《2.4G全向》.docVIP

Home-brew Compact 6dBi Collinear Antenna (first published September 2005) This page details the construction of an easy-to-make collinear 360 degrees omni-directional, vertically polarised, antenna for 802.11b/g wireless networking. The antenna is very robust and compact, and has a gain of approximately 5-6dBi. Background Various websites detail the construction of a collinear antenna suitable for 2.4GHz wireless networking, including wireless.gumph.org and guerrilla.net. However, these antennas are quite complex to build, being made up of numerous short lengths of coax which must be accurately cut to length. You also need to know the velocity factor of the coax that is being used, as most of the measurements are based on it. A variation of the coax collinear is constructed from brass rod and brass tubing, but is still just as fiddly to construct. Some time ago, I made an 8-element coax collinear, using the wireless.gumph.org instructions. Antenna comparison testing confirmed the gain was approximately 8dBi. However, it took many hours to construct, and the antenna has very little physical strength. I resorted to cable-tying a length of dowel to the coax, and then encasing it all inside some 25mm electrical conduit. I was particularly intrigued when a friend pointed out a much simpler collinear, consisting of just a length of copper wire appropriately bent, as detailed here, with a claimed gain of about 6dBi. This version provides a number of benefits over the coax construction, requiring far less effort to construct, and providing a smaller and more robust antenna. While the 6dBi gain is less than that of an 8 element coax collinear, the gain could be improved by increasing the number of elements. Doubling the number of elements will increase the gain by 3dBi, ie, double the gain. Parts Required The materials required: approx 300mm 2.5mm2 copper wire panel-mount female N-connector 250mm length of 20mm light-duty electrical conduit 2 end-caps