MIMO antenna systems can greatly improve the capacity and transmission rate of wireless communication. In this letter, two four-port multiple-input-multiple-output (MIMO) antenna systems are proposed in mobile devices. An algorithm of calculating envelope correlation (ρe) between antenna units is also proposed. By this algorithm the ρe of the PIFA-MIMO antenna system has been calculated. First, a PIFA-MIMO antenna system is designed for ISM (2.4 GHZ) application. The slots are etched on the ground and the antenna units are placed in such a way that the polarization diversity is exploited to enhance the impedance matching and isolation. Based on this, a printed wideband MIMO antenna system is proposed for portable 3G and 4G applications by means of multi-branch and the defect of ground technology, increasing the bandwidth and reducing mutual coupling between the antennas. The simulation results show that the return loss and isolation of the two antenna systems can meet the performance requirements of the antennas in the mobile phone.
With the rapid development of wireless communication technology and the increasing demand of multimedia service, it is extremely urgent to realize the data communication with high speed and large capacity. As the core technology of wireless communication, MIMO technology has not only achieved a great increase in the capacity of communication, but also greatly improved the communication quality. By the literature [
In recent years, multiple-input-multiple-output (2 × 2 MIMO) communication systems use the multiple antennas that are equipped at receiver and transmitter ends to enhance not only the available data rate but the capacity in multipath environments. In order to improve the isolation between the two ports of the MIMO antenna, many designs have adopted the defect ground structure to meet the requirements of high isolation in MIMO antenna [
Beyond the existing performance standards for a single-receiver mobile device, there are two antenna parameters that impact mobile receive diversity (MRD) performance: 1) the gain difference between the two antennas, and 2) the fading (envelope) correlation coefficient,
The fading (envelope) correlation coefficient
Let me identify one of two mobile antenna ports. According to [
The variance of the total received signal can be expressed as follows:
Similarly, the cross-correlation between the complex signal-envelopes received at the two antennas can be expressed as follows:
XPR is the cross-polarization power ratio, XPR = PV/PH. Using the two signal variances and the cross-corre- lation, the complex correlation coefficient can be calculated as follows:
The envelope correlation
In order to compute the variance and correlation, the wireless channel is modeled to specify the incident field angular density function (or incident field distribution). The incident field distribution depends upon the scattering properties of the wireless environment. The most common assumption is that there are numerous scatterers present around the mobile, causing a uniform incident field in azimuth. Gaussian and Laplacian distributions are also used for cases when the incident wave is more concentrated from certain directions (smaller angular spread).
Several example incident field distribution expressions are provided below; they are all applicable to both polarizations and are all linear functions (not logarithmic).
1. Uniform in both azimuth and elevation:
2. Uniform in azimuth, Gaussian in elevation:
3. Gaussian in both azimuth and elevation:
In engineering, the envelope correlation coefficient is calculated from the measured complex quantities
XPR = PV/PH;
Finally, the envelope correlation coefficient is calculated from:
The complex antenna pattern correlation method recommended above takes into account many factors that can impact the correlation between signals from dual antennas on handsets in a mobile environment. The designer may prefer to use more simple and rapid method to estimate the envelope correlation coefficient. For example, S Blanch et al. describes a calculation of envelope correlation coefficient using S formula:
Although attractive in its simplicity and ease of measurement, this expression only considers the direct contribution of mutual coupling to the antenna correlation, the properties of the incident RF field and its interaction with the antennas’ gain patterns are not considered in this expression.
Due to the low profile and easy to match of the PIFA antennas, Mobile phone built-in antenna always adopts PIFA (Planar inverted F antenna) antennas. This part presents a design of 4 × 4 MIMO antenna system model, operating in 2.4 GHZ (ISM band). The antenna system uses air as the medium. Because of the four antenna elements sharing one floor, the current of one antenna element will be coupled to another antenna element through the floor, which leads to mutual coupling and reduces the isolation between antenna elements. The antenna system adopts defect ground structure to extending the current length, as a result, effectively reducing the mutual coupling between the antenna elements. In addition, the antenna space-coupling by space radiation field will influence the performance of the MIMO antenna system. In this chapter, the four port antenna elements of this antenna system are placed vertically with each other, reducing the space-coupling between antenna units, increasing the isolation. Simulation results show that the antenna can meet the performance requirements of the MIMO antenna systems.
overall size of the machine is 120 × 60 × 10 mm3, and the size of each PIFA antenna element is 16 × 7.5 × 10 mm3.
The specific size of antenna elements: Lg = 120 mm, Wg = 60 mm, L = 16 mm, W = 7.5 mm, S1 = 27 mm, g2 = 30 mm.
As shown in
Using the simulation software (HFSS) to simulate the antenna model, as shown in
Printed monopole antenna has been widely used in many wireless devices due to its low cost, light weight and easy processing. As a new type of antenna, high dielectric antenna has the advantages of small size, simple structure and low cost. With the application of 4G wireless communication, the MIMO antenna systems operating in 3G and 4G-LTE frequency band have a good application prospect and demand. In order to achieve the large bandwidth of the antenna system, this paper mainly uses the multi-branch technology to achieve the principle of multi-resonant, through connecting the two or more adjacent resonant frequency band together, hence, obtaining the expansion of the bandwidth.
In this paper, the design of a broadband monopole-MIMO antenna system is composed of four monopole printed antennas, floor and dielectric substrate. The overall structure of the antenna system is shown in
By simulation, the return loss of the four single pole printed antennas is shown in
The MIMO antenna system designed in this paper is composed of four printed monopole antennas with nearly identical multi branch. The four antenna elements are located on the four side of the dielectric substrate respectively, without floor under the antenna elements. In order to obtain a better impedance matching and increase the isolation between adjacent antenna units, the floor under the medium substrate is slotted; the slotted size is 46 mm × 1 mm, so that the floor is divided into two parts, as shown in
In this paper, Section 1 mainly introduces the present status of research on MIMO antenna systems at home and abroad. In Section 2, an algorithm calculating envelope correlation coefficient between MIMO antenna elements is proposed. The third chapter and the fourth chapter designed a PIFA-MIMO antennas system and a monopole MIMO antennas system respectively, which were all widely used in the design of antennas system in mobile phone. And based on the formula calculating
DeshunSun,ChongyuWei, (2016) Analysis and Design of 4 × 4 MIMO-Antenna Systems in Mobile Phone. Journal of Computer and Communications,04,26-33. doi: 10.4236/jcc.2016.42004