Directional Antenna 1

[hwst]

Hi all,

Looking for a special small size cellular band antenna with very sharp front end radiation pattern. I hope it could be less than 10 degree at half power point. Of course the smaller the better. I have tried Yagi, but it's not narrow enough. The antenna will be used as a receiver only, and we want it to receive the signal in a range of 40 ft away and at most 12 ft wide.
I'm thinking of small size parabolic antenna or special Yagi antenna. I wonder if there is any "magic" to make the antenna small in size and sharp in radiation pattern.
You guys have any idea about this?
Thanks a lot.

 

[VEBill]

In addition to all the other questions that come to mind, you'll eventually need to define what you mean by Cellular. There are at least four bands these days (as witnessed by quad-band 'cellular' or 'mobile' or 'wireless' phones).

Also, what is your purpose? You mentioned range and 40 feet. Is this for testing of some sort?

 

[hwst]

The bands I would like to cover are all cellphone bands. 800-1000MHz and 1800-2000MHz.
It's a kind of cellphone signal receiver.

 

[VEBill]

10 degrees @ 3 dB ~=~ 25 dBi gain ????

Yikes.

 

[VEBill]

What is the 40 feet?

 

[hwst]

Antenna Gain is not important for us. And we could always add amplifier to the link.

 

[hwst]

40 ft away from the antenna. in another word, the object we are about to detect RF signal is 40 ft away.

 

[VEBill]

Beamwidth and gain go hand-in-hand (plus or minus losses). Disregarding any added attenuators, a 10-degree beamwidth is a relatively high gain antenna. 2-m dish at 1GHz.

Are you assuming that you require a very narrow beamwidth in order to measure the pattern of your device under test?

 

[hwst]

Actually, the narrow beamwidth is used to distinguish unwanted objects.
I think parabolic antenna should have relatively narrow lobe compared to Yagi.

 

[VEBill]

There are plenty of antenna beamwidth/gain calculators available on the www.

http://www.google.com/search?q=antenna+beamwidth+gain+calculator

These calculators will allow you to see the relationship between beamwidth, gain, losses, diameter, frequency, etc.

There are many antenna test ranges that seen to get by without such stringent beamwidth requirements on their EMC antenna. You might want to review the situation to see how they do it without, for example, using a 2-m dish to test a cellphone.

 

[hwst]

Thanks, VE1BLL.

 

[Higgler]

If you only need to distinguish things horizontally, that's alot easier than both vertically and horizontally. A 16 element horizontal array of antennas, fed by a power divider from minicircuits and 16 cables will give you pretty good results.
Space antenna elements 0.8 lambda at 2 ghz and you'd get a 10 degree beamwidth at 800 Mhz and 4.25 degree beamwidth at 2 ghz. You could even the beamwidths up by curving the shape of your array if the 4.25 degree beam is too narrow.
It's 75 inches long x very thin if that works. H pole is easiest to make, consider a notch antenna array. Cheap to build too.

kch

 

[Sawbux]

I've heard of "fox hunt" directional antenna that consisted of a vertical antenna mounted inside of a coffee can! The metal of the can blocks any reception from the rear. Sort of a crude dish antenna.