Patent Application
20090051598
This invention generally relates to microstrip patch antennas and, more particularly, to a method for making such antennas substantially smaller with marginal compromise to overall performance by introducing a plurality of converging perturbations about the perimeter of the patch so that the flow of electromagnetic current progressing along the perimeter of the patch is perturbed and results in an effective electromagnetic diameter substantially greater than the actual physical diameter of the patch.
Microstrip patch antennas are increasing in popularity for use in wireless applications due to their low-profile, light weight and low volume configuration which can be easily made to conform to a host surface. Other principal advantages include low fabrication cost and support for both linear and circular polarization. A typical microstrip patch antenna is comprised of three components: a base conductor layer (the groundplane), a dielectric spacer (the substrate), and a signal conductor layer (the microstrip). The microstrip can be fashioned into any number of possible geometries called “the patch”, where round and rectangular geometries are the most typical. Due to the physical characteristics and performance, microstrip patch antennas are extremely compatible as embedded antennas in portable handheld wireless devices such as cellular phones, pagers, etc. . . .
Unfortunately, however, conventional microstrip patch antennas suffer from a number of disadvantages as compared to conventional antennas. Some of their major disadvantages include narrow bandwidth, low efficiency and low gain. Microstrip patch antennas radiate primarily because of the fringing fields between the patch edge and the ground plane. For good antenna performance, a thick dielectric substrate having a low dielectric constant is desirable since this provides better efficiency, larger bandwidth and better radiation. However, such a configuration leads to a larger antenna size. To design a compact microstrip patch antenna, higher dielectric constants must be used, which are costly, less efficient, result in narrower bandwidth. Illustratively, the operating frequency for a given patch is directly related to the physical size of the patch, and the relative electrical permittivity (ετ) of the substrate. The size of the patch for a given frequency is inversely proportional to the ετ of its substrate. As ετ increases, so do internal losses, which leads to narrow bandwidth and low efficiency. Concomitantly, the cost of substrates is proportional to ετ, imposing an economic penalty for employing this technique. Consequently, this technique of using materials with high dielectric constants has practical limits in terms of useful performance and affordability.
Another technique for reducing size entails dielectrically loading an antenna, in which a traditional conductive radiating patch is covered with or encased in a dielectric material that modifies the resonance characteristics of the patch. While dielectrically-loading an antenna by placing a dielectric superstrate material over the patch yields a smaller patch antenna, it suffers similar drawbacks, namely increased cost and substantial internal losses, which leads to narrow bandwidth and low efficiency.
The invention is directed to overcoming one or more of the problems and solving one or more of the needs as set forth above.
In one aspect of the invention, an exemplary microstrip patch antenna according to principles of the invention includes a base conductor layer, a dielectric spacer disposed on the base conductor layer; and a signal conductor layer disposed on the dielectric spacer. The signal conductor layer includes a microstrip patch with a central hub having a hub radius and a plurality of perturbations extending only radially from the central hub. The microstrip patch has a circular shape with a periphery and a patch radius. A plurality of perturbations each comprises a channel extending only radially from the central hub to the periphery of the microstrip patch. A coupling means such as a connecting element conductively coupling the base conductor layer to the patch, an aperture configured for electromagnetic field coupling of the base conductor layer to the patch, or configuration of the base conductor layer and patch for proximity coupling therebetween, may be utilized. The plurality of perturbations lengthens the effective radiating current path of the microstrip patch. The hub radius may be less than ½ of the patch radius, less than ¼ of the patch radius, or even infinitesimal so long as it provides adequate structural integrity. Each of the channels includes a pair of opposed radial edges and a hub edge. The pair of pair of opposed radial edges include a first radial edge and an opposed second radial edge. The hub edge is a circular arc-shaped edge of hub radius subtending a perturbation angle and having opposed first and second endpoints. The first radial edge extends radially from the first endpoint of the hub edge to the periphery of the circular patch and the second radial edge extends from the second endpoint of the hub edge to the periphery of the circular patch. The perturbation angle is less than 90 degrees, and may be no greater than 15 degrees.
In another aspect of the invention, patch shapes other than circular are utilized. The microstrip patch may include a conductor having a shape from the group consisting of circular, rectangular, polygonal, elliptical, oval, semicircular and deltoid, with a periphery and a patch radius. In this embodiment, the plurality of perturbations each comprises a channel extending radially from the central hub to the periphery. Each of the channels includes a pair of opposed radial edges and a hub edge. The pair of opposed radial edges include a first radial edge and an opposed second radial edge. The hub edge has the same geometric shape as the periphery, subtends a perturbation angle and has opposed first and second endpoints. The first radial edge extends radially from the first endpoint of the hub edge to the periphery and the second radial edge extends from the second endpoint of the hub edge to the periphery. The perturbations lengthen the effective radiating current path of the microstrip patch. The hub radius may be less than ½ of the patch radius, less than ¼ of the patch radius, or even infinitesimal so long as it provides adequate structural integrity. The perturbation angle is less than 90 degrees, and may be no greater than 15 degrees. The channels may be evenly spaced.
In yet another aspect of the invention, the plurality of perturbations comprises protrusions extending radially from the central hub to the periphery. Each of the protrusions has a pair of opposed radial edges and a peripheral edge. The pair of opposed radial edges include a first radial edge and an opposed second radial edge. The peripheral edge has the same geometric shape as the hub. The peripheral edge subtends a perturbation angle and has opposed first and second endpoints. The first radial edge extends radially from the first endpoint of the peripheral edge to the hub. The second radial edge extends from the second endpoint of the peripheral edge to the hub. The perturbations lengthen the effective radiating current path of the microstrip patch. The hub radius may be less than ½ of the patch radius, less than ¼ of the patch radius, or even infinitesimal so long as it provides adequate structural integrity. The perturbation angle is less than 90 degrees, and may be no greater than 15 degrees. The protrusions may be evenly spaced.
The perturbations lengthen the effective radiating current path of the patch. Thus, the effective size of the patch may be substantially reduced relative to a given frequency of operation. The perturbations also help decrease internal losses (Q) of the antenna and increase antenna impedance bandwidth. Thus, given a particular operating frequency or wavelength, a microstrip patch antenna according to principles of the invention may have a reduced size as compared to prior conventional microstrip patch antennas. Conversely, given a particular physical size of an antenna, a microstrip patch antenna according to principles of the invention can operate at a lower frequency (i.e., a longer wavelength) than prior conventional microstrip patch antennas. Furthermore, given a particular operating frequency or wavelength, a microstrip patch antenna according to principles of the invention has a larger impedance bandwidth than prior conventional microstrip patch antennas.
The foregoing and other aspects, objects, features and advantages of the invention will become better understood with reference to the following description, appended claims, and accompanying drawings, where:
Those skilled in the art will appreciate that the invention is not limited to the exemplary embodiments depicted in the figures or the shapes, relative sizes, proportions or materials shown in the figures.
Referring to
The exemplary microstrip patch antenna 100 may be fed by a variety of devices now known or hereafter developed. Such devices can be classified into two categories-contacting and non-contacting. In a contacting scheme, a connecting element, such as a microstrip line or coaxial connector 120 (as shown in
The patch 115 may be comprised of conducting material (e.g., copper or gold) used in conventional microstrip patch antennas, features a unique geometric configuration as described more fully below. The patch 115 may be photo etched on the dielectric spacer (the substrate) 110 using conventional processing techniques for patch antenna manufacturing.
A patch 115 according to principles of the invention may be any solid geometry. While circular 115 and square 400 patches are conceptually illustrated in
Referring now to
Notably, the perturbations 200 extend only radially. Thus, all perturbations have edges that can be traced through the center of the patch. No perturbations extend inwardly or outwardly in a non-radial manner.
The perturbations 200 serve several purposes. First, the perturbations 200 lengthen the effective radiating current path of the patch 115. Thus, the effective size of the patch may be reduced relative to a given frequency of operation. It is estimated that a reduction in patch size of approximately 25% to 75% can be achieved. A second benefit of the slots is a decrease in internal losses (Q) of the antenna and an attendant increase in antenna impedance bandwidth. Thus, given a particular operating frequency or wavelength, a microstrip patch antenna 100 according to principles of the invention has a reduced size as compared to prior conventional microstrip patch antennas. Conversely, given a particular physical size of an antenna, a microstrip patch antenna 100 according to principles of the invention can operate at a lower frequency (i.e., a longer wavelength) than prior conventional microstrip patch antennas. Furthermore, given a particular operating frequency or wavelength, a microstrip patch antenna 100 according to principles of the invention has a larger impedance bandwidth than prior conventional microstrip patch antennas.
As will be readily apparent to those skilled in the art, other features such as cross-polarization or circular or elliptical polarization can be obtained with a microstrip patch antenna 100 according to principles of the invention by applying conventional techniques known in the prior art.
The geometry of an exemplary perturbation 200 according to principles of the invention is shown in
While the hub radius R2 may be any length that is less than patch radius R1, a relatively short hub radius R2 is preferred. Advantageously, the shorter the hub radius R2, the greater the increase in the effective radiating current path of the patch. In a preferred embodiment, the distance R2 is less than ½ of R1. In a particular preferred embodiment the distance R2 is less than ¼ of R1. Indeed, the hub radius may be infinitesimal (i.e., immeasurably small), as long as structural integrity of the patch is maintained.
A patch according to the principles of the invention is not limited to a particular size. In a preferred embodiment, the patch radius R1 may be dimensioned approximately one-eighth (⅛) to one-half the wavelength at a frequency of interest (i.e., the free-space wavelength, λ). A patch 115 according to the invention can be smaller than its conventional Euclidean counterpart (e.g., circular without perturbations) while providing at least as much or nearly as much gain and frequencies of resonance, a low Q and resultant good bandwidth. Additionally, the patch is very thin such that t<<λ (where t is the patch thickness). The height h of the dielectric substrate may be approximately 0.003λ≦h≦0.05λ.
Referring now to
The geometry of an exemplary perturbation 405 for an exemplary rectangular patch 400 according to principles of the invention is shown in
The hub edge 420 may be any distance d2 from the center 430 of the patch 400, up to approximately the periphery 425 of the patch 400. However, a relatively short distance d2 is preferred. Advantageously, the closer the edge 420 is to the center of the patch 400, the greater the increase in the effective radiating current path of the patch 400. In a preferred embodiment, the distance d2 is less than ½ of d1. In a particular preferred embodiment the distance d2 is less than ¼ of d1. Indeed, this distance d2 may be infinitesimal (i.e., immeasurably small), as long as structural integrity of the patch 400 is maintained.
A rectangular patch 400 according to the principles of the invention is not limited to a particular size. In a preferred embodiment, the base of the patch Bp may be dimensioned approximately one-eighth (⅛) to one wavelength, λ, at a frequency of interest. The width Wp of the patch 400, may be the same as the base Bp, or another dimension approximately one-eighth (⅛) to one wavelength, λ, at a frequency of interest. A rectangular patch 400 according to the invention can be smaller than its conventional Euclidean counterpart (e.g., circular without perturbations) while providing at least as much or nearly as much gain and frequencies of resonance, a low Q and resultant good bandwidth.
Advantageously, the present invention allows for the use of traditional, economical substrates and does not require a superstrate to achieve a size reduction. A patch with perturbations according to principles of the invention results in a microstrip antenna that is compact, yet has the benefits and performance of a conventional patch antenna. The plurality of perturbations about the perimeter of the patch perturbs the flow of electromagnetic current progressing along the perimeter of the patch. These perturbations result in an effective electromagnetic diameter substantially greater than the actual physical diameter of the patch. These perturbations, used in conjunction with an additional set of perturbations employed for the purpose of generating a signal that is circularly-polarized, can result in a microstrip antenna that has electrical performance (e.g., gain, axial ratio and return loss bandwidth) equivalent to a microstrip antenna constructed by traditional methods nearly twice its size.
Referring now to
The perturbations 605 serve several purposes. First, the perturbations 605 lengthen the effective radiating current path of the patch 600. Thus, the effective size of the patch may be reduced relative to a given frequency of operation. It is estimated that a reduction in patch size of approximately 25% to 75% can be achieved. A second benefit of the slots is a decrease in internal losses (Q) of the antenna and an attendant increase in antenna impedance bandwidth. Thus, given a particular operating frequency or wavelength, a microstrip patch antenna 635 according to principles of the invention has a reduced size as compared to prior conventional microstrip patch antennas. Conversely, given a particular physical size of an antenna, a microstrip patch antenna 635 according to principles of the invention can operate at a lower frequency (i.e., a longer wavelength) than prior conventional microstrip patch antennas. Furthermore, given a particular operating frequency or wavelength, a microstrip patch antenna 635 according to principles of the invention has a larger impedance bandwidth than prior conventional microstrip patch antennas.
As will be readily apparent to those skilled in the art, other features such as cross-polarization or circular or elliptical polarization can be obtained with a microstrip patch antenna 635 according to principles of the invention by applying conventional techniques known in the prior art.
The patch 600 has a circular hub 625 of radius R1. A plurality of perturbations 605 extend radially from the hub 625. A pair of opposed radial edges 610, 615 and a perturbation edge 620 define the exemplary perturbation 605. An exemplary perturbation 605 resembles a radially extending spoke. The perturbation edge 620 is a circular arc-shaped edge of hub radius R1, subtending a central perturbation angle θ and having opposed first and second endpoints. The perturbation angle θ may range from infinitesimal to approximately 90 degrees, although an angle of approximately 2 to 15 degrees is preferred. A first radial edge 610 extends radially from the first endpoint of the perturbation edge 620 to the periphery of the circular hub 625. A second radial edge 615 extends from the second endpoint of the perturbation edge 620 to the periphery of the circular hub 625. The opposed radial edges 615, 620 of each perturbation can be imaginarily extended linearly through the center of the hub 625.
While the hub radius R2 may be any length that is less than radius R1, a relatively short hub radius R2 is preferred. Advantageously, the shorter the hub radius R2, the greater the increase in the effective radiating current path of the patch. In a preferred embodiment, the distance R2 is less than ½ of R1. In a particular preferred embodiment the distance R2 is less than ¼ of R1. Indeed, the hub radius R2 may be infinitesimal (i.e., immeasurably small), as long as structural integrity of the patch is maintained.
A patch according to the principles of the invention is not limited to a particular size. In a preferred embodiment, the patch radius R1 may be dimensioned approximately one-eighth (⅛) to one-half the wavelength at a frequency of interest (i.e., the free-space wavelength, λ). A patch 600 according to the invention can be smaller than its conventional Euclidean counterpart (e.g., circular without perturbations) while providing at least as much or nearly as much gain and frequencies of resonance, a low Q and resultant good bandwidth. Additionally, the patch is very thin such that t<<λ (where t is the patch thickness). The height h of the dielectric substrate may be approximately 0.003λ≦h≦0.05λ.
Advantageously, various patch and perturbation geometries and configurations may be applied to introduce multiple resonances as well as input impedance matching. A multiple mode antenna (i.e., an antenna which can resonate at different frequencies to allow a communication device to operate in multiple bands) is highly desirable. Those skilled in the art will appreciate that perturbations can be configured to meander currents and create multiple resonances, providing a multiple band antenna that can be tuned to multiple resonant frequencies. A central principle of the present invention is that different perturbations of an antenna according to principles of the invention are resonant at different frequencies. It will be appreciated by one skilled in the art that a variety of different patterns for the metal strips could be selected in order to achieve the desired resonances. At some frequencies, certain perturbations may cause resonance, while at other frequencies other perturbations may cause resonance. Thus, an antenna structure according to principles of the invention as a whole may exhibit a plurality of resonant frequencies that is simply not possible to achieve with a conventional microstrip antenna.
Referring now to
Notably, the perturbations 700, 705 extend only radially. Thus, all perturbations have edges that can be traced through the center of the patch. No perturbations extend inwardly or outwardly in a non-radial manner.
Also notably, the exemplary perturbations are arranged as matching opposed pairs. Thus, opposed perturbations are equally dimensioned in the exemplary embodiment of
The perturbations 700, 705 serve several purposes. First, the perturbations 700, 705 lengthen the effective radiating current path of the patch 115. Thus, the effective size of the patch may be reduced relative to a given frequency of operation. It is estimated that a reduction in patch size of approximately 25% to 75% can be achieved. A second benefit of the slots is a decrease in internal losses (Q) of the antenna and an attendant increase in antenna impedance bandwidth. Thus, given a particular operating frequency or wavelength, a microstrip patch antenna 100 according to principles of the invention has a reduced size as compared to prior conventional microstrip patch antennas. Conversely, given a particular physical size of an antenna, a microstrip patch antenna 100 according to principles of the invention can operate at a lower frequency (i.e., a longer wavelength) than prior conventional microstrip patch antennas. Furthermore, given a particular operating frequency or wavelength, a microstrip patch antenna 100 according to principles of the invention has a larger impedance bandwidth than prior conventional microstrip patch antennas.
Advantageously, circular polarization can be achieved with a microstrip patch antenna 100 having unevenly sized slot-like perturbations according to principles of the invention. Thus, the tip of an electric field vector, at a fixed point in space, describes a circle as time progresses. The electric field vector, at one point in time, describes a helix along the direction of wave propagation. The magnitude of the electric field vector is constant.
With reference to
Notably, the perturbations 805, 810 extend only radially. Thus, all perturbations have edges that can be traced through the center of the patch. No perturbations extend inwardly or outwardly in a non-radial manner.
Also notably, the exemplary perturbations are arranged as matching opposed pairs. Thus, opposed perturbations are equally dimensioned in the exemplary embodiment of
Furthermore, the frequency of perturbations (i.e., the number of perturbations per unit of circumference of the patch 800, is modulated (i.e., varied). By way of example and not limitation, the first and third quadrants between the 12 o'clock and 3 o'clock position and between the 6 o'clock and 9 o'clock positions, respectively, each feature nine perturbations. The second and fourth quadrants between the 3 o'clock and 6 o'clock position and between the 9 o'clock and 12 o'clock positions, respectively, each feature twenty-one perturbations.
The perturbations 805, 810 serve several purposes. First, the perturbations 805, 810 lengthen the effective radiating current path of the patch 800. Thus, the effective size of the patch may be reduced relative to a given frequency of operation. It is estimated that a reduction in patch size of approximately 25% to 75% can be achieved. A second benefit of the slots is a decrease in internal losses (Q) of the antenna and an attendant increase in antenna impedance bandwidth. Thus, given a particular operating frequency or wavelength, a microstrip patch antenna according to principles of the invention has a reduced size as compared to prior conventional microstrip patch antennas. Conversely, given a particular physical size of an antenna, a microstrip patch antenna according to principles of the invention can operate at a lower frequency (i.e., a longer wavelength) than prior conventional microstrip patch antennas. Furthermore, given a particular operating frequency or wavelength, a microstrip patch antenna according to principles of the invention has a larger impedance bandwidth than prior conventional microstrip patch antennas.
Advantageously, circular polarization with a degree of cross polarization rejection (i.e., a bias towards circular polarization) can be achieved with a microstrip patch antenna having unevenly spaced amplitude modulated slot-like perturbations according to principles of the invention. Concomitantly, bandwidth, the range of frequencies over which the microstrip patch antenna is effective, is increased. Adjusting the frequency of the perturbations 905, 910 adjusts the inductance.
With reference now to
Notably, the perturbations 905, 910 extend only radially. Thus, all perturbations have edges that can be traced through the center of the patch. No perturbations extend inwardly or outwardly in a non-radial manner.
Also notably, the exemplary perturbations are arranged as matching opposed pairs. Thus, opposed perturbations are equally dimensioned in the exemplary embodiment of
The perturbations 905, 910 serve several purposes. First, the perturbations 905, 910 lengthen the effective radiating current path of the patch 900. Thus, the effective size of the patch may be reduced relative to a given frequency of operation. It is estimated that a reduction in patch size of approximately 25% to 75% can be achieved. A second benefit of the slots is a decrease in internal losses (Q) of the antenna and an attendant increase in antenna impedance bandwidth. Thus, given a particular operating frequency or wavelength, a microstrip patch antenna according to principles of the invention has a reduced size as compared to prior conventional microstrip patch antennas. Conversely, given a particular physical size of an antenna, a microstrip patch antenna according to principles of the invention can operate at a lower frequency (i.e., a longer wavelength) than prior conventional microstrip patch antennas. Furthermore, given a particular operating frequency or wavelength, a microstrip patch antenna according to principles of the invention has a larger impedance bandwidth than prior conventional microstrip patch antennas.
Advantageously, circular polarization with a degree of cross polarization rejection (i.e., a bias towards circular polarization) can be achieved with a microstrip patch antenna having amplitude modulated slot-like perturbations according to principles of the invention. Concomitantly, bandwidth, the range of frequencies over which the microstrip patch antenna is effective, is increased. Adjusting the amplitude of the perturbations 905, 910 adjusts the capacitance.
While an exemplary embodiment of the invention has been described, it should be apparent that modifications and variations thereto are possible, all of which fall within the true spirit and scope of the invention. With respect to the above description then, it is to be realized that the optimum relationships for the components and steps of the invention, including variations in order, form, content, function and manner of operation, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention. The above description and drawings are illustrative of modifications that can be made without departing from the present invention, the scope of which is to be limited only by the following claims. Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents are intended to fall within the scope of the invention as claimed.
