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Figure 5 shows the designed and fabricated dual-frequency antennas. The CPW dual-frequency metamaterial antenna is composed of top metal patches, shorted meander lines, and a CPW ground plane. The feed line for impedance matching between the 50-Ω ports and the antenna circuitry is designed by impedance transition line and coupling capacitance. The antenna’s dimensions are as follows: antenna length, L = 28.6 mm; antenna width, W = 22.4 mm. The widths of the CPW feed lines are W1 = 3 mm, W2 = 0.4 mm, and W3 = 6 mm. The CPW trace length is L1 = 1 mm. The line lengths are L1 = 1 mm, L2 = 5.8 mm, L3 = 24.8 mm, and L4 = 0.6 mm. The gap between the CPW trace and the resonant antennas, g1, is 0.4 mm. The widths of the left-hand interdigital capacitors are g2 = 0.4 mm and g3 = 1 mm. The width of the left-hand shorted meander lines is g4 = 0.2 mm. Finally, the width of the left-hand gap between the CPW ground and the top patch is g5 = 0.2 mm.

5. The top diagram shows the basic layout for a dual-frequency antenna based on a CPW CRLH TL unit resonator, while the photograph on the bottom is a fabricated CPW CRLH TL dual-frequency antenna.

The fabricated antenna measures 22.4 x 28.6 mm. Its performance was modeled using the High-Frequency Structure Simulator (HFSS 11) electromagnetic (EM) simulation software from Ansoft/Ansys. Figure 6 shows the simulated and measured return losses of the antenna for a one-cell CPW CRLH TL. Variations found between the simulations and measurements stem from fabrication errors and dimensional tolerances. The resonant frequencies of the zero- and first-order modes were simulated (measured) at 2.45 GHz (2.50 GHz) and 4.25 GHz (4.20 GHz), respectively.

6. These plots show the simulated and measured return loss for the CPW CRLH TL dual-frequency antennas.

These measured and simulated results show good agreement with the theoretical results from the dispersion curves in Fig. 4. The reflection cofficient is lower than the lower and upper 10-dB bandwidths of 2.485 to 2.515 GHz and 4.16 to 4.34 GHz ; as a result, 10-dB bandwidths of 1.2 and 4.2%, respectively, were achieved for the fabricated antenna. The electrical size of the CRLH TL’s unit cell is 0.254λ0 x 0.258λ0 at 2.54 GHz. The overall size of the antenna is approximately 0.331λ0 x 0.258λ0 x 0.011λ0.

Figure 7 shows the simulated and measured radition patterns of the antenna at in its zero- and first-order resonant modes, which are the E-plane (y-z plane) and H-plane (x-z plane) modes at 2.5 and 4.2 GHz. The measured and simulated results agree closely. Maximum gains for the dual-frequency antenna in the E-plane (y-z plane) were simulated as 2.31 dBi at 2.5 GHz and 3.52 dBi at 4.2 GHz, compared to measured maximum gains of 1.85 dBi at 2.5 GHz and 3.05 dBi at 4.2 GHz. The radiation patterns show that the antenna’s measured cross-polarization levels are higher than the simulated cross-polarization levels. These differences are also due to the fabrication limitation resulting from the fine meander lines, as well as the measurement error resulting from the much smaller size of the aperture, compared with that of the RF cable in the test environment.

7. These simulated and measured responses show the antenna’s zero- and first-order mode responses for its E- and H-plane patterns: (a) zero-order in E-plane, (b) zero order in H-plane, (c) first order in E-plane, and first-order in H-plane.

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