EP2975695A1

EP2975695A1 - Antenna system

Info

Publication number: EP2975695A1
Application number: EP15163144.7A
Authority: EP
Inventors: Shin-Chiang Lin; Liang-San Hsu
Original assignee: Compal Broadband Networks Inc
Current assignee: Compal Broadband Networks Inc
Priority date: 2014-07-17
Filing date: 2015-04-10
Publication date: 2016-01-20
Anticipated expiration: 2035-04-10
Also published as: HUE032981T2; PL2975695T3; TWI530020B; EP2975695B1; TW201605119A

Abstract

An antenna system (10) includes a first antenna unit (AU1) and a second antenna unit (AU2). The first antenna unit (AU1) includes a first antenna element (AE1_1) and a second antenna element (AE1_2), wherein the first antenna element (AE1_1) and the second antenna element (AE1_2) are disposed on a first plane (SUB1) to receive and transmit a first frequency band signal and a second frequency band signal respectively. The second antenna unit (AU2) includes a third antenna element (AE2_1) and a fourth antenna element (AE2_2), wherein the third antenna element (AE2_1) and the fourth antenna element (AE2_2) are disposed on a second plane (SUB2) to receive and transmit a third frequency band signal and a fourth frequency band signal respectively. The first plane (SUB1) is substantially perpendicular to the second plane (SUB2).

Description

Field of the Invention

The invention relates to an antenna system, and more particularly, to an antenna system having a small size, supporting multi-band operation and covering signals of different polarization directions.

Background of the Invention

With the evolving technology in wireless communications, the modern electronic products such as a laptop, a Personal Digital Assistant (PDA), a wireless LAN, a mobile phone, a smart meter, and a USB dongle are able to communicate wirelessly, for example, through the Wi-Fi technology to replace the physical cable for data transmission or receiving. A wireless communication device or system transmits and receives wireless waves via an antenna, so as to deliver or exchange wireless signals, and further to access wireless networks. The communication system of a wireless local network is in general divided into a plurality of frequency bands; therefore an antenna complying with operation of multiple frequency bands becomes more demanding. Besides, the trend of the antenna dimension is getting smaller to accommodate with the same interests, i.e., smaller dimension of electronic products, while antenna isolation and radiation pattern still play a role.
Therefore, it is a common goal in the industry to provide a relative small sized, multi-band supported, efficient, and cost effective antenna.

Summary of the Invention

An objective of the present invention is to provide an antenna system having a small size, supporting multi-band operation and covering signals of different polarization directions.
This is achieved by an antenna system according to claim 1. The dependent claims pertain to corresponding further developments and improvements.
As will be seen more clearly from the detailed description as follows, the claimed antenna system comprises a first antenna unit and a second antenna unit. The first antenna unit comprises a first antenna element and a second antenna element, wherein the first antenna element and the second antenna element are disposed on a first plane to receive and transmit a first frequency band signal and a second frequency band signal respectively. The second antenna unit comprises a third antenna element and a fourth antenna element, wherein the third antenna element and the fourth antenna element are disposed on a second plane to receive and transmit a third frequency band signal and a fourth frequency band signal respectively. The first plane is substantially perpendicular to the second plane.

Brief Description of the Drawings

In the following, the invention is further illustrated by way of example, taking reference to the accompanying drawings. Thereof

FIG. 1 is a schematic diagram illustrating an antenna system according to an embodiment of the present invention;
FIG. 2 is a schematic diagram illustrating an antenna unit shown in FIG. 1;
FIG. 3 is a schematic diagram illustrating an antenna unit shown in FIG. 1;
FIG. 4 is a schematic diagram illustrating an antenna unit shown in FIG. 1;
FIG. 5 is a schematic diagram illustrating antenna isolation measurement results of the antenna elements shown in FIG. 2;
FIG. 6 and FIG. 7 are schematic diagrams illustrating 2D radiation pattern simulation results for the antenna unit shown in FIG. 2 operated at 2.45 GHz and 5.5 GHz respectively;
FIG. 8 is a schematic diagram illustrating return loss of the antenna elements shown in FIG. 2;
FIG. 9 and FIG. 10 are schematic diagrams illustrating 3D radiation pattern measurement results for the antenna units shown in FIG. 1 operated at 2.45 GHz and 5.5 GHz respectively;
FIG. 11 is a schematic diagram illustrating radiation elements according to an embodiment of the present invention;
FIG. 12 is a schematic diagram illustrating radiation elements according to an embodiment of the present invention; and
FIG. 13 is a schematic diagram illustrating an antenna element according to an embodiment of the present invention.

Detailed Description

FIG. 1 is a schematic diagram illustrating an antenna system 10 according to an embodiment of the present invention. The antenna system 10 comprises antenna units AU1, AU2 and AU3. The antenna unit AU1 comprises antenna elements AE1_1 and AE1_2. The antenna elements AE1_1 and AE1_2 are disposed on a substrate SUB1 and are coplanar (i.e., both on the yz plane), but polarizations of the antenna elements AE1_1 and AE1_2 are orthogonal. The antenna unit AU2 comprises antenna elements AE2_1 and AE2_2. The antenna elements AE2_1 and AE2_2 are disposed on a substrate SUB2 and are coplanar (i.e., both on the xy plane), but polarizations of the antenna elements AE2_1 and AE2_2 are orthogonal. The antenna unit AU3 comprises antenna elements AE3_1 and AE3_2. The antenna elements AE3_1 and AE3_2 are disposed on a substrate SUB3 and are coplanar (i.e., both on the xz plane), but polarizations of the antenna elements AE3_1 and AE3_2 are orthogonal. To cover signals of one frequency band but of different polarization directions, the antenna elements AE1_1, AE2_1 and AE3_1 can receive and transmit signals of the same frequency bands (such as 5GHz), and the antenna elements AE1_2, AE2_2 and AE3_2 can receive and transmit signals of the same frequency bands (such as 2.4GHz). In other words, the two antenna elements (e.g., the antenna elements AE1_1 and AE1_2) of one single antenna unit are used to receive and transmit signals of different frequency bands, and all the antenna units AU1, AU2 and AU3 together receive and transmit signals of two different frequency bands as well, but not limited thereto. Besides, since both the antenna elements AE1_1 and AE1_2 are disposed on the substrate SUB1, manufacturing procedures for the antenna elements AE1_1 and AE1_2 can thus be simplified. Similarly, because both the antenna elements AE2_1 and AE2_2 are disposed on the substrate SUB2, and because both the antenna elements AE3_1 and AE3_2 are disposed on the substrate SUB3, assembly processes can become easier and more efficient.
It is worth noting that the polarizations of the antenna elements of one single antenna unit are orthogonal when the antenna elements are adequately disposed (e.g., at right angles) with respect to each other in order to ensure the orthogonality of the polarization directions of the antenna elements. Because of the orthogonal relationship between the antenna elements on the same substrate, they are substantially decoupled and may be independently tuned over wide operating frequency ranges. In this case, isolation between the antenna elements can satisfy requirements of wireless transmission, and the antenna elements can be closely configured so as to minimize the size of the antenna unit. In addition, the substrates are positioned orthogonal relative to each other, so interference between the antenna elements on different substrates SUB1, SUB2, SUB3 can be reduced to further minimize the volume of the antenna system 10.
Specifically, FIG. 2 is a schematic diagram illustrating the antenna unit AU1; FIG. 3 is a schematic diagram illustrating the antenna unit AU2; FIG. 4 is a schematic diagram illustrating the antenna unit AU3. Since the structures and/or operations of the antenna units AU1, AU2 and AU3 are basically similar, the following illustration and descriptions will only focus on the antenna unit AU1, and the similar parts of the antenna units AU2 and AU3 are not detailed redundantly to provide a better understanding. First of all, the antenna elements AE1_1 and AE1_2 of the antenna unit AU1 comprises radiation elements 110, 120, 130, 140 and feed-in points 111, 121, 131, 141 respectively so as to form a dipole antenna as shown in FIG. 2. The radiation elements 110, 120 and the radiation elements 130, 140 are disposed in opposite directions to receive and transmit signals, and are bent to provide a relative small size. For example, if the radiation element 110 and 120 are straightened out, the total length is substantially half the wavelength of the signals to be received or transmitted (such as signals of 5 GHz). However, with those bends, the length L1 between the two ends of the radiation elements 110 and 120 is substantially 0.37 of the wavelength, and hence the radiation elements 110 and 120 can be fully contained in a narrow space as 22 × 10 mm². Likewise, after being bent, the length L2 between the two ends of the radiation elements 130 and 140 is substantially 0.3 of the wavelength of the signals to be received or transmitted (such as signals of 2.4 GHz), and hence the radiation elements 130 and 140 can be fully contained in a narrow space as 38 × 13 mm² to further reduce the dimensions. However, bending the radiation elements 110, 120, 130 and 140 of a dipole antenna could threaten antenna gain. In such a situation, the radiation elements 110 and 120 have a U-shaped structure with two branches for each radiation element, and the radiation elements 130 and 140 have a U-shaped structure with two branches for each radiation element as well to expand current paths and compensate for the loss of antenna gain caused by those bends. The two branches of the radiation element 120 are oriented in the +y direction, meaning that a y-directed vector directed along the positive y-axis is generated from the feed-in point 121 on the radiation element 120 to the opening 122 formed between the ends of the two branches of the radiation element 120. In the meanwhile, the two branches of the radiation element 110 are oriented in the -y direction, thereby making the antenna element AE1_1 polarized along the y axis. On the other hand, the two branches of the radiation element 130 of the antenna element AE1_2 are oriented in the +z direction (meaning that a z-directed vector directed along the positive z-axis is generated from the feed-in point 131 on the radiation element 130 to the opening 132 formed between the ends of the two branches of the radiation element 130), and the two branches of the radiation element 140 are oriented in the -z direction, thereby making the antenna element AE1_2 polarized along the z axis. Obviously, the antenna elements AE1_1 and AE1_2 are orthogonal.
In other words, by bending the radiation elements 110, 120, 130 and 140, the size of the antenna elements AE1_1 and AE1_2 can be minimized. Since the antenna elements AE1_1 and AE1_2 on the same substrate are orthogonal, the antenna elements AE1_1 and AE1_2 can be closely configured to further reduce the dimension of the antenna unit AU1 and to assure the isolation between the antenna elements AE1_1 and AE1_2.
FIG. 5 is a schematic diagram illustrating antenna isolation measurement results of the antenna elements AE1_1 and AE1_2 shown in FIG. 2. As shown in FIG. 5, from 5.15 GHz to 5.82 GHz and from 2.41 GHz to 2.47 GHz, isolation between the antenna elements AE1_1 and AE1_2 is at least 15 dB or above. Moreover, FIG. 6 and FIG. 7 are schematic diagrams illustrating 2D radiation pattern simulation results for the antenna unit AU1 shown in FIG. 2 operated at 2.45 GHz and 5.5 GHz respectively. Because the antenna elements AE1_1 and AE1_2 are symmetrical and orthogonal, omni-directional radiation pattern can be formed on the xy plane when operated at 2.45 GHz, and omni-directional radiation pattern can be formed on the xz plane when operated at 5.5 GHz. Similarly, as shown in FIG. 3 and FIG. 4, the antenna element AE2_1 is polarized along the x axis, while the antenna element AE2_2 is polarized along the y axis, such that the antenna elements AE2_1 and AE2_2 are disposed in a mutually orthogonal relationship. The antenna element AE3_1 is polarized along the z axis, while the antenna element AE3_2 is polarized along the x axis, such that the antenna elements AE3_1 and AE3_2 are disposed in a mutually orthogonal relationship. Accordingly, the antenna elements AE2_1, AE2_2, AE3_1 and AE3_2 of the antenna units AU2 and AU3 respectively provide ideal isolation and radiation pattern.
Furthermore, as shown in FIG. 2, the radiation elements 110 and 120 of the antenna element AE1_1 (or the feed-in points 111 and 121 more specifically) are spaced out by a gap D1, and the geometry and size of the gap D1 can affect parasitic capacitance between the radiation elements 110 and 120. Likewise, the radiation elements 130 and 140 of the antenna element AE1_2 (or the feed-in points 131 and 141) are spaced out by a gap D2, and the geometry and size of the gap D2 can affect parasitic capacitance between the radiation elements 130 and 140. Therefore, by properly adjusting the geometry and size of the gaps D1 and D2, electrical characteristics such as impedance of the antenna elements AE1_1 and AE1_2 may vary and thus increase radiation efficiency.
FIG. 8 is a schematic diagram illustrating return loss of the antenna elements AE1_1 and AE1_2 shown in FIG. 2, wherein the dashed line indicates return loss simulation results of the antenna element AE1_1, and the solid line indicates return loss simulation results of the antenna element AE1_2. As shown in FIG. 8, if the gaps D1 and D2 are appropriately designed, return loss of the antenna element AE1_1 operated in a range of 4.00 GHz to 6.50 GHz and return loss of the antenna element AE1_2 operated in a range of 2.17 GHz to 2.84 GHz have values below -10 dB, meaning that more than 90% of energy is radiated out into space and radiation efficiency is enhanced. Namely, there is no need to add an matching circuit into the antenna elements AE1_1 and AE1_2 of the present invention as in the prior art to improve impedance matching, while impedance matching can be easily achieved by delicately-designed pattern of the antenna elements AE1_1, AE1_2 and appropriately-adjusted dimension of the gaps D1, D2.
Moreover, as shown in FIG. 1, because the yz plane (where the antenna elements AE1_1 and AE1_2 are located), the xy plane (where the antenna elements AE2_1 and AE2_2 are located) and the xz plane (where the antenna elements AE3_1 and AE3_2 are located) are orthogonal, interference between the antenna elements on different substrates can be reduced to further minimize the dimension of the antenna system 10. The polarization direction (i.e., toward the x direction) of the antenna element AE2_1 of the antenna unit AU2 is perpendicular to the polarization directions (i.e., toward the y and z directions) of the antenna elements AE1_1 and AE1_2 of the antenna unit AU1 adjacently disposed. The polarization direction (i.e., toward the y direction) of the antenna element AE2_2 of the antenna unit AU2 is perpendicular to the polarization direction (i.e., toward the x direction) of the antenna element AE3_2 of the antenna unit AU3 adjacently disposed. However, the present invention is not limited to this and the antenna units AU1, AU2 and AU3 may be assembled in other arrangements. Besides, FIG. 9 and FIG. 10 are schematic diagrams illustrating 3D radiation pattern measurement results for the antenna units AU1, AU2 and AU3 shown in FIG. 1 operated at 2.45 GHz and 5.5 GHz respectively. As shown in FIG. 9 and FIG. 10, the antenna units AU1, AU2 and AU3 can cover different polarization directions.
Please note that the antenna system 10 is an exemplary embodiment of the invention, and those skilled in the art can make alternations and modifications accordingly. For example, the antenna elements AE1_1, AE2_1 and AE3_1 of the present invention have reflection symmetry, and the antenna elements AE1_2, AE2_2 and AE3_2 have rotational symmetry. That is to say, each of the antenna elements AE1_2, AE2_2 and AE3_2 looks the same after rotation by an angle of 180° with respect to its center. Alternatively, the antenna elements may be asymmetrical according to practical consideration of the antenna design. Also, the pattern and type of the antenna elements are not limited herein, and the dimension of the antenna elements may be properly adjusted according to operating frequency requirements. The substrates SUB1, SUB2, SUB3 may be a fiber glass composite laminate conforming to the FR4 specifications, while other kinds of dielectric substrates may be used depending on the application.
In addition, a centerline CL_1 of the antenna element AE1_1 passes through the feed-in points 111 and 121; the centerline CL_2 of the antenna element AE1_2 passes through the feed-in points 131 and 141. The centerline CL_1 of the antenna element AE1_1 and the centerline CL_2 of the antenna element AE1_2 are spaced out by a distance D, the magnitude of the distance D and the polarization of the feed-in points 111, 121, 131 and 141 can be modified according to different system requirements in order to optimize the performance of the antenna elements AE1_1 and AE1_2. Besides, the feed-in points 111 and 121 are connected to a central conductor and an outer grounded conductor (not shown) of a coaxial cable (or a transmission line) in order to transmit signals from the radiation elements 110 and 120 to a back-end processing circuit (not shown) or in order to provide signals to the radiation elements 110 and 120. The feed-in points 131 and 141 are connected to a central conductor and an outer grounded conductor of another coaxial cable in order to transmit signals from the radiation elements 130 and 140 to the back-end processing circuit or in order to provide signals to the radiation elements 130 and 140. That is to say, with the feed-in points 111, 121, 131 and 141, the antenna elements AE1_1 and AE1_2 transmitting and receiving signals of different frequency bands can form a dual-feed-in dual-band antenna structure. Therefore, it is not necessary to add a switching circuit or a diplexer to filter signals of different frequency bands into the antenna system 10 of the present invention as is needed in a conventional dual-band antenna with only one single feed-in point. In this way, the dual-feed-in dual-band antenna structure of the present invention costs less and prevents unnecessary switching circuits or diplexers from influencing antenna characteristics, thereby ensuring bandwidth, gain and radiation efficiency.
Geometric structures of the radiation elements may be properly adjusted according to system requirements. For example, the radiation element 110 shown in FIG. 2 comprises 3 portions, and the radiation element 130 comprises 15 portions. However, the number of portions of one bent radiation element can be properly adjusted and thus increased or decreased to any integer for further reducing the dimension of the antenna element. Besides, the widths of the portions of each antenna element can be different - For example, the feed-in points 131 and 141 shown in FIG. 2 are disposed on the wider portions of the radiation element 130 and 140 respectively. The inward corner facing the center of the portions is a right angle as shown in FIG. 2, but is not limited herein and the angle enclosed by two adjacent portions can be in a range of 90 to 180 degrees.
FIG. 11 is a schematic diagram illustrating radiation elements 420 and 430 according to an embodiment of the present invention. The radiation element 420 can replace the radiation elements 110 and 120 shown in FIG. 2; the radiation element 430 can replace the radiation elements 130 and 140 shown in FIG. 2. The outward corner not facing the center of the radiation elements 420 and 430 may be chamfered to reduce the parasitic capacitance due to the effect of discontinuity.
FIG. 12 is a schematic diagram illustrating radiation elements 520 and 530 according to an embodiment of the present invention. The radiation element 520 can replace the radiation elements 110 and 120 shown in FIG. 2; the radiation element 530 can replace the radiation elements 130 and 140 shown in FIG. 2. Particularly, the radiation elements 520 and 530 are in the shape of a curve.
FIG. 13 is a schematic diagram illustrating an antenna element AE4_2 according to an embodiment of the present invention. The antenna element AE4_2 can replace the antenna elements AE1_2, AE2_2 and AE3_2 shown in FIG. 1. The width of the gap between the radiation elements 630 and 640 of the antenna element AE4_2 is variant, which changes from D3 to D4 and then from D4 back to D3, such that the geometric structures of parasitic capacitor alter.
To sum up, more than one antenna element is disposed on one substrate of the present invention so that manufacturing procedures and assembly processes can thus be simplified. Also, because the antenna elements of one single antenna unit are orthogonal, isolation between the antenna elements can satisfy requirements of wireless transmission, and the size of the antenna unit can be minimized. Besides, the substrates are mutually orthogonal, so interference between the antenna elements on different substrates can be reduced to further minimize the dimension of the antenna system 10. Corresponding to configuration of the antenna elements, the pattern of the antenna elements of the present invention are properly designed to minimize the total volume of the antenna elements, to simultaneously assure antenna gain and impedance matching and to increase radiation efficiency.

Claims

An antenna system (10), characterized by:
a first antenna unit (AU1), comprising a first antenna element (AE1_1) and a second antenna element (AE1_2), wherein the first antenna element (AE1_1) and the second antenna element (AE1_2) are disposed on a first plane (SUB1) to receive and transmit a first frequency band signal and a second frequency band signal respectively; and

a second antenna unit (AU2), comprising a third antenna element (AE2_1) and a fourth antenna element (AE2_2), wherein the third antenna element (AE2_1) and the fourth antenna element (AE2_2) are disposed on a second plane (SUB2) to receive and transmit a third frequency band signal and a fourth frequency band signal respectively;

wherein the first plane (SUB1) is substantially perpendicular to the second plane (SUB2).
The antenna system (10) of claim 1, further characterized in that the first antenna element (AE1_1) has a first polarization direction and the second antenna element (AE1_2) has a second polarization direction which are orthogonal to each other, and the third antenna element (AE2_1) has a third polarization direction and the fourth antenna element (AE2_2) has a fourth polarization direction which are orthogonal to each other.
The antenna system (10) of any of claims 1-2, further characterized in that the first frequency band signal and the third frequency band signal are within a first frequency band, the second frequency band signal and the fourth frequency band signal are within a second frequency band, and wherein the first frequency band is different from the second frequency band.
The antenna system (10) of any of claims 1-3, further characterized by further comprising a third antenna unit (AU3), wherein the third antenna unit (AU3) comprises a fifth antenna element (AE3_1) and a sixth antenna element (AE3_2), the fifth antenna element (AE3_1) and the sixth antenna element (AE3_2) are disposed on a third plane (SUB3) to receive and transmit a fifth frequency band signal and a sixth frequency band signal respectively, and the third plane (SUB3) is substantially perpendicular to the first plane (SUB1) and the second plane (SUB2).
The antenna system (10) of any of claims 1-4, further characterized in that the first antenna element (AE1_1) comprises:
a first radiation element (110), having a U-shaped structure with two branches;

a second radiation element (120), having the U-shaped structure with two branches, wherein the first antenna element (AE1_1) has reflection symmetry, and the first radiation element (110) and the second radiation element (120) are spaced out by a first gap (D1) to form parasitic capacitance;

a first feed-in point (111), disposed on the first radiation element (110); and

a second feed-in point (121), disposed on the second radiation element (120).
The antenna system (10) of claim 5, further characterized in that the first radiation element (110) extends along the first polarization direction, and the second radiation element (120) extends along a direction opposite to the first polarization direction.
The antenna system (10) of claims 5 or 6, further characterized in that the second antenna element (AE1_2) comprises:
a third radiation element (130), comprising a plurality of portions to form a U-shaped structure with two branches; and

a fourth radiation element (140), comprising a plurality of portions to form the U-shaped structure with two branches, wherein the second antenna element (AE1_2) has rotational symmetry, and the third radiation element (130) and the fourth radiation element (140) are spaced out to form parasitic capacitance;

a third feed-in point (131), disposed on the third radiation element (130); and

a fourth feed-in point (141), disposed on the fourth radiation element (140).
The antenna system (10) of claim 7, further characterized in that the third radiation element (130) extends along the second polarization direction, and the fourth radiation element (140) extends along a direction opposite to the second polarization direction.