Research On Ultra - Wideband / Multi - Band Antenna And High Isolation MIMO Antenna

With the wide application of all kinds of wireless communication system, the existing spectrum resource has become more and more scarce. It has severely restricted the development of wireless communication technology. Ultra-wideband (UWB) technology and multiple input multiple output (MIMO) technology are two kinds of effective methods to solve the above problem. The UWB technology can effectively increase the system bandwidth, while MIMO technology can significantly improve the spectral utilization ratio at double in the case of not increasing bandwidth. Therefore, the above two techniques has became the research hot in wireless communication field now, and corresponding UWB and MIMO antenna has also received widespread attention. In addition, with the diversity of the function of mobile terminal equipment, it makes the antenna need to be able to send and receive radio signals of different frequency band at the same time. It has stimulated the rapid development of multiband antenna. In short, the current research of antenna is developing in the direction of broadband, multiband and multi-antenna.At present, many UWB and multi-band antenna both have some disadvantages, such as too large size, too narrow bandwidth and so on. Many UWB antennas can’t completely cover or just barely cover the 3.1-10.6 GHz UWB frequency band. While some of current multi-band antenna can’t cover all working frequency bands of the multi-band wireless communication system. The band-notched techniques that adopted by many current UWB antennas are too old. And it need to innovate and improve. Although there are a few antennas using the electromagnetic band gap (EBG) structure to realized band rejection, but it mostly confined to the traditional type of mushroom EBG structure. This kind of EBG structure have some defects, such as owning too large size, needing to etch metal via, difficult to produce, having poor performance on band rejection and so on. While for many of current MIMO antennas, there are still many deficiencies. For example, the size are too large, there are too few antenna elements, and the isolation are too low and so on. The existing isolation techniques have many deficiencies, needing to be improved.Therefore, this paper puts forward five new antenna designs. The first antenna is a new kind triple-band antenna, which introduces a "comb" shape parasitic element. Its dimension is 29mm×29mm×1.6mm. The three working frequency bands of it can cover all the current WLAN and WiMAX working bands.The second antenna is a new kind of compact UWB antenna. The antenna design incorporates a variety of broadband technologies (including methods such as adopting round radiation patch, etching slots, gradient processing for part of patch). Finally, the dimension of this antenna is only 20mm×15mm×1.6mm. The -10dB impedance bandwidth of the proposed antenna reaches up to 10.32GHz (2.97-13.29 GHz), which is far more than 7.5GHz (3.1-10.6 GHz) that is required by the general UWB antenna. The third antenna is a new frequency notched UWB antenna, which introduces a new kind of "double fork" shape EBG structure. By introducing the above EBG structure into the second proposed UWB antenna, the third antenna realized the band notch characteristic. By placing the new coplanar EBG structure at the back of the antenna, the antenna gets two notched frequency bands, which are 5.12-6.21 GHz and 7.07-8.92 GHz. The fourth antenna is a new kind high isolation MIMO antenna, which introduces a double layer of net shape coupler. The antenna consists of four antenna elements. Its dimension is only 60mm×60mm×1.6mm. The minimum isolation between the adjacent antenna units is 26.41dB. The introduction of double layer coupler makes the minimum isolation between the antenna units that located at the diagonal position increasing from 16.26dB to 25.59dB, having increased 9.33 dB. The fifth antenna is a new kind high isolation MIMO antenna, which introduces a new kind of "Butterfly" shape coplanar EBG structure. The number of antenna units and the overall size of this antenna are the same as the fouth antenna’s. The minimum isolation between the adjacent antenna units is 22.86dB. While, in most of the working frequency band, the isolations are greater than 25dB. The adding "Butterfly" shape EBG structure makes the minimum isolation between the antenna units that located at the diagonal position increasing from 16.26dB to 24.70dB, having increased 8.44dB.