148
4 Image Theory of RFID System Physical Anti-Collision
Fig. 4.27 Changes of return loss with impedance loop length
a is 16 mm, the antenna impedance is closest to 50, so the return loss is minimal
at this time. As a increases, the real part of the impedance increases in turn, while
the imaginary part gradually decreases. It can be inferred that when a is less than
16 mm, the antenna does not match the impedance of the chip, and the return loss will
increase instead. Therefore, when the impedance matching loop length a is 16 mm
or 18 mm, the antenna performance is superior.
As can be seen from Fig. 4.28, the values of the real and imaginary parts of the
impedance change significantly. When the impedance matching loop length is determined, the antenna impedance curve will always approach the conjugate matching
condition at a certain frequency, which is also the reason why the antenna center
frequency shifts. However, the degree of impedance matching is different, so the
return loss of the antenna does not increase as the length of the impedance matching
loop increases. When a is 20 mm, the return loss value is relatively large.
The antenna gain visualization images are shown in Fig. 4.29. The red part represents a high antenna gain and the green part represents a low antenna gain. As can
be seen from Fig. 4.29, the gain of the five images is basically the same. This shows
that the antenna parameter changes the return loss, but has no effect on the antenna
gain. In antenna design, when changing the impedance loop length, it is no longer
necessary to consider the antenna gain. When changing the other parameters of the
antenna impedance matching loop, the simulation results show that the antenna gain
is also unchanged. This shows that the antenna gain is not affected by the antenna
parameters, but it is affected by the antenna structure.
(3) Analysis of the influence of the impedance matching loop width on antenna
performance
Changing the size of the impedance matching loop width b, the result is shown in
Fig. 4.30. The center frequency of each antenna works slightly changed, but the
4 Image Theory of RFID System Physical Anti-Collision
Fig. 4.27 Changes of return loss with impedance loop length
a is 16 mm, the antenna impedance is closest to 50, so the return loss is minimal
at this time. As a increases, the real part of the impedance increases in turn, while
the imaginary part gradually decreases. It can be inferred that when a is less than
16 mm, the antenna does not match the impedance of the chip, and the return loss will
increase instead. Therefore, when the impedance matching loop length a is 16 mm
or 18 mm, the antenna performance is superior.
As can be seen from Fig. 4.28, the values of the real and imaginary parts of the
impedance change significantly. When the impedance matching loop length is determined, the antenna impedance curve will always approach the conjugate matching
condition at a certain frequency, which is also the reason why the antenna center
frequency shifts. However, the degree of impedance matching is different, so the
return loss of the antenna does not increase as the length of the impedance matching
loop increases. When a is 20 mm, the return loss value is relatively large.
The antenna gain visualization images are shown in Fig. 4.29. The red part represents a high antenna gain and the green part represents a low antenna gain. As can
be seen from Fig. 4.29, the gain of the five images is basically the same. This shows
that the antenna parameter changes the return loss, but has no effect on the antenna
gain. In antenna design, when changing the impedance loop length, it is no longer
necessary to consider the antenna gain. When changing the other parameters of the
antenna impedance matching loop, the simulation results show that the antenna gain
is also unchanged. This shows that the antenna gain is not affected by the antenna
parameters, but it is affected by the antenna structure.
(3) Analysis of the influence of the impedance matching loop width on antenna
performance
Changing the size of the impedance matching loop width b, the result is shown in
Fig. 4.30. The center frequency of each antenna works slightly changed, but the