ESPAR Antenna Questions

Hi,

I am from Computer Science background who likes to work with electronics. Presently for low powered Wireless Application(IEEE 802.15.4 based) I am working on designing an Electronically Switched Parasitic Antenna, the basic design being a central monopole at the center with number of parasititc monopole like elements around the monopole which are grounded or isolated to control antenna gain in particular direction.

The design is based on -

http://www.sics.se/~luca/papers/ostrom10spida.pdf

and

**broken link removed**

Now, I have made the antenna, and I have few questions, if someone could answer this it would be very helpful( I am learning the Antenna design part using book of Balanis, but still at early stage) :

a) If the Central hexagonal plate (originally made using FR4 material) which is always grounded is replaced with plate not from FR4, will this have an effect on antenna gain ? The reason is, I have made one antenna, while I see the directionality, but the gain compared to the omni directional is not there ? Can someone explain if changing the central plate around central monopole to not FR4 have an effect ?

b) Should we put LC filter on the control line (from microcontroller ) controlling mosfet switches which control grounding or isolation of parasitic element ? can this lead to improvement of performance ?

c) In my initial experiments done in anechoic chamber, I am struggling to get consistent performance from diffeent legs ? my geometrical construction is correct ? Is there some good way to diagnose this ?

d) At the receiving side, if we see gain while sending, assuming reciprocacity of antenna to be true, should we receive similar pattern in terms of signal strength ? or how close is it to sending pattern in real life ?

I am sorry for array of questions, but as I said, I am not from Antenna design background, merely someone who indulges in hobby electronics.

Thanks again for the help.

First of all, thanks, for sharing this very interesting construction!

But I can only answer (a).

You say it's "grounded", which make me believe it has a layer of copper or what? Actually, it doesn't matter as it the answer is: YES, it will change things. Due to your question, you probably need to better understand "Aperture interference" and parasitic elements. The aperture is the region within 5/16 λ from any part of the elements. Anything that enters into the aperture of an antenna will affect the operation of the antenna. Your focus on "gain" also seem to imply that you have not yet modeled the radiation pattern. This is definitely important as any changes to the antenna configuration will distort the radiation lobes... Try to make a model in 4NEC2.

Good luck!

Actually your design look very similar to that of Rick Karlquist:

http://www.n6rk.com/7_hex_array.pdf
http://www.n6rk.com/driving_the_7_hex.pdf
http://www.n6rk.com/7_hex_eznec.html