using ESP. However, ESP is not much reliable in terms of the antenna input impedance, which is the case when a modeled structure is complicate. So, measured results, shown in Figure 4, are reasonably considered for the resonance bandwidth [9]. The bandwidth and the center frequency are presented in Table 1. The measured resonance frequency for the MTA is found at 3.38 GHz, giving the resonance bandwidth of 4.0% [ϭ (135/3372.5) ϫ 100]. The measured resonance frequency and bandwidth for the IFA are 3.05 GHz and 7.0%, respectively. Thus, the changes in the resonance frequency and bandwidth are about 10% [ϭ (3.38 Ϫ 3.05) ϫ 100/3.3] and 3%. Concerning the input impedance bandwidth, the IFA shows (about 80 MHz) wider bandwidth than that of the MTA.
COMPARISON OF RADIATION CHARACTERISTICS OF MTA AND IFAIn the previous section, normalized far-zone radiation patterns of the G and G components at 3.4 GHz have been discussed for the MTA. Figure 5 shows the maximum values of the total gains from G and G components in the elevation plane over the frequency band from 3.05 to 3.55 GHz. In the input impedance bandwidth for the MTA, gain variations are less than 2 dB, based on the ESP simulation, so that it is expected the radiation patterns sustain their shape. Here it should be noted that the efficiency is assumed to be 100% in ESP simulations, which means that the gain equals the directivity.Measured far-zone radiation patterns for 3.1-3.5 GHz are illustrated in In Figures 6(c)-6(f), HP is about 60°and front-to-back ratio (FB) is more than 7.5 dB for both the antennas over the measured frequencies. The designed antennas in the handset model are supposed to be used in situation that the antenna part faces opposite to the plane ground, which is intended to be touched to a human head. Since the main electromagnetic radiation part is going outward from a human head in the elevation plane in the normal handset grip, this can be an additive advantage in terms of specific absorption rate (SAR). That is, as the FB is larger in the elevation plane, more power will be radiated to the positive z-axis direction, reducing the SAR value.From the point of view of the radiation characteristics, the far-field patterns of the MTA are close to those of the IFA in the azimuth and elevation planes as shown in Figure 6. That is the broad beamwidth of HPϷ120°in the azimuth plane and more than 7.5-dB FB in the elevation plane are observed for both the antennas. However, accordingly as the shorting point is present or not, which is the only structural difference between MTA and IFA, it should be noted that the center frequency of the resonance band is located 329-MHz shifted with the impedance bandwidth difference. Also, note that, in Figure 6, the maximum gains of the IFA tend to be larger than those of the MTA over the frequencies lower than 3.2 GHz and the reverse turns out over the frequencies higher than 3.2 GHz, which consents to the fact that, referring to Figure 4, the better VSWR (less value) provides the better gain performance.
CONCLUSIONS...