Patent Grant
8743009
1. Statement of the Technical Field
The inventive arrangements relate to antennas, and more particularly to broadband antennas for portable devices
2. Description of the Related Art
Short flexible monopole antennas are commonly used for portable communication devices. For example, Harris Corporation of Melbourne, Fla. offers a broadband blade antenna (Model No. 12011-2710-01) which operates over a 30 to 512 MHz frequency range and is 13 inches long, and a unity gain rubber-duck antenna (Model 12102-2700-01) which operates over (30-870 MHz), which is only 9 inches long. These antennas are compact in size to satisfy customer demands. However, antenna size also has an effect on antenna performance, and it is common for smaller antennas to sacrifice performance to facilitate smaller physical size.
Antenna matching networks are often required in order to facilitate use of a single antenna over a broad range of frequencies. These matching networks perform an impedance transformation function. At each frequency of operation, the matching network transforms an impedance of the antenna to approximately match the input or output impedance of the communication device. This impedance matching function facilitates efficient power transfer between the antenna and the communication device. Matching networks can be formed from lumped elements, RF transmission line sections, or a combination of the two.
Some short flexible monopole antenna designs include matching networks integrated directly into the antenna assembly. Usually, the matching network is integrated into the base of the antenna, near where it connects to the portable communication device. Typically the matching network extends from an output port or antenna connector of the portable communication device, to a base end of the monopole antenna radiating element that is nearest to the radio. Consequently, the RF feed gap of the monopole radiating element may be spaced somewhat away from the chassis of the portable radio in order to accommodate the physical length of the matching network. From the foregoing, it can be understood that a first portion of the overall length of the antenna can be allocated to the matching network and a second portion of the overall length can be allocated to the radiating element. Consequently, the overall length of the antenna assembly is directly affected by the size and arrangement of the matching network. The matching network can be relatively large, particularly when an antenna is designed for handling relatively high power levels. For a fixed length matching network, the relative or percentage portion of the overall antenna length devoted to the matching network actually increases as the radiating element length is decreased.
Embodiments of the invention concern an antenna and a method of making an antenna which facilitates recovering the length of a radiating element that is normally sacrificed in an vertical monopole antenna design to accommodate a matching network. The invention can also be thought of as facilitating a reduction in overall length of a vertical monopole antenna by having a first part of the vertical radiating element occupy the same volume as the matching network.
The antenna of the present invention includes at least one elongated radiating element having a length extending along an antenna axis. The radiating element has a first end portion including an RF feed gap, and a second end opposed to the first end portion. At least a portion of the elongated radiating element closest to the feed gap is arranged to have a helical form comprised of a plurality of coils. The helical form has a helical axis which can be centered on the antenna axis.
A matching network is at least partially disposed within a volume enclosed by the plurality of coils. The matching network is operative to provide an impedance transformation to approximately match an impedance of the radiating element to a portable communication device over a range of frequencies. According to one aspect of the invention, substantially an entire elongated length of the matching network is disposed within the plurality of coils. The matching network will generally include a plurality of lumped element components, and an elongated conductor extending in a direction aligned with the axis. Notably, a conductor forming the plurality of coils is substantially orthogonal to the elongated conductor of the matching network, at least in an area of the helical form nearest the feed gap. The helical form has a coil diameter, a coil pitch and wire diameter which, in combination, are of a configuration operative to achieve a diminution in a reduction in a radiation resistance of the antenna caused by a proximity of the elongated conductor to the feed gap.
In some embodiments, an RF connector extends from the first end portion of the radiating element, and can be electrically coupled to the matching network. The elongated conductor can be electrically connected to the RF connector proximal to a bottom end of the matching network. In such arrangements the elongated conductor extends along a path from the bottom end to a location proximal to an opposing top end, and then continues to a location proximal to the bottom end, where the elongated conductor is electrically coupled to the first end portion of the radiating element. Notably, the antenna of the present invention can be a monopole radiating element, or can be formed as a dipole antenna including two elongated radiating elements.
The invention also concerns a method for reducing a length of an antenna. The method can include forming at least one elongated radiating element having a length extending along an antenna axis, such that the radiating element has a first end portion and a second end portion opposed to the first end portion. The method can continue with arranging at least a portion of the elongated radiating element closest to the feed gap to have a helical form. The helical form can be made of a plurality of coils, such that the coils define a helical axis that is substantially centered on the antenna axis. The method also includes locating an RF feed gap at the first end portion, and coupling the RF feed gap to a matching network including an elongated conductor.
The matching network is advantageously positioned at least partially within a volume enclosed by the plurality of coils so that the elongated conductor extends in a direction aligned with the antenna axis. In some embodiments, the method can include disposing substantially an entire elongated length of the matching network within the plurality of coils. The matching network is positioned such that the elongated conductor is substantially orthogonal to a conductor forming the plurality of coils, at least in an area of the helical form nearest the feed gap. Finally, the method includes selectively determining a coil diameter, a coil pitch and wire diameter of the helical form to achieve a decreased reduction in a radiation resistance of the antenna caused by a proximity of the elongated conductors to the feed gap.
The method can also include positioning an RF connector at the first end portion of the radiating element, and electrically coupling the RF connector to the matching network. Further, the method can include coupling the elongated conductor to the RF connector proximal to a bottom end of the matching network. The elongated conductor can run from the bottom end to a location proximal to an opposing top end, and then continue to a location proximal to the bottom end, where the elongated conductor is coupled to the first end portion of the radiating element.
Embodiments will be described with reference to the following drawing figures, in which like numerals represent like items throughout the figures, and in which:
The invention is described with reference to the attached figures. The figures are not drawn to scale and they are provided merely to illustrate the instant invention. Several aspects of the invention are described below with reference to example applications for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the invention. One having ordinary skill in the relevant art, however, will readily recognize that the invention can be practiced without one or more of the specific details or with other methods. In other instances, well-known structures or operation are not shown in detail to avoid obscuring the invention. The invention is not limited by the illustrated ordering of acts or events, as some acts may occur in different orders and/or concurrently with other acts or events. Furthermore, not all illustrated acts or events are required to implement a methodology in accordance with the invention.
The antenna pattern of certain physically small antennas can improve as the length of the antenna's radiating element is increased. For example, with reference to
Still, it may be noted that only a portion of the overall length of each antenna 102a, 102b is devoted to a radiating element 104a, 104b, and it is the radiating element part of the antenna that primarily affects the antenna pattern. The remainder of the length of each antenna is devoted to the antenna matching network 106, which does not generally affect the antenna radiation pattern. In the example shown, the antenna matching network 106 consumes about 20% of the overall length of the antenna 102b, and about 33% of the overall length of antenna 102b. This means that a relatively large portion of the overall length of each antenna 102a, 102b is effectively wasted because it is used to accommodate the matching network 106 rather than the radiating element 104a, 104b.
Many antenna matching networks 106 are comprised of lumped elements including inductors, capacitors, and resistors. As will be appreciated by those skilled in the art, the size of an element or component in relation to the wavelength of energy propagated through the element, determines whether it is treated as a lumped element versus distributed element. If the size of the element or component is much smaller than a wavelength of the applied RF energy, then the element is normally considered a lumped element. In contrast, where the size of the component is approximately the same as or larger than the wavelength of applied RF energy, then the component functions as a distributed element. The antenna matching network can also include some length of conductors used to communicate RF signal. The conductors are commonly formed as conductive traces on a printed wiring board, and can couple RF energy to the one or more lumped components comprising the antenna matching network. In some cases, the conductive traces can be in the form of an RF transmission line, such as microstrip. In general, such conductive traces extend at least from the antenna connector 101, to a feed gap 108, which is located at a base end of the radiating element. As such, at least a portion of the conductive trace will extend in a direction which is generally parallel to the direction of the radiating element 104a, 104b.
In order to provide for a longer radiating element, without increasing the overall length of the antennas 102a, 102b, a radiating elements 104a, 104b could be extended from the feed gap 108 to the antenna port 101. The antenna matching network 106 can be disposed adjacent to the radiating element. For example, if the antenna radiating element is formed as a hollow conductive tube, the matching network 106 can be disposed inside a hollow tubular portion of the antenna radiating element. Referring now to
The conductive traces used to communicate RF energy to the components on the matching network 106 will generally need to extend from approximately a bottom end 210 toward a top end 212 of the matching network for communicating RF energy to the various components forming the matching network. In order for the antenna to continue to function as a true monopole antenna, the feed gap 108 must remain at the base end 214 of the radiating element 204 as shown. In order to complete this circuit, the conductive trace would also generally need to extend back from the top end 212 to the bottom end 210.
While the arrangement described with respect to
Referring now to
An antenna is most efficient (accepting energy and radiating energy) at the frequency where it has a purely resistive impedance (i.e., the reactance is zero). This condition is sometimes referred to as the resonant frequency. In
Referring now to
Dipole antennas, which have two radiating elements, are modeled in the plots shown in
The above-described problem with radiation efficiency is solved in an embodiment of the invention shown in
The embodiment in
The antenna 402 includes a matching network 406. The matching network can be comprised of a printed wiring board on which is mounted a plurality of lumped element components similar to those shown in
As can be observed in
The conductor 412 is electrically coupled to the radiating element 404 at the base end 409. The base end of the radiating element is the portion nearest to the chassis of portable communication device 400. According to a preferred embodiment, the conductor 412 can be galvanically connected to the radiating element 404 at base end 409, but the invention is not limited in this regard. Other types of inductive or capacitive coupling arrangements are also possible. The specific path of the conductor 412 as shown in
In the embodiment of the invention shown in
When the elongated conductor 412 comprising the matching network 406 is close to and extends across the feed gap 408, the adverse effect upon radiation resistance will tend to be greater when the elongated conductor is aligned with the conductor forming the radiating element. As shown in
If the elongated conductor 412 forming the matching network is further from the feed gap, it will tend to have less interaction with the antenna with regard to radiation resistance. It should be understood that the invention is not limited to matching networks positioned at any particular distance from the feed gap. The invention includes any antenna where interaction between the antenna radiating element and a matching network situated near the antenna feed gap is minimized as hereinafter described by using a radiating element with a helical coil structure at or near the feed gap.
In a preferred embodiment, the coil diameter, wire diameter, and pitch of the helical coils forming the antenna radiating element 404 are selected using computer modeling. The pitch is the distance along the helix axis corresponding to one coil or turn. The modeling can include an iterative process in which coil diameter, wire diameter, and pitch are varied to determine the effect upon radiation resistance and other antenna parameters. Of course, such modeling and optimization must be limited by design constraints such as the desired overall length and diameter of the antenna. The iterative process can further involve selecting an optimal coil diameter, wire diameter, and pitch of the coils forming the helically wound radiating element 404. The pitch and diameter of the helical coils forming the radiating element are considered optimized when the maximum antenna performance is obtained relative to a set of design goals. These design goals can include desired values for radiation resistance, antenna gain, antenna impedance, antenna length, antenna diameter, power handling capability, and so on. The frequency range of interest can include a range of frequencies over which the antenna is designed to operate with relatively low Voltage Standing Wave Ration (VSWR).
The pitch, wire size and diameter of the coils forming radiating element 404 can be the same or different at different locations along the length of the antenna 402. For example, the pitch and coil diameter in the area surrounding the matching network can be selected based on computer modeling to minimize any decrease in radiation resistance caused by conductor 412. However, other portions of the radiating element 404 that are spaced at greater distances from the feed gap will generally tend to have less interaction with the matching network. Accordingly, the pitch and diameter of the helical coils at such locations is less critical, at least with regard to the problem of radiation resistance. Such other portions can have a different helical pitch and diameter or can have a linear form which is absent of any turns. In
With the foregoing arrangements, the antenna matching network 406 can be disposed within or adjacent to a portion of the volume enclosed by the antenna radiating element 404. This permits a shorter antenna to be constructed which is shorter by comparison to the antenna illustrated in
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
All of the apparatus, methods and algorithms disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the invention has been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the apparatus, methods and sequence of steps of the method without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain components may be added to, combined with, or substituted for the components described herein while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined.
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| Number | Date | Country | |
|---|---|---|---|
| 20130044038 A1 | Feb 2013 | US |
