Abstract
Mutual coupling always seriously degrades the antenna performance in multiple-input multiple-output (MIMO) systems but this issue has been rarely investigated for antennas with circular polarization. In this paper, a planar and compact circularly polarized MIMO patch antenna with the polarization diversity is presented. Three grounded stubs and a mirrored F-shaped defected ground structure are used to achieve simultaneous matching and isolation between the two patches with offset feeding for circular polarization. The antenna elements are closely packed with the edge-to-edge distance of $0.06\lambda _{0}$ at the desired frequency of 2.5 GHz. The measured results indicate that the proposed antenna achieves the impedance matching ( $\text{S}_{11} dB), high isolation ( $\text{S}_{12} dB), and circular polarization (axial ratio< 3 dB) within the frequency band of 2.5-2.55 GHz. The radiation patterns and realized gains are measured, showing good agreement between the simulation and measurement.
Highlights
The multiple-input multiple-output (MIMO) technology has become popular due to the increased link capacity especially in complex multipath environments [1]
The superiority of a Circularly polarized (CP) MIMO antenna system over linearly polarized (LP) MIMO system has been extensively studied in [4]. Both multipath and line of sight (LOS, point to point) cases have been investigated by comparing their diversity gain, envelope correlation coefficient, and channel capacity
From a practical point of view, the multiple antennas in MIMO systems should be closely spaced for compactness
Summary
The multiple-input multiple-output (MIMO) technology has become popular due to the increased link capacity especially in complex multipath environments [1]. Numerous techniques have been explored to reduce mutual coupling such as the defected ground structure (DGS) [5], [6], electromagnetic band gap (EBG) structure [7], [8], microstrip stubs [9], shorting pins [10], and parasitic elements [11], [12], etc. These techniques are mostly reported to reduce mutual coupling of LP antennas but the impact of these techniques on the axial ratio (AR) of the CP antenna has been rarely discussed. Three grounded stubs and a mirrored F-shaped DGS are employed for high isolation and the simple offset feeding is adopted for circular polarization. Measurement results show that the ARBW of around 2.2% can be achieved
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