TWI523327B - Circular polarization antenna for multi-input multi-output wireless communication system - Google Patents

Description

Circularly polarized antenna for a multiple input multiple output wireless communication system

The present invention relates to a circularly polarized antenna for a multiple input multiple output wireless communication system, and more particularly to a circularly polarized antenna formed by orthogonally combining two identical linearly polarized antennas.

Electronic products with wireless communication functions, such as a notebook computer, a personal digital assistant, etc., transmit or receive radio waves through an antenna to transmit or exchange radio signals to access a wireless network. Therefore, in order to make it easier for users to access the wireless communication network, the bandwidth of the ideal antenna should be increased as much as possible within the allowable range, and the size should be minimized to match the trend of shrinking electronic products.

In a wireless communication system, a circular polarization antenna can avoid polarization loss caused by polarization mismatch between the transmitting antenna and the receiving antenna. Therefore, the position of the receiving device can be made more flexible in application. However, generally circularly polarized antennas are used under single-frequency system architectures, such as satellite communication systems, and do not have high directivity radiation patterns, and thus cannot meet the needs of current wireless communication products.

In addition, as wireless communication technologies continue to evolve, the number of antennas configured for electronic products may increase. For example, the wireless local area network standard IEEE 802.11n supports multi-input multi-output (MIMO) communication technology, that is, related electronic products can synchronously transmit and receive wireless signals through multiple sets of antennas, so as not to increase the frequency. In the case of wide or total transmit power loss (Transmit Power Expenditure), the data throughput (Throughput) and transmission distance of the system are greatly increased, thereby effectively improving the spectrum efficiency and transmission rate of the wireless communication system, and improving communication quality.

However, each of the above-mentioned multiple input multiple output systems has a fixed polarization direction and cannot be adjusted according to system requirements, so that transmission efficiency may be affected by polarization mismatch.

Accordingly, it is a primary object of the present invention to provide a circularly polarized antenna for a multiple input multiple output wireless communication system.

The invention discloses a circularly polarized antenna for a multi-input and multi-output wireless communication system. The circularly polarized antenna includes a first substrate, a second substrate, a first linearly polarized antenna, and a second linearly polarized antenna. The second substrate is vertically formed on the first substrate. The first linearly polarized antenna is formed on the first substrate for generating a radiation electric field having a first polarization direction according to a first feed signal. The second linearly polarized antenna is formed on the second substrate and has the same structure as the first linearly polarized antenna for generating a radiated electric field having a second polarization direction according to a second feed signal. The first polarization direction and the second polarization direction are orthogonal, and the first feed signal and the second feed signal are the same feed signal having a specific phase difference.

Please refer to FIG. 1. FIG. 1 illustrates the design concept of a circularly polarized antenna 10 of the present invention. The circularly polarized antenna 10 can be used in a wireless communication system with multiple inputs and multiple outputs, such as a wireless communication system conforming to the IEEE 802.11n standard, but is not limited thereto, and is used for synchronous transmission and reception of wireless signals. As shown in FIG. 1, the circularly polarized antenna 10 includes a horizontally polarized antenna 11 and a vertically polarized antenna 12. The horizontally polarized antenna 11 and the vertically polarized antenna 12 can be realized by two identical linearly polarized antennas, and are respectively arranged to combine one horizontal substrate 13 and one vertical substrate (not shown) in an orthogonal manner. Therefore, the horizontally polarized antenna 11 and the vertically polarized antenna 12 can be respectively used to provide a horizontal polarization (Electrical Polarization) radiation electric field and a vertical polarization (radiation polarization) electric field. In this case, a signal having a specific phase difference is fed into the horizontally polarized antenna 11 and the vertically polarized antenna 12, respectively, to generate a circularly polarized radiated electric field.

In detail, the circularly polarized antenna 10 of the present invention can provide two forms of circularly polarized radiation electric fields according to the signal feeding mode to meet the requirements of the wireless communication system. For example, if the size of the feed signal is the same and the feed signal of the horizontally polarized antenna 11 leads the phase difference of the feed signal of the vertically polarized antenna 12 by ninety degrees, a left hand circular polarization (Left-Hand) can be generated. Circular Polarization); if the feed signal of the horizontally polarized antenna 11 is less than the ninety degree phase difference of the feed signal of the vertically polarized antenna 12, a right-hand circular polarization (Right-Hand Circular Polarization) can be generated. Radiation electric field.

Of course, the circularly polarized antenna 10 of the present invention can also adjust the input mode of the feed signal according to actual needs, and generate radiation electric fields of various polarization directions, such as horizontal polarization, vertical polarization or elliptical polarization (Elliptical Polarization). Wait. Such corresponding changes are also within the scope of the invention. For example, if only the horizontally polarized antenna 11 is fed with a signal without feeding any signal to the vertically polarized antenna 12, the circularly polarized antenna 10 will generate a horizontally polarized radiated electric field; likewise, if only The vertically polarized antenna 12 feeds the signal without feeding any signal to the horizontally polarized antenna 11, and the circularly polarized antenna 10 will generate a vertically polarized electric field. In addition, if the phase and size of the feed signals of the horizontally polarized antenna 11 and the vertically polarized antenna 12 are appropriately adjusted, various linear or elliptical polarized radiation electric fields can be generated.

Please note that the horizontally polarized antenna 11 and the vertically polarized antenna 12 described above can be realized by any form of linearly polarized antenna. However, in order to meet the requirements of a single antenna high gain and multi-band in a multiple input multiple output system, the present invention provides a printed dual frequency directional antenna, such as a printed dual frequency Yagi antenna (Yagi-Uda), in the following embodiments. Antenna), a circularly polarized antenna implemented to improve polarization matching and improve transmission efficiency.

Please refer to FIG. 2, which is a schematic diagram of a circularly polarized antenna 20 according to an embodiment of the present invention. The circularly polarized antenna 20 includes a horizontal substrate 21, a vertical substrate 22, a horizontally polarized antenna 23, and a vertically polarized antenna 24. The horizontal substrate 21 and the vertical substrate 22 are respectively realized by an FR4 glass fiber double-layer plate and are bonded to each other in an orthogonal manner. The horizontally polarized antenna 23 and the vertically polarized antenna 24 are respectively formed in two metal layers of the horizontal substrate 21 and the vertical substrate 22 for generating a horizontally polarized electric field and a vertically polarized electric field. In the embodiment of the present invention, the horizontally polarized antenna 23 and the vertically polarized antenna 24 are respectively implemented by a printed dual-frequency Yagi antenna, and includes a feeding terminal FED1 and FED2, drivers DRV1 and DRV2, and a director DIR1. DIR2, and reflectors REF1 and REF2.

The feed terminals FED1 and FED2 are used to receive the same feed signal having a specific phase difference. The drivers DRV1 and DRV2 are each composed of two dipole antennas of different operating frequencies and are used to provide the radiation pattern of the two frequency bands. The directors DIR1 and DIR2 are used to pull the radiation pattern generated by the drivers DRV1 and DRV2 in the +Y-axis direction. The reflectors REF1 and REF2 are coupled to a system ground to reflect the radiation pattern generated by the drivers DRV1 and DRV2 in the +Y-axis direction. In this way, the dual-frequency printed Yagi antenna can provide a highly directional antenna radiation field type on the same plane. For the practice of the printed dual-band Yagi antenna, refer to the description of the "Double-Frequency Printed Yagi Antenna" of the Republic of China Patent Application No. 098135250, which will not be repeated here.

In the embodiment of the present invention, the circularly polarized antenna 20 further includes a bonding mechanism 25 for orthogonally bonding the horizontal substrate 21 and the vertical substrate 22. For example, the bonding mechanism 25 can be realized by one of the slots formed in the horizontal substrate 21 and one of the inserts formed on the vertical substrate 22, without being limited thereto. In addition, the embodiment of the present invention can lengthen the length of the vertical substrate 22, for example, 5 millimeters (mm), to prevent the live wires of the two antennas from being short-circuited with the ground.

In this case, if the size of the radiator of the circularly polarized antenna 20 is appropriately adjusted, the circularly polarized antenna 20 is applied to a dual-band (about 2.4 GHz and 5.12 GHz) wireless local area network system conforming to the IEEE 802.11 standard. The overall size of the horizontally polarized antenna 23 is about 50 mm × 50 mm × 1.6 mm, and the overall size of the vertically polarized antenna 24 is about 50 mm × 55 mm × 1.6 mm, and the size of the bonding mechanism 25 is about 15 mm × 10 mm × 1.6. Mm. For the simulation results of the antenna characteristics of the circularly polarized antenna 20, please refer to Figs. 3 to 6. 3 is a reflection coefficient diagram of the circularly polarized antenna 20, FIG. 4 is a Coupling Coefficient diagram of the circularly polarized antenna 20, and FIGS. 5A to 5D are antenna gain diagrams of the circularly polarized antenna 20, The 6A and 6B graphs are the Axial Ratio diagram of the circularly polarized antenna 20.

As shown in Fig. 3, if the reference frequency is -10 dB, the low frequency bandwidth of the circularly polarized antenna 20 falls between 2.39 GHz and 2.51 GHz, and the high frequency bandwidth falls between 4.79 GHz and 6.46 GHz. Since both the high-frequency and low-frequency reflection coefficients are below -10dB, most of the energy can be fed into the antenna body, which produces a good radiation effect.

Figure 4 illustrates the coupling coefficient between the horizontally polarized antenna 23 and the vertically polarized antenna 24 in such a manner that the vertically polarized antenna 24 is the signal output terminal and the horizontally polarized antenna 23 is the signal input terminal. The measurement or simulation is obtained by the proportion of energy transmitted (coupled) by the horizontally polarized antenna 23 to the vertically polarized antenna 24. Since the polarization directions of the two antennas are orthogonal, the coupling coefficient in the operating frequency band is below -20 dB, and has good isolation.

As shown in FIGS. 5A to 5D, the antenna radiation pattern of the circularly polarized antenna 20 has excellent directivity regardless of whether it is high frequency or low frequency. In addition, the circularly polarized antenna 20 of the embodiment of the present invention has stronger radiation field directivity and higher antenna gain than the dual-frequency printed Yagi antenna implemented on the plane.

Finally, FIGS. 6A and 6B illustrate the axial ratio of the circularly polarized antenna 20 in the high frequency band and the low frequency band, respectively. In Fig. 6A, the broken line represents 2.4 GHz, the solid line represents 2.45 GHz, and the dotted line represents 2.5 GHz; in Fig. 6B, the broken line represents 5 GHz, the solid line represents 5.5 GHz, and the dotted line represents 5.8 GHz. As shown, the circularly polarized antenna 20 has a sufficiently low axial ratio in the direction of directivity, and provides a good circularly polarized radiation pattern.

In summary, the present invention implements a circularly polarized antenna for a multiple input multiple output system by orthogonally combining two identical linearly polarized antennas. In addition, the circularly polarized antenna of the present invention can generate radiation electric fields of various polarization directions according to the input mode of the feed signal, such as left-hand circular polarization, right-hand circular polarization or elliptical polarization, etc., to enhance polarization. Matching improves transmission efficiency.

The above are only the preferred embodiments of the present invention, and all changes and modifications made to the scope of the present invention should be within the scope of the present invention.

10, 20. . . Circularly polarized antenna

11,23. . . Horizontally polarized antenna

12, 24. . . Vertically polarized antenna

13, 21. . . Horizontal substrate

twenty two. . . Vertical substrate

FED1, FED2. . . Feed end

DRV1, DRV2. . . driver

DIR1, DIR2. . . Director

REF1, REF2. . . reflector

25. . . Combined mechanism

Figure 1 illustrates the design concept of the circularly polarized antenna of the present invention.

2 is a schematic diagram of a circularly polarized antenna according to an embodiment of the present invention.

Fig. 3 is a reflection coefficient diagram of the circularly polarized antenna in Fig. 2.

Fig. 4 is a diagram showing the coupling coefficient of the circularly polarized antenna in Fig. 2.

Fig. 5A to Fig. 5D are antenna gain diagrams of the circularly polarized antenna in Fig. 2.

Fig. 6A to Fig. 6B are diagrams showing the axial ratio of the circularly polarized antenna in Fig. 2.

10. . . Circularly polarized antenna

11. . . Horizontally polarized antenna

12. . . Vertically polarized antenna

13. . . Horizontal substrate

Claims (11)

A circularly polarized antenna for a multi-input and multi-output wireless communication system, comprising: a first substrate; a second substrate vertically formed on the first substrate; and a first linearly polarized antenna formed on The first substrate is configured to generate a radiation electric field having a first polarization direction according to a first feed signal; and a second linear polarization antenna is formed on the second substrate, and the first line The polarized antenna has the same structure for generating a radiated electric field having a second polarization direction according to a second feed signal; wherein the first polarization direction is orthogonal to the second polarization direction, and the The first feed signal and the second feed signal are the same feed signal having a specific phase difference. The circularly polarized antenna of claim 1, wherein the first feed signal leads the nineteenth phase difference of the second feed signal. The circularly polarized antenna of claim 1, wherein the first feed signal is less than ninety degrees out of phase with the second feed signal. The circularly polarized antenna of claim 1, wherein the first substrate comprises a slot, the second substrate comprises an insert, and the slot and the insert form a bonding mechanism of the first substrate and the second substrate . The circularly polarized antenna of claim 1, wherein the first linearly polarized antenna and the second linearly polarized antenna are a printed dual-frequency directional antenna. The circularly polarized antenna of claim 5, wherein the first linearly polarized antenna and the second linearly polarized antenna are a printed dual-frequency Yagi-Uda antenna. The circularly polarized antenna of claim 6, wherein the first linearly polarized antenna comprises a feed end, a driver, a director and a reflector, the feed end is configured to receive the first feed In the signal, the reflector is coupled to a system ground. The circularly polarized antenna of claim 6, wherein the second linearly polarized antenna comprises a feed end, a driver, a director and a reflector, the feed end is configured to receive the second feed Signal, the reflector is coupled to a system ground. The circularly polarized antenna of claim 1, wherein the first linearly polarized antenna and the second linearly polarized antenna have a radiation pattern that is directed to a third direction, the third direction and the first polarization The direction and the second polarization direction are orthogonal. The circularly polarized antenna of claim 1, wherein the first substrate and the second substrate are respectively an FR4 fiberglass substrate. The circularly polarized antenna of claim 1, wherein the first polarization direction is parallel to the first substrate, and the second polarization direction is parallel to the second substrate.