Steerable Parasitic Array Radiator Antenna Research Articles

Analog Beamforming Using ESPAR for Single-RF Precoding Systems

A novel analog beamforming technique that utilizes single radio frequency (single-RF) electronically steerable parasitic array radiator (ESPAR) antennas is proposed. The ESPAR beamforming techniques are aimed at precoding in multiple antenna wireless communication systems using the single or hybrid RF approach. One advantage of ESPAR analog beamforming compared to conventional analog beamforming using phase shifters is that arbitrary patterns can be straightforwardly formed. Therefore, ESPAR analog beamforming can provide performance almost identical to digital beamforming. More importantly, ESPAR analog beamforming does not require phase shifters and power splitters, overcoming implementation challenges of conventional analog beamforming. It also has a more compact size compared to conventional beamforming using uniform antenna arrays. We analyze and optimize ESPAR analog beamforming and propose a channel approach based on beamspace pilot transmission to acquire channel state information (CSI). In addition, we propose limited feedback ESPAR analog beamforming based on a beamforming selection strategy. Simulation results for average gain show that ESPAR analog beamforming has almost identical performance to digital beamforming and better performance than analog beamforming using phase shifters. Energy efficiency simulations show that the technique has the highest efficiency among all the beamforming techniques. Therefore, ESPAR analog beamforming has near optimal performance, high energy efficiency, low circuit complexity, low cost, compact size and can be an effective alternative to conventional analog beamforming.

ESPAR array design for the UHF RFID wireless sensor communication system

SummaryIn this paper, in order to improve the received signal strength (RSS) and signal quality, three arrays of electronically steerable parasitic array radiator (ESPAR) antennas are suggested for the ultra‐high frequency (UHF) radio frequency identification (RFID) communication and sensing system applications. Instead of the single antenna, the array antennas have recently been widely used in many communication systems because of their peak gains, better radiation patterns, and higher radiation efficiency. Also, there are some important issues to use the antenna array like high data rates in wireless communication systems and to better understand the many targets or sensors. In this article, a wireless sensor network (WSN) is being investigated to overcome multipath fading and interference by antenna nulling technology that can be achieved through beam control ESPAR array antennas. The proposed ESPAR array antennas exhibit higher gains like 9.63, 10.2, and 12 dBi and proper radiation patterns from one array to another. Moreover, we investigate the mutual coupling effect on the performance of array antennas with different spacing (0.5λ, 0.75λ, λ) and configurations. It is found that the worst mutual coupling reduced by −28 to −34 dB for 2 × 2 array, −3 to −43 dB for 2 × 3 array, and finally −42 dB to −51 dB due to the antenna spacing from 0.5λ to λ. Thus, these suggested antennas could effectively be applied in the WSN communication systems, internet of things (IoT) networks, and massive wireless and backscatter communication systems.

Miniaturized Electronically Steerable Parasitic Array Antenna

In this article we propose a miniaturized dual-band electronically steerable parasitic array radiator (ESPAR) antenna. The antenna can generate up to two steerable beams. The beam-steering range of the proposed antenna is 360˚ in the azimuth plane. The antenna’s eual-band coverage includes the frequency ranges from 2.3 GHz to 2.53 GHz and from 2.9 GHz to 3.7 GHz. The antenna consists of six folded parasitic monopole elements surrounding an active conical element. The folded monopole element design offers three times lower antenna height than that of the conventional ESPAR antennas. The active element has conical shape and it is larger in length than the parasitic monopole elements, this enables the dual-band operation. Thus, the proposed design is not only smaller than the conventional ESPAR antennas but it also achieves dual-band operation. Despite its compact design, the antenna has a peak gain of 6.3 dBi, which is equivalent to the gain of conventional ESPAR antennas. These characteristics make the antenna a good candidate for next generation communication systems.

Direction of Arrival Estimation Based on Received Signal Strength Using Two-Row Electronically Steerable Parasitic Array Radiator Antenna.

In this paper, we present a novel approach to direction-of-arrival (DoA) estimation using two-row electronically steerable parasitic array radiator (ESPAR) antenna which has 12 passive elements and allows for elevation and azimuth beam switching using a simple microcontroller, relying solely on received signal strength (RSS) values measured at the antenna output port. To this end, we thoroughly investigate all 18 available 3D antenna radiation patterns of the antenna measured in an anechoic chamber with respect to radiation coverage in the horizontal and vertical direction and propose a generalization of the power-pattern cross-correlation (PPCC) algorithm involving a high number of multiple calibration planes (MCP) as well as specific combinations of radiation pattern sets. Additionally, a new way of RSS-based DoA estimation accuracy assessment, which involves thorough testing conducted along the elevation direction when RF signals impinging on the antenna arrive from arbitrary θ angles, has been reported in this paper to verify the overall algorithm’s performance. The results obtained for different signal-to-noise ratio (SNR) levels indicate that two-row ESPAR antenna can produce, even for low SNR values, accurate DoA estimation in the horizontal plane without prior knowledge about the elevation direction of the unknown RF signals by using appropriate combinations of only 12 3D antenna radiation patterns.

Relay-Aided Wireless Sensor Network Discovery Algorithm for Dense Industrial IoT Utilizing ESPAR Antennas

Industrial Internet-of-Things (IIoT) applications require reliable and efficient wireless communication. Assuming dense wireless sensor networks (WSNs) operating in a harsh environment, a concept of a time-division multiple access (TDMA)-based WSN enriched with electronically steerable parasitic array radiator (ESPAR) antennas is proposed and examined in this work. The utilized antenna provides one omnidirectional and 12 directional radiation patterns that can be electronically switched by the sensor node. We introduce a relay discovery algorithm, which selects those sensor nodes with an ESPAR antenna capable to act as relay. The selection of the relay nodes is based on a certain link quality threshold that algorithm uses as input. The outcome is a reduction in the number of layers or hops with a guaranteed Quality of Service (QoS). To emphasize the physical aspect of the wireless propagation, we introduce the measured antenna radiation patterns and consider two different path-loss propagation models representing blockage-free and blockage-prone industrial environments. A number of network simulations were performed and signal-to-noise ratio (SNR) as a link quality measure was examined with respect to the network density and different measured radiation pattern settings. The main outcomes show a tradeoff between SNR per link and the percentage of nodes that can serve as relays. As a result, we propose network design guidelines that take under consideration the QoS range with respect to SNR together with an optimal number of antenna radiation patterns that should be selected as a tradeoff between latency, energy consumption, and reliability in a network.

Two-Row ESPAR Antenna With Simple Elevation and Azimuth Beam Switching

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.

A broadband reconfigurable antenna with parasitic water radiation Array

This article introduces a wideband pattern reconfigurable antenna made of seawater. A special funnel-shaped metal structure is used for feeding to increase the bandwidth of the antenna. The antenna-design refers the electronically steerable parasitic array radiator antenna principle, and arc-shaped water columns are introduced around the seawater monopole antenna to operate as parasitic passive oscillators. These parasitic elements turn the omnidirectional antenna into a directional antenna. The proposed antenna has more than one mode. When the number of parasitic elements is 2, 3, and 4, it respectively corresponds to three different working modes: dual-beam radiation, wide-angle radiation, and directional high-gain radiation. And in all these three modes, changing the position of the parasitic elements can achieve 360° beam-sweeping in the 1.66 ~ 2.78 GHz. A prototype is fabricated and verified, and the experimental results are in good agreement with the simulated results. The antenna is filled with seawater when in use, and the weight can be reduced by draining the seawater when not in use. There is great application potential in the field of maritime communications.

Calibration-Free Single-Anchor Indoor Localization Using an ESPAR Antenna.

In this paper, we present a novel, low-cost approach to indoor localization that is capable of performing localization processes in real indoor environments and does not require calibration or recalibration procedures. To this end, we propose a single-anchor architecture and design based on an electronically steerable parasitic array radiator (ESPAR) antenna and Nordic Semiconductor nRF52840 utilizing Bluetooth Low Energy (BLE) protocol. The proposed algorithm relies on received signal strength (RSS) values measured by the receiver equipped with the ESPAR antenna for every considered antenna radiation pattern. The calibration-free concept is achieved by using inexpensive BLE nodes installed in known positions on the walls of the test room and acting as reference nodes for the positioning algorithm. Measurements performed in the indoor environment show that the proposed approach can successfully provide positioning results better than those previously reported for single-anchor ESPAR antenna localization systems employing the classical fingerprinting method and relying on time-consuming calibration procedures.

Digital pattern synthesis with a compact MIMO antenna of half-wavelength diameter

The paper presents a compact multiport antenna, with beamforming capabilities and a realized gain of 4.31 dBi with the size of λ/2. The antenna allows digital beamforming with independent control over three parameters: main-beam direction, beamwidth, and null-depth. Those parameters can be dynamically adjusted within a continuous range, create multiple beams for different frequency channels, and simultaneously generate multiple digital patterns. Due to digital beamforming capabilities, the proposed antenna offers much greater flexibility over switch-based analogue beamforming of Electronically Steerable Parasitic Array Radiator (ESPAR) antennas. The reconfiguration properties are achieved by using superposition of three dipole-like radiation patterns, where each radiator generates different spherical mode, i.e. with different angular phase distribution in the horizontal plane. This allows beamsteering with compact size, while the use of different modes ensures low Envelope Correlation Coefficient (ECC) from 10−4 to 3.2 × 10−5 for the operating frequency of 2.4 GHz. The proposed technique allows for significantly greater pattern reconfiguration than any reconfigurable antenna or array of comparable size and is a perfect candidate for Software Defined Radios.

Slot-Based Pattern Reconfigurable ESPAR Antenna for IoT Applications

In this article, a slot-based electronically steerable parasitic array radiator (ESPAR) antenna suitable for Internet-of-Things (IoT) applications is proposed. The antenna can provide 12 directive and two slightly different omnidirectional radiation states. The 12 directive patterns allow the antenna to focus the radiated energy toward six different directions uniformly distributed in the azimuth plane and with two different beamwidths. The reconfiguration of the radiation pattern is based on the use of low-capacitance low-power consuming diodes that can be digitally controlled. This article details the design of the antenna structure and the practical implementation of the reconfiguration mechanism, discussing the effects of real electronic components on the antenna performance. The antenna effectiveness is numerically and experimentally assessed.

Low-Complexity Implementation of Channel Estimation for ESPAR-OFDM Receiver

Electronically steerable parasitic array radiator (ESPAR) antenna is a novel low-cost technique to gain comparable diversity order to that of using multiple antennas while maintaining one radio frequency (RF) front-end, low power consumption, and simple wiring at the mobile receiver. It has huge potential to realize high energy efficiency for multiple and massive antennas systems. The main drawback of the ESPAR based OFDM system is that the channel estimation (CE) usually should be realized in time-domain with a huge computational complexity (CC) because the received signal to each parasitic element is overlapped each other both in frequency and time domain. This article will propose three ways to reduce the complexity of CE for the ESPAR-OFDM system. The parallel multi-column compressive sensing (CS) algorithm was first introduced to detect all locations of channel impulse response simultaneously using one small segment of sensing matrix. Furthermore, by exploiting the symmetrical properties of Digital Fourier transform (DFT), the size of matrix to decrease the CC of matrix operation. Finally, by selecting a small set of row vectors of sensing matrix at the receiver side, the CC involved in CS algorithm can be reduced. From the analysis and simulated results, the proposed method can obtain more than 90% CC reduction for CE of ESPAR-OFDM receiver can be confirmed.

A Circular Beam-Steering Antenna With Parasitic Water Reflectors

In this letter, a salty water antenna with beam-steering characteristics is proposed. The antenna combines the idea of the electronically steerable parasitic array radiator (ESPAR) antenna and the water antenna to realize a 360° beam steering. The unique features of water antennas, such as transparency, reconfigurability, and liquidity, are fully utilized. Both the computer simulations and measurements are conducted to validate the performance. The proposed design has a frequency range from 334 to 488 MHz ( S 11 60%), 13 different working states, and a maximum gain of 5.8 dB. Compared with existing pattern-reconfigurable liquid antennas, this new antenna has a wider bandwidth, more working states, and better invisible ability. It is, therefore, a promising candidate for a range of very high-frequency or ultrahigh-frequency applications, such as Internet of Things and maritime applications.

Beam Selection and Discrete Power Allocation in Opportunistic Cognitive Radio Systems With Limited Feedback Using ESPAR Antennas

We consider an opportunistic cognitive radio (CR) system consisting of a primary user (PU), secondary transmitter (SUtx), and secondary receiver (SUrx), where SUtx is equipped with an electrically steerable parasitic array radiator (ESPAR) antenna with beam steering capability for sensing and communication, and there is a limited feedback channel from SUrx to SUtx. Taking a holistic approach, we develop a framework for integrated sector-based spectrum sensing and sector-based data communication. Upon sensing the channel busy, SUtx determines the beam corresponding to PU's orientation. Upon sensing the channel idle, SUtx transmits data to SUrx, using the selected beam corresponding to the strongest channel between SUtx and SUrx. We formulate a constrained optimization problem, where SUtx- SUrx link ergodic capacity is maximized, subject to average transmit power and interference constraints, and the optimization variables are sensing duration, thresholds of channel quantizer at SUrx, and transmit power levels at SUtx. Since this problem is non-convex we develop a suboptimal computationally efficient iterative algorithm to find the solution. Our numerical results quantify the capacity improvement provided by the ESPAR antenna and demonstrate that our CR system yields lower outage and symbol error probabilities, compared with a CR system that its SUtx has an omni-directional antenna.

λ/64‐spaced compact ESPAR antenna via analog RF switches for a single RF chain MIMO system

In this study, an electronically steerable parasitic array radiator (ESPAR) antenna via analog radio frequency (RF) switches for a single RF chain MIMO system is presented. The proposed antenna elements are spaced at λ/64, and the antenna size is miniaturized via a dielectric radome. The optimum reactance load value is calculated via the beamforming load search algorithm. A switch simplifies the design and implementation of the reactance loads and does not require additional complex antenna matching circuits. The measured impedance bandwidth of the proposed ESPAR antenna is 1,500 MHz (1.75 GHz–3.25 GHz). The proposed antenna exhibits a beam pattern that is reconfigurable at 2.48 GHz due to changes in the reactance value, and the measured peak antenna gain is 4.8 dBi. The reception performance is measured by using a 4 4 BPSK signal. The measured average SNR is 17 dB when using the proposed ESPAR antenna as a transmitter, and the average SNR is 16.7 dB when using a four‐conventional monopole antenna.

RSS-Based DoA Estimation for ESPAR Antennas Using Support Vector Machine

In this letter, it is shown how direction-of-arrival (DoA) estimation for electronically steerable parasitic array radiator (ESPAR) antennas, which are designed to be integrated within wireless sensor network nodes, can be improved by applying support vector classification approach to received signal strength (RSS) values recorded at an antenna's output port. The proposed method relies on ESPAR antenna's radiation patterns measured during the initial calibration phase of the DoA estimation process. These patterns are then used in the support vector machine (SVM) training process adapted to handle ESPAR antenna-based DoA estimation. Measurements using a fabricated ESPAR antenna indicate that the proposed SVM approach provides more accurate results than available RSS-based estimation algorithms relying on power pattern cross-correlation method.

Low-Profile ESPAR Antenna for RSS-Based DoA Estimation in IoT Applications

In this paper, we have introduced a low-profile electronically steerable parasitic array radiator (ESPAR) antenna that can successfully be used to estimate the direction-of-arrival (DoA) of incoming signals in wireless sensor network (WSN) applications, in which the height of the complete antenna has to be low. The proposed antenna is over three times lower than high-profile ESPAR antenna designs currently available in the literature for the DoA estimation; it can provide eight unique main beam directions and relies on simplified beam steering, which makes it applicable to simple and inexpensive WSN nodes. Measurements using our fabricated ESPAR antenna prototype indicate that relying solely on the received signal strength values recorded at the antenna output port, it is possible to achieve accurate DoA estimation results with error levels similar to those available for high-profile ESPAR antennas relying on the similar energy-efficient simplified beam steering concept and having 12 unique main beam directions. As a consequence, the overall time required for the DoA estimation using the proposed antenna can be reduced by 33%.

Multiple Beam Parasitic Array Radiator Antenna for 2.4 GHz WLAN Applications

A multiple beam parasitic array radiator (MBPAR) antenna is proposed in this letter. The MBPAR antenna can cover all angles in horizontal plane by generating six wide beams with angle-step of 60° in 2.4 GHz wireless local area network (WLAN) bands. The MBPAR antenna consists of six active elements, a center parasitic reflector, twelve parasitic isolation elements, and a ground structure. Six active elements located in the ground edge use a common center parasitic reflector to realize six beams. The parasitic isolation elements located on the angular bisectors are used to improve the isolation between adjacent ports. Unlike the traditional electrically steerable parasitic array radiator antenna, the MBPAR antenna can realize six beams at the same time, which remarkably increase the communication capacity. To validate the proposed design, an MBPAR antenna has been designed and prototyped at 2.45 GHz. The MBPAR antenna exhibits VSWR <2 and isolations better than −20 dB in 2.4G-WLAN bands. The peak realized gain of 7.3 dBi and efficiency of 95.7% of the MBPAR antenna are obtained. The MBPAR antenna with large communication capacity and low wind resistance is suitable for the outdoor WLAN applications.

Broadband ESPAR antenna using sleeve wires

A broadband electrically steerable parasitic array radiator (ESPAR) antenna is presented. The proposed broadband ESPAR antenna consists of an active monopole, 12 parasitic sleeve wires, 6 parasitic elements and a ground structure. By introducing the sleeve wires into the ESPAR antenna, the operation bandwidth of the ESPAR antenna is broadened effectively. Six copper wires placed around the circular ground plane constitute the ground skirt of the ESPAR antenna. The ground skirt, with low wind resistance, reduces the elevation angle of the radiation beam. A broadband ESPAR antenna operating at 2.2 GHz is designed and fabricated. From the results, the impedance bandwidth, with a 2 VSWR, can operate from 1.70 to 2.70 GHz, which is wider than a conventional ESPAR antenna. The working band of the proposed ESPAR antenna covers the GSM1800/1900/UMTS, LTE2300/2500, and 2.4G-WLAN bands. The electronic beam steering across a range from 0° to 360° with a step size of 60° is realized and the gain from 6.15 to 7.37 dBi is obtained over the operation band.

Characteristics of high‐gain ESPAR antenna using collinear dipole array

AbstractIn this study, a high‐gain electrically steerable parasitic array radiator (ESPAR) antenna using a collinear dipole array as a feed element is proposed, and its radiation characteristic is discussed. The feed element of the proposed antenna has a higher gain than existing ESPAR antennas, and it makes impedance matching easier via a length of coaxial cable between the arrayed feed elements and the thickness of the dielectric, using a collinear dipole array of circular dipole antennas. The proposed antenna is structured with feed elements of two‐layer collinear circular dipole arrays surrounded by four parasitic elements with an array radius of λ/16. The variable directional radiation pattern and high‐gain characteristic can be achieved through changes in reactance between the parasitic elements. The gain of the proposed antenna is 7.2 dBi approximately at the center frequency, and the return loss is less than −15 dB at the used frequencies of 2.4–2.5 GHz.

Opportunistic Beamforming Using Dumb Basis Patterns in Cognitive Multiple Access Channels

In this paper, we investigate multiuser diversity in interference-limited multiple access underlay cognitive radio systems with line-of-sight (LoS) interference between the secondary and primary networks. Assuming Rician-K interference channels and N secondary users, it is shown that the secondary network sum capacity scales like log((K 2 + K)/W(KeK/N)), where W(.) is the Lambert-W function. Thus, LoS interference hinders the achievable multiuser diversity gain experienced in Rayleigh interference channels, where the sum capacity grows like log(N). To overcome this problem, we propose the usage of a single radio Electronically Steerable Parasitic Array Radiator antenna at each of the secondary mobile terminals. These antennas will be used to induce artificial fluctuations in the interference channels to restore the log(N) growth rate by assigning random weights to orthogonal basis patterns. This technique will be referred to as random aerial beamforming (RAB). It is also shown that by using RAB, one can actually exploit LoS interference to improve multiuser interference diversity by boosting the effective number of users with minimal hardware complexity.