Patent Grant
9281564
The present invention generally relates to antennas, and relates in particular to antenna systems that provide adjustment of reception and transmission field shapes associated with the antenna systems.
Monopole antennas typically include a single pole that may include additional elements with the pole. Non-monopole antennas generally include antenna structures that form two or three dimensional shapes such as diamonds, squares, circles etc. Monopole antennas typically produce a transmission field (and are characterized as having a reception field) that radiates in two adjacent generally circular or elipto-spherical shapes that are joined at the antenna.
Multiple antenna structures produce a wide variety of transmission fields (and corresponding reception fields) according to the physical layout of the antennas and/or transmission signal phase modulations placed on signals that are directed to or received by each of the antennas in an antenna structure. For example, as disclosed in “A Primer on Digital Bean forming” by Toby Haynes, http://www.spectrumsignal.com, Spectral Signal Processing, Mar. 26, 1998, beam shaping antenna structures may be provided by positioning adjacent monopole antennas a distance apart of about ½λ in a linear direction wherein the wavelength is the center wavelength of the signal being either transmitted or received. Beam shaping may also be provided by using a plurality of monopole antennas that are fed electronically through a phase multiplexer and are also each about ½λ apart. As further disclosed in this reference, however, certain wireless transmission systems, such as cellular telephones, operate at a wavelength of 35 cm, while FM radio operates at a wavelength of 3 meters and AM radio operates at a wavelength of 300 meters. Providing beam shaping for such wireless systems clearly requires a not insubstantial antenna area or integrated circuit real estate.
Beam shaping in such wireless transmission systems may have significant value in myriad applications. For example, shaping radio frequency interrogation beams in medical imaging systems, such as magnetic resonance imaging (MRI) systems, may be very beneficial to providing more targeted interrogation MRI fields within a patient, and in other applications, such systems may have a wide variety of applications in monitoring devices such as, for example, tire monitoring devices in automobiles. U.S. Patent Application Publication No. 2007/0159315, for example, discloses a tire pressure monitoring system that employs a fixed antenna array to detect signals from each of four tires using shaped beams.
As wireless communication systems become more ubiquitous, the need for smaller and more efficient antennas systems increases, and in particular for antenna system that provide beam shaping without requiring a large amount of antenna volume or integrated circuit real estate.
There is a need, therefore, for more efficient and cost effective implementation of a antenna systems that provide selectively highly directional beam shaping.
In accordance with an embodiment, the invention relates to an antenna system that provides a directional radiation field. The antenna system includes at least two monopole antennas, each of which provides a differential connector, wherein each differential connector is associated with a signal having a different phase such that a radiation field associated with the antenna system is other than a radiation field that would exist if each differential connector were associated with the signal having the same phase.
In accordance with a further embodiment, the antenna system includes at least two distributed load monopole antennas each of which includes a radiation resistance unit coupled to a transmitter base, a current enhancing unit for enhancing current through the radiation resistance unit; and a conductive mid-section intermediate the radiation resistance unit and the current enhancing unit. The conductive mid-section has a length that provides that a sufficient average current is provided over the length of the antenna. Each of the two distributed load monopole antennas is coupled to a connector, and at least one connector is coupled to a phase changing device such that the directional radiation field is provided by the antenna system responsive to the phase changing device.
In accordance with a further embodiment, the invention relates to a method of providing a directional radiation field in an antenna system. The method includes the steps of providing at least two monopole antennas; coupling at least one of the monopole antennas to a phase modulation device; and operating the antenna system such that each monopole antenna operates at a different phase to provide the directional radiation field.
The following description may be further understood with reference to the accompanying drawings in which:
The drawings are shown for illustrative purposes only.
It has been discovered that multiple antenna systems may be provided that achieve beam shaping without requiring that the antennas be positioned at least ½λ apart. Such multiple antenna systems may be provided by employing a plurality of distributed loaded monopole (DLM) antennas as disclosed, for example, in U.S. Pat. No. 7,187,335, the disclosure of which is hereby incorporated by reference.
In particular,
The radiation resistance unit may, for example, be separated from the current enhancing unit by a distance of 2.5316×10−2λ of the operating frequency of the antenna to provide a desired current distribution over the length of the antenna. The choice of the distance A of the load coil above the helix impacts the average current distribution along the length of the antenna. The average current distribution over the length of the antenna varies as a function of the mid-section distance for a 7 MHz distributed loaded monopole antenna. The conductive mid-section has a length that provides that a sufficient average current is provided over the length of the antenna and provides for increasing radiation resistance to that of 2 to nearly 3 times greater than a ½λ antenna (i.e., from for example, 36.5 Ohms to about 72-100 Ohms or more).
The inductance of the load coil should be larger than the inductance of the helix. In addition to providing an improvement in radiation efficiency of a helix and the antenna as a whole, placing the load coil above the helix for any given location improves the bandwidth of the antenna as well as the radiation current profile. The helix and load coil combination are responsible for decreasing the size of the antenna while improving the efficiency and bandwidth of the overall antenna.
As stated above, applicant has discovered that multiple antenna systems may be provided that achieve beam shaping without requiring that the antennas be positioned at least ½λ apart. For example,
Because the antenna system 50 includes two differential inputs, the signal being either transmitted or received may be shaped by providing that one or both of the differential inputs is phase shifted with respect to the other. For example, the signal associated with the connector 76 may be at a first phase φ1 and first amplitude while the signal associated with the connector 78 is at a second phase φ2 and second amplitude. The antenna system may be fed from one antenna or the other antenna or from both antennas. The common base may be coupled to ground or may float at a virtual ground, or may be held another potential.
In each of the distributed load dipole antenna systems 50 and 80, the radiation field may be shaped by changing the difference between the phases (φ1−φ2). The physical layout of the monopole antennas may also be changed. For example,
By employing combinations of such distributed load monopole antennas in various structural combinations in dipole systems and by using signals have a phase difference, a wide variety of radiation field shapes may be provided for transmission, reception or both transmission and reception. Because each monopole antenna in the antenna system includes a separate differential connector (for either transmission or reception), the phase of each may be changed to provide a desired beam shape, and there is no need to physically separate each antenna from one another by a distance of at least ½λ. Each of the above antenna systems may be readily scaled in size to accommodate signal frequencies from less than 1 MHz to over 1000 MHz (e.g., 75 MHz may be employed), and although the above antenna systems use plano-spiral circuit antennas such as shown in
The half-loop antenna system 200 may be formed on a printed circuit board with the connector portions being coupled together by via connectors as discussed above with reference to
As shown, for example, in
Full-loop antenna systems may also be provided as shown at 250 in
Because the element base is at a virtual ground, it may be coupled to ground or any other potential, which permits excellent element isolation, permitting each element to operate independently. This allows tuning of the antenna system to a frequency of resonance by varying the value of capacitors 362 and 364. The impedance of the connectors is, in an embodiment, 50Ω so that it matches most commonly used coaxial connectors.
Each monopole antenna 322, 324, 324 and 326 includes a differential connector such as a 50Ω coaxial feed (366, 368, 370 and 372 respectively) that is coupled with one lead to a coupling point on a respective radiation resistance unit (330, 332, 334 and 336), and includes a second (typically ground) lead that is coupled to the common base. The signal associated with the connector 366 may be at a first phase φ1 and a first amplitude, the signal associated with the connector 368 may be at a second phase φ2 and a second amplitude, the signal associated with the connector 370 may be at a third phase φ3 and a third amplitude, and the signal associated with the connector 372 may be at a fourth phase φ4 and a fourth amplitude. The control circuit may include, for example, four receivers that are each coupled to a connector 366, 368, 370 and 372, and the receiver outputs of which are each coupled to a receiver output switching network that is coupled to a beam forming circuit such as, for example, an AD8333 DC to 50 MHz, dual I/Q demodulator and phase shifter circuit sold by Analog Devices, Inc. of Norwood, Mass. The full-loop antenna system 320 may operate at, for example, 75 MHz, at which frequency it will measure about six inches by six inches. At twice this frequency (at 150 MHz) the size will reduce to 3 inches by 3 inches. Because the system may be scaled to many further frequencies such as 315 MHz or 433 MHz, the size may become very small.
The field shaping may be accomplished using integrated circuits that may perform the beam shaping using programmable phase delays over 360 degrees of phase in 22.5 degree increments. This wide operating frequency permits using a receiver with a down converting mixer and intermediate frequency amplifier to bring each received array signal within the operating range of the beam forming circuit.
The plano-spiral full-loop antenna system 320 of
An antenna system of certain embodiments of the invention, for example, may be employed in a tire monitoring system of an automobile as shown in
An antenna system in accordance with a further embodiment of the invention is shown at 460 in
Antenna systems using linear arrays may also be provided using non-planar antennas as shown, for example in
The tuning of antennas system whether by the use of phasing antenna elements by adjusting spacing or length as well as using electronic beam forming may be facilitated by the use of a signal generation test system 600 as shown in
In this example, the array consists of only four elements using four beam formers. To facilitate programming adjustments, the following method may be used to rapidly determine when optimum antenna response has been achieved by either physically adjusting antenna parameters like element spacing and length and/or programming of electronic beam formers.
The antenna under test, whether it be a phased array where phase relationships between antenna elements determines antenna directivity or any other antenna array where physical relationships between antenna elements determines operating performance. To determine the basic four parameters, forward gain, front to back ratio and adjacent front to side ratio the four signals generators or transmitters are utilized. Each signal source is placed into one of each quadrants of the antenna receiving response indicated above.
As shown in
Adjustments of the antenna under test are made while observing the four demodulated tones on the outputs of the receiver 620 which is coupled to a high frequency oscillator 622. The outputs of the receiver are provided to band frequency unit 624 that also receives a clock signal from band frequency clock 626. The outputs of the unit 624 are provided to a summing amplifier 628, which is coupled to a fast Fourier transform spectrum analyzer 630. A possible spectrum output of the analyzer 630 is shown at 632. By adjusting antenna parameters and observing the displayed tones one can rapidly and simultaneously determine how physical adjustment of antenna elements impacts antenna performance for any or all of the desired antenna response directions. This is a much more rapid method then making adjustments and then either rotating the antenna structure or moving around the antenna structure the signal source to determine the response pattern. The adjustment system may be applied to any antenna array. Also there is no limit to the number of transmitters or signal generators than be utilized as long as they demodulate to different audio tones indicative of any number of different antenna response directions.
Those skilled in the art will appreciate that numerous modifications and variations may be made to the above disclosed embodiments without departing from the spirit and scope of the invention.
This application is a continuation application of PCT/US2009/036151 filed on Mar. 5, 2009, which claims priority to U.S. Provisional Patent Application Ser. No. 61/033,953 filed Mar. 5, 2008, the entire disclosure of which is hereby incorporated by reference.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3518692 | Kuecken | Jun 1970 | A |
| 5479176 | Zavrel, Jr. | Dec 1995 | A |
| 6861981 | Park et al. | Mar 2005 | B2 |
| 6987493 | Chen | Jan 2006 | B2 |
| 7187335 | Vincent | Mar 2007 | B2 |
| 20040140862 | Brown et al. | Jul 2004 | A1 |
| 20050273218 | Breed et al. | Dec 2005 | A1 |
| 20060022883 | Vincent | Feb 2006 | A1 |
| 20060025897 | Shostak et al. | Feb 2006 | A1 |
| 20070159315 | Murata et al. | Jul 2007 | A1 |
| Entry |
|---|
| Dossche, S.; Blanch, S.; Romeu, J., “Decorrelation of a closely spaced four element antenna array,” Antennas and Propagation Society International Symposium, 2005 IEEE , vol. 1 B, No., pp. 803,806 vol. 1B. |
| Haynes, A Primer on Digital Beamforming, Spectrum Signal Processing, pp. 1-15, spectrumsignal.com, USA, Mar. 26, 1998. |
| Evaluation Board for the AD8333 I/Q Demodulator. AD8333-EVAL, Analog Devices, Norwood, MA, 10 pages. |
| Analog Devices Corporation, DC to 50 MHz Dual I/Q Demodulator and Phase Shifter, AD8333 Data Sheet, http://www.analog.com/en/prod/0,,770—849—AD8333,00.html, 3 pages. |
| AD8333 DC to 50 MHz, Dual I/Q Demodulator and Phase Shifter Product Description, “Analog Devices Technology Simplifies medical Ultrasound Design”, http: findarticles.com/p/articles/mi—m0EIN/is—2005—April—25/ai—n13650847, Feb. 12, 2008, 3 pages. |
| Spatial Spectrum Analysis With Low Sample Support Via Adaptive Beamforming, Masters Thesis of Yifan Liang, Purdue University, Aug. 2004, 88 pages. |
| Sun et al., Fast Beamforming of Electronically Steerable Parasitic Array Radiator Antennas: Theory and Experiement, IEEE Transactions on Antennas and Propagation, pp. 1819-1832, vol. 52, No. 7, IEEE, USA, Jul. 2004. |
| Ready et al., System Architectures for Narrowband Reconnaissance Receivers and Beamforming Applications, DSP & Multimedia Technology, pp. 1-6, Applied Signal Technology, Inc., USA, May/Jun. 1998. |
| Converse et al., Ultrawide-Band Microwave Space-Time beamforming for Hyperthermia Treatment of Breast Cancer: A Computational Feasibility Study, IEEE Transactions on Microwave Theory and Techniques, pp. 1876-1889, vol. 52 No. 8, IEEE, USA, Aug. 2004. |
| Montebugnolli et al., “Some Notes on Beamforming” The Medicina IRA-SKA Engineering Group, IRA N. 353/04, 11 pages. |
| International Preliminary Report on Patentability issued on Sep. 7, 2010 in connection with International Application No. PCT/US2009/036151, 7 pages. |
| International Search Report and Written Opinion issued on Apr. 22, 2009 in connection with International Application No. PCT/US2009/036151, 10 pages. |
| Number | Date | Country | |
|---|---|---|---|
| 20110210900 A1 | Sep 2011 | US |
| Number | Date | Country | |
|---|---|---|---|
| 61033953 | Mar 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2009/036151 | Mar 2009 | US |
| Child | 12871239 | US |
