Lab 5 Essay Modern Day

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Horizontal and Vertical PolarizationThe dipole transmits a vertically polarized signal. This means that the electrical component of the energy, the so-called "E-field," is parallel to the dipole element and perpendicular to the floor. By turning the dipole 90 degrees (so its axis is horizontal) it will radiate a horizontally polarized signal, where the E-field vector is parallel to the ground. In my experience, horizontally polarized antennas generally propagate better within a building, probably due to reflections from the floor and ceiling. When the WLAN signal hits an object, such as a metal cabinet or pole, it is reflected, and its polarization is scattered. Inside any work area there will be a mixture of vertically and horizontally polarized signals. PCMCIA Cards Have Terrible Inbuilt AntennasAnd this leads us nicely into the real world. The designers of the antennas for PCMCIA cards face a real problem. It is not easy to form antennas onto the small circuit board inside the bulbous plastic cover that sticks of the end of the PCMCIA card. I won't go into the technology here, but below is plotted a typical sensitivity measurement for a laptop equipped with a PCMCIA WLAN card. The effective gain of this antenna is low, less than 0 dBi (typically -4 dBi) and it is very directional. You can see that the sensitivity varies greatly with Azimuth, and is quite unlike a well-behaved antenna. If you look at the blue trace you can see that the antenna is 6 dB more sensitive (twice the range) for signals coming in at 165 degrees compared with those at 330 degrees. There are also deep nulls, from which directions no signal at all is received. The red trace shows sensitivity to vertically polarized signals. It is significantly lower than for horizontal polarization. I always recommend the use of horizontally polarized access point antennas when a significant number of PCMCIA-equipped workstations will be in use. It should now be obvious why you have to jiggle and...