This dissertation describes a method of mutual coupling suppression and broadband method of MIMO antenna for mobile communication systems.
Chapter 2 describes a method of mutual coupling suppression of planar array antenna and meander line MIMO antenna and/or PCS antenna for mobile terminal. The antenna with -27 dB mutual coupling suppression for IEEE 802.11a band designed and fabricated. Proposed antenna has an inverted U structure with via hole between array antennas. From application of inverted U structure, mutual coupling problem of microstrip patch antenna is solved and gain also increased about 2 dB over. The MIMO antenna for IEEE 802.11b and PCS antenna also are proposed. PCS antenna designed at limited area between meander line antennas for IEEE 802.11b. Mutual coupling between reference antenna and PCS antenna is suppressed under -18 dB by using shorting stub on PCS antenna. Gain of reference antenna and PCS antenna are 3.61 dBi and 0.05 dBi, respectively.
Chapter 3 describes a mutual coupling suppression by design of low profile MIMO antenna for small base station. Two type antenna designed for 698~787 MHz and 1.71~2.17 GHz band. Low band antenna with impedance matching cylinder is a metal component that distance between ports is λ/8 to obtain high isolation. As a results, the mutual coupling between ports is suppressed as -19 dB. Measured gain is 6.07 dBi which is good performance. Low band MIMO antenna with 30 mm height has a low profile structure for small base station. The patch antenna for high band proposed as a type of PCB circular patch. The mutual coupling between ports is suppressed -18 dB by application ofλ/2 feeding line and perpendicular structure. Proposed antenna has high gain of 5.98 dBi and low profile structure with 24.565 mm.
Chapter 4 describes a phase adjustable MIMO array antenna for 700 MHz band base station. Broadband single dipole antenna with dual polarization for array antenna proposed for 698~960 MHz band. It has 31.6 % bandwidth which is 12.2 % broader than bandwidth 19.4 % of reference antenna. Isolation between ports is under -26 dB. Because of the radiators is located at λ/4 wavelength distance from reflector plane and center of balun. Measured gain is 10.2 dBi at 960 MHz. Broadband 5-port phase shifter with electrical down tilting is designed. Measurement results of amplitude and phase has a good agreement compare with simulation's one. Array antenna is fabricated and measured. Total electrical down tilting range is from -14∘ to 0∘. The array antenna has a good S-parameters performance over all frequency band and tilting range. Measured gain and horizontal HPBW are 14.5~15.5 dBi and 65∘±5∘, respectively. Upper SLL of proposed MIMO array antenna is -15.5 dB which level is not affected to neighbor base station antenna systems.
Chapter 5 describes the conclusion of this dissertation. The method of mutual coupling suppression between MIMO antennas was proposed for mobile terminal and small base station. Broadening method of the bandwidth dual polarization dipole antenna for base station is also proposed and evaluated.