Patent Application
20150249288
There are many cases where a radio transceiver needs to be physically located in an environment that is non-ideal for electromagnetic wave propagation, such as below ground level water utility metering pits. Radio signals that are generated from below ground level in such environments are often absorbed, refracted, and reflected, resulting in poor radio frequency (RF) propagation. When the pit structure includes a metal lid, RF propagation may be even more impacted. For fixed water utility metering networks that are comprised of radio transceivers located in the ground attached to water meters and base station receivers located on buildings and towers, poor RF propagation can result in significant cost increases as some meters cannot be read (unless manually) and some can only be read remotely if more base stations are installed. When more base stations are required to supply adequate network coverage, the meter transceivers' transmit power levels often need to be increased, which in turn reduces battery life or requires additional batteries to be included at significant cost, impacting corporate profits significantly.
One solution to mitigating poor RF propagation environments, such as the below ground water pit example, is to transfer the RF energy from the radio transceiver below ground to a radiating structure located above ground, which is a much more suitable RF propagation environment. In addition, the physical environment of the water pit example above requires the meter transceiver and associated electronics to be completely hermetically sealed to guarantee a twenty year operating life and maintain a barrier for water vapor that destroys the electronics over time. Because of this constraint, no physical contacts may be used to transfer the RF energy from the meter transceiver located below ground, to the above ground radiating structure, such as cables or contact connectors.
Wireless communication devices are finding applications that require new antenna designs to address inherent limitations of the devices and to enable new capabilities. With conventional antenna structures, a certain physical volume is required to produce a resonant antenna structure at a particular frequency and with a particular bandwidth. However, effective implementation of such antennas is often confronted with size constraints due to a limited available space in the device.
Antenna efficiency is one of the important parameters that determine the performance of the device. In particular, radiation efficiency is a metric describing how effectively the radiation occurs, and is expressed as the ratio of the radiated power to the input power of the antenna. A more efficient antenna will radiate a higher proportion of the energy fed to it. Likewise, due to the inherent reciprocity of antennas, a more efficient antenna will convert more of a received energy into electrical energy. Therefore, antennas having both good efficiency and compact size are often desired for a wide variety of applications.
Conventional loop antennas are typically current fed devices, which generate primarily a magnetic (H) field. As such, they are not typically suitable as transmitters. This is especially true of small loop antennas (i.e. those smaller than, or having a diameter less than, one wavelength). The amount of radiation energy received by a loop antenna is, in part, determined by its area. Typically, each time the area of the loop is halved, the amount of energy which may be received is reduced by approximately 3 dB. Thus, the size-efficiency tradeoff is one of the major considerations for loop antenna designs.
Voltage fed antennas, such as dipoles, radiate both electric (E) and H fields and can be used in both transmit and receive modes. Compound antennas are those in which both the transverse magnetic (TM) and transverse electric (TE) modes are excited, resulting in performance benefits such as wide bandwidth (lower Q), large radiation intensity/power/gain, and good efficiency. There are a number of examples of two dimensional, non-compound antennas, which generally include printed strips of metal on a circuit board. Most of these antennas are voltage fed. An example of one such antenna is the planar inverted F antenna (PIFA). A large number of antenna designs utilize quarter wavelength (or some multiple of a quarter wavelength), voltage fed, dipole antennas.
Compound loop (CPL) antennas are finding applications that are not appropriate for other types of antennas. The CPL antenna includes a loop and a radiator, but may also include multiple radiators or radiating elements that are part of the loop. Similar to a conventional loop antenna, that is typically current fed, the loop element of the CPL antenna may generate a magnetic (H) field. The radiating element, having the series resonant circuit characteristics, effectively operates as an electric (E) field radiator (which of course is an E field receiver as well due to the reciprocity inherent in antennas). In order to operate as a CPL antenna, the generating/receiving E and H fields must be substantially orthogonal to each other, even though the loop and radiator element may be coplanar. This orthogonal relationship has the effect of enabling the electromagnetic waves emitted by the antenna to effectively propagate through space. In the absence of the E and H fields arranged orthogonal to each other, the waves will not propagate effectively beyond short distances. To achieve this effect, the radiating element is generally placed at a position where the E field produced by the radiating element is 90 ° or 270 ° out of phase relative to the H field produced by the loop element. Specifically, the radiating element is placed at the substantially 90° (or) 270° electrical length along the loop element from a feed point. Alternatively, the radiating element may be connected to a location of the loop element where current flowing through the loop element is at a reflective minimum.
In addition to the orthogonality of the E and H fields, it is desirable that the E and H fields are comparable to each other in magnitude. These two factors, i.e., orthogonality and comparable magnitudes, may be appreciated by looking at the Poynting vector (vector power density) defined by P=E×H (Volts/m×Amperes/m=Watts/m2). The total radiated power leaving a surface surrounding the antenna is found by integrating the Poynting vector over the surface. Accordingly, the quantity E×H is a direct measure of the radiated power, and thus the radiation efficiency. First, it is noted that when the E and H are orthogonal to each other, the vector product gives the maximum. Second, since the overall magnitude of a product of two quantities is limited by the smaller, having the two quantities (|H| and |E| in this case) as close as possible will give the optimal product value. As explained above, in the CPL antenna, the orthogonally is achieved by placing the radiating element at the substantially 90° (or) 270° electrical length along the loop element from a feed point. Furthermore, the shapes and dimensions of the loop element and the radiating element can be each configured to provide comparable, high |H| and |E| in magnitude, respectively. Therefore, in marked contrast to a conventional loop antenna, the CPL antenna, such as a planar CPL antenna, can be configured not only to provide both transmit and receive modes, but also to increase the radiation efficiency.
Size reduction can be achieved by introducing a series capacitance in the loop element and/or the radiating element of the CPL antenna. Such an antenna structure, referred to as a capacitively-coupled compound loop antenna (C2CPL), has been devised to provide both transmit and receive modes with greater efficiency and smaller size than a conventional antenna. Examples of structures and implementations of the C2CPL antennas are described in U.S. patent application Ser. No. 13/669,389, entitled “Capacitively Coupled Compound Loop Antenna,” filed Nov. 5, 2012, which is incorporated herein by reference.
The compound coupling interface described herein is a passive, non-contact system for efficiently transferring the RF energy from one CPL antenna to another CPL antenna, thereby requiring relatively little power and resulting in little dB loss. Rather, the two CPL antennas are both capactively coupled and inductively coupled at the same time, which is possible due to the unique operating structure of the CPL antenna.
While other wireless antenna coupling designs have been implemented in the past, such designs typically utilize one of two possible simple-field coupling technologies: substantially capacitive coupling or substantially inductive coupling. Capacitive coupling using parallel plates of conductive material is inherently highly sensitive to translation and alignment between the two coupling structures. The coupling areas are maximized along the edges of conductive plates and very slight translations (fractions of a millimeter) can cause frequency shift and significant increases in loss of RF energy. Capacitive coupling is more sensitive to material interactions because of the fringe electric fields along the edges of the conductive plates. These drawbacks have limited the use of capacitive coupling in commercial applications where low coupling loss is desired.
Unlike the compound coupling architecture of the present disclosure, it is also typically not possible to realize a dual mode radiator and a coupler with one artwork. One of the two capacitive plates cannot typically function as both an antenna and a coupler, both at the same frequency of operation.
Inductive coupling using a pair of conductive loops requires a larger aperture, and thus larger volume to implement, than capacitive or compound coupling to achieve low coupling loss. When the pair of inductive loops are realized to be less than a wavelength in circumference (small loops), in order to reduce overall size, the feeding mechanism becomes more critical to maintain low coupling loss. Typically, the small loops are fed with unbalanced feeds and common mode current can interact with the feed, reducing coupling efficiency and increasing RF energy loss.
Unlike the compound coupling architecture of the present disclosure, it is also typically not possible to realize a dual mode radiator and a coupler with one artwork. One of the two loops cannot typically function as both an antenna and coupler both at the same frequency of operation.
The compound coupling architecture of the present disclosure enables both CPL antennas to simultaneously capactively couple and inductively couple, with relatively high efficiency and relatively little coupling loss. In addition, when the CPL antennas are not being used to couple with one another, either or both CPL antennas can function as a radiator.
Since the two CPL antennas of the compound coupling system do not require any physical connections in order to couple, both CPL antennas and their associated assemblies may be completely sealed, i.e., hermetically sealed, so as to protect the antennas, the associated assembly circuitry, and the re-radiating antenna structure from any type of environmental intrusion, such as water. One particular appropriate application is that of a water meter wireless endpoint. Water lines are typically buried underground. Water meters that measure the flow (and therefore the usage of water) through such lines are usually located in a pit buried in the ground. The pits are typically constructed from rigid plastic or non-corrosive metal and can extend many feet into the ground, with the water pipe running through the bottom of the pit. The top of the pit is flush with the ground surface and is usually covered with a lid. The pits are not water proof, so due to water leaks, high water tables, and run-off from other sources, the pits may be completely flooded. The water meter generates a signal that is output through a sealed cable extending from the meter. The cable typically connects to an electrical device that receives the metered signal from the water meter and transmits the metered signal to a remotely located host station. Merely being buried in the ground is one obstacle to transmitting a strong signal. Interference from surround water, the material forming the pit and the material forming the lid can be further factors limiting the efficiency of the transmission of the electrical device.
In an embodiment illustrated in
Since the two antennas 22 and 24 are compound loop antennas, which enable simultaneous capactive coupling and inductive coupling, the coupling arrangement between the two CPL antennas is referred to herein as “compound coupling.” The two CPL antennas 22 and 24 are placed parallel to each other, but not in direct contact, to efficiently transfer RF energy from the source of the PCB assembly 16 to the re-radiating CPL antenna 26. When the CPL antennas 22 and 24, which may both be half wave CPL antennas, are configured in close proximity to one another, such as about 5 mm, both antennas may operate as efficient wireless compound couplers, transferring RF energy across a boundary of various dielectric material with approximately 1 dB loss. CPL antenna 26 is also located in the second plastic housing. While it is described in this embodiment as a low profile, vertically polarized CPL antenna, operating as a re-radiator, the antenna need not be a CPL antenna and other types of antennas could be used in place of a CPL.
Other examples of a compound coupling to re-radiating antenna solution can be seen in
A full wave CPL antenna to a full wave CPL antenna compound coupling is illustrated with respect to
While the water meter pit example is one particularly appropriate example, the present disclosure is not limited to just that particular application and could be utilized in any application where it is useful to have two different assemblies in wireless communication, but located in close proximity to one another. For example, Wi-Fi enabled devices are often designed to lay flat for various industrial design and aesthetic reasons. For example, a 802.11ac 5 GHz enabled Wi-Fi router may lay down flat on a desktop or table. The efficient propagation of radio waves from this flat lying device at 5 GHz is known in the field to be dependent on maximizing the vertical polarization (electric field polarization with respect to the earth) of the antenna system of the device. This performance requirement has led industry designers and manufacturers of such devices to utilize a certain type of antenna implementation: those that are separated from the main device printed circuit board (PCB), connected with cables to the PCB and mounted perpendicular to the PCB along the perimeter of the plastic housing. This antenna implementation is often referred to as off-board and is inherently more expensive than if an antenna solution were to be printed on the main PCB directly, in the same plane as the PCB. The cost of coax cable, connectors, and manual assembly processes of the off-board antennas drive the added expense. Printed, or on-board antennas are far more cost effective however, when implemented at 5 GHz in a lying flat device, but the polarization is a mix of horizontal and vertical so the performance suffers.
It should be appreciated that orientations of the pair of compound coupling CPL antennas, as described above, are only given by way of example. To meet space and design limitations, or other requirements of implementations, the compound coupling CPL antennas may be oriented in a variety of ways relative to their surroundings. For example, in the example illustrated in
Conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements, and/or steps. Thus, such conditional language is not generally intended to imply that features, elements and/or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or steps are included or are to be performed in any particular embodiment. The terms “comprising,” “including,” “having,” and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list.
While certain example embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope the disclosures herein. Thus, nothing in the foregoing description is intended to imply that any particular feature, characteristic, step, module, or block is necessary or indispensable. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosures herein. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of certain of the disclosures herein.
This application claims benefit under 35 U.S.C. §119(e) of Provisional U.S. Patent Application No. 61/996,773, filed May 14, 2014; this application is also a continuation-in-part of U.S. patent application Ser. No. 14/103,684, filed Dec. 11, 2013; and a continuation-in-part of U.S. patent application Ser. No. 14/565,379, filed Dec. 9, 2014, which claims the benefit of Provisional U.S. Patent Application No. 61/913,789, filed Dec. 9, 2013, the contents of each of which are incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61966733 | Feb 2014 | US | |
| 61913789 | Dec 2013 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14103684 | Dec 2013 | US |
| Child | 14712804 | US | |
| Parent | 14565379 | Dec 2014 | US |
| Child | 14103684 | US |
