Non-uniform bending line monopole antenna based on WLAN application

0 Preface
The bending line structure has become a new hot spot in modern antenna design in terms of reducing antenna size and improving antenna bandwidth characteristics. In order to improve the performance of the bent line antenna, the researchers proposed a variety of improved structures for different applications and characteristics, including double bend line antenna, folded bent line antenna, three-dimensional bent line antenna, and tapered bent line antenna. , traveling wave bending line antenna and bending line slot antenna.
In this paper, a non-uniform bent line monopole antenna with a coupling patch on the back is proposed. Through the finite difference time domain method, the influence of the geometrical dimensions of each bending section of the bending line on the resonance characteristics of the antenna is studied, and the effect of the coupling patch is analyzed. Finally, a band coverage IEEE 802.11b/g is obtained. 4 to 2.484 GHz) and IEEE802.11a (5.15 to 5.35 GHz, 5.725 to 5.825 GHz) dual-band antennas for WLAN applications.

1 Antenna Modeling and Structural Parameter Analysis The monopole antenna structure of the non-uniform bending line is shown in Figure 1. The substrate was made of Rogers 4350B substrate with a thickness of 0.762 mm and a relative dielectric constant of 3.48. For the convenience of analysis, the radiation element is divided into three segments; the antenna is fed with a 50 Ω microstrip line.

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1.1 The influence of the geometric parameters of the bending joint on the performance of the antenna changes the line length Ln (n=1, 2, 3) and the line width Wn (n=1, 2, 3) of each bending section in turn, and calculates the antenna. The first resonant frequency f1 and the second resonant frequency f2. By adjusting the variation of f2/f1, the adjustment effect of the geometric parameters of each bending joint on the resonance characteristics of the antenna is studied.
Fig. 2 shows the variation of the antenna f2/f1 with the length Ln of each bending pitch. In Fig. 2, W = 58 mm, L = 38 mm, LG = 17 mm, HB = 3 mm, S1 = S2 = S3 = 1 mm, and W1 = W2 = W3 = 2 mm.

Figures 2(a) to 2(f) show almost the same trend of change. As the bending line length Ln increases, f2/f1 gradually decreases, and the two resonance modes approach each other. The adjustment of the first and second resonance modes can be achieved by changing the line length of each of the bent segments in the meander line antenna.
Figure 3 shows the variation of the antenna f2/f1 with the width Wn of each bend. In Fig. 3, W = 58 mm, L = 38 mm, LG = 17 mm, HB = 3 mm, Sl = S2 = S3 = 1 mm, L1 = L2 = L3 = 5 mm. Compared with the variation of the bending line length Ln in FIG. 2, the variation of f2/f1 with the bending line width Wn is complicated.

Fig. 3(a) shows the variation of the antenna f2/f1 with W1 when W2 = 1 mm. It can be seen that as W1 increases, f2/f1 gradually decreases, the two resonant frequencies gradually approach, and almost the same rate of decrease is maintained at different W3.
Figure 3(b) shows the variation of antenna f2/f1 with W1 when W3 = 1 mm. It can be seen that with the increase of W1, f2/f1 gradually decreases, but as W2 increases, the rate of decrease of f2/f1 gradually becomes smaller, and finally remains almost unchanged.
Figure 3(c) shows the variation of the antenna f2/f1 with W2 when W1 = 2 mm. When W3 is small, with W2 increasing, f2/f1 first shows an increasing trend; then, when W3 increases to a certain value, f2/f1 hardly changes with W2; finally, with the continuation of W3 When increased, f2/f1 shows a decreasing trend.
Figure 3(d) shows the variation of the antenna f2/f1 with W2 when W3 = 2 mm. It can be seen that when W1 is small, f2/f1 first shows a decreasing trend; then, when W1 increases to a certain value, f2/f1 hardly changes with the change of W2; finally, as W1 continues to increase , f2/f1 shows an increasing trend.
Figure 3(e) shows the variation of the antenna f2/f1 with W3 when W1 = 1 mm. As W3 increases, f2/f1 gradually increases, and as W2 increases, the rate of increase of f2/f1 gradually decreases.
Figure 3(f) shows the variation of antenna f2/f1 with W3 when W2 = 1 mm. As W3 increases, f2/f1 gradually increases, and at the same value of W1, the same rate of increase is maintained substantially.
The influence of the line width of the bending line on the antenna f2/f1 can be understood as changing the line width of the bending section to change the radiation current distribution state of the first and second resonance modes, thereby changing the effective of the radiation elements in the two modes. The electrical length causes a change in f2/f1. The roles of W1 and W3 are reversed. As W1 increases, f2/f1 decreases. As W3 increases, f2/f1 increases; the effect of W2 is still between W1 and W3. According to the above discussion, it can be obtained that the line width of each bending section of the antenna in the bending line can be changed, and the adjustment of f2/f1 can be realized.
1.2 Effect of coupled patch geometry on antenna performance Figure 4(a) shows the echo of the antenna when the width (WB) of the coupling patch is 5 mm, 7 mm, 9 mm, 11 mm and 13 mm, respectively. Loss simulation curve. The effect of the width of the coupled patch on the resonant performance of the antenna is mainly concentrated in the high frequency band. As the width of the coupled patch increases, the resonant mode matching characteristics produced by the coupled patch become better, while the intrinsic higher order mode shifts toward the low frequency and gradually disappears.

Figure 4(b) shows the return loss simulation curve of the antenna when the coupling patch length (LB) is 7 mm, 9 mm, 11 mm, 13 mm and 15 mm, respectively. As the length of the coupled patch increases, the lowest resonant mode of the antenna moves toward the low frequency, while the matching characteristics become better, but the impedance bandwidth decreases. For the high frequency band, when the value of LB is less than 9 mm, the resonant mode generated by the coupled patch does not appear. The reason for this may be that the resonant mode generated by the coupled patch coincides with the intrinsic high-order mode. As the LB continues to increase, the resonant mode produced by the coupled patch appears and moves in the low frequency direction, while the two modes of the high frequency band gradually move away.
Figure 4(c) shows the return loss simulation curve of the antenna when the height of the coupling patch from the ground plane (HB) is 1 mm, 2 mm, 3 mm, 4 mm and 5 mm. As can be seen from the figure, all resonance modes move in the low frequency direction. When the height of the coupling patch is 2 to 3 m from the grounding plate, two resonant modes appear in the high frequency band; as the height of the coupling patch continues to increase from the grounding plate, the two resonant modes of the high frequency band are far away, and the matching characteristics are simultaneously matched. Getting worse.
As can be seen from the above discussion, the effect of coupled patches on antenna performance is mainly concentrated in the high frequency band. Reasonable selection of the geometry of the coupling patch and the height from the grounding plate can improve the matching characteristics of the second resonant mode and expand the impedance bandwidth without affecting the first resonant mode of the antenna.

2 Antenna actual test results Based on comprehensive consideration of impedance bandwidth and radiation characteristics, the following optimized antenna geometry parameters are obtained, where L=29 mm, L1=6 mm, L2=6 mm, L3=6.5 mm, W1=3 mm, W2=1 mm, W3=2.5 mm, S1=S2=S3=1 mm, LB=11 mm, WB=9 mm, WG=26 mm, HB=3 mm, LG=7 mm , LMS = 10 mm. The antenna is shown in Figure 5.

Figure 6 shows the return loss curve for a non-uniform meander line monopole antenna. As can be seen from the figure, the simulation results are in good agreement with the actual test results. The impedance bandwidth measured in the low band (S1-1<-10 dB) is approximately O. 5 GHz (2.2 to 2.7 GHz); the actual measured impedance bandwidth (S11 < -10 dB) at the high frequency band is approximately 1.8 GHz (4.48 to 6.28 GHz). Figures 7(a)-(c) show gain plots for non-uniform bend line monopole antennas at 2.442 GHz, 5.25 GHz, and 5.775 GHz, respectively, with gains of 0.7 dBi, 1 .65 dBi and 2.3 dBi.

3 Conclusion A planar non-uniform bending line monopole antenna with a coupling patch on the back side is proposed. The relative position of the first and second resonant frequencies in the bending line antenna is adjusted by changing the geometrical dimensions of the bending sections of the bending line. To achieve the dual-frequency adjustable purpose; improve the resonance characteristics of the high-order resonance mode of the bending line antenna through the back-coupled patch, and finally design a frequency band covering IEEE 802.11b/g (2.4 to 2.48 GHz) and The IEEE 802.11a (5.15 to 5.35 GHz, 5.725 to 5.825 GHz) dual-frequency bent line monopole antenna has gains of 2.42 GHz, 5.25 GHz, and 5.775 GHz, respectively. 7 dBi, 1.65 dBi and 2.3 dBi for WLAN applications.