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Prototypes of the LHM patch antenna were numerically simulated, fabricated, measured, and characterized. Computer simulations were based on the standard finite-difference-time-domain (FDTD) method with commercial simulation software from Computer Simulation Technology (CST). The return loss of the antenna was measured with a Model N5244A PNA-X vector-network analyzer (VNA) from Agilent Technologies, with measured and simulated results depicted in Fig. 3.

Metamaterial Extends Microstrip Antenna, Fig. 2

Metamaterial Extends Microstrip Antenna, Fig. 3

As that figure shows, the measured and simulated results are in good agreement, and the impedance bandwidth of 124% extends from approximately 3.2 to 14 GHz with a center frequency of 8.7 GHz. The bandwidth is enhanced by the fact that different sections of the LHM cells are excited at different frequencies; it is a reason why the structure achieves broadband-frequency operation.

Metamaterial Extends Microstrip Antenna, Fig. 4

The gain of the novel LHM patch antenna was simulated within the frequency band of interest, as shown in Fig. 4. Antenna gain was generally greater than 6 dB, with peak gain of 8.9 dB. Compared with a conventional microstrip patch antenna, the gain of the proposed antenna has been improved.19 As Fig. 5 shows, the measured VSWR remains well below 2.0:1 for the full operating frequency band.

Metamaterial Extends Microstrip Antenna, Fig. 5

Because of the transmission characteristics of left-handed materials, the wave propagation along the patch induces the strongest radiation in the horizontal direction rather than the vertical direction of a conventional patch antenna.16 The measured radiation patterns of the antenna in the X-Y and Y-Z planes at 6.2 and 11.0 GHz — both within the working bandwidth — are shown in Fig. 6. In the X-Y plane, the radiated energy is mainly focused in the Y-direction in the case of the copolarization.

Metamaterial Extends Microstrip Antenna, Fig. 6

In the Y-Z plane, in the case of the copolarization, the radiation level is well suppressed except in the Y-direction. This indicates that the strongest radiation is in horizontal direction and the cross-polarized radiation pattern is always orthogonal with the copolarized radiation pattern. Across the full frequency range, the radiation pattern of the proposed antenna maintains good performance. The antenna achieves a broad impedance bandwidth of 124% from 3.2 to 14.0 GHz with maximum gain of 8.89 dB.

Due to the transmission characteristics of LHM materials, the overall size of this patch antenna is smaller than a conventional patch antenna on standard substrates. The proposed antenna is simple in its design and fabrication. It demonstrates that LHM materials offer many potential opportunities, and that better antenna performance can be obtained by loading left-handed materials. This new antenna design may find use in a variety of applications, including in satellite-communications (satcom) and mobile-communications systems.

Jiangpeng Liu, Professor

Yongzhi Cheng, Engineer

Yan Nie, Engineer

Rongzhou Gong, Engineer

Huazhong University of Science and Technology, Department of Electronic Science & Technology, 430074, Luoyu Road No.1037, Wuhan, Hubei, People’s Republic of China; +86 13720361628, FAX: 027-87547337.

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