22-08-2014, 03:46 PM
A MULTIBAND Y SHAPED PATCH ANTENNA WITH IMPROVED BANDWIDTH AND ISOLATION FOR MIMO SYSTEMS
A MULTIBAND.docx (Size: 393.84 KB / Downloads: 10)
Abstract:
A compact Y-shaped patch antenna for multi-band applications with improved bandwidth and isolation characteristics is presented in this paper. The proposed antenna resonates at multiband of 4.2 GHz, 6 GHz, 7 GHz, 7.44 GHz, 10 GHz and 11.48 GHz frequencies for VSWR ≤ 1.6, with an improved impedance bandwidth of 33% and a reduced mutual coupling of -38 dB. These results are better compared to a normal E shaped and H shaped antennas designed with same size and thickness. The developed antenna system can be widely used for the 4G, WLAN and Wi-MAX applications. The proposed antenna is a good choice for MIMO systems operating for several Wideband applications
1) Introduction
The microstrip patch antenna is one of the most preferred antennas for its low cost, light weight, simple implementation process and conformability. The microstrip patch antennas radiate primarily because of the fringing fields between the patch edge and the ground plane. The general microstrip antenna has some drawbacks they are narrow bandwidth which limits their application in modern communication systems like MIMO systems etc. In recent years the demand for the design of triband [1] or multiband antenna operation has increased since this type of antennas can integrate more than one communication standards in a single compact system. In this paper, we introduced a Y-shaped microstrip patch antenna. The main goal of our project is to achieve multiple band operation with improved bandwidth and reduced mutual coupling with a simpler structure.
The major problem faced by the MIMO system [2] engineers for small electronic devices is mutual coupling, which mainly arises due to the smaller spacing between the elements. Hence, in multiple input and multiple output systems the basic aim is to minimize the correlation between the multiple signals. The parameter that describes the correlation between the received signals in highly diversified environments is mutual coupling, which deteriorates the performance of the communication system [3]. By using mutual coupling we can estimate the electromagnetic interaction between the elements of a MIMO system. If the mutual coupling is more it reduces the efficiency of the antenna.
The mutual coupling depends on the distance between the elements in a MIMO system. If the distance is more, the mutual coupling between antennas becomes less and vice versa. That means by increasing the distance between the elements we can reduce the mutual coupling between the antennas. However, the distance between the antennas cannot be maintained too large, since MIMO systems have their major applications in Mobile terminals, laptops, and WLAN Access Points Wireless communications [4]. The main source of mutual coupling is surface currents flowing through ground. To reduce these surface currents flowing on the ground we have some techniques they are Electromagnetic band gap structure [10], defected ground structure [11], decoupling techniques, etc.
2) Antenna design
Patch antennas play a vital role in present wireless communication. The main drawback of patch antenna is narrow bandwidth so our work mainly focused on the improvement of impedance bandwidth. We can improve bandwidth of patch antenna by using various techniques like introducing parasitic elements, increasing the thickness of substrate and modifying the shape of the antenna and by introducing slots on the patch. The presently designed shape offers an improved bandwidth of 33%, which is better than bandwidth obtained in [6] and [7]. The patch antennas are fabricated with various shapes, the most widely designed antennas are E shaped patch antenna, H shaped patch antennas [8], U slotted patch antennas [12], etc.. Among all these antennas, E shaped patch antennas are widely used, because they are proved to be the better one in terms of both impedance bandwidth and mutual coupling. In the present work, a Y shaped patch antenna is proposed and the results of this antenna are good compared to all the above mentioned antennas in terms of both impedance bandwidth and mutual coupling.
The antenna geometry is shown in fig.1. The dimensions of the geometry are given in the Table.1. For good performance a thick dielectric substrate having a low dielectric constant is desirable because this provides better efficiency, larger bandwidth and better radiation. Here, the substrate selected for the design of the proposed antenna is RT/duroid®5880 of thickness 3.2 mm and with low permittivity (εr=2.2). The dimensions of the substrate are 100 × 90 × 3.2 mm^3.
3) Two element MIMO array using the proposed model:
The major parameter that affects the performance of the MIMO system is mutual coupling. The main aim of any MIMO system engineer is to reduce mutual coupling between antennas in closer spacing. However, when multiple antennas are involved at closer spacing the design issues are more complicated compared to a SISO (Single Input Single Output) system.
4) Conclusions:
In this paper, Y shaped patch antenna is proposed and a two element MIMO array is developed by using it. The proposed antenna resonates at a multiband of frequencies 4.2 GHz, 6 GHz, 7 GHz, 7.44 GHz, 10 GHz and 11.48 GHz with an improved impedance bandwidth of 33% and a reduced mutual coupling of –38 dB. These characteristics are well suited for all 4G MIMO applications. The proposed study can be extended by employing more no. of antennas in MIMO system for improving the channel capacity of the MIMO systems.