Reference is now made to
Antenna 10 comprises a feed post 24, a section 30, and a section 32, all of which are advantageously formed from one planar conductive sheet which is cut and bent to shape, and which is attached to support 16 as described above. Section 30 comprises the section of the sheet on support 16 and acts as a short arm resonating element of the antenna. Section 32 comprises the section of the sheet attached to the side of support 16, and acts as a long arm resonating element of the antenna. Thus section 30 acts as a conductor which resonates in a relatively high frequency band, and section 32 acts as a conductor which resonates in a relatively low frequency band. Dimensions of the sections may be varied, for example by incorporating tuning and/or radiating slots in the sections, to alter the tuning of the sections. Thus, dimensions of a slot 38 in section 30 may be altered to vary the tuning of the antenna in the relatively high band. In some embodiments, dimensions of ground plane section 14 may also be varied to alter the tuning of the antenna. Typically a length of section 14 is so varied, and the length is selected so that a resonant frequency of section 14 with section 30, or with section 32, is within a particular band of frequencies.
Antenna 10 is fed by a coaxial cable 18 having a central conductor 20 connected to feed post 24. A ground shield 21 of the coaxial cable is connected to ground plane 14. Other methods for feeding antenna 10 may be used, such as for example a microstrip, and will be familiar to those having ordinary skill in the art. The feed mechanism couples circuitry 13, typically mounted on PCB 12, with antenna 10. Circuitry 13 typically comprises a receiver and/or a transmitter.
Antenna 10 comprises a ground plate element 28. Ground plate element 28 is a conductive sheet that is attached to support 16, and the ground plate is galvanically connected by a tab 26 to ground plane 14. In contrast with a “standard” inverted F antenna which has a ground that is galvanically connected to its radiating elements, the ground plate element of embodiments of the present invention is not galvanically connected to either section 30 or section 32 of antenna 10. Instead of being galvanically connected to these sections, element 28 is capacitively coupled to section 30, so that element 28 acts as gamma match for antenna 10. Thus, there is an insulating space 34 between a first part of section 30 and ground plate element 28, and an insulating space 36 between a second part of section 30 and the ground plate element. Typically, the width of the insulating spaces is of the order of 0.5 mm or less.
In antenna 10 ground plane element 28 and section 30 may or may not be coplanar. By way of example, element 28 is assumed to be maintained by posts 19 substantially in a plane 33 comprising section 30. The capacitance between the section and the ground plane element, which forms the capacitive coupling, is generated substantially between an edge 31 of section 30 and an upper edge 37 of element 28, and between an edge 39 of section 30 and a side edge 35 of element 28. Edge 31 and 39 comprise a region of section 30 that capacitively couples to element 28.
Varying the capacitive coupling affects the bandwidth and/or resonant frequencies of resonant elements of the antenna 10. Typically, as the coupling increases, the bandwidth of each element increases, and overall dimensions of the antenna elements may be decreased without adversely affecting the antenna performance. In addition, varying the capacitive coupling enables the impedance of antenna 10 to be correctly matched to the desired impedance of cable 18.
Methods for adjusting the capacitive coupling include:
In an alternative embodiment of antenna 10, ground plate element 28 is not co-planar with section 30, and the separation between the element and the section is sufficient to enable them to overlap. In the alternative embodiment, in addition to the methods given above for altering the capacitive coupling, the coupling may also be altered by adjusting the overlap between the section and the ground plate element, and/or adjusting a separation distance between the plane of the ground plate element and the plane of the section.
Ground plate element 96 may advantageously be formed as part of a bracket 97. Element 96 is galvanically connected, typically via bracket 97, to a conducting ground plane 98. Ground plane 98 is assumed, by way of example, to be formed on a PCB 99.
Antenna 80 also comprises a conductive section 86 having a feed post 90. The section and feed post are advantageously formed from one planar conductive sheet which is cut and bent to shape, and which is attached to carrier 82 by posts 91 mating with corresponding holes in section 86. Section 86 is attached to carrier 82 so that the section is beneath plane 83 of ground plate element 96. However, although the section and ground plate element 96 do not galvanically touch, there is no requirement that element 96 and the section are in different planes. By way of example, a portion 87 of section 86 is assumed to be overlapped by, but not to galvanically contact, ground plate element 96. Section 86 acts as short arm of antenna 80, and dimensions of the short arm may be varied so that the section resonates in a relatively high frequency band. Dimensions of the section may be varied by incorporating tuning and/or radiating slots in the section, such as a slot 84, to alter the tuning of the section, generally as described above for antenna 10.
A rod 88, typically a cylindrical conducting wire or a planar section, is galvanically connected to section 86, and is fixedly connected to carrier 82 by a retaining clip 93. A length of rod 88 may be selected, and dimensions of the part of section 86 connected to the rod may be varied, so that the rod together with the connected part form a long arm of antenna 80 that resonates in a relatively low frequency band. Typically, using rod 88 as a cylindrical element connected to planar section 86 improves the operation performance of the long arm compared to using just planar sections.
Antenna 80 may be fed substantially as antenna 10. Herein, by way of example, antenna 80 is assumed to be fed by a coaxial cable 92 having a central conductor 94 connected to feed post 90. A ground shield 93 of the coaxial cable is connected to ground plane 98. The feed mechanism couples circuitry 100, typically mounted on PCB 99, with antenna 80. Circuitry 100 typically comprises a transmitter and/or a receiver.
As for antenna 10, in antenna 80 ground plate element 96 is not galvanically connected to section 86. Rather, as for antenna 10, element 96 is capacitively coupled to the section. There is an insulating space 102 between an edge 103 of section 86 and ground plate element 96, and an insulating space 100 between portion 87 and the ground plate element. A capacitance for space 102 is substantially dependent on a separation between an edge 101 of element 96 and edge 103 of section 84, and the common length of the edges. A capacitance for space 100 is substantially dependent on the separation between portion 87 and element 96, and the common area of overlap. Typically, the dimensions of the separations are similar to that of the insulating spaces in antenna 10.
The capacitive coupling of antenna 80 may be varied using generally the same methods as those for antenna 10, described above. Thus, capacitive coupling of antenna 80 may be varied by changing dimensions of spaces 100 and/or 102, changing dimensions and/or positions of elements defining the spaces, and/or positioning a dielectric at least partly in one or both of the spaces. Variation of the capacitive coupling produces generally similar results for both antennas. Thus, varying the capacitive coupling of antenna 80 may be used to correctly match the antenna to its feed, as well as to alter the bandwidth of section 86 and/or rod 88.
Antenna 180 comprises an insulating substrate 182 of a PCB 183. Conductive strips 191 and 193 are formed on substrate 182, and the planes are separated by an insulating gap 195. A reactive matching circuit 188, comprising one or more reactive elements such as capacitors and/or inductors, is connected between conductive strips 191 and 193. A ground plate element 196, generally similar to element 96, is mounted on substrate 182 so as to galvanically connect to strip 193, and element 196 and substrate 192 are fixedly held in relation to carrier 82 by posts 91.
Antenna 180 comprises a section 186, which except as described below, is generally similar in structure and operation to section 86 of antenna 80. Rod 88 is galvanically connected to a portion of section 186. Section 186 does not comprise a section that is overlapped by element 196, but does include a feed post 185 that is galvanically connected to conducting strip 191.
Antenna 180 is fed by a coaxial cable 200 which has an outer conductor 206 of the cable galvanically connected to ground plate element 196. An inner conductor 204 of the cable is galvanically connected to feed post 185. Thus, section 186 is fed from inner conductor 204. Cable 200 couples antenna 180 with circuitry 210, typically mounted on PCB 99, which comprises a transmitter and/or a receiver.
Because of being mounted on substrate 182, ground plate element 196 is not coplanar with section 186, and there is an insulating gap 202 between section 186 and element 196. The gap provides capacitive coupling between the element and the section, substantially similar to the capacitive coupling provided by gap 102 of antenna 80. The capacitive coupling may be varied generally as described above for antennas 10 and 80.
The capacitive coupling, and the reactance of matching circuit 188, may be varied to match the impedance of antenna 180 in its radiating bands with the impedance of cable 200, as well as to vary the bandwidth of the radiating sections.
A diagram 254 (
It will be understood that the principles of present invention are not limited to a particular type of antenna, such as the inverted F antennas exemplified above. A diagram 260 (
Other types of antenna which may have a capacitive coupling to ground, such as a meander monopole and a multiband antenna having more than two resonating sections, will be apparent to those having ordinary skill in the art, and all such antennas are assumed to be comprised within the scope of the present invention.
It will be appreciated that embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.
This application claims the benefit of U.S. Provisional Patent Application 60/799,956, filed 11 May, 2006, which is incorporated herein by reference.
Number | Date | Country | |
---|---|---|---|
60799956 | May 2006 | US |