The present invention is directed to antennas capable of tuning over a large frequency range, and, more specifically, to an antenna with a selectable radiating surface area.
Many present day analog and digital devices are capable of receiving and/or transmitting radio frequency (RF) signals. Such devices include, for example, radios, computers, video games, televisions, and wireless telephones. A large of number of these devices are required to tune over many different frequencies with a single antenna in order to operate as required by the particular application. For example, a wireless telephone may need to operate over several different frequency bands in order to tune signals on the different bands, such as a GSM band and an analog band.
As is understood, such systems require antennas having tuning circuitry in order to tune the device to the proper frequency. As frequency ranges increase, the cost and efficiency of the tuning circuitry also increases. Furthermore, the overall efficiency may drop at frequencies that are not within an optimum tuning range of the antenna.
The present invention provides a relatively compact antenna and system that is capable of tuning RF signals over a relatively large range of frequencies while having relatively simple (and thus relatively inexpensive) tuning circuitry. An antenna element is provided that has a selectable length, thus providing different center frequencies for the antenna element depending upon the selected length of the antenna element. Tuning circuitry may tune the antenna element to a range of frequencies about the center frequency. A control line is used to switch the length of the antenna element, with the control line coupling to the antenna element at substantially the same RF frequencies throughout the range of frequencies the antenna element is required to operate.
In one embodiment, a selectable length meander line antenna system, is provided comprising: (a) a first meander line antenna portion operably interconnected to an RF feed and a tuning circuit; (b) a switch element operably interconnected to the first meander line antenna portion at an end thereof away from the RF feed; (c) a second meander line antenna portion operably interconnected to the switch element; and (d) a control line operably interconnected to a controller and to the switch element. The switch element is operable to receive a signal from the control line and electrically connect the second meander line antenna portion to the first meander line antenna portion. The control line is routed in close proximity to the first meander line antenna portion throughout the entire length of the first meander line antenna portion. The first meander line antenna portion has a first center frequency of operation and a first range of operation, and the first and second meander line antenna portions have a second center frequency and a second range of operation when the switch element electrically connects the first and second meander line antenna portions. The first and second meander line antenna portions may be configured in a serpentine fashion, with the control line configured in a corresponding serpentine fashion corresponding to the first meander line antenna portion. The switch element may comprise two PIN diodes connected in series between the control line and the first and second meander line antenna portions. The switch element may also comprise a MEMS device, a relay, or other switching device.
In another embodiment, the antenna further comprises a second switch element operably interconnected to the second meander line antenna portion at an end thereof away from the RF feed, a third meander line antenna portion operably interconnected to the second switch element, and a second control line operably interconnected to the controller and to the second switch element. In this embodiment, the second switch element is operable to receive a signal from the second control line and electrically connect the second meander line antenna portion to the third meander line antenna portion. The second control line is routed in close proximity to the first and second meander line antenna portions throughout the entire length of the first and second meander line antenna portions.
The present invention recognizes that antennas are designed having a center frequency at which the antenna may be tuned with relatively little requirements for tuning and matching circuitry. The antennas include tuning and matching circuitry that are capable of adjusting the antenna properties to tune frequencies over a specified frequency range relative to the center frequency. As this frequency range increases, the complexity (and thus cost) of the tuning and matching circuitry increases, and the efficiency of the antenna may decrease. The present invention thus provides an antenna element with a switchable extension that may be used to change the size of the radiating surface and provide an antenna that has two or more separate center frequencies. Thus, the range of frequencies that may be tuned by the antenna is enhanced, while maintaining relatively low complexity tuning and matching circuitry. Switching for the extension is performed by a switching element that is located at the point of connection of the extension. A control line supplies a control signal to the switching element to enable and disable the extension. The control line is positioned in close proximity to the antenna element to enhance coupling between the antenna element and the control line. The present invention, and some exemplary embodiments thereof, is now described with reference to drawing
Referring now to
In one embodiment, the control line 66 and the meander line 62 are routed in close proximity to one another. Close proximity, as used herein, means that the distance between the control line and meander line is such that the two lines are electrically coupled at the operating frequencies of the meander line and have substantially the same resonance frequencies. The effect of placing the control line 66 in close proximity to the meander line 62 increases the coupling between the control line 66 and the meander line 62 when the antenna is operating. The coupling is further increased by placing relatively large capacitors at various locations, such as the terminal ends, of the meander line 62. These capacitors effectively block DC between the control line 66 and meander line 62 and also serve as a RF short circuit between the control line 66 and the meander line 62. The coupling between the control line 66 and meander line 62 results in the control and meander lines 66, 62 resonating at substantially the same frequencies and providing enhanced bandwidth to the meander line 62. This improvement in bandwidth is the result of having an effectively larger wire for the meander line 62. The control line 66 connects to the switch 70 that connects the meander line 62 with the meander extension 74 thus changing the resonant frequency of the antenna system 32. An RF system employing such an antenna system 32 may thus selectively be enabled to transmit and/or receive RF signals across a wider range of frequencies while still maintaining tuning and matching circuitry 50 which is relatively inexpensive. The tuning and matching circuitry 50 may be designed to provide tuning over a frequency range that is less than the entire operating range required of the antenna system 32.
The switch 70, in one embodiment, is comprised of two PIN diodes. In this embodiment the control signal from the control circuitry 54 is a positive voltage which is connected through the PIN diodes, in series, to the control signal negative. Thus, when the signal from the control circuitry 54 is switched, the extension on the meander line antenna is enabled and/or disabled. As mentioned above, the switch 70 may comprise other components rather than, or in addition to, PIN diodes, such as MEMS devices, relays, and FETs, to name a few. In such cases, the control circuitry 54 provides an appropriate control signal to actuate the switch 70 to enable/disable the meander line extension. The components illustrated in
Referring now to
A control line 120 runs in close proximity with the meander line 116. As mentioned above, by running the control line 120 in close proximity to the meander line 116, the two lines couple at approximately the same frequency, and thus coupling between the lines is enhanced. Control lines, by nature of their inherent length, couple to antenna elements. In the event that such a control line is routed in a different configuration than the radiating element, the control line will couple with the element at different frequencies than the operating frequency of the element, causing undesirable anti-resonances that reduce the efficiency and effectiveness of a variable matching network. A potential solution to this coupling is the placement of inductors along the length of the control line, thus mitigating the coupling. However, such inductors both increase the cost of the antenna system, and at substantial fractions of a wavelength from the feed point, the antenna impedance increases such that practical inductor sizes do not have enough impedance to block the RF on the control line. Thus, by placing the control line in close proximity to the antenna element, the coupling of the control line and antenna element is increased such that the control line becomes part of the antenna element, thereby reducing or eliminating spurious resonances while also enhancing operating bandwidth of the antenna.
Referring still to
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While the invention has been particularly shown and described with reference to embodiments thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made without departing from the spirit and scope of the invention.
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6489925 | Thursby et al. | Dec 2002 | B1 |
6624795 | Boyle | Sep 2003 | B1 |
6894656 | Apostolos et al. | May 2005 | B1 |
20050225496 | Apostolos et al. | Oct 2005 | A1 |