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A compact high isolation ultrawideband (UWB) multiple-input-multiple-output (MIMO) antenna is designed. The proposed MIMO antenna consists of a rectangular monopole antenna and a slot antenna fed by two microstrip lines, respectively. To improve the impedance matching, a circular coupling structure is designed to feed the tapered slot antenna. The parasitic resonance introduced by the ground stub helps to extend the impedance bandwidth of monopole antenna at the upper UWB band. Commonly used complex decoupling or coupling structures are eliminated that endow the proposed antenna minimized foot print, which is preferred in mobile handset. Although without decoupling structure, high isolation is obtained between two antenna elements. Simulation and measurement verify the antenna's desirable performance, showing a broad impedance bandwidth of 3.1-10.6 GHz with |S 11 | < −10 dB and |S 21 | < −20 dB over 3.4-10.6 GHz, and |S 21 | < −18 dB from 3.1-3.4 GHz.

A shared-radiator dual-band dual-sense circularly-polarized (CP) microstrip antenna with duplexing and filtering functions is presented. For each band, there is a coupling network, which consists of a hairpin resonator, a straight slot, and a U-slot, and thus two paths with an inherent 90 • or-90 • phase difference are available for the input signal to couple to the patch, left-handed CP (LHCP) characteristic and right-handed CP (RHCP) characteristic are respectively realized at different bands for the proposed antenna with a single patch. Such a dual-band dual-sense CP patch antenna is highly integrated and outperforms other traditional CP antennas state-of-the-art. Moreover, the duplexing and filtering functions are seamlessly integrated into the dual-band patch antenna with a low-profile (0.044λ o), and application of such an integrated device in wireless systems can potentially reduce the volume, complexity, and cost of RF front-ends. Based on resonator-based topologies, the principles of achieving the dual-sense CP, duplexing, and filtering functions are illustrated. As a proof-of-concept, an antenna working at C-band is prototyped and tested. Good agreements between the measured and simulated results are achieved, showing an LHCP radiation characteristic for the low-band operation and a RHCP radiation characteristic for the high-band operation, respectively. The antenna also exhibits very good frequency selectivity and out-of-band rejection performance. At the low-band, the impedance and 3-dB axial-ratio (AR) bandwidths are 4.7% and 1.1%. At the high-band, the impedance and AR bandwidths are about 7.3% and 3.2%. The isolation between the two channels/bands is over 24 dB. INDEX TERMS Antenna, patch antenna, dual-band, dual-polarized, circularly-polarized, filtering antenna, duplexing antenna.