The present application relates to antennas, and, more particularly, to radiating dielectric elements that may be used in an antenna employing constant-speed or accelerated superluminal polarization currents and in small form-factor standard antennas based on polarization currents moving at constant superluminal speeds.
Various designs for superluminal (faster than light in vacuo) radiating elements and arrays have been proposed. See, for example, U.S. Pat. Pub. No. 2013/0201073, which is incorporated by reference. Briefly, while matter or energy themselves cannot exceed the speed of light, an array of dielectric radiating elements may be excited in a sequence such that a polarization-current distribution (i.e., wave, chirp, or pulse) moves superluminally. Such a superluminally moving polarization-current distribution emits radiation; superluminal emission technology can be applied in a number of areas including radar, directed energy, communications applications, and ground-based astrophysics experiments.
It is desirable to build such a system using a modular approach with identical dielectric radiator elements closely spaced along a line or along a curve designed to give a desired, quasi-continuous trajectory in the whole volume of the dielectric for the polarization current. Previously designed modular antenna elements had a coaxial cable connected to each antenna element. For each antenna element, the inner conductor of the coaxial cable was connected to the electrode on one side of the dielectric radiator element and the outer conductor (ground) to an electrode on the other side of the dielectric radiator element. The application of a voltage signal to such a connection establishes an electric field across the dielectric radiator element and hence creates the polarization. The connection to ground is straightforward due to the accessibility of the outer conductor. However, the inner conductor requires careful shaping to establish a smooth change in impedance. Moreover, the relative height of the outer conductor to the inner conductor must be replicated to a high precision for each antenna element. Given the manufacturing tolerances, small variations in the relative heights of the conductors may result in wide performance variations. In addition, a concentric conducting tube was provided around the coaxial cable to act as a quarter-wave stub. However, in the original embodiment it was found that the performance of the quarter-wave stub was susceptible to slight variations in manufacturing tolerance, leading to variations in performance from almost identical elements. This is undesirable for industrial antenna production. Besides the inherent complexity, the prior approach with the cable in the z-direction also precluded small form-factor implementation for commercial applications.
A superluminal antenna element having an improved transmission line feed structure, and an array comprising a plurality of such antenna elements, is disclosed herein. The antenna element includes a dielectric base portion having a cutout area, a mode transition element, such as a patch element coupled to the cutout, a transmission line, such as a stripline transmission line connected to the mode transition, and a dielectric radiator element disposed within the cutout.
The cutout of the dielectric base portion has a first plurality of steps and a second plurality of steps, the first and second pluralities of steps being arranged in opposing pairs. The direction between opposing pairs defines an x-direction. The mode transition element is located below and coupled to the cutout area of the dielectric base portion, and energy is transitioned from the stripline to the cavity of the cutout by the mode transition element. In one example, the transmission line is oriented parallel to the x-direction and positioned under the antenna element to form a compact construction. First and second conductive elements substantially cover the first and second pluralities of steps, respectively. The dielectric radiator element is mounted within the cutout area. The dielectric radiator element has first and second spaced ends mounted in a pair of opposing pair of steps. Imposing a time-varying signal on the dielectric radiator element by way of the transmission line, mode transition element, and stepped cutout induces a polarization current in the dielectric radiator element.
The transmission line may comprise a stripline transmission line. In such an example, the stripline transmission line may comprise a metallic trace disposed on a dielectric substrate and be located between two metallic ground planes. The mode transition element may comprise a patch element coupled to the cutout. The patch element may be grounded at one end to at least one of the metallic ground planes of the stripline. A first end of the stripline transmission line may tenninate at a coaxial connector and a second end of the stripline transmission line may terminate at the mode transition element.
The cutout area of the dielectric base portion may be plated with conductive material to form the first and second conductive elements. The dielectric base portion may comprise a glass epoxy laminate.
The dielectric radiator element may be formed from a low-loss-tangent dielectric. The dielectric radiating element may be mounted within an outermost pair of opposing steps. The polarization current in the dielectric radiator element has an electric field that has a strong directional component parallel to the x-direction, which is the direction parallel to the direction between the pairs of opposing steps.
A superluminal antenna array may comprise an array of such antenna elements. When excited in sequence, the polarization current flows through the dielectric radiating element or elements along a length of the array in the y-direction.
A superluminal antenna array may include a dielectric base portion having a cutout, the cutout having a first plurality of steps and a second plurality of steps, the first and second pluralities of steps arranged in opposing pairs; a plurality of mode transition elements, located below and coupled to the cutout area of the dielectric base portion; and a plurality of transmission line feed lines, each being connected to one of the plurality of mode transition elements. A first conductive element may substantially cover the first plurality of steps and a second conductive element may substantially cover the second plurality of steps.
A dielectric radiator element is mounted within the cutout area, the radiator element having first and second spaced ends mounted in an opposing pair of steps. Imposing a time-varying signal on the plurality of feed lines induces a polarization current in the dielectric radiator element.
The plurality of transmission lines comprises a plurality of stripline transmission lines. Each stripline transmission line comprises a metallic trace disposed on a dielectric and is located between two metallic ground planes, and wherein each mode transition element comprises a patch element.
The array may comprise individual antenna elements or larger blocks or groups of components. For example, the first and second conducting elements may be segmented into a plurality of pairs of first and second conducting elements, and each segmented pair of first and second conducting elements corresponds to one patch element and one transmission line feed. Alternatively, the first and second conducting elements comprise metallic plated elements that continue for a length of the antenna array. Additionally, the dielectric radiating element and/or base portion may extend for the length of the antenna array.
The superluminal antenna may have the plurality of transmission feed lines coupled to a plurality of amplifiers. Alternatively, the superluminal antenna may have the plurality of transmission feed lines are coupled to a passive feed network. The passive feed network may comprise a plurality of power dividers and a plurality of delay lines.
The implementation in
The application of voltage across a pair of electrodes creates a polarized region in the dielectric radiator elements 118 between the electrodes 114, 116, which can be moved by switching voltages between the electrodes on and off, or by applying oscillatory voltages with appropriate phase difference between radiator elements. Superluminal speeds can readily be achieved using switching speeds or oscillatory voltages in the MHz-GHz frequency range. The dielectric radiator element 118 between each pair of electrodes 114, 116 contains the polarization current that emits the desired radio-frequency (RF) electromagnetic waves, and thus functions as the radiating medium of each radiator element.
The individual antenna elements 110 allow for a modular approach that is easier to manufacture than previous designs. Superluminal antennas can be made by arrangement of individual antenna elements 110 in different ways. For example, while a straight line array is illustrated in
Though desirable in many applications, a modular approach is not necessary with this new design. Referring to
The cut-out with the larger radius (360) is for guiding the radiation field. The cut-outs and surfaces exposed to the RF-fields are copper-plated to form electrodes 114, 116. In an array of antenna elements, a gap may be provided between the copper plating of adjacent elements. The arrangement shown in
The dielectric radiator element may be made from any low-loss-tangent dielectric with a reasonably high dielectric constant, such as high purity alumina, which has εr=10.
The stripline RF feed 500 illustrated in
The solution
The figures present an optimized solution for a 50Ω strip-line. The inventive concept, however, is more generic and extends to drives of arbitrary impedance and related optimized patch antennas and cut-outs. In another example the stripline drivers are fabricated separately from the antenna elements and then attached.
The drive concept in
Unique properties of this concept include the transfer of a stripline mode into a linear polarization field and current. The mode transfer occurs where the patch 512 or other mode conversion element couples radio frequency energy to the cutout area 310. The concept implementation requires an arrangement (in linear or radial direction) of multiple elements like the one shown in
An advantage of an array of such antenna elements is that they may be excited such that the polarization current has a phase velocity νph along the array faster than the speed of light c (at least in part of or some of the dielectric radiating elements). This phase velocity may be arranged to increase or decrease, yielding acceleration, which is important for focusing of the emitted radiation. Desired operation includes phase velocities larger than c everywhere in the dielectric (both in linear or circular arrangements), and a mode of operation where the phase velocity makes a transition from νph<c to νph>c in the tangential direction as the radius increases for a circular arrangement of elements. The optimization also includes a design with a bandwidth of at least 20% of the center frequency.
Strip-line or micro-strip-line antenna drives according to the present invention are superior for implementation of low-cost low-complexity drives with fixed or increasing phase advance from element to element. The strip-line directly feeds into the antenna element. Strip-lines are preferable to micro-strip-lines, as they are shielded and avoid cross-talk between neighboring feeds. This approach does not preclude an overall coaxial feed, but any conversion from coaxial to strip-line mode is removed from the antenna element itself. Implementation with striplines only, or with coax-to-stripline transitions in the x-direction (instead of the z-direction) also provides superior antennas with a uniquely flat form-factor.
The strip-line to cutout feed allows for a significant reduction of fabrication steps and handling of small elements. Any arrangement of radiator elements can be cut from one piece of G10 dielectric material, and then copper plated to form electrodes. The polarization dielectric can also be added as one single machined piece covering all antenna elements of an arrangement. Then the individual strip-line feeds can be added or one printed circuit board with all striplines of an arrangement can be added (
The design also includes the arrangement of individual elements (
In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention.
This invention was made in part with government support under Contract No. DE-AC52-06NA25396 awarded to Los Alamos National Security, LLC (LANS) by the U.S. Department of Energy and made in part under CRADA number LA11C10646 between CommScope, Inc. of North Carolina and LANS. The government has certain rights in the invention.
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/US16/58857 | 10/26/2016 | WO | 00 |
Number | Date | Country | |
---|---|---|---|
62246369 | Oct 2015 | US |