1420MHz PCB Yagi Antenna

The latest PCB Yagi antenna has been successfully tested, see the project https://oshwhub.com/bi6mht/1420MHzde-PCBba-mu-tian-xian-xin

S11 parameters of the antenna: Generally required to be less than -10dB in the working frequency band.

The resonance point of the antenna: the minimum value of the S11 curve within the operating frequency.

Target antenna (as shown below): 1420MHz resonance, S11 parameters

The current situation

The red curve in Figure 1 is the S11 simulation curve of the antenna iterated 8 times. At this time, it is basically close to the converged solution. It can be seen that the resonant frequency is 1413MHz, and the S11 parameter at the resonant frequency is -9.42dB. Considering the actual situation, S11 will deteriorate and the resonant frequency will shift after the actual product is made. Figure 2 shows the radiation pattern of the E-plane and H-plane after 8 iterations of the antenna. The gain is about 8.74dBi. It can be seen that on the profile of Phi=90°, the pattern deviates slightly from 0°. This is probably due to the unbalanced feed of the Yagi antenna excitation element, so the feed structure needs to be improved.

Figure 1: S11 curve of antenna simulation

Figure 2: Radiation pattern of the E and H surfaces of the antenna simulation

The upper right corner of Figure 3 is the measured S11 simulation curve of the antenna. Reading the red line on the right side of Figure 3 shows that the resonant frequency is 1389MHz, the S11 parameter at the resonant frequency is -7.12dB, and the S11 parameter at 1420MHz is only -3.48 dB, this is very bad. Judging from the current results, the difference between the measured resonant frequency and the simulated resonant frequency is 24MHz, and the S11 parameter is about 2.5dB different. It can be roughly speculated that when the results of the next simulation converge, the 24*2=48MHz bandwidth around the resonant frequency will be Within, the S11 parameters should be less than -2.5-10=-12.5dB or so. However, this estimate is ultimately inaccurate. Conservatively speaking, the bandwidth of the antenna with S11 less than -10dB near the resonance point during simulation should be as large as possible. For narrow-band antennas such as the Yagi antenna, the bandwidth should be greater than 100Mhz, and the bandwidth at the resonance point should be greater than 100Mhz. Only when the S11 parameter is <20dB can the reliability of the object be guaranteed. As for the radiation pattern, it was not measured as cheap instruments were not available.

Figure 3: S11 curve measured with NanoVna

In addition, this feed structure was messed up by me, and the initial simulation did not converge. I mistakenly thought there was no problem, so I handed over the printed PCB. However, after delivery, after trying to converge the grid, it was found that the S11 parameters deteriorated sharply. It seems that after roughly simulating the antenna in the future, the grid must be encrypted to see the converged S11 simulation results. The S11 parameters and radiation pattern when the results did not converge at the beginning are shown in Figure 4. In the future, we should repeat the classic PCB Yagi antenna and not mess with the feed structure ourselves, so as to ensure the stability of the equipment.

Figure 4: S11 parameters and radiation pattern without convergence

Physical pictures and test pictures