Open Access
Add to BibSonomy
Abstract
A high gain antenna with controlling electromagnetic surface propagation and radiation for terahertz application is proposed based on a holographic artificial impedance surface. The artificial impedance surface is composed of sub wavelength square metallic patches on a grounded dielectric slab. The effective surface impedance depends on the size of the patches and can be varied as a function of position and direction. Using the holographic technique enables the desired direction radiation and high gain to be achieved. The detailed design procedure of impedance modulation and the simulation results are presented.
© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Recently, terahertz (THz) spectrum has been receiving great attention due to its advantage of broader bandwidth, low energy, strong penetrating power, and so on. THz covers the frequency range from 0.1 to 10 THz, which is between the infrared and the microwave band [1–12]. With the rapid development of THz technology, THz communications has been attracted much attention. As known antenna is one of the most important components in THz communications systems [13–23]. To date, some researchers have explored various THz antennas with high performances to enhance THz pulse emission [24] and detect microorganisms such as yeast cells [25]. These antennas for THz communications applications have, more or less, limitations. Thus, THz antennas with high gain, low profile, and a radiation pattern in a desired direction especially deviating from normal radiations are required. One of the popular solutions is the use of reflection antennas. Nevertheless, such a scheme yields to a bulky volume and massive. Recently, a broadband and low profile THz antenna based on complementary ring resonator was proposed [26]. The achieved gain was not high and the antenna was hard to realize a desired radiation characteristics. Holographic antennas are excellent candidates for this purpose due to its high gain, low profile, and easy to realize a desired radiation pattern [27–29].
In this paper, a high gain antenna with desired direction radiation is proposed based on holographic artificial impedance surfaces. The artificial impedance surface is composed of a grounded dielectric layer with square patches on it. The relationship between the size of the square patches and the surface impedance is discussed. Using the holographic technique, the interference pattern can be determined based on a source field and the desired radiation field. The shape of the impedance surface is dedicated to match the desired interference pattern. For verification purpose, an antenna radiates around 30°off the normal plane at 1 THz is designed, and good radiation pattern with high gain is found.
2. Holographic artificial impedance surface
Holographic antenna is composed of source antenna and interference surface, as shown in Fig. 1. The source antenna is used to generate the reference wave and the interference surface is built as a collection of scatterers which scatters the reference wave to form the object wave. In this design, the interference surface is based on artificial impedance surface, a two-dimensional modulated impedance surface that adopts the holographic principle to direct the radiating leaky waves toward the desired direction. Our proposed holographic artificial impedance surface is based on a square lattice of sub wavelength metal patch on a grounded dielectric slab, as shown in Fig. 2. The substrate used here has a relative dielectric constant of 2.2 and a thickness of 18.84 um. For this analysis, a phase difference per cell should be chosen for the periodic boundary conditions. The phase difference determines the location on the dispersion curve. In other words, it affects the operating frequency. Figure 3 shows the frequency against the phase difference with the gap variation when the length of the lattice is chosen as 46 um. It can be found that as the phase difference increases, the frequency increases. It also should be noted that as the gap increases, the frequency increases. The surface impedance can be expressed as
where η0 is the wave impedance of the free space, a is the length of the lattice, c is the speed of light, ω is the angular frequency, is the phase difference in the x direction, and is the phase difference in the y direction. In this design, is fixed at 0, while is equal to the phase difference as shown in Fig. 3. Based on Eq. (1), the relationship between the effective impedance and the size of the gap between the square patch and the edge of dielectric substrate can be easily obtained. In this case, thirteen points are calculated, which are marked by “*” in Fig. 4. Then, the curve of the impedance versus the gap can be curve fitting, as shown in Fig. 4. The effective surface impedance is determined by the size of the square patch. As shown in Fig. 4, the effective impedance decreased from 137.7 jΩ to 72.2 jΩ as the gap increased from 4 um to 28 um at 1 THz. Based on the calculated impedance and corresponding gap for a fixed frequency of 1 THz, the impedance as a function of the gap can be curve fitting by using MATLAB. Then, the relationship between the impedance, i.e. Z, and the gap, i.e. g, can be given byIn this Equation, the impedance Z is in Ω and the gap g is in um. By using Eq. (2), the gap size can be easily obtained to match the desired impedance. Then an artificial impedance surface can be established using holographic principle.
The impedance of interference surface is devised by a reference wave, i.e. Ψref, and an object wave, i.e. Ψrad. The reference wave corresponds to the currents which generated by the source antenna, while the object wave corresponds to the desired radiation pattern. In this design, a monopole antenna is used to generate the reference wave. Then its pattern can be approximated expressed as
where k is the wave vector of the free space, n is the effective refractive index, and r is the distance from the source to field point. Assuming the desired radiation pattern is a narrow pencil beam in the direction θL in the X-Z plane, given bywhere x is the distance from the source to focal point at the X-axis and θL is the desired radiation direction. The surface impedance modulation function can be described bywhere Xs is the average value of surface impedance and M is the real modulation depth. Substituting (3) and (4) into (5), the surface impedance as a function of position can be found. Combining the surface impedance with the impedance data shown in Fig. 4, the gap among the lattices can be obtained. Then the holographic pattern is determined. As an example, a narrow pencil beam at θL = 30° is used to design the holographic surface, as shown in Fig. 5. The surface is fed by a monopole antenna located at the focus of the ellipses shown in Fig. 5. The proposed holographic artificial impedance surface is composed of 51 × 51 square lattices. The length of each square lattice is 46 um. The dimensions of each square metal patch on the grounded dielectric slab are corresponding to its surface impedance. The proposed holographic pattern is bilateral symmetry. Thus, the dimensions of each square metal patch of a half of the pattern are shown in Tables 1 to 6. The dimensions of the length and width of the proposed holographic pattern and the location of the monopole are: l1 = 2346 um, l2 = 1150 um, w1 = 2346 um, w2 = 1150 um.
Table 1. Dimensions of The Square Metal Patches
Table 2. Dimensions of The Square Metal Patches
Table 3. Dimensions of The Square Metal Patches
Table 4. Dimensions of The Square Metal Patches
Table 5. Dimensions of The Square Metal Patches
Table 6. Dimensions of The Square Metal Patches
3. Simulation results
Based on the above design procedure, the holographic artificial impedance surface and a monopole antenna are used together to form the holographic antenna. Simulation was accomplished using HFSS [30–32], a full-wave electromagnetic simulator based on the Finite Element Method (FEM). In the HFSS, the holographic artificial impedance surface is built based on the above design procedure at first. The monopole antenna is located at the focus of the ellipses. Then, an air box is enclosed to the proposed holographic antenna. The distance between the air box and the holographic antenna is between λ/4 and λ/2, where λ is the wavelength of operating frequency. The boundary condition of the air box is set as radiation. Figure 6 shows the simulated frequency responses of the proposed holographic antenna. The center operation frequency of the proposed antenna is around 1 THz. The reflection coefficient is lower than −10 dB from 0.88 to 1.32 THz. The fractional bandwidth of the antenna is 44%. The simulated radiation pattern of the proposed antenna in X-Z plane is shown in Fig. 7. From this figure we can see that the proposed antenna has achieved the gain of 12.67 dB with angle of 37° at 1 THz. At this radiation direction, the 3-dB beam width is from 33.5° to 42°. The 3-D radiation pattern of the proposed antenna at 1 THz is shown in Fig. 8. It is found that the proposed antenna characterizes the desired directive radiation with high gain. The simulated surface current and surface electric fields of the antenna are shown in Fig. 9.
4. Conclusion
A planar holographic surface is designed to form a pencil beam with high gain in a desired direction using sinusoidal surface impedance modulation based on the holographic theory. A holographic antenna radiated around 30° off the normal plane at 1 THz is designed and simulated in this paper. The simulated results verify our study.
Funding
Seed Funding Programme for Basic Research, the NSFC (project nos.: 61601063, 61271025).
References and links
1. P. H. Siegel, “Terahertz technology,” IEEE Trans. Microw. Theory Tech. 50(3), 910–928 (2002). [CrossRef]
2. J. Federici and L. Moeller, “Review of terahertz and subterahertz wireless communications,” J. Appl. Phys. 107(11), 111101 (2010). [CrossRef]
3. N. Chimot, J. Mangeney, L. Joulaud, P. Crozat, H. Bernas, K. Blary, and J. F. Lampin, “Terahertz radiation from heavy-ion-irradiated In0.53Ga0.47As photoconductive antenna excited at 1.55 um,” Appl. Phys. Lett. 87(19), 193510 (2005). [CrossRef]
4. S. G. Park, A. M. Weiner, M. R. Melloch, C. W. Sider, J. L. Sider, and A. J. Taylor, “High-power narrow-band terahertz generation using large-aperture photoconductors,” IEEE J. Quantum Electron. 35(8), 1257–1268 (2002). [CrossRef]
5. S. Cao, W. Yu, T. Wang, H. Shen, X. Han, W. Xu, and X. Zhang, “Meta-microwindmill structure with multiple absorption peaks for the detection of ketamine and amphetamine type stimulants in terahertz domain,” Opt. Mater. Express 4(9), 1876–1884 (2014). [CrossRef]
6. W. Lai, N. Born, L. M. Schneider, A. Rahimi-Iman, J. C. Balzer, and M. Koch, “Broadband antireflection coating for optimized terahertz beam splitters,” Opt. Mater. Express 5(12), 2812–2819 (2015). [CrossRef]
7. M. Shalaby, H. Merbold, M. Peccianti, L. Razzari, G. Sharma, T. Ozaki, R. Morandotti, T. Feurer, A. Weber, L. Heyderman, B. Patterson, and H. Sigg, “Concurrent field enhancement and high transmission of THz radiation in nanoslit arrays,” Appl. Phys. Lett. 96(4), 041110 (2011). [CrossRef]
8. S.-G. Park, K. H. Jin, M. Yi, J. C. Ye, J. Ahn, and K.-H. Jeong, “Enhancement of terahertz pulse emission by optical nanoantenna,” ACS Nano 6(3), 2026–2031 (2012). [CrossRef] [PubMed]
9. H. Tanoto, J. Teng, Q. Wu, M. Sun, Z. Chen, S. Maier, B. Wang, C. Chum, G. Si, A. Danner, and S. J. Chua, “Greatly enhanced continuous-wave terahertz emission by nano-electrodes in a photoconductive photomixer,” Nat. Photonics 6(2), 121–126 (2012). [CrossRef]
10. S. J. Park, J. T. Hong, S. J. Choi, H. S. Kim, W. K. Park, S. T. Han, J. Y. Park, S. Lee, D. S. Kim, and Y. H. Ahn, “Detection of microorganisms using terahertz metamaterials,” Sci. Rep. 4(1), 4988 (2014). [CrossRef] [PubMed]
11. D. Headland, P. Thurgood, D. Stavrevski, W. Withayachumnankul, D. Abbott, M. Bhaskaran, and S. Sriram, “Doped polymer for low-loss dielectric material in the terahertz rang,” Opt. Mater. Express 5(6), 1373–1380 (2015). [CrossRef]
12. J. T. Hong, S. J. Park, J.-Y. Park, S. Lee, and Y. H. Ahn, “Terahertz slot antenna devices fabricated on silver nanowire network films,” Opt. Mater. Express 7(5), 1679–1685 (2017). [CrossRef]
13. P. Mühlschlegel, H.-J. Eisler, O. J. F. Martin, B. Hecht, and D. W. Pohl, “Resonant optical antennas,” Science 308(5728), 1607–1609 (2005). [CrossRef] [PubMed]
14. M. I. Amanti, M. Fischer, C. Walther, G. Scalari, and J. Faist, “Horn antennas for terahertz quantum cascade lasers,” Electron. Lett. 43(10), 573–574 (2007). [CrossRef]
15. H. R. Park, S. M. Koo, O. K. Suwal, Y. M. Park, J. S. Kyoung, M. A. Seo, S. S. Choi, N. K. Park, D. S. Kim, and K. J. Ahn, “Resonance behavior of single ultrathin slot antennas on finite dielectric substrate in terahertz regime,” Appl. Phys. Lett. 96(21), 211109 (2010). [CrossRef]
16. H. Galal and M. Agio, “High efficient light extraction and directional emission from large refractive-index materials with a planar Yagi-Uda antenna,” Opt. Mater. Express 7(5), 1634–1646 (2017). [CrossRef]
17. T. K. Nguyen, S. Kim, F. Rotermund, and I. Park, “Design of a wideband continuous-wave photomixer antenna for terahertz wireless communication systems,” J. Electromagn. Waves Appl. 28(8), 976–988 (2014). [CrossRef]
18. G. Kaplan, K. Aydin, and J. Scheuer, “Dynamically controlled plasmonic nanoantenna phased array utilizing vanadium dioxide,” Opt. Mater. Express 5(11), 2513–2524 (2015). [CrossRef]
19. S. Abdellatif, K. Kirah, H. Ghali, and W. Anis, “Spectral and spatial distribution effects on nanowires inside nanoring optical antennas for photovoltaic arrays,” Opt. Mater. Express 2(10), 1432–1436 (2012). [CrossRef]
20. Z. Yi, J. Luo, Y. Yi, X. Kang, X. Ye, P. Bi, P. Wu, X. Jiang, Y. Yi, and Y. Tang, “Study of strong dipole and quadrupole plasmon resonance in Ag nanorings antenna,” Opt. Mater. Express 5(2), 210–217 (2015). [CrossRef]
21. Y. G. Liu, W. C. H. Choy, W. E. I. Sha, and W. C. Chew, “Unidirectional and wavelength-selective photonic sphere-array nanoantennas,” Opt. Lett. 37(11), 2112–2114 (2012). [CrossRef] [PubMed]
22. J. Lloyd-Hughes, G. Scalari, A. van Kolck, M. Fischer, M. Beck, and J. Faist, “Coupling terahertz radiation between sub-wavelength metal-metal waveguides and free space using monolithically integrated horn antennae,” Opt. Express 17(20), 18387–18393 (2009). [CrossRef] [PubMed]
23. R. Singh, C. Rockstuhl, C. Menzel, T. P. Meyrath, M. He, H. Giessen, F. Lederer, and W. Zhang, “Spiral-type terahertz antennas and the manifestation of the Mushiake principle,” Opt. Express 17(12), 9971–9980 (2009). [CrossRef] [PubMed]
24. S.-G. Park, Y. Choi, Y.-J. Oh, and K.-H. Jeong, “Terahertz photoconductive antenna with metal nanoislands,” Opt. Express 20(23), 25530–25535 (2012). [CrossRef] [PubMed]
25. S. J. Park, B. H. Son, S. J. Choi, H. S. Kim, and Y. H. Ahn, “Sensitive detection of yeast using terahertz slot antennas,” Opt. Express 22(25), 30467–30472 (2014). [CrossRef] [PubMed]
26. J. Xu, L. Tao, R. Zhang, Y. Hao, S. Huang, and K. Bi, “Broadband complementary ring-resonator based terahertz antenna,” Opt. Express 25(15), 17099–17104 (2017). [CrossRef] [PubMed]
27. B. H. Fong, J. S. Colburn, J. J. Ottusch, J. L. Visher, and D. F. Sievenpiper, “Scalar and tensor holographic artificial impedance surfaces,” IEEE Trans. Antenn. Propag. 58(10), 3212–3221 (2010). [CrossRef]
28. S. Pandi, C. A. Balanis, and C. R. Birtcher, “Design of scalar impedance holographic metasurfaces for antenna beam formation with desired polarization,” IEEE Trans. Antenn. Propag. 63(7), 3016–3024 (2015). [CrossRef]
29. T. Quach, D. A. Mcnamara, and A. Petosa, “Holographic antenna realized using interference patterns determined in presence of dielectric substrate,” IET Electron Lett. 41(13), 724–725 (2005). [CrossRef]
30. P. Li, Y. Shi, H. Bagci, and L. J. Jiang, “A hybrid time-domain discontinuous Galerkin-boundary integral algorithm for 3-D electromagnetic scattering analysis,” IEEE Trans. Antenn. Propag. 62(5), 2841–2846 (2014). [CrossRef]
31. P. Li and L. J. Jiang, “Integration of arbitrary lumped multiport circuit networks into the discontinuous Galerkin time-domain analysis,” IEEE Trans. Microw. Theory Tech. 61(7), 2525–2534 (2013). [CrossRef]
32. P. Li and L. J. Jiang, “A hybrid electromagnetics-circuit simulation method exploiting discontinuous Galerkin finite element time domain method,” IEEE Microw. Wirel. Compon. Lett. 23(3), 113–115 (2013). [CrossRef]
