Title: High‐gain antipodal Vivaldi antenna with metamaterial covers
Abstract: IET Microwaves, Antennas & PropagationVolume 13, Issue 15 p. 2654-2660 Research ArticleFree Access High-gain antipodal Vivaldi antenna with metamaterial covers Minjie Guo, Minjie Guo School of Geophysics and Information Technology, China University of Geosciences, Beijing, 100083 People's Republic of ChinaSearch for more papers by this authorRongyi Qian, Rongyi Qian School of Geophysics and Information Technology, China University of Geosciences, Beijing, 100083 People's Republic of ChinaSearch for more papers by this authorQisheng Zhang, Qisheng Zhang School of Geophysics and Information Technology, China University of Geosciences, Beijing, 100083 People's Republic of ChinaSearch for more papers by this authorLinyan Guo, Corresponding Author Linyan Guo [email protected] School of Geophysics and Information Technology, China University of Geosciences, Beijing, 100083 People's Republic of ChinaSearch for more papers by this authorZhengwei Yang, Zhengwei Yang School of Geophysics and Information Technology, China University of Geosciences, Beijing, 100083 People's Republic of ChinaSearch for more papers by this authorZiyu Xu, Ziyu Xu School of Geophysics and Information Technology, China University of Geosciences, Beijing, 100083 People's Republic of ChinaSearch for more papers by this authorZiye Wang, Ziye Wang School of Geophysics and Information Technology, China University of Geosciences, Beijing, 100083 People's Republic of ChinaSearch for more papers by this author Minjie Guo, Minjie Guo School of Geophysics and Information Technology, China University of Geosciences, Beijing, 100083 People's Republic of ChinaSearch for more papers by this authorRongyi Qian, Rongyi Qian School of Geophysics and Information Technology, China University of Geosciences, Beijing, 100083 People's Republic of ChinaSearch for more papers by this authorQisheng Zhang, Qisheng Zhang School of Geophysics and Information Technology, China University of Geosciences, Beijing, 100083 People's Republic of ChinaSearch for more papers by this authorLinyan Guo, Corresponding Author Linyan Guo [email protected] School of Geophysics and Information Technology, China University of Geosciences, Beijing, 100083 People's Republic of ChinaSearch for more papers by this authorZhengwei Yang, Zhengwei Yang School of Geophysics and Information Technology, China University of Geosciences, Beijing, 100083 People's Republic of ChinaSearch for more papers by this authorZiyu Xu, Ziyu Xu School of Geophysics and Information Technology, China University of Geosciences, Beijing, 100083 People's Republic of ChinaSearch for more papers by this authorZiye Wang, Ziye Wang School of Geophysics and Information Technology, China University of Geosciences, Beijing, 100083 People's Republic of ChinaSearch for more papers by this author First published: 11 September 2019 https://doi.org/10.1049/iet-map.2019.0449Citations: 9AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract A metamaterial slab covered antipodal Vivaldi antenna (MSAVA) is proposed to improve the radiation properties of the antipodal Vivaldi antenna (AVA). The metamaterial covers (MCs) consist of two types of metal rectangular ring arrays that have a higher effective permittivity than the substrate. The MCs can achieve a guiding effect and direct electromagnetic waves radiated from the side of AVA to the end-fire direction. The original AVA and the proposed MSAVA are simulated, fabricated and measured. The results show that of the two antennas is less than −10 dB in the frequency band of 0.95–11 GHz. Due to the introduction of MCs, MSAVA obtains a much narrower H-plane's half-power beamwidth, and the E-plane's is narrowed as well. The radiation gain is also improved in the frequency band. Moreover, the maximum gain of the proposed MSAVA is 17.67 dBi. Compared with the original AVA, the maximum gain is enhanced by 6.86 dB for the proposed MSAVA. The presented MSAVA featuring broad bandwidth, high gain and narrow beam has a high potential in ground penetrating radar, microwave imaging application and other broadband wireless systems. 1 Introduction Antipodal Vivaldi antenna (AVA) was proposed by Ehud Gazit in 1988 based on traditional antipodal tapered slot antenna. It exhibits attractive features such as broadband, high gain, light weight and easy fabrication, and is widely used in many wireless and radar systems through integration and array. To obtain better radiation capability, conventional methods such as slots, parasitic patches and composite apertures are used without changing the original structure and size of AVAs. Rectangular slots and leaf-shaped slots are typically etched on both radiation patches to achieve high gain by increasing the current path [[1]–[4]]. Double-slot structures [[5], [6]] and parasitic patches [[7], [8]] can also increase the antennas’ radiation gain. In [[9], [10]], composite aperture structures are proposed to improve the phase centre characteristic and achieve a gain enhancement. Besides, in [[11], [12]], the antenna performance can be improved by smoothing the corners of the radiation patches to eliminate diffraction from sharp ends. In addition, using a dielectric lens in the end-fire direction is another effective way of increasing gain and directivity [[13]–[15]]. Recently, metamaterials with special characteristics have been widely used to improve gain, operation bandwidth, efficiency of antennas such as bow-tie antennas, horn antennas, AVA and so forth. In general, the application of metamaterials in antennas mainly includes metamaterial lenses, reflectors, absorbers and covers. As one of the most common applications for metamaterials, the metamaterial lens in front of the antenna can concentrate electromagnetic waves to achieve high directivity and gain enhancement [[16]–[18]]. The metamaterial reflector can suppress the backward radiation of antennas to achieve high directivity and gain in a broadband [[19], [20]]. By combining these two approaches, Guo et al. proposed an antipodal tapered slot antenna with metamaterial lens and reflector to improve the gain in a broad bandwidth [[21]]. Additionally, metamaterial absorber can be used to reduce the in-band radar cross-section of high-gain antennas [[22]]. Those researches all have a positive effect on gain enhancement. However there is still room for further improvement of H-planes’ half-power beamwidth (HPBW) while that of the E-planes’ has been narrowed. Li et al. proposed an ultra-wideband metamaterial slab covered AVA, which exhibits stable radiation patterns with a narrower beamwidth and lower side lobe level in both the E- and H-planes than the original AVA [[23]]. In this paper, a new type of AVA with metamaterial covers (MCs) is proposed. The MCs can significantly increase the antenna gain in the frequency band of 0.95–11 GHz and reduce the H-planes’ HPBW without altering the antenna size. The maximum gain of the proposed MSAVA can reach 17.67 dBi, which is 6.86 dB higher than that of the original AVA. The simulation and measurement results show that MCs have a positive effect on gain enhancement and narrow H-planes’ HPBW. Obviously, it provides a different way of improving the properties of AVA. The structure of this paper is as follows. In Section 2, a new type of AVA, MCs and metamaterial slabs covered antipodal Vivaldi antenna (MSAVA) are proposed. In Section 3, the original AVA and the proposed MSAVA are simulated, fabricated and measured. Finally, the paper is concluded in Section 4. 2 Antenna design 2.1 AVA design Fig. 1 shows the structure of the original AVA. The coordinate origin is located at the centre of the substrate. The substrate of AVA is Rogers RO4003C with a thickness of 1.52 mm . The metal is copper with a thickness of 0.0175 mm ( S/m). The top metal marked in red consists of two major parts. One part is a microstrip feed line with a length of 60 mm matching with the SMA connector. The other part is a tapered radiation patch with rectangular slots. The bottom metal is made of an elliptically tapered ground and a bottom radiation patch. The exponential curve of patches is determined by , while the curve of the ground is a quarter of an ellipse, as shown in Table 1. Besides, there are 19 symmetric rectangular slots with a length of 34.3 mm and a width of 4 mm at the edges of patches. The space between two adjacent rectangular slots is 2 mm. These rectangular slots are etched to further lower the operating frequency. Other geometry sizes of AVA are listed in Table 2. Fig. 1Open in figure viewerPowerPoint Configurations of AVA Table 1. Equations and curvature parameters in Fig. 1 Curves Equation R outer curve 0.61 −1.09 0.08 inner curve 1.4 3.1 0.017 ellipse ground Table 2. Parameters of the AVA and MCs (unit: mm) l l1 l2 l3 l4 l5 240 120 0.406 7.88 7.88 2.4 l6 l7 l8 l9 w w1 2.4 0.8 1.6 1.14 152 53.5 w2 w3 w4 w5 w6 w7 49.24 3.4 6.2 3.1 5 2.5 w8 w9 w10 w11 r1 r2 0.6 0.3 0.8 0.4 74.3 46.16 2.2 Metamaterial cover units Fig. 2 shows the structures of MC units. Four metal rectangular rings are etched on the top and bottom of the Rogers RO4003C substrate with a thickness of 0.406 mm. The metal marked in yellow is copper which has a thickness of 0.035 mm. There are two types of metal units presented here. One is MCs-1 (as shown in Fig. 2c) focusing on gain enhancement at the lower frequency band, and the other is MCs-2 (as shown in Fig. 2d) optimising the gain at the higher frequency band. Based on the optimised sizes of the MCs units shown in Table 2, the arrangement of MCs needs further optimisation since it has a great effect on the MSAVA's radiation performance. The metal rectangular rings selected as unit cells have the following advantages. First, the unit cells have the advantages of a simple structure, easy fabrication and realisation. Second, there are less number of parameters that need to be optimised and it is easy to realise the optimisation requirements of the radiation gain. Moreover, excited by the electric field in the x direction, MCs-1 and MCs-2 have different cut-off frequencies. In their non-resonant regions below the cut-off frequencies, MCs-1 and MCs-2 arrays improve the radiation performances at the lower and higher frequency bands of the original AVA, respectively. Therefore, the presented MCs improve the antenna performance over a wide frequency band. Fig. 2Open in figure viewerPowerPoint Structures of MCs units (a) Simulation model of MCs unit, (b) Side view of MCs unit, (c) Front view of MCs-1, (d) Front view of the MCs-2 The effective relative permittivity of MCs-1 and MCs-2 is extracted from their S-parameters based on the Kramers–Kronig relationship [[24]]. Periodic perfect electric conductor and perfect magnetic conductor boundaries are applied along the x-axis and the z-axis, respectively. Most of the electromagnetic waves radiated from AVA travel along the y-axis and the z-axis when the electric field polarises along the x-axis. Fig. 3 shows the real parts of the effective permittivity of the MC units and the Rogers RO4003C substrate. It shows that the real part of MCs-1's effective permittivity is stable above 20, and MCs-2's real part is stable above 13. Moreover, the real parts of MCs-1's and MCs-2's effective permittivities are much higher than that of the Rogers RO4003C substrate. At the same time, the imaginary parts of MCs-1's and MCs-2's effective permittivity are close to 0 (not shown here), which illustrate that the loss of MCs is very small. Fig. 3Open in figure viewerPowerPoint Effective permittivity comparison diagram of MCs-1, MCs-2 and substrate 2.3 MSAVA design The design criterion is to maximise the radiation gain of MSAVA while ensuring the antenna's operating band and end-fire radiation. Therefore, the arrangement of the MCs-1 array and MCs-2 array needs to be optimised. This paper uses the exhaustive method when optimising the MCs’ arrangement. Limited by the size of the AVA, the number of rows and columns of the MCs-1 array and MCs-2 array is a finite integer. This allows us to perform parameter optimisation in a limited searching space and the computational complexity of exhaustive search is acceptable. As shown in Fig. 4, the proposed MSAVA is composed of AVA and two types of MCs. These MCs are symmetrically placed at a height of h from both sides of AVA. The proposed MC has a width of 76.8 mm and a length of 200 mm. The MCs-1 array is placed on the left and right sides of MCs, while the MCs-2 array is located in the middle of MCs. Initially, the MCs array has N rows and columns. It consists of a MCs-1 array with the dimension of and a MCs-2 array with the dimension of . The final arrangement of the MCs-1 and MCs-2 array is chosen by comparing the gain of MSAVA. Fig. 4Open in figure viewerPowerPoint Schematic of the MSAVA (a) Front view of MSAVA, (b) Side view of MSAVA, (c) Arrangement of the MCs array In this paper, the initial values of the row and column are set to and , respectively. To determine the optimal dimension of the MCs-1 array, we increase the number of columns of the MCs-1 array while keeping the MCs-2 array unchanged. The simulation results are shown in Fig. 5a. As shown in this figure, the MSAVA's gain in 1–8.5 GHz is kept stable with the increasing of . However in 9–11 GHz, with the increase of , the gain increases first and then decreases. When , the radiation gain reaches the maximum value. Finally, and are the optimal dimensions for the MCs-1 array. Fig. 5Open in figure viewerPowerPoint Effects of varying the columns of array on gain of MSAVA (a) Effect of varying , (b) Effect of varying After the optimal MCs-1 array is determined, the MCs-2 array is optimised as follows. The initial value of the MCs-2 array is set to . Restricted by the space condition, the number of columns, , is an integer varying from 1 to 4. To achieve a better comparison, the calculation results are compared with the results when the MCs-2 units are replaced by MCs-1, as shown in Fig. 5b. Hence, the dimension of the MCs-1 array is . The solid line in this figure represents the MCs-2 array, and the dotted line indicates the result when MCs-1 units are used to replace all MCs-2 units. It can be seen that the gain of MSAVA is almost the same within 1–8 GHz when changes. However, the gain will change significantly in 8–11 GHz with the increment of . Compared with the results using the MCs-1 array only, the extra added MCs-2 array can get a higher gain in the high-frequency band. The optimal result is obtained when . From the above discussion, the array is divided into two parts: MCs-1 array and MCs-2 array. The dimension of the MCs-2 array is . The array is located in the middle of the substrate with a distance of between two MCs-2 units in the x direction. At the same time, the MCs-1 array is evenly divided into two parts, which are, respectively, located on the left and the right side of the MCs-2 array. The distance between two MCs-1 units in the x direction is . After obtaining the optimal number of rows and columns, the height of MCs is optimised as follows. The initial value of the distance between MCs and AVA in the z direction is mm. Different results can be obtained when h changes in the range of 9–13 mm. The results are shown in Fig. 6. In 1–5 GHz, the gain of MSAVA change is very small with the increase of h. In 5–9 GHz, the gap of the gain increases as h increases. In 9–11 GHz, the gap of the gain decreases as h increases. In all cases, the maximum gain can be obtained at h = 10 mm when low-frequency gain is guaranteed. Hence, h = 10 mm is selected as the final height value. Based on the above analysis, two optimised MCs are symmetrically placed at both sides of AVA. The MCs can form a guiding wave cavity to direct the electromagnetic waves to the end-fire direction as much as possible. Fig. 6Open in figure viewerPowerPoint Effect of varying height h on gain of MSAVA 3 Measurement results and discussion According to the parameters listed in Tables 1 and 2, the proposed AVA and MSAVA are fabricated by a high-solution printed circuit board technology. As shown in Fig. 4, four insulated screws are installed symmetrically to support MCs. The MCs’ width is slightly larger than that of the tapered slots. The prototypes of AVA and MSAVA are shown in Fig. 7. Fig. 7Open in figure viewerPowerPoint Photographs of the presented antennas (a) AVA, (b) MSAVA 3.1 S-parameters The S-parameters obtained by a simulation software are shown in Fig. 8a. It can be seen that the −10 dB impedance bandwidth of AVA is 0.95–11 GHz. Besides, the S-parameters measured by the Agilent E8362B vector network analyser are shown in Fig. 8b. This figure shows that the measured impedance bandwidth is from 0.92 to 11 GHz. It means that the loaded MCs have little impact on the proposed MSAVA. In addition, the measured and simulated S-parameters maintain the same variation trend in the whole frequency region. Effected by the test environment, the measured S-parameters are slightly larger than −10 dB in several frequency bands. Fig. 8Open in figure viewerPowerPoint S-parameters (a) Simulated S-parameters, (b) Measured S-parameters 3.2 Gain Fig. 9 shows the simulated and measured gain of the antennas. It can be observed that the gain of AVA can be effectively improved by loading MCs. In 1–3 GHz, the gain increase is about 0.5 dB. In 3–9 GHz, MSAVA's gain curve shows a rapid growth trend. In 9–11 GHz, the gain curve shows a decline trend, but the gain increase is also obvious. In the operating frequency band, the maximum gain reaches 17.67 dBi at 9 GHz, which is 6.86 dB higher than that of AVA. However, there are some mismatches between the simulated and measured results since the test environment is a free space rather than a microwave anechoic chamber. The measured results are interfered by other electromagnetic waves in the free space, but it does not affect the use of the presented antennas. Fig. 9Open in figure viewerPowerPoint Simulated and measured gains of AVA and MSAVA (a) Simulated results, (b) Measured results Fig. 10 shows the radiation efficiency of the proposed MSAVA. It is clear that MSAVA has a good radiation efficiency which is more than 88% over the whole frequency range. Fig. 10Open in figure viewerPowerPoint Simulated radiation efficiency of the proposed MSAVA 3.3 Radiation patterns To analyse the antennas’ radiation performance, three frequency points are chosen to analyse the radiation patterns. As both AVA and MSAVA have stable radiation patterns in the operating band, we choose the frequency points at 1, 9 and 11 GHz. Fig. 11 shows the simulated radiation patterns taking the antennas gain into consideration. It can be seen that MSAVA has a higher gain than the AVA for the three chosen frequency points. At the same time, both the E-plane and H-plane of MSAVA have higher directivity. This means the energy radiated from AVA is more concentrated due to the loaded MCs. Fig. 11Open in figure viewerPowerPoint Simulated radiation patterns of AVA and MSAVA considering antenna gain (a), (c), (e) E-plane at 1, 9 and 11 GHz, respectively, (b), (d), (f) H-plane at 1, 9 and 11 GHz, respectively Fig. 12 shows the measured radiation patterns considering the antennas’ gain at 1, 9 and 11 GHz. The radiation patterns of MSAVA have better directivity and radiation effect than that of AVA in the main lobe direction. The measured radiation patterns match well with the simulated results. Due to the influence of other electromagnetic waves in the free space, the back lobe level increases slightly. Fig. 12Open in figure viewerPowerPoint Measured radiation patterns of AVA and MSAVA considering antenna gain (a), (c), (e) E-plane at 1, 9 and 11 GHz, respectively, (b), (d), (f) H-plane at 1, 9 and 11 GHz, respectively Table 3 and Fig. 13 illustrate the antennas’ HPBW of the E-planes and H-planes. From the table and figure, the HPBW of the E-planes and H-planes decrease significantly when the frequency increases. Comparing the HPBW of MSAVA and AVA, it can be seen that the radiation energy is more concentrated in the end-fire direction. Therefore, the proposed MSAVA can obtain better directivity and higher gains in the operating frequency band. That means MCs have a positive influence on the antenna's performance. Table 3. E/H-planes’ HPBW of AVA and MSAVA Frequency, GHz AVA E-plane, deg MSAVA E-plane, deg AVA H-plane, deg MSAVA H-plane, deg 1.0 62.8 60.9 126.3 117.8 2.0 55.6 54.1 89.0 79.8 3.0 65.9 66.3 59.6 54.8 4.0 73.0 56.8 47.5 44.1 5.0 60.1 49.6 47.9 39.8 6.0 36.3 32.2 41.9 34.3 7.0 26.6 27.4 37.7 30.7 8.0 35.9 24.1 36.6 28.7 9.0 35.5 19.2 36.4 28.2 10.0 29.7 15.1 38.6 27.1 11.0 18.2 12.0 40.9 25.3 Fig. 13Open in figure viewerPowerPoint E/H-planes’ HPBW of AVA and MSAVA To better understand the effect of MCs, Fig. 14 shows the E-field distributions of AVA, AVA with MCs-1 and MSAVA at 1, 9 and 11 GHz, respectively. The E-field intensity in the tapered slot and flare termination is enhanced by the proposed MSAVA. Besides, the guided waves produce a smoother wave-front compared with AVA when the waves transmitting along the MCs superpose at the end-fire direction. Fig. 14Open in figure viewerPowerPoint E-field distributions at 1, 9 and 11 GHz (a) AVA, (b) AVA with MCs-1, (c) MSAVA In addition, to distinguish our results from other existing works, Table 4 compares the operating frequency band, maximum gain, gainenhancement mechanism and other metrics. In this table, some parameters areestimated from the results of these works. It shows that MSAVA has a wider − 10 dB impedance bandwidth than that of the works in [[17], [22], [23], [24]]. Moreover, MSAVA has a higher gain at low frequency and a wider−3 dB gain bandwidth than the proposed antenna in [[23]]. It also has a higher maximum gain than the works in[[17], [21], [22], [24]]. Compared to the published works, the proposed MSAVAhas a wider −10 dB impedance bandwidth and a higher maximum gain. Table 4. Performance comparison of the proposed MSAVA and similar works −10 dB impedancebandwidth −3 dB gainbandwidth Maximum gain, Gain range, Gain enhancementmechanism dBi dBi this paper 0.95–11 GHz (168.2%) 6.5–11 GHz (51%) 17.67 7.3–17.67 metamaterial covers [[17]] 6–19 GHz (104%) ∼7.5–19 GHz (86.8%) 12 7.1–12 artificial material [[21]] 0.43–7 GHz (176.9%) 2–7 GHz (111.1%) 14.1 11.3–13.3 metamaterial lens and reflector [[22]] 3.5–16.5 GHz (130%) ∼9–16.5 GHz (58.8%) 14.2 5.2–14.2 shaped dielectric covers [[23]] 3.68–43.5 GHz (168.8%) ∼26–43.5 GHz (50.3%) 17.7 4–17.7 metamaterial slabs [[24]] 3–12 GHz (120%) ∼6–11.5 GHz (62.9%) 14 9–14 anisotropic zero-indexmetamaterials 4 Conclusion In this paper, MCs consisting of two types of unit cells are presented. They are installed on the two sides of AVA to direct the electromagnetic waves to the end-fire direction. Compared to other works, H-planes’ HPBW of the proposed MSAVA is narrowed significantly while that of E-planes is narrowed as well. Furthermore, the radiation gain is improved in the whole operating bandwidth, especially at a high-frequency band. The measured results indicate that the maximum gain of MSAVA is 17.67 dBi which is increased by 6.86 dB compared to that of AVA. Based on the simulated and measured results, the proposed MSAVA with MCs has the advantages of ultra-wideband, high-gain and end-fire radiation. These advantages ensure that the MCs-based MSAVA can be used in the short-pulse ground penetrating radar, microwave imaging and other broadband wireless systems requiring high gain and directivity. 5 Acknowledgment This work was supported by the National Natural Science Foundation of China under grant 41704176 and 41574131, the National Key Research and Development Program of China under grant 2017YFF0105704 and the Fundamental Research Funds for the Central Universities of China. 6 References [1]Oliveira, A., Perotoni, M., Sergio, T., et al.: ‘A palm tree antipodal Vivaldi antenna with exponential slot edge for improved radiation pattern’, IEEE Antennas Wirel. Propag. Lett., 2015, 14, pp. 1334– 1337 [2]Teni, G., Zhang, N., Qiu, J., et al.: ‘Research on a novel miniaturized antipodal Vivaldi antenna with improved radiation’, IEEE Antennas Wirel. Propag. Lett., 2013, 12, pp. 417– 420 [3]Karahan, M., Sahinkaya, D.: ‘A reduced size antipodal Vivaldi antenna design for wideband applications’. IEEE Int. Symp. Antenna and propagation (APSURSI), Memphis, TN, USA, July 2014 [4]Biswas, B., Ghatak, R., Poddar, D.: ‘A fern fractal leaf inspired wideband antipodal Vivaldi antenna for microwave imaging system’, IEEE Trans. Antennas Propag., 2017, 65, (11), pp. 6126– 6129 [5]Wang, Y., Wang, G., Zong, B.: ‘Directivity improvement of Vivaldi antenna using double-slot structure’, IEEE Antennas Wirel. Propag. Lett., 2013, 12, pp. 1380– 1383 [6]Zhang, Y., Wang, C., Guo, G., et al.: ‘Radiation enhanced Vivaldi antenna with double-antipodal structure’, IEEE Antennas Wirel. Propag. Lett., 2017, 16, pp. 561– 564 [7]Sang, L., Li, X., Chen, T., et al.: ‘Analysis and design of tapered slot antenna with high gain for ultra-wideband based on optimization of metamaterial unit layout’, IET Microw. Antennas Propag., 2017, 11, (6), pp. 907– 914 [8]Nassar, I., Weller, T.: ‘A novel method for improving antipodal Vivaldi antenna performance’, IEEE Trans. Antennas Propag., 2015, 63, (7), pp. 3321– 3324 [9]Arezoomand, A., Sadeghzadeh, R., Naser-Moghadasi, M.: ‘Novel techniques in tapered slot antenna for linearity phase center and gain enhancement’, IEEE Antennas Wirel. Propag. Lett., 2017, 16, pp. 270– 273 [10]Arezoomand, A., Sadeghzadeh, R., Naser-Moghadasi, M.: ‘Investigation and improvement of the phase center characteristics of Vivaldi antenna for UWB applications’, Microw. Opt. Techn. Lett., 2016, 58, (6), pp. 1275– 1281 [11]Dastranj, A.: ‘Wideband antipodal Vivaldi antenna with enhanced radiation parameters’, IET Microw. Antennas Propag., 2015, 9, (15), pp. 1755– 1760 [12]Moosazadeh, M., Kharkovsky, S.: ‘Design of ultra-wideband antipodal Vivaldi antenna for microwave imaging applications’. IEEE Int. Conf. on Ubiquitous Wireless Broadband (ICUWB), Montreal, QC, Canada, October 2015 [13]Moosazadeh, M., Kharkovsky, S.: ‘A compact high-gain and front-to-back ratio elliptically tapered antipodal Vivaldi antenna with trapezoid-shaped dielectric lens’, IEEE Antennas Wirel. Propag. Lett., 2015, 15, pp. 552– 555 [14]Moosazadeh, M., Kharkovsky, S., Case, J., et al.: ‘Improved radiation characteristics of small antipodal Vivaldi antenna for microwave and millimeter-wave imaging applications’, IEEE Antennas Wirel. Propag. Lett., 2017, 16, pp. 1961– 1964 [15]Moosazadeh, M., Kharkovsky, S., Case, J.: ‘Microwave and millimetre wave antipodal Vivaldi antenna with trapezoid-shaped dielectric lens for imaging of construction materials’, IET Microw. Antennas Propag., 2016, 10, (3), pp. 301– 309 [16]Su, Y., Chen, Z.: ‘A flat dual-polarized transformation-optics beamscanning Luneburg Lens antenna using PCB-stacked gradient Index metamaterials’, IEEE Trans. Antennas Propag., 2018, 66, (10), pp. 5088– 5097 [17]Chen, L., Lei, Z., Yang, R., et al.: ‘A broadband artificial material for gain enhancement of antipodal tapered slot antenna’, IEEE Trans. Antennas Propag., 2015, 63, (1), pp. 395– 400 [18]Ramaccia, D., Barbuto, M., Monti, A., et al.: ‘Exploiting intrinsic dispersion of metamaterials for designing broadband aperture antennas: theory and experimental verification’, IEEE Trans. Antennas Propag., 2016, 64, (3), pp. 1141– 1146 [19]Gregory, M., Bossard, J., Zachary, M., et al.: ‘A low cost and highly efficient metamaterial reflector antenna’, IEEE Trans. Antennas Propag., 2018, 66, (3), pp. 1545– 1548 [20]Feng, D., Zhai, H., Xi, L., et al.: ‘A broadband low-profile circular-polarized antenna on an AMC reflector’, IEEE Antennas Wirel. Propag. Lett., 2017, 16, pp. 2840– 2843 [21]Guo, L., Yang, H., Zhang, Q., et al.: ‘A compact antipodal tapered slot antenna with artificial material lens and reflector for GPR applications’, IEEE. Access., 2018, 6, pp. 44244– 44251 [22]Jia, Y., Liu, Y., Zhang, W., et al.: ‘High-gain Fabry-Perot antennas with wideband low monostatic RCS using phase gradient metasurface’, IEEE. Access., 2019, 7, pp. 4816– 4824 [23]Li, X., Zhou, H., Gao, Z., et al.: ‘Metamaterial slabs covered UWB antipodal Vivaldi antenna’, IEEE Antennas Wirel. Propag. Lett., 2017, 16, pp. 2943– 2946 [24]Szabo, Z., Park, G., Hedge, R., et al.: ‘A unique extraction of metamaterial parameters based on Kramers–Kronig relationship’, IEEE Trans. Microw. Theory, 2010, 58, (10), pp. 2646– 2653 Citing Literature Volume13, Issue15December 2019Pages 2654-2660 FiguresReferencesRelatedInformation
Publication Year: 2019
Publication Date: 2019-08-16
Language: en
Type: article
Indexed In: ['crossref']
Access and Citation
Cited By Count: 13
AI Researcher Chatbot
Get quick answers to your questions about the article from our AI researcher chatbot