Abstract
Wireless sensor networks (WSN) are increasingly requiring directional antennas that not only provide higher capacity, security, transmission range or robustness against interference, but also contribute with smart antenna capabilities such as adaptive beamforming or multi beam radiation patterns. Standard phased arrays provide these features, but employing feeding networks based on digitally controlled variable phase shifters (VPSs) which have the disadvantage of high cost and limited angular resolution. Instead, time-modulated arrays (TMAs) use switched feeding networks governed by digital periodic sequences which allow harmonic patterns to be radiated and endows (TMAs) with attractive multifunctional capabilities. In this paper, we analyze and properly combine (TMA) switched feeding networks capable of time-modulating an antenna array with discretized amplitude modulation (AM) and phase modulation (PM) waveforms. The advantages of the proposed innovative dual-beam (TMA) with respect to the competing architectures are, on the one hand, its power efficiency and beamsteering (BS) phase sensitivity and, on the other, its hardware simplicity, which allows for an excellent relative cost advantage.
Highlights
If the nodes are endowed with smart-antenna extra functionalities such as beam steering, direction finding, secure signal transmissions, etc., the antenna feeding network will need to be equipped with variable phase shifters (VPSs), which will substantially increase the costs and radiation power losses
The benefits of using directional antennas built with switched beamforming networks (BFNs) rather than VPSs have been investigated [4,5] but in these approaches the utility of the switches consists in shifting between a set of possible positions for different radiation patterns
The fact that the frequency ωc + ω0 appears with its mirrored counterpart ωc − ω0 means that we have a double sideband (DSB) time-modulated arrays (TMAs), which generates harmonic diagrams with the same shape (Fourier coefficients with the same modulus), but pointing towards directions that are symmetric with respect to the broadside of the array
Summary
A wireless sensor network (WSN) often consists of spatially distributed autonomous sensors nodes—capable of monitoring in real-time certain physical variables—and one or more base stations connected to the end-users [1]. If the nodes are endowed with smart-antenna extra functionalities such as beam steering, direction finding, secure signal transmissions, etc., the antenna feeding network will need to be equipped with variable phase shifters (VPSs), which will substantially increase the costs and radiation power losses. The main contribution of this paper is the design of efficient dual-beam SSB TMAs based on the combination of switched networks, which are simpler than those in [18], capable of generating discretized AM and PM periodic time-modulating signals, and being well-suited for WSN application.
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