This paper presents a new concept to realize a multifrequency Oscillator-type active printed monopole antenna. The concept of period doubling route to chaos is exploited to generate the multiple frequencies. The chaotic Colpitts oscillator is integrated with the printed monopole antenna (PMA) on the same side of the substrate to realize an Oscillator-type active antenna where the PMA acts as a load and radiator to the chaotic oscillator. By changing the bias voltage of the oscillator, the antenna can be made to operate at single or multiple frequencies. To test the characteristics of the antenna at single and multiple frequencies of operation, two similar prototype models of printed monopole broadband antennas are developed. One of these antennas used at transmit side is fed by the chaotic Colpitts oscillator while the other is used as the receive antenna. It is observed that the antenna receives single or multiple frequencies simultaneously for particular values of the bias voltage of the oscillator at the transmit end. 1. Introduction During the last decades, tremendous attention has been devoted to the design and applications of active antennas and chaotic circuits. The active antenna is an active microwave circuit in which the output or input port is free space instead of a conventional 50-？ interface [1]. The integration of active devices with a radiating element forms an active antenna. The integration of active devices directly in the antenna structure is known as active integrated antenna (AIA). Depending on the functions of active devices used in the structure the active antennas are classified into three categories; amplifier type active antenna, Oscillator-type active antenna, and frequency conversion type active antenna [2]. The present work deals with the Oscillator-type active antenna employing a nonlinear device. Most of the nonlinear devices exhibit chaotic modes of operation under certain parametric conditions. There are different routes to chaos. To achieve the multifrequency operation the concept of deterministic chaos exhibited by the chaotic Colpitts oscillator is used. Colpitts oscillator exhibits bifurcation phenomena for certain values of the circuit parameter and in this way it exhibits periodic, multiperiodic, and chaotic motion [3]. The applications of chaotic circuits have been already reported in the past in chaotic communication, spread spectrum communication, low power communication, and so forth. In [4] a robust assessment for the Colpitts oscillator and the application of chaotic circuit in encrypted data transmission
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