Multimode MIMO Antenna Design For Future Mobile Communications

Future mobile communications need to overcome varieties of new challenges due to the emerging applications and industries. There is no doubt that future mobile communication systems will have higher communication rate, wider signal processing bandwidth (BW), more available communication frequencies, lower power consumption, higher spectrum utilization efficiency, and so on. Since low frequency spectrum,i.e. < 6 GHz, has mostly been applied to varieties of communications,how to fully integrate and utilize the available communication frequencies more efficiently, and how to further optimize the related techniques such as Orthogonal Frequency Division Multiplexing (OFDM)and Multiple Input Multiple Output (MIMO) to improve the channel capacity and spectral efficiency will be important research topics in the future mobile communications. Furthermore, due to the inherent advantages of the millimeter-wave (MMW) technique, the application of MMW technique will highly increase the communication rate for the future mobile communications. So it can be deduced that the design of multri-frequency and wideband antennas as well as MIMO antennas and arrays will be essential tasks in the research work for the future communications.Multimode resonators (MMR) can achieve more than one resonance modes just by using a single resonance structure?so MMR shows competitive advantages in designing high performance multi-frequency and wideband components with a much smaller size. This dissertation has comprehensively studied the MMR theories from the perspective of filters and antennas design, and summarized the operating principles and applications of MMRs under different scenarios. The dissertation has focused on the design of compact multi-frequency and wideband antennas as well as MIMO antennas and reconfigurable antennas based on MMRs. Firstly, based on the design of multimode wideband bandpass filters (BPF), the advantages of MMRs in the design of components with wide operating band and high BW tunability has been studied; secondly,resonances of MMRs have been fully used to design multi-band antennas,multi-band filters and reconfigurable antennas; finally, based on the inherent characteristics of MMRs, three types of multimode MIMO antennas have been designed: multimode spatial diversity slot antenna,multimode wideband dual-polarized slot antenna and high gain switch beam antenna array for 60 GHz applications. The main contents and innovations of the dissertation are summarized as the following three sections:1. As for the design of wideband BPFs, a novel dual-mode defected ground structure resonator (DMDGSR) is proposed and utilized to design a wideband dual-mode BPF with high selectivity and wide stopband. The comprehensive equivalent circuit model of the BPF is proposed. Then, by capacitively connecting two DMDGSRs, a quad-mode defected ground structure resonator (QMDGSR) is achieved for the first time in the literature, and its operating principle is fully studied using the even-odd mode theory, equivalent circuit model, current and field analysis. In the end, a compact quad-mode BPF is realized with simple structure,extremely high selectivity and wide stopband.2. As for the design of multi-frequency antennas and multi-frequency filters, firstly, by fully utilizing the high-order resonance modes of the DMDGSR, a dual-frequency slot antenna is achieved, fed by a coplanar waveguide (CPW) feeding line. The high-order resonance modes are specially analyzed based on the electric field distribution characteristics and the nonuniform transmission line theory. The reconfiguration of the dual-frequency antenna is achieved based on the generalized complementary multimode principle. Secondly, by feeding the QMDGSR with source-load coupled microstrip feeding lines, a tri-band bandpass structure is proposed due to the newly generated transmission zeros (TZ),and a tri-band BPF with six TZs is designed with high selectivity and deep rejection stopband. Finally, by combining a shorted stub loaded MMR and two mix-coupled DGSRs, a tri-band BPF with high selectivity and wide stopband is proposed.3. As for the design of multimode MIMO antennas, firstly, the dual-frequency slot antenna in section 2 is utilized to design a compact spatial diversity slot MIMO antenna, the port isolation of which is enhanced by connecting the radiation bodies of the two slot antenna elements using a neutralization line to produce a TZ between the two ports. Furthermore, the reconfiguration of the neutralization line is also achieved. Secondly, for the first time in the literature,by feeding a slot-line resonator (SLR) at the edge using a microstrip feeding line, three resonance modes are achieved,and a slot antenna with a very wide operating band is proposed. To realize a wideband dual-polarized slot antenna with compact size, a wideband novel cross-shaped dual-mode monopole is designed in the slot antenna. Since the coupling capacitance between the monopole and the ground is mainly concentrated on the cusp sections, the reconfiguration of the monopole is achieved by connecting the cusp sections to the ground using two lumped capacitors. Finally, a cavity-backed high gain switch beam substrate integrated waveguide(SIW) antenna array for 60 GHz applications is designed based on a 4×4 Butler matrix feeding network (BMFN). After finely adjusting the resonance modes of the feeding slot and the radiation patch, a wide operating band is achieved.