Open Access
Add to BibSonomy
Abstract
This paper proposes an electronically reconfigurable unit cell for transmit-reflect-arrays in the X-band, which makes it possible to control the reflection or transmission phase independently by combining the mechanisms of reconfigurable transmitarrays and reconfigurable reflectarrays. The fabricated unit cell was characterized in a waveguide simulator. The return loss in the reflection mode and insertion loss in the transmission mode are smaller than 1.8 dB for all states at 10.63 GHz, and a 1-bit phase shift for both modes is achieved within 180° ± 10°. When compared to full-wave electromagnetic simulation results, the proposed unit cell shows good results and is thus verified.
© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Reconfigurable bit arrays, such as reconfigurable transmitarrays (RTAs) [1], reconfigurable reflectarrays (RRAs) [2], and active pattern-reconfigurable arrays [3,4] are generating considerable interest in wireless communication and radar applications because of their high radiation gain. Compared to phased arrays, reconfigurable unit cells are typically integrated with tunable devices, such as PIN diodes [1–4], RF-MEMS switches [5], or varactors [6,7], which can electronically achieve phase control without using lossy phase shifters or expensive transmit/receive (T/R) modules. Moreover, for large antenna apertures, the spatial feeding mechanism of RTAs and RRAs drastically reduces the loss and complexity of the power division network, especially at millimeter-wave frequencies. In recent years, multi-bit reconfigurable arrays have been presented to implement multifunctional wavefront control because of the lower quantization error and the more diverse patterns [8–13].
Many RTAs and RRAs have been proposed in the last decade. For RTAs, unit cells can be realized by using a receiver–transmitter structure [1,13–15], coupled slots [6], or multilayer frequency selective surfaces (M-FSS) [16]. The receiver–transmitter structure is the most popular solution in electronically RTA design since it can be utilized for multi-bit RTAs design and precise phase shifts control. For RRAs, most designs are realized by using an anisotropic unit cell with binary coding reflective performance obtained along a particular direction with PIN diodes [2,17–21]. Electrically controlled RTAs and RRAs have also been applied in various applications such as microwave imaging [22,23], wireless communications [24,25], and self-adaptive systems [26]. In our previous work, several reconfigurable arrays for beam control [4,10] and radar cross section (RCS) reduction [11,12] in the X-band were demonstrated.
Reconfigurable transmit-reflect-arrays (RTRA), however, have not been studied as much as RTAs or RRAs. Recently, several designs have been proposed for RTRAs. A tunable metasurface was introduced for RTRAs after the analysis of the required surface electric and magnetic impedances, where either arbitrary transmission magnitude and phase or arbitrary reflection magnitude and phase could be achieved [27]. Yang et al. proposed a high-gain transmit-reflect-array (TRA) with simultaneous bidirectional coverage [28]. By changing both the polarization and direction of incident waves, a novel transmission-reflection-integrated coding metasurface was proposed, which could simultaneously generate three independent functionalities in the same frequency band [29]. Zhang et al. proposed a 1-bit metasurface with the function of full-space orbital angular momentum vortex beams generation [30]. Xi et al. presented an innovative dual-polarization and low-profile RTRA [31]. With the help of elaborately designed ultra-thin Pancharatnam–Berry elements, several novel metasurfaces were presented with multifunctional characteristics [32] and high-efficiency characteristics [33] for full-space EM wave applications. RTRAs for beam switching applications were studied, which have reconfigurable transmission/reflection modes [34,35]. The concept of the polarization-dependent reflection-transmission amplitude code was introduced to realize full-space EM control [36]. Wu et al. proposed a reconfigurable anisotropic coding metasurface, which could independently control the reflection and transmission modes of differently polarized EM waves [37]. Wang et al. proposed a 1-bit bidirectional RTRA by utilizing the current reversal mechanism and the continuity of the cross-polarized electric field on the unit cell surface [38], which is the electronically reconfigurable version of the TRA in [28].
However, the aforementioned designs have a few limitations. The metasurface is regarded as a whole, and unit cells could not be controlled independently in [27]. The radiation characteristics of the unit cells proposed in [28–33] are fixed. The unit cells in [34,35] do not have phase control capability. The phase response is not electronically reconfigurable in [36,37]. In [38], the RTRA cannot manipulate the transmitted and reflected beams independently.
To the best of our knowledge, only one report so far has demonstrated a unit cell for electronically RTRA with independent full-space phase-control capability [6]. However, this unit cell consisted of five varactor diodes biased with five independent bias lines. By contrast, the design proposed by us is less complex and only uses two PIN diodes and two bias lines per unit cell. Furthermore, the scattering performance presented in [6] is strongly affected by the large value of the varactor diode resistance, with insertion loss variation of more than 2.3 dB. In addition, the 3-dB fractional transmission bandwidth (BW) could not be obtained.
In this paper, an electronically reconfigurable unit cell for RTRAs in the X-band is presented, which utilizes only two PIN diodes and four metal layers. The unit cell is capable of working independently in transmission mode or reflection mode. Low loss and good phase shifts were obtained for all modes within the frequency band of interest. The performance of this design was validated by utilizing the standard waveguide approach. The remainder of this paper is organized as follows. The architecture of the proposed unit cell is described in Section 2. The simulation results under two conditions, and the measurement results of the fabricated prototype are presented in Section 3. The conclusions are presented in Section 4.
2. Design and architecture of proposed unit cell
The proposed unit cell can achieve four states by using only two diodes: ‘OFF/OFF’ (‘00’), ‘OFF/ON’ (‘01’), ‘ON/OFF’ (‘10’), and ‘ON/ON’ (‘11’). When the diodes are at ‘00’ or ‘11’ state, the unit cell works in the reflection mode with a 180° phase shift. When the diodes are at ‘01’ or ‘10’ state, the unit cell works in transmission mode with a 180° phase shift. Figure 1 shows the four states of the proposed unit cell.
Fig. 1. Schematic showing the direction and phase shift of EM wave propagation at four different states of two PIN diodes with distinct control signals: (a) reflection mode at ‘00’ state, (b) transmission mode at ‘01’ state, (c) reflection mode with phase reversal at ‘11’ state, (d) transmission mode with phase reversal at ‘10’ state.
The unit cell consists of four metal layers and two substrates bonded by a bonding film, as shown in Fig. 2(a). The design frequency is 10.5 GHz in the X-band, and the unit cell size is 9.6 mm × 9.6 mm × 3 mm. This design has an extremely small size, 0.336λ × 0.336λ× 0.105λ (λ is the wavelength at the center frequency of 10.5 GHz), which is smaller than that of all the designs proposed in [1–6,13–21]. F4B with a permittivity of 2.65 and a loss tangent less than 0.002 is chosen as the substrate material, and the bonding film is made of FR-4 with a permittivity of 4.3 and a loss tangent less than 0.025. These materials used for constructing the structure are easily available and relatively low-cost. The transmitter layer, ground layer, bias line layer, and receiver layer are labeled as M1, M2, M3, and M4, respectively. There are two simple rectangular rings on M4. Each rectangular ring is connected to the ground through a PIN diode. Four via holes are arranged at the minimum-electric-field point in transmission mode with two bias lines. Although only a single connection per unit cell is necessary for biasing, a dual connection was preferred to maintain symmetry. This led to lower cross-polarization levels similar to that of the unit cell of 1-bit RTA proposed in [1]. Moreover, the length between the two bias lines for each of the PIN diodes is carefully measured and designed to reduce the influence of the bias circuit. M1 can be regarded as a side-shorted patch connected to the ground by two rows of via holes at the edge of each short side. A metalized via hole is located at the center of the unit cell and connects M1 and M4 so that the current can flow toward M1 from M4 through the ground plane. Details of the dimensions of the proposed unit cell are listed in Table 1. Two PIN diodes (MACOM MADP-000907-14020) are used as RF switches owing to their stable performance and low losses, as proven in [14]. The PIN diode is modeled as an equivalent RL series circuit (R = 7.8 Ω, L = 30 pH) and an equivalent LC series circuit (L = 30 pH, C = 25 fF) for the ON and OFF states, respectively. The parameters of the equivalent circuit of the PIN diodes are presented in Table 2.
Fig. 2. Schematic view of the proposed unit cell: (a) exploded view, (b) transmitter layer (M1), (c) ground layer (M2), (d) bias line layer (M3), and (e) receiver layer (M4).
Table 1. Dimensions of the proposed unit cell
Table 2. Equivalent circuit parameters of the PIN diode
2.1 Operation mechanism of proposed unit cell
This design can be considered as a combination of a receiver–transmitter type RTA and an RRA. The design principles of these devices are incorporated in the proposed unit cell design to achieve full-space 1-bit electronic phase-controlling capability.
M4 is a dual functional layer, which works as a reflective patch in the reflection mode and a receiver patch in the transmission mode. In fact, the design of M4 is derived from the O-slot patch in [1]. The conventional receiver–transmitter type RTA works in the OFF/ON or ON/OFF states. It is obvious that the OFF/OFF and ON/ON states are redundant. Here, we modify the structure of the O-slot to utilize redundant states but maintain the operation mechanism. Although the O-slot patch is the transmitter patch of a receiver–transmitter type RTA, it can act as a receiver patch owing to the reciprocity principle. Figure 3 demonstrates the process of the evolution from the O-slot to the proposed structure on M4, to further enhance the understanding of this design. For the OFF/ON and ON/OFF states, we turn over the central microstrip with the biasing point outside the rectangular ring and obtain two configurations, which are mirror images of each other. Then the two configurations swap places and join together at the connection point. Certainly, the current reversal mechanism does not change after the evolution of the receiver patch, as shown in Fig. 3. In addition, the two PIN diodes can be manipulated by two independent control signals, which is a significant advantage of the proposed design. This improvement allows the two PIN diodes to control four different states, instead of only two states. When the bias voltage of one diode is 1.34 V and that of the other is 0 V, the two diodes are in the ‘ON/OFF’ or ‘OFF/ON’ state. The central via hole is always short-circuited with one of two rectangular rings, and the current flows toward M1, which works as the transmitter patch of the receiver–transmitter type RTA. Depending on the bias current signal, the incident field is transmitted in phase or with a 180° rotation on the current reversal mechanism, resulting in a 1-bit phase shift (0°/180°).
Moreover, M1 is a dual functional layer, which works as the ground in the reflection mode and the transmitter patch in the transmission mode. The simulated current distribution on the side-shorted patch is shown in Fig. 4(a). It is evident that the current on one side of the transmitter patch flows from the center via hole, and the current on the other side is excited. The horizontal electric field through the slot is equivalent to a vertical magnetic current source along the slot, as shown in Fig. 4(b). However, the most important reason behind designing this structure as the transmitter is that this structure is an ideal ground compared to other structures such as the O-slot patch in [1]. Owing to the set of via holes, which mimics a metal wall connecting it to the ground, there is little energy leaking into the upper half-space in reflection mode. When the bias voltages are both set as 1.34 V, the two diodes are ‘ON’. When both the bias voltages are set as 0 V and the bias lines are connected to the ground, the two diodes are ‘OFF’. For the ‘OFF/OFF’ state, M1 with the central via hole is open-circuited from M4. For the ‘ON/ON’ state, M1 with the central via hole is short-circuited from M4 since the impedance of the PIN diodes in the ‘ON/ON’ state is extremely low compared to that in the ‘OFF/OFF’ state (ZON/ZOFF = 5.3 × 10−4). Thus, two different resonance frequencies in the ‘OFF/OFF’ and ‘ON/ON’ states can be obtained, respectively. Between the two resonance frequencies, we can get a certain frequency range, where the phase shift meets performance requirements. Depending on the bias current signal, the incident field is reflected in phase or with a 180° rotation due to different equivalent circuit parameters of PIN diodes being introduced, resulting in a 1-bit phase shift (0°/180°).
Fig. 4. Operation principle of the transmitter patch: (a) simulated current distribution, (b) equivalent radiation source of magnetic currents.
2.2 Design of bias circuits
The bias circuit is an essential part of the unit cell for electronically reconfigurable arrays. To control the PIN diodes embedded in M4, the bias circuit is connected with the microwave circuit. A good isolation of microwave and direct-current (DC) circuits is necessary for low losses of the unit cell. However, because of the limited available space, two open-ended radial stubs cannot be arranged for two bias lines. Here, we use the symmetry of the proposed design. As shown in Figs. 2(c)–2(e), the structure from M4 to M2 is completely symmetrical. Therefore, the currents at points A and B, as shown in Fig. 5, are the same. It is possible to change the length difference of the current path between A and B (i.e., the value of lb), such that the currents J1 and J2 can cancel each other out. Using Kirchhoff's current law at point A, current J3 is nearly zero when the sum of J1 and J2 approaches zero. Moreover, we place the biasing points at the positions with the weakest electric field on M4. All of these measures ensure good isolation of the RF and DC signals. Figure 6(a) shows the simulated electric field distribution on M4. Figure 6(b) shows the simulated x-direction current distribution on M3, which is perpendicular to the polarization of the incident wave.
Fig. 6. (a) Simulated electric field distribution on the receiver layer. (b) Simulated current distribution on the bias lines.
3. Simulation results and experimental validation
The commercial 3D electromagnetic field simulation software CST Studio Suite 2020 was used to analyze and optimize the proposed unit cell. The unit cell boundary condition and two Floquet ports are applied to realize a periodic boundary condition (PBC), where the unit cell is simulated under an array environment, and the simulation frequency ranges from 10 GHz to 11 GHz.
To characterize and validate the proposed design, several samples with a bias structure were fabricated and measured in a standard rectangular WR-75 waveguide (19.05 mm × 9.525 mm). The waveguide walls around the sample can constitute an equivalent infinite periodic boundary condition, where image theory is used to produce virtual periodic unit cells. However, M1 does not have rotational symmetry despite symmetrical M2-M3. As a result, the transmission performance involved with the asymmetric part under the equivalent infinite periodic boundary condition will be different than that under PBC. Therefore, both the PBC and waveguide simulator (WGS) are provided in the simulation.
Several prototypes of two unit cells were fabricated by standard Printed Circuit Board (PCB) process which is a mature and low-cost fabrication technology, as shown in Fig. 7(a). The fabricated unit cell was assembled between two WR-75 waveguides for measurement, as shown in Fig. 7(b). In addition, the measurement system consisting of a unit cell, two waveguides, a vector network analyzer (VNA) and a DC power supply is shown in Fig. 7(c). The forward-bias current and the reverse voltage are set as 10 mA and 0 V, respectively, and the measurement frequency ranges from 10 GHz to 11 GHz. The phases and magnitudes in both the transmission and reflection modes can be measured with this setup.
The measurement and simulation results are shown in Fig. 8. The magnitude in the reflection mode is stable and relatively high since M1 acts as an ideal ground, even though the resistance of the PIN diodes affects the measurement performance at ‘11’ state. The measurement phase shift in the reflection mode fluctuates between 155° and 222° in the frequency range between 10 GHz to 11 GHz. Owing to the current reversal mechanism, the phase shifts under two simulation conditions in the transmission mode are precise 180°. The measurement result is stable despite a slight irregularity as expected. Whereas the measurement magnitude has a sharp drop to below -3 dB at 10 GHz and 11 GHz in transmission mode. This is the main limitation on the bandwidth of the proposed unit cell. Both the simulation and measurement results in the frequency range between 10.33 GHz to 10.73 GHz are in good agreement. In this bandwidth, the return loss in the measurement is less than 1 dB in the reflection mode, as shown in Figs. 8(a) and 8(b). Simultaneously, the insertion loss in the measurement is less than 3 dB in the transmission mode, as shown in Figs. 8(c) and 8(d). The reflection phase shift is 180° ± 20° in the reflection mode between ‘00’ and ‘11’ states, as shown in Fig. 8(e). Moreover, the transmission phase shift is 180° ± 14° in the transmission mode between ‘01’ and ‘10’ states, as shown in Fig. 8(f). Furthermore, the measured magnitudes are more than -1.8 dB, and the phase shifts are 180° ± 10° in both modes at approximately 10.63 GHz. These results are generally acceptable for practical RTRA applications. A slightly higher loss in the ‘01’ state and some frequency shift can be attributed to the uncertainty of fabrication and soldering.
Fig. 8. Simulation and measurement results: (a) amplitudes at ‘00’ state, (b) amplitudes at ‘11’ state, (c) amplitudes at ‘01’ state, (d) amplitudes at ‘10’ state, (e) phase shifts in the reflection mode, and (f) phase shifts in the transmission mode.
4. Conclusion
An electronically RTRA unit cell with extremely small dimensions is proposed, simulated, fabricated, and fully characterized in a waveguide measurement setup. Only two PIN diodes are embedded in one unit cell to achieve independent full-space electronic phase control with low losses. The unit cell allows independent control of the upper half-space and lower half-space, that is, the reflection mode and the transmission mode, respectively. A few samples containing two unit cells were fabricated and measured. The experimental results show reasonably good agreement when compared to full-wave electromagnetic simulation results under both PBC and WGS, which verifies the proposed unit cell design. The PIN diodes with solders appear on M4, which might lead to undesirable scattering and hence deteriorate the performance of unit cells. In the future, the PIN diodes, as well as other lumped components, can be arranged on M1 to improve the performance. Owing to its unique advantages of low profile, miniature structure, simple fabrication, and low cost, the proposed electronically RTRA unit cell provides a potential solution for full-space reconfigurable intelligent surfaces (RIS), next generation wireless communication networks, and modern radar systems.
Funding
National Key Research and Development Program of China (2017YFA0100203).
Disclosures
The authors declare no conflicts of interest.
References
1. A. Clemente, L. Dussopt, R. Sauleau, P. Potier, and P. Pouliguen, “1-Bit Reconfigurable Unit Cell Based on PIN Diodes for Transmit-Array Applications in X-Band,” IEEE Trans. Antennas Propag. 60(5), 2260–2269 (2012). [CrossRef]
2. H. Yang, F. Yang, S. Xu, Y. Mao, M. Li, X. Cao, and J. Gao, “A 1-Bit 10 × 10 Reconfigurable Reflectarray Antenna: Design, Optimization, and Experiment,” IEEE Trans. Antennas Propag. 64(6), 2246–2254 (2016). [CrossRef]
3. X. G. Zhang, W. X. Jiang, H. W. Tian, Z. X. Wang, Q. Wang, and T. J. Cui, “Pattern-Reconfigurable Planar Array Antenna Characterized by Digital Coding Method,” IEEE Trans. Antennas Propag. 68(2), 1170–1175 (2020). [CrossRef]
4. S. Li, F. Xu, X. Wan, T. J. Cui, and Y.-Q. Jin, “Programmable Metasurface Based on Substrate-Integrated Waveguide for Compact Dynamic-Pattern Antenna,” IEEE Trans. Antennas Propag. (to be published).
5. C.-C. Cheng, B. Lakshminarayanan, and A. Abbaspour-Tamijani, “A Programmable Lens-Array Antenna With Monolithically Integrated MEMS Switches,” IEEE Trans. Microwave Theory Tech. 57(8), 1874–1884 (2009). [CrossRef]
6. J. Y. Lau and S. V. Hum, “A Planar Reconfigurable Aperture With Lens and Reflectarray Modes of Operation,” IEEE Trans. Microwave Theory Tech. 58(12), 3547–3555 (2010). [CrossRef]
7. R. Feng, B. Ratni, J. Yi, K. Zhang, X. Ding, H. Zhang, A. de Lustrac, and S. N. Burokur, “Versatile Airy-Beam Generation Using a 1-Bit Coding Programmable Reflective Metasurface,” Phys. Rev. Appl. 14(1), 014081 (2020). [CrossRef]
8. Y. Yuan, K. Zhang, B. Ratni, Q. Song, X. Ding, Q. Wu, S. N. Burokur, and P. Genevet, “Independent phase modulation for quadruplex polarization channels enabled by chirality-assisted geometric-phase metasurfaces,” Nat. Commun. 11(1), 4186 (2020). [CrossRef]
9. Y. Yuan, S. Sun, Y. Chen, K. Zhang, X. Ding, B. Ratni, Q. Wu, S. N. Burokur, and C.-W. Qiu, “A Fully Phase-Modulated Metasurface as An Energy-Controllable Circular Polarization Router,” Adv. Sci. 7(18), 2001437 (2020). [CrossRef]
10. F. Zhang, G.-M. Yang, and Y.-Q. Jin, “Low-Profile Circularly Polarized Transmitarray for Wide-Angle Beam Control With a Third-Order Meta-FSS,” IEEE Trans. Antennas Propag. 68(5), 3586–3597 (2020). [CrossRef]
11. Y. Saifullah, A. B. Waqas, G.-M. Yang, F. Zhang, and F. Xu, “4-Bit Optimized Coding Metasurface for Wideband RCS Reduction,” IEEE Access 7, 122378–122386 (2019). [CrossRef]
12. Y. Saifullah, A. B. Waqas, G.-M. Yang, and F. Xu, “Multi-bit dielectric coding metasurface for EM wave manipulation and anomalous reflection,” Opt. Express 28(2), 1139–1149 (2020). [CrossRef]
13. A. Clemente, F. Diaby, L. D. Palma, L. Dussopt, and R. Sauleau, “Experimental Validation of a 2-Bit Reconfigurable Unit-Cell for Transmitarrays at Ka-Band,” IEEE Access 8, 114991–114997 (2020). [CrossRef]
14. Y. Wang, S. Xu, F. Yang, and M. Li, “A Novel 1 Bit Wide-Angle Beam Scanning Reconfigurable Transmitarray Antenna Using an Equivalent Magnetic Dipole Element,” IEEE Trans. Antennas Propag. 68(7), 5691–5695 (2020). [CrossRef]
15. M. Wang, S. Xu, F. Yang, N. Hu, W. Xie, and Z. Chen, “A Novel 1-Bit Reconfigurable Transmitarray Antenna Using a C-Shaped Probe-Fed Patch Element With Broadened Bandwidth and Enhanced Efficiency,” IEEE Access 8, 120124–120133 (2020). [CrossRef]
16. B. D. Nguyen and C. Pichot, “Unit-Cell Loaded With PIN Diodes for 1-Bit Linearly Polarized Reconfigurable Transmitarrays,” Antennas Wirel. Propag. Lett. 18(1), 98–102 (2019). [CrossRef]
17. H. Yang, X. Cao, F. Yang, J. Gao, S. Xu, M. Li, X. Chen, Y. Zhao, Y. Zheng, and S. Li, “A programmable metasurface with dynamic polarization, scattering and focusing control,” Sci. Rep. 6(1), 35692 (2016). [CrossRef]
18. H. Yang, F. Yang, S. Xu, M. Li, X. Cao, and J. Gao, “A 1-Bit Multipolarization Reflectarray Element for Reconfigurable Large-Aperture Antennas,” Antennas Wirel. Propag. Lett. 16, 581–584 (2017). [CrossRef]
19. H. Yang, F. Yang, X. Cao, S. Xu, J. Gao, X. Chen, M. Li, and T. Li, “A 2017-Element Dual-Frequency Electronically Reconfigurable Reflectarray at X/Ku-Band,” IEEE Trans. Antennas Propag. 65(6), 3024–3032 (2017). [CrossRef]
20. J. Han, L. Li, G. Liu, Z. Wu, and Y. Shi, “A Wideband 1 bit 12 × 12 Reconfigurable Beam-Scanning Reflectarray: Design, Fabrication, and Measurement,” Antennas Wirel. Propag. Lett. 18(6), 1268–1272 (2019). [CrossRef]
21. H. Zhang, X. Chen, Z. Wang, Y. Ge, and J. Pu, “A 1-Bit Electronically Reconfigurable Reflectarray Antenna in X Band,” IEEE Access 7, 66567–66575 (2019). [CrossRef]
22. T. Sleasman, M. Boyarsky, M. F. Imani, J. N. Gollub, and D. R. Smith, “Design considerations for a dynamic metamaterial aperture for computational imaging at microwave frequencies,” J. Opt. Soc. Am. B 33(6), 1098–1111 (2016). [CrossRef]
23. L. Li, H. Ruan, C. Liu, Y. Li, Y. Shuang, A. Alù, C.-W. Qiu, and T. J. Cui, “Machine-learning reprogrammable metasurface imager,” Nat. Commun. 10(1), 1082 (2019). [CrossRef]
24. J. Y. Dai, W. K. Tang, J. Zhao, X. Li, Q. Cheng, J. C. Ke, M. Z. Chen, S. Jin, and T. J. Cui, “Wireless Communications through a Simplified Architecture Based on Time-Domain Digital Coding Metasurface,” Adv. Mater. Technol. 4(7), 1900044 (2019). [CrossRef]
25. L. Dai, B. Wang, M. Wang, X. Yang, J. Tan, S. Bi, S. Xu, F. Yang, Z. Chen, M. D. Renzo, C.-B. Chae, and L. Hanzo, “Reconfigurable Intelligent Surface-Based Wireless Communications: Antenna Design, Prototyping, and Experimental Results,” IEEE Access 8, 45913–45923 (2020). [CrossRef]
26. Q. Ma, G. D. Bai, H. B. Jing, C. Yang, L. Li, and T. J. Cui, “Smart metasurface with self-adaptively reprogrammable functions,” Light: Sci. Appl. 8(1), 98 (2019). [CrossRef]
27. B. O. Zhu, K. Chen, N. Jia, L. Sun, J. Zhao, T. Jiang, and Y. Feng, “Dynamic control of electromagnetic wave propagation with the equivalent principle inspired tunable metasurface,” Sci. Rep. 4(1), 4971 (2015). [CrossRef]
28. F. Yang, R. Deng, S. Xu, and M. Li, “Design and Experiment of a Near-Zero-Thickness High-Gain Transmit-Reflect-Array Antenna Using Anisotropic Metasurface,” IEEE Trans. Antennas Propag. 66(6), 2853–2861 (2018). [CrossRef]
29. L. Zhang, R. Y. Wu, G. D. Bai, H. T. Wu, Q. Ma, X. Q. Chen, and T. J. Cui, “Transmission-Reflection-Integrated Multifunctional Coding Metasurface for Full-Space Controls of Electromagnetic Waves,” Adv. Funct. Mater. 28(33), 1802205 (2018). [CrossRef]
30. D. Zhang, X. Cao, H. Yang, J. Gao, and X. Zhu, “Multiple OAM vortex beams generation using 1-bit metasurface,” Opt. Express 26(19), 24804–24815 (2018). [CrossRef]
31. B. Xi, Q. Xue, Y. Cai, Y. Wang, S. Yang, R. Zhang, and L. Zhang, “Design of a dual-polarized reflect-transmit-array,” Microw Opt Technol Lett 62(2), 949–955 (2020). [CrossRef]
32. C. Zhang, G. Wang, H.-X. Xu, X. Zhang, and H.-P. Li, “Helicity-Dependent Multifunctional Metasurfaces for Full-Space Wave Control,” Adv. Opt. Mater. 8(8), 1901719 (2020). [CrossRef]
33. R. Mao, G. Wang, T. Cai, K. Liu, D. Wang, and B. Wu, “Ultra-thin and high-efficiency full-space Pancharatnam-Berry metasurface,” Opt. Express 28(21), 31216–31225 (2020). [CrossRef]
34. S. Chaimool, T. Hongnara, C. Rakluea, P. Akkaraekthalin, and Y. Zhao, “Design of a PIN Diode-Based Reconfigurable Metasurface Antenna for Beam Switching Applications,” Int. J. Antennas Propag. 2019, 1–7 (2019). [CrossRef]
35. W. Li, Y. Wang, S. Sun, and X. Shi, “An FSS-Backed Reflection/Transmission Reconfigurable Array Antenna,” IEEE Access 8, 23904–23911 (2020). [CrossRef]
36. R. Y. Wu, L. Zhang, L. Bao, L. W. Wu, Q. Ma, G. D. Bai, H. T. Wu, and T. J. Cui, “Digital Metasurface with Phase Code and Reflection–Transmission Amplitude Code for Flexible Full-Space Electromagnetic Manipulations,” Adv. Opt. Mater. 7(8), 1801429 (2019). [CrossRef]
37. L. W. Wu, H. F. Ma, R. Y. Wu, Q. Xiao, Y. Gou, M. Wang, Z. X. Wang, L. Bao, H. L. Wang, Y. M. Qing, and T. J. Cui, “Transmission-Reflection Controls and Polarization Controls of Electromagnetic Holograms by a Reconfigurable Anisotropic Digital Coding Metasurface,” Adv. Opt. Mater. 8(22), 2001065 (2020). [CrossRef]
38. M. Wang, S. Xu, F. Yang, and M. Li, “A 1-Bit Bidirectional Reconfigurable Transmit-Reflect-Array Using a Single-Layer Slot Element With PIN Diodes,” IEEE Trans. Antennas Propag. 67(9), 6205–6210 (2019). [CrossRef]
