employs a circuit board material having a relatively low dielectric constant (about 9.8), for example, TMM10i or alumina. These materials are relatively inexpensive and, therefore, antenna 300 represents a low-cost realization of a dual band stacked patch configuration. The overall dimensions of the first dielectric layer (35 mm by 35 mm, 4 mm thick) and second dielectric layer 306 (35 mm by 35 mm, 3 mm thick) are as described above for antenna 100. First radiating element 304 is formed as a 27 mm by 27 mm square with truncated opposing corners, and second radiating element 308 is formed as a 19 mm by 19 mm square with truncated opposing corners that correspond to the non-truncated corners of first radiating element 304. As mentioned above in connection with antenna 100, both radiating elements 304/308 are offset (off-axis) from signal feed 310. In contrast to antenna 100, first radiating element 304 does not “share” a side with second radiating element 308. As depicted in
Antenna 400 employs a circuit board material having an even lower dielectric constant (about 6.0), for example, TMM6 or other Duroid materials. The overall dimensions of the first dielectric layer (35 mm by 35 mm, 4 mm thick) and second dielectric layer 306 (35 mm by 35 mm, 3 mm thick) are as described above for antenna 100. First radiating element 404 is generally formed as a 33 mm by 33 mm square with truncated opposing corners. Notably, first radiating element 404 incorporates slits 412 in order to make the overall package more compact while benefiting from the very low dielectric constant (without slits 412, the dimensions of first radiating element 404 would extend beyond the 35 mm by 35 mm form factor boundary). Here, each slit 412 extends 9.0 mm inward from the outside edge of first radiating element 404, and each slit 412 is 1.0 mm wide. Moreover, a portion of each slit 412 extends beneath second radiating element 408 (as shown in the projected view of
Second radiating element 408 is formed as a 23 mm by 23 mm square with truncated opposing corners that correspond to the non-truncated corners of first radiating element 404. As depicted in
To summarize, embodiments of a dual band stacked patch antenna described herein are capable of simultaneously receiving both RHCP satellite signals within the L1 GPS frequency band and LHCP satellite signals within the SDARS frequency band. In addition, embodiments of the antenna described herein provide improved SDARS vertical linear polarization gain for terrestrial signal reception at low elevation angles as compared to current state of the art SDARS patch antennas. This improved VLP gain is achieved in part by placing an SDARS patch antenna element above a GPS patch antenna element, thereby raising the SDARS radiating element further above the ground plane, relative to conventional standalone SDARS patch antennas. Moreover, the compact, low profile, stacked patch design of the antenna reduces the overall size of the antenna module, which in turn decreases the rooftop surface area required to mount the antenna on a vehicle. Furthermore, the antenna employs a single feed that is utilized to propagate signals in both the GPS band and the SDARS band. This single feed approach reduces design complexity, manufacturing costs, cabling costs, and assembly time.
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.
