The present invention relates generally to the field of microstrip antennas, and more particularly to wideband circularly polarized single layer compact microstrip antennas.
Prior art wideband circularly polarized microstrip antennas generally feature elements that are larger than one wavelength, which is not useful for array antennas. There has been a long-felt need for smaller sized antennas, particularly antenna sizes that are smaller than a wavelength. This invention's long-awaited electrically small wideband circularly polarized compact microstrip antenna with a uniquely shaped radiating arch offers a number of advantages over prior art antennas. An electrically small wideband circularly polarized compact microstrip antenna with a size smaller than a wavelength can be a quite advantageous compact antenna or excellent antenna array structure. The electrically small wideband circularly polarized single layer compact microstrip antenna of the present invention provides the same high efficiency as conventional microstrip antennas, but it also offers a number of key advantages that permit significant decreases in antenna size, without suffering from the disadvantages, limitations and shortcomings of prior art antenna structures.
The present invention fulfills the long-standing need for a significantly reduced antenna length and an electrically small antenna with a microstrip antenna structure fabricated with a segmented radiating arch stacked on a dielectric substrate along with an innovative electrical feed arrangement that produces circularly polarized leaky-wave radiation and permits both a considerably reduced antenna length and high efficiency antenna performance, without suffering from the disadvantages, shortcomings and limitations of prior art microstrip antennas. The antenna of the present invention has a very wide circularly polarized bandwidth for its small size, because it is a successful leaky wave antenna with a bandwidth that is further enhanced due to the curvature of its structure which causes wave propagation path length difference, whether the portion of the wave is propagating near the structures R1 or R2 radius or anywhere in between.
It is an object of this invention to provide an electrically small wideband circularly polarized single layer compact microstrip antenna.
It is another object of this invention to provide an electrically small wideband circularly polarized single layer compact microstrip antenna that permits a substantial reduction in antenna size.
It is yet another object of this invention to provide an electrically small wideband circularly polarized single layer compact microstrip antenna having a semicircular radiating arch stacked on a dielectric substrate and an electrically-isolated feed arrangement that permits both a considerably reduced antenna length and significantly high efficiency antenna performance.
These and other objects are advantageously accomplished with the present invention providing an electrically small wideband circularly polarized single layer compact microstrip antenna comprising stacking a radiating arch, a dielectric substrate and a ground plane to provide a substantially reduced antenna length and significantly high efficiency antenna performance. This invention also encompasses an antenna array with a number of radiating arches and methods for providing substantial reduction in antenna size with an electrically small wideband circularly polarized single layer compact microstrip antenna.
The electrically small wideband circularly polarized single layer compact microstrip antenna of the present invention advantageously comprises a radiating arch, a microstrip dielectric substrate, a ground plane and a coaxial connector that is insulated from one segment of the radiating arch in an innovative stacking arrangement that provides an electrically small, reduced length for a microstrip antenna. Leaky-wave radiation can be excited in the waveguide of periodically placed microstrip patches on a dielectric substrate stacked on a ground plane. When several segments of the radiating arch form a microstrip antenna cavity with narrow gaps between the segments, the radiation is emitted not only from the conventional radiation edges but also from the dielectric substrate's top surface gaps, which is usually covered by a single patch in a prior art rectangular microstrip antenna. In fact, the radiation from the top surface gaps of the conventional leaky-wave microstrip antenna is much stronger than the radiation emitted from the edge of the dielectric substrate surfaces. When the radiated power increases relative to the stored energy in the cavity, the Q factor becomes small, which results in a large bandwidth. However, impedance matching will be harder to accomplish for a large bandwidth because the resistive part of the input impedance exceeds the maximum value when a conventional electrical feed is used. Therefore, a different type of electrical feed arrangement is needed for impedance matching when the Q value becomes very small.
In order to overcome the shortcomings and limitations of prior art leaky-wave microstrip antennas and incorporate a different type of electrical feed arrangement, the present invention provides a center probe that is insulated from the radiating patches so that the electrical feed current is confined to the center probe to provide an increased input resistance. This insulated feed approach, the stacking arrangement and the circularly polarized radiation all result in a significantly reduced antenna length that is substantially shorter than conventional prior art microstrip antennas, without suffering from any of the disadvantages, drawbacks and limitations associated with much longer prior art conventional antennas.
The size of any microstrip antenna is determined by the wavelength within the substrate. For example, the length of a rectangular microstrip antenna is about half of the wavelength within the dielectric medium under a radiating patch. In order to reduce the size of the segments of the radiating arch, the dielectric constant must be increased substantially for a smaller effective wavelength in the medium. The antenna's efficiency usually decreases with a substrate having a high dielectric constant. This invention's electrically small wideband circularly polarized single layer compact microstrip antenna advantageously combines a number of antenna components, including a microstrip dielectric substrate, in an innovative stacking arrangement that provides a significant reduction in antenna length.
Referring now to the drawings,
The electrical fields in this invention's electrically small wideband circularly polarized single layer compact microstrip antenna 10 are perpendicular to all straight edges of the segments 16–20 found across the gaps 21 and the ends 27 and 28. As the energy leaks by propagating under the segments 16–20 of the radiating arch 13, the electrical filed rotates. When the wave propagates a quarter guide wavelength in the dielectric substrate 12 under the radiating element 13, the antenna gap direction also rotates 90°, thus making the antenna circularly polarized. The radiating arch 13 may be made from any conductive metal, and in the preferred embodiment it is composed of copper. Ground plane 13 may also be made from conductive materials such as copper and aluminum. The low-loss dielectric substrate 12 may be composed of any suitable dielectric material such as Duroid™.
A number of variations of the electrically small wideband circularly polarized single layer compact microstrip antenna 10 are considered to be within the contemplation of this invention. For example, the arc-shaped segments 16–20 may be flat and can be arranged in a semicircular shape, the plurality of gaps 21 can be narrow and may have a gap width of about 0.2 mm, the ground plane and radiating arch can each be composed of a conductive metal, including copper. Additionally, the increased bandwidth being achieved by increasing a ratio of R2/R1 or by adjusting said gap width.
The compactness of this invention's electrically small wideband circularly polarized single layer compact microstrip antenna 10 also permits the antenna array embodiment depicted in
In this particular antenna array 40 depicts a 3 by 3 element array structure, which can be in any M by N array where M and N are any numbers. In this antenna array 40 of the present invention, instead of feeding the nine radiating arches 42 with nine coaxial connectors, one can simplify and economize the power supply requirements by using a stripline power divider network behind the ground plane and feeding the RF energy by using coupling holes through the ground plane, by means well known in the antenna arts. Many of the variations that apply to the antenna embodiments can also apply to the antenna array.
The present invention also encompasses a method for decreasing a wideband circularly polarized compact microstrip antenna with a given length, AL, comprising the steps of arranging a plurality of flat arc-shaped segments in a semicircle, the segments terminating in straight edges that define a group of narrow gaps between the segments; forming a radiating arch from the segments, with the radiating arch having an inner edge, an outer edge, a first straight end, a second straight end and a path length difference between the narrow gaps in the radiating arch, the inner edge being shorter than said outer edge; placing the radiating arch on a top surface of a microstrip dielectric substrate, the dielectric substrate being thicker than the radiating arch; stacking the microstrip dielectric substrate on a conductive ground plane, with the dielectric substrate being at least as thick as said ground plane and projecting a center probe of a coaxial connector upwardly through the ground plane, dielectric substrate and an opening in a first segment, the opening having an opening diameter greater than a probe diameter of the center probe in order to prevent electrical contact between the center probe and the first segment. Forming the antenna with the given length, AL, and a given bandwidth to generate a leaky wave radiation, the antenna being electrically small; generating a plurality of electrical fields perpendicular to the first end, the second end and the straight edges and permitting the leaky wave radiation to leak by propagating under the segments, the radiating arch, perpendicular electrical fields and path length difference advantageously causing an increased bandwidth and resulting in a wideband circularly polarized radiation with a 47% bandwidth permitting a decreased antenna length, AD. Many of the variations that apply to the device embodiments can also apply to this invention's method.
It is to be understood that such other features and modifications to the foregoing detailed description are within the contemplation of the invention, which is not limited by this description. As will be further appreciated by those skilled in the art, any number of configurations, as well any number of combinations of circuits, differing materials and dimensions can achieve the results described herein. Accordingly, the present invention should not be limited by the foregoing description, but only by the appended claims.
The invention described herein may be manufactured, used, imported, sold, and licensed by or for the Government of the United States of America without the payment to me of any royalty thereon.
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