Spatial diversity antenna for WLAN application

achieved this scaled design at 300 MHz as well; however, we choose to report the smaller ka design at this frequency to allow a direct connection between these results and those reported in Refs. 2 and 3. The differences between Designs 1 and 2 show that the copper losses significantly impact the radiation efficiency of this resonant system. The performance of the scaled limit case at 300 MHz is essentially the same as its higher frequency versions. The overall efficiencies of these electrically-small-limit systems are very high. The complex input impedance behavior and the far-field radiation patterns for the GPS-frequency Design 3 are shown in Figure 2. The resistance and reactance curves in Figure 2(a) exhibit characteristics analogous to the anti-resonant behavior of an electrically-small circular loop (i.e., a magnetic dipole) antenna [5, 6]. In particular, it is clear from Figure 2(a) that the EZ antenna is antiresonant and matched to the feedline at the source frequency. Figure 2(b) also demonstrates that the EZ antenna is acting like a magnetic dipole over a PEC ground plane. Figure 3 shows the E-and H-field vector plots using xy-plane cuts in the stub and just above the semi-circular loop antenna, respectively, and the current vector plots on the metamaterial-inspired structure. From Figs.3(a) and 3(b), one clearly sees that the metamaterialinspired radiating structure is acting like a uniformly extruded CLL element. 3. CONCLUSIONS This research work introduced an efficient electrically-small antenna design methodology in which a self-resonant capacitive structure that is driven by an electrically-small semi-circular loop antenna coaxially-fed through a finite ground plane was obtained. These designs realized an inexpensive, easy-to-build, efficient, and electrically-small antenna. The proposed antenna system is linearly scalable to a wide range of frequencies. The overall efficiency of the antenna system depends on the choice of overall electrical size. Highly electrically-small versions exhibit large conductor losses because of their resonant nature. The type of metal used for the designs can be selected to improve this characteristic. Electricallysmall-limit versions were shown to be highly efficient. Preliminary proof-of-concept experiments have confirmed these results and will be reported elsewhere.