Patent Grant
8482475
The present invention relates to the structure of a compact radiating element structure to be implemented in a fully electronic steerable beam antenna.
Many existing and future mobile vehicular applications require high data rate broadcasting systems ensuring full continental coverage. With respect to terrestrial networks, satellite broadcasting facilitates having such continuous and trans-national coverage of a continent, including rural areas. Among existing satellite systems, Ku-band and Ka-Band capacity is widely available in Europe, North America and most of the other regions in the world and can easily handle, at a low cost, fast and high-capacity communications services for commercial, military and entertainment applications.
The application of Ku/Ka-band to mobile terminals typically requires the use of automatic tracking antennas that are able to steer the beam in azimuth, elevation and polarization to follow the satellite position while the vehicle is in motion. Moreover, the antenna should be “low-profile”, small and lightweight, thereby fulfilling the stringent aerodynamic and mass constraints encountered in the typical mounting of antennas in airborne and automotive environments.
Typical approaches for beam steering are: full mechanical scan or hybrid mechanical electronic scan. The main disadvantages of the first approach for mobile terminals is the bulkiness of the structure (size and weight of mechanical parts), the reduced reliability (mechanical moving parts are more subject to wear and tear than electronic components) and high assembling costs (less suitable for mass production). The main drawback of hybrid electronic steering is that the antenna still requires mechanical pointing; partially maintaining the drawbacks of mechanical scan antennas.
An advantageous approach is to use a full electronic steerable beam antenna, where, in azimuth and in elevation, the scan is performed electronically. This approach doesn't require mechanical rotation. These characteristics facilitate a reduction in the size and the “height” of the antenna that is important in airborne and automotive applications, and facilitate a better reliability factor than a mechanical approach due to the lack of mechanical parts.
In fully electronic phased arrays, the integration of the electronic components within the antenna aperture represents a big challenge due to the high number of components required. Often, this aspect drives the antenna design (element spacing, array lattice, element rotation) leading to a decrease of the antenna performance. The ideal configuration would consist in a radiating element integrating all the electronics in a surface area not larger than a patch antenna of the radiating element. In this way, the complete array would be designed around the radiating element only and optimized for its radiating performance.
In an exemplary embodiment, a radiating cell of an antenna array comprises a compacted hybrid as part of a stripline feeding network, a radiating element having slots rotated with respect to the compacted hybrid, and a feed circuit layer in communication with the stripline feed network via vias. Furthermore, the compacted hybrid has two input ports and two output ports, where the input and output ports of the compacted hybrid are non-orthogonal and non-parallel to the slots of the radiating element. In another embodiment, blind vias connect the compacted hybrid with the feed circuit layer. The length of the blind vias is smaller than the diameter of the vias. Moreover, in an exemplary embodiment, the radiating cell is compact and has a radius of ½ wavelengths or less.
In accordance with another exemplary embodiment, a modular phased array comprises a ground plane with a first side and a second side, where the ground plane has a slot. The modular phased array also comprises a patch antenna located on the first side of the ground plane, and a feed network located on the second side of the ground plane. In an exemplary embodiment, the ground plane isolates the patch antenna from the feed network. The feed network includes a compacted hybrid with two output ports. In an exemplary embodiment, the ground plane comprises slots that are non-orthogonal and non-parallel to the two output ports of the feed network. In another exemplary embodiment, the distance from the center of the patch antenna to the farthest output port of the two output ports of the compacted hybrid is ½ wavelengths or less.
Advantages of the invention and the specific embodiments will be understood by those of ordinary skill in the art by reference to the following detailed description of preferred embodiments taken in conjunction with the drawings, in which:
While exemplary embodiments are described herein in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that logical electrical and mechanical changes may be made without departing from the spirit and scope of the invention. Thus, the following detailed description is presented for purposes of illustration only.
In accordance with an exemplary embodiment, and with reference to
In an exemplary embodiment, this separation of layers prevents, or substantially prevents, the spurious radiation from the feed circuit layer from affecting the overall pattern of the antenna. The radiation from patch antenna 115 does not pass through ground plane 110, thereby substantially isolating patch antenna 115 and feed line 105 from each other. This isolation improves the signals by decreasing mutual-inference from circuitry radiation 103 and patch antenna radiation 101. In contrast, as depicted in
In an exemplary embodiment, an antenna assembly includes at least one radiating element, at least one dielectric layer, a ground plane with a slot, and a microstrip line. The ground plane is located between the microstrip line and the radiating element(s). In one embodiment, the radiating element is a patch antenna. In another embodiment, the radiating element is at least one of a dipole, a ring, and any other suitable radiating element as would be known to one skilled in the art.
In an exemplary embodiment, radiating element structure 100 further comprises a dielectric layer that separates other antenna assembly components from one another. The dielectric may be air or any material that separates patch antenna 115 from ground plane 110 and allows signals to pass through the dielectric layer. In an exemplary embodiment, the dielectric material is a foam material. For example, the foam material may be Rohacell HF with a gradient of 51 or 71. Moreover, dielectric material may be any suitable material as would be known in the art.
In an exemplary embodiment, a ground plane with slots is configured to communicate signals through the slots only, thereby substantially separating the feed circuit layer from the radiating circuit layer. The substantially complete separation of the feed circuit layer from the radiating circuit layer facilitates separately optimizing the materials and independently designing the two layers of the antenna. Typically, requirements for microwave circuits and antennas are very different: microwave circuits often use “high permittivity” dielectric substrates to reduce the size of the circuit, reduce the lines' spurious radiated power and reduce the coupling between the lines. Furthermore, patch antennas are typically based on “low-permittivity” dielectric substrates that facilitate higher radiation efficiency, lower losses and larger bandwidth.
The two ideals for microwave circuits and antennas are clearly in contrast if the radiators and the feed lines are on the same side of the ground plane and share the same dielectric material. In an exemplary embodiment, the separation of feed circuit and radiators by a ground plane simplifies the design since the feed circuit layer on a first side and the radiating circuit layer on an opposite second side may be independently adjusted, and designed without heavily considering the possible interactions (couplings) between feed circuits and radiators. In an exemplary embodiment, the slot, the patch antenna, and the feed network can be optimized independently since all three are separated and on different layers. An exemplary radiating element structure facilitates locating lines and/or components very close to the slots without affecting the radiation characteristics. In typical prior art configurations with feed circuit and radiators on the same side of the ground plane, it is preferable to leave as much empty surface as possible under the patches to avoid unwanted coupling between feeding circuits and patches. This unused area represents a large portion of the antenna, reducing the space available for feed line routing. In accordance with an exemplary embodiment, with a ground plane separating the patch antenna and the feed circuit layer, feed lines are routed throughout the area underneath the patch antenna while avoiding the area near the slots.
In accordance with an exemplary embodiment, a slot is used to couple excitation signals from the feed lines to the patch antenna. In an exemplary embodiment, and with reference to
Furthermore, in an exemplary embodiment, the size of the slots is optimized in order to obtain the best impedance matching between the patch antenna and the feed circuit without changing the size of the patch. In one exemplary embodiment, optimization is accomplished using computer simulations. For example, in one exemplary embodiment, the length of the slot is smaller than a ½ wavelength. Once the best impedance matching is achieved, the patch size can be modified to center the frequency band as desired without affecting the matching. Therefore, the presence of the slots gives additional degrees of freedom when trying to satisfy simultaneous requirements of impedance matching and frequency characteristics, such as tuning and bandwidth.
The benefits of using a compact slot, such as an “H”-shaped slot, include a more compact size compared to a linear slot and offering a smaller required surface for coupling with the patches. Stated another way, more patches can be fit in the same space with a compact “H”-shaped slot, or any similar compact slot, than with a linear slot. In addition, a compact slot design with optimized size increases the polarization purity as described above, and ensures a low coupling between two orthogonal polarizations.
In an exemplary embodiment, a slot feed excites a very pure resonant mode on a patch antenna with a very low cross polarization component. This excitation method provides much better polarization results than other feed models, such as, for example, line feed, coaxial-pin feed, and electromagnetic coupling feed models. In an exemplary embodiment, the cross polarization level is below −15 dB. In another embodiment, the cross polarization level is below −20 dB. In yet another exemplary embodiment, the cross polarization level is below −25 dB. As previously described, in an exemplary embodiment, a ground plane is located between microstrip lines and the radiating element such that spurious radiation generated by the microstrip lines does not contribute to the total radiation pattern. The separation of feed line circuits from radiating elements avoids spurious radiation from circuits, and thus avoids causing the cross-polarization level to rise.
An exemplary array antenna comprises radiating elements based on the use of stacked patch resonators. The designed “stacked resonator” structure provides enhanced design flexibility and facilitates various improvements. In accordance with an exemplary embodiment and with reference to
In an exemplary embodiment, the two patches on the stack are positioned at a given spacing and have a small difference in size that allows increasing the bandwidth of the radiating element. Adjusting the size of the two patches relative to one another is another design factor as would be known to one skilled in the art. In addition, other factors may be adjusted as would be known to one skilled in the art. In an exemplary embodiment, each patch is optimized to resonate on a specific frequency band, and the combination of the different bands results in a larger bandwidth. This is an important characteristic where more than 20% of bandwidth is required in a design. The stacked configuration provides more bandwidth than necessary and hence gives more flexibility in the design to meet other design requirements. In accordance with an exemplary embodiment, the combination of the slot in a quasi resonant mode with the resonant patch facilitates an increase in the matched bandwidth of the radiating element. In one exemplary embodiment, the bandwidth is increased from 5% of bandwidth of a simple line-fed patch to more than 20% of bandwidth of a stacked patch configuration. In another embodiment, the bandwidth is increased from 5% to 30% of bandwidth, depending on the specific application.
With respect to an antenna array and spacing between radiating element structures, in phased array antennas, the scan range determines the element spacing. In an exemplary embodiment, for a broad scan range (e.g. >+/−50°) the elements remain within a distance less than 0.6 wavelengths of each other. The design of a radiating element for an array grid smaller than 0.6 wavelengths involves complex design aspects. For example, in such complex designs the directivity of the element needs to be compatible with the element spacing. An approximate rule to determine the directivity (D) from the element spacing is:
Applying this rule, an array lattice spaced at 0.6 wavelengths would require an element directivity of 5.8 dBi. The achievement of such directivity is rather challenging with single patch elements. In an exemplary embodiment, stacked patches can be used to decrease the directivity of the radiating element.
Moreover, in an exemplary embodiment and with reference to
To scan at low elevations in phased array antennas, it is important that the radiating element offers a uniform radiation in azimuth with a usable value of directivity at low elevation. The use of a combination of stacked patches and slotted patches allows obtaining a radiating element with a broad radiation pattern, for example with a roll-off of 6.5 dB from Zenith down to 20° of elevation as depicted in
A phased array antenna is composed of a large number of radiating element structures. In accordance with an exemplary embodiment, each radiating element structure comprises a large number of components. The components may include RF combiners, electronic components, power supplies, interconnections, and the like. An assembly defined by the radiating element structure and all the components can be defined as an “elementary radiating cell” of the phased array. In an exemplary embodiment, the elementary radiating cell is designed using three principles that combined together lead to a unique optimized design.
Elementary radiating cells typically require a large amount of space and can have a strong impact on the antenna layout by limiting the minimum distance to which the elements may be spaced. This results in a limitation of the antenna scan capabilities.
In contrast,
In an exemplary embodiment, the combiner is optimized to reduce the length of the cell.
In addition, in an exemplary embodiment, a dual polarized radiating element is connected to a hybrid combiner using two paths of equal length. As illustrated by
In an exemplary embodiment, a compact hybrid combiner comprises two input ports and two output ports. The two input ports and two output ports are part of the two transmission paths. Furthermore, in an exemplary embodiment, the two input ports and two output ports of the compact hybrid are non-orthogonal and non-parallel to the slots of the radiating element. In other words, a center axis of a slot in the ground plane is oriented at an angle to the ports of the compact hybrid. In one embodiment, a center axis of the slot of the ground plane is at a 45° angle to the output ports of the compact hybrid, which is part of the feed network. In another embodiment, a center axis of the slot of the ground plane is at an angle to the output ports of the compact hybrid within the range of 20-70°. Moreover, a center axis of the slot of the ground plane may be at any angle to the output ports of the compact hybrid that is not n*90°, where n is an integer.
In accordance with an exemplary embodiment, electronic components like LNA, phase shifters, DC power supply and control logic are integrated within the elementary radiating cell without increasing the elementary radiating cell size in the radial direction starting from the radiating element center. As previously described with respect to
In accordance with an exemplary embodiment and with reference to
In one exemplary embodiment, an asymmetrical configuration of stripline layers is implemented. For example, beam forming network layers and feed line circuit layers may have an asymmetrical configuration. This specific selection allows reducing the length of the vias on the bottom part of the radiating cell buildup. In an exemplary embodiment, the reduction of these vias is of primary importance in order to allow them to be implemented as “blind vias”. In an exemplary embodiment, blind vias are vias manufactured by drilling the boards to a particular depth, but not all the way through the boards. In an exemplary embodiment, the vias are metalized by depositing copper or similar metal from the open end. Blind vias are limited in that the length is generally less than the diameter of the via. Therefore, their length determines the minimum diameter. In other words, the longer the blind via, the larger the diameter of the via.
In an exemplary embodiment, the diameter of the vias is also related to the RF performance of the vias themselves. For example, a thin via would allow a better RF impedance matching in comparison to a thick via. Therefore, for RF applications it is of primary importance to limit the length of the blind vias in order to be able to implement them with a small diameter. In an exemplary embodiment and with reference to
A compact elementary radiating cell is useful if designing a phased array antenna with limited space that is configured for low elevation scanning. It is also beneficial to implement a triangular lattice for improved radiation pattern.
The size of the elementary radiating cell is of primary importance for an effective phased array implementation. An oversized large elementary radiating cell would require more spacing and result in the element having a limited scan capability. Moreover, the element rotation may also be determined by the elementary radiating cell size and shape. Additional details can be found in U.S. patent application Ser. No. 12/417,513, entitled “Subarray Polarization Control Using Rotated Dual Polarized Radiating Elements”, which was filed on Apr. 2, 2009 and is incorporated herein by reference. A particular element rotation may result in improved polarization characteristics. However, the elementary radiating cell consumes an adequate size and shape to arrange the elements in this particular configuration.
In an exemplary embodiment and with reference to
The present invention has been described above with reference to various exemplary embodiments. However, those skilled in the art will recognize that changes and modifications may be made to the exemplary embodiments without departing from the scope of the present invention. For example, the various exemplary embodiments can be implemented with other types of power supply circuits in addition to the circuits illustrated above. These alternatives can be suitably selected depending upon the particular application or in consideration of any number of factors associated with the operation of the system. Moreover, these and other changes or modifications are intended to be included within the scope of the present invention, as expressed in the following claims.
This application claims priority to and benefit of U.S. Provisional Application No. 61/230,491, filed on Jul. 31, 2009, and entitled “MODULAR PHASED ARRAY APPROACH”, and further claims priority to and benefit of U.S. Provisional Application No. 61/241,284, filed on Sep. 10, 2009, and entitled “MODULAR PHASED ARRAY APPROACH”, both of which are hereby incorporated by reference.
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| Number | Date | Country | |
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| 20110025574 A1 | Feb 2011 | US |
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