A novel asymmetric coplanar strip (ACS)-fed multiple-input-multipleoutput (MIMO) antenna working in the ultra-wideband (UWB) frequency band with a shared radiator is discussed. The proposed antenna is composed of a radiator which is shared by two antenna elements in order to achieve a very compact size of 26 × 26 mm 2 . By etching an I-shaped slot in the radiator and attaching a rectangular patch on the back, the operating bandwidth is broadened and a high isolation between the two antenna elements is realised. The stub from the ground also has a great effect on the return loss and isolation. The measured results show that the working frequency band of the MIMO antenna covers 3.1-10.6 GHz with an isolation of more than 15 dB. Furthermore, the simple feeding structure and compact size could enable the proposed antenna to be used in portable devices.Introduction: Ultra-wideband (UWB) technology possesses great merits including high data rate, low cost and easy fabrication [1], but this excessively researched technology suffers from multipath fading. To solve this problem, a multiple-input-multiple-output (MIMO) antenna was introduced [2]. However, when two antenna elements work closely to each other, the mutual coupling between the two antenna elements becomes strong and the MIMO antenna cannot reach high isolation and a wide operating band without further steps being taken [3]. Li and Feresidis [4] introduced a double-layer EBG structure where three slit-patch structures are inserted in the ground plane between two closely placed UWB monopoles, and the isolation of the whole working frequency band is larger than 15 dB. Gao and He [5] presented a 5.5 GHz band-notched UWB-MIMO antenna using a coplanar waveguide (CPW)-fed to achieve a small size of 48 × 48 mm 2 and a stub from the ground, which could enhance the isolation to more than 15 dB in its operating frequency band. Liu and Wang [6] demonstrated a MIMO antenna using an asymmetric coplanar strip (ACS)-fed structure to reach a compact size of 28.5 × 28.5 mm 2 ; in order to raise the isolation between the two antenna elements, a stub stretched from the ground is introduced, the impedance bandwidth of the antenna covers the UWB frequency band with an isolation of more than 15 dB.

Abstract-A novel CPW-fed dual-band multiple-input multiple-output (MIMO) antenna with a common radiating element for WiMax/3.5G and WLAN/5.8G is proposed in this paper. The proposed MIMO antenna which has dimensions of 30 mm × 30 mm × 1.6 mm consists of an irregular ring-shaped ground plane and a shared radiating element. Furthermore, this MIMO antenna has a good performance in the port isolation by using a T-shaped structure and four slots on the ground. The measured bandwidths of the designed MIMO antenna are 3.32-3.74 GHz and 5.45-6.05 GHz. In the meantime, the measured isolation of the MIMO antenna is higher than 20 dB in both bands.

Abstract-A compact 4-port asymmetric coplanar strip (ACS)-fed MIMO antenna working in the ultra-wideband (UWB) frequency band with two shared radiators is presented in this paper. The proposed antenna is composed of two radiators, and each radiator is shared by two antenna elements in order to achieve a very compact size of 36 × 36 mm 2 . By etching two I-shaped slots in the radiators and attaching a rectangular patch on the back, the operating band width is broadened, and the isolation between any two antenna elements is enhanced. The stub of the ground also has great effect on the return loss and isolation. The working frequency band of the MIMO antenna covers 3.1-10.6 GHz with isolation over 15 dB between any two antenna elements. Furthermore, the proposed antenna with a simple feeding structure and compact size makes it possible to be used in portable devices.

No abstract

No abstract