Patent Grant
9136588
Current antenna design for mobile devices is directed to extracting more radiator length from a given radiator size, examples being a helix or meander radiator. This typically leads to poor bandwidth and low gain. Also, due to size limitations in mobile devices, efficient antennas are too large to be located within the mobile device, typically being attached to a top portion thereof. Numerous designs have been developed for small antennas, but all are understood to be subject to some performance compromise, whether it be bandwidth, gain, radiation efficiency, impedance, etc. Therefore, there has been a longstanding need in the mobile radio devices community for a versatile, small antenna with reasonable performance characteristics.
In view of the above, the following description details new electrically small, antenna system(s) and method(s) with performance characteristics that are superior to comparable sized antennas.
In one aspect of the disclosed embodiments, an electrically short, cable based antenna is provided, comprising: a truncated ground plane; an asymmetric transmission line radiator having a length (LTL) oriented substantially planar to and proximal to the ground plane, the transmission line also having at one end an input/output connector, and at an other end a feed point at least one of above a ground plane and proximal to its edge; and an exciter antenna in a form of a plate or bent wire coupled to the feed point and disposed exterior to the edge of the ground plane and oriented substantially orthogonal to the ground plane, the exciter antenna having a larger dimension length (LEA) that is at least 50% smaller than the length LTL, wherein an overall length of a perimeter of the antenna is approximately ½ a wavelength of a center frequency of the antenna.
In yet another aspect of the disclosed embodiments, a method for fabricating an electrically short, cable based antenna is provided, comprising: truncating a ground plane; placing an asymmetric transmission line radiator having a length (LTL) substantially planar to and proximal to the ground plane, the transmission line also having at one end an input/output connector, and at an other end a feed point proximal to an edge of the ground plane; and coupling an exciter antenna in a form of a plate or bent wire to the feed point and disposing the exciter antenna exterior to the edge of the ground plane in an orientation substantially orthogonal to the ground plane, the exciter antenna having a larger dimension length (LEA) that is at least 50% smaller than the length LTL, wherein an overall length of a perimeter of the antenna is approximately ½ a wavelength of a center frequency of the antenna.
The principles governing the overall current distributions of the antenna embodiments described herein are a modification of those found in planar inverted F antennas (PIFA) and inverted F antennas (IFA), which are known to operate as full size quarter wave antennas over large ground planes with standard feed forms. Therefore, these quarter wave antennas are limited in their ability to be reduced in size.
The new antenna embodiments disclosed herein are, generally speaking, a “twisted” version of the PIFA/IFA structure but include a floating asymmetrical (e.g., coaxial) feed structure that allows a lower operating frequency. Due to the additional energy radiated by the floating coaxial feed structure and its transformer properties, these antenna embodiments can be much smaller than prior art antennas with nearly equivalent or better performance characteristics. In some instances, the disclosed antennas can be up to ten times smaller than the current state-of-the-art. In reference to certain features and/or structures shown in the following FIGS., it is understood that they may not be drawn to scale, the appropriate proportions being easily devisable to one of ordinary skill in the art.
The fc is principally determined by the coaxial length A+B and will be approximately a free-space quarter wavelength (λ/4) (noting that the internal coaxial cable wavelength is a function of the characteristic impedance Z0, being nearly λ/6 for most radio grade coaxial cables). Length C generally will be smaller than A+B, being usually one quarter (¼) to one third (⅓) the length of A+B. Of course, depending on the implementation, the proportions may vary, as evident to one of ordinary skill in the art. Length B can be arbitrary, representing the source point connection to the coaxial radiator 20. It is understood, however, that length C may be adjusted to effect a certain degree of matching to the coaxial radiator 20.
In some embodiments, the length A+B portion (10, 15) acts as a λ/4 transformer to the coaxial radiator 20, however, in addition to the radiating currents on the coaxial radiator 20, “unbalanced” radiating currents will travel along the shield portion of coaxial cable 10 to ground via coupler 35, effectively adding another radiator to the system. Thus, a superpositioning of the two radiating currents can be arranged form constructive fields for more radiation of energy.
In experimental models for frequencies in the mobile communications UHF band (e.g., approximately 380-520 MHz), using a truncated ground plane with width W of 5 cm and height H of 10 cm, using 50 Ohm and 75 Ohm coaxial lines, length A was designated as approximately 12 cm, length B as approximately 2 cm, and length C as approximately 7 cm with acceptable results. It should be expressly noted that the above dimensions, separations, sizes, etc. are frequency dependent, accordingly, if other frequency bands or performance characteristics are desired, then the associated parameters will be need to be appropriately altered. For example, the separation distance between the coaxial radiator 20 from the top edge of the truncated ground plane 50 can be varied, with higher radiation efficiency discovered for a distance of 2.5 cm and lower radiation efficiency for a distance of 10 mm.
For this embodiment, a good rule of thumb is that the perimeter of the antenna translates to approximately the half wavelength of the center frequency. For example, for an embodiment suitable for the mobile communications UHF band (e.g., approximately 380-520 MHz), the truncated ground plane 50 was designed with a height of 10 cm and a width of 5 cm. The top radiator 80 was 10 mm×50 mm with a separation distance of approximately 2.5 cm from the top of the truncated ground plane 50. In this case the perimeter is approximately (10 cm+2.5 cm)*2+(5 cm)*2=35 cm, corresponding to the half wavelength, wherein the center frequency would then be approximately 428 MHz. Having equal proportions along the sides of the perimeter of the antenna is understood to provide better performance characteristics (e.g., top+side 1=bottom+side 2). In some embodiments, the center frequency is obtained by having a length A of the asymmetrical transmission line 10 as approximately ⅙ the free space center wavelength, with the internal impedance of the asymmetrical transmission line 10 devised so that the length A corresponds to approximately ¼ the internal center wavelength.
The center frequency can also be altered by trimming the asymmetrical transmission line 10. For increased efficiency (e.g., above 50%), the top radiator 80 should be separated from the truncated ground plane by approximately 0.05 wavelength or more.
Experimental data showing performance characteristics for representative models tested for azimuthal gain for variations of the embodiments of
It should be appreciated that the various embodiments in the foregoing FIGS. illustrate that the asymmetrical transmission line radiator can be mated with various radiators (e.g., wire, cable, plate, meander, ballast, etc.), thus providing multiple degrees of freedom for an antenna engineer, allowing various configurations for deployment.
The embodiments of
The exciter antenna is disposed exterior to the edge of the truncated ground plane and, if having a plate antenna configuration, it is positioned in an orientation substantially orthogonal to the truncated ground plane, the exciter antenna having a larger dimension length (LEA) that is at least 50% smaller than the length LTL, wherein an overall length of a perimeter of the entire antenna embodiment is approximately ½ a wavelength of a center frequency of the antenna.
The process also accommodates the optional step (denoted with dashed lines) of attaching 110 a ground connection to an exterior of the asymmetric transmission line radiator, a position of the ground connection along the length LTL on the asymmetric transmission line radiator being understood to alter a center frequency of the antenna. Additional optional step (denoted with dashed lines) can be the 112 positioning of a secondary feed point of the asymmetric transmission line radiator below the truncated ground plane and coupling another exciter antenna, acting as a ballast, to the secondary feed point. After completion of step 108 or optional steps 110, 112, the process stops 114.
It is understood that while the embodiments described herein are stated in the context of radiating antennas, it is understood by one of ordinary skill in the art that antennas are by their very nature capable of both radiating and receiving, under the principle of duality. Therefore, while not explicitly stated as such, all of the embodiments are capable of receiving as well as transmitting. Also, while the embodiments are characterized for mobile UHF frequencies, other frequencies and/or bands are possible by altering the respective dimensions of the appropriate elements of the embodiments.
In the foregoing specification, specific embodiments have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present teachings.
The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.
Moreover in this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” “has”, “having,” “includes”, “including,” “contains”, “containing” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, has, includes, contains a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a”, “has . . . a”, “includes . . . a”, “contains . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises, has, includes, contains the element. The terms “a” and “an” are defined as one or more unless explicitly stated otherwise herein. The terms “substantially”, “essentially”, “approximately”, “about” or any other version thereof, are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the term is defined to be within 10%, in another embodiment within 5%, in another embodiment within 1% and in another embodiment within 0.5%. The term “coupled” as used herein is defined as connected, although not necessarily directly and not necessarily mechanically. A device or structure that is “configured” in a certain way is configured in at least that way, but may also be configured in ways that are not listed.
It will be appreciated that some embodiments may be comprised of one or more generic or specialized processors (or “processing devices”) such as microprocessors, digital signal processors, customized processors and field programmable gate arrays (FPGAs) and unique stored program instructions (including both software and firmware) that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of the method and/or apparatus described herein. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used.
Moreover, an embodiment can be implemented as a computer-readable storage medium having computer readable code stored thereon for programming a computer (e.g., comprising a processor) to perform a method as described and claimed herein. Examples of such computer-readable storage mediums include, but are not limited to, a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a ROM (Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory) and a Flash memory. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation.
The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.
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