The MM coating and the monopole were fabricated and assembled, as shown in Fig. 1.4a. Four polypropylene washers were used as a frame to mechanically support the coating and to ensure correct inner and outer layer diameters. The impedance measurements were performed using a network analyzer. Figure 1.4b compares the simulated and measured voltage standing wave ratio (VSWR) curves of the monopole with and without the MM coating on a 32 cm x 32 cm ground plane. The measured of the monopole alone is almost identical to the simulated results, having an 511 < -10 dB band from 2.3 to 2.7 GHz. With the MM coating present, a broad < -10 dB band is achieved from 2.15 to 4.6 GHz, i.e., a 2.14:1 ratio bandwidth. The radiation patterns of the monopole coated with the MM were measured in an anechoic chamber. Figure 1.4c presents the simulated and measured Я-plane and Я-plane patterns at the center frequency of 3.3 GHz. In the Я-plane, an omnidirectional radiation pattern is observed, with a gain variation of around 0.5 dB and 1.2 dB for simulated and measured results, respectively. The increased measured gain variation as a function of the azimuthal angle is primarily caused by the imperfection of assembly and measurement noise, as well as the antenna rotation platform. In the Я-plane, characteristic ear-shaped patterns are obtained, which are very similar to the patterns for the monopole alone, indicating that the added MM coating has negligible impact on the radiation properties of the monopole. The gain of the MM-coated monopole is about 4 dBi with the direction of the maximum at 26° from the horizon due to the employed finite-sized ground plane used in both simulation and measurement. The measured gain is 0.5 dB lower than the simulated values. The overall good agreement between the simulated and measured results confirms the expected performance of the proposed MM coating for monopole antennas.
Figure 1.4 (a) Photographs of the fabricated MM coating placed over a
monopole. (b) Simulated and measured 5n of the monopole with and without the MM coating. (c) Simulated and measured gain patterns in the E- and H-planes at 3.3 GHz.