BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a V-shaped notch serving as a perturbation or radiator in a transmission line which functions as a low profile distributed antenna (LPDA) according to one embodiment of the present invention.
FIG. 2 is a cross-sectional view of the LPDA transmission line embedded in a foam conduit and encased in a plastic outer shell.
FIG. 3 is a top-view of the LPDA transmission line with the multiple perturbations represented by the V-shaped notches cut in its top plate.
FIG. 4 is schematic diagram illustrating a feed circuit for the LPDA.
FIGS. 5A and 5B are cross-sectional views of splicing structures for joining two LPDA transmission lines.
DESCRIPTION
The present invention provides an external radio energy propagation channel through the introduction of a low-profile linear distributed antenna (LPDA). The disclosed LPDA provides controlled radiation customized for each environment of interest. Further, it is a very cost-effective solution even though it is applied in terms of long lengths to provide the desired coverage within enclosed areas.
FIG. 1 is a perspective view of a V-shaped notch serving as a perturbation or radiator in a transmission line which functions as a low profile distributed antenna (LPDA) according to one embodiment of the present invention. The notched transmission line 100 comprises two thin-line parallel conductive plates 110 and 120 with bi-lateral V-shaped notches 113 and 115 cut at the top plate 110. As a result of the V-shaped notches 113 and 115, the notched transmission line 100 is “pinched” at the narrowed location, which causes radio energy to “leak out” or radiate. Therefore the notched transmission line 100 can serve as one example of a perturbation radiator. Although V-shaped notches 113 and 115 are used to create the perturbation, one having skills in the art would appreciate various other perturbation structures, either by cutting out notches of shapes other than the V-shape or by adding protruding objects on the transmission line, may be applied to turn the transmission line into a radiator.
FIG. 2 is a cross-sectional view of the LPDA transmission line 100 embedded in a foam conduit 230 and encased in a predetermined outer shell 240 which can be made by various suitable materials such as plastic or rubber. The foam conduit 230 is a spacer and has very low-loss for RF energies. In a field application, the LPDA transmission line 100 may be placed on a mounting surface 250 on a bottom side closer to the bottom plate 120. Although the bottom plate 120 as shown in FIG. 2 is wider than the top plate 110 for practical purposes, one having skills in the art would recognize that a bottom plate can be the same or even smaller width than the top plate 110, though it may not perform as well. The V-shaped notches 113 and 115 shown in FIG. 1 are cut on the top plate 110. One having skills in the art may also recognize that the V-shaped notches 113 and 115 or any other perturbations may be added to either the top plate 110 or the bottom plate 120 or even on both plates 110 and 120. The shape, size and orientation of the perturbations may be used to control the radiation bandwidth, level, polarization, etc.
Referring to FIG. 2, the conduit is shown as a solid structure surrounding the LPDA transmission line 100. This conduit can also be designed in terms of two pieces that can be taken apart to adjust the radiators or to add splice sections as discussed later. To allow for easy access these two conduit pieces can be snapped together, for example. That being the case, one can change the LPDA antenna in the field. This may be very useful in complex application environments.
FIG. 3 is a top-view of the LPDA transmission line 300 with multiple V-shaped notches 313[0:n] and 315[0:n] cut in its top plate 310 to serve as perturbation radiators. In this embodiment, a bottom plate 320 has no notch, and is wider than the top plate 310. The V-shaped notches 313[0:n] and 315[0:n] are cut symmetrically on both edges of the top plate 310, i.e., 313[0] and 315[0], 313[1] and 315[1], etc., are symmetrical. The V-shaped notches 313[0:n] and 315[0:n] may be cut at a regular interval L or at an irregular length across the length of the notched transmission line 300. The interval is determined by signal strengths of the radiations from the notches 313[0:n] and 315[0:n] to make sure that the areas in between the perturbation radiator locations are covered by the radiations therefrom. When radio frequency (RF) signal is fed at a left end 332 from a base station 340, the LPDA transmission line 300 will function as a low profile distributed antenna (LPDA) for the RF signal. To terminate the RF energy transmission at a right end 336, a termination 350 is connected thereto. This specific termination 350 is designed to provide better illumination of the enclosed environment.
Referring to FIG. 3, a depth of the notch, D0 for notch 313[0], D1 for notch 313[1] or Dn for notch 313[n], determines the amount of radiation from the notch. The deeper the notch is, the higher the radiation comes from the notch. At the same time the farther the RF signal propagates along the LPDA transmission line 300, the more it is attenuated. In order to keep the relative radiation from each notch uniform along the length of the transmission line 300, the depth of the notches 313[0:n] and 315[0:n] varies from small to large from the feed end 332 to the termination end 336. For example, D1 is designed to be larger than D0, and Dn is the largest among all the notches as it is at the right end 336 of the notched transmission line 300. It is this controlled radiation that provides a uniform coverage for the wireless system. Also by controlling the width of the notches one can also ensure that very little energy is lost due to reflections back into the feed or absorption at the termination.
As the LPDA transmission line 300 may be constructed by other perturbation structures, one having skills in the art would employ different mechanisms for controlling the radiations that are appropriate for the respective perturbation structures, yet still produce similar uniform radiation patterns as described above, or a prescribed radiation pattern for a specific application.
In an alternative embodiment, the notched transmission line 300 may be divided into multiple sections of various lengths. Notches within a section may have the same or different depths, while notches in sections farther away from the feed end 332 become deeper as the distances grow. This allows the radiation to become more uniform along the full length of the LPDA.
Although, as shown in FIG. 3, the perturbations or notches, 313[0:n] on one edge and 315[0:n] on the other of the top plate 310, are symmetrical, one having skills in the art would realize that the perturbations can be unsymmetrical or even just on one edge to emphasize radiation on that edge of the LPDA transmission line 300.
FIG. 4 is schematic diagram illustrating a feed circuit 400 specially designed for the LPDA formed by the LPDA transmission line 300 as shown in FIG. 3. The feed circuit 400 matches the parallel plates 310 and 320 of the notched transmission line 300 to a standard coaxial cable 420 from a RF signal transmitter (not shown), so that reflections back into the transmitter are minimized. In one case, the feed circuit 400 comprises a 180 degree hybrid 410 with input difference terminal 0 connected to the coax cable 420. A 0 degree hybrid output 2 is connected to the top plate 310 or bottom plate 320 of the LPDA transmission line 300, while a 180 degree output 3 is connected to the other plate. The feed circuit 400 may also be used for the termination of the LPDA transmission line 300 in the matched load 350 as shown in FIG. 3. The feed can also be done by using a standard cable connection in which the outer conductor is connected to one of the plates and the coaxial center conductor to the other plate.
In addition, one wants to match the impedance of the LPDA transmission line with the feed impedance. This may be done having the LPDA parallel-plate spacing transition from its normal dimension to one that provides the desired impedance. At the same time, the conductor widths can be changed if needed to provide the desired impedance level to match that of the feed network as described previously.
With the parallel plate structure, two pieces of the transmission line 300 can be easily joined together or even spliced in the field when greater length of coverage by the LPDA is needed.
FIGS. 5A and 5B are cross-sectional views of splicing structures for joining two LPDA transmission lines. The cross-sections are made along lengths of the LPDA transmission lines. Referring to FIG. 5A, a left-hand-side transmission line has a top plate 510 and a bottom plate 515. A right-hand-side transmission line of the same dimension as the left-hand-side transmission line has a top plate 520 and a bottom plate 525. In order to join the left-hand-side and right-hand-side transmission lines, a splice conductor having a top plate 530 and a bottom plate 535 is used. One can think of the LPDA transmission lines being mounted in the conduit 230 as shown in FIG. 2. The conduit 230 is made in two parts that separate and can be snapped, bonded or held together. That being the case, the splice piece 535 can be placed in the bottom section of the conduit 230. The two LPDA transmission lines are laid on top of this splice piece 535. After that the top splice piece 530 is added and the top of the conduit 230 is used to hold everything together. With continued reference to FIG. 5A, one can see that a connection between the top plates 510 and 520 is made through the top plates 530, and a connection between the bottom plates 515 and 525 is made through the bottom plate 535.
Referring to FIG. 5B, the left-hand-side transmission line remains the same as shown in FIG. 5A, however, the right-hand-side transmission line has a wider space between a top end-plate 570 and a bottom end-plate 575. The rest of the top plate 560 and bottom plate 565 of the right-hand-side transmission line have the same spacing as the top and bottom plates 510 and 515 of the left-hand-side transmission line. The wider space between a top end-plate 570 and a bottom end-plate 575 just allows the top and bottom plates 510 and 515 to slide in and maintain tight contacts between the top end-plate 570 and the top plate 510 and between the bottom end plate 575 and the bottom plate 515. In such a way, the left-hand-side transmission line and the right-hand-side transmission line are spliced. However, splice connectors for joining the left-hand-side and the right-hand-side transmission lines need to be carefully designed to minimize reflections from the junctions. Note that the conduit structure can be used to hold the LPDA transmission in alignment even though the LPDA transmission line itself can be rather flimsy.
Designing of the LPDA can be assisted by electromagnetic (EM) modeling software to determine the radiator size, shape, orientation, etc. A properly designed LPDA may be used to cover indoor wireless bands from 800 MHz up to 6 GHz and even beyond.
Although the present disclosure uses notches to illustrate the inventive LPDA structure, one having skills in the art would appreciate that the essence of the present invention lies in the fact that one can use any perturbation along the length of this parallel-plate transmission line to cause radiation. The size, shape and orientation of these radiators can be used to control the radiation bandwidth, radiation level, radiated polarization, etc. Therefore, other kinds of radiators may also be used to form the LPDA, as long as at least one conductor of the transmission line has a plurality of radiators from each of them a substantial amount of transmitted RF energy can be radiated from the transmission line.
The above illustration provides many different embodiments or embodiments for implementing different features of the invention. Specific embodiments of components and processes are described to help clarify the invention. These are, of course, merely embodiments and are not intended to limit the invention from that described in the claims.
Although the invention is illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention, as set forth in the following claims.
Patent Application
20070273528
