Design of orthogonal MIMO handset antennas based on characteristic mode manipulation at frequency bands below 1 GHz
H. Li, Z. Miers, B. K. Lau
IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION
vol. 62, no. 5,May 2014
Antenna array, mobile antenna, multiple-input multiple-output (MIMO) systems, mutual coupling
Multi-antenna design in compact mobile handsets at frequency bands below 1 GHz is very challenging, since severemutual coupling is commonly induced by simultaneous excitation of the chassis’ fundamental dipole mode by more than one antenna element. To address this problem, a novel multi-antenna design approach
is proposed herein to obtain efficient and uncorrelated antennas.
Bymanipulating the chassis structure,more than one characteristic
mode is enabled to resonate at frequencies below 1 GHz.
With proper excitations for different characteristic modes, which
are orthogonal to each other, well matchedmulti-antennaswith low
coupling and correlation are achieved. A chassis loaded with two
T-shaped metal strips above its longer edges is taken as an example
modification to illustrate the effectiveness of the proposed design
approach at 900 MHz. This modification creates a new characteristicmode which resonates near 900 MHz. Afterward, two antenna feeds were designed to efficiently excite the chassis’ fundamental dipole mode and the T-strip mode with very low correlation. The T-strip antenna covers LTE Band 8 (880–960MHz), and the dipole mode antenna covers both LTE Band 5 (824–894 MHz) and LTE Band 8. The proposed dual-antenna design was found to outperform a reference design significantly, both with and without user
interactions (i.e., one-hand and two-hand data grips). Practical aspects
of mobile handset antennas are also investigated. The prototype
was also fabricated and measured, and the measured results
show reasonable agreements with the simulated results.
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