It is called "resistor"

<nbucska@pcperipherals.com>

The term "virtual antenna" (used seriously) would normally be used to mean the reflection, in its ground plane, of a quarter-lambda vertical Ground Plane antenna (for example).  In other words, the 'missing half' of a dipole when actually using a monopole with a ground plane.

Since that is not what you mean, I did a quick search on Google to find out what the heck you're referring to...

www.google.com/search?q=virtual+antenna

This immediately popped up with a website in Germany that is promoting or marketing a passive antenna system that they have dubbed a 'virtual antenna'.  The German connection (being a translation) explains why they have unintentially used the term "virtual antenna" with a whole new meaning.

This is simply a resonant antenna designed to extend (very slightly) the range of an RFID system.  The same "advanced technology" is used in those usually-useless cell phone extenders that clip onto the rear view mirror of your car, or slip behind the battary pack of your portable phone.

It's just an antenna.  That's the answer to your question.

Effective application of this technique is very limited.  You have to realize that the power density at the 'virtual antenna' is going to be very low (unless the first antenna is plopped right in the middle of the 'virtual antenna').  There's simply not enough power to make a huge difference.

Slight difference yes, big difference no.

One example of 'virtual antennas' that DO make a difference are the passive elements (reflector, directors) on a Yagi.  Of course, they're only about 0.15 of a wavelength away from the driven element.

Another example might be where you "beam" the power, using a high gain antenna, onto the 'virtual antenna'.  That should work over a longer range.

If the power density at the 'virtual antenna' is low, then why bother ?  There's nobody home.

You get the idea.

Suggestion: Visit
http://www.spacedaily.com/news/milspace-02ze.html
for Virtual Antenna Array that will consist of satellites, possibly, micro satellites. This concept is identified as having its merit.