Multi mode antenna system

An antenna system comprising a first antenna element, a second antenna element, the first and second elements defining at least in part a slot element, an active switching network in communication with one or both of the first and second antenna elements, the switching network operable to cause the antenna system to resonate in each of two modes: a first mode wherein the first element resonates at a first set of frequencies, and the first element and a second element resonate together at a second set of frequencies; and a second mode wherein the first element resonates at the first set of frequencies, and the slot element resonates at a third set of frequencies.

TECHNICAL FIELD

Various embodiments of the invention relate in general to antenna systems and, more specifically, to active antenna systems.

BACKGROUND OF THE INVENTION

Currently, there are a multitude of wireless systems in place, including, inter alia, four varieties of Global System for Mobile Communications (GSM)—GSM 850, 900 GSM, 1800 GSM, 1900 GSM, as well as third generation (3G) systems and emerging fourth generation (4G) systems. BLUETOOTH® and wireless Local Are Network (LAN) capability is also being implemented in mobile phones. Users are demanding more and more functionality, and many wireless engineers are discovering that they need bigger antennas but cannot increase the sizes of handsets.

As a side effect of the popularly recognized Moore's Law for semiconductors, customers and handset suppliers expect consumer technology to keep shrinking in size and increasing in functionality, without regard to the constraints of physics. For many applications, there are fundamental size limitations of antennas that have been reached with today's technology. The antenna, unlike other components inside a handset, sometimes cannot keep decreasing in size. Before the existence of cellular systems, a scientist postulated the physical law responsible for governing antenna size, and the law is now known as “Wheeler's Theorem.” In short, Wheeler's Theorem states that for a given resonant frequency and radiation efficiency, the total bandwidth of the system is directly proportional to the size of the antenna. Further, as resonant frequency decreases, antenna size usually increases, and as efficiency increases, antenna size usually increases. Thus, changes to efficiency, bandwidth, or frequency often require changes to antenna size, and changes to frequency, efficiency, or size, often affect bandwidth. This generally represents the physical constraints facing engineers as they design antennas systems for consumer and other devices.

The implications of Wheeler's Theorem for the continued expansion of wireless systems are contrary to consumer expectations regarding bandwidth and size. The space required by antennas in handsets is currently between 5 to 20% of the total space. Generally, either antennas will become much larger to accommodate additional bandwidth, or antenna performance will decrease to accommodate smaller applications. Using what is known about current systems, it is believed that if required bandwidth doubles and performance stays the same, handset size will accordingly increase by up to 20%.

Engineers use active antenna systems to decrease antenna size while giving the appearance of attaining performance gains. Whereas most antennas are passive antennas with up to two connections (feed and ground) to the motherboard/Printed Circuit Board (PCB) and no additional power requirements, an active antenna uses a switching circuit to physically control parts of the antenna. The active antenna system uses the switching element to re-configure the driven antenna elements therein, changing the resonant frequency and maintaining similar efficiency and bandwidth performance for each frequency. Each setting of the antenna acts as a separate antenna for purposes of Wheeler's Theorem; thus, using an active antenna system can seem, in some respects, like receiving several antennas for the physical cost of one. Using this technique, an engineer can design an antenna system that has acceptable performance for multiple wireless networks without incurring the cost in space to accommodate separate antennas.

One kind of active antenna system uses one or more switchable ground connections and/or feed connections on an element to provide a variety of possible feed and/or ground locations, each location causing a different frequency response. One disadvantage of such systems is a lack of ability to independently tune the resonances. Another disadvantage is that such systems generally provide only small shifts in resonant frequency with each adjustment.

The prior art includes no active antenna system that provides independent tuning of one or more frequencies of a multi-band antenna while also providing larger shifts in frequency with each adjustment and which is contained in a volume-efficient package.

BRIEF SUMMARY OF THE INVENTION

Various embodiments of the present invention are directed to systems and methods for providing active antenna systems with two or more operating modes. In one example embodiment, a first conductive plate and a second conductive plate are arranged such that the space between them defines a slot element. Accordingly, the system includes at least three antenna elements. Switching networks are provided that are operable to cause the system to radiate in at least two modes. In a first mode, the first conductive plate radiates Radio Frequency (RF) signals at a first set of resonances, and further, both the first and second conductive plates radiate together at a second set of resonances. In the second mode, the first conductive plate and the slot element radiate RF signals in their respective native frequencies. Accordingly, such example system may be referred to as a “dual mode” antenna system. The switching can include making and breaking connections to grounds, and/or connecting a signal feed to the first conductive plate or the second conductive plate. In one example dual mode antenna system, a signal feed is in communication with one of the antenna elements (first or second conductive plates), and a switchable ground connection is in communication with one of the first or second conductive plates. When the ground connection is open, the system operates in the first mode, and when the ground connection is closed, the antenna system operates in the second mode.

Other embodiments may provide more than two modes. For example, one embodiment includes a switchable ground connection on both of the conductive plates. Each of the four different ways that ground can be connected (or not connected, as the case may be) represents one mode. Accordingly, such a system may be referred to as a “quad mode” antenna system.

Some embodiments may provide for more than four modes. For instance, one example system includes an active switching network on each of the first and second conductive plates, the active switching networks both switching ground and signal feed. Such a system may provide at least eight modes.

In an example method, an antenna system according to at least one embodiment of the invention radiates in each of at least two modes. In the first mode, a first metal plate radiates at it native frequencies while the first conductive plate also radiates together with a second conductive plate at a second set of resonant frequencies. In a second mode, the first conductive plate and a slot element radiate RF signals, the slot element being defined by the placement of the first and second conductive plates. The switching of modes is accomplished, for example, by switching ground and/or feed connections on one or both of the conductive plates, as described above.

The method may further include radiating signals from the system in more than two modes. In one example method, RF signals are fed to the first conductive plate while ground connections are switched at both of the first and second conductive plates. In another example method, each of the first and second conductive plates includes a switching network that switches both ground and signal feed. The example method includes switching the grounds and feeds to provide at least eight modes.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is an illustration of exemplary antenna system100adapted according to one embodiment of the invention. Antenna system100includes antenna elements101and102and slot element103. Slot element103is defined by the placement of elements101and102.

Antenna system100also includes active switching network104that is in electrical communication with one or both of elements101and102. Switching network104is operable to switch one or more connections (e.g., signal, ground), thereby causing antenna system100to resonate in each of two modes. In the first mode, antenna element101resonates at a first set of resonant frequencies while elements101and102radiate together at a second set of resonant frequencies. In the second mode, antenna element101and slot element103both resonate. Accordingly, antenna system100has at least two different operating modes. The modes themselves and techniques and structures for switching are described in more detail below.

FIG. 2is an illustration of exemplary antenna system200adapted according to one embodiment of the invention. System200represents one specific, example implementation of a system according to the principles of system100(FIG. 1). System200includes antenna elements201and202and slot element203. Elements201and202may be disposed, e.g., on a Printed Circuit Board (PCB, not shown). In this example, slot element203is a gap between elements201and202, and, therefore, is defined by the placement of elements202and203.

System200further includes signal feed204, which is adapted to receive a signal from a Radio Frequency (RF) module (not shown). Matching network206provides impedance matching between elements201and202, and it may include a capacitive, inductive, and/or resistive component, depending on design constraints. Active switching network205provides system200with a selectable connection to ground from element202. Switching network205selectively makes and breaks a connection to ground, and in some embodiments, may be as simple as a transistor (e.g., a GaAs FET Switch), a Micro Electronic Mechanical System (MEMS) switch, or a pin diode. In this specific example, it is the switching of the ground connection that causes system200to operate in one of two modes.

In the first operating mode, switching network205breaks the connection to ground. As a result, antenna element202is at least partially ungrounded. In this operating mode, element201radiates at its set of native frequencies, and both element201and202radiate in another set of resonant frequencies. The first and second set of resonant frequencies may include one or more possibly overlapping frequency bands. The shape of antenna elements201and202may be designed to provide performance in one or more established communication bands when in the first operating mode.

In the second operating mode, switching network205connects element202to ground, thereby at least partially grounding element202. In this mode, element201resonates, as does slot element203. In this example, in the second mode, element201resonates substantially at the same frequencies at which it resonates in the first mode—“substantially” being within 6%. Elements201and203can resonate in one or more possibly overlapping frequency bands, according to the specific design of system200. The shape of antenna elements201and202may be designed to provide performance in one or more established communication bands when in the second operating mode. In one example, antenna system200provides performance from 824.2 MHz to 959.8 MHz and 1710.2 MHz to 1989.8 MHz in the first operating mode, thereby a facilitating communication in Global System for Mobile communications (GSM) 850, 900, 1800, and 1900 bands. In the same example, system200can provide performance from 1710.2 MHz to 2500 MHz in the second operating mode, thereby facilitating communication in GSM 1800 and 1900, Universal Mobile Telecommunications System (UMTS) 3G, and Wireless Fidelity (WiFi, IEEE 802.11b and g) bands. Accordingly, an example use for system200is in handheld devices, such as phones, Personal Digital Assistants (PDAs), email devices, laptop and notebook computers, and the like; however, various embodiments are not limited to any particular application or frequency bands.

System200further includes capacitor207, which affects the tuning of one or more frequency bands in first operating mode without affecting the performance of other frequency bands in the seconding operating mode. Specifically, in this example, capacitor207has significant effect on the tuning of the resonant frequencies created by element201and element202together in first operating mode. The effects of capacitor207are determined, at least in part, on its position in system200and its size. In addition to, or alternatively to, using a capacitor some designs may employ inductors and/or resistors to achieve desired tuning. Further, some designs may employ a variable capacitor, metal strip, or other element to provide post-manufacturing tuning capabilities, including during operation of the device. In this specific example, capacitor207also provides Direct Current (DC) isolation between elements201and202.

FIG. 3is an illustration of exemplary system300adapted according to one embodiment of the invention. System300is similar to system200(FIG. 2) but includes the addition of active switching network301and control system302. Control system302operates switching network301and provides RF signals to feed204. Network301may be the same as or similar to network205, and in this example, performs the same function—making and breaking a connection to ground. Active switching network301connects antenna element201to ground, thereby at least partially grounding element201when it is closed. On the other hand, switching network301disconnects element201from ground when open, thereby at least partially ungrounding antenna element201. Accordingly, system300offers at least four operating modes:1. Network205open, network301open2. Network205open, network301closed3. Network205closed, network301open4. Network205closed, network301closed

Modes one and three are the same as described above with regard toFIG. 2. Additionally, system300offers modes two and four. In mode two, element202and element201together contribute a set of resonant frequencies for radiation, while antenna element201, itself, provides an additional set of resonant frequencies. This is similar to mode one, but with slightly different resonances. In mode four element201resonates, as does slot element203, but with slightly different resonances than in mode three.

Accordingly, system200(FIG. 2) may be referred to as a “dual mode” antenna system, and system300may be referred to as a “quad mode” antenna system. In some applications, a quad mode system requires little more complexity in design that does a corresponding dual-mode system, such that the gain in performance from using a quad mode antenna may be achieved with little additional cost.

While systems200and300(FIGS. 2 and 3, respectively) employ devices for making and breaking connections to ground, other embodiments further make and break connections to signal feeds.FIG. 4is an illustration of exemplary system400adapted according to one embodiment of the invention. System400includes antenna elements401and402as well as slot element403. System400also includes tuning element407, which is a capacitor in this example, but can be an inductive and/or capacitive component in other embodiments. Active switching networks405and406switch feeds404and ground and may also, in some embodiments, include impedance matching circuitry. Accordingly, by switching feed404either to element401or to element402, system400offer two modes, assuming ground connections remain constant. For instance, in one example, feed404is at element401, and element401resonates at its native frequencies while elements401and402resonate together at another set of frequencies. By keeping the same ground configuration when feed404is at element402, element402resonates at its native frequencies while elements401and402resonate together at another set of frequencies.

In addition to switching feeds, system400can also offer four modes (i.e., “quad mode operation”) by switching grounds. In this case, either one of switching networks405or406is used for switching ground. There are two configurations for quad mode operation. The configurations and their modes are:

FIG. 5is an illustration of exemplary system500adapted according to one embodiment of the invention. System500is an embodiment constructed according to the principles of systems100(FIG. 1) and 200(FIG. 2); however, systems100and200are not limited to the embodiment shown as system500.

System500includes antenna elements501and502, slot element503, tuning element509, and PCB507. Antenna elements501and502and slot element503are mounted on a part of PCB507separate from the portion that includes many of the electronic components of system500, including active switching network505(in this example, a pin diode), feed element504, and matching network506. The lower portion of PCB507also includes the ground in communication with active switching network505and matching network506. System500further includes RF module508, which sends RF data signals to feed line504.

Sizes of antenna elements and ground planes affect, at least in part, the frequency response of antenna systems. Various portions of system500are given dimensions inFIG. 5, and an antenna system can be constructed according to the dimensions inFIG. 5to provide communication performance in GSM800/900/1800/1900, UMTS, WLAN, and the 900 MHZ and 2.4 GHz bands of Industrial, Scientific, and Medical Band (ISM).

FIG. 6is a graph of the frequency response of an example prototype antenna system built according to the dimensions of system500. In a first mode (mode0), active switching network505(FIG. 5) is opened, thereby causing element502to be ungrounded. Element501resonates at its native frequencies, and elements501and502resonate together at another set of frequencies. The frequency response of system500in mode0is shown in dashed lines inFIG. 6.

In a second mode (mode1), active switching network505is closed, thereby grounding element502. Element501and slot element503resonate. The frequency response is shown in a solid line inFIG. 6. In this example, the frequency responses of both modes overlap. In fact, both responses show a resonance centered approximately in the 1950 MHz range, and such resonance is a result of element501, which radiates in both modes. The left-most resonance of mode0is produced by element501and element502resonating together. The right-most resonance of mode1is produced by slot element503.

Various embodiments are not limited to the shapes and sizes of the example implementations ofFIGS. 1-5, nor do they have to be mounted on PCBs Further, various components of any embodiment may be shaped and/or scaled for different performance characteristics. For instance, geometries and placements of antenna elements affect the frequency response of any given system. Further, component types and values of a tuning component and a matching component may also affect the performance of a given antenna system.

FIG. 7is an illustration of exemplary system700adapted according to one embodiment of the invention. System700has a different shape than that of the systems of the previous examples, but its principles of operation are the same. System700includes antenna elements701,702, slot element703, feed704, and matching network706, tuning element707. Similar to system200(FIG. 2), system700also includes active switching network705that makes and breaks a connection to ground from element702.

System700includes two modes. In the first mode, active switching network705is open while RF signals are received from feed704, and element701resonates at its native frequencies. The first mode employs element702to resonate together with element701at another set of frequencies. In the second mode, active switching network705is closed while RF signals are received from feed704. In this mode, both element701and slot element703resonate.

Embodiments according to the design ofFIG. 7, as well as other embodiments, may be adapted to include another active switching network (not shown) connecting element701to ground, thereby providing at least four modes of operation, similar to the performance described above with regard toFIG. 3. Additionally or alternatively, system700may include switched feed networks (not shown) to provide two modes, four modes and eight modes of operation, as explained above with regard toFIG. 4. Modifications of various systems are possible to adapt those systems to provide two, four, or eight modes.

FIG. 8is an illustration of exemplary system800adapted according to one embodiment of the invention. Like system700, system800has a different shape than that of the systems of the previous examples, but its principles of operation are the same. System800includes antenna elements801,802, slot element803, feed804, and matching network806, tuning element807. System800also includes active switching network805that makes and breaks a connection to ground from element802. System800can be operated in modes, as described above with regard to systems200(FIG. 2) and 700.

FIGS. 9A-9Eare illustrations of exemplary configurations901-905of antenna systems according to several embodiments. Configurations901-905show positional relationships between ground plane920and component910that may be employed in various embodiments. Component910includes at least a first, second, and slot element for an antenna system. Configuration901shows component910completely overlapping with ground plane920. By contrast, configuration902shows component910co-planar with ground plane920, and there is no overlap. Configuration903is similar to configuration902, except that configuration903includes some amount of z-axis offset by component910, such that component910and ground plane920are not co-planar, but rather, are in parallel planes. Configuration904shows component910placed in a plane that is not parallel with ground plane920. Configuration905shows partial overlap between component910and ground plane920. There is also some amount of z-axis offset in configuration905. Configurations901-905are exemplary, andFIG. 9is not exhaustive of the configurations that may be used with one or more embodiments.

FIG. 10is an illustration of exemplary method1000adapted according to one embodiment of the invention. Method1000may be performed, for example, by an antenna control system (e.g., control system302ofFIG. 3) that operates switching networks and provides RF signals to an antenna system, such as those described in the above examples. In step1001, a first antenna element is resonated a first set of frequencies, and the first and a second antenna element in the antenna system are resonated at a second set of frequencies. Step1001may be performed, for example, by providing RF signals to the first antenna element and at least partially disconnecting the second antenna element from a ground. Various techniques may be used to provide RF signals to the first antenna element while at least partially disconnecting the second element from ground. In one embodiment, a fixed signal feed is connected to the first antenna element, and an active switching network provides a connection from the second antenna element to ground. Additionally or alternatively, active feeding networks may be used, which switch both ground and feed and are connected to each of the first and second antenna elements.

In step1002, an active switching network that is in communication with one or more of the first and second antenna elements is adjusted, thereby resonating the first antenna element at the first set of frequencies and a slot element at a third set of frequencies. Further, the slot element is defined by the placement of the first and second antenna elements. Step1002may be performed, for example, by providing RF signals to the first antenna element while at least partially grounding the second antenna element, and such operation may be facilitated by the use of fixed feed/active ground switching and/or active feeding networks, as explained above.

Although method1000is described in terms of “steps,” it should be noted that various embodiments are not limited to any particular order of performing those steps. For instance, it is within the scope of the invention for an antenna system to operate in a mode wherein a first antenna element and a slot element resonate and then to switch to a mode wherein the first antenna element resonates and the first and second antenna elements resonate together. Further, various embodiments are not limited to two modes, but may be adapted to perform at least four or eight modes in any given order.

Various embodiments of the present invention provide one or more advantages over the prior art. For instance, switching between the use of a slot element and a second antenna element may provide larger frequency band jumps than systems that merely switch parasitic elements. Accordingly, various embodiments of the invention may provide modes that span a larger spectrum, in contrast to systems that merely switch parasites on or off to modify the operation of parasites.

Another advantage of some embodiments is efficiency of volume. For instance, various embodiments use two antenna elements to define a third element—a slot element—thereby using space between the elements as a resonating element. Efficiency of volume may allow various embodiments to be used in applications that are especially space-sensitive and demanding of bandwidth.

Yet another advantage is that a tuning element, such as element207(FIG. 2), can be used in various embodiments to independently tune the set of resonances caused by the first and second antenna elements resonating together. Accordingly, such frequency bands can be tuned while requiring little, if any, accounting for the effects thereof on the other resonances provided by the antenna system.