Wideband antenna and related radio-frequency device

A wideband antenna is disclosed. The wideband antenna includes a ground element electrically connected to a ground, a feed element for feeding in a Radio-Frequency signal, a radiation element electrically connected to the feed element for radiating the Radio-Frequency signal, and at least one meta-material structure electrically connected between the radiation element and the ground element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wideband antenna and related Radio-Frequency device, and more particularly, to a wideband antenna and related Radio-Frequency device utilizing at least one meta-material structure to change a center frequency.

2. Description of the Prior Art

An antenna is used for transmitting or receiving radio waves, to communicate or exchange wireless signals. An electronic product with a wireless communication function, such as a laptop or a personal digital assistant (PDA), usually accesses a wireless network through a built-in antenna. Therefore, for facilitating easier access to the wireless communication network, an ideal antenna should have a wide bandwidth and a small size to meet the trends of compact electronic products within a permissible range, so as to integrate the antenna into a portable wireless communication equipment.

However, the antenna requires a longer current route to induce a lower frequency RF signal. It is difficult to reach multiple radiation frequency bands in the lower frequency within a limited antenna space.

Therefore, how to improve antenna bandwidth effectively to apply to wireless communication systems with wide frequency bands such as long term evolution (LTE) has become a goal of the industry.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a wideband antenna and related Radio-Frequency device.

An embodiment of the present invention discloses a wideband antenna. The wide band antenna comprises a ground element electrically connected to a ground, a feed element for feeding in a Radio-Frequency signal, a radiation element electrically connected to the feed element for radiating the Radio-Frequency signal, and at least one meta-material structure electrically connected between the radiation element and the ground element.

Another embodiment of the present invention discloses a Radio-Frequency device. The Radio-Frequency device comprises a Radio-Frequency signal processor for generating a Radio-Frequency signal, and a wideband antenna coupled to the Radio-Frequency signal processor comprising a ground element electrically connected to a ground, a feed element for feeding in the Radio-Frequency signal, a radiation element electrically connected to the feed element for radiating the Radio-Frequency signal, and at least one meta-material structure electrically connected between the radiation element and the ground element.

DETAILED DESCRIPTION

Meta-materials or Left-Handed Materials are artificial materials engineered to have properties that may not be found in nature, e.g. negative permittivity and permeability. Anti-Snell's Effect, Anti-Doupler Effect or Anti-Cerenkov Effect may be shown when electromagnetic waves propagate in such materials. Meta-materials usually gain their properties from structure rather than composition, microwave frequency meta-materials are usually synthetic, constructed as arrays of electrically conductive elements (such as loops of wire) which have suitable inductive and capacitive characteristics.

Please refer toFIG. 1, which is a schematic diagram of a wideband antenna10according to an embodiment of the present invention. The antenna10comprises a ground element100, a radiation element102, a feed element104and at least one meta-material structure106. The ground element100is electrically connected to ground for providing grounding. The feed element104is electrically connected between the radiation element102and the ground element100for feeding a Radio-Frequency (hereinafter called RF) signal RF_sig to the radiation element102. During signal transmission, the feed element104may receive the RF signal RF_sig from an RF signal processor to transmit to the radiation element102to perform radio wave transmission. During signal reception, the radiation element102may induce the RF signal RF_sig from the air to transmit to the RF signal processor through the feed element104. The meta-material structure106is electrically connected between the radiation element102and the ground element100, the meta-material structure106may be disposed periodically and each meta-material structure106may be equivalent to a resonator to form such artificial materials to have properties that may not be found in nature, i.e. the negative permittivity and permeability.

Please refer toFIG. 2, which is a schematic diagram of an equivalent circuit of the antenna10. The meta-material structure106comprises a capacitive element108and an inductive element110. As shown inFIG. 2, the capacitive element108is electrically connected to the radiation element102, the inductive element110is electrically connected to the ground element100. In such a structure, the capacitive element108and inductive element110may form the meta-material structure106to have a longer length of an effective current route on the radiation element102, such that a center frequency Fc of the antenna10may be shifted to a lower frequency, which effectively reduces a size of the antenna10.

In other words, the present invention may add the meta-material structure106to the radiation element102of the antenna10, such that the center frequency Fc of the antenna10may be shifted to the lower frequency, which effectively reduces a size of the antenna10if a length of the radiation element102remains unchanged. Those skilled in the art may make modifications or alterations accordingly. For example, a number of the meta-material structures106is not limited, a designer may increase or decrease the number of the meta-material structures106to adjust an amount of frequency shift of the center frequency Fc to meet practical requirements. Specifically, the more the meta-material structures106, the lower the center frequency Fc. Moreover, the designer may adjust a position of the meta-material structure106electrically connected to the radiation element102, which may generate different amounts of frequency shift of the center frequency Fc and change a bandwidth of the antenna10as well.

Please refer toFIG. 3AandFIG. 3B.FIG. 3Ais a schematic diagram of an antenna30and antennas32and34having a meta-material structure according to an embodiment of the present invention.FIG. 3Bis a schematic diagram of Voltage Standing Wave Ratios (hereinafter called VSWR) of the antennas30,32and34. Structures of the antennas30,32and34are similar and same elements are denoted with the same symbols. As shown inFIG. 3A, the antenna30is a monopole antenna whose radiation center frequency Fc is determined by a length of effective current route of its radiation element, e.g. the length may be equal to a quarter wavelength of the center frequency Fc. The antennas32and34comprise different meta-material structures106and306, which may generate different amounts of the center frequency Fc shift between the antennas32and34. For the meta-material structure106, the capacitive element108is located between the inductive element110and the feed element104. On the other hand, for the meta-material structure306, an inductive element310is located between a capacitive element308and the feed element104.

InFIG. 3B, the VSWR of the antenna30is denoted with a solid line, the VSWR of the antenna32is denoted with a dash line, and the VSWR of the antenna34is denoted with a dotted line. As shown inFIG. 3B, a center frequency Fc_30of the antenna30is around 1.68 GHz, a center frequency Fc_32of the antenna32is around 1.52 GHz, and a center frequency Fc_34of the antenna34is around 1.56 GHz, wherein a bandwidth difference between the antennas32and34is about 0.4 GHz. As can be seen, the highest to the lowest center frequency is Fc_30>Fc_34>Fc_32. Thus, adding the meta-material structure106to the antenna32, or adding the meta-material structure306to the antenna34, may generate different amounts of the center frequency Fc shift. Besides, changing the structure of the meta-material structures106or306, i.e. the relative positions between the capacitive elements108and308and the inductive elements110and310, may generate different amounts of the frequency shift as well.

Hence, if the length, the area and the shape of the radiation element102remain unchanged, the center frequency Fc_30of the antenna30may be shifted to the lower center frequency Fc_32or Fc_34by adding the meta-material structure106or306to the antenna32or34, which reduces an antenna size of the antenna30effectively.

Moreover, shapes of the capacitive elements108and308and the inductive elements110and310have no limitation. For example, please refer toFIG. 4AtoFIG. 4C, which are schematic diagrams of the inductive element having different shapes. As shown inFIG. 4AtoFIG. 4C, an inductive element410shown inFIG. 4Acomprises an arm and inductive elements411and412respectively shown inFIG. 4BandFIG. 4Ccomprise a bended arm, wherein a position where the inductive element412is connected to the ground element100is different from where the inductive element411is connected to the ground element100, which may generate different amounts frequency shift.

Please refer toFIG. 5AtoFIG. 5C, which are schematic diagrams illustrating the capacitive element and the inductive element having different shapes. As shown inFIG. 5AtoFIG. 5C, the capacitive elements518and528comprise at least one arm, an inductive element511comprises two arms to form an F-shape, while the capacitive element518comprises two arms to form an up-side-down F-shape. Such various shapes of the meta-material structure may generate different amount of frequency shift.

Besides, the antennas30,31and32may further comprise a branch to be electrically connected to the ground element100to form a Planar Inverted-F Antenna (hereinafter called PIFA). Please refer toFIG. 6AtoFIG. 6F, which are schematic diagrams of antennas60,61,62,63,64and65according to embodiments of the present invention. InFIG. 6A, the radiation element102of the antenna60further comprises a branch600electrically connected to the ground element100to form a PIFA, such that a center frequency of the antenna60may be shift to a lower frequency by adding a meta-material structure, which effectively reduces an antenna size of the PIFA, i.e. antenna60.FIG. 6BtoFIG. 6Fillustrate different shapes and relative positions of the capacitive element and the inductive element to form different meta-material structures.

Furthermore, since the meta-material structure has a characteristic of changing the radiation center frequency of the antenna, the antenna may further comprise a switch circuit for switching the center frequency of the antenna. As a result, the single antenna may be able to operate between different center frequencies to effectively broaden a bandwidth of the antenna.

Specifically, please refer toFIG. 7, which is a schematic diagram of a Radio-Frequency device7according to an embodiment of the present invention. The RF device7comprises an antenna70and an RF signal processor72. The RF signal processor72is coupled to the antenna70for generating an RF signal RF_sig to be radiated in the air by the antenna70. The antenna70comprises a ground element700, radiation elements702,712and722, a feed element704, a meta-material structure706and a switch circuit720. The ground element700is electrically connected to the ground for providing grounding. The radiation element702comprises a branch730electrically connected to the ground element700, such that the antenna70is a PIFA. The feed element704is electrically connected between the ground element700and the radiation elements702,712and722for feeding the RF signal RF_sig to the radiation elements702,712and722. During signal transmission, the feed element704may receive the RF signal RF_sig from an RF signal processor72to transmit to the radiation elements702,712and722to perform radio wave transmission. During signal reception, the radiation elements702,712and722may induce the RF signal RF_sig from the air to transmit to the RF signal processor72through the feed element704. As shown inFIG. 7, the radiation elements702and712may comprise, at least one, bends7020and7120, and the radiation elements712and722may be regarded as branches of the radiation element702for generating different current routes, such that antenna70may operate in multiple operating bands at once.

The meta-material structure706comprises a capacitive element708and an inductive element710, the capacitive element708is electrically connected to the radiation element702, and the inductive element710is electrically connected to the switch circuit720. The switch circuit720comprises a switch D, a resistor R and an inductor L. The switch D is coupled between the inductive element710and ground element700for switching a connection between the inductive element710and the ground element700according to a switch signal CR_sig outputted by the RF signal processor to adjust a radiation center frequency Fc of the antenna70. The resistor R is coupled to the switch signal CR_sig for attenuating the switch signal CR_sig to protect the switch D from damaged by an overcurrent. One end of the inductor L is coupled to the resistor R, another end is coupled to the switch D and the inductive element710for blocking the RF signal RF_sig on the inductive element710from mixing with the switch signal CR_sig, which ensures a radiation characteristic of the antenna70. The switch D may be a Positive-Intrinsic-Negative diode or a Bipolar Junction Transistor.

Noticeably, the radiation element702has longest length and thus is mainly used for radiating the RF signal RF_sig within a low frequency band, the meta-material structure706is electrically connected to the radiation element702, so as to change the center frequency Fc within the low frequency band.

In such a structure, the center frequency Fc of the antenna70may be adjusted by the switch circuit720. In operation, when the switch D connects the inductive element710with the ground element700, the center frequency Fc of the antenna70is a first frequency F1, while when the switch D disconnects the inductive element710from the ground element700, the center frequency Fc of the antenna70is shifted to a second frequency F2. The second frequency F2is greater than the first frequency F1due to the characteristic of the meta-material structure706.

Please refer toFIG. 8AandFIG. 8B, which are schematic diagrams of VSWR and efficiency of the antenna70corresponding to different switch states. A switch state State_on refers to the switch D connecting the inductive element710with the ground element700and is denoted with a solid line. A switch state State_off refers to the switch D disconnecting the inductive element710from the ground element700and is denoted with a dash line. As shown inFIG. 8A, in the low frequency band that the VSWR less than 3, the center frequency Fc is the first frequency F1(≈740 MHz) at the switch state State_on, and the center frequency Fc is the second frequency F2(≈870 MHz) at the switch state State_off. In comparison, the VSWR at a high frequency band nearly remains unchanged. As shown inFIG. 8B, in the low frequency band that the radiation efficiency is greater than 40%, the center frequency Fc is the first frequency F1at the switch state State_on, and the center frequency Fc is the second frequency F2at the switch state State_off, while the efficiency nearly remains unchanged at the high frequency band.

Noticeably, a bandwidth (704˜787 MHz) in which the first frequency F1lies may meet a requirement of the Long Term Evolution and a bandwidth (791˜960 MHz) in which the second frequency F2lies may meet a requirement for 800 MHz and 900 MHz bands of the Global System for Mobile Communications (GSM). As a result, the center frequency Fc within the low frequency band of the antenna70may be adjusted by the switch circuit720switching the connection between the inductive element710and the ground element700, which effectively reduces the antenna size within a limited space. Therefore, the antenna70may be able to operate in different operating frequency bands of the telecommunication systems as well.

Please refer toFIG. 9, which is a schematic diagram of an antenna90according to an embodiment of the present invention. The antenna90is derived from the antenna70, and same elements are denoted with the same symbols. A meta-material structure906of the antenna90is different from the meta-material structure706of the antenna70. That is, the meta-material structure906comprises capacitive elements908and918and an inductive element910, and the meta-material structure906may be equivalent to cascade two capacitors and shunt one inductor to the radiation element702of the antenna90. The capacitive elements908and918and inductive element910may comprise at least one arm to generate different amounts of frequency shift.

Please refer toFIG. 10AandFIG. 10B, which are schematic diagrams of VSWR and efficiency of the antenna90corresponding to different switch states. The switch state State_on refers to the switch D connecting the inductive element910with the ground element700, and is denoted with a solid line. The switch state State_off refers to the switch D disconnecting the inductive element910from the ground element700, and is denoted with a dash line. As shown inFIG. 10A, in the low frequency band that the VSWR less than 3, the center frequency Fc is the first frequency F1(≈740 MHz, lies in 704˜787 MHz) at the switch state State_on, and the center frequency Fc is the second frequency F2(870 MHz, lies in 791˜960 MHz) at the switch state State_off, while the VSWR at a high frequency band nearly remains unchanged. As shown inFIG. 10B, in the low frequency band that the radiation efficiency is greater than 35%, the center frequency Fc is the first frequency F1at the switch state State_on, and the center frequency Fc is the second frequency F2at the switch state State_off, while the efficiency at a high frequency band nearly remains unchanged.

To sum up, the present invention adds the meta-material structure to the radiation element of the antenna, such that the center frequency of the antenna may be shifted to a lower frequency if the length, the area and the shape of the radiation element remain unchanged, which effectively reduces the antenna size. Moreover, the present invention further combines the switch circuit with the antenna to switch the connection between the inductive element and the ground element, such that the antenna may be able to operate in different operating bands of the telecommunication system accordingly.