5 Element Yagi for BlueTooth or WLAN applications

I decided to build this antenna for a great friend of mine who needed a bit more range from his new electric blue Microsoft bluetooth wireless mouse. Bluetooth operates on the 2.4GHz ISM band (which was defined because 2450Mhz is the resonant frequency of water, so 50Mhz on either side is supposed to be kept free for microwaves and heaters). Bluetooth uses 2400MHz to 2483.5MHz:

These are the electronics found inside the little USB receiver/transmitter:

The antena is the white IC marked "A2H2" and the white square at the right is the blue led, which you will need to remove if you want to run the cable upstraight from the antenna tracks on the PCB. I removed the A2H2 antenna IC and connected the coax directly to the two tracks.

The antenna design comes from DL6WU and is fed directly with the teflon-insulation 50-ohm coax to the center split dipole. As discussed somewhere else in this pages, newsgroups and other webs, this 50 to 75 ohm is not the ideal but is simple and the practical results are more than acceptable. The theretical SWR and far-field plots for this antenna look like this:

The antenna dimensions can be seen here (all numbers are mm):

This is what the antenna looked like before connecting it to the USB device. The 2mm diameter copper wire elements are soldered to a long piece of fiberglass PCB where all the copper but the needed to solder the elements has been removed. You can see there how the coax connects to the mid-split dipole keeping the leads as short as possible. It is a good idea to epoxy the connection so it gets mechanically robust:

And this is what the final work looks like over the table:

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