Patent Application
20140035792
The invention relates generally to radio-frequency (RF) electromagnetic signal communication antennas. More particularly, the invention relates to directional antenna radiators and associated signal distribution apparatus for low- to medium-power transmitting and transceiver functions. Even more particularly, the invention relates to directional antenna radiators and associated signal distribution apparatus for low- to medium-power transmitting and transceiver functions, wherein the radiators and associated signal distribution apparatus are configurable to support single or dual feed and linear or circular (elliptical to any chosen extent) polarization.
A number of concepts are not present in the prior art and may enhance performance, increase reliability, lower material and/or labor costs, etc., each of which can be separately beneficial, particularly in high-volume and cost-sensitive applications.
Panel antenna beam characteristics such as dip angle (i.e., elevation compared to perpendicular to an integral ground plane) and beam height (typically gain-related) have nominal values based on antenna design. The prior art includes typical inputs and outputs that terminate in small-diameter, polymer-filled, and thus relatively lossy coaxial lines. Such prior art embodiments would not be readily adaptable to lower-loss signal distribution technologies such as stripline, microstrip, air-filled coax, etc., nor to structural methods not relying on circuit board techniques, with strength depending on lossy reinforced polymer construction. The arrangements described may have other drawbacks, as well, so that what is needed in the art is a technology capable of higher efficiency than existing practice.
The foregoing needs are met, to a great extent, by the invention, wherein in one aspect an apparatus is provided that in some embodiments is a multi-radiator panel antenna that has at least one row of discrete dual-feed crossed-dipole hybrid-coupled radiators fed by a plurality of microstrip-based power dividers, with the microstrip technology extending continuously from at least one coaxial input connector to a plurality of terminations that couple to the individual radiators. The same core design may be adapted to use for transmitting, receiving, and combined (transceiver) applications in a variety of frequency regimes, with dimensions, materials, manufacturing processes, coatings, etc., modified as required for use in each such application.
In accordance with one embodiment of the invention, an antenna panel using microstrip feed is disclosed. The panel includes a generally-vertical ground plane having a planar first face orthogonal to a principal direction of radiation of the antenna panel, and a plurality of radiators positioned in a uniform array, each radiator having four coplanar, bilaterally symmetrical, electrically closed conductive loops arranged with four-fold rotational symmetry about an axis parallel to the principal direction of radiation, each loop being supported by a support tab and being configured to function as a monopole radiator, the plane of the loops being generally parallel to the first face of the ground plane, and spaced away therefrom by a distance approximating a quarter wavelength of a frequency within an intended operational band.
The antenna panel further includes a first microstrip branch feed array, having a plurality of terminal nodes, the first array being so configured as to present a selected portion of a signal applied to an input port of the first array at each respective terminal node of the first array, and a first plurality of microstrip crossover strips, each being so configured as to extend away from the ground plane in the principal direction of radiation, each further being so configured as to couple a first portion of signal to a first loop within the radiator, to extend beyond the first loop and diagonally across a radiator, to extend back toward the ground plane, to couple a second portion of signal to a second loop orthogonal to the first loop, and to terminate in a stub.
In accordance with another embodiment of the invention, a method of directing an electromagnetic signal beam is disclosed. The method includes configuring at least one interface port to couple an electromagnetic signal for at least one of transmitting and receiving, defining a conductive ground plane having sufficient length to so function for a plurality of radiators arranged generally uniformly in a straight line along the ground plane, the radiators using crossed loop-shaped dipoles carried by support straps and electromagnetically coupled from monopole to monopole by hybrid coupler forms, the individual crossed-dipole radiators being spaced apart by a distance corresponding to a wavelength of a signal within the bandwidth of the radiators, and providing branch feed distribution of a signal between the interface port and the plurality of defined radiator locations using signal conduction between a repeatedly split and step-impedance-adjusted asymmetric microstrip-style signal transport medium and a proximal one of a plurality of walls of a chamber extending at least along the length of the straight line of the ground plane.
The method further includes coupling the signal to the radiators using extended conductors fastened to terminal nodes of the transport medium, where each extended conductor includes a face that extends the surface of one of the respective microstrips that is oriented toward the proximal chamber wall, each extended conductor passing out of the chamber through a pass aperture therein, traversing a distance parallel to a first support tab with a selected spacing, crossing over to the opposite monopole, traversing a distance parallel to a second support tab with a selected spacing, and terminating as a stub.
There have thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention which will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be used as a basis for the designing of other structures, methods, and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
The invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. An embodiment in accordance with the present invention provides a multiple-radiator antenna that realizes beam forming according to a selected performance standard, and that provides signal distribution within the antenna using air-dielectric microstrip technology effectively to the exclusion of other transmission line technologies. In some embodiments, such an antenna can combine exceptionally low losses with inexpensive components, ease of manufacture, and desirable levels of reliability over a useful range of ordinary climate environments.
The invention may include a conductive enclosure 22 that can be a unitary metallic extrusion, for example, with the outer face on which the radiators 20 are mounted functioning as a ground plane 24 for the array of radiators 20. Other constructions are contemplated as well. If the radiators 20 are configured with integral conducting mounting structures 26, also discussed in greater detail below, the loop elements 28 of the radiators 20 can be economically spaced at roughly one quarter wavelength (H,
The conductive enclosure 22 style shown in
The spacing from each face or edge of a microstrip to the proximal chamber wall according to the instant disclosure may be consistently less than spacing suggested by traditional stripline and microstrip analysis. These smaller and in some cases irregular distances may make classical pencil-and-paper analysis non-obvious, but where ray tracing can be applied to modeling using robust software and relatively fast computers, a revised and simplified set of rules may allow initial estimates to be refined quickly with modest dimensional adjustments. These rules include the following.
First provide an application that allows a high-stiffness structure achievable by a single extrusion or welded equivalent, a set of interlocking extrusions, a welded equivalent, or the like. A plausible material may be any of a range of extrusion-compatible aluminum alloys, although a stiffer rolled alloy or other metals may be used in some applications. Some uses of the invention may call for yet other materials.
Next employ microstrip conductors, likewise made from a stiff alloy, such as rolled, cut, and formed aluminum. These may be held in place by spacers that cooperate with conductor stiffness that may make the electrical structure largely dimensionally invariant except for temperature-induced expansion, caused largely by environmental factors but including a power-dissipation component. Performance analysis by simulation may be made more rigorous by including a wide range of temperatures for each component.
Next fabricate the radiators from aluminum-clad cast zinc alloy, punched and folded aluminum alloy, or another material and fabrication process achieving similar performance. Raw zinc alloy has relatively high skin-effect penetration at the likely frequencies for antennas of the designs considered here, so that a nickel preparative coating and aluminum plating may beneficially decrease losses and provide more uniform operation. Other construction concepts may likewise realize the high performance, reliability, and low cost of those indicated.
The inventive concepts presented herein may relate to electronic systems over a broad range of frequencies, but application to microwave and near-microwave art (traditionally with a free-space wavelength shorter than 1 meter, corresponding to frequencies higher than 300 MHz) may be of particular interest as well. Frequencies of interest for typical applications may include at least cellular telephone bands, such as the GSM 900 MHz band and the 1710 MHz-2170 MHz band, as well as the reclaimed high-UHF television frequencies around 700 MHz-800 MHz, the low cellular bands around 450 MHz, satellite communications bands, etc. The concept as taught herein may be scalable over a wide range, so that significantly higher and lower frequencies than these may likewise be considered, with radiator and backplane adjusted in size to realize performance levels comparable to those already simulated and prototype tested. It is to be understood that lower frequencies do not bar use of the concepts except insofar as manufacturing costs for the very large components needed for lower frequencies may become greater, and that limitations at higher frequencies relate to dimensions of components with respect to voltage withstand at power levels high enough to be useful. At frequencies significantly higher than present cellular telephone ranges, related art currently uses circuit-board methods and materials in building numerically large two-dimensional arrays of low-power components. While miniaturization may make manufacturing of low-loss air-dielectric antennas more difficult, it is anticipated that there may be considerable overlap between the various antenna arts.
In some embodiments, a user may elect that all power levels, signal phase values, and impedances to be found at the respective radiators be identical to one another. Assuming ideal radiators, this may provide a beam perpendicular to the ground plane 24, with each radiator 20 emitting a so-called skull pattern, and with the patterns, as detected at far field, effectively superimposed. Net antenna gain at each azimuth in such embodiments can be approximated by multiplying the (voltage) gain of a single radiator by the number of radiators. To the extent that the radiators 20 themselves are not ideal, a beam so formed may exhibit so-called “squint,” i.e., may have a beam not concentric with the radiator's axis of rotational symmetry 66. The superposition of the beams may likewise be non-ideal, reducing far-field gain from nominal. Although squint is not further addressed in the presentation that follows, existence of such artifacts may be assumed, modeled, tested, and compensated for in practice.
At least in non-orthogonal embodiments, phasing and impedance may have fixed values, and power levels may be made unequal according to a plan that causes the beam to be non-uniform in elevation and directed (tilted) below the horizon toward which the array 10 is directed (this applies to terrestrial broadcasting; for aircraft communication and applications that call for different patterns, other power distribution plans may be developed using similar approaches). Similarly, assigning different phasing to each radiator 20 according to some plans may allow a tilt comparable to that of a varied-power embodiment. For either of these, beam shape may be symmetric about a nominal elevation angle to a greater or lesser extent. Altering the third variable above, i.e., assigning different impedances to different power distribution output ports may be also feasible, although requiring corresponding (non-uniform) input port impedances to the radiators 20 to limit return losses. In addition to the above realizations of beam direction, an entire panel array 10 can be tilted to direct a uniform (perpendicular to the ground plane 24) beam. These methods may be combined, although not all can interoperate equally well in shaping gain (transmitted signal strength, received signal sensitivity) over an area.
Continuing with
As shown in
The embodiment shown may use corporate (also termed branch) feed, with the input signal being split repeatedly and each radiator preferably receiving a portion of the signal energy on the same cycle of the waveform, within a phase range determined by spacing of splits, size of impedance steps, etc. In some microstrip embodiments, other feed methods may be used, such as traveling wave (TW) feed, wherein a single pair of feed lines (in a dual-input embodiment) may traverse all radiators in succession, with a portion of the signal energy in the feed lines coupled to the dipoles of each radiator. With judiciously selected dimensions for power coupling and signal phasing, TW couplers can tap off substantially all of the input power before reaching a terminal load, and the timing and strength of each output can be set according to a selected scheme. It is to be understood that in the particular case of TW feed, each successive radiator may receive its input one cycle later than the radiator next closer to the source, a phenomenon having negligible deleterious effect for many applications. Extending this concept, half-wave, double-wave, and other spacings of radiators and feed lines can produce comparable results if considerations peculiar to each such spacing, such as grating lobes, may be accommodated.
Branch feed lines may be readily analyzed and simulated using commercial stripline and microstrip analysis software. The same analysis and simulation software can include flat tabs and input feeds found in terminal portions of circuits used in embodiments of the invention. A microstrip 12 branch feed power tee divider 96, 98, 100 may be placed asymmetrically in a chamber 34 that may be effectively grounded on all walls 50, 56, 60, 64. That is, a first face 46 of the microstrip 12 is positioned proximal to a first wall 50 of the chamber 34 at a roughly uniform first face distance, a first edge 58 of the microstrip 12 may be continuous and may be positioned at a roughly continuous first edge distance from a second chamber wall 60, a second face 52 of the microstrip 12 may be positioned at a roughly uniform second face distance from a third chamber wall 56, and the second edge 62 of the microstrip 12 may be stepped as required for impedance transformation and consequently may be positioned with nonuniform spacing with respect to the fourth chamber wall 64. The microstrip 12 may not be spaced five times its width from the second and fourth chamber walls 60, 64 as dictated by conventional practice in the microstrip and stripline art, so computer modeling of the interaction of the surfaces may be advisable. Similarly, the spacing between the first microstrip face 46 and the first chamber wall 50 may be sufficiently closer than the spacing between the second microstrip face 52 and the third chamber wall 56 that the term microstrip may be appropriate with respect to at least the first face 46, with a much larger part of the transmission line energy found in the waveguide-like region located between the first face 46 and the first wall 50 than in the region between the second face 52 and the third wall 56.
The chamber 34 in some embodiments may be arranged with a partition that incompletely splits it along its longitudinal axis into at least two longitudinal sub-chambers. The power divider in such embodiments may be located in part on each side of the partition, with one or more links across the partition between parts of the divider. This arrangement may beneficially serve to provide sufficient microstrip-to-wall surface for dividing the signal power effectively while keeping artifacts such as crosstalk and PIM at low levels. Other embodiments may use a single chamber, may include transverse instead of longitudinal partitions, may have partitions extending entirely across the chamber with feed lines coupling signal power through the partitions at required locations, etc.
Consistent with chamber profile and space constraints, the microstrip 12 may be formed and folded in such a way that a first portion 110 may be proximal to a wall—in the embodiment in the drawings, the third wall 56 of
In many embodiments incorporating the inventive apparatus, microstrip 12 positioning may require standoff fittings 114, 116, 118 to maintain a substantially fixed spacing between the surfaces of the microstrip 12 and the chamber walls, as well as controlled positioning of the feed tabs with respect to the loop radiator support strips, discussed below. Such standoff fittings 114, 116, 118 can be implemented in a variety of shapes, as shown in
Other stabilization styles may also be successfully applied, such as metallic-conductor quarter-wave standoffs. While somewhat more frequency-sensitive than fittings using dielectric insulators, shorted stubs can perform filtering and phase adjusting functions as well as providing mechanical stability.
Returning to
To the extent that disassembly for repair may be impractical for some configurations of antenna panels incorporating aspects of the inventive concepts disclosed herein, permanent fixing of standoffs and/or the power divider microstrips to the inside of the chambers may be preferred in some embodiments. Examples of attachment provisions (permanent or otherwise) may include adhesives that bond standoffs to housing/chamber walls, metallurgical bonding of standoffs to chamber walls, etc. Metallurgical bonding methods may include providing dielectric standoffs to which joining plates may be affixed, then providing joining ports through the extrusion and soldering or brazing the plates into place; spot welding the plates, etc. Conductive standoffs may be fixed similarly. Adhesives may be applied to standoff surfaces prior to assembly in order to permit attachment may afterward be activated chemically, mechanically, thermally, by scintillating or other radiation, or by other means. Such attachment processes may be reversible in some embodiments. Where welding or similar joining methods may be used, modeling and simulation may consider possible reflection, reradiation, PIM, etc., by added or deformed conductive materials.
Some approaches—i.e., arrays of relatively low-power radiators driven generally in parallel to form high-gain directional beams—may employ either a separate feed line from a power divider to each radiator input node or a TW equivalent. Largely with a view to economy. A small diameter polymer-dielectric coaxial cable may interconnect the divider and the radiating elements. Such cable can have drawbacks. For example, solid or foamed polymer dielectric used in coaxial cables, twin lead cables, striplines, and microstrips consistently introduces higher losses than equivalent conductor arrangements using air dielectric. Also, for a given construction and material choice, coax losses generally increase as diameter decreases.
Coax effectively may serve as its own high-uniformity shield, so that it contains signal energy more effectively than microstrip and stripline. All things being equal, dielectric-filled coax may have lower loss (and higher propagation velocity) than comparable stripline, with similar microstrip somewhat more lossy than stripline. For air-filled equivalents, attenuation may be significantly lower and velocity may be appreciably higher, which introduces a tradeoff. Using stripline or microstrip, despite its possible lossy signal transmission, can keep total price and manufacturing complexity low, even though one or more of transmitter power, receiver gain, filter complexity, and antenna element count for a specific level of performance may increase. It is submitted that contemporary practice has failed to fully evaluate and develop a category of apparatus, namely air-dielectric microstrip. The present application is the first that provides a fully realized microstrip-feed panel in conjunction with a one- or two-dimensional array of low-cross-coupling, low-mutual-coupling crossed-dipole radiators having polarization determined by feed phase.
If a first signal is applied to one of the panel input ports 18 and a second signal to the other, where the signals may be uncorrelated but on the same channel, then beams formed by the emission of these signals may remain separate and have polarization axes of 45 degrees positive and 45 degrees negative, respectively, until mixed by reflections, which may cause each signal to appear as a noise component in the other. Feed to each input 18 may instead include energy combining two uncorrelated signals in the same channel. Each signal may be phased to create circular/elliptical polarization by setting phase delay to the respective inputs for a first one of the signals to be opposite in sign to phase delay to the respective inputs for the second signal. A beam formed by a panel 10 so fed may contain two elliptically polarized signals of the same frequency but opposite handedness. If the two instances of each signal are generally orthogonal in phase and generally equal in magnitude, then the polarization may approach circular for each. The relative magnitudes of such left- and right-hand polarized signals can be independent.
Single-channel programs, multiple frequency-hopping and/or time-domain multiplexed band-sharing signals over a band, broad-spectrum multiple-channel transmissions, and other applications can be suitable for antennas according to at least some of the embodiments of the invention, limited by the achieved bandwidth of each complete configuration. Allowable applied and radiated panel power levels may be determined by aperture (panel height), the number of independent radiators operating together, material selection, and heat dissipation due to losses, as well as by regulations. Increased radiator loop 28 material thickness may lower Q, i.e., can broaden an antenna's working frequency range. This may also increase reflective losses at all frequencies, i.e., increasing the lowest (best) value of VSWR. Incorporating a plurality of concentric loops may realize a wider usable bandwidth than a similar single loop, but may have a plurality of lowest −VSWR frequency ranges separated by at least one intermediate range with higher VSWR.
With alternative ground plane configurations, such as an open-backed extruded section, a ground plane fabricated from multiple parts, a ground plane assembled as a series of laterally-mated pieces, the H-configuration described below, etc., may be employed in place of a unitary extrusion having multiple internal chambers, a group of feed tabs 124 and an associated microstrip 12 can be a single unit. This potentially may allow the power division and distribution microstrip 12 to be made by a single cutting step and one or more forming steps, avoiding soldering or other fastening steps that can increase production cost and add to any risk of introducing PIM source locations.
In either configuration, the feed tabs 124, 126 may pass through clearance holes in the panel 24, and may further pass through holes 120, 122 in the base of each radiator 20, then may rise parallel to respective first supporting flat tabs 84, 82, cross above the respective first monopoles 74, 72, may descend along respective second supporting flat tabs 80, 78, and may terminate at a specified distance along the second tabs 80, 78. Where needed for stability, spacing between the riser strips 124, 126 and the flat tabs 84, 82 may be controlled by insulating structural elements 138 in clip or other form, preferably physically small and having a low effective value of dielectric constant so that their influence on electrical performance of the antenna may be kept low. Any clips selected for use may attach to the radiators 20 and/or the feed tabs 124, 126 and may use detents or holes in the conductive elements, may wrap around the parts to any selected extent, may be retained using adhesive, etc., as selected for an embodiment. Setting and/or foaming polymers—in effect, blobs of material—may be used in place of clips.
Considering the portion of a microstrip 14 proximal to each radiator 20, each feed tab 126 in conjunction with its respective flat tab 82 may form a first hybrid coupler that may transfer a first portion of its signal energy to a first monopole 72. In conjunction with a second respective flat tab 78, the terminal stub 134 of the feed tab 126 may form a second hybrid coupler that may transfer a second portion of its signal energy to a second monopole 68. The two monopoles 72, 68 may operate jointly as a dipole. Since low loss may be associated with high coupling efficiency, riser strip to monopole interface design may be improved by precise initial simulation. While rising alongside a first flat tab 82, a feed tab 126 may act first as a microstrip parallel to a ground reference, then may form a coupler that may transfer signal energy to a core-proximal portion of a loop 74 that may include a perimeter length of approximately a half wavelength. Passing beyond this loop 74, the microstrip 126 may traverse an approximation of free space for a distance of approximately a half wavelength, then may form a second hybrid configured to terminate in a tuned stub 134 alongside a second flat tab 78. The effect of an arrangement with accurately selected dimensions may be to couple the largest portion of the remaining signal energy into the second loop 68. In such a construction, any remaining signal energy may be reflected off the termination impedance of the stub arriving back at the first loop 72 in phase with the next cycle of signal energy arriving from the input. Thoughtful layout and simulation can provide an operational design with minimal experimentation. Radiator configuration using crossed pairs of loop-shaped dipoles is an advancement. The concept may be substantially free of cross-coupling and other artifacts. Disk-shaped parasitic elements 136 may be added at will, preferably aligned with each radiator's beam axis 66 and may be isolated using standoffs 142, and can alter radiator gain largely independently of polarization. A typical parasitic may be ¼ wavelength in diameter for some frequency in the pass band, and may have diameter, thickness, conductivity, and spacing selected according to simulated and tested performance. Multiple parasitics on each radiator may further enhance performance, but typically exhibit diminishing benefit.
In some embodiments, a single input port may be used in place of the dual ports 18 shown. In a simpler embodiment, the second microstrip may not be installed, and the second dipole in each radiator may be unused, which may result in a 45 degree slanted signal polarization. In another embodiment, an internal power splitter may drive a second microstrip with a zero or 180 degree delay, which may provide a linearly polarized signal, with a 90 degree delay, providing circular polarization, or with an intermediate phase delay that may provide elliptical (non-circular) polarization.
Circular polarization may serve linearly polarized receiving antennas at any orientation, albeit with 3 dB less signal than circularly polarized receiving antennas would achieve, while allowing circularly polarized receiving antennas with like polarization to reject reflections. In receiver and transceiver applications, circularly polarized configurations can receive linearly polarized signals, with the received signal strength largely independent of remote antenna orientation. Embodiments may have a single row of radiators, or two or more rows. Where two rows may be used, the second row may duplicate the signals of the first row or carry signals unrelated to those of the first row. Where the signals are duplicated, the remaining input nodes 18 may be driven separately, or with the same single connector and two more feed lines within the housing 22 and may provide a single linearly or circularly polarized transmitted signal. Rows that may be parallel and staggered may show lower mutual- and cross-coupling than those with other relative positioning.
The radiators 20 are described above as being manufactured from any of a variety of materials as preferred for an application. One example is the range of common zinc-manganese alloys, which may be quite inexpensive and easy to work with—for example, they use of inexpensive material that may be readily cast using molds that are uncomplicated and durable. While the intrinsic conductivity of these alloys may be low compared to copper, silver, or aluminum, applications that use low or moderate power levels may be essentially unaffected by this attribute. The alloys also may accept plating readily, so platings or other coatings in various metals, inherently thicker than skin depth at the frequencies contemplated for these devices, may allow such radiators 20 to have electrical performance approximating that of solid copper or aluminum equivalents.
The radiators 20 may likewise be fabricated from nonconducting or semiconducting materials that accept metallization, as dictated by cost, durability, and suitability to mass-production assembly. In one instance, the radiators 20 and the enclosure or housing 22 may be manufactured from fiber-filled and foamed polymer material, and then plated. If the polymer readily accepts assembly by a method such as gluing or plastic welding, has sufficient ability to withstand weather extremes, and may be stable and not self-heating in response to radio signals at power levels of interest, then a virtually all-plastic antenna panel 10 may be provided. Such an implementation may transmit and/or receive using only a layer of plating over a “plastic” structure to carry the signals, including the microstrips 12, 14, which still may have the properties of air dielectric waveguides when signals are carried between continuous surface plating on the microstrips 12, 14 and the enclosure 22 inner wall. Carbon fiber and nanotube materials as structure and/or filler can be robust and somewhat conductive, and may be used to advantage, even if more costly than zinc alloy. In practice, since the surface, whether plated or not, necessarily may function as the signal conductor in VHF and higher bands, any candidate material requires an adequately smooth surface finish. Particularly where recovery for reuse may be infeasible, a “plastic” antenna may be usable for short-duration tasks, even if such a device is not suited for long service. If materials and labor are sufficiently inexpensive, such a device may be disposable or recyclable.
As noted, signals reaching the ends of the microstrips 12, 14 may be further coupled by feed strips 124, 126, preferably with close control of dimensions and thus with scant signal reflection at the transition. The feed strips 124, 126 carrying signals from the microstrips 12, 14 may be parallel to support flat tabs 78, 80, 82, 84, with a selected width and spacing. These dimensions may be viewed as permitting propagation of applied signal power substantially as does a waveguide—that is, any signal above cutoff as defined by the chamber 34 width propagates more readily. The spacing in embodiments of the invention between a microstrip face 46 and the proximal chamber wall 50, etc., and their extensions, the feed tabs 124, etc., may strongly affect impedance, while suitability for carrying particular propagation modes, such as TE10 mode, may be affected by chamber 34 width, along with microstrip 46 width, at each point during propagation. The edge walls of a classic waveguide operating in the dominant mode TE10 may be uniformly electrically null, serving to provide greater structural integrity, air seal, and a barrier against electrical leakage. For this reason, waveguide-type walls may be omitted where not needed, as in some embodiments of the invention, leaving the chamber 34, the microstrips 12, 14, the feed strips 124, 126 and the support flat tabs 78, 80, 82, 84 to define a signal propagation path.
The signal paths may effectively turn, at the microstrip termini 102, 104, from a route that may be uniformly spaced away from a chamber 34 wall—specifically, from the inner housing surfaces 50 that may be the other side of the external ground plane 24 on which the radiators 20 may be mounted—to a route orthogonal to that surface 50. The feed tabs 124, 126 may be soldered or otherwise attached to the microstrips 12, 14 at the latters' termini 102, 104. The feed tabs 124, 126 may exit the chamber 34, with proximal faces of the feed tabs 124, 126 and the support flat tabs 78, 80, 82, 84 may be parallel. Spacing between the feed tabs 124, 126 and the support flat tabs 78, 80, 82, 84 may be substantially the same as spacing between the microstrips 12, 14 and the proximal chamber wall 50, etc., over the part of the path within the enclosure 22. Spacing may be adjusted as required to control impedance and insert additional reactive terms.
The support flat tabs 78, 80, 82, 84 may be at ground potential at the ground plane 24 and may extend perpendicularly thereto in an approximation of the beam direction 66. The support flat tabs 78, 80, 82, 84 may terminate ¼ wavelength distal to the ground plane 24, with the support flat tab termination possibly having the form of a tee from which two conductors extend at right angles to one another, then may turn within a plane parallel to the ground plane 24 and may join to define monopole loops 68, 70, 72, 74. The quarter-wave spacing may substantially isolate the loops 68, 70, 72, 74 from the ground plane 24. An associated feed tab 126 may cross over from the first support flat tab 82 to a second support flat tab 78 with a specified conductor length, then may pass along the second support flat tab 78 and may terminate as a stub 134 in the feed tab's characteristic impedance. The second support flat tab 78 may begin at the radiator base 86 (proximal to the ground plane 24) and may terminate ¼ wavelength away in a tee that itself may begin a second monopole loop 68. Signal coupling from the stub-terminated feed tab 126 to each of the first and second support flat tabs 82, 78 and from the respective support flat tabs 82, 78 to the first and second monopole loops 72, 68 may be a function of the physical dimensions of the feed tab 126 and the stub termination 134, as well as the physical dimensions of the respective support flat tabs 82, 78 and the impedance associated with the spacings between the feed tab 126 and the support flat tab 82 and between the stub termination 134 and the support flat tab 78.
A propagation time for traverse of the distal crossover portion 144 of one of the feed tabs 126 may give the signal applied to the two monopoles 72, 68 driven by that feed tab 126 opposite phase at each moment in time. A consequence of this may be that the monopoles 72, 68 may function jointly as a first dipole.
The configuration of the instant invention may result in application of a drive signal to both monopoles 72, 68 of a pair 30 (refer to
Considering next the proximal feed tab 124—that is, the drive element feeding the two monopoles of the second dipole 32 in each radiator 20—the function of the proximal feed tab 124 may be substantially the same as that of the proximal feed tab 126, except that it may pass between the distal feed tab 126 and the loop elements 28. In at least some embodiments, the propagation path for the signal carried by the proximal and distal feed tabs 124, 126 may be somewhat unequal. Dimensions for the feed tabs 124, 126 can be selected by user preference. In embodiments wherein the feed tabs 124, 126 may be respectively shorter and longer than an optimum length, respective feed timings may be slightly different from, although close to, an ideal half-wavelength. This provides an approximation of a nominal beam pattern. In at least the embodiments shown in
Interaction between the two feed tabs 124, 126 may remain small, at least by virtue of the tabs' signal paths being substantially orthogonal. That is, any signal coupled from one of the tabs into the other may induce a current at right angles to the direction of signal propagation for the other, resulting in a slight back EMF in the first tab due to the presence of the second, and vice versa, but little else.
The presence of the “other” tab may be measurable as an impedance lump in each, although more pronounced in the distal feed tab 126. This is because the signal may be present largely as a field between the proximal feed tab 124 and its associated support tabs 84, 82, and between the distal feed tab 126 and its associated support tabs 82, 78. The signal intended to propagate on the proximal feed tab 124 may be oriented away from the distal feed tab 126, while the signal intended to propagate on the distal feed tab 126 may be present largely on the face directed toward the proximal feed tab 124. As a result, the signal on the distal feed tab 126 may be somewhat more susceptible to interaction with the other strip than is the signal on the proximal feed tab 124. Overall, however, signal coupling into each strip from the other may be slight.
It may be possible to cause the realized beam direction in embodiments of the invention taught herein to approximate a nominal beam direction using basic dimensions—that is, values for dimensions that may closely follow arbitrary center frequencies, ideal propagation rates, simplified assumptions about interaction of dielectric lumps, etc. Slight variations of the basic dimensions, however, can be applied in such a way as to provide a realized beam direction that yet more closely approximates a nominal beam direction. As noted above, one such variation makes the feed strip propagation path lengths almost exactly the same. This can be further enhanced by causing whichever of the two paths may be shorter to be the one that has greater capacitive phase delay, for example, so that phase difference due to difference in physical length compensates in part for reactively-sourced phase difference. Similarly, since some embodiments of the radiators 20 may include a single pair of pass holes 120, 122, selected dimensions of such radiators 20, such as support tab width, loop perimeter, etc., may be made slightly asymmetrical, with the radiator 20 pass holes 120, 122 providing positive keying to ensure that such asymmetry may be uniformly applied and compensates for any demonstrated tendency for a fully symmetric radiator 20 to output an asymmetric signal. Similar keying may be possible for punched-and-bent or otherwise fabricated radiators. Optimization of dimensions may be preferably realized by inputting accurate initial dimensions into simulation software and analyzing the effect of small changes until a solution within a practical range is reached.
Adjacent portions of each two loops 28 may be parallel, may have generally matching facing surface widths, and may be spaced apart with a separation selected to form a hybrid coupler. Each facing surface has a physical length on the order of a tenth of a wavelength for a frequency in the working range for which the radiator 20 may be intended. Dimensions for achieving a particular radiative efficacy goal at a given center frequency and bandwidth may be best verified through simulation and prototype testing, including balancing these dimensions with loop height H above the ground plane 24, loop circumference, and other dimensions.
The practitioner may be able to establish a second usable band for a given radiator size. The perimeter shape for each loop 28 may be square or non-square, but is preferably convex. The characteristic curvilinear perimeter shape of the loops shown herein is not mandatory, but may prove beneficial in minimizing PIM distortion of received signals in the presence of transmitted signals that may be over 100 dB greater in magnitude and located with 5% in frequency. The loops 28 need not necessarily be formed of continuous conductors if one or more additional capacitive or hybrid segments in combination with conductors establish a continuous signal path. Extensive testing has demonstrated, however, that using other shapes, such as the radial straight-line (non-hybrid) monopoles or ring-shaped loops as in some antennas, may severely degrade the ability of each radiator to support low cross coupling between the dipoles formed by loops 28 in the instant invention. Such other (non-hybrid) shapes may also inhibit realizing low mutual coupling between dipoles in proximal but separate radiators. Some designs may render impedance matching in arrays of uniformly-distributed crossed dipoles, such as single-row arrays, two-row staggered arrays, and others essentially infeasible.
A radome may be included in order to enclose the antenna panel radiators, largely for weather protection, but additionally to conceal the radiators from view and for other purposes selected by a user. A single extruded, bent, or vacuum formed sheet of polymer or other material selected for its dielectric properties can freely pass radiation to and/or from the panel while blocking rain and contaminants from the radiators and the feed system. Including a radome may allow the feed strip pass holes to be left open, for example, rather than requiring an individual barrier plug in each. A radome may also guard the individual feed strips and any dielectric support fittings used to stabilize them from being damaged by impacts of wind-blown objects, animal contact, etc. Top and bottom elements of a radome may be integral with side walls and a single surface through which most radiation passes, or may be separate parts. Since the top, bottom, and side walls may be not major factors in propagation, any of these may be conductive, either integral with or separate from the ground plane. In embodiments wherein any of these may be conductive, the conductive component may affect beam elevation. The radome may be vacuum-formed or bent from sheet stock, extruded, or otherwise put into a shape meeting operational requirements. While simple and concealing enclosure shapes may be common in panel antenna practice, some embodiments may incorporate a plurality of more-conformal radome shapes or separate radomes for individual radiators or groups of radiators. Conductive, resilient, or other forms of closures may be affixed to the top and bottom openings of the chambers behind the ground plane front surface. Downward-facing radome and chamber openings may be completely uncovered or have covers that include open vents in some embodiments not requiring pressurization.
The many features and advantages of the invention are apparent from the detailed specification, and, thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and, accordingly, all suitable modifications and equivalents may be resorted to that fall within the scope of the invention.
This application claims the benefit from U.S. Provisional Application No. 61/679,535 filed on Aug. 3, 2012, which is hereby incorporated by reference in its entirety for all purposes as if fully set forth herein. This application is related to U.S. Provisional Application No. 61/679,589 filed on Aug. 3, 2012, which is hereby incorporated by reference in its entirety for all purposes as if fully set forth herein.
| Number | Date | Country | |
|---|---|---|---|
| 61679535 | Aug 2012 | US |
