Analysis of 2 Styles of Homebrew Antennas

Electromagnetic theory basics

• Classic Dipole Analysis

How big should our antennas be?

• frequency range 2.45GHz

• Lambda * frequency = speed of light– Lambda = (3e8m/s)/(2.45e9s^-1)

• Lambdba = 0.122m or 4.8in

The “Cantenna”

• The first type of antenna and very common in the Homebrew world is the can-based antenna or cantenna.

• Fabrication Parts– Can

– Piece of standard 50ohm wire– N-type connector

Fabrication leads to:

So what does a cantenna radiation beam look like?

Printed Dipole Array

• This uses antenna strip idea as opposed to hollow conductive waveguides to do its work.

• Fabrication– Glass substrate– Adhesive copper roll– Vinyl cutter

Fabrication leads to

Recognizing the dipole array

• multiple dipoles squeezing beam and increasing gain

Dipole Array E&M field patterns

Why the tapered feed line (balun)?

• Balance/unbalance transmission line for VSWR characteristics

The Printed Dipole Array Antenna beam?

Which is the better antenna?

VS.

Top of vassar parking structure

Field Testing

• Duplicate parameters of cantenna test found online and compare results– 1320ft Line of Sight distance– Standard dipole on AP/Source/tx– Laptop using plug-in card for destination/rcvr

1320 ft

Access Point/source

Laptop

w/card

Roof of my home

Cantenna test results

• http://home.carolina.rr.com/harothberg/Test2.htm

• Control: only using pc and wireless card– Signal Level: -89dBm -> 1.26e-12W

• Actual test: using can design– Signal Level: -68dBm -> 1.58e-10W

• dBi = log[base 10](P1/P2)– 2.1dBi when compared to power from card

Printed Dipole Array Test Setup• Views from Source/AP and Destination/Laptop

1320 ft: AP on home roof

1320 ft: laptop site on Vassar parking

Printed Dipole Array Test Results• Control: only using pc and wireless card

– Signal Strength Level: -91dB• Actual test: using printed dipole array design

– Signal Strength Level: -65dB• dBi = log[base 10](P1/P2)

– 2.6dBi when compared to power from card

Wireless Card

Printed Dipole Array

Test Results Findings

• Absolutes [Cantenna vs. P.D.]• Antenna Strength: 2.1dBi vs. 2.6dBi

• Surprise results of holding P.D antenna with and without one’s hand:– An unintended experiment happened as the antenna

was being tested. One test run involved me holding the antenna with my hand (accidentally), while the other involved me holding the antenna in a nonconducting paper bag.

• Antenna gain showed a relative increase of +9dB in the signal when no hands were used to hold the antenna. That is a 3 time doubling of power in the signal. These results simply stress the significant affect biological contact can have on performance and points to better ways of insulating the printed dipole antenna from conductive influences.

The better antenna, based on analysis:

• Gain/power and coverage– P.D.: 3 dipoles focused in 1D

• great gain and coverage, good for community setting

– Can: has 1 dipole that is focused in 2D• okay on gain, low on coverage, good for point to point

• Fabrication – P.D.: mass production easier– Can: one-off production easier

• Portability– P.D.: low profile(2D), lightweight, durable– Can: bulky(3D), lightweight, durable