High isolation antenna system

An antenna system supports a common resonance mode and differential resonance mode, each with approximately equal radiation resistance and bandwidth at a given operating frequency band. The antenna system includes a resonant antenna section, a counterpoise, and two antenna ports. The resonant antenna section includes two spaced-apart poles and a distributed network therebetween. Each of the poles has a proximal end connected to the distributed network and an opposite distal end. The distal ends of the poles are separated from each other by a distance of ⅓ to ⅔ of the electrical wavelength at the given operating frequency. Each of the two antenna ports is defined by a pair of feed terminals with one feed terminal located on the counterpoise and the other feed terminal located on a different one of the poles of the resonant antenna section. The resonant antenna section, counterpoise, and ports are configured such that a signal within the given operating frequency band applied to one port is isolated from the other port.

BACKGROUND

The present invention relates generally to antenna systems in portable communications devices.

Many portable communications devices, including cellular handsets, personal digital assistants, smart phones, laptops, notebooks, netbooks, and tablet computers, include two or more radio communications devices operating independently and simultaneously in the same frequency band or adjacent frequency bands. For example, many devices use both Bluetooth and 802.11 radios for wireless networking. Bluetooth and 802.11n operate in the same frequency band at 2.4 to 2.5 GHz, and can interfere with each other and reduce the performance of either or both communication streams. To improve performance, high isolation is needed between the antenna ports used for the two radios.

BRIEF SUMMARY OF EMBODIMENTS OF THE INVENTION

An antenna system in accordance with one or more embodiments supports a common resonance mode and differential resonance mode, each with approximately equal radiation resistance and bandwidth at a given operating frequency band. The antenna system includes a resonant antenna section, a counterpoise, and two antenna ports. The resonant antenna section includes two spaced-apart poles and a distributed network therebetween. Each of the poles has a proximal end connected to the distributed network and an opposite distal end. The distal ends of the poles are separated from each other by a distance of ⅓ to ⅔ of the electrical wavelength at the given operating frequency. Each of the two antenna ports is defined by a pair of feed terminals with one feed terminal located on the counterpoise and the other feed terminal located on a different one of the poles of the resonant antenna section. The resonant antenna section, counterpoise, and ports are configured such that a signal within the given operating frequency band applied to one port is isolated from the other port.

An antenna system in accordance with one or more further embodiments provides isolated antenna connections to two radio communications devices operating independently and simultaneously in the same frequency band or adjacent frequency bands. The antenna system comprises a resonant antenna section, a counterpoise, and two antenna ports. The resonant antenna section comprises two spaced-apart poles and a distributed network therebetween. Each of the poles has a proximal end connected to the distributed network and an opposite distal end. The distal ends of the poles are separated from each other by a distance of ⅓ to ⅔ of the electrical wavelength at a given operating frequency. Each of the two antenna ports is associated with one of the radio communications devices. Each port is defined by a pair of feed terminals with one feed terminal located on the counterpoise and the other feed terminal located on a different one of the poles of the resonant antenna section. The resonant antenna section, counterpoise, and ports are configured such that a signal within the given operating frequency band applied to one port is isolated from the other port.

Like reference numerals generally represent like parts in the drawings.

DETAILED DESCRIPTION

Various embodiments are directed to antenna systems in communications devices providing isolated antenna connections to two or more radio devices operating independently and simultaneously in the same frequency band or adjacent frequency bands.

FIG. 1illustrates an exemplary antenna system or assembly100in accordance with one or more embodiments. In this example, the antenna system100comprises a planar structure. In particular, it comprises a flexible printed circuit formed on a structural supporting dialectic layer102. The antenna system100includes a resonant antenna section104, a counterpoise106, and two antenna ports108,110. The resonant antenna section104, counterpoise106, and ports108,110are configured such that a signal within a given operating frequency band applied to one port is isolated from the other port.

The resonant antenna section104includes two spaced-apart poles112,114and a distributed network116therebetween. The distributed network116comprises a connecting element that increases the isolation between the two antenna ports108,110.

The poles112,114of the resonant antenna section104, each include a proximal end118connected to the distributed network116and an opposite distal end120. The distal ends120of the poles112,114are preferably separated from each other by a distance of ⅓ to ⅔ of the electrical wavelength at the given operating frequency of the antenna. The operating frequency of the antenna system100is substantially determined by the electrical lengths of the two antenna poles112,114, each approximately ¼ of the operating wavelength in this example. The frequency response may be raised or lowered by making the poles112,114electrically shorter or longer, respectively.

Each of the two antenna ports108,110is defined by a pair of feed terminals. One of the feed terminals is located on the counterpoise106, and the other feed terminal is located on one of the poles112,114of the resonant antenna section104.

The antenna system100can also include two inductive shorting sections122,124, each connecting the counterpoise106to a different one of the poles112,114of the resonant antenna section104. In one or more embodiments, the inductive shorting sections122,124serve to match the antenna input impedance to 50 ohms at the desired operating frequency.

High isolation between the feed points is obtained at a resonant frequency dependent on the average electrical length of both antenna poles112,114. The impedance matching frequencies for the feed points are dependent on the relative lengths of the antenna poles112,114. The exemplary antenna system100shown inFIG. 1is designed to be positioned in an asymmetric location (e.g., the corner of a display panel of a notebook computer) so that the natural frequency response from two feed points is different. Accordingly, the relative lengths of the antenna poles112,114are different to obtain an impedance match at the same frequency, while the mean length of the antenna poles112,114is set to obtain high isolation at the same frequency.

The counterpoise106provides for the common or ground side connection of the feed points. In one exemplary application, the counterpoise106is connected to a larger conductor object such as the LCD display or foil shield in a notebook computer either by direct connection or by capacitive coupling. By way of example,FIG. 2illustrates integration of the antenna system100in a notebook computer by placing it behind the LCD panel150of the computer. In a typical notebook product, the notebook manufacturer bonds a sheet of aluminum foil154to the back shell152of the computer display section, which may serve as an EMI shield. The antenna assembly100may be attached to the foil shield154with adhesive such that the counterpoise portion106directly overlays the foil shield154, while the resonant antenna section104extends beyond the foil shield154(and the LCD panel150). Bonding the antenna assembly100to the foil shield154and back shell152with adhesive provides sufficient capacitive coupling between the antenna counterpoise106and foil shield154such that direct galvanic connection is not required.

FIG. 3illustrates an exemplary arrangement of the antenna system100with respect to the LCD panel150, foil shield154, and back shell152of a notebook computer. For generally optimal isolation and bandwidth performance, the end of antenna pole portion112is placed at the outside corner of the back shell assembly152. Coaxial cables154,155are attached to the antenna feed by soldering the shields to the counterpoise portion106at156and the center conductors to the antenna portion at158. The cables are routed within the area of the foil shield154or LCD panel150in the manner illustrated for maintaining high isolation.

The antenna system100has been found to provide high isolation between the antenna ports. In particular, isolation exceeding 30 dB has been found at a separation of the antenna poles of about 0.5 wavelength.

The antenna system100can provide high isolation in devices operating in various frequency bands. For example, the operating frequency band can be 2.4 to 2.5 GHz. As another example, the operating frequency band can fall within 2.3 to 2.7 GHz.

Radios associated with the ports can operate in different frequency bands. For example, the operating frequency band for one radio is 2.4 to 2.5 GHz and the operating frequency band for the other radio is within 2.3 to 2.7 GHz. In one example, one of the radios is a Bluetooth radio, and the other radio is an 802.11 radio. Alternately, one of the radios can be a WiMAX (Worldwide Interoperability for Microwave Access) radio or LTE (Long Term Evolution) radio, and the other radio is an 802.11 radio. In yet another example, one of the radios can be a WiMAX radio, and the other radio can be an LTE radio.

FIG. 4shows the VSWR measured at test ports of the antenna system100ofFIG. 1.FIG. 5shows the coupling (S21or S12) measured between the test ports. In this example, the VSWR and coupling are advantageously low at frequencies of 2.4 to 2.5 GHz.FIG. 6shows the measured radiation efficiency referenced from the test ports.

In the example ofFIG. 1, the antenna system100comprises a planar structure comprising a flexible printed circuit. It should be understood that various other structures are also possible in accordance with embodiments of the invention. For example,FIG. 7illustrates an exemplary antenna system400comprising a three-dimensional structure in accordance with one or further more embodiments. The antenna system400can comprise a stamped metal antenna. It includes a resonant antenna section402, a counterpoise404, and two antenna ports406,408. The resonant antenna section402includes two spaced-apart poles410,412and a distributed network416therebetween.

The poles410,412of the resonant antenna section402, each include a proximal end connected to the distributed network416and an opposite distal end. The distal ends of the poles410,412are preferably separated from each other by a distance of ⅓ to ⅔ of the electrical wavelength at the given operating frequency of the antenna. The operating frequency of the antenna system400is substantially determined by the electrical lengths of the two antenna poles410,412, each approximately ¼ of the operating wavelength. The frequency response may be raised or lowered by making the poles410,412electrically shorter or longer, respectively.

The antenna system400can also include two inductive shorting sections418,420, each connecting the counterpoise404to a different one of the poles410,412of the resonant antenna section402.

The exemplary antenna system400can be mounted on an LCD panel assembly as shown in the example ofFIG. 8. Coaxial cables450,452are attached to the antenna feed by soldering the shields to the counterpoise portion404and the center conductors to poles410,412of the resonant antenna section402.

FIG. 9shows the VSWR measured at test ports of the antenna system400ofFIG. 7.FIG. 10shows the coupling (S21or S12) measured between the test ports. In this example, the VSWR and coupling are advantageously low at frequencies of 2.4 to 2.5 GHz.FIG. 11shows the measured radiation efficiency referenced from the test ports.

It is to be understood that although the invention has been described above in terms of particular embodiments, the foregoing embodiments are provided as illustrative only, and do not limit or define the scope of the invention.

Various other embodiments, including but not limited to the following, are also within the scope of the claims. For example, the elements or components of the various antenna systems described herein may be further divided into additional components or joined together to form fewer components for performing the same functions.

Having described preferred embodiments of the present invention, it should be apparent that modifications can be made without departing from the spirit and scope of the invention.