Abstract
In this letter, we propose a two-row electronically steerable parasitic array radiator antenna designed for direction-of-arrival (DoA) estimation in Internet of Things (IoT) applications relying on simple microcontrollers. The antenna is capable of elevation and azimuth beam switching using a simple microcontroller-oriented steering circuit, and provides 18 directional radiation patterns, which can be grouped in 3 distinctive sets having different directions in the elevation. For each elevation direction, there are six different beam configurations that cover 360° in the horizontal plane. Measurements of the realized antenna prototype carried out in an anechoic chamber show good agreement with numerical simulations. The antenna prototype provides low sidelobe level, low half power beamwidth in both elevation and horizontal directions, and exhibit monotonous drop from the maximum value for all 18 radiation patterns. Therefore, the antenna is a good candidate for IoT nodes capable of DoA estimation in situations when radio frequency signals are impinging the antenna from different directions in elevation.
Highlights
I N MANY modern Internet of Things (IoT) applications, information about position of IoT nodes or direction of received radio frequency (RF) signals is required to improve the network operation with respect to a number of aspects, such as energy-efficiency, connectivity, security, and privacy [1]–[4]
When different elevation angles of incoming RF signals impinging the antenna are considered, DoA estimation accuracy deteriorates for low θ angles [15]–[17], which is related to the conical radiation pattern of electronically steerable parasitic array radiator (ESPAR) antenna having a directional beam
The final antenna prototype, measured in an anechoic chamber, has 18 different configurations that can be grouped in three distinctive sets having directional radiation patterns with different inclination in the elevation plane to provide 10◦ switching range in the elevation, which has not been earlier achieved for this kind of antenna
Summary
I N MANY modern Internet of Things (IoT) applications, information about position of IoT nodes or direction of received radio frequency (RF) signals is required to improve the network operation with respect to a number of aspects, such as energy-efficiency, connectivity, security, and privacy [1]–[4]. One of the most promising reconfigurable antenna concepts that can be integrated with a simple low-cost wireless sensor network (WSN) node is electronically steerable parasitic array radiator (ESPAR) antenna originally proposed in [11] Such antennas have a number of passive elements, which are connected to electronically steerable reactance, surrounding a single active element in the center. By setting the reactance to specific values, low-cost and energy-efficient realizations of ESPAR antennas can provide electronic beam steering capability for currently available on the market commercial off-the-shelf transceivers, which have only a single RF chain, to create a WSN node with DoA estimation capability [9]. When different elevation angles of incoming RF signals impinging the antenna are considered, DoA estimation accuracy deteriorates for low θ angles [15]–[17], which is related to the conical radiation pattern of ESPAR antenna having a directional beam. Six directional beam configurations in the horizontal plane are possible, which was proven to reduce complexity and cost of the switching circuit [25] together with time necessary for the DoA estimation process [16] without a critical impact on the overall DoA estimation accuracy in the horizontal direction [16], [25]
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