Patent Application
20090009399
The present invention generally relates to improved feed line networks for antenna arrays operating at millimeter wave frequencies and, in particular, a planar antenna array printed on the surface of a dielectric substrate wherein the planar antenna array includes an array of planar radiator elements interconnected through a feed line network of planar coplanar transmission lines to provide high-efficiency operation at millimeter wave operating frequencies.
In the wireless communications industry, market demands for ubiquitous network access to information and services has been met with rapid and widespread development of wireless network applications for wireless PAN (personal area network), wireless LAN (local area network), wireless WAN (wide area network), cellular networks, and other types of wireless communication systems. Moreover, recent advances in semiconductor technologies and microwave and millimeter-wave planar antenna circuit technologies have made it possible to combine the solid-state devices with the planar antennas to produce more compact, reliable and wide-band microwave and millimeter-wave devices.
In general, micros trip antenna technologies are commonly used for integrated RF solutions as microstrip antennas (or printed antennas) such as microstrip patch antennas (or patch antenna) allow for low profile, low cost and reliable antenna designs. As is well known in the art, a patch antenna is typically fabricated by patterning an antenna radiator element on one side of an insulating dielectric substrate that has a continuous metal layer (ground plane) on the opposite side of the substrate. A single patch antenna provides a maximum directive gain of around 6-9 dBi. For applications such as wireless USB, where the operating distance is limited to about a meter, a single patch antenna with about 7 dBi of gain at an operating frequency of 60 GHz will provide the necessary antenna gains. However, for distances of 10 meters or more or other point-to-point applications, antenna gains as high as 40 dBi are needed depending on the application. To achieve such high gain, antenna arrays with as many as 256 radiating elements are typically required.
Planar antenna arrays are generally designed with 2D array of radiating elements, such as micro-strip patches, dipoles, folded dipoles, slots, etc., that are interconnected using a microstrip feed line network such as a corporate feed network, a series feed network or a combination of corporate and series feed networks. By way of example,
In the conventional corporate-structured microstrip feed line structure of
Although
Moreover, it is well known that a microstrip antenna structure having a microstrip feed network and patch array on the same level (on the same substrate surface) cannot be optimized simultaneously because the requirements for microstrip antennas and microstrip transmission lines are different. For microstrip patch antennas, the relative permittivity and thickness of the substrate largely determines the electrical characteristics of the antenna a low dielectric constant substrate enhances the radiation efficiency of the antenna while a thicker substrate increases antenna bandwidth. However, lower dielectric constant substrates and thicker substrates can result in spurious radiation from microstrip line and step discontinuities. For applications at operating frequencies lower than millimeter wave frequencies (e.g., less than about 30 GHz), microstrip feed lines can be readily implemented on printed circuit board (PCB) with substrate as thin as 300 microns. For low frequency application, microstrip lines are well behaved and have acceptable electrical characteristics, e.g., acceptable dispersions, relatively constant characteristic impedance over operating band of interest, and low coupling between feed lines and radiating elements (due to weak, fringe fields).
However, for applications at millimeter wave operating frequencies and beyond, microstrip patch antenna arrays cannot be easily implemented on a substrate as thin as 100 um or thinner due to mechanical reliability and limitations of the manufacturing process, as is understood by those of ordinary skill in the art. As a result the substrate is usually too thick for microstrip lines operating at mmWave and higher frequencies. Due to the too thick substrate thickness, microstrip line impedance changes significantly with frequencies due to dispersion. In addition, the microstrip line fringe field is very strong because of the lower ratio of the microstrip line width to the substrate thickness. Under these conditions, the microstrip line does not properly operate as a feed line, but operates as a radiating element as well. Therefore, for millimeter wave frequencies and beyond, it is virtually impossible to design efficient planar antenna arrays with coplanar microstrip lines, even for small arrays with, e.g., four elements.
In general, exemplary embodiments of the invention include improved feed line networks for antenna arrays operating at millimeter wave frequencies. In particular, exemplary embodiment of the invention include methods for constructing planar antenna arrays printed on the surface of a dielectric substrate wherein the planar antenna arrays are designed with an array of planar radiator elements interconnected through a feed line network of planar coplanar transmission lines which enable high-efficiency operation at millimeter wave operating frequencies. For example, an antenna array comprising an array of antenna radiator elements and feed network that is coplanar with the antenna elements can be formed with the feed network comprising coplanar strip line transmission lines including one or more coplanar strip line (CPS) and one or more coplanar waveguide (CPW) transmission line, which are interconnected using balun structures.
More specifically, in one exemplary embodiment of the invention, an antenna includes a planar substrate comprising an antenna array comprising an array of planar radiating elements and a feed network formed on a surface of the planar substrate. The planar radiating elements include a first pair of patch radiators including a first patch radiator having a first edge, and a second patch radiator having a second edge. The first and second patch radiators are arranged such that the first and second edges are adjacent edges that are spaced apart and face each other. The feed network comprises a first balanced coplanar strip line having first and second signal lines. The first balanced coplanar strip line is disposed between the first and second edges of the first and second patch radiators. Moreover, a first conductive strip connects the first signal line to the first edge of the first patch radiator, and a second conductive strip connects the second signal line to the second edge of the second radiator patch.
In one exemplary embodiment, the antenna is configured such that the first and second edges are points of opposite phase for a given operating frequency and the first and second patch radiators are fed by the first balanced coplanar strip line such that the first and second patch radiators radiate in phase.
In another exemplary embodiment of the invention, an antenna inlcudes a planar substrate comprising an antenna array comprising an array of planar radiating elements and a feed network formed on a surface of the planar substrate. The feed network inlcudes a network of coplanar strip line transmission lines that include one or more coplanar strip lines (CPS) and one or more coplanar waveguide (CPW) transmission lines. The the feed network may comprise a corporate feed structure or a combination of a corporate feed and series feed network.
The feed network further comprises one type of balun structure to connect a CPW transmission line and a CPS transmission line, which are transversely disposed to each other, and another type of balun structure to connect tow CPS transmission lines that are transversely disposed to each other.
In another exemplary embodiment of the invnetion, the planar radiating elements are arranged in pairs where each pair of radiating elements is differentially fed by a balanced CPS transmission line. The radiating elements may be rectangular patch elements, wherein each pair of radiating elements includes a first patch radiator having a first edge, and a second patch radiator having a second edge. The first and second patch radiators are arranged such that the first and second edges are adjacent edges that are spaced apart and face each other. The balanced CPS transmission line includes first and second signal lines disposed between the first and second edges of the first ana second patch radiators, wherein a first conductive strip connects the first signal line to the first edge of the first patch radiator and a second conductive strip connects the second signal line to the second edge of the second radiator patch. In this embodiment, the balanced CPS transmission line has an impedance that is about twice an impedance of the first conductive strip and first patch radiator, and the impedance of the second conductive strip and the second patch radiator. Moorever, the antenna is configured such that the first and second edges are points of opposite phase for a given operating frequency and the first ana second patch radiators are fed by the balanced CPS transmission line such that the first and second patch radiators radiate in phase.
These and other exemplary embodiments, aspects, features and advantages of the present invention will be described or become apparent from the following detailed description of exemplary embodiments, which is to be read in connection with the accompanying drawings.
Depending on the application, the antenna array in
The superstrate framework of
Referring now to
In particular, the balun B1 is formed by extending the signal line S of the CPW line (220) through an open (discontinuous) portion of the signal line S2 of the CPS line (221) and connecting the signal line S of the CPW line (220) to the signal line S1 of the CPS line (221). The ground lines G of the CPW (220) are connected to the ends of the signal traces S2. In effect, the balun B1 splits the CPS branch line (221) into two balanced CPS transmission lines (221A) and (221B), providing a matched 3 db power divider (or power combiner) where the impedances of the two branch CPS lines (221A) and (221B) are the same and twice the impedance of the CPW feed line (220). In this instance, the power transmitted on the CPW line (220) will split evenly into the two CPS branch line portions (221A) and (221B).
The CPS branch line (221A) includes a right angle bend (b1) from which the CPS line (221A) extends to a branch CPS line (222) that extends transverse at right angles to the branch CPS line (221A). The branch CPS line (221A) is connected to the branch CPS line (222) via a balun B2 transition forming a T-junction power divider/combiner, where the branch CPS line (221A) branches into two CPS lines (222A) and (222B). Similarly, the CPS branch line (221B) includes a right angle bend (b2) from which the CPS line (221B) extends to a branch CPS line (223) which extends transverse at right angles to the branch CPS line (221B). The branch CPS line (221B) is connected to the branch CPS line (223) via a balun B3 transition forming a T-junction power divider/combiner. In one exemplary embodiment of the invention, each balun B2 and B3 is formed of a back to back CPS-to-CPW-to-CPS transition structure, as will be explained with reference to
The CPW line (230) of the balun (B3) includes a signal line S interposed between two ground lines G. The CPW-to-CPS transition structure of the balun 83 is similar to the transition of the balun B1 discussed above, where the signal line S of the CPW line (233) extends through an open (discontinuous) portion of the signal line S2 of the CPS line (223) and connects to the signal line S1 of the CPS line (223) (which branches into signal lines S1 of branch CPS lines (223A) and (223B). Moreover, the ground lines G of the CPW (230) are connected to the ends of the separate signal traces S2 of the branch lines (223A) and (223B).
As further shown in
The balun B2 transition in
As further depicted in
The exemplary antenna array arrangement depicted in
The antenna array (200) achieves in-phase radiation of the patch elements (210) by ensuring symmetry about lines L1-L1 and L2-L2 in
Moreover, to evenly distribute the power to/from the patch elements (210) and to minimize losses/reflections in the feed network, impedance matching between each element and the feed network, as well as within the feed network, to prevent reflections. In one exemplary embodiment, the feed network is designed so that the input impedance of the patch (210) and microstrip line (224) as seen from the branch CPS connection is transformed by the power divider network to a desired impedance at the input to the antenna array, where impedance matching within the feed network is achieved by using coplanar strip lines having different widths (different impedances) such that at a point where a single line divides into two, the parallel combination of the impedance of the two lines is equal to that of the single line. For instance, assume that impedance of the patch (210) and microstrip feed line (224) are 100 ohms at the resonant operating frequency. The CPS lines (222) and (223) would foe designed to have a characteristic impedance of about 200 ohms (each line S1 and S2 of the CPS lines (222) and (223) would effectively have an impedance of 100 ohms to match the input impedance of 100 ohms of the patch (21)/microstrip (224) combination. The impedance of the CPS branch lines (222A/B) and (223A/B) can be selected by, e.g., varying the width of the signal lines S1 and S1 and the spacing between the lines, as is understood by those of ordinary skill in the art. In this regard, the impedance at the junctions of the balun B2 and B3 would be about 100 ohms (as the impedance would be determined by a pair of 200 ohm resistors in parallel). To match this 100-ohm resistance, each branch 221A, 221B of the CPS line (221) would be designed to have an impedance of about 100 ohms at the operating frequency. At the junction between the CPS line (221) and the input CPW line (220), an effective resistance of 50 ohms would be seen as determined by the parallel 100 ohm resistance of the branch CPS lines (221A and 221B). The input CPW line (220) would be designed to have an impedance of 50 ohms (at the resonant frequency). In this manner, the impedance of the CPW line (220) (e.g., 50 ohms) can be matched to the impedance of each patch (210) and microstrip feed line (224) (100 ohms) via effective power division over the feed network.
Moreover, transmission line losses (resistive, radiation, etc.) are minimized by implementing the CPS and CPW feed network architectures. Indeed, since CPS and CPW lines have a reliable return current path, the line characteristic impedance remains substantially constant in the operating frequency band of interest regardless of the thickness of the substrate (201). Moreover, the field remain primarily between the coplanar signal lines and ground lines, so the fringed field is weak. As a result, the coupling between feed lines and between feed lines and the radiating elements are weak. This makes the feed structure and radiating elements design much easier.
With the proposed feed network, a combination of series and parallel patches are possible as shown in
Each branch CPS line (322A) and (322B) feeds a pair of patch elements (310) via separate microstrip lines (324) which extend at right angles to the branch lines (322A, 322B. In the exemplary embodiment, the radiator elements pairs (310) in the column direction are conductively joined to respective the different signal lines S1 and S2 of the balanced transmission lines (322) such the each radiator patch (310) is feed at opposite ends, the pair will radiator in phase. This allows the inter-element spacing Dy in the column direction to λo/2 at the desired operating frequency. Moreover, a plurality of series connected patches (311) are conductively joined to respective patches (310) by thin conductive microstrip lines (325). In each series feed line, the radiator elements are conductively joined at opposite, adjacent edges. The patches (310) and (311) have resonant lengths of λg/2 and the lengths of the microstrips (325) are about λg/2. In this arrangement all patch elements (310) and (311) will radiate in phase.
As noted above, exemplary antenna arrays can be constructred using a superstrate frame-work where no ground plane is disposed on the back of the antenna substrate.
The antenna module (403) comprises an integrated antenna device (404) mounted to an antenna socket structure (405). The integrated antenna device (404) comprises a planar substrate (404a) mounted to the socket structure (405), which (as depicted in
As further depicted in
In general, the socket structure (405) is designed to shield the antenna radiators from the surrounding materials and components of the package apparatus (400), thereby providing a closed EM environment allowing the antenna to be designed with a desired performance irrespective of the package structures and technologies.
Further, as depicted in
The socket structure (405) can have any suitable framework. For example, the antenna socket structure (405) can be a hollow metallic structure formed from metallic material (e.g., copper, aluminum) having outer walls (405a˜405d) and a planar metallic (bottom) surface, wherein the metallic bottom surface is bonded to the package frame (401). With this framework, the socket structure (405) provides a defined cavity region having metallic sidewalls and bottom surface, wherein the bottom surface of the socket provides a reference ground or reflector for the antenna. With the antenna substrate (404a) mounted to the socket structure (15), the radiating elements of the antenna (200) are disposed within a predefined, closed EM environment and are shielded from the surrounding package material. Indeed, the socket structure (405) provides a natural barrier to prevent lossy encapsulant material from flowing into the enclosed cavity region between the printed antenna (200) and reference ground during an encapsulation process.
In other exemplary embodiments of the invention, the socket structure (405) can be a metallic/dielectric frame structure comprising outer walls (405a-405d) with no planar bottom (ground) surface. With this structure, a metallic ground plane can be formed on (or integrally formed from) the package frame (401), whereby the antenna socket structure (405) is mounted to the package frame (401) such that the inner region (405e) is aligned to the metallic ground plane. As with an exemplary socket structure providing an integrally formed ground plane, the ground plane of the package frame (401) operates as an antenna reference ground or reflector to ensure that no energy is radiated into the hoard on which the package (400) is mounted. In all instances, the metallic ground plane effectively limits the antenna radiation to the upper hemisphere above the antenna and enables consistent antenna performance.
It is to be further appreciated that exemplary antenna modules with providing closed cavity regions with controlled EM environments and reference ground planes renders antenna performance less sensitive to the ground size and surrounding dielectric material. For instance, a controlled air space provides better bandwidth and radiation efficiency for the antenna. In comparison to conventional antenna designs with floating ground planes of a same size, a closed cavity region reduces unwanted backside radiation.
It is to be understood that the exemplary package of
Furthermore, various types of IC chips may foe integrally packaged with an antenna module to construct electronic devices having highly integrated, compact radio communications systems. For instance, the IC chip (402) may be an integrated transceiver circuit, an integrated receiver circuit, an integrated transmitter circuit, and/or other support circuitry, etc., can be packaged with one or more antenna modules to provide compact radio communications chips. These radio communications chips can be installed in various types of devices for wireless communication applications.
In other exemplary embodiments, the input CPW feed line (220) may foe a balanced CPS line, or combination of CPW and CPW with an appropriate transition, to provide the necessary inductive/capacitive impedance matching between a device/component (e.g., power amplifier, LNA, etc.) formed on the IC chip and the printed antenna structure, and provide the necessary impedance depending on, e.g., the impedance that is need for the given application and/or the type of devices to which the antenna may be connected. For example, if the antenna is connected to an integrated transmitter system, the input feed line (220) of the feed network of the antenna array (200) will be designed to provide the proper connections and impedance matching for, e.g., a power amplifier. By way of further example, if the antenna array (100) is connected to a receiver system, the feed network may be designed to provide the proper connections and impedance matching for, e.g., an LNA (low noise amplifier).
Moreover, although
Although exemplary embodiments have been described herein with reference to the accompanying drawings for purposes of illustration, it is to be understood that the present invention is not limited to those precise embodiments, and that various other changes and modifications may be affected herein by one skilled in the art without departing from the scope of the invention.
This invention was made with Government support under Contract No. N66001-02-C-8014 and N66001-05-C-8013 awarded by DARPA (Defense Advanced Research Projects Agency). The Government has certain rights in this invention.
