A Multiple Input Multiple Output (MIMO) antenna consisting of two 90 • angularly separated semicircular monopoles with steps for Bluetooth, Wi-Fi, Wi-MAX and UWB applications is proposed. Initially, an array of two coplanar circular monopoles with element separation of 25 mm is investigated. In this configuration, mutual coupling is < −5 dB and < −10 dB over 2 GHz-3 GHz and 3 GHz-10.6 GHz, respectively. Mutual coupling is reduced by using 90 • angularly separated semicircular monopoles. With semicircular configuration, though the mutual coupling is improved, impedance bandwidth is reduced due to reduction in electrical length. A step like structure is introduced in the semicircular monopoles, and ground plane is modified and extended between the two elements to improve the impedance bandwidth and mutual coupling. Impedance bandwidth from 2.0 GHz-10.6 GHz with S 21 < −20 dB and −14 dB is achieved over 3.1 GHz-10.6 GHz and 2.0-3.1 GHz respectively. The antenna is fabricated using 46 mm × 37 mm RT Duroid substrate. Measurement results agree with the simulation ones. Radiation patterns are stable, and correlation coefficient is < 0.02 over 2.0-10.6 GHz.

In this paper, a circularly polarized (CP), high gain and wide bandwidth metal plated microstrip antenna (MSA) using partially reflecting surface (PRS) and artificial magnetic conductor (AMC) layers is proposed. The bandwidth of MSA is increased primarily, using AMC layers, and gain is increased by placing the antenna in a Fabry-Perot cavity (FPC) resonator. The two slotted AMCs are designed to resonate at two frequencies which electromagnetically couple to provide wide bandwidth. The FPC antenna with PRS and AMC layers provides higher gain, more impedance bandwidth, less gain variation and more miniaturization than the antenna without AMC layers. The proposed antenna provides S 11 < −10 dB, axial ratio (AR) < 3 dB and 17.4 dBi peak gain with gain variation < 3 dB over 5.725 GHz to 6.4 GHz frequency band. Broadside radiation patterns have side lobe level (SLL) < −20 dB, cross polarization (CPL) < −16 dB and front to back (F/B) lobe ratio > 20 dB. The overall antenna dimensions are 2.83λ 0 × 3.23λ 0 × 0.49λ 0 , where λ 0 is the free space wavelength corresponding to the central frequency of 5.725-6.4 GHz. The proposed structure is fabricated, and the measured results agree with simulation ones.

A cross configuration of directional Ultra Wideband (UWB) antennas for multidirectional pattern diversity characteristics is presented. Initially, a printed UWB circular monopole having an asymmetric curve shaped CPW feed is designed as a base antenna for obtaining a directional radiation pattern, direction of which remains fairly same for the entire UWB. This base antenna is attached to similar antennas, in a four element cross-configuration to achieve multidirectional pattern diversity characteristics. The proposed structure provides high inter-element isolation of more than 20dB, with an impedance bandwidth (VSWR < 2) of 19.7 GHz i.e. 1.3 GHz to 20 GHz. Transmission and diversity characteristics of the proposed antenna are analyzed. Good agreement between simulated and measured results indicates that the proposed antenna is suitable for UWB pattern diversity applications.

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