Efficient synthesis of multi-ring coding facilities

1 Antenna Analysis and Design

This study uses HFSS simulation software to analyze and design the antenna.

The antenna is composed of a dielectric plate, an air layer, and a reflective plate. The double annular arm is a radiating element, and the two short stubs are the adjusting nodes.

The radiation characteristics of the antenna can be explained by the surface current distribution of the antenna. The antenna is like a hollow butterfly printed antenna. The surface current distribution is very similar to that of a half-wave array. At the same time, the excess current on the patch is removed, the current distribution is more regular and compact, and cross polarization is reduced.

1.1CPS Feeder Design

In order to facilitate integration with the system, this design antenna uses the CPS feed form. w and s are the width of the strip line and the distance between the two, and εeff is the effective dielectric constant. In the characteristic impedance calculation of CPS, k′=1-s 2ω2.

The used dielectric plate thickness h1=0.8mm, dielectric constant εr=2.65mm, and loss tangent 0.001. The geometric dimension of the CPS is s=0.4mm, w=0.8mm, so that the characteristic impedance of the CPS is 170Ω.

1.2 Design and Analysis of Droplet Loop Antenna

Each drip loop has an opening angle of 90° and a perimeter of 1.24λ0. The reflector is placed at the bottom of the dielectric plate at 0. 21 λ0 to increase the antenna gain, and at the same time reduce the back radiation of the antenna and increase the front-to-back ratio of the lobe. The main parameters of the antenna:

L1=14.84mm, l2=10.85m, l3=12.10mm, l4=0.80mm, l5=0.80mm. The input impedance Zd=263-j6(Ω), and the E-plane cross polarization is lower than -38dB. In addition, the The antenna has a lobe width greater than 70°.

The following analysis of the main geometric parameters of the antenna affects the performance of the antenna. When analyzing the influence of a parameter, other parameters keep the above values ​​unchanged. The frequency points change with the circumference of the antenna arm. As the perimeter increases, the resonance point continues to decrease. The simulation also shows that l1 can be used to adjust the imaginary part of the antenna. With the extension of l1, the imaginary part of the antenna shows an upward trend. When l1=14.85mm, the matching of the antenna is achieved. At the same time, l1 brings convenience to the array.

1.3 Antennas and Balun

Since the CPS-fed antenna is a balanced antenna, and the coaxial cable is an unbalanced transmission line, if it is directly connected, the outer conductor of the coaxial cable will have high-frequency current flowing through it, which will affect the radiation of the antenna, so it is necessary to Balance 2 baluns are added between the antenna and the cable to shield the current flowing outside the cable shield. Barron is a device that connects balanced double wires to unbalanced coaxial lines. Therefore, in order to actually test the antenna performance, a microstrip balun design needs to be introduced.

In this solution, Balun not only provides balanced unbalanced conversion, but also provides impedance conversion for two different types of lines to achieve a matching effect, as shown by the antenna balun. Due to the balun's own radiation and loss, the antenna's gain and cross polarization and bandwidth are affected. At a center frequency of 5.8 GHz, the gain of the antenna is 10.8 dB, the gain of the antenna plus balun is 9.7 dB, and the antenna of the antenna and antenna plus Barron is S11, both of which are -38 dB.

2 measured results

This study designed and measured a water droplet circular printed antenna operating at 5.8 GHz. The experimental result of the reflection coefficient S11 is given. At a frequency of 5.8 GHz, S11 is -22 dB. The measured center frequency is shifted by 100 MHz from the simulated value. The antenna gain is shown as shown in the maximum direction at a frequency of 5.9 GHz. The gain is 9.8dB.

Because the fixing of the reflector is done manually, the distance between the reflector and the dielectric plate has an error compared with the simulation value, plus the machining error, which causes the antenna frequency to shift.

3 Conclusion

This study proposes a dual loop printed antenna with high gain, low cross polarization, wide lobe, and CPS feed. To facilitate this antenna test, the design of the CPS2 microstrip line balun was introduced. The simulation results are in good agreement with the actual measurement results. The antenna can be used for rectenna systems at low power densities and radio front ends for wireless communication systems.

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