A planar loop sector antenna for WLAN card terminal

In wireless local area network (WLAN) systems, a sector antenna technique is widely used to solve the multipath fading and shadowing problems. For a small card terminal, it is preferable that the miniaturized sector antenna is formed in a planar structure. We previously proposed a six-sector antenna which can be built in the edge of a PCMCIA card (Una, H. et al., IEEE Topical Conf. on Wireless Commun. Technology, 2003). However, an even smaller size of sector antenna is desirable to mount on an ultracompact terminal like the CF (Compact Flash) card. We propose a further small six-sector configuration, which is realized by an arrangement of three beam-switched loop antennas. The beam-switched loop antenna is composed of a square loop with a plate reflector, two detour elements and two feed points. The main beam is tilted more than 45 degrees to the direction along the loop plane, and the beam direction can be inverted by selectively exciting at the two feed points. The planar size of this configuration is 30% smaller than that of our previous proposal. Moreover, we present the slot structure of the beam-switched loop antenna, which is fed by a microstrip line (MSL) and radiates a vertical polarization component.