Superluminal antenna

A superluminal antenna element integrates a balun element to better impedance match an input cable or waveguide to a dielectric radiator element, thus preventing stray reflections and consequent undesirable radiation. For example, a dielectric housing material can be used that has a cutout area. A cable can extend into the cutout area. A triangular conductor can function as an impedance transition. An additional cylindrical element functions as a sleeve balun to better impedance match the radiator element to the cable.

FIELD

The present application relates to antennas, and, more particularly, to a superluminal antenna for generating a polarization current that exceeds the speed of light.

BACKGROUND

Charged particles cannot travel faster than the speed of light, as is known by Einstein's Special Relativity theory. However, a pattern of electric polarization can travel faster than the speed of light by a coordinated motion of the charged particles. Experiments performed at Oxford University and at Los Alamos National Laboratory established that polarization currents can travel faster than the speed of light. Two rows of closely-spaced electrodes were attached on opposite sides of a strip of dielectric alumina. At time t, a voltage was applied across the first pair of opposing electrodes to generate a polarization current in the dielectric alumina. A short time later, t+delta t, a voltage was applied to the second, adjacent pair of opposing electrodes, whilst the voltage applied to the first electrode pair was switched off, thus moving a polarization current along the dielectric. This process continued for multiple pairs of electrodes arranged along the dielectric. Given the sizes of the devices, superluminal speeds can be readily achieved using switching speeds in the MHz range. More subtle manipulation of the polarization current is possible by controlling magnitudes and timings of voltages applied to the electrodes, or by using carefully-phased oscillatory voltages. The superluminal polarization current emits electromagnetic radiation, so that such devices can be regarded as antennas. Each set of electrodes and the dielectric between them is an antenna element. Since the polarization current radiates, the dielectric between the electrodes is a radiator element of the antenna.

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 antenna elements closely spaced along a line or along a curve designed to give a desired, quasi-continuous trajectory in 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. 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, a relative height of the outer conductor to the inner conductor proved difficult to replicate for each antenna element. Given the manufacturing tolerances, small variations in the relative heights of the conductors resulted 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 very susceptible to slight variations in manufacturing tolerance, leading to large variations in performance from almost identical elements. This is clearly undesirable for antenna applications.

SUMMARY

A superluminal antenna element is disclosed that is operationally stable and easy to manufacture.

In one embodiment, the superluminal antenna element integrates a sleeve (or bazooka) balun and a triangular impedance transition to better match the impedance of the coaxial cable to the rest of the antenna element, preventing undesirable stray signals due to reflection. For example, a dielectric housing material can be used that has a cutout area. A cable can extend into the cutout area. A coaxial, cylindrical conductor connected to the screen of the cable and terminated below the conductive shielding element functions as a sleeve balun analogous to those used in conventional dipole antennas. A triangular impedance transition connects the central conductor of the coaxial cable to one side of the radiator element. The other side of the radiator element is connected by a planar conductor and/or conducting block to the screen of the coaxial cable.

By including a sleeve balun and by using the triangular impedance transition, improved impedance matching can be established between a cable (e.g., 50 Ohms impedance) and free space (e.g., 370 Ohms in the air, gas or vacuum above the radiator element). Not only does the impedance matching provide better performance (e.g. reduced leakage), but the current embodiment of the sleeve balun and impedance transition also allows the antenna element to be very consistent in its operation and replication, irrespective of slight variations in the manufacturing process.

DETAILED DESCRIPTION

FIG. 1shows a superluminal antenna100having a plurality of antenna elements, such as shown at120. Each antenna element has its own cable140coupled thereto for delivering the desired voltage signal to the antenna element. Each antenna element comprises a pair of electrodes, placed on either side of a dielectric material. Individual amplifiers (not shown) are coupled to the antenna elements120via the cables and can be used to control the polarization currents by applying voltages to the electrodes at desired time intervals or phases. The application of voltage across a pair of electrodes creates a polarized region in between, which can be moved by switching voltages between the electrodes on and off, or by applying oscillatory voltages with appropriate phases. Superluminal speeds can readily be achieved using switching speeds or oscillatory voltages in the MHz-GHz frequency range. The dielectric between each pair of electrodes contains the polarization current that emits the desired radio waves, and thus functions as the radiator element of each antenna element.

The individual antenna elements allow for a modular approach, which is easier to manufacture than previous designs. Although the superluminal antenna100is shown as circular, other geometric shapes or configurations can be used. For example, a straight line, curved line or sinusoidal form can be used. Though desirable in many applications, a modular approach is not necessary, and larger blocks of antenna elements can be made using the same principles as described here. For example, radiator elements between antenna elements can be formed from a single monolithic unit or divided into groups of larger antennas.

FIG. 2shows a base portion200of an antenna element. The base portion200is generally a dielectric housing material having a cutout area210and an aperture225for receiving a cable. The dielectric housing material can be formed from a wide variety of dielectrics, such as glass epoxy laminates (e.g., G10). Example permittivity values are between 4 and 5, but other permittivity values can be used. The base portion is shown as wedge shaped, but other shapes can be used. The cutout area210has a main section220into which the cable passes, and a series of opposing steps230,240, the outer pair of which,240, are for mounting a radiator element made from any low loss-tangent dielectric with a reasonably high dielectric constant, such as alumina, as further described below. The cutout area can be a wide variety of shapes, depending on the particular application.

FIG. 3shows the metal components of the antenna element that mount within the base portion200. The inner walls of the base portion200adjacent the cutout area are lined with a conductive material320,370(e.g., copper) for carrying transmission signal and ground to opposing ends of a dielectric radiator element in the fully assembled antenna element. The conductive material forms a ground conductor320and a signal conductor370electrically separated by a layer of non-conductive material360, such as Teflon. When in use, the dielectric radiator element310rests between the upper vertical boundaries of conductors320and370. The radiator element310can be made from any low loss-tangent dielectric with a reasonably high dielectric constant. The coaxial cable350enters the base of the unit, and is surrounded by the coaxial tube functioning as a sleeve balun340. The lower extremity of the sleeve balun340is connected to the screen of the coaxial cable350; the upper extremity can be not connected. A conductive, triangular impedance transition380is coupled between the central conductor of cable350and the signal conductor layer370. At an end wherein the impedance matching element380couples to the signal conductor370, the impedance matching element is approximately the width of the signal conductor and then tapers at an opposite end to couple to the drive conductor in the cable. In applications where negligible leakage of radiation into the area below the antenna element is desired. a conductive block390may be attached to the screen of cable350, but may not make contact with, the upper part of the sleeve balun340. Additional isolation of the balun340can be provided by a circular gap330.

FIG. 4shows an alternative compact embodiment that gives similar antenna performance. Here, the conductive block390is replaced by a conductive slab450that is connected directly to the ground conductor460, and covers (but does not touch) the end of the sleeve balun430. Electrical insulation between the ground conductor460and the signal conductor470is provided by a gap. The coaxial cable440, sleeve balun430and connection410between the cable's central conductor and the conductive impedance transition can be similar to the previously described embodiment.

As shown below, the impedance transition when used in conjunction with the sleeve balun430,340establishes better impedance matching from the coaxial line to the radiator element. This improvement makes the antenna element operationally stable and greatly increases reproducibility against slight variations in manufacturing. The cable can be a coaxial cable having multiple conductors for carrying a signal and ground. Additionally, the cable can include dielectric material positioned between the signal and ground conductors. The cable can be replaced with any desired signal conductor, such as a waveguide, traces on a printed circuit board, etc.

FIG. 5shows a simplified section of the element to illustrate the electrical connection of the cable and sleeve balun to the signal and ground conductors; this differs from previous designs. The signal conductor540couples a drive line530from the coaxial cable to one side of the radiator element. A ground conductor550, encompassing the top of the conductive element (i.e., block or slab), couples the ground from screen520of the cable to the opposite side of the radiator element. The sleeve balun510is connected to a lower part of the screen of the coaxial cable. Consequently, by creating a sleeve balun, and by including the impedance transition, impedance matching is established between the coaxial cable (50 Ohms impedance) and free space (370 Ohms impedance in the air, gas or vacuum directly above the radiator element). Not only does the impedance matching provide better performance, but the sleeve balun and the impedance transition also allow the antenna element to be consistent in its operation and replication.

FIG. 6shows an assembled antenna element400. A conductive block410is positioned within the cutout area and includes a hole therein through which the sleeve balun340containing the coaxial passes. As explained previously, the conductive block is an exemplary conducting element and can be replaced by alternative elements. A dielectric radiator element420is mounted within the cutout area so as to couple at one end to the signal conductor370and, at an opposite end, to ground conductor320. The radiator element can be made from any low loss-tangent dielectric with a reasonably high dielectric constant. The impedance transition and the sleeve balun340act to make the antenna element operationally stable and increase reproducibility against slight variations in manufacturing. The cable can be a coaxial cable having multiple conductors for carrying a signal and ground. Additionally, the cable can include dielectric material positioned between the signal and ground conductors. With suitable modifications to the balun geometry, the cable can be replaced with any desired signal conductor, such as a waveguide, traces on a printed circuit board, etc.

FIG. 7shows a second embodiment of an antenna element wherein a base portion500is rectangular shaped. The rectangular-shaped base portion500can include protruding blocks520positioned at opposing ends of a radiator element530. The blocks520may improve the radiation pattern. Not all features of the antenna element will be described, as it is similar to the wedge-shaped embodiment.

FIG. 8is a flowchart of a method for shielding a superluminal antenna element. In process block910, an array of superluminal antenna elements are provided. In process block920, varying voltage signals are provided, one for each element in the array. The voltage signals can be provided using a series of coaxial or other input cables, signal conductors, or waveguides. In process block930, a voltage signal is transmitted from each cable, signal conductor, or waveguide to its corresponding radiator element. The transmission is made via components that function as a sleeve balun and an impedance transition. In process block940, the transmitted voltage signals are used to induce a moving polarization current inside the dielectric volume formed by the array of radiator elements.