A dipole antenna is a basic unit form that can be used independently or as a radiating element for a large antenna array. Printed dipole antennas with microstrip balanced balun feeds are widely used due to their thin profile, light weight, small size, low cost, ease of integration and array formation. The general printed dipole antenna has the disadvantages of narrow bandwidth and high cross polarization level. In this paper, a double-sided printed dipole antenna is proposed. On the basis of the single-sided dipole of the traditional microstrip balun feed, the layered medium is double-sidedly printed on both sides of the balun, which changes the balun. The electric field distribution of the feed causes the transverse cross-polarized electric field components to cancel each other to reduce the cross-polarization characteristics of the antenna. And by adjusting the balun structure, a good double resonance matching is obtained, and the effect of widening the bandwidth is achieved. The printed dipole antenna consists of two parts: a balanced balun feed structure printed on one side of the dielectric plate and a dipole arm printed on the other side. The structure of the conventional single-sided printed dipole antenna is shown in Figure 1; the structure of the double-sided printed dipole antenna is shown in Figure 2. From the comparison of the two figures, the former is a layer of medium, one side is a dipole arm, the other side is a microstrip balun; the latter is a double layer medium, both sides are dipole arms, and the middle is equivalent to a strip line. Lun. As can be seen from the right side of Figure 1, the balun of the single-sided dipole antenna will bring the transverse cross-polarization electric field component; while in Figure 2, the transverse electric field components of the double-sided dipole antenna balun cancel each other out, thus greatly The cross polarization level of the antenna is reduced. Figure 1 Single-sided printed dipole antenna The microstrip balun plays a role in balance-unbalance conversion and impedance matching. Its equivalent circuit model is shown in Figure 3: Figure 2 double-sided printed dipole antenna Figure 3 Balanced balun structure equivalent circuit diagram Printed vibrators generally have a double harmonic characteristic, that is, there are two resonance points in the bandwidth. When the two resonance points are far apart, the standing wave curve near each resonance point is sharp, and the standing wave at the frequency point of the resonance point is Larger, it is only possible to obtain a larger bandwidth under the condition that the standing wave requirement is satisfied when the two resonance regions are partially overlapped. By adjusting the parameters s, hs, hm, Wm, and lm (i.e., the length of the open path width and the width of the slot and the length of the matching segment), the impedance can be matched over a wide frequency band. The double-sided printed dipole antenna proposed in this paper consists of two layers of Er=2.55, each layer of t=0.7mm thick double-sided printed dipole arms, and an intermediate printed balun structure. In order to unidirectionally radiate the antenna, a metal base plate is added to the bottom of the antenna. The size parameters of the antenna are shown in Figure 4: w1, w2, h1, h2, L determine the size of the dipole arm; s, hs, hm, Wm, lm determine the size of the balun. Figure 4 antenna size parameter map The antenna of this paper is simulated and the size parameters are basically determined as: w1=35mm, w2=25mm, h1=60mm, h2=25mm, L=40mm; s=1.5mm, hs=1mm, wm=1mm, lm=20mm, hm =25mm. By continuously optimizing these parameter variables, a bandwidth of 1-1.51 GHz (about 40%) with a return loss of less than -10 dB at 1.25 GHz is obtained, as shown in Figure 5: Figure 5 antenna return loss diagram The gain of the antenna in this frequency range is 5-9dBi, as shown in Figure 6: Figure 6 Antenna gain graph The patterns of the antennas at 1 GHz, 1.25 GHz, and 1.5 GHz are shown in Figures 7, 8, and 9, respectively. Figure 7 Figure at 1GHz Figure 8: 1.25 GHz pattern Figure 9: Figure at 1.5 GHz The double-sided printed dipole antenna designed in this paper reduces the cross-polarization level at 1.25 GHz from the -30 dB to -50 dB compared to the conventional single-sided dipole, as shown in Figures 10 and 11: Figure 10 Cross-polarization of a traditional single-sided printed dipole Figure 11 Cross-polarization of a double-sided printed dipole In this paper, a double-sided printed dipole antenna is designed. The double-layer planar dipole structure is used to reduce the cross-polarization level, and the double-resonance point expansion bandwidth is obtained by balanced balun matching. Finally, 40% of the return loss is less than -10dB, the in-band gain is 5-9dBi, and the cross-polarization level is less than -50dB. It provides an effective method and approach for the broadband and low cross-polarization design of printed antennas.
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Analysis of a double-sided printed dipole antenna
1 Introduction