Does the size of an antenna matter?

[Miss Amy]

Hello. I have a very small antenna and I was wondering if it can receive and/or transmit low frequency signals (or if it can only receive/transmit high frequencies). Likewise, do I need a very large antenna to receive/transmit low frequencies? I've read somewhere on the internet that the antenna's size scales up the lower down the frequency you go so I wanted to double check what you folks know. I've used a spectrum analyzer with ~8in antennas and they were able to pick up a band between 15MHz-2.7GHz, so that's where my confusion starts with the size. Thanks for reading.

 

[gneill]

The antenna length tells you the frequency at which the antenna will resonate, and thus be most efficient. Antennas used for frequencies other than their resonant frequency will often use a matching network of some kind to get better efficiency.

The Wikipedia article on dipole antennas does a pretty good job of covering this:

Dipole antenna - Wikipedia

 

[DaveE]

Yes size matters, if you want a good antenna, that is. The study of antenna design is complicated and is mostly about dealing with how to make a good antenna when making a great antenna is too hard or impossible.
As gneill suggested, start with understanding the dipole antenna.

 

[berkeman]

a very small antenna and I was wondering if it can receive and/or transmit low frequency signals

A small antenna can be a reasonable receive (Rx) antenna, but will not be able to transmit (Tx) high power efficiently. See the pictures below for an AM radio Rx (ferrite rod) antenna from a portable radio, and the corresponding AM radio Tx antenna...

I've used a spectrum analyzer with ~8in antennas and they were able to pick up a band between 15MHz-2.7GHz,

Do you have access to a Vector Network Analyzer (VNA) and two of your 8" antennas? If so, scan S11 first on one antenna to see what its input impedance looks like. Then scan S21 with antennas on each of the two VNA ports to see how the transfer from one to the other works. You will see the resonances that work well around the resonant lengths of the two antennas.

Rx AM Ferrite Rod Antenna:

http://www.rfcafe.com/references/el...e-am-antenna-readers-digest-stereo-800-xr.jpg

Tx AM Antenna:

http://blogs.dailybreeze.com/history/files/import/33838-P1000132.JPG