active antenna in wikipedia

An active antenna is an antenna that contains active electronic components. This allows the construction of antennas of limited size and / or wide frequency range. Most active antennas use antenna parts of minimal conducting area, e.g., a small whip, connected to the active component (usually an FET). The signal attenuation caused by the antenna-size-to-wavelength mismatch is compensated by an active circuit. The active circuit consists of an impedance translating stage and an optional amplification stage. This arrangement is especially useful for constructing compact low frequency antennas which, due to budgetary, spacial, or practical requirements (e.g., installation in vehicles), must be downsized. Low frequency signal wavelengths range from one to ten kilometers

Is there anyone could elaborate more on "impedance translating stage" and how could this help on "constructing compact low frequency antennas "?

Hi, you can get more on Google and I was reading a article on antenna and sharing here for your help.
http://ezinearticles.com/?Antenna-De...ide&id=3514310