Directional Antenna design

Hi,

I want to design an antenna for point-to-point communication in the 2.4GHz band. I have gone through basic antenna theory but obviously that's not good enough to start making an antenna.

I'm not yet sure what material would be required, or how to go about making even a short dipole, monopole, or any of the simple designs.

My end goal is to construct a directional antenna for point-to-point communication with a range of about 100ft. From what I understand, increasing the length (wrt to the wavelength), having a phased array, or a reflector are some techniques that can be used to achieve directionality. There are some antennas such as Yagi/Log-periodic/Dish that are similar to what I want to achieve.

Can someone help me how I can proceed?

Thanks.

2.4 GHZ ~.3/2.4 m wave length ~12cm, so a quarter wave length is about 3cm. So get a piece of coaxial cable, strip the outer back about 35mm, unpick the braid and make it in to a pigtail. Remove the inner insulation, lash the bits of wire to a piece of plastic rod pointing away from each other, making sure that they are not shorted at the junction with the cable. You have made a dipole. To convert it into a yagi will require more thin plastic strips or rods onto which you can mount additional elements.
Frank

Thanks for the practical implementation of dipole!

Where can I find resources to learn about how to start designing one given certain specifications... Also what specifications apart from the frequency are needed before starting your design?

Parametres to be considered, forward gain, bandwidth (and centre frequency of course!) and back to front ratio. Gain and bandwidth are inversely coupled, you can't have a large gain and a wide bandwidth. Back to front ratio has little effect on forward gain but is useful in rejecting a powerful interfering signal.
I learn't my (limited) aerial knowledge from the RSGB handbook (Amateur radio "bible") fifty years ago.
Frank

For a range of 100ft you're not going to need much of an antenna at each end, unless the power is very low.
For a simple design look at making the antenna on a PCB, it could be the same one as the tranceiver. Try this design, it looks simple enough and should do what you want.
http://www.ti.com/lit/an/swra350/swra350.pdf
A search for PCB yagi antenna brings up plenty of hits as should yagi antenna design. You could aslo use a patch antenna. Directional antennas may make the system more prone to reflections, particularly from objects along the path. This problem can be reduced by using circular polarisation; the reflected signal is in the oposite sense and rejected by the receive antenna.

I would think that the first place you would want to go is to perform a link analysis to see what kind of antenna characteristics you might need.

Look at the environment. Also where will the antenna be mounted? What is your budget? Any special requirements? What radio? How does it connect? Size restrictions? Once you have the characteristics you need mapped then it would make sense to consider the particulars of an antenna.

There are not many pure point to point connections with Wifi as there are so many reflections that can cause fading loss or deadspots.

If you can measure RSSI somehow with link tests or use a Router & Laptop for testing using some software like NetStumbler to measure dB vs position at your distance. If you are below -80dBm, you will have problems but -70dBm ok. Then with antenna gain , you can solve the problems.

As someone commented a link budget analysis would be useful. But I suspect that you don't know what the transmitter power is or what is the minimum signal to noise ratio needed. So that is almost vertainly impractical.

An axial mode helical antenna is worth thinking about. They are easy to design (make the circumstance 1:wavelength, pitch angle 12 degrees). About 5 turns should work well, but more will give higher gain but I suspect is unnecessary.

If you want a quick solution there are a number of poorly designed Yagis on eBay for under S10 from China. One clains 25 dBi gain, but I measured one and foung it was a little exaggerated - roughly by a factor of 10000000000000. But even though the gain is considerably less than claimed, they are a cheap quick solution.