Plasmonics https://doi.org/10.1007/s11468-018-0870-8
Electronic Beam Switching of Circularly Polarized Plasma Magneto-Electric Dipole Array with Multiple Beams Saber Helmy Zainud-Deen 1 & Hend Abd El-Azem Malhat 2 Received: 3 August 2018 / Accepted: 5 November 2018 # Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract In this paper, different array arrangements based on magneto-electric (ME) dipole antenna with wideband circular polarization (CP) characteristics are designed and investigated. Planar, triangular prism, square prism, and hexagonal prism array arrangements are considered. Each prism face has a sub-array comprises 2 × 2 ME-dipole elements. Each sub-array has wide impedance matching of 73.7%, a maximum gain of 16.6 dBi, and CP bandwidth of 78.2%. It employs the plasma frequency of the MEdipole antenna to control its radiation characteristics. Frequency-independent lumped element equivalent circuit is constructed for a single antenna element. It is used to represent the antenna input impedance at different plasma electron densities with fixed physical structure. The proposed equivalent circuit comprises a single series section used for matching enhancement with feeder circuit, and three parallel tuned circuits corresponding to the three resonance frequencies in the input impedance. The best values of the equivalent circuit elements are computed using the particle swarm optimization (PSO) technique. Different array arrangements, planar, triangular, square, and hexagonal prism are designed to create single or multiple beams in different directions. An electronic beam switching is achieved by tuning in the plasma inside the ME-dipole in the desired direction. The radiation characteristics are analyzed and investigated using the finite integration technique (FIT). Keywords Magneto-electric antenna . Beam-switching . Plasma antenna . Lumped equivalent circuit . PSO
Introduction The emerging development in modern communication, wireless systems, increases the interests in designing wideband low-profile antennas to match the suggested services [1]. Wideband antennas are recommended to work in different applications such as ultra-speed multimedia connectivity, high gain radar systems, and high capacity communications [2]. The complementary antenna concept is used to design magneto-electric (ME) dipole antenna as introduced in [1]. It contains a couple of vertical quarter-wave shorting wall representing a magnetic dipole placed orthogonal to a
* Hend Abd El-Azem Malhat
[email protected] Saber Helmy Zainud-Deen
[email protected] 1
Department of Electrical Engineering, Faculty of Engineering and Technology, Badr University, Badr City, Egypt
2
Department of Electrical and Communication Engineering, Faculty of Electronic Engineering, Menoufia University, Menoufia, Egypt
horizontal electric dipole. Both are proximity fed using a single probe with different configurations. The ME-dipole antenna offers many advantages such as stable gain, high Copolarization level, low back radiation, and wide impedance matching bandwidth [3]. They have been applied in different applications such as imaging radars, mobile communications (base station), and wideband communications [4]. Circularly polarized (CP) antennas have been used in modern communication systems due to their plentiful advantages [5, 6]. The sequential feeding technique in phase and orientation has been applied to enhance the gain and axial-ratio (AR) bandwidth. It involves a sequential rotation of the array element’s orientation and orthogonal phase to radiate orthogonal field components [7, 8]. Linearly dual-polarized and CP ME-dipole antennas with different configurations have been investigated in [9–11]. The CP characteristics of the ME- antennas of 33% and 27.67% are controlled by power dividers and hybrid couplers as introduced in [12, 13]. In [14], the CP performance of 71.5% is achieved via complex antenna structure. It consists of two rotationally symmetric half-ellipse arcs, two rectangular patches with chamfered edges, two small rectangular patches, and two cavity gaps. Different wireless communication applications use the beam switching technique due to its
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plentiful advantages [15]. The ME-dipoles with reconfigurable patterns and polarization diversity of different wireless communication applications have been investigated [1]. In [16–18], the beam switching is achieved using PIN diodes and electronic switches to generate multi-beams whose output may be switched to a receiver or a bank of receivers. Recently, antenna structure based on voltage controlled materials such as plasma, graphene, and quartz is investigated in different wireless applications. The conventional conducting medium in traditional antennas is replaced by ionized noble gases such as argon in plasma antennas [19]. The radiation characteristics of the plasma antennas are electrically controlled by using a DC ionizing voltage. It has many advantages such as reconfigurable radiation characteristics and reduced radar cross sections [20]. Different antenna elements based on plasma in the literature such as reflectarray, transmitarray, microstrip antenna, and the dipole are investigated in [21, 22]. The equivalent circuit of the antenna is important the communication system implementation for proper choice of the matching circuit [23]. The equivalent circuit model of an antenna is a two-terminal circuit comprises a set of lumped resistors (R), capacitors (C) and inductors (L) joined in series or parallel connections [24]. An equivalent circuit comprises a five-lumped element was introduced for different antennas such as dipole, dielectric resonator antenna, and microstrip patch antenna [25, 26]. The particle swarm optimization (PSO) is used to estimate the values of the lumped elements of the equivalent circuit by satisfying a pre-defined fitness function [27]. PSO is characterized by a simple concept, easy to implement, and computationally efficient. PSO is a flexible technique which employs a few parameters to adjust, and a comparatively minor number of function evaluations to converge to the optimum values [28]. Theoretically, the equivalent circuit of the ME-dipole antenna is presented by a parallel tuned circuit representing the magnetic dipole and series tuned circuit representing the electric dipole as investigated in [1]. This theoretical equivalent circuit does not present an adequate model to the wideband multiresonance behavior of the calculated input impedance, and more tuned circuit sections must be added [29]. In this paper, single and multiple beams with fixed or switched directions are achieved by using a reconfigurable CP plasma ME-dipole antenna array. It investigates the sequential feed array arrangement for gain and CP bandwidth enhancement for the 2 × 2 sub-array. The radiation characteristics of the antenna are investigated using timedomain based finite integration technique (FIT) [30] and are compared with that calculated in the frequency-domain based on the finite element method (FEM) [31]. An equivalent circuit consisting of a series capacitor, series inductor, and three parallel resonant circuits are proposed to represent the ME-dipole antenna. It uses the PSO to extract the optimal values of the lumped elements of the
equivalent circuit at different plasma electron densities. Different array arrangement such as planar, triangular, square, and hexagonal geometries has been investigated. The beam is switched in different directions based on the plasma medium reconfigurable characteristics.
Antenna Design The detailed structure of a single element CP-plasma based ME-dipole antenna with reconfigurable bandwidth has been presented in [32] and is shown in Fig. 1. The antenna structure includes a rectangular metallic cavity shorted with vertical plasma boxes orthogonal to horizontal plasma boxes. It represents magnetic and electric dipoles. The horizontal boxes have a trapezoidal configuration offset by a distance L and are proximity fed using Γ-shaped plasma dipole. The rectangular cavity has two unsymmetrical gaps and acts as a ground plane. All the plasma parts in the MEdipole antenna are enclosed in dielectric containers with εrd = 1.6 and thickness td = 0.2 mm and are filled with argon gas with thickness, tp = 4 mm. The optimized MEdipole antenna dimensions in millimeters for maximum impedance matching are given by GL = 180, G1 = 60, G2 = 60, W = 60, W1 = 7, W2 = 11, W3 = 23.5, L = 39.6, L1 = 62.5, L2 = 97.4, L3 = 15, H = 30, H1 = 28.5, H2 = 21.2, S1 = S2 = 3, d = 8.7, dx = 16.8, and dy = 33.5. W2
z
W1 H2
H1 td d
H dy
x
b. Top view
dx y
G1 G2 a. 3D view
c. Side view
Fig. 1 The detailed construction of the CP ME-dipole antenna
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The ionized plasma inside the ME-dipole antenna boxes have reconfigurable dispersive properties expressed by [19]: "
ω2p
#
ð1Þ
ε ¼ εo 1− ω ω− jν p
where εo is the permittivity of free space, ω is the angular frequency of the antenna, νp is the angular collision frequency of the plasma, and ωp is the angular frequency of plasma defined by,
FIT FEM
sffiffiffiffiffiffiffiffiffiffi ne e2 ωp ¼ εo me
a. The reflection coefficient
ð2Þ
where e is the charge of the electron, ne is the electron density of the plasma, and me is the electron mass. A linear relationship between electron density ne and applied voltage VRF has been reported in [33, 34]. While different relationship is predicted by analytic modeling is given by [35, 36]: 3=2
ε V RF ffi ne ≈ pffiffiffiffiffiffiffiffiffi ekT e t 2p
FIT FEM
ð3Þ
where Te is the electron temprture, k is the boltzman constant. The conductivity of the plasma medium is is inversely related to the operating frequency and depends on the electron collision frequency, given by
b. The gain and axial ratio Fig. 2 The frequency response of reflection coefficient and the radiation characteristics for ME-dipole antenna
σ¼
εo ω2p jω þ ν p
ð4Þ
Fig. 3 The surface current distributions on the ME-dipole antenna at different frequencies
a. f=1.75 GHz
b. f=2.5 GHz
c. f=3.5 GHz
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The plasma medium electron density ne varies from 2.84 × 1017 to 3.15 × 1020 m−3 at vp = 20.1 × 109 rad/s at room temperature of 300 K. At a constant electron density, ne, the dielectric constant increases with increasing frequency, while the losses are decreased [21]. The reflection coefficient variation versus frequency at an electron density ne = 3.15 × 1020 m−3 is depicted in Fig. 2a. The impedance matching bandwidth is 2.06 GHz, (from 1.64 to 3.7 GHz) with high radiation efficiency above 97.01%. The gain and AR over a frequency range normal to the element are plotted in Fig. 2b. The antenna has a peak gain of 10.46 dBi with CP of 64%. Good agreement between the results calculated using FIT and FEM is achieved. The surface current distributions on the ME-dipole antenna at different frequencies are plotted in Fig. 3. The current rotates in the clockwise
direction and it radiates left-hand circular polarization (LHCP). The CP radiation characteristics are controlled by the offset shift, and the cutting edges of the trapezoidal patches in the antenna. This structure is simpler than that presented in [14]. The 3D gain patterns at different frequencies are plotted in Fig. 4. Broadside fields with the half-power beam width (HPBW) of 64 degrees in x-z plane and 48 degrees in the y-z plane at 2.25 GHz are obtained. The reconfigurable plasma electric properties effect on the radiation properties of the MEdipole antenna has been investigated in [26] and is summarized in Table 1. The CP response of the antenna is controlled by the horizontal patches and vertical walls while the impedance matching bandwidth is controlled by the Γ-shaped feed.
Plasma ME-Dipole Antenna Equivalent Circuit Estimation Using Particle Swarm Optimization
a. f1=2.25 GHz
Equivalent circuit estimation for the antenna is essential for choosing the proper matching circuits for maximum power transfer. To adequately convey the multi-resonance wideband input impedance behavior of the ME-dipole antenna, cascaded resonance circuits are added to the conventional five-elements equivalent circuit [25]. The proposed equivalent circuit for the ME-dipole antenna is shown in Fig. 5. It consists of series section with Cs and Ls is used to compensate reactive impedance of the parallel-resonant circuits to enhance matching with the feeing network. The equivalent circuit includes three parallel resonant sections with elements Ri, Li, and Ci where (i = 1,2, 3) whose values are effective in the frequency range of interest. The initial value of Ri is chosen equal to the largest resistance at the resonance frequency fri. The initial values of Li and Ci are chosen according to the resonance frequency f ri ¼
b. f2=2.75 GHz
1 pffiffiffiffiffiffiffiffiffi 2π Li C i
ð5Þ
It employs a PSO technique to estimate the values of the lumped elements of the equivalent circuit. The PSO consists Table 1 The effect of varying the plasma electron density on the radiation properties of the ME-dipole antenna
c. f3=3.5 GHz Fig. 4 The 3D gain radiation patterns of the ME- dipole antenna at different frequencies
Electron density ne (m−3)
Impedance BW (%)
Efficiency (%)
Peak gain G (dBi)
2.84 × 1017 5.04 × 1017 1.13 × 1018 3.15 × 1018 1.26 × 1019 3.15 × 1020
17.3% 45.1% 56.01% 66.5% 71.7% 73.7%
46.83% 72.1% 76.4% 91.27% 92.1% 97.01%
6.2 dBi 8.7 dBi 9.2 dBi 10 dBi 10.07 dBi 10.46 dBi
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Cs Ls
L1 C1
R1
L2
C2
R2
L3
C3
R3
Fig. 5 The proposed lumped-elements equivalent circuit for the MEdipole antenna
of an initially populated random swarm of particles, which move iteratively through the problem space to search the
Rin
Xin FIT Equivalent circuit
new solutions [28]. The ith particle of the swarm can be represented by a D-dimensional position vector, Xi = (xi1, xi2, ……., xiD)T. The particle velocity is given by Vi = (vi1, vi2, ….., viD)T. The best particle is denoted by, g, with earlier best position denoted as Pi = (pi1, pi2, …., piD)T. It manipulates the swarm, according to two equations given by [27]: nþ1 ¼ χ ω vnid þ c1 r1 pnid −xnid þ c2 rn2 pngd −xnid vid ð6Þ nþ1 nþ1 ¼ xnid þ vid xid
ð7Þ
where d = 1, 2, …, D; i = 1, 2, …, N, and N is the size of the swarm. r1 and r2 are random numbers, uniformly distributed in [0,1], which is the cooperation among the particles; and n = 1, 2, …..determine the iteration number. ω is called inertia weight; c1, and c2 are two positive constants, called cognitive and social parameters, respectively. The χ is a constriction factor, used to limit the velocity. It provides a detailed discussion of the particle swarm optimizer used in this paper in [28]. The optimization is performed to minimize the square norm F [27]: h 2 FIT 2 i N f FIT F ¼ ∑n¼1 Re Z in ð f n Þ −Re Z PSO þ Im Z in ð f n Þ −Im Z PSO in ð f n Þ in ð f n Þ
a. ne=3.15×1020 m-3
ð8Þ
Rin
Xin FIT Equivalent circuit
b. ne=3.15×1018 m-3
FIT where Nf is the FIT number of frequency points, Re Z in ð f n Þ and Im Z in ð f n Þ are the real and imaginary parts of the input impedance calculated theFIT technique, respectively. using PSO Re Z PSO in ð f n Þ and Im Z in ð f n Þ are the real and imaginary parts of the input impedance calculated using the equivalent circuit model with its components are optimized by PSO algorithm. The equivalent circuit estimation starts with the initial values of the lumped elements calculated from Eq. (5) and it uses the PSO to find their optimum values based on the fitness function given in Eq. (8) for each plasma electron density. The variations of the input impedance versus frequency using the
Rin Xin FIT Equivalent circuit
c. ne=1.13×1018 m-3
Rin
Xin FIT Equivalent circuit
d. ne=5.04×1017 m-3
Fig. 6 The estimated input impedance versus frequency of the ME-dipole antenna using the equivalent circuit model
Table 2 The values of lumped-elements in the equivalent circuits at different electron density for a single ME-dipole antenna ne (m−3) Element
3.15 × 1020
3.15 × 1018
1.13 × 1018
5.04 × 1017
Cs Ls R1 L1 C1 R2 L2 C2 R3 L3 C3 RMSE
2.75 × 10−12 1.65 × 10−9 485 65 × 10−9 0.53 × 10−11 85 3.7 × 10−9 0.98 × 10−12 256 67 × 10−11 21.3 × 10−13 0.17%
3.2 × 10−12 2 × 10−9 72 0.57 × 10−9 1.75 × 10−11 89.6 3.9 × 10−9 1.08 × 10−12 300.46 80.1 × 10−11 20.6 × 10−13 0.16%
3.95 × 10−12 1.91 × 10−9 130.25 0.87 × 10−9 1.3 × 10−11 89 3.6 × 10−9 1.53 × 10−12 325 90.2 × 10−11 21.5 × 10−13 0.13%
3.1 × 10−12 0.72 × 10−9 60.25 0.75 × 10−9 1.4 × 10−11 110 2.6 × 10−9 1.53 × 10−12 180 80.2 × 10−11 21.5 × 10−13 0.23%
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FIT are calculated and compared to that calculated by the proposed equivalent circuit for different plasma electron densities with fixed physical structure are shown in Fig. 6. The results are closely matched with a maximum root-mean-square error (RMSE) of 0.17% for ne = 3.15 × 1020 m−3. The elements R1, L1, and C1 are effective in the lower frequency band around 1.58 GHz. The elements R2, L2, and C2 are effective in the frequency band around 2.45 GHz, while the elements R3, L3, and C3 are effective in the upper frequency band around 3.85 GHz as depicted from Eq. (5). The physical structure of the ME-dipole antenna is fixed and the values of the lumped-element equivalent circuit depend on the operating plasma electron density. Table 2 lists the lumped-element equivalent circuit values at different plasma electron density, ne and the corresponding MSE.
Plasma ME-Dipole Antenna Array with Sequential Feed Array arrangements with sequential feeding technique are used to increase the peak gain and the CP bandwidth of the single antenna element. A unit-pair consists of two ME-dipole antenna separated by a distance GL and fed with equal magnitudes, with 90° phase shift and rotated 90° relative to each other is depicted in Fig. 7a. The S-parameters frequency responses for the unit-pair are shown in Fig. 7b. It maintains the impedance matching wide bandwidth of 77.2% over the unit-pair configuration with high isolation of −27.5 dB due to the large size (~ λ2.5 GHz) ground plane. A sub-array consists of 2 × 2 sequentially fed antenna
F2
elements at ne = 3.15 × 1020 m−3 is investigated in Fig. 8a. The sub-array elements are rotated by 90° to achieve an orthogonal field component with equal amplitude. The 3D gain pattern at 2.5 GHz is shown in Fig. 8b. The vertical walls in the ground plane reduce the side lobe level (SLL) to 8.8 dB below the main beam. The gain and the axial ratio versus frequency are shown in Fig. 8c. The 2 × 2 sub-array introduces a peak gain of 16.6 dBi with a CP of 78.2%. An arrangement comprises 16 ME-dipole elements, compromising four 2 × 2 sub-arrays are investigated for gain improvement as shown in Fig. 9a. The gain and AR variations versus frequency at ne = 3.15 × 1020 m−3 are plotted in Fig. 9b. The 3-dB gain variation is 1.32 GHz with the CP broad bandwidth of 87.8%. The maximum gain increases to 22.8 dBi with the first SLL of 13.3 dB below the peak lobe at 2.5 GHz as shown in Fig. 9c. The radiation efficiency frequency response for the 2 × 2 and 4 × 4 array arrangements are plotted in Fig. 10. The radiation efficiency varies from 90.8 to 99% over the frequency band from 1.5 to 3.7 GHz.
Beam Switching Using Sequential Feed Plasma ME-Dipole Antenna Array Electronic beam-switching has been employed in different communication systems and directional of arrival applications [15, F2=90o
F1=0o
F3=180o F4=270o
=90o
F1=0o GL
a
b
a.
b. Fig. 7 a The unit-pair arrangement of ME-dipole antenna array. b The Sparameters versus frequency for the unit-pair arrangement at separation distance GL = 180 mm
c Fig. 8 a The arrangement of the 2 × 2 sub-array. b The 3D normalized gain patterns at 2.5 GHz. c The gain and axial ratio frequency response for the sub-array
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2×2 subarray
directed to a specific direction by ionizing the plasma inside the ME-dipole sub-array, while deionizing the plasma inside the other sub-arrays. When the plasma is ionized (tuned in- by applying a voltage source) with electron density ne = 3.15 × 1020 m−3, the radiation characteristics of the antenna are the same as presented in Fig. 8. When the plasma is deionized (tuned out-disconnecting the voltage source), the ME-dipole is no more resonates and only the ground plane effect is existing.
a
Triangular Prism Plasma ME-Dipole Antenna Array Three 2 × 2 ME-dipole sub-arrays placed with 60° rotation angle regarding each other, forming an equilateral triangular prism with each face has an arm length of 180 mm is shown in Fig. 11a. It maintains the gain of each sub-array # A1
b
2×2 subarray # A2
# A3
c a.
Fig. 9 a The arrangement of the 4 × 4 array. b The gain and axial ratio versus frequency. c The 3D normalized gain pattern at 2.5 GHz
16]. The 2 × 2 plasma ME-dipole sub-array investigated in Fig. 8 is used as a building block for different array configurations. The beam switching arrays are designed to produce single or multiple beams in different directions. Based on the reconfigurable properties of the plasma material the beam is
# A3
# A1
# A1
#A2
#A2 b. Single beam
c. Dual beams
# A3
2×2 array arrangement 4×4 array arrangement
# A1
#A2 d. Three-beams
Fig. 10 The radiation efficiencies versus frequency for 2 × 2 and 4 × 4 array arrangements
Fig. 11 a The arrangement of the triangular prism antenna array. b–d The normalized gain pattern in x-y plane at 2.5 GHz for the tariangular prism array at different states of plasma ionization
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on the prism face at 16.6 dBi with the CP bandwidth at 78.2%. Single, dual, and triple beams can be achieved using the triangular prism arrangement. The normalized gain patterns in x-y plane are plotted for the electronic beam switching arrangement in different cases. In Fig. 11b, it switches into a single beam in three different directions at 60o when the plasma inside the sub-array A1 is tuned in and the plasma inside the sub-arrays A2 and A3 are tuned out. Similarly, single beam at 180° is achieved when A2 is tuned in, and 330° when A3 is tuned in and the plasma in the other two faces is tuned out. Dual-beams
# A3
Square Prism Plasma ME-Dipole Antenna Array Figure 12a introduces a square prism array arrangement consists of four 2 × 2 ME-dipole sub-arrays arranged with 90° rotation angle to each face. The square prism array is designed and investigated for single or multiple beams in different directions to cover the 360° space. The horizontal gain patterns for different ionization modes are shown in Fig. 12. It achieves a single directive beam at 0°, 90°, 180o, or 270o by tuning in the plasma inside the corresponding square prism face A1, A2, A3, or A4, respectively as in Fig. 12b. Similarly, dual or three simultaneous beams are achieved by proper activation of plasma in the corresponding faces of the square prism as in Fig. 12c, d. It can produce four beams at the same time by tuning in the plasma in the four faces A1, A2, A3, and A4 as in Fig. 12e.
# A4
# A2
are got when the plasma in the two faces of the prism are tuned in and the third one is tuned out as appeared in Fig. 11c. When the plasma in the three faces of the triangular prism is tuned in, three beams separated by 120° appear at the same time as shown in Fig. 11d.
# A1 a.
# A4
# A1
# A1
# A5
# A2
# A6
# A2
# A2 # A4
# A3
# A4
# A3
# A3
b. Single beam
# A1 a.
c. Dual beams # A1
# A1
# A2
# A3
# A2 # A4
# A3 d. Three-beams
# A4
# A4
# A3 e. Four-beams
Fig. 12 a The arrangement of a square prism antenna array. b–e The normalized gain pattern in x-y plane at 2.5 GHz for the square prism array at different states of plasma ionization
# A1
# A6
# A5 b.
Fig. 13 a The arrangement of a hexagonal prism antenna array. b The normalized gain pattern in x-y plane at 2.5 GHz for the hexagonal prism array at different states of plasma ionization
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References 1.
2.
Triangular array arrangement Square array arrangement Hexagonal array arrangement
Fig. 14 The radiation efficiency versus frequency for different array arrangements
3. 4.
5.
6.
Hexagonal Prism Plasma ME-Dipole Antenna Array
7.
8.
Six 2 × 2 ME-dipole sub-arrays are used to construct a hexagonal prism array arrangement as shown in Fig. 13a. By ionizing plasma in each face sequentially the beam is turned in six directions separated by 60° as appeared in Fig. 13b. Different numbers of simultaneous beams are produced by tuned in the plasma in the required faces. The radiation efficiency versus frequency for different array arrangement is shown in Fig. 14. High efficiency of 90 to 98% is maintained over the operating frequency band.
9.
10. 11.
12.
Conclusion An electronic beam switching using CP ME-dipole antenna array with reconfigurable characteristics has been investigated in this paper. The single ME-dipole has matching bandwidth of 73.7%, and high radiation efficiency of 97.01%. An equivalent circuit consists of a series resonance circuit and three parallel resonant sections is proposed to represent the antenna performance. The PSO algorithm is used to estimate the values of the lumped elements of the equivalent circuit at different values of plasma electron density. The results are closely matched with a RMSE of 0.17% for ne = 3.15 × 1020 m−3. A 2 × 2 ME-dipole subarray is designed to increase the CP bandwidth to 78.2% and peak gain of 16.6 dBi. Different array arrangements based on reconfigurable characteristics of the plasma medium have been investigated. In the triangular prism array, a single beam is turned in three different directions at 60°, 180°, and 330° when the plasma in the corresponding face is tuned in and the plasma in the other faces is tuned out. By ionizing plasma in each face sequentially, the beam is turned in six directions separated by 60° using a hexagonal prism array arrangement.
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14.
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