Research On Compact MIMO Antenna For WLAN Applications

In recent years,multiple-input multiple-output(MIMO)antennas have been widely used in wireless local area network(WLAN),meanwhile these antennas are often required to be installed against a wall or on a ceiling surface for indoor wireless access point(AP)applications or point-to-point communications.Consequently,the designs and studies of the compact MIMO antennas possessing features of directional radiation,high port isolation and covering WLAN 2.4 GHz(2.4-2.485 GHz)and 5 GHz(5.15-5.85 GHz)bands have important significance and application value.In this thesis,three compact MIMO antennas with good performance for WLAN applications are proposed.The works and research contents are as follows:A MIMO antenna comprises two dual-band low-profile microstrip antenna elements is presented.A single-feed,dual-frequency and wideband microstrip antenna element with low profile is proposed for Wireless Local Area Network(WLAN)applications.The compact MIMO antenna can be attained by placing two antenna elements symmetrically with extremely narrow edge-to-edge inter-element space.By inserting an inverted Z-shaped neutralization line between two antenna elements and placing a rectangular parasitic patch below two antenna elements,the isolation nearby center frequency of lower band is improved significantly.Measured results show that the lower and upper operating bandwidths(|S11|<-10 dB)are 2.4-2.5 GHz and 5-6.29 GHz,respectively.Besides,a dip of 60 dB in the lower band and the gain of near 6.78 dBi and 7.99 dBi at 2.45 GHz and 5.5 GHz,respectively,are obtained.A compact MIMO antenna comprises two planar inverted-F antenna(PIFA)elements is proposed.A low-profile dual-band rectangular slotted inverted-F antenna for wireless local area network(WLAN)applications is proposed.The compactness is realized by making the ends of two inner inverted L-shaped arms couple with the central symmetrical metal patch and providing additional capacitance.The size of the radiator shows an average compactness of around 46%with respect to a conventional rectangular unslotted planar inverted-F antenna.The compactness of the proposed MIMO antenna can be attained through using the proposed miniaturized antenna elements and meanwhile employing an extremely narrow edge-to-edge inter-element space(3 mm).By etching three rectangular slots on the common ground side by side,the port isolation can be enhanced.Measured results show that the proposed MIMO antenna can cover the dual WLAN bands and even reach a maximum of 54 dB at 2.45 GHz.A compact directional MIMO antenna with high isolation comprises two dipole antenna elements is proposed.In this thesis,the dipole antenna element is used to generate dual WLAN bands.The mutual coupling between antenna elements is suppressed by applying orthogonal polarization between two adjacent elements and separating the ground of each antenna element.By adopting the balun with a length of quarter wavelength,the current on the outer conductor of the coaxial line is effectively suppressed,and the isolation between the antenna elements is further increased.By using the defected ground structure,the MIMO antenna possesses a certain lightning protection ability,which shows it has a good application prospect.Measured results show that the proposed MIMO antenna can cover the dual WLAN bands and the isolation is upper than 40 dB over the whole operating bands.