with a 4-port switch to enable other wired network devices to share the printer and use the wireless station as a bridge to other devices on the wireless network. Figure 3-15 shows a range of wireless printer servers. Wireless LAN Antennas Traditional Fixed Gain Antennas Antennas for 802.11b and 11g networks, operating in the 2.4 GHz ISM band, are available to achieve a variety of coverage patterns. The key features that dictate the choice of antenna for a particular application are gain, measured in dBi (see the Section "Antenna Gain, p. 107") and angular beamwidth, measured in degrees. The most common WLAN antenna, standard in all NICs and in most access points, is the omnidirectional antenna, which has a gain in the range from 0 to 7 dBi and a beamwidth, perpendicular to the antenna axis, of a full 360°. A range of WLAN antennas is shown in Figure 3-16 and typical parameters are summarised in Table 3-5. For sector antennas with a given horizontal beamwidth, the trade-off for higher gain is a narrower vertical beamwidth, which will result in a smaller coverage area at a given distance and will require more precise alignment. A further important feature of an antenna is its polarisation, which refers to the orientation of the electric field in the electromagnetic wave emitted Outdoor omnidirectional Indoor directional panel Indoor omnidirectional High gain Yagi Figure 3-16: Wireless LAN Antenna Types (courtesy of D-Link (Europe) Ltd.) Chapter Three Table 3-5: Typical Wireless LAN Antenna Parameters for 2.4 GHz Operation Antenna type Sub-type Beamwidth (Degrees) Gain (dBi) Omnidirectional Patch / Panel 15-75 Sector 10-17 Directional 10-30 Parabolic reflector 14-30 by the antenna. Most common antennas, including all those listed in the table above, produce linearly polarised waves, with the electrical field oriented either vertically or horizontally - hence vertical or horizontal polarisation. WLAN antennas that produce circular polarisation are also available (helical antennas) but are less common. It is importan