To show the flexibility of the proposed technique, an anisotropic MM coating was further designed for a C-band (4-8 GHz range) quarter-wave monopole antenna. The design procedure is similar to that already discussed for the S-band MM coating. The unit cell of the MM coating has the same shape and is printed on the same substrate material. The optimized geometrical dimensions are (all in millimeters): a = 2.5, ds = 0.051, dc = 0.017, w = 1.9, b = 3.9, c = 1.1, g = 0.5, and I = 2.6. The monopole was designed to resonate at 4.5 GHz, which corresponds to a length of 15 mm. The outer radius of the MM is 3.7 mm or about A0/24 at 4.5 GHz, ensuring that the ultrathin subwavelength coating is compact in the radial direction. The monopole with and without the MM coating was simulated in HFSS. The simulated curves are reported in Fig. 1.5. The monopole
alone yields an < -10 dB band of 0.5 GHz, namely from 4.5 to
5.0 GHz. When the actual MM coating is present, the 511 < -10 dB bandwidth is considerably broadened to 4.35 GHz, namely from 3.85 to 8.2 GHz. The fundamental resonance shifts down slightly to 4.55 GHz, while the second resonance occurs at 7.0 GHz. In all, this type of flexible MM coating is compact in size, extremely light weight, low in cost, and can be easily scaled to different frequency bands, thereby paving the way for widespread use as radiating elements in, for example, broadband arrays, wideband radios, and various portable wireless devices.
Figure 1.5 Simulated 5n of the monopole with and without the MM coating.