1. Technical Field
The present disclosure relates to antenna design and more specifically to a solderless antenna feed for transmitting and/or receiving a circularly polarized microwave signal.
2. Introduction
Microwave transmission signals are typically transmitted with either linear or circular polarization. In linear polarization, the receiving antenna aligns its frame of reference with the transmitting antenna to achieve acceptable communications. Because this frame of reference can change depending on factors such as feed and reflector orientation, as well as Faraday rotation, antenna designers often exchange linear polarization for circular polarization, which is less affected by such factors. Circular polarization creates a rotating electric field resulting from two orthogonal linear components Ex and Ey, where both Ex and Ey have sinusoidally varying magnitudes equal in amplitude and 90° out of phase with one another. As Ex and Ey vary sinusoidally, a rotating signal is created by combining the horizontal polarization Ex and the vertical polarization Ey.
A common method of creating a circularly polarized signal is to connect a single antenna patch or a set of antenna patches to a feed network which rotates sequentially, with uniform angular spacing between feed points. Due to uniform angular spacing, uniform phase differences of 90° exist between each feed point. As the feed network rotates the signal phase, the feed points sequentially contact the antenna patch or patches with the signal 90° out of phase at each contacting feed point, creating a rotating signal within the antenna.
Microstrip transmission lines, also referred to as circuits, are commonly used to create accurate feed networks. Microstrip transmission lines are pieces of conductive material in the form of narrow strips near a wider grounded conductor which conduct the signal in this application to antenna feed points such that the signal undergoes a 90° phase shift between each feed point. This phase shift occurs by determining specific lengths of the transmission lines to provide the appropriate phase shifts. Because of the thin, planar nature of microstrip transmission lines, a dielectric substrate, which could be solid or a lightweight rigid honeycomb material, often supports the microstrip transmission lines. One disadvantage of traditional microstrip transmission line designs is the use of solder, and particularly the need to solder the microstrip transmission lines to the input points and antenna feed points. Extreme heat, cold, corrosion, or vibration, such as those found in space-based applications, can damage solder joints and break or reduce the signal transmission and reception characteristics of the antenna.
In an ideal, perfect antenna, the creation of the circularly polarized microwave signal would have no energy loss. However for real antennas, energy is lost in three ways: A small fraction of the energy is dissipated as heat and is minimized by using good conducting materials. More significant amounts of energy are lost in the feed network by being reflected back and when the signal conversion to transmitted radiation or from received radiation involves cross-polarization. The reflection loss is minimized by optimizing wave impedance matching in the feed network. Circular cross-polarization occurs due to the lack of a perfect 90° phase shift and/or equal signal amplitude between the two orthogonal linear field components. A cross-polarized signal is a signal polarized orthogonally to the desired polarization. For example, if a transmitting, circularly polarized antenna is creating a Right Hand Circularly Polarized (RHCP) signal, a cross-polarization signal can also be created which is Left Hand Circularly Polarized (LHCP). The cross-polarization weakens the effective signal strength of the intended signal. Therefore, reduction of cross-polarization transmitted or received by the antenna is a desirable characteristic.
Additional features and advantages of the disclosure will be set forth in the description which follows, and in part will be obvious from the description, or can be learned by practice of the herein disclosed principles. The features and advantages of the disclosure can be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the disclosure will become more fully apparent from the following description and appended claims, or can be learned by the practice of the principles set forth herein.
Disclosed herein is an antenna design that requires no solder, thereby increasing reliability, and which can generate and/or receive circularly polarized signals. Instead, all parts are mechanically supported via metal to metal clamping and screw attachments. Similarly, no dielectric is required, although certain embodiments can incorporate a small amount of dielectric material, such as in the input connection. In one exemplary embodiment, all components, except for the final resonance disk on a first end of the antenna, and the lid on the second end of the antenna, contain apertures. A central pin then connects to the final resonance disk, passes through the apertures of all the components, and attaches to the lid on the second end of the antenna. Attachment of the central pin to the final resonance disk and to the lid can occur through threading, nuts, crimping, or other means for securing a pin or screw to a component known within the art.
In another aspect, the central post supports one or more radiating disks, or resonance disks. These disks, which can be electromagnetically coupled, resonate at specific frequencies and power levels, creating a microwave signal. Having two disks stacked together creates a wider operational impedance matching bandwidth than a single disk. The system can incorporate a single disk, two disks, or more than two disks, depending on the desired performance characteristics. The disks can be bowl shaped, and in one embodiment the final resonance disk faces down and the penultimate disk faces up, or in other words, the concave portions of the disks face each other. The radii of curvature of the bowl shaped disks, and whether the bowls are turned up or down, provides a mechanism to help balance the E- and H-plane patterns of the antenna over large angles away from the boresight. In addition, the bowl shapes can provide added mechanical stiffness and strength.
In a transmitting configuration, an input signal is distributed by the feed network such that it excites the resonating disks at four opposite and orthogonally directed points surrounding an aperture in the circuit cavity. The central pin bisects this aperture in a similar fashion as the penultimate disk. The circuit cavity aperture, unlike the penultimate disk aperture, contains crossed slots. Each of the four branches of these crossed slots are excited via electromagnetic coupling from four microstrip feed lines at four excitation points, defined as the regions where each microstrip feed line crosses over an associated slot. The four microstrip feed lines are each short-circuited at one end while they are connected at four successive points along a single microstrip delay line at their other ends. These four connection points are spaced at quarter wavelength intervals, creating progressive 90° phase delayed excitations in each slot branch, which in turn couple electromagnetically to the disks. This arrangement results in resonant currents continuously flowing in a circle around the disks, giving rise to circularly polarized electromagnetic radiation. The use of four feed points also ensures better circular symmetry than the use of only two feed points, and therefore a wider bandwidth of good circular polarization performance, i.e., low cross-polarization effects, particularly on boresight. For good circular polarization operation off boresight, the E-plane (plane of maximum electric field gradient) and H-plane (plane of maximum magnetic field gradient) radiation patterns, which are in constant rotation, need to be of equal amplitude and phase for corresponding angles away from boresight.
The circuit cavity can be an integral or separate subcomponent of the housing. The housing, in addition to containing the circuit cavity, can serve as the grounding plane for the resonating disks. The said grounding plane can also contain crossed slots. In the disclosed embodiment, the grounding plane is flat, however in other embodiments the grounding plane can be non planar in the form of a bowl or a cone, etc. An optional series of fingers positioned at the edge of the housing can extend parallel to the central pin and towards the resonating disks. These optional fingers can improve the off-boresight losses associated with cross-polarization, and further extend the electrical ground.
The circuit cavity is further designed to hold the circuit in close proximity to the crossed slots in the roof of the circuit cavity. Formed from a conductive material, the circuit receives an input signal and outputs the received signal to four excitation points. Those excitation points in turn couple via the slots to the resonating disks. Unlike standard, planar, microstrip transmission line circuits, the circuit disclosed herein is a non-planar circuit. For example, while all the microstrip transmission lines in the feed network are formed in three dimensions, standard microstrip transmission circuits are formed primarily in two dimensions, length and width, ignoring height. Previous antenna designs incorporate a solid dielectric material, a lightweight honeycomb material or expanded foam material to maintain rigidity, essentially supporting the planar microstrip transmission circuit so that it stays in position and does not bend. These standard microstrip transmission circuits also can utilize solder to maintain connections between the circuit and the antenna input/output port, as well as the antenna points or resonating disks. Soldering can be eliminated with standard planar microstrip transmission lines by also using slots in a ground plane to couple to the resonating disks, but the limited two-dimensional topology usually requires longer and awkwardly meandering microstrip feed lines to reach the excitation points while maintaining proper separation from the slots. This is a consequence of the fact that the three λ/4 long microstrip delay line sections usually cannot circle the relatively large crossed slot aperture geometrically in a full 270° arc to allow equal lengths of feed lines to reach the feed points.
By contrast, the disclosed circuit, which is topologically equivalent to a microstrip transmission line, utilizes a non-planar design to overcome the layout problems of two dimensions. In the disclosed circuit for instance, the effective lengths of the delay line sections are shortened by curving them into a cylinder. A conical curvature may also have been used instead, for longer or shorter effective delay line lengths. In addition, the circuit has sufficiently low mass with interconnecting support and curvature in three-dimensions, length, width, and height, to provide sustainable rigidity. In one example, to assure impedance matching everywhere along the circuit, and that the correct phase and power is maintained at each of the excitation points, the strip width in the circuit decreases from the input point to the final excitation point. The amount of mass can be reduced by reducing the separation between the circuit and the cavity walls, thereby requiring a corresponding reduction in strip width to maintain the same transmission line impedance, or by decreasing the thickness of the microstrip transmission circuit, for example. Other mass reduction approaches can be used as well. In another approach, the above mass reduction methods can be replaced by or used in conjunction with different materials which have lower density but sufficiently high surface conductivity, such as low density metals or metal plated plastics. The central pin extends through an aperture in the non-planar circuit, after which it connects to the lid, at which point the antenna can be connected to a satellite, a vehicle, a fixed object, and/or any other location.
In order to describe the manner in which the above-recited and other advantages and features of the disclosure can be obtained, a more particular description of the principles briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only exemplary embodiments of the disclosure and are not therefore to be considered to be limiting of its scope, the principles herein are described and explained with additional specificity and detail through the use of the accompanying drawings in which:
a and 6b illustrate an exemplary housing component;
a and 7b illustrate an exemplary assembled antenna embodiment; and
a and 8b illustrate a second exemplary circuit component.
Various embodiments of the disclosure are discussed in detail below. While specific implementations are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without parting from the spirit and scope of the disclosure.
The present disclosure addresses the need in the art for low-maintenance, solderless and virtually dielectric free antenna with low cross-polarization. When used herein, such terms as “horizontal”, “vertical”, “top”, “bottom”, “upper”, “lower”, “left” and “right” are for descriptive purposes only and are not intended to limit the antenna or components thereof to any particular orientation. Furthermore, the antenna disclosed herein can be reciprocal in that it can receive signals as well as transmit them. Consequently, references herein to “transmitting”, “radiating”, and “generating” signals apply equally to receiving signals. The antenna disclosed herein will be further described with reference to
Having described the overall configuration of the antenna, the disclosure turns to some exemplary components in more detail.
The crossbars leading to the excitation points 406 in this illustrated example are connected at a central point containing the aperture 408, allowing the excitation points 406 to be located as close as possible to the central axis of the antenna. This is desirable since decreasing the distance between the excitation points 406 and the central axis improves off-boresight cross-polarization.
The various embodiments described above are provided by way of illustration only and should not be construed to limit the scope of the disclosure. For example, the principles herein apply equally to space and terrestrial antenna systems, and can include multiple layers of disks, multi-band transmission or reception, and can be adjusted to various materials, such as gold, aluminum, or plastics. Those skilled in the art will readily recognize various modifications and changes that may be made to the principles described herein without following the example embodiments and applications illustrated and described herein, and without departing from the spirit and scope of the disclosure.
Number | Name | Date | Kind |
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4825223 | Moore | Apr 1989 | A |
7123203 | Le Geoff et al. | Oct 2006 | B2 |
20020075197 | Shrader | Jun 2002 | A1 |
Number | Date | Country |
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0393875 | Jan 1995 | EP |
Number | Date | Country | |
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20130050048 A1 | Feb 2013 | US |