Patent Application
20080001840
The accompanying figures, wherein like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages, all in accordance with the present invention. The drawings are not always drawn to scale, but are, for example, enlarged, in order to facilitate a better understanding of the invention.
In overview, the present invention concerns a small transceiver device having a compact antenna. More particularly, various inventive concepts and principles embodied in methods and apparatus may be used for making and using a small transceiver device having compact loop antennas.
While the antennas of particular interest may vary widely, one embodiment may advantageously be used in a wireless communication device or system, or a wireless networking system, such as a network of ZigBee compatible devices.
The instant disclosure is provided to further explain, in an enabling fashion, the best modes at the time of the application of making and using various embodiments in accordance with the present invention. The disclosure is further offered to enhance an understanding and appreciation for the inventive principles and advantages thereof, rather than to limit the invention in any manner. The present invention is defined by the appended claims, including any amendments made during the pendency of this application, and all equivalents of those claims as issued.
It is further understood that the use of relational terms, if any, such as first and second, top and bottom, and the like, are used solely to distinguish one entity or action from another without necessarily requiring or implying any such actual relationship or order between such entities or actions.
Some of the inventive functionality and inventive principles can be implemented with, or in, integrated circuits (ICs), or printed circuit board or other substrate technologies. It is expected that one of ordinary skill, when guided by the concepts and principles disclosed herein, will be readily capable of generating such substrates embodying the antenna systems described herein with minimal experimentation, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations. Therefore, in the interest of brevity and minimization of any risk of obscuring the principles and concepts according to the present invention, further discussion of such substrate technologies, if any, will be limited to the essentials with respect to the principles and concepts of the various embodiments.
With reference now to
In another embodiment, the substrate 102 may be made of a semiconductor wafer material, wherein the material has a low or acceptable, material loss, such as low loss tangent, low metallic loss, etc.
In the embodiment shown, the substrate 102 is planar. In other embodiments, the substrate 102 can have a curved surface. For example, the substrate 102 can be a flexible substrate material, which can be bent into a curved surface. Additionally, the substrate 102 can be a rigid material that is curved to conform to a shape of a product, or configured as part of the structure or housing of a product that uses the transceiver device 100.
On a first surface 103 of the substrate 102, circuit traces 104 are formed to connect various electronic components, such as a transceiver integrated circuit 106, to form the electrical circuitry of the transceiver device 100. The circuit traces 104 can be made of a conductive metal laminated to, or deposited on, a surface 103 of the substrate 102. In one embodiment, the metal can be copper. In other embodiments, the metal can be gold, silver, aluminum, copper, nickel, or other similar metals.
The transceiver integrated circuit 106 in one embodiment can be implemented with a 2.4 GHz, low power transceiver that operates in accordance with the IEEE 802.15.4 wireless standard, which supports star and mesh networking, or another similar wireless communication standard. An example of the integrated circuit 106 is the integrated circuit sold under part number MC13192 by Freescale Semiconductor, Inc., Austin, Tex., USA.
Other components mounted on a first surface 103 of the substrate 102 can include capacitors, inductors, a crystal for a crystal oscillator, etc.
Radio frequency outputs of the integrated circuit 106 can be coupled to feed points of a transmit loop element 108, which serves as the transmit antenna for the transceiver device 100. The transmit loop element 108 occupies a transmit loop area 110 (as illustrated by dimension lines), which in one embodiment is 15 millimeters (mm) by 15 mm (e.g., 225 mm2). This can be one-half (½) of the area of the substrate 102, which, in the embodiment shown, measures 15 mm by 30 mm. The dimensions recited are for one embodiment that is arranged for operation at or around 2.4 GHz. It will be appreciated that other embodiments operating at other frequencies will have different dimensions. For example at lower frequencies, e.g., 2 GHz, these dimensions will be larger and at higher frequencies, e.g., 3 GHz, these dimensions can be smaller.
In order to reduce the transmit loop area 110 occupied by the transmit loop element 108, the transmit loop element 108 has a plurality of transmit loop segments 112 disposed in a zigzag configuration 114, or, as shown in
With reference now to
The receive loop element 204 is formed on the second surface 202, and occupies a receive loop area 210 (indicated by dimension lines), which, in one embodiment, is an area (15 mm)2 in the upper half of a 15 mm by 30 mm the substrate 102. In the embodiment shown in
The receive loop element 204 includes a plurality of receive loop segments 212, which, in order to reduce the received loop area 210, are disposed in a receive zigzag configuration 214, or, as shown in
Referring now to
Some segments in the transmit loop element 108 may be referred to as transmit loop connecting segments, because they are used to connect to the transmit loop segments 112 that are disposed in the one or more transmit zigzag configurations 114. For example, the transmit loop connecting segment 306 can be used to connect the group 308 of transmit loop segments 112 to the group 310 of the transmit loop segments 112. The transmit loop connecting segments 312-318 can be used to connect the feed points 302 and 304 to the groups 308 and 310. Additionally, short transmit loop connecting segments 319 may be used at the vertices 320 and 322 (where a vertex is a point (as of an angle, polygon, polyhedron) that terminates a line or curve or comprises the intersection of two or more lines or curves). Such a vertex is formed where adjacent transmit loop segments 112 of the transmit zigzag configurations 114 meet. The purpose of the transmit loop connecting segments 319 is to ease or round the sharp corners at the vertices 320 and 322.
The transmit loop element 108 defines a central transmit loop area 324 in the center part of the loop. In the embodiment shown, the central transmit loop area 324 is rectangular, having a boundary 326 that is shown with a dashed line. In other embodiments, the central transmit loop area 324 can have other shapes.
The transmit loop segments 112 that are in transmit zigzag configurations 114 each extend away from the boundary 326 of the central transmit loop area 324 at an angle (e.g., angles 328 and 329) that is less than or equal to 90° from a first vector 330 having a first direction. For example, if the first vector 330 points downward, parallel to a central axis 332 of the central transmit loop area 324, each of the transmit loop segments 112 extending outward from the transmit loop area 324 forms an angle (e.g., angles 328 and 329) with reference to the first vector 330 that is less than or equal to 90°, thus producing the transmit loop segments 112 in the transmit zigzag configuration 114 that are either horizontal (e.g., at 90°) or sloped downward (e.g., less than 90°) toward the feed points 302 and 304.
Note that alternate segments (e.g., every other segment) in the zigzag configuration, such as segments 334 and 336, may or may not be parallel. As an example, the segment 334 is at a 75° angle with respect to the first vector 330, and the segment 336 is at an 80° angle with respect to the first vector 330, which means that the segments 334 and 336 are not parallel.
In one embodiment, the transmit loop segments 112 in the groups 308 and 310 are symmetrical about an axis 332, which is preferred for a design with differential inputs. The symmetrical shape provides a symmetrical radiation pattern about the axis 332. In other embodiments of the present invention, groups of loop segments need not be symmetrical about an axis.
In one embodiment of the present invention, the transmit loop element 108 has selected dimensions shown in the Table 1, below. Note that reference numbers 378 and 380 are shown in
In one embodiment of the present invention, selected angles between transmit loop segments 112 in transmit zigzag configurations 114 are shown in Table 2, below.
The transmit loop element 108 having the selected dimensions and angles in Tables 1 and 2 has an overall length of approximately 190 mm measured from the feed point 302 to the feed point 304, which is 1.55 times a wavelength at a center frequency of 2.42 GHz. Additionally, the transmit loop element 108 can fit within a square area that is 15 mm on a side.
Referring now to
As similarly described above with reference to the transmit loop element 108, the loop element 208 in
The receive loop element 204 defines a central receive loop area 422 in the center part of the receive loop. In the embodiment shown, the central receive loop area 422 is rectangular, with a boundary 424 shown as a dashed line. In other embodiments, the central receive loop area 422 can have other shapes.
The receive loop segments 212 that are in receive zigzag configurations 214 each extend away from the boundary 424 at an angle (e.g., angles 426 and 427) that is less than 90° from a second vector 428, wherein the second vector 428 is in a direction opposite to the first vector 330. For example, the second vector 428 points upward parallel to receive loop axis 430, and each receive loop segment 212 extends outward from the central receive loop area boundary 424, forming an angle with the second vector 428 that is less than 90°, thus creating the receive loop segments 212 disposed in one or more receive zigzag configurations 214, where such segments slope upward (e.g., angles 426 and 427 are less than 90°), away from the feed points 402 and 404.
Note that alternate receive loop segments in the receive zigzag configurations 214, such as the segments 432 and 434, may or may not be parallel. In the embodiment shown, the segment 432 extends away from the boundary 424 at an angle of 10° with respect to the second vector 428, while the segment 434 extends away from the boundary 424 at an angle of 15° with respect to the second vector 428, which means that the segments 432 and 434 are not parallel. Other pairs of alternate segments in
In one embodiment, the receive loop segments 212 in the groups 406 and 408 are symmetrical about the receive axis 430. In other embodiments, groups of segments in zigzag configurations need not be symmetrical about an axis.
In one embodiment, the receive loop element 204 has selected dimensions that are listed in Table 1, above. The selected angles between the receive loop segments 212 in the receive zigzag configurations 214 are listed in Table 2, above.
Turning now to
As illustrated, the transmit loop element 108 (shown with a dashed line) and receive loop element 204 (shown with a solid line) occupy generally the same area on their respective surfaces. In the embodiment shown, they both fit within a 15 mm×15 mm square area. Boundaries 326 and 424 (See
The area of overlap 504 is reduced by configuring the transmit loop segments 112 and receive loop segments 212 that are close to each other so that they are skew, which means that they are set, placed, or run obliquely with respect to each other, or that they are slanting with respect to the other. It can also be said that the transmit loop segments 112 and the complimentary or corresponding receive loop segment 212 are not coextensive, or do not have substantially the same orthographic projection or intersection, wherein such complimentary or corresponding segments are opposite one another on either side of the substrate 102, are related through the symmetry of the transmit loop element 108 and receive loop element 204, and are a pair of elements most likely to electrically couple with one another due to orientation and proximity. Thus, the transmit loop segment 112 and corresponding receive loop segment 212 are not parallel.
It should be apparent to those skilled in the art that the method and system described herein provides a number of improvements over the prior art. First, the transmit loop element 108 and receive loop element 204 are compact and occupy small areas 110 and 210, respectively. Compact antennas reduce the overall size of the transceiver 100, which can reduce manufacturing cost and make the transceiver 100 easier to locate within a device or apparatus that is to be connected to a wireless network. The size of the stacked antennas is reduced without significantly reducing the gain of either antenna.
As a second advantage, a separate transmit loop element and receive loop element eliminates the need for a balun or a radio frequency (RF) switch in the transceiver device 100. A balun is a device designed to convert between balanced and unbalanced electrical signals, and an RF switch can be used to alternately connect a single loop antenna between a transmitter and a receiver.
As a third advantage, the stacked antenna configuration can be ideal for coupling to the differential input and output of the integrated circuit radio 106 in the transceiver 100, which works best with a 100 ohm impedance match.
The processes, apparatus, and systems, discussed above, and the inventive principles thereof are intended to produce a more effective compact transceiver system. By stacking compact transmit and receive loop antennas, a small transceiver device can be produced that has better antenna gain and radiation efficiency than a dipole or other differential input antenna. Additionally, by skewing corresponding zigzag elements in the transmit and receive loops, reduced electrical coupling and additional efficiency are achieved.
This disclosure is intended to explain how to fashion and use various embodiments in accordance with the invention, rather than to limit the true, intended, and fair scope and spirit thereof. The foregoing description is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications or variations are possible in light of the above teachings. The embodiment(s) were chosen and described to provide the best illustration of the principles of the invention and its practical application, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims, as may be amended during the pendency of this application for patent, and all equivalents thereof, when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.
