Modeling of quasi-tapered microstrip antenna based on expansion-exponential tapered method and its application for wideband MIMO structure

In this paper, a quasi-tapered wideband antenna using a circular-shaped with an inverted-omega ground structure is presented. A tapered antenna is usually developed based on linear-shape, exponential-shape, or Klopfenstein-shape tapper. Here, we proposed an expansion of the exponential tapered model to investigate the circular-shaped tapered structure. In detail, the proposed antenna is divided into circular divergent and circular convergent-tapered sections. Then, the impedance ratio is utilized to analyze the tapered structure. Moreover, the ABCD parameter based on the transmission line model is used to investigate the overall antenna structure. The proposed model was verified by finite element method and also step impedance resonance evaluation. Furthermore, the proposed wideband antenna is also developed with multiple input multiple output (MIMO) and mutual coupling reduction structure. The antenna was fabricated on a Rogers RT/Duroid 5880 substrate with & epsilon;r = 2.2, thickness of h = 1.6 mm, and dielectric loss tan d = 0.0009. As a result, the proposed MIMO antenna can successfully cover the 4G (3.3 GHz), mid-band 5G (3.4-3.8 GHz), WLAN (5.8 GHz), X-band (10-11 GHz), and high-band 5G (24.5-26 GHz) communications. A good agreement between the simulated and measured results validates the proposed method.