Spectral control of integrated active antennas

Integrated active antennas are of increasing interest as system designers require more complex functions to be implemented in reduced space. Many of these systems require very low levels of harmonic and spurious radiation in order to meet electromagnetic compatibility specifications. Active antennas introduce nonlinear devices directly into the antenna and thus they can exhibit high levels of harmonic radiation, moreover, due to size constraints, filters can not be easily added as in conventional systems. In the case of active receiving antennas it seems that by suppressing the harmonic resonances of the antenna the harmonic reception problem can be reduced. However, with patch oscillators, due to the interdependence of the active device and the patch, the solution to the problem of harmonic radiation is more complex. This work aims to investigate these problems, especially in the case of the patch oscillator since these devices seem to pose the greatest challenge. The final goal is to obtain closed form expressions for the level of harmonics in terms of physical circuit parameters. Although numerical methods could be used to solve this problem it is felt that greater physical insight can be obtained from closed form expressions, allied to this they will be useful for CAD of patch oscillators. Closed form expressions would allow designers to realise low levels of harmonic radiation either by modifying the patch geometry or by altering the active device configuration.