Multiple input multiple output antenna

1. Field of the Invention

The invention relates to multiple input multiple output (MIMO) antennas, and particularly to a MIMO antenna for use in ultra-wideband (UWB) communication systems.

2. Description of Related Art

A frequency band of an UWB wireless communication system is 3.1-10.6 GHz. In a wireless communication system, the antenna is a key element for radiating and receiving radio frequency signals. Therefore, an operating frequency band of the antenna must be 3.1-10.6 GHz or greater. In wireless communications, the number of users continues to increase and data traffic is becoming an increasing more important part of the wireless communication system. Both of these factors mean that it is important for operators to look for methods of increasing the capacity of their wireless communication systems to meet future demands.

A relatively new radio communications technology known as multiple input multiple output (MIMO) systems provides for increased system capacity. A number of antennas are used on both the transmitter and receiver, which together with appropriate beam forming and signal processing technologies are capable of providing two or more orthogonal radio propagation channels between the two antennas. The antennas are spaced apart in order to decorrelate the signals associated with adjacent antennas.

There is a need for improved antenna arrangements for use with UWB MIMO systems.

An exemplary embodiment of the present invention provides a MIMO antenna disposed on a substrate including a first surface and a second surface. The MIMO antenna includes a first antenna and a second antenna. The first antenna and the second antenna each include a radiating body for transmitting and receiving radio frequency (RF) signals, a feeding portion for feeding signals, and a metallic ground plane. The radiating body includes a first radiating portion, a second radiating portion, and a gap formed between the first radiating portion and the second radiating portion. The feeding portion is electrically connected to the radiating body. The radiating body and the feeding portion of the first antenna and the ground plane of the second antenna are laid on the first surface of the substrate, and the radiating body and the feeding portion of the second antenna and the ground plane of the first antenna are laid on the second surface of the substrate.

Other advantages and novel features will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic plan view of a multi input multi output (MIMO) antenna of an exemplary embodiment of the present invention, the MIMO antenna including a first antenna and a second antenna;

FIG. 2 is similar to FIG. 1 , but viewed from another aspect;

FIG. 3 is a schematic plan view illustrating dimensions of the first antenna of the MIMO antenna of FIG. 1 ;

FIG. 4 is a graph of test results showing a voltage standing wave ratio (VSWR) of the first antenna of FIG. 1 ;

FIG. 5 is a graph of test results showing a VSWR of the second antenna of FIG. 2 ; and

FIG. 6 is a graph of test results showing an isolation between the first antenna and the second antenna of FIG. 1 .

FIG. 1 is a schematic plan view of a multi input multi output (MIMO) antenna 20 of an exemplary embodiment of the present invention. In the exemplary embodiment, the MIMO antenna 20 is printed on a substrate 10 .

Referring also to FIG. 2 , the substrate 10 comprises a first surface 102 , a second surface 104 parallel to the first surface 102 , a first side 106 , and a second side 108 perpendicular to the first side 106 .

The MIMO antenna 20 comprises a first antenna 20 a and a second antenna 20 b.

The first antenna 20 a comprises a radiating body 22 a , a metallic ground plane 24 a , and a feeding portion 26 a . The radiating body 22 a and the feeding portion 26 a are printed on the first surface 102 . The ground plane 24 a is printed on the second surface 104 .

The radiating body 22 a transmits and receives radio frequency (RF) signals. The radiating body 22 a comprises a first radiating portion 222 a , a second radiating portion 226 a , a first connecting portion 224 a , and a second connecting portion 228 a . A gap 28 a is formed among the first radiating portion 222 a , the second radiating portion 226 a , and the first connecting portion 224 a , and extends from a side of the radiating body 22 a adjacent to the first side 106 of the substrate 10 to the first connecting portion 224 a . The first radiating portion 222 a is electrically connected to the second radiating portion 226 a via the first connecting portion 224 a . The second radiating portion 226 a is electrically connected to the feeding portion 26 a via the second connecting portion 228 a . In an alternation embodiment, the first connecting portion 224 a is defined as a part of the first radiating portion 222 a , and the second connecting portion 228 a is defined as a part of the second radiating portion 226 a.

The feeding portion 26 a is electrically connected to and feeds signals to the second radiating portion 226 a . The feeding portion 26 a is generally parallel to the first side 106 of the substrate 10 , and is a 50Ω transmission line.

The ground plane 24 a is adjacent to the second connecting portion 228 a , and comprises a rectangular first ground portion 242 a , a rectangular second ground portion 246 a , and a rectangular third ground portion 244 a connecting the first ground portion 242 a with the second ground portion 246 a . A length of the first ground portion 242 a along a direction parallel to the second side 108 is greater than that of the second ground portion 246 a.

The second antenna 20 b comprises a radiating body 22 b , a metallic ground plane 24 b , and a feeding portion 26 b . The radiating body 22 b comprises a first radiating portion 222 b , a second radiating portion 226 b , a first connecting portion 224 b , and a second connecting portion 228 b . A gap 28 b is formed among the first radiating portion 222 b , the second radiating portion 226 b , and the first connecting portion 224 b . The first radiating portion 222 b is electrically connected to the second radiating portion 226 b via the first connecting portion 224 b . The second radiating portion 226 b is electrically connected to the feeding portion 26 b via the second connecting portion 228 b . The ground plane 24 b comprises a first ground portion 242 b , a second ground portion 246 b , and a third ground portion 244 b . Configurations of all elements of the second antenna 20 b and relations among the elements of the second antenna 20 b are the same as those of the first antenna 20 a . The radiating body 22 b and the feeding portion 26 b of the second antenna 20 b are printed on the second surface 104 of the substrate 10 . That is, the radiating body 22 b and the feeding portion 26 b of the second antenna 20 b , and the ground plane 24 a of the first antenna 20 a are laid on the same second surface 104 of the substrate 10 . The ground plane 24 b of the second antenna 20 b is printed on the first surface 104 of the substrate 10 . That is, the radiating body 22 a and the feeding portion 26 a of the first antenna 20 a , and the ground plane 24 b of the second antenna 20 b are located on the same first surface 102 of the substrate 10 .

In the exemplary embodiment, the radiating bodys 20 a , 20 b increase bandwidth of the MIMO antenna 20 .

In addition, the MIMO antenna 20 has a low profile and a small size because of the gaps 28 a / 28 b formed between the first radiating portions 222 a / 222 b and the second radiating portions 226 a / 226 b.

FIG. 3 is a schematic plan view illustrating dimensions of the MIMO antenna 20 of FIG. 1 . In the exemplary embodiment, a length d 1 of the MIMO antenna 20 is generally 28 mm, and a width d 2 of the MIMO antenna 20 is generally 14.5 mm. A width d 3 of the radiating body 22 a of the first antenna 20 a is generally 11 mm. A width d 8 of the first radiating portion 222 a is generally 4 mm. A width d 10 of the second radiating portion 226 a is generally 5.75 mm. A length d 4 of the gap 28 a is generally 10.5 mm. A width d 9 of the gap 28 a is generally 1 mm. A length d 5 of the ground plane 24 a is generally 9.5 mm. A width d 6 of the ground plane 24 a is generally 2.5 mm. A width d 7 of the feeding portion 26 a is generally 1.2 mm. A length of the feeding portion 26 a is generally equal to d 6 . That is, the length of the feeding portion 26 a is equal to the width of the ground plane 24 a . Lengths and widths of the all elements of the second antenna 20 b are generally equal to those of the first antenna 20 a , respectively.

FIG. 4 is a graph of test results showing voltage standing wave ratio (VSWR) at UWB frequencies, of the first antenna 20 a . A horizontal axis represents the frequency (in GHz) of the electromagnetic signals traveling through the first antenna 20 a , and a vertical axis represents a VSWR. VSWR of the first antenna 20 a over the UWB range of frequencies is indicated by a curve. As shown in FIG. 4 , the first antenna 20 a has a good performance when operating at frequencies from 3.1-10.6 GHz. The amplitudes of the VSWRs in the band pass frequency range are less than 2, which is what is required for an antenna used in UWB systems.

FIG. 5 is a graph of test results showing voltage standing wave ratio (VSWR) at UWB frequencies, of the second antenna 20 b . A horizontal axis represents the frequency (in GHz) of the electromagnetic signals traveling through the second antenna 20 b , and a vertical axis represents a VSWR. VSWR of the first antenna 20 a over the UWB range of frequencies is indicated by a curve. As shown in FIG. 5 , the second antenna 20 b has a good performance when operating at frequencies from 3.1-10.6 GHz. The amplitudes of the VSWRs in the band pass frequency range are also less than 2.

FIG. 6 is a graph of test results showing isolation between the first antenna 20 a and the second antenna 20 b of the MIMO antenna 20 . A horizontal axis represents the frequency (in GHz) of the electromagnetic signals traveling through the MIMO antenna 20 , and a vertical axis indicates amplitude of isolation. A curve represents amplitudes of isolation over the range of frequencies. As shown in FIG. 6 , the values of isolation never go higher than approximately −12.68 dB over the UWB range of frequencies. The highest isolation value is less than −10, indicating the MIMO antenna 20 is suitable for use in UWB systems.

In this embodiment, the radiating portion 22 a of the first antenna 22 a and the radiation portion 22 b of the second antenna 22 b are disposed on different surfaces of the substrate 200 , therefore, the isolation between the first antenna 22 a and the second antenna 22 b is good.

While embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only and not by way of limitation. Thus the breadth and scope of the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.