Design of Three-frequency single-pole antenna for WLAN/WiMAX (1)

With the rapid development of modern Wireless communication technology, Wireless Local Area network (WLAN) is widely used. WLAN uses wireless communication technology to transmit data, voice and video signals in the air, so that users can exchange information anytime, anywhere. Worldwide Interoperability for MicrowaveAccess (WiMAX) is a new broadband wireless access technology that provides high-speed internet-oriented connections, and the data transmission distance is up to 50 km. Currently, WLAN mainly works at 2.45 GHz (2.4 ~ 2.484 GHz), 5.2 GHz (5.15 ~ 5.35 GHz) and 5.8 GHz (5.725 ~ 5.825 GHz), while WiMAX operates at 2.5 GHz (2.5 ~ 2.69 GHz), 3.5 GHz (3.4 ~ 3.69 GHz) and 5.5 GHz (5.25 ~ 5.85 GHz ).

In the field of wireless communication, the practical needs of micro-band antennas, such as multi-band, low cost, miniaturization and ease of processing, have aroused widespread attention. The common miniaturized multi-frequency antenna structure is based on some deformation of the inverted F antenna. These designs take advantage of the miniaturization and low profile advantages of the inverted F antenna, multi-frequency resonance is achieved by means of Slotting and adding support segments. However, to implement multi-frequency operations, the introduced structure is often complicated. Based on this, we have designed a micro-band antenna that can work in WLAN (2.4 GHz and 5.8 GHz) and WiMAX (3.5 GHz) at the same time. The antenna uses three L-shaped micro-strips with a 1/4-Wavelength Single Pole combination to implement three-frequency band operations. The antenna has a simple geometric structure and the medium Board uses a 1.52-mm Rogers R04003, which facilitates integrated design with microwave integrated circuits.

1. Structure Design of Antenna

(1) multi-band method of micro-band patch antenna. The basic methods for dual-frequency or multi-frequency SMD structure and physical structure such as substrates are classified as follows: 1) using a single SMD, use several different natural modes to achieve dual-frequency or multi-frequency operations. 2) A single patch is used to change the field distribution of various natural models of the patch by loading or slotting, so that the resonance frequency is affected and the dual-frequency or multi-frequency operation is realized. 3) A single-layer substrate and multiple patches are used. For example, the characteristics of Multi-resonance can be formed by patches with different resonance frequencies, or multiple radiation units can be used to form a multi-frequency resonant micro-band antenna. 4) The Multilayer overlapping patch structure is used. For example, a multi-band patch structure is used to form multiple resonator to produce the characteristics of multi-band operation. A dual-band antenna with dual-band operating characteristics is obtained using a circular patch structure fed by the multilayer patch overlapping. In view of the above theoretical method of multi-band patch antenna, the single-layer substrate and multiple patches are used to make the antenna work in multiple frequencies.

(2) A 1/4-wavelength single-pole antenna with a micro-band structure. The 1/4 wavelength single pole antenna is obtained by introducing the dipole antenna to the grounding plane using the mirror method. Compared with the dipole antenna, the 1/4 wavelength single pole antenna is introduced to the grounding plane, electromagnetic waves only have radiation power above the ground, so that the radiation power is only 1/2 of the half-wave dipole. However, the directionality coefficient of the 1/4 wavelength dipolar antenna and the half-wave dipolar antenna are both 2.15 dB. The 1/4-wavelength single-pole antenna can be implemented using the microline structure shown in 1 (a). To further reduce the geometric size of the antenna, the antenna can be folded into an L-shaped structure shown in 1 (B. When the antenna operates at the 2.4 GHz, 3.5 GHz, and 5.8 GHz frequencies, the 1/4 wavelength of the electromagnetic waves with three central frequencies is about 31mm, 21mm mm, and 13mm respectively in free space; if an electromagnetic wave is transmitted in a medium with a relative dielectric constant of 3.38, the corresponding 1/4 wavelength is about 15mm, 10mm, and 3mm respectively. For the center frequency of 1/4 GHz, if the free-space wavelength is used, the length of the 1/4 wavelength single pole antenna is 31mm. If the wavelength in the medium is used, the length of the wavelength single pole antenna is 15mm. For the micro-band single-pole antenna on the PCB, the wave propagation passes through both the medium and free space. Therefore, the actual wavelength should be between the guide wave length of the medium and the working wavelength of the free space, in this way, the length of the 2.4 Wavelength Single Pole antenna in the 1/4 GHz operating band should be between 15 and 15 ~ 31mm. Similarly, the length of the 3.5-Wavelength Single Pole antenna with 1/4 Gz operating frequency can be obtained from 10 to 10 ~ The length of a 5.8-wavelength single-pole antenna at a 1/4 GHz operating frequency ranges from 3 ~ 13mm. The impedance matching of the antenna is realized by adjusting the position of the micro-band feeder.

(3) three-frequency single pole antenna structure design. According to the design method of a 1/4 wavelength single pole antenna with a micro-band structure, a three-frequency single pole antenna with a structure as shown in Figure 2 is designed. The antenna structure is roughly divided into six parts: dielectric layer, L-type high-frequency (5.8 GHz) single-pole antenna, L-type medium-frequency (3.5 GHz) single-pole antenna, L-type low-frequency (2.4 GHz) single Pole antenna, micro-band feeder, and reference area. The materials on the dielectric layer use the Rogers R04003, and the relative dielectric constant is 3.38. the upper surface of the dielectric layer is a micro-band feeder and an L-type single pole antenna. The structure 2 is shown in. The required antenna resonance frequency can be obtained by adjusting the length of three L-shaped single pole antennas on the surface of the media layer. The L-type antenna on the left is an intermediate frequency single-pole antenna, which works in the 3.5 GHz band. The intermediate L-type single-pole antenna is a high-frequency single-pole antenna, which works in the 5.8 GHz band; the L-type single-pole antenna on the right is a low-frequency single-pole antenna, which works in the 2.4 GHz band. The bottom surface of the dielectric layer is the reference location of the L-type single pole antenna, as shown in structure 2 (B. The designed antenna is simulated and optimized based on the principle of the dipolar antenna and the single pole antenna and the high-frequency structure simulation software, as shown in table 1.

In conclusion, the length of the low frequency single pole antenna after optimization is in the formula (1 )~ In formula (3), the actual length of the Single Pole sub-antenna after optimization is about 1/4 wavelength, and the length of the 2.4 GHz low frequency single pole sub-antenna is closer to the corresponding 1/4 wavelength; the actual length of the high-frequency single-pole antenna is smaller than that of the low-frequency single-pole antenna.