TWI416796B - Printed dual-band yagi-uda antenna - Google Patents

Abstract

A printed dual-band Yagi-Uda antenna is disclosed, which includes a substrate, a first driver, a first director, a second driver and a reflector. The first driver is formed on the substrate, and is utilized for generating a radiation pattern of a first frequency band. The first director is formed at a side of the first driver on the substrate, and is utilized for directing the radiation pattern of the first frequency band toward a first direction. The second driver is formed between the first driver and the first director on the substrate, and is utilized for generating a radiation pattern of a second frequency band. The reflector is formed at another side of the first driver on the substrate, and is utilized for reflecting both the radiation patterns of the first frequency band and the second frequency band toward the first direction.

Description

Dual-frequency printed Yagi antenna

The invention relates to a dual-frequency printed Yagi antenna, in particular to a dual-frequency printed Yagi antenna with a high directivity radiation field type.

In the modern information society, various wireless communication networks have become one of the most important ways for the public to exchange voice or text messages, data, materials, and audio and video files. Access to these wireless communication networks carrying information by wireless electromagnetic waves requires the use of antennas. Therefore, the development of antennas has become one of the focuses of modern information vendors. In order to realize a wireless communication device that is smaller and more convenient for the user to carry around, such as a mobile phone, a personal digital assistant (PDA), and a wireless USB transmitter (Wireless USB Dongle), the size of the antenna should also be minimized to the antenna. Integrated into a portable communication device.

Since the printed antenna has the advantages of light weight, small size, and high compatibility with various circuits, it has been widely used in various wireless communication products in recent years. In general, in order to reduce the dead angle of receiving or transmitting signals, printed antennas in wireless communication products are mostly implemented as "omnidirectional" antennas, such as printed dipole antennas. In the horizontal plane, the signal of the omnidirectional antenna is radiated at three hundred and sixty degrees, and the change of the signal within a short distance is small, so it is suitable for practical applications. However, with the introduction of antenna arrays or smart antenna technologies, a single antenna often requires an antenna radiation pattern with high gain and high directivity. Under this circumstance, the prior art proposes a printed Yagi Antenna, which utilizes the high directivity of the Yagi antenna to improve the antenna gain in the used frequency band, and further improve the communication quality.

Please refer to FIG. 1 , which is a schematic diagram of a conventional Yagi antenna 10 . The Yagi antenna 10 has one of the most basic architectures of the Yagi antenna, and is composed of a driver 11, a reflector 12, and a director 13. The driver 11 is typically implemented as a dipole antenna for generating a resonance based on the time-varying current fed to generate a radiated electric field. The reflector 12 and the director 13 are formed of a metal piece or a metal plate, which respectively excites a radiation electric field which is opposite to and in phase with the driver 11 through electromagnetic coupling. In this way, the reflector 12 and the director 13 can reflect or draw the radiation pattern generated by the dipole antenna in a specific direction, thereby increasing the gain of the antenna. Of course, the number of parasitic elements such as reflectors and directors can be adjusted according to the actual antenna gain requirements, which are known to those skilled in the art and will not be described here.

However, the conventional printed Yagi antenna is a single-frequency antenna, which cannot meet the needs of the current multi-band of wireless communication products, and therefore has the need for improvement.

Accordingly, it is a primary object of the present invention to provide a dual frequency printed Yagi antenna.

The invention discloses a dual-frequency printed Yagi antenna, which comprises a substrate, a first driver, a first director, a second driver, a reflector and a transmission line. The first driver is formed on the substrate for generating a radiation pattern of the first frequency band. A first director is formed on the substrate on a side of the first driver along a first direction for pulling the radiation pattern of the first frequency band toward the first direction. The second driver is formed on the substrate between the first driver and the first director for generating a radiation pattern of a second frequency band. Wherein the distance between the second driver and the first director is such that the first director forms an open circuit component of the second frequency band. The reflector is formed on the other side of the substrate opposite to the first direction, and is configured to reflect the radiation pattern of the first frequency band and the radiation field pattern of the second frequency band to the first direction . The transmission line is formed on the substrate along the first direction, and is coupled to the reflector, the first driver and the second driver in sequence.

Please refer to FIG. 2, which is a schematic diagram of an embodiment of a dual-frequency printed Yagi antenna 20 of the present invention. The dual-frequency printed Yagi antenna 20 includes a substrate 21, a low frequency driver 22, a low frequency director 23, a high frequency driver 24, a reflector 25 and a transmission line 26. A low frequency driver 22 is formed on the substrate 21 for generating a low frequency band radiation pattern. The low frequency director 23 is formed on one side of the low frequency driver 22 on the substrate 21 for pulling the radiation pattern of the low frequency band to radiate in the +Y axis direction. The high frequency driver 24 is formed on the substrate 21 between the low frequency driver 22 and the low frequency director 23 for generating a high frequency band radiation pattern. For the high frequency signal generated by the high frequency driver 24, the distance between the high frequency driver 24 and the low frequency director 23 will cause the low frequency director 23 to be the same open circuit component. The reflector 25 is formed on the other side of the low frequency driver 22 on the substrate 21 for reflecting the radiation pattern of the low frequency band and the radiation field pattern of the high frequency band in the +Y axis direction. The transmission line 26 is formed on the substrate 21 along the Y-axis direction, and is coupled to the reflector 25, the low-frequency driver 22 and the high-frequency driver 24 for transmitting the feed signal to the low-frequency driver 22 and the high-frequency driver 24. In addition, the dual-frequency printed Yagi antenna 20 further includes a high frequency matching unit 27 formed on the substrate 21 in the vicinity of the high frequency driver 24 for use as a reactive load of the high frequency driver to increase the bandwidth of the high frequency band signal. .

In the embodiment of the present invention, the substrate 21 can be realized by an FR4 double-layer fiberglass board having two upper and lower metal layers. The low frequency driver 22 and the high frequency driver 24 are respectively realized by one dipole antenna in the parallel X-axis direction. Each dipole antenna includes two radiating arms formed on the upper layer and the lower layer of the substrate 21, respectively. The reflector 25 is realized by a metal sheet, is formed on the lower layer of the substrate 21, and is coupled to a system ground end, and the low frequency director 23 and the high frequency matching unit 27 are formed on the upper layer of the substrate 21. The transmission line is implemented by a microstrip line, and one end coupled to the reflector 25 forms a signal feed end FEED of the antenna. For details on the structure of the dual-frequency printed Yagi antenna 20, please refer to Figures 3 to 5. Fig. 3 is a perspective view of a dual-frequency printed Yagi antenna 20, Fig. 4 is a metal layout of the upper layer of the dual-frequency printed Yagi antenna 20, and Fig. 5 is a metal layout of the lower layer of the double-frequency printed Yagi antenna 20.

For detailed functions of each part of the printed Yagi antenna, please continue to refer to the following instructions. In the embodiment of the present invention, the low frequency driver 22 and the high frequency driver 24 are respectively implemented by dipole antennas parallel to the X-axis direction for generating antenna radiation patterns of high frequency band and low frequency band. When the reflector 25 and the low frequency director 23 are not considered, the antenna radiation field generated by the dipole antenna is omnidirectional. In general, the length of the radiating arm of the dipole antenna is about one quarter of the wavelength corresponding to the radiated frequency of the antenna, and the distance between the low frequency driver 22 and the reflector 25 is about 0.1 to 0.25 times the low band wavelength.

The low frequency director 23 mainly pulls the radiation field generated by the low frequency driver 22 to the +Y axis direction to make the radiation pattern of the low frequency band produce stronger directivity. In general, the distance between the low frequency director 23 and the low frequency driver 22 is designed to be about 0.1 to 0.25 times the low frequency band wavelength. Please refer to FIG. 6. FIG. 6 is a schematic diagram showing the current distribution of the low frequency director 23 excited by the time-varying current of the low frequency driver 22. As shown in FIG. 6, the time varying current of the low frequency driver 22 is in the same direction as the current on the low frequency director 23, and therefore, the low frequency director 23 is a good director for the low frequency driver 22, but The radiation field pattern of the low frequency band is de-radiated in the +Y-axis direction. In addition, in the embodiment of the present invention, the distance between the low frequency director 23 and the high frequency driver is appropriately adjusted, so that the low frequency director 23 forms the same open circuit component for the high frequency signal generated by the high frequency driver 24. As such, the low frequency director 23 will not affect the radiation pattern generated by the high frequency driver 24.

Please note that in the embodiment of the present invention, the high frequency driver 24 does not generate the effect of the director for the low frequency driver 22, mainly because the distance between the high frequency driver 24 and the low frequency driver 22 is too close, and the director generally needs to be A wavelength of 0.1 to 0.25 times the drive will have a significant function.

The reflector 25 mainly has the following two functions: (1) as the ground end of the entire antenna and (2) the radiation field pattern generated by the reflected low frequency driver 22 and the high frequency driver 24, so that the radiation field pattern of the antenna can have directivity. effect. Please refer to FIG. 7 and FIG. 8. FIG. 7 and FIG. 8 are schematic diagrams showing current distributions of the reflector 25 excited by the time-varying currents of the low frequency driver 22 and the high frequency driver 24. As shown in FIG. 7, for the low frequency band, the ground current direction of the antenna is completely opposite to the time varying current on the low frequency driver 22. As shown in Fig. 8, for the high frequency band, the ground current direction of the antenna and the time varying current on the high frequency driver 24 are also opposite directions. That is to say, in the embodiment of the present invention, the reflector 25 can simultaneously serve as a reflector for the high frequency driver and the low frequency driver, and the antenna radiation field pattern of the high frequency band and the low frequency band can be de-radiated in the +Y axis direction.

Finally, the high frequency matcher 27 is used to provide a capacitive impedance to match the inductive load generated by the transmission line 26, while increasing the bandwidth of the high frequency reflection coefficient and having little effect on the low frequency bandwidth. For the high frequency signal generated by the high frequency driver 24, the high frequency matcher 27 also does not have the effect of the director, mainly because of its close relationship with the high frequency driver. The director generally has a relatively significant function from 0.1 to 0.25 times the wavelength of the driver. Therefore, in the embodiment of the present invention, the high frequency matcher 27 is an impedance matcher that boosts the bandwidth of the high frequency band.

In short, the embodiment of the present invention utilizes the ground end of the antenna as the reflector of the low frequency driver 22 and the high frequency driver 24, and designs the placement positions of the low frequency director 23 and the high frequency driver 24 to make the low frequency director 23 The low-frequency radiation field has a push-pull effect but does not affect the high-frequency radiation pattern. In this way, the embodiment of the present invention does not require an additional mechanism or device to change the radiation pattern of the antenna, so that a high-directional dual-frequency Yagi antenna can be realized in the same plane.

Of course, the above dual-band printed Yagi antenna architecture can be applied to any dual-band system, for example, to an IEEE 802.11 dual-band wireless local area network system. In the embodiment of the present invention, the dual-frequency printed Yagi antenna 20 feeds the signal to the signal feed terminal FEED in a single-feed mode, and in other embodiments, a similar Yagi antenna can be used. The differential feed method requires a balanced-unbalanced converter (Balun) to be added to the structure. The above related changes are well known to those of ordinary skill in the art and will not be further described herein.

In the embodiment of the present invention, the overall size of the dual-frequency printed Yagi antenna 20 is about 50 mm×50 mm×1.6 mm, and the low frequency driver and the high frequency driver are respectively used to generate corresponding to IEEE 802.11b/g and IEEE 802.11a. Operating frequency. In this case, the simulation results of the dual-frequency printed Yagi antenna 20 are shown in Figs. 9 to 11 respectively. Figure 9 is a reflection coefficient diagram of the dual-frequency printed Yagi antenna 20, and Figs. 10A to 10C are low-band antenna gain maps of the dual-frequency printed Yagi antenna 20, and the 11A to 11C diagrams are dual-frequency. High-band antenna gain map of printed Yagi antenna 20. As shown in Figure 9, the low-frequency bandwidth of the dual-band printed Yagi 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. . It can be seen that the high frequency matcher 27 can effectively increase the high frequency band bandwidth of the dual frequency printed Yagi antenna 20.

As shown in Figures 10 and 11, the antenna radiation pattern has excellent directivity regardless of whether it is high frequency or low frequency. However, since the dual-frequency printed Yagi antenna 20 has one more director in the low frequency portion than the high frequency portion, the antenna gain of the low frequency portion is better than that of the antenna portion of the high frequency portion. Further, although the low frequency director 23 is longer than the high frequency driver 24, the low frequency director 23 is open to the high frequency signal generated by the high frequency driver 24 as long as the appropriate position is selected.

In summary, the present invention provides a dual-frequency printed Yagi antenna that does not require an additional mechanism or device to change the radiation pattern of the antenna, but has a high directivity antenna field pattern at both high and low frequencies. .

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. . . Yagi antenna

11. . . driver

12. . . reflector

13. . . Director

20. . . Dual-frequency printed Yagi antenna

twenty one. . . Substrate

twenty two. . . Low frequency driver

twenty three. . . Low frequency director

twenty four. . . High frequency driver

25. . . reflector

26. . . Transmission line

27. . . High frequency matcher

FEED. . . Signal feed

Figure 1 is a schematic diagram of a conventional Yagi antenna.

2 is a schematic view showing an embodiment of a dual-frequency printed Yagi antenna according to the present invention.

Figure 3 is a perspective view of the dual-frequency printed Yagi antenna in Figure 2.

Figure 4 is a metal layout of the upper layer of the dual-frequency printed Yagi antenna in Figure 2.

Figure 5 is a metal layout of the underlying layer of the dual-frequency printed Yagi antenna in Figure 2.

Figure 6 is a schematic diagram showing the current distribution of the low frequency director in Fig. 2 excited by the time varying current of the low frequency driver.

Figure 7 is a schematic diagram showing the current distribution of the reflector in Fig. 2 excited by the time-varying current of the low frequency driver.

Figure 8 is a schematic diagram showing the current distribution of the reflector in Fig. 2 excited by the time-varying current of the high frequency driver.

Figure 9 is a reflection coefficient diagram of the dual-frequency printed Yagi antenna in Fig. 2.

10A to 10C are low-band antenna gain diagrams of the dual-frequency printed Yagi antenna in Fig. 2.

11A to 11C are high-band antenna gain diagrams of the dual-frequency printed Yagi antenna in Fig. 2.

20. . . Dual-frequency printed Yagi antenna

twenty one. . . Substrate

twenty two. . . Low frequency driver

twenty three. . . Low frequency director

twenty four. . . High frequency driver

25. . . reflector

26. . . Transmission line

27. . . High frequency matcher

FEED. . . Signal feed

Claims (12)

A printed Yagi-Uda antenna includes: a substrate; a first driver formed on the substrate for generating a radiation pattern of a first frequency band; a first director Forming on the substrate, the first driver is along a side of a first direction for pulling the radiation pattern of the first frequency band toward the first direction; and a second driver is formed on the substrate. Between the driver and the first director, a radiation field pattern of a second frequency band is generated, wherein a distance between the second driver and the first director causes the first director to form the second One of the frequency band open-circuit elements; a reflector formed on the substrate on the other side of the first driver opposite to the first direction for radiating the first frequency band and the radiation field of the second frequency band The pattern is reflected in the first direction; and a transmission line is formed on the substrate along the first direction, and is coupled to the reflector, the first driver and the second driver in sequence; a matching device is formed on the substrate Near the second drive, used as an electric And increasing the bandwidth of the second frequency band; wherein the substrate has a first metal layer and a second metal layer, the matching device is formed on the first metal layer, and the reflector is formed on the second metal layer . The dual-frequency printed Yagi antenna according to claim 1, wherein the first driver system A dipole antenna is disposed perpendicular to the first direction, and the dipole antenna includes a first radiating arm and a second radiating arm formed on the first metal layer and the second metal layer, respectively. The dual-frequency printed Yagi antenna according to claim 1, wherein the second driver is a dipole antenna perpendicular to the first direction, the dipole antenna includes a first radiating arm and a second radiating arm, respectively Formed on the first metal layer and the second metal layer. The dual-frequency printed Yagi antenna according to claim 1, wherein the first director is formed on the first metal layer. The dual-frequency printed Yagi antenna according to claim 1, wherein the transmission line is a microstrip line. The dual-frequency printed Yagi antenna according to claim 1, further comprising a signal feeding end, wherein the transmission line is coupled to one end of the reflector. The dual-frequency printed Yagi antenna according to claim 1, wherein the reflector is coupled to one end of the dual-frequency printed Yagi antenna. The dual-frequency printed Yagi antenna according to claim 1, wherein a distance between the first driver and the first director is about 0.1 to 0.25 times corresponding to the first frequency band. wavelength. The dual-frequency printed Yagi antenna according to claim 1, wherein a distance between the first driver and the reflector is about 0.1 to 0.25 times corresponding to a wavelength of the first frequency band. The dual-frequency printed Yagi antenna according to claim 1, wherein the lengths of the first driver and the second driver respectively correspond to one-half of the wavelengths of the first frequency band and the second frequency band. The dual-frequency printed Yagi antenna according to claim 1, wherein the substrate is an FR4 double-layer fiberglass board. The dual-frequency printed Yagi antenna according to claim 1, wherein the first frequency band and the second frequency band respectively correspond to operating frequencies of IEEE 802.11b/g and IEEE 802.11a.