This invention relates generally to radio frequency (RF) antennas and antenna circuitry and, more particularly, pertains to extendable/retractable antennas.
It is well known in the art to provide RF antennas that can be extended so as to protrude from a device during use of the device. For example, in a radiotelephone, which could also be referred to as a wireless terminal, a personal communicator, a mobile station or as a cellular telephone, it is known to provide two different antennas. Referring also to FIG. 1, a first antenna 1 intended for use with a first set of transmission and reception frequency bands is formed as a meander transmission line, or simply as a helically wrapped length of conductor, that is disposed about a circular cylindrical or otherwise shaped form 2. The first antenna 1 is assumed to be fixed in position. The form 2 is hollow, and contains within (when fully retracted) a second antenna 3. The second antenna 3 can be a rod-shaped whip-type antenna that is capable of sliding within the form 2 so that it can be extended by the user. In the presently preferred embodiment the form 2 is contained within the body of a wireless terminal 4. When the second antenna 3 retracted only the first antenna 1 is electrically active. The first antenna 1 is coupled, via a duplexer 5, to an RF transceiver 6. When the second antenna 3 is fully extended, shown in dashed outline, it makes electrical contact at 3A with the distal end of the first antenna 1, and is coupled through the first antenna 1 to the RF transceiver 6 (or to a second RF transceiver, not shown).
It can be important to detect the position of the second antenna, as the specified maximum radiated power may be different when using the first antenna as compared to the second antenna. For example, one may reasonably assume that the first antenna 1 is used when transceiving RF signals in accordance with a CDMA air interface standard, and that the second antenna 3 is used when transceiving RF signals in accordance with a second air interface standard, such as one known as AMPS. Generally, when in the AMPS mode it is typically desirable to use more transmitted power than when in the CDMA mode. The increase in transmitted power is preferably made, however, when the second antenna is extended out of the body of the wireless terminal 4, and not retracted into the body of the wireless terminal 4. This enables an increase in performance in the AMPS mode, while still meeting predetermined RF emission limits.
It is possible to position a mechanical switch 7 so as to detect when the second antenna is in the fully retracted position, and to couple an output of the switch 7 to a control unit 8, such as a microprocessor, within the wireless terminal 4. By detecting the state of the switch 7 the control unit 8 is enabled to determine whether it can transmit with maximum power using the second antenna 3.
However, the use of the mechanical switch 7 has several disadvantages, including increased cost, decreased reliability, and increased manufacturing and testing complexity.
It is a first object and advantage of this invention to provide an improved technique for detecting a position of a moveable antenna.
It is a further object and advantage of this invention to provide a technique for detecting the position of a retractable antenna that does not use a mechanical switch, and that thus does not experience the problems inherent in the use of a mechanical switch.
The foregoing and other problems are overcome and the foregoing objects and advantages are realized by methods and apparatus in accordance with embodiments of this invention.
A circuit and method are disclosed for detecting a position of a movable antenna relative to a fixed antenna. The circuit includes an electrical contact positioned for being electrically coupled to the movable antenna only when the movable antenna is in a first predetermined position relative to the fixed antenna; and an RF detection circuit having an input coupled to the electrical contact for detecting a presence of RF energy that is coupled into the movable antenna from said fixed antenna. The detected presence of the RF energy is indicative of the moveable antenna being in the predetermined position relative to the fixed antenna. The fixed antenna is disposed along a length of the movable antenna when said movable antenna is in said first predetermined position. For example, the fixed antenna is disposed circumferentially about a hollow form and the movable antenna is a rod-shaped, whip-type antenna that is disposed within the form such that it is slidable therein between a fully retracted position and a fully extended position. When in the first predetermined position the movable antenna is in the fully retracted position. In the presently preferred embodiment the RF detection circuit includes a detection diode, at least one RF filter coupled in series between an input of the detection diode and the electrical contact, a capacitance coupled to an output of the detection diode for storing charge detected by the detection diode such that the capacitance has a potential impressed thereon by the charge, and a comparator for comparing the potential to a predetermined potential. The comparator has an output the state of which indicates whether or not the first antenna is in the first predetermined position.
Also disclosed is a method for use in a wireless terminal for detecting a position of a retractable antenna relative to a fixed antenna. The method has steps of positioning an electrical contact for being electrically coupled to the retractable antenna only when the retractable antenna is retracted within a body of the wireless terminal, and at least partially contained within the fixed antenna; detecting a presence of RF energy that is coupled into the retractable antenna from the fixed antenna, wherein the detected presence of the RF energy is indicative of the retractable antenna being in the retracted position; and, if the retractable antenna is not indicated to be in the retracted position, transmitting RF energy from the retractable antenna using more RF power than if the retractable antenna were indicated to be in the retracted position. In the preferred embodiment the retractable antenna is used when operating in the AMPS mode, and the fixed antenna is used when operating in other than the AMPS mode, such as when operating in the CDMA mode.