Patent Application
20050285798
The present invention generally relates to receiving broadcast radio signals, such as AM or FM at a portable radio transceiver such as a mobile station that receives communications over different channels. The invention particularly relates to a whip antenna adapted such that a portable device may receive broadcast radio signals over the whip antenna and two-way communications such as using a CDMA protocol over either the same whip antenna or a separate planar antenna.
A strong trend in consumer electronics is to consolidate disparate functions into a single device to minimize the frequency with which users need to carry multiple portable electronic devices. While different demographic segments desire different combinations of functions, an appreciable number of consumers have adopted mobile stations that have the capability to receive broadcast radio such as AM and FM in addition to their more traditional two-way communication functions, which were once predominantly voice communications but are increasingly voice and/or data. However, broadcast radio signals and two-way communications use fundamentally different transmission protocols, and mobile stations having a FM reception capability typically included separate antennas for the distinct communication types.
When an antenna is in resonance at a resonance frequency, there will be an electromagnetic (EM) wave excited corresponding to the resonance frequency. The operating length of the antenna is designed based on the wavelength λ of the intended resonance frequency, generally λ/n of a wavelength where n is an even integer. To avoid antenna breakage and enhance signal reception, the planar inverted-F antenna (PIFA) antenna has been recently developed that decreases operating length of an antenna structure to λ/4 in a PIFA, as compared to λ/2 typically used for whip antennas. For an example of a PIFA antenna, see co-assigned U.S. Pat. No. 6,646,610. Also, the PIFA can be placed above a ground plane and embedded within a durable housing of the mobile station, protecting the PIFA from damage and obscuring it from view. Most mobile stations operate in accordance with GSM 900 and/or GSM 1800, so their resonance frequency is 900 MHz or 1800 MHz. By contrast, in the United States the frequency band for broadcast FM radio is between 88 and 108 MHz. As wavelength is inversely proportional to frequency, reception of FM signals requires a longer antenna than reception of GSM signals.
To enable the same mobile station to receive broadcast FM radio signals as well as engage in traditional two-way (voice or data) communications, two antennas were generally used. The two-way communications antenna may have been a whip antenna or a PIFA, whereas the broadcast FM reception antenna was embodied in a wire leading to an earpiece or headset. Given the popularity of wireless headsets for listening to a mobile station's traditional two-way communications, it is envisioned that consumers would also support a wireless headset that will additionally receive broadcast FM signals, at least when they are not actively engaged in a telephone conversation or other two-way communication of data over traditional mobile phone links. Listening to broadcast radio through a mobile device's built-in speaker without the need for a headset as antenna is also desirable. As the wire of prior art headsets acted as the FM reception antenna, the anticipated consumer need is not readily evident. While there have been attempts at integrating an FM antenna internal to a mobile station, their reception quality has generally been poor.
One prior art innovation to effect the above result is disclosed in co-owned U.S. Pat. No. 6,466,173, herein incorporated by reference in its entirety, which describes a whip antenna transducer and a patch or PIFA antenna that is internal to the device, each connected to radio circuitry via a switch that is actuated based on the position of the whip antenna, extended or retracted. As such, only one antenna is coupled to receiving circuitry at any time. Another co-owned prior art invention, U.S. Pat. No. 6,486,835 B1, discloses detecting a position of a retractable antenna relative to a fixed antenna, and is incorporated by reference in its entirety as relevant to a switch actuated based on a position of a retractable antenna.
What is needed in the art is a mobile station or other portable electronic device that is enabled to receive both two-way communications and broadcast radio signals, at least broadcast FM radio signals, each with low loss characteristics and without the need for a conductor extending many times the length of the mobile station housing.
This invention is in one aspect an antenna assembly for a portable electronic device such as a mobile station. The portable electronic device includes a housing. The antenna assembly has an antenna and first and second radio leads. The antenna has an elongated shaft that is slideable between extended and retracted positions through an aperture defined by the housing of the portable device. The first radio lead is electrically coupled to the antenna, and is for coupling the antenna to a mobile telephony receiver at least when the antenna is in the extended position. The second radio lead is also electrically coupled to the antenna, but is for coupling the antenna to a broadcast radio receiver at least when the antenna is in the extended position. The mobile telephony receiver and the broadcast radio receiver are disposed within the housing but do not form part of the antenna assembly. In one embodiment, the second radio lead has a RF choke such as an inductor that separates received signals in the frequency domain. In an alternative embodiment, the first radio lead is coupled to the whip antenna via capacitive coupling and a fixed antenna internal to the housing. In that alternative embodiment, preferably the whip antenna is decoupled from a common potential to prevent undesirable capacitive parasitic coupling. Various implementations are detailed below.
The present invention is in another aspect an improvement on a mobile station that has a transceiver for communicating over a two-way communication system and a receiver for receiving broadcast radio signals, each within a housing of the mobile station. The improvement includes a whip antenna coupled to a first and second radio lead. The whip antenna has an elongated shaft that is moveable between an extended position that protrudes beyond the housing and a retracted position. The first radio lead is for electrically coupling the transceiver to the whip antenna. The second radio lead is coupled at one end to the receiver and at an opposed end to the whip antenna, at least when the whip antenna is in the extended position. Preferred and alternative embodiments as in the above paragraph are also within this aspect of the invention.
In yet another aspect, the present invention is a method for receiving a signal at a mobile station. The method includes providing a mobile station having a retractable whip antenna, extending the whip antenna to a fully extended position, and receiving a signal at the fully extended whip antenna. Particularly novel is that, in the case that the signal is above a threshold frequency, the method provides the received signal to a mobile telephony receiver via a first radio lead, and in the case that the signal is below a threshold frequency, the method provides the received signal to a broadcast radio receiver via a second radio lead. Specific embodiments on how to affect that frequency-selective providing to the different receivers is detailed below.
These and other features, aspects, and advantages of embodiments of the present invention will become apparent with reference to the following description in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention.
The two-way communication system has both an uplink 40a (from the mobile station) and a downlink 40b (to the mobile station) between the mobile station 22 and the base station 34, whereas the broadcast radio has only a downlink 26. The two-way communication system encompasses a plurality of mobile stations and base stations, as well as several radio network controllers that each controls several base stations. Users operating an individual mobile station do so on a subscriber basis, and each mobile station is uniquely identified to the two-way communications network via an identification number that it transmits to the base station upon call setup or initial power-on. In contrast, receivers in general, and the FM receiving mobile station of
In a preferred embodiment, the mobile station 22 receives both mobile telephony signals and broadcast radio signals via the whip antenna 24. In an alternative embodiment, the mobile station receives broadcast radio signals via the whip antenna 24 and mobile telephony signals over a separate antenna such as a PIFA internal to a durable mobile station housing. It is noted that the mobile station will be described as receiving via the antenna 24 signals over the two-way communication network, but it is understood that transmissions on the uplink 40a from the mobile station 22 are also via that same antenna 24. Those embodiments are detailed further herein.
An antenna assembly 42 according to the preferred embodiment of the present invention is detailed in schematic form at
The whip antenna 24 is slideable between an extended position (
Generally, a portable radio device according to the present invention will include a mobile telephony transceiver (not shown) coupled through a transmit/receive switch to the mobile telephony radio feed 50. The mobile telephony transceiver may have a RAKE receiver as known in the art for receiving, demodulating and decoding signals on the downlink 40b of the two-way communication system. The portable radio device generally also includes a broadcast radio receiver coupled to the broadcast radio feed 50 for receiving signals over the downlink 26 of the broadcast radio system. Preferably, such a broadcast radio receiver is to receive frequency modulated signals and is a super heterodyne receiver having a limiter and a Foster-Seeley discriminator for detecting and demodulating a FM signal. The RAKE and super heterodyne receiver may share components as fabricated on a circuit board, but are functionally different receivers.
The FM radio feed includes a radiofrequency (RF) choke such as a decoupling inductor 52. Also within the FM radio feed is a matching inductor 54 in series with the RF choke. The RF choke is used as a signal blocking element, and apart from a small inductor, may also be embodied as a transistor such as a field effect transistor (FET), preferably with ferrite beads on leads thereof to minimize parasitic oscillations within nearby circuitry. The RF choke (e.g., the decoupling inductor 52) isolates the FM radio signal 26 from the downlink mobile telephony signal by frequency. Where the downlink signals 40a of the two-way communication system are above about 800 MHz, a decoupling inductor exhibiting an inductance of about 50 nH and greater effectively prevents the received mobile telephony signal 40a from passing while incurring little loss to the FM radio signal of about 88-108 MHz. The matching inductor 54 matches with the whip antenna 24 for the desired frequencies to be received, and in the above example for FM radio would exhibit an inductance of about 470 to 810 nH. While the antenna assembly is described specifically with reference to reception of broadcast FM signals, it may be adapted to receive broadcasts in the HF or UHF bands by changing the matching inductor 54 (and other matching components in the receiver) to tune the whip antenna 24 to the desired frequency.
While the whip antenna 24 is in the extended position of
While in the retracted position, the whip antenna 24 would generally exhibit high loss for FM radio reception due to proximity to other electronic components and shielding due to those components and to the housing 47 of the mobile station 22. Consequently, an optional feature is a means to disable the connection between the FM radio receiver and the whip antenna 24 when the whip antenna 24 is retracted. This may be embodied in a switch that is opened, for example, by the bottom 56 of the whip antenna 24 when the whip antenna is in the fully retracted position (e.g., the cap 44 in contact with the upper surface 46a of the stub antenna 46, a spring clip that engages the FM radio lead 48 only when the whip antenna 24 is fully extended, a detector that senses (mechanically, optically) when the bottom 56 of the whip antenna is in a position corresponding to the fully retracted position, etc. The bottom 56 is that end of the whip antenna 24 opposed to the cap 44.
An alternative embodiment of the present invention uses a retractable whip antenna 24 and a separate internal antenna within the mobile station housing, preferably a planar antenna such as a PIFA. This alternative embodiment is detailed in the schematic diagram of
The internal antenna 58 and the whip antenna 24 are in close proximity to one another but not in direct physical contact. The proximal distance between them is such that they undergo parasitic coupling in the area indicated by the dotted circle 64, at least when the mobile station 22 receives and transmits on frequencies appropriate to the two-way communications system (e.g., greater than about 900 MHz) and the whip antenna 24 is extended. Preferably, the elongated shaft 24 of the whip antenna and the internal antenna are within approximately 5 mm of one another to facilitate strong parasitic coupling. In parasitic coupling, one antenna reflects or re-radiates energy from a second antenna and thereby maintains a phase relationship with the second antenna. In the particular instance of
While receiving and transmitting at mobile telephony frequencies, it is an important aspect of the alternative embodiment of the invention that the whip antenna 24 be disconnected from a common potential 60 or ground. This is to enable the whip antenna to enter and maintain phase relation with the internal antenna 58, and properly re-radiate energy sensed at the parasitic coupling area 64. Typical within mobile stations and other portable radio devices, RF circuits are constructed in shielded enclosures, often with internal grounded partitions between sections of the circuitry to prevent coupling. It is common to build such RF circuitry on two-sided PC board, with one side used as a ground plane. Alternatively, a circuit may be constructed immediately adjacent to a shield or other grounded surface.
It is noted that for most common inductors that may be used within the present invention as detailed above, parasitic capacitance will effectively limit broadcast radio reception to frequency bands only up to about several hundred MHz. This is seen as a limitation inherent in commonly available components rather than a limitation to the broader aspects of the invention, as it may be overcome by advances in inductor technology.
While there has been illustrated and described what is at present considered to be preferred and alternative embodiments of the claimed invention, it will be appreciated that numerous changes and modifications are likely to occur to those skilled in the art. It is intended in the appended claims to cover all those changes and modifications that fall within the spirit and scope of the claimed invention.
