Patent Grant
7385555
Part of the work performed during development of this invention utilized U.S. Government funds. The U.S. Government has certain rights in this invention.
1. Field of the Invention
The present invention generally relates to microstrip patch antennas. More particularly, the present invention relates to deriving dual-band performance from micro-strip patch antennas.
2. Related Art
Micro-strip patch antennas are popular because of their compact size, light weight, and low cost to fabricate. Their low profile and their ability to conform to the shape of an aircraft fuselage make these microstrip antennas particularly attractive for airborne satellite communications and navigation systems. Additionally, micro-strip patch antennas can easily be constructed using printed circuit technology. However, a major limitation is their relatively narrow bandwidth capability.
Many patch antenna applications, such as navigational, vehicular, wireless communication systems, and radar systems, require dual-band, or wideband, operation. The narrow bandwidth capability of conventional micro-strip antennas, however, limits their use in these applications. Since patch antennas are so desirable, however, significant research and development has been devoted to adapting these antennas to dual-band operation.
A common technique to obtain dual-band operation from a conventional micro-strip antenna is known as stacking. Stacking entails simply piling micro-strip antennas or radiators, each operating at different frequencies, on top of each other. Stacking conserves space in a transverse or lateral direction. In a stacked patch design, the second frequency is achieved by the lower patch radiator. This lower patch is larger in size compared to the upper patch and is tuned to the lower of the two desired frequencies. Unfortunately, however, the performance of the lower patch is degraded by blockage from the upper patch and by any other patches in close proximity thereto. And the gain and beam width of the bottom patch antenna radiator is often degraded by stacking.
Stacking also increases the vertical height of the antenna, making it unattractive for low-profile and conformal applications. An additional complication of stacking is the need for bonding the top and bottom patch antennas together with glue or some other bonding agent. This bonding further increases the overall cost and complexity of building the antenna.
A second technique used to derive dual-band performance from a conventional micro-strip patch is to provide slots in the antenna. Although a variety of slotted micro-strip antennas have been designed, most are limited by their polarization characteristics, bandwidth, and/or gain. For example, most slotted dual-band patch antennas are either linearly polarized or have poor circular polarization performance at the desired dual frequency bands.
An exemplary environment in which micro-strip antennas can operate is that of satellite communications and satellite navigation. In satellite communications, for example, circular polarization is preferred over other types of polarization. Circular polarization, among other things, factors into account the movement of the satellite with respect to the Earth. Circular polarization also takes into account other anomalies, such as Faraday rotation and depolarization caused by precipitation particles such as rain and ice in the atmosphere.
Global positioning system (GPS) satellites, used in navigation for example, require circular polarization. In fact, optimizing the performance of GPS requires not only circular polarization, but requires that the corresponding circular polarization electromagnetic components, be relatively pure. Also, slots that are traditionally used to provide dual-band operation from conventional micro-strip antennas are generally designed as narrow-band filters.
GPS and other satellite communication systems, however, require much wider bandwidths for optimal performance. In fact current military GPS navigation systems require GPS antennas to operate in two separate frequency bands centered at 1575 and 1227 MHz in order to provide better precision accuracy in range by allowing correction for errors introduced by the ionosphere.
GPS navigation systems are also being modernized. To accommodate military M code signals, future GPS systems starting in 2005, will require at least 24 megahertz (MHz) bandwidth antennas. In addition a third frequency band called L5, operating at a center frequency of 1176 MHz will also be added to the current frequency bands, L1 (center frequency of 1575 MHz) and L2 (center frequency of 1227 MHz).
Civilian navigation systems, including the FAA, will rely mainly on the L1 and L5 frequency bands whereas U.S. military systems will rely primarily on L1 and L2 frequency bands, both of which will have an enhanced bandwidth of 24 MHz to also accommodate the new military M Code signals.
The operating bandwidths of conventional micro-strip patch antennas are much too narrow to satisfy these future GPS multiband frequency requirements and will place an additional emphasis on the need for newer microstrip antenna designs capable of providing dual band or even triple band operation with the desired bandwidth, gain and circular polarization characteristics to meet operational needs in both civilian and military GPS navigational systems.
Additionally, the European Union will also be launching in 2005 their own version of a GPS navigation system called “Galileo”. The Galileo frequencies are 1575 and 1176 MHz—which is the same as for the modernized U.S. GPS system as well as two new frequencies centered at 1207 MHz and 1279 MHz. Hence there will be strong commercial interest in developing broadband dual-band or even triple-band GPS antennas that cover all or some of both the U.S. GPS and the European Galileo navigation systems to be launched starting in 2005.
Some of the other slotted bandwidth enhancement designs restrict radio frequency (RF) current flow on the surface of the patch to narrow areas. This current restriction generally decreases the antenna gain at the second, or resonant, frequency achieved by inserting the slot. The radiation pattern at the resonant frequency is also asymmetric and distorted because of this uneven current flow. This asymmetry further decreases performance.
What is needed, therefore, is a compact and light-weight micro-strip patch antenna that is capable of operating in at least two different frequency bands. It is desirable that this dual-band patch antenna be circularly polarized and located on top of a single dielectric substrate layer or a plurality of dielectric substrate layers. It is also desirable that this patch antenna provide good gain over a large portion of the upper hemisphere to acquire signals from multiple satellites over a wide range of elevation angles.
What is also needed is a dual band co-planar antenna having a broad enough bandwidth to cover both the U.S. GPS and Galileo frequencies at 1176 and 1575 MHz as well as the additional Galileo frequency centered at 1207 MHz.
Consistent with the principles of the present invention as embodied and broadly described herein, the present invention includes an antenna assembly capable of dual-frequency band operation. The antenna assembly includes a conducting ground plane, a dielectric substrate layer mounted above the conducting ground plane, and a central patch radiator element mounted above the dielectric substrate layer and configured to radiate within a first frequency band. A number of probes (i) extend up through the conducting ground plane and the dielectric substrate and (ii) are physically connected to the central patch element. A parasitic ring is disposed in a concentric manner around the central patch element and reactively coupled thereto. The parasitic ring is configured to radiate within a second frequency band that is lower in frequency than attributed to the centrally located circular patch.
Further embodiments, features, and advantages of the present invention, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.
The accompanying drawings, which are incorporated in and constitute part of the specification, illustrate embodiments of the invention and, together with the general description given above and the detailed description of the embodiment given below, serve to explain the principles of the present invention. In the drawings:
The following detailed description of the present invention refers to the accompanying drawings that illustrate exemplary embodiments consistent with this invention. Other embodiments are possible, and modifications may be made to the embodiments within the spirit and scope of the invention. Therefore, the detailed description is not meant to limit the invention. Rather, the scope of the invention is defined by the appended claims.
It would be apparent to one of skill in the art that the present invention, as described below, may be implemented in many different embodiments of software, hardware, firmware, and/or the entities illustrated in the figures. Any actual software code with the specialized control of hardware to implement the present invention is not limiting of the present invention. Thus, the operational behavior of the present invention will be described with the understanding that modifications and variations of the embodiments are possible, given the level of detail presented herein.
Satellite communication and navigation technologists, in general, and the GPS community in particular, have been pushing towards more robust satellite navigation links. For example, the GPS community has been striving at increasing GPS receiver anti-jamming capabilities within real estate and cost constraints.
The ringed patch antenna technique of the present invention assists in achieving these more robust communications and satellite navigation links such as for the above mentioned GPS system. This achievement is due not only to the fact that the patch antenna is compact and inexpensive to produce, but also because it can operate in at least two GPS bands. For example, it can operate at 1.575 gigahertz (GHz) (e.g., band 1) and at 1.227 GHz (e.g., band 2). The ringed patch can replace the conventional double-layer stacked patch design currently used throughout the industry.
The ringed patch of the present invention, also offers significant performance advantages over the conventional stacked patch design, particularly at the lower frequency (band 1). In the conventional stacked patch design, as noted above, the lower frequency is achieved by the lower patch whose performance is degraded by blockage from the upper patch. The ringed patch approach of the present invention does not suffer from these limitations, as the two radiators are co-planar.
The exemplary ringed patch of the present invention does not use lumped elements or extra cost components. Instead, the present invention achieves dual-band capability by utilizing a simple parasitic passive ring radiator. This approach significantly increases production quality and reduces cost. The size of the ringed patch antenna of the present invention is also smaller than the conventional stacked patches. The small size allows extra space, for example, between elements in an antenna array within the same area.
Another potential use of the present invention is in wireless communications, where multi-band compact patches are desirable. For example, universal cellular phone handsets are highly desirable. These handsets have the capability of working in different frequency bands and operating systems in different areas. These different operating systems include time division multiplexing (TDM), global system for mobile communications (GSM), code division multiple access (CDMA) and universal mobile telecommunication system (UMTS). TDM, GSM, CDMA, UMTS, etc., are capable of operating domestically as well as internationally.
In the antenna array 200, each of the micro-strip elements 202-207 can be used as a single element within the multi-element array 200. Alternatively, each of the elements 202-207 can be used as a separate, independently radiating antenna. As known in the art, antenna beams produced by the array 200 can be steered by shifting their phase. For example, in the antenna array 200, beams constructively and/or destructively interfere with one another so as to steer a relatively broad combined beam, or individual beams, in a desired direction.
The dielectric substrate layer 302 has a relatively high dielectric constant. In some designs, the dielectric constant is as high 12.8 to 36, and is used to reduce the size of the microstrip antenna for airborne applications where space available for antenna deployment is generally very limited. The high dielectric constant also broadens the antenna beam allowing the antenna to receive signals from various satellites covering a wide range of elevation angles.
Next, the micro-strip element 202 includes a central patch radiator portion 304 positioned on or near a surface of the dielectric substrate 302. The central patch 304 comprises a radiating patch of any planar geometry (e.g., annular, square, elliptical, and rectangular) on one side of the dielectric substrate 302. The patch 302 can be constructed of any suitable conductive material, such as aluminum or copper.
The conducting ground plane is positioned on the other side of the dielectric substrate 302. The central patch 304 is fed by two orthogonal probes 308, excited with equal amplitudes but with a relative phase difference of 90 degrees to generate the desired type of circular polarization (CP). A parasitic ring radiation portion 306 surrounds the patch 304 and is fundamental to generating the second frequency band. An exemplary thickness of the central patch 304 can be, from about 1 to 2 mils.
As shown in
The present invention does not strictly require the use of two probes for exciting the central patch portion 304, as shown in
As noted above, the central patch 304 and the parasitic ring 306 are not limited to any particular shape. Additionally, the ground plane 300 in the dielectric substrate 302 can also include different shapes. In addition two different dielectric substrates, each with different dielectric constants can be used instead of a single dielectric layer 302. The use of two different dielectric layers instead of a single dielectric layer in 302 allows more design options such as varying the width of the antenna beam or controlling the bandwidth. The probes 308 are connected to coaxial cables 310, which extend through the dielectric substrate and the ground plane 300. The cables 310 connect the central patch portion 304 to a transmission line and/or radio (not shown).
The micro-strip element 202 provides a broad antenna beam serving an almost hemispherical coverage area. This enables the antenna to acquire signals from multiple satellites covering a wider range of elevation angles allowing better range position accuracy in GPS navigation systems. Further, the element 202 can be configured as a stand alone antenna (radiator), or can also be used as an element of a multi-element array, such as the array 102, shown in
In
As noted above, there is no direct metal connection between the central patch 304 and the parasitic ring 306. As such, the parasitic ring 306 is considered to be reactively coupled to the central patch 304. That is, only the central patch portion receives electrical excitation. The central patch portion 304 receives a signal via the orthogonal probes 308 by way of the coaxial connectors 310. When energized, electromagnetic currents generally flow evenly throughout the central patch portion 304.
Achieving acceptable antenna gain across each of the operational frequency bands is also a desirable characteristic of the micro-strip patch antenna 202 shown in
When the central patch 304 is energized via the probes 308, the currents that flow across the central patch 304 electromagnetically couple into the parasitic ring 306. The parasitic ring 306 thereby passively radiates (albeit at a different frequency) the energy that was directly fed into the central patch portion 304 via the probes 308.
The inventors have discovered through experimentation that the direct radiation of the central patch portion 304 and the passive radiation of the parasitic ring 306 both occur at relatively high gain levels and both naturally radiate circularly polarized signals. In the embodiment of
In the embodiment of
For example, if a distance (gap) between the central patch 304 and parasitic ring 306 is too small, the gain and other characteristics of the band 2 signal greatly diminish. Thus, it is desirable that the physical dimensions of the central patch 304 and parasitic ring 306 be carefully controlled and moderated. It is particularly desirable that the diameter of the parasitic ring 306, and its distance from the central patch 304, be carefully determined. These aspects of the present invention will be discussed in additional detail below.
The micro-strip patch element 400 includes a conducting ground plane 402 and a dielectric substrate layer 404. In
The first and second frequency bands produced by the central patch 406 and parasitic ring 408 are about 1.679 GHz and 1.365 GHz, respectively. Each of the first and second frequency band signals has a bandwidth of about 24 MHz. A gain of about 4.28 dB is achieved at the 1.679 GHz band. A gain of about 1.944 dB is achieved at the 1.365 GHz frequency band.
The micro-strip patch element 202 of
In the embodiments of
The micro-strip patch element 202 operates at the band 1 and the band 2 frequencies. The band 1 signal is produced by the central patch 304 and has a center frequency of about 1.575 GHz and an effective bandwidth of about 24 MHz. The band 2 signal is produced by the parasitic ring 306. The band 2 signal has a center frequency of about 1.227 GHz and a bandwidth of about 24 MHz. The physical dimensions discussed below facilitate the generation of these specific frequency characteristics. Additionally, a gain of about 3.274 dBic (Decibel-Isometric-Circular) for right hand circular polarization is achieved at the 1.575 GHz frequency band. A gain of about 1.897 dBic for right hand polarization is also achieved at the 1.227 GHz frequency band. Generally, for example, a patch diameter is inversely proportional to its frequency.
A length and height measurement 502 of the patch 202 is about 1.56 inches. Next, a diameter 504 of the central patch 304 is about 1.076 inches, while a diameter 506 of the parasitic ring 306 is about 1.232 inches. Exemplary widths of the ring 306 are within a range of about 0.9 to 1.3 inches. An exemplary distance 508, between the central patch 304 and the parasitic ring 306, is within a range of about 0.03 to 0.08 inches.
The diameter 506 and the distance 508 are a function of the diameter 504 of the central patch 304. That is, once the diameter 504 has been selected, based upon a desired band 1 frequency, the diameter 506 and the distance 508 must then be carefully selected. For example, if the distance 508 between the central patch 304 and the parasitic ring 306 is too large, or too small, the proper gain and frequency characteristics of the band 2 frequency cannot be achieved. The inventors empirically determined exemplary values for the diameters 506 and the distance 508, for a range of diameters 504. These empirical determinations were pursued to ensure that acceptable gain and center frequency characteristics can be achieved in any micro-strip patch antenna, based on user selected performance requirements.
As shown in
The present invention provides a micro-strip patch antenna which is capable operating in two different frequency bands. The antenna provides a broad beam serving a hemispherical coverage. The compact size light weight and low cost to fabrication of the micro-strip patch antenna of the present invention makes it particularly applicable to current navigation, vehicular, wireless communications, and radar systems that require dual frequency and/or wideband operation.
The present invention has been described above with the aid of functional building blocks illustrating the performance of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.
The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented, herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.
The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
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| Number | Date | Country | |
|---|---|---|---|
| 20060103576 A1 | May 2006 | US |
