Patent Application
20080284660
Not applicable.
Not applicable.
Not applicable.
1. Technical Field
This invention generally relates to radio wave antennas for communications and, more specifically, to planar type antennas.
2. Background Art
The primary antenna requirements for numerous communication networks, particularly of mobile type, are compact structure, wide beam, and enough efficiency over a specific bandwidth. Cellular telephone handsets and GPS (global positional system) user equipment are examples of devices which typically have such requirements.
Another important requirement is enough isolation between the antenna and the platform to which the antenna is attached to minimize detuning of the antenna due to the presence of the platform.
The patch antenna is one type widely used when attempting to fill the above requirements. Although patch antenna have low profiles, they usually cannot provide as much isolation from the environment as is desired.
The quadrifilar helical antenna (QFH), particularly of printed type, is another typical candidate. One of the main drawbacks for QFH antennas, however, is that they often do not have low profiles and substantial miniaturization effort may then be necessary. Mass production of these antennas can also be difficult and expensive, particularly when they are loaded with a dielectric material such as ceramic.
Accordingly, there remains a need for improved antennas, particularly for mobile communications applications.
Accordingly, it is an object of the present invention to provide an improved planar antenna.
Briefly, one preferred embodiment of the present invention is a planar antenna. A top and bottom conductor are provided that are both nominally planar in shape and that are oriented substantially planarly parallel. The top and bottom conductor thus form an antenna interior region there between. The top conductor includes two radiating conductors that each have an inner end and a distal end. A feed extends from outside of the planar antenna, through the antenna interior region, and to the top conductor. The feed includes a balun and has a first feed conductor that connects to the inner end of the first radiating conductor and a second feed conductor that connects to the inner end of the second radiating conductor.
These and other objects and advantages of the present invention will become clear to those skilled in the art in view of the description of the best presently known mode of carrying out the invention and the industrial applicability of the preferred embodiment as described herein and as illustrated in the figures of the drawings.
The purposes and advantages of the present invention will be apparent from the following detailed description in conjunction with the appended figures of drawings in which:
a-b are perspective views of a balanced planar antenna in accord with the present invention, wherein
In the various figures of the drawings, like references are used to denote like or similar elements or steps.
A preferred embodiment of the present invention is a planar antenna. As illustrated in the various drawings herein, and particularly in the view of
a-b are perspective views of a balanced planar antenna 10 in accord with the present invention, wherein
When oriented as shown in the figures herein, the planar antenna 10 can be described as having a defined top 12 and a defined bottom 14. The planar antenna 10 is preferably embodied having an overall shape that is either rounded or rectangular (as shown), but considerable variation is also possible. For example, rounded embodiments can resemble circular, elliptical, or other cylinders and cuboid embodiments can resemble cubes, rectangular boxes, or trapezoidal box shapes and can even have rounded comers.
The principle features of the planar antenna 10 are an antenna body 16 having a top conductor 18, a bottom conductor 20, one or more side walls 22, and an antenna interior region 24 formed there between. The planar antenna 10 further includes a feed structure 26 and a balun 28, and the planar antenna 10 may optionally include a radial choke 30 (shown in all of the figures herein).
The top conductor 18 and the bottom conductor 20 preferably are nominally planar and oriented to be substantially planarly (in respective planes) parallel to each other. The side wall 22 (or side walls 22, in the case of the square embodiment shown) may be either conductive or not. In
The antenna interior region 24 may be filled with an ambient gas or vacuum, or filled with another dielectric material. In the inventors experience, the antenna interior region 24 is preferably of a material having a high dielectric constant, e.g., greater than 4.
The top conductor 18 includes two substantially similar radiating conductors 32 which are preferably spiral shaped and which each extend from a respective inner end 34 to a respective distal end 36. [Of course, the inventive planar antenna 10 can be used both for transmitting and receiving and the radiating conductors 32 emit energy when used for transmitting and absorb energy when used for receiving.]
The feed structure 26 is preferably coaxial. In the embodiment of the inventive planar antenna 10 shown in
The feed structure 26 is electrically connected to the top conductor 18 in any of various manners. In the embodiment shown in
The impedance “seen” by the feed structure 26 is not necessarily equal to its characteristic impedance, e.g., 50 Ohms, so it may be desirable to provide impedance matching in the planar antenna 10. Various conventional techniques can be used for this. On example is quarter wavelength matching. Another is the use of a matching circuit comprising a capacitance (or capacitive element) and an inductance (or inductive element) at the feed point. This can then be provided at the antenna top (for the case shown in
To have the planar antenna 10 be balanced the balun 28 is provided, and this can also be of various types. For example, in
The feed structure 52 again preferably includes a coaxial line 56 that has an inner conductor 58, an outer conductor 60, and a feed interior region 62. Instead of a coaxial line passing through the antenna body 64, however, here two conductive posts 66 pass through an appropriately modified antenna body 64.
The inner conductor 58 is electrically connected at a first juncture 68 to one post 66 that, in turn, connects to a feed point 70 at the inner end 34 of one radiating conductor 32. This post 66 can be a discrete element (as shown) or it can simply be a part of the inner conductor 58 that extends beyond the coaxial line 56 all the way to the top conductor 18. The outer conductor 60 is electrically connected at a second juncture 72 to the other post 66 that, in turn, connects to a connection point 74 at the inner end 34 of the other radiating conductor 32. The balun 54 in the embodiment of the planar antenna 10 depicted here in
All of the figures include the optional radial choke 30. The radial choke 30 provides improved isolation between the planar antenna 10 and the environment that the planar antenna 10 is used in, The radial choke 30 also helps the balun 28, 54 to provide sufficient electrical performance. When present, the radial choke 30 includes a conductive top plate 76, a conductive bottom plate 78, and a choke interior region 80 located there between. The top plate 76 typically is the same as the bottom conductor 20 of the antenna body 16. The bottom plate 78 may by a discrete element or it may be provided by the application in which the inventive planar antenna 10 is being employed. The choke interior region 80 is preferably also filled with a dielectric material.
Various techniques and materials can be used to manufacture embodiments of the inventive planar antenna 10. For example, the top conductor 18 and the bottom conductor 20 can be made from sheet metal (e.g., copper) or can be deposited (e.g., plated, sputtered, etc.) on to a solid dielectric material in the antenna interior region 24. As already noted, the side walls 22 of the antenna body 16, 64 can be covered with a conductive layer or not. In the inventor's experience, this may particularly depend on the dielectric material filling the antenna interior region 24. If this material has a very high dielectric constant, e.g. greater than 70, then using non-conductive side walls 22 may provide better electrical performance for the balun 28, 54 or for the planar antenna 10 as a whole.
Many known miniaturization techniques can also be used in embodiments of the planar antenna 10. For example, dielectric loading and meandering the radiating conductors can be utilized to reduce antenna size. The bandwidth can also be increased using shapes for the radiating conductors (e.g., a tapered form), as is generally known in the art.
The planar antenna 10 can particularly utilize materials with high dielectric constant, e.g. greater than 4, and a balance structure to constrain the antenna near field. As the planar antenna 10 is balanced, it prevents common mode noise from entering the receiver through the antenna path. Embodiments of the planar antenna 10 therefore are highly tolerant to the proximity of people, other components and other antennas.
Using material with a high dielectric constant can also help reduce the antenna size, while maintaining high application efficiency. This also can help such embodiments have a very sharp filtering response, and hence reduce the need for any additional filtering between the planar antenna 10 and a receiver or transmitter.
While various embodiments have been described above, it should be understood that they have been presented by way of example only, and that the breadth and scope of the invention should not be limited by any of the above described exemplary embodiments, but should instead be defined only in accordance with the following claims and their equivalents.
This application claims the benefit of U.S. Provisional Application No. 60/948,420, filed Jul. 6, 2007, hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60948420 | Jul 2007 | US |
