Communications: radio wave antennas – Antennas – Slot type
Reexamination Certificate
1998-09-09
2001-09-11
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
Slot type
C343S897000
Reexamination Certificate
active
06288685
ABSTRACT:
BACKGROUND
The invention relates to a slot antenna.
Wireless radio systems are used in remote metering (e.g., utility metering) applications in which electronic components must be placed in spaces not originally designed for such components. In water metering applications, for example, a transceiver and an antenna typically must fit within a small underground housing originally intended only for a mechanical water meter. In such an application, antenna performance is impeded because the antenna must transmit through the walls and lid of the underground housing and through the ground itself.
SUMMARY
In one aspect, the invention features an annular serrated slot antenna having two annular conductive elements separated by a slot having a serrated edge. A third conductive element, e.g., a shorting post, connects the annular conductive elements together at some point along the slot.
In some embodiments, the annular antenna may be formed on a flexible substrate, and the conductive elements may be formed from conductive tape affixed to the flexible substrate. The serrations may be evenly spaced, and each may have a width that is equal to the spacing between the serrations.
In another aspect, the invention features a serrated slot antenna that is not annular. The antenna includes two generally parallel conductive elements separated by a slot having a serrated edge. A third conductive element connects the conductive members together at some point along the slot.
In other aspects, the invention relates to making a slot antenna. For example, an annular slot antenna may be formed by joining two ends of a generally straight slot antenna to form an annular slot structure. Alternatively, a slot antenna may be made by positioning two annular or straight conductive elements to form a slot between them and connecting a third conductive element to each of the annular conductive elements to form at least one end of the slot. The antenna also may be made by forming a slot pattern on the conductive surface of a flexible substrate. Two ends of the flexible substrate may be joined to form an annular slot antenna. An annular slot antenna also may be formed by removing material from a conductive tubing to form two conductive rings connected by a shorting element at some point along a perimeter of the tubing. Serrations may be formed along an edge of the slot in any of these antennas to create a serrated slot antenna.
Each embodiment of the invention may provide any one or more of several advantages. For example, the antenna may be made small enough to fit entirely or partially within a pre-drilled hole formed in a standard underground housing lid. The antenna also may be housed within a protective structure that passes through such a pre-drilled hole and that positions the antenna above the ground.
Vertical polarization of an antenna may be achieved with a very small vertical dimension (e.g., 0.5″ or less). A simple slot structure may be used to create an antenna having an omnidirectional radiation pattern. The conductors used to form the slot structure may have different heights (an “offset slot” structure), which allows, among other things, more clearance between the radiating slot and an underground housing lid. Furthermore, the antenna may be fed at a position offset from the center of the slot, which provides a simple way to match the input impedance of the antenna with the characteristic impedance of the conductor feeding the antenna.
The antenna may include a dielectric other than air to reduce the wavelength of a transmitted or received signal in the antenna, which in turn allows, among other things, reduction of the slot length and thus reduction of the antenna's overall dimensions. Furthermore, an antenna with a serrated slot operates at a lower resonant frequency than an otherwise identical antenna and therefore reduces or eliminates the need for a dielectric to reduce the antenna's resonant frequency.
The antenna may be fabricated easily and inexpensively from, e.g., a conventional straight slot antenna or from conductive wires, strips, or tape. Other embodiments and advantages of the invention will become apparent from the following description and from the claims.
REFERENCES:
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patent: 2611865 (1952-09-01), Alford
patent: 2611866 (1952-09-01), Alford
patent: 4819003 (1989-04-01), Goto et al.
patent: 5298894 (1994-03-01), Cerny et al.
patent: 5621419 (1997-04-01), Meek et al.
patent: 5917454 (1999-06-01), Hill et al.
patent: 2 291 272 (1996-01-01), None
Fish & Richardson P.C.
Schlumberger Resource Management Services, Inc.
Wimer Michael C.
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