PCS antenna design: the challenge of miniaturisation

As mobile communication equipment become smaller and lighter, antennas must follow the trend. However, antenna size reduction is done at the expense of gain and bandwidth. This follows from the fact that an antenna is used to transform a free wave into a radiated wave. One understands easily that an antenna can perform this transformation only with a poor efficiency when its size is much smaller than the wavelength. If the loss of gain can be, to some extent, compensated by amplification, this is obviously not the ease for the bandwidth. For a given configuration, the design of the antenna should be done in order to use the maximum volume available. This maximum volume will theoretically give the upper bound for both gain and bandwidth.