The antenna was designed and simulated using Ansoft’s HFSS full-wave simulator. Figure 40 shows the relation about the MIMO antenna construction of Figure 35. Because the phase of power to two antennas is out of phase, it does not have good performance of MIMO performance.
In this research, good performance is like high isolation between two an-tennas and omni-directional radiation pattern. So, we modify the path from Figure 35 to Figure 37. It will have the same degree of phase to feed two antennas. To reach inphase of the power, we construct the coupler to Figure 36. For port1 to port3 and port1 to port4, we can find that the difference of degree is 0°. Figure 42 shows the difference of degree. In other words, they are inphase. Then, for port2 to port3 and port2 to port4, we can find that the difference of degree is about 180°. Figure 43 shows the difference of degree. Because the period of electromagnetic wave length is 180°, it is inphase too. The Figure 38 is the method of being inphase about two antennas. It has the relation about two antenna in Figure 41.
It can decrease the relation about 2dB from the value of the difference of Figure 40 and Figure 41 in 2.4GHz. This construction can also improve the performance of the radiation pattern. Figure 44 shows the radiation pat-tern of the construction of Figure 37. The radiation patpat-tern become more omni-directional after the construction is modified. Figure 45 shows the radiation pattern. We can compare the radiation pattern between Figure 44 and Figure 45. The construction of Figure 37 can improve the radiation pattern to omni-direction. So, we can demonstrate that the method can improve the performance for MIMO antenna. To enhance the isolation, we add the strip resonator on the ground between two antennas. The con-struction is like as Figure 38. The isolation is shown in Figure 46 after we add the strip resonator. We can find that the isolation is decreasing about 3dB after the rod is added. The isolation is about -25dB in the Fig-ure 46. It is effective to decrease the relation by adding the rod between
research, the open stubs is used to match the input impedance. Figure 47 shows the input impedance before we use open stubs. It does not match in the bandwidth that we design. So, we design the construction to solve the problem. The construction is like as Figure 39. The input impedance is shown in Figure 48 after open stubs is designed. The input impedance is matched in the bandwidth that we design. It can reach less than -10dB in the bandwidth that we want. Figure 39 is the final construction of MIMO antenna. Figure 49 is the simulated S-parameter of the research for com-plete MIMO antenna. Figure 50 is the measurement S-parameter of the research for complete MIMO antenna. The simulated result is agreement with the measurement result about S-parameter. The measurement radia-tion pattern of the proposed MIMO antenna is shown in Figure 51. Figure 51 and Figure 52 displays the radiation pattern of the simulated and mea-surement result. The environment of meamea-surement result of Figure 51 is the proposed MIMO antenna to be fed in port 1, and to be terminated in port 2. Then the environment of measurement result of Figure 52 is the proposed MIMO antenna to be fed in port 2, and to be terminated in port 1.
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Figure 41: The simulated S-parameter of the contribution of Figure 33
Figure 42: The simulated relationship between two ports of Figure 35
Figure 43: The difference of degree from port1 to port3 and port1 to port4 respectivly
Figure 44: The difference of degree from port2 to port3 and port2 to port4 respectivly
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Figure 45: The radiation pattern for the structure of Figure35
Figure 46: The radiation pattern for the structure of Figure39
Figure 47: The simulated relationship between two ports of Figure 36
Figure 48: The S-parameter before we add open stubs to match
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Figure 49: The S-parameter after we add open stubs to match
Figure 50: The simulated S-parameter for the proposed MIMO antenna
Figure 51: The measurement S-parameter for the proposed MIMO antenna
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Figure 52: The radiation pattern about simulated and measurement result
Figure 53: The radiation pattern about simulated and measurement result
4.4Conclusion
Here, we have presented the MIMO antenna. This structure is com-posed by quadrature hybrid and monopole antenna. The quadrature hybrid can offer high isolation by its property. For handset device, we have to have omni-directional radiation pattern. So, the monopole antenna is selected.
Quadrature hybrid and monopole antenna can provide good performance that we want in wireless communication. To enhance the isolation, we add the strip resonator between two antennas. It can guide the energy of antenna coupling each other to the ground. Hence, we have high isolation MIMO antenna.
We know what high isolation is equal to high S/N. From Shannon equation, high S/N can increase the channel capacity. So, the higher iso-lation the better performance for MIMO antenna.
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Chapter5
Conclusion And Future Study 5.1Conclusion and Summary
Here, we will summarize the conclusions of three topics. The first topic, on-chip antenna, has been integrated in the MMIC or the RFIC.
It can provide specifications that we want. Like as radiaion pattern and return loss. For radiation pattern, high F/B ratio is what we want to have.
Due to the proposed on-chip antenna be designed to avoid the radiation pattern interfering with the back circuit, high F/B ratio is more important obviously. So we select the construction of Yagi-Uda to implement the effect.
Then, the second topic, a novel structure antenna for leaky-wave an-tenna, we have reached performance of the wide frequency sacnning range and the decreasing side lobe level. The proposed antenna of monopole at the open end of the leaky wave antenna is the mainly design.
For the third topic, high isolation MIMO antenna, we have provided the antenna of performance of high isolation about two antennas and the omni-directional radiation pattern. The isolation can reach about -25dB.
It can increase the channel capacity and S/N ratio when the isolation of two antennas is high. It can also cancel the effect of antenna array to reach omni-directional radiation pattern for personal communication device in-directly. The other antenna characteristic is omni-directional radiation pattern. Because we have the proposed antenna to apply to personal com-munication device, the omni-directional radiation pattern is designed.