Design of small broadband open slot antenna

0 Introduction

Today, the wireless communication industry is developing rapidly, and PDAs, laptops and mobile phones have become necessities in people's lives. At the same time, communication systems also require broadband to achieve high-speed wireless transmission and reception of multimedia information. Because microstrip-fed slot antennas have advantages such as wide impedance bandwidth and simple structure, easy processing and low price, this type of antenna is also being widely used in various wireless transmission equipment.

In fact, although people have conducted extensive and in-depth research on microstrip-fed slot antennas, it is still a difficult task to simultaneously achieve miniaturization and broadband characteristics of the antenna. At present, researchers have proposed two microstrip open slot structures (L-type and inverted T-type), which can achieve broadband characteristics and reduce the size of the antenna.

This paper proposes a new design method for open slot antenna. The antenna uses FR4 dielectric board and adopts 50Ω impedance matching microstrip feeding. Since the floor is placed on one side of the dielectric board and the microstrip feed line is placed on the other side of the dielectric board, the wideband characteristics of the antenna can be achieved by coupling the open slot through the microstrip line.

1 Antenna size design

Figure 1 shows the specific structural dimensions of the antenna. The antenna is made on a 0.8 mm thick FR4 dielectric board with a dielectric constant of 4.4. The size of the dielectric board is 27 mm x 30 mm. When designing, an open slot can be opened on the floor. The position of the slot should make the entire floor asymmetric. The microstrip feed line is located on the other side of the dielectric board. In this way, the broadband characteristics of the entire small antenna can be achieved through the coupling between the 50 Ω impedance-matched microstrip feed line and the open slot on the back.

2 Antenna Structure

The opening slot of the antenna is a rectangular structure, with length L and width W as its main parameters. The slot length L determines the resonant mode at the lower frequency band, while the resonant mode at the higher frequency band is excited by the slot width W. In this way, by properly selecting the size of the opening slot, that is, the length and width of the slot, the two modes can be well coupled to achieve a wider impedance bandwidth. At the same time, the position of the opening slot on the floor or the position of the microstrip feed line can also be adjusted to make the antenna have better impedance matching characteristics.

3 Performance parameters

Figure 2 shows the return loss curve obtained by simulation of the antenna. The working frequency band of the antenna is 2.89～6.74 GHz, the impedance bandwidth is about 80.2%, and the return loss is less than -10 dB. Table 1 lists the working frequency bands corresponding to different sizes of floors when L2 is unchanged. Figure 3 is the gain curve of the antenna. It can be seen that the antenna gain change in the entire working frequency band is less than 3 dB. At the same time, the radiation direction of the antenna is also acceptable for wireless transmission equipment.

4 Conclusion

This paper presents a design method for a miniaturized broadband antenna. The antenna has the floor located on one side of the dielectric plate and the microstrip feeder located on the other side. The broadband characteristics of the antenna can be achieved through coupling between the microstrip feeder and the open gap. The size of the antenna is 27mm×30mm×0.8 mm, and the impedance bandwidth is 80.2%. The small structure and broadband characteristics of the antenna make it very suitable for application in mobile terminal devices.