Design Of Multiband Mobile Terminal Antennas Based On CRLH-TL

As a wireless device that directly connects users,the mobile terminal occupies an important position in the communication system.In order to meet the functional and design requirements of mobile terminals,the embedded antenna is constantly moving toward multiband and miniaturization.At present,terminal antennas are often in the form of conventional antennas,such as monopole antennas,inverted F-shaped antenna antennas(IFAs),and loop antennas.Since the above-mentioned conventional antennas are essentially based on the right-hand transmission lines,they can only generate positive-order resonant modes,and the resulting resonant modes are strictly related to the size of the antenna structure.Therefore,under the increasingly strict requirements,if the current terminal antenna form is still used,it will be prone to bring about design bottlenecks.The composite right/left-handed transmission line(CRLH-TL)is a combination of the electromagnetic metamaterial and the transmission line theory.Compared with the right-hand transmission line,in addition to positive-order resonant modes,the CRLH-TL can also generate lower negative-order resonance modes and zero-order resonant mode.The zero-order resonant mode is very suitable for achieving miniaturization of microwave devices and antennas because its resonance frequency is theoretically independent of the structure size.Therefore,in this thesis theory of the CRLH-TL is introduced into the design of terminal antennas,and several CRLH-TL based multiband mobile terminal antennas are proposed.The main contributions of the thesis are summerized as follows.1.An LTE/WWAN terminal antenna based on CRLH-TL zero-order resonance is designed.The proposed antenna adopts a method to construct a CRLH-TL unit equivalent structure in a traditional multi-branch IFA antenna.The zero-order resonant mode generated by the equivalent structure cooperates with the resonant modes generated by the multi-branch IFA antenna to cover the LTE/WWAN band(698-960/1710-2690 MHz).Since the zero-order resonant frequency is theoretically independent of the physical size of the structure,using it to cover the lower frequency band allows the antenna to possess multiband performance and reduces its physical size at the same time.The simulated and measured results show that,in the LTE/WWAN bands,the reflection coefficients of the antenna are less than-6 dB,and the normalized gain patterns of the antenna show good omni-directional features in the YOZ plane.In the operating band,the measured far-field radiation efficiencies of the antenna meets the requirement.2.A multiband 5G terminal antenna element based on CRLH-TL zero-order resonance is designed.By using this element,an 8×8-element MIMO terminal antenna is also designed.The proposed 5G terminal antenna element adopts a method to construct a CRLH-TL unit equivalent structure in a loop antenna.The zero-order resonant mode cooperates with the resonant modes generated by the loop antenna to cover three 5G communication bands(1.49-1.71/3.3-3.6/4.8-5 GHz).In addition,in order to solve the problem that the bandwidth of zero-order resonant mode is narrow,a band-stop matching circuit is designed on the feed structure of the proposed antenna element.It is verified by the simulation that the performances of the proposed 5G element meet the design requirements.In order to better reflect the performance of the proposed element,an 8×8-element MIMO terminal antenna formed by eight proposed elements are also shown in thesis.There is no decoupling structure between any two elements in the MIMO antenna,and the only decoupling method is adjusting the relative position between the elements.The simulated and measured results show that,in the 1.49-1.71/3.3-3.6/4.8-5 GHz frequency bands,the reflection coefficients of each element in the MIMO antenna are less than-6 dB.The far-field radiation efficiencies of each element meet the requirement.Between any two element in the MIMO antenna,the isolation features are all greater than 10 dB,and the envelope correlation coefficients are less than 0.23.3.A WLAN/WiMAX/5G terminal antenna based on CRLH-TL multi-order resonance is designed.The proposed antenna is designed by loading two?-type CRLH-TL equivalent unit structures on a loop monopole.The-1st-and+1st-order resonant modes generated by the two loaded structures cooperate with the resonant mode generated by the loop monopole to cover the WLAN/WiMAX/5G band(2.4-2.485/3.35-3.65/4.5-6 GHz).In addition,due to the special interdigital capacitor structure,the physical sizes of the loaded units are further reduced.The proposed antenna adopts a planar design,and its planar size is 22×16.5 mm~2.The simulated and measured results show that,in the WLAN/WiMAX/5G frequency band,the reflection coefficients of the proposed antenna are less than-10 dB,and the normalized gain patterns of the antenna show good omni-directional features in the YOZ plane.In the operating band,the measured far-field radiation efficiencies of the antenna meet the requirement.