Patent Grant
8681050
The present invention relates to Radio Frequency (RF) antennas. Wireless device performance is limited by the operation of the radiator, antenna. Designers seek to optimize the antenna operation while decreasing the size or footprint of the wireless device.
This application relates to antenna structures and specifically antenna structures based on metamaterial designs.
The propagation of electromagnetic waves in most materials obeys the right-hand rule for the (E, H, β) vector fields, which denotes the electrical field E, the magnetic field H, and the wave vector β (or propagation constant). In these materials, the phase velocity direction is the same as the direction of the signal energy propagation (group velocity) and the refractive index is a positive number. Such materials are referred to as Right/Handed (RH) materials. Most natural materials are RH materials, but artificial materials may also be RH materials.
A metamaterial (MTM) is an artificial structure which behaves differently from a natural RH material alone. Unlike RH materials, a metamaterial may exhibit a negative refractive index, wherein the phase velocity direction is opposite to the direction of the signal energy propagation where the relative directions of the (E, H, β) vector fields follow a left-hand rule. When a metamaterial is designed to have a structural average unit cell size ρ which is much smaller than the wavelength of the electromagnetic energy guided by the metamaterial, the metamaterial behaves like a homogeneous medium to the guided electromagnetic energy. Metamaterials that support only a negative index of refraction with permittivity ∈ and permeability μ being simultaneously negative are pure Left Handed (LH) metamaterials.
A metamaterial structure may be a combination or mixture of an LH metamaterial and an RH material; these combinations are referred to as Composite Right and Left Hand (CRLH) metamaterials. A CRLH metamaterial behaves like an LH metamaterial under certain conditions, such as for operation at low frequencies; the same CRLH metamaterial may behave like an RH material under other conditions, such as operation at high frequencies.
Implementations and properties of various CRLH MTMs are described in, for example, Caloz and Itoh, “Electromagnetic Metamaterials: Transmission Line Theory and Microwave Applications,” John Wiley & Sons (2006). CRLH MTMs and their applications in antennas are described by Tatsuo Itoh in “Invited paper: Prospects for Metamaterials,” Electronics Letters, Vol. 40, No. 16 (August, 2004).
CRLH MTMs may be structured and engineered to exhibit electromagnetic properties tailored to specific applications. Additionally, CRLH MTMs may be used in applications where other materials may be impractical, infeasible, or unavailable to satisfy the requirements of the application. In addition, CRLH MTMs may be used to develop new applications and to construct new devices that may not be possible with RH materials and configurations.
As used in this application, MTM and CRLH MTM structures and components are based on a technology called “Metamaterial” which applies the concept of Right-handed and Left-handed (LH) structures.
As used herein, the term “Metamaterial,” “MTM,” “CRLH,” and “CRLH MTM” refer to technology and technical means, methods, devices, inventions and engineering works which allow compact devices composed of conductive and dielectric parts and are used to receive and transmit electromagnetic waves and behave as unique structures which are much smaller than the free space wavelength of the propagating electromagnetic waves. Using MTM technology, antennas and RF components may be made very compactly in comparison to competing methods and may be very closely spaced to each other or to other nearby components while at the same time minimizing undesirable interference and electromagnetic coupling. Such antennas and RF components further exhibit useful and unique electromagnetic behavior that results from one or more of the following structures to design, integrate, and optimize antennas and RF components inside wireless communications devices.
Composite Right Left Handed (CRLH) structures exhibit simultaneous negative permittivity (∈) and permeability (μ) within certain frequency bands and simultaneous positive ∈ and μ within other frequency bands.
Transmission-Line (TL) based CRLH structures enable TL propagation and exhibit simultaneous negative permittivity (∈) and permeability (μ) within certain operating frequency bands and simultaneous positive ∈ and μ within other operating frequency bands
TL-based Left-Handed (TL-LH) structures enable TL propagation and exhibit simultaneous negative ∈ and μ within certain frequency bands and simultaneous positive ∈ and μ within extremely high-frequency non operating bands.
Combination of the above may be designed and built incorporating conventional RF design structures. Antennas, RF components and other devices may be referred to as “MTM antennas,” “MTM components,” and so forth, when they are designed to behave as an MTM structure. MTM components may be easily fabricated using conventional conductive and insulating materials and standard manufacturing technologies including but not limited to: printing, etching, and subtracting conductive layers on substrates such as FR4, ceramics, LTCC, MMICC, flexible films, plastic or even paper.
As wireless devices continue to shrink and pack more integrated components, the space available for layout of the various antenna structures of the device can be challenging to meet certain layout constraints such as device enclosure size and dimensions. Integrated peripheral components may include, for example, a microphone, a speaker, a camera, or a vibe motor. In some cases, it may be necessary to reroute connection lines or modify the shape of certain components for incorporation into a device design. Rerouting connection lines and adapting the shape and size of the components provide some relief and additional space savings necessary to meet these layout constraints. However, as the devices continue to get shrink, rerouting lines and adapting the shape may not be enough to meet progressively smaller design requirements, especially in compact wireless devices that are formed on a single printed circuit board (PCB) substrate. Thus, alternative and novel designs and methods of producing antenna structures that can maximize the use of a limited area may be of increasing interest as the layout constraints continue to shrink.
A CRLH MTM design may be used in a variety of applications, including wireless and telecommunication applications. The use of a CRLH MTM design for elements within a wireless application often reduces the physical size of those elements and improves the performance of these elements. In some embodiments, CRLH MTM structures are used for antenna structures and other RF components.
CRLH MTM structures may be used in wireless devices having a variety of features, antenna structures and elements. CRLH structures provide several benefits for constructing a compact antenna while supporting a broad range of frequencies. Some of these structures are described in the U.S. patent application Ser. No. 12/270,410 entitled “Metamaterial Structures with Multilayer Metallization and Via,” filed on Nov. 13, 2008, the disclosure of which is incorporated herein by reference. CRLH structures may include conductive elements such as, for example, a feed structure, a launch pad, a cell patch, a via, a via line. The conductive elements may take on a variety of geometrical shapes and dimensions to meet certain design requirements as described in U.S. patent application Ser. No. 12/270,410. For example, the cell patch may be rectangular, polygonal, irregular, circular, oval, or combination of different shapes. The via line and the feed line can be polygonal, irregular, zigzag, spiral, meander or combination of different shapes. The launch pad can be rectangular, polygonal, irregular, circular, oval, or combination of different shapes. Although various elements of the CRLH structure can be designed to meet the space limitations within the compact wireless device, placement of the integrating peripheral components proximate the CRLH structure can nevertheless be challenging, especially in designs which limit the placement of the peripheral components to a predetermined or fixed location. Thus, smaller integrated wireless devices may benefit from the use of alternative CRLH designs and techniques that offer improved integration as well as size reduction. Such CRLH designs may include, for example, a hollow cell patch, which may be in the form of a polygon, structured to have an exterior conductive portion and a non-conductive interior portion; a meandered line formed within the interior of the hollow cell patch design; and a cell patch ring formed along the periphery and side wall of a substantially circular structure defined by an opening in the PCB substrate. In addition, other designs may include a combination of multiple CRLH antenna structures distributed over the main PCB substrate and the elevated PCB substrates, supporting multiple frequency bands.
In operation, the CRLH antenna device 100 may include a series inductor LR, a series capacitor CL, a shunt inductor LL and a shunt capacitor CR where LL and CL determine a left-handed (LH) mode propagation properties and LR and CR determine a right-handed (RH) mode propagation properties. Certain structural elements contribute to forming LR, CR, LL, and CL that govern the RH and LH modes, respectively. For example, the coupling gap 107 formed between the feed line 103 and the cell patch 105 may generate the series capacitance CL, the via line 111 may produce the shunt inductor LL, while the LR may be attributed to a current propagation along the cell patch 105, and CR is due to the substrate 101 being sandwiched between the cell patch 105 and the via line 109.
According to this embodiment, the cell patch 205 is designed to have structural features that mimic the cell patch 105 of the first embodiment, having a similar polygon shape and similar dimensions. However, in the second example embodiment, the cell patch 205 is structured to include an enclosed conductive portion 215 formed along the exterior edge of the cell patch 205, leaving an interior portion 217 of the cell patch 205 to partially expose the substrate 201. In other words, the enclosed conductive portion 215 of the cell patch 205 forms an opening or “hollow” interior 217 to the substrate 201, freeing up valuable real estate for the inclusion of other components. Therefore, the CRLH antenna device 200, with the hollow interior cell patch design, offers the advantage of providing additional room on the PCB for implementing integrated components such as, for example, a microphone, a speaker, a camera, or a vibe motor.
In operation, the CRLH antenna device 200 may include a series inductor LR, a series capacitor CL, a shunt inductor LL and a shunt capacitor CR where LL and CL determine left-handed (LH) resonance mode propagation properties and LR and CR determine right-handed (RH) resonance mode propagation properties. Certain structural elements contribute to forming LR, CR, LL, and CL that govern the RH and LH modes, respectively. For example, the coupling gap 207 formed between the feed line 203 and the cell patch 205 may generate the series capacitance CL, the via line 211 may produce the shunt inductor LL, while the LR may be attributed to a current propagation along the cell patch 205, and CR is due to the substrate 201 being sandwiched between the cell patch 205 and the via line 209. The effect of the hollowing out the interior of the cell patch 205 in the second embodiment may result in reducing CR and thus may have the benefit of increasing the bandwidth of the LH resonance. A shift in both LH and RH resonances may also occur, as LR and CL are also governed by the properties of the cell patch 205. By modifying the size and shape of certain structural elements in the CRLH antenna device 200, the LH and RH resonances may be compensated or tuned to match the resonances of the previous antenna device 100, as presented in the next embodiment.
According to this embodiment, the cell patch 305 is designed to include structural features that mimic the cell patch 305 of the second embodiment, having a similar hollow cell interior design, polygon shape and similar dimensions. However, in the third example embodiment, the via line 311 is extended to increase its total length in order to tune the LH and RH resonances to better match the resonances of the CRLH antenna device 100. In other words, in order to tune the CRLH antenna device 200 to fall in the same frequency as the CRLH antenna device 300, the via line 311 was extended in length to maintain the same size cell and have a fair comparison between the two CRLH antenna devices 100 and 300.
In operation, the CRLH antenna device 300 may include a series inductor LR, a series capacitor CL, a shunt inductor LL and a shunt capacitor CR where LL and CL determine left-handed (LH) resonance mode propagation properties and LR and CR determine right-handed (RH) resonance mode propagation properties. Certain structural elements contribute to forming LR, CR, LL, and CL that govern the RH and LH modes, respectively. For example, the coupling gap 307 formed between the feed line 303 and the cell patch 305 may generate the series capacitance CL, the via line 311 may produce the shunt inductor LL, while the LR may be attributed to a current propagation along the cell patch 305, and CR is attributed to the substrate 301 being sandwiched between the cell patch 305 and the via line 309. In the third embodiment, the extended via line 309 results in an improved matching between the original CRLH antenna device 100 and the tuned hollow cell CRLH antenna device 300. The return loss and efficiency results of the three CRLH antenna devices are illustrated in
According to
Other variations of hollow cell patch designs include a hollow cell patch with an extended stub, a meander hollow cell patch, an inverted meander cell patch, a cell patch hole, and a multi-hollow cell patch design. These and many more designs of various hollow cell patch structures are presented in the ensuing examples.
Depending on the tuning or matching requirements, the via line 711 may be extended or reduced in length and configured in a variety of shapes to influence the shunt inductor LL. To properly connect the cell patch 705 to a desired configuration of the via line 711, the extended stub 717 may be positioned anywhere along the interior conductive edge of the cell patch 705 and structured in a variety of lengths and shapes to align and couple to the via line 711.
According to this embodiment, the hollow cell patch 805 provides additional room within the CRLH antenna device 800 to accommodate the meander conductive line 819 for increasing the total length of the feed line 803, which in turn may produce an extra resonance mode.
According to this embodiment, an opening in the cell patch 905 in the shape of a meander line 915 exposes a portion of the substrate 901, modifying the available conductive area of the cell patch 905, which may affect CR and the bandwidth in the LH mode.
The concept of the hollow cell patch design presented in the previous embodiments may be applied to multi-band CRLH antenna devices. For example,
According to this embodiment, multiple CRLH antenna structures are formed on a single substrate to provide multi-band frequency operations. In addition, by applying the hollow cell patch structures in this multi-band CRLH antenna device 1000, a significant amount free space near the hollow cell patch is available for other components or other uses, thereby making the implementation of highly integrated and compact antenna devices simpler and more cost effective.
Another variation of the hollow cell patch design may include a cell patch formed along an opening or hole in the PCB substrate as shown in
Table 1 and Table 2 summarize a description of conductive elements used in a single CRLH antenna structure and a multi-CRLH antenna structures, respectively.
Other antenna configurations include variations of the hollow cell patch designs. For example, hollow cell patch designs may include multiple cutouts of varying shapes, multiple rings, multiple cutouts within each other, or a combination thereof. In addition, such designs may be applied to sophisticated CRLH antenna structures, including multiple layers, 3-D or elevated substrates. These designs may support a variety of antenna configuration where space, performance and integration are a necessity.
While this specification contains many specifics, these should not be construed as limitations on the scope of an invention or of what may be claimed, but rather as descriptions of features specific to particular embodiments of the invention. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or a variation of a subcombination. Only a few implementations are disclosed. However, it is understood that variations and enhancements may be made.
This application claims priority under 35 U.S.C. 119(e) to U.S. Patent Application Ser. No. 61/320,481, entitled “HOLLOW CELL CRLH ANTENNA DEVICES” and filed on Apr. 2, 2010, which is incorporated herein by reference in its entirety.
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| Number | Date | Country | |
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| 61320481 | Apr 2010 | US |
