Communications: radio wave antennas – Antennas – Slot type
Reexamination Certificate
1999-05-24
2001-11-13
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
Slot type
C343S770000
Reexamination Certificate
active
06317094
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to antennas for use in wireless point-to-point and/or point-to-multipoint communication. In particular, the present invention relates to tapered slot antenna elements which radiate and receive microwave and millimeter wave energy and to structures for feeding these elements.
BACKGROUND OF THE INVENTION
Most antennas are passive devices which either radiate or receive electromagnetic radiation. A passive antenna structure can either transmit or receive, and an antenna's transmitting properties can be derived from its receiving characteristic or vice versa. The antenna is connected to a transmission line which carries an electrical signal that is transformed into electromagnetic radiation (in a transmitting antenna) or transformed from electromagnetic radiation (in a receiving antenna). An antenna design should be able to meet the desired criteria for gain, beamwidth, sidelobe level, polarization performance, and bandwidth requirements, while maintaining size/profile (including weight), cost of fabrication, and ease of fabrication at a minimum.
Tapered slot antennas are printed, travelling wave antenna structures which can provide a very wide bandwidth and are also relatively inexpensive to fabricate and integrate with a microwave transmission line. These antennas have a slot which is etched between metallization layers either on the surface of a dielectric substrate or in air. The slot tapers into a narrow slot line which is commonly fed by a microstrip line or other printed transmission line. The microstrip line is a strip conductor which is separated from a ground conductor by a dielectric substrate. However, a problem with the microstrip line is that it has a high transmission loss at high frequencies.
Phased arrays of tapered slot elements provide improved beam reconfiguration capability and improved beam pattern characteristics, particularly in terms of antenna gain. However, prior art feed techniques have limited the number of elements that can be combined into a tapered slot antenna array, because the increasing complexity of prior art feed structure results in increasing transmission losses. At the same time, if feed structures other than printed transmission lines are used, this results in an increase in the antenna array size, particularly thickness, and also in a band-limiting effect.
For instance, U.S. Pat. No. 5,036,335 to Jairam relates to a 45° twist balun configuration for a microstrip line fed tapered slot antenna which improves the return loss of the antenna over a desired bandwidth. However, the feed structure disclosed by Jairam remains unsuitable for feeding a large array of antenna elements, for the reasons given above. Furthermore the structure disclosed by Jairam provides only a limited ability to optimize the return loss for different frequency bands.
As a result, there is a need for structures capable of feeding a tapered slot antenna, and particularly arrays of these antenna elements, which minimize transmission losses, provide a wide band transition that does not significantly curtail the wide band properties of the tapered slot element, is of small size, allow for easy and inexpensive fabrication and integration, and still enable desired performance requirements (including return loss, gain, beamwidth, sidelobe levels, and cross-polarization criteria) to be met.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide improved feed structures for tapered slot antennas.
In a first aspect, the present invention provides a tapered slot antenna structure comprising: (a) a transmission line having a dielectric substrate, a strip conductor feed, and a ground layer, the dielectric substrate having first and second opposing surfaces and the ground layer having front and back opposing surfaces, the strip conductor feed running along one of said first and said second surfaces of the dielectric substrate, the back surface of the ground layer facing and being disposed in parallel to the second surface of the dielectric layer, the dielectric substrate and the ground layer thereby having a parallel disposition relative to one another, and the ground layer further having a feed slot formed within it; (b) a metallization layer lying in a plane which intersects the ground layer at an intersection angle, said metallization layer having a base end connected to the front face of the ground layer and an aperture end, and said metallization layer having a tapered slot formed within it, said tapered slot having an aperture width at the aperture end of said metallization layer and said tapered slot forming a slot line having a slot line width narrower than the aperture width at the base end of said metallization layer; and (c) said feed slot having a first portion and a second portion, the first portion of said feed slot intersecting the slot line in the ground layer and the second portion of said feed slot crossing over the strip conductor feed in a parallel plane manner, whereby the slot line and the strip conductor feed are electromagnetically coupled.
Preferably, the intersection angle is in the range of 45°-90°, and in one embodiment the intersection angle is equal to 90°, so that the metallization layer lies in a plane which is perpendicular to the ground layer and the dielectric substrate.
The structure may be fed by a suspended microstrip line wherein the strip conductor feed runs along the first surface of the dielectric substrate, and the ground layer faces, is disposed in parallel to the second surface of said dielectric substrate, and is spaced from the dielectric substrate such that an air gap is formed between the second surface and said ground layer. Alternatively, the structure may be fed by an inverted suspended microstrip line wherein the strip conductor feed runs along the second surface of the dielectric substrate, and the ground layer faces, is disposed in parallel to the second surface of said dielectric substrate, and is spaced from the dielectric substrate such that an air gap is formed between the second surface and said ground layer. The structure can also be fed by a standard microstrip line wherein the strip conductor feed runs along the first surface of the dielectric substrate, and the ground layer faces and is disposed in parallel to and directly against the second surface of said dielectric substrate.
In a preferred embodiment of the feed slot, the width of the first portion of said feed slot equals the slot line width. Also preferably, the first portion of said feed slot has first and second ends and the second portion of said feed slot has first and second ends, and the first end of the first portion is connected to the first end of the second portion by way of a transition portion in said feed slot such that the first portion and the second portion run perpendicularly to one another. In another embodiment, the feed slot further includes a termination segment connected to the second end of the second portion of said feed slot.
In another aspect, the present invention provides an M×N array of tapered slot antenna elements, where M and N are positive integers greater than or equal to one, comprising: (a) a transmission line having a dielectric substrate, a beam forming network feed, and a ground layer, the dielectric substrate having first and second opposing surfaces and the ground layer having front and back opposing surfaces, the beam forming network running along one of said first and said second surfaces of the dielectric substrate, the back surface of the ground layer facing and being disposed in parallel to the second surface of the dielectric layer, the dielectric substrate and the ground layer thereby having a parallel disposition relative to one another, the ground layer further having a feed slot for each of said tapered slot antenna elements formed within it, and the beam forming network having a strip conductor feed for each of said tapered slot antenna elements; (b) M metallization layers each lying in a plane which intersects the ground layer
Litva John
Wu Chen
Bereskin & Parr
Litva Antenna Enterprises Inc.
Wimer Michael C.
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