Miniaturized device for passive microwave UWB beamforming
Résumé
—A 1 × N SIMO device is developed to achieve UWB beamforming in a passive way. The time reversal properties of time and spatial focusing are exploited to focus independent weighted signals on the device's output ports, depending on the unique input waveform. By connecting an antenna array to the device, beamforming can be achieved without any active device or moving part, over an ultra wideband. The principle of passive UWB beamforming is reminded in this paper, followed by recent results and the development of a new compact passive device. I. INTRODUCTION In recent years, the enhancement of UWB technologies has opened access to high resolution imaging in the microwave range [1] [2]. Using UWB signals, the time reversal can take full benefits of the propagation media's richness to achieve focusing of signals in time and space [3]. Whereas, the main weakness of this technique is its sensitivity to the channel variation. Indeed the phase compensation is not effective if the signal is pre-filtered by a channel that does not correspond to the crossed medium anymore. Against this background, a solution has been proposed in [4] to achieve beamforming of UWB signals. Using the demultiplexing capacity of a SIMO component presenting orthogonal channels [5], weighted signals can be focused on the component's outputs depending on the only input waveform. Thus, in this closed device the channels' stationarity ensure the time reversal to be efficient. By connecting an antenna array to these outputs, beamforming is achieved without any active device or moving part (Fig. 1).