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This dissertation describes research into “Antennas with Frequency Domain Control for Future Communication Systems” and several novel antennas are shown, each of which addresses a specific issue for current and future communication systems, in terms of wideband coverage, channel capacity, antenna isolation and band-rejection. These antenna designs may be candidates for implementation in future multiband radios, and software defined radio (SDR) and cognitive radio (CR) systems, which are two new concepts in wireless communications in the foreseeable future, although it is evident that there are as yet no clear specifications for those future systems. A novel two-port reconfigurable antenna which can operate within a narrowband or wideband mode is presented. Three different structures of wideband reconfigurable balanced antennas, with a wide tuning range, have been proposed. When the balanced antenna is combined with the two-port chassis antenna, it becomes a reconfigurable MIMO antenna for small terminals and at least 15 dB of isolation is achieved. Several designs of conical monopole antennas, incorporating different types of slots to achieve good band-rejection behaviour, have been introduced. These are the 2 Cshaped, 4 C-shaped slots, 4 U-shaped slots, 4 tilted-U-shaped slots and 4 U-C-shaped slots. The study of wideband antennas with notched-band behaviour using a simple equivalent circuit model has been proposed. It has been noted that increasing the number of resonators and the coupling factor will increase the band-rejection. However, it will also widen the bandwidth of the frequency notched band. A novel pyramidal monopole antenna, with four loop shaped slots, offering wide tunable band-notch, is also presented.