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The design of a reconfigurable intelligent surface (RIS) for mm-waves with arbitrary polarization is proposed. At mm-wave frequencies, the RF switches needed in the RIS suffer from low isolation, and therefore a parasitic enhancing structure (PES) is also proposed to improve switch performance. In the RIS element, a dual-port dual-polarized patch antenna is used for scattering. Both ports of the antenna are connected to independent phase-reconfigurable circuits based on diodes, with PES, and these can provide 180-degree phase shifts. Simulation results show that the RIS can operate effectively for two orthogonal polarized waves and therefore an arbitrarily polarized wave. © 2023 IEEE.

A new dual-port reconfigurable antenna design with both polarization and pattern diversity is described. For each polarization, beam-steerable function can be realized in the same steering range by utilizing two pairs of complementary reconfigurable parasitic elements. Four RF switches are located on these parasitic elements to provide reconfiguration. The bandwidth for each port is 3.4-3.8 GHz with more than 20 dB port isolation for all reconfigurable states. This reconfigurable antenna can be utilized in multiple wireless communication or sensing scenarios to provide performance gains. © 2023 IEEE.

A dual-port 1×2 antenna array incorporating a parasitic pixel surface in front of the array is proposed. By optimizing the pixel surface, different radiation patterns can be provided by each port. To demonstrate the effectiveness of the approach, a dual-port design, with patterns directed to 112° and 66° and gains of 7.87 dBi and 6.95 dBi respectively at 28 GHz, is provided. A feature of the design is that no RF switches are needed in the pixel surface. The proposed antenna array can be suitable for future fifth-generation (5G) wireless communication systems. © 2023 IEEE.

A novel method incorporating joint perturbation sensitivity analysis is proposed in this paper to design frequency reconfigurable planar antennas with a pixelated surface. Using our method, an antenna design having two switched working frequency bands and omnidirectional radiation patterns, is optimized. The simulation results verify its efficacy and potential computation efficiency. © 2023 IEEE.

We investigate the performance of a reconfigurable intelligent surface (RIS) assisted single-input single-output (SISO) communication system where RIS elements are narrowly spaced so that the channels between the RIS elements and receiver are spatially correlated. Adjacent RIS elements are grouped together to reduce the channel estimation overhead. The statistical properties of the optimal received SNR are analytically derived and these are used to characterize the coverage probability of the system. An analytical upper bound for the average achievable rate is also derived. This analysis provides insight into the impact of the grouping strategy and element spatial channel correlation level on the coverage probability and the achievable rate of the system. Numerical results validate the tightness of the closed-form expressions. Our results show that the average achievable rate for a given group size is higher for the spatially correlated RIS elements as compared to the uncorrelated configuration.

Active reconfigurable intelligent surfaces (RISs) have recently been proposed to complement and generalize passive RIS. In this work, the design for an active RIS based on phase-reconfigurable reflection amplifiers is proposed. The proposed active RIS elements’ design consists of a two-layer patch antenna and a phase-reconfigurable reflection amplifier that is realized by a cascade of a phase shifter and a reflection amplifier. Theoretical and numerical analyses are used to quantify key parameters that need to be met in the design of the reflection amplifier and phase shifters. These show that a tradeoff between the reflection amplifier’s gain and the phase shifter’s return and insertion loss is required to be balanced to obtain a stable and effective overall design. In particular, a reflection amplifier with about 13-dB gain and a 2-bit phase shifter with only about 1.9-dB insertion loss and $-$ 25-dB return loss are designed. The final RIS element obtains 8.5-dB gain with four reconfigurable phases ranging from 0 $^{\circ}$ to 360 $^{\circ}$ with small root mean square (rms) gain and phase errors. An active RIS can be constructed by concatenating these elements together, and an efficient analytical method to calculate the scattered pattern by the active RIS is also proposed. Experimental results for a $2$ $\times$ $2$ element active RIS prototype are also provided. These show that the active RIS provides received powers around 8.5 dB higher than that from using an equivalent passive RIS. The results demonstrate the f

The channel estimation overhead of reconfigurable intelligent surface (RIS) assisted communication systems can be prohibitive. Prior works have demonstrated via simulations that an adaptive transmission scheme where neighbouring RIS elements are grouped together can help to reduce the pilot overhead and improve achievable rate. In this paper, we present an analytical study of RIS element grouping. We derive a tight closed-form upper bound for the achievable rate and then maximize it with respect to the group size. Our analysis reveals that more coarse-grained grouping is important when the channel coherence time is low (high mobility scenarios) or the transmit power is large. We also demonstrate that optimal grouping can yield significant performance improvements over simple ‘On-Off’ RIS element switching schemes that have been recently considered.

The channel estimation overhead of reconfigurable intelligent surface (RIS) assisted communication systems can be prohibitive. Prior works have demonstrated via simulations that an adaptive transmission scheme where neighbouring RIS elements are grouped together can help to reduce the pilot overhead and improve achievable rate. In this paper, we present an analytical study of RIS element grouping. We derive a tight closed-form upper bound for the achievable rate and then maximize it with respect to the group size. Our analysis reveals that more coarse-grained grouping is important when the channel coherence time is low (high mobility scenarios) or the transmit power is large. We also demonstrate that optimal grouping can yield significant performance improvements over simple ‘On-Off’ RIS element switching schemes that have been recently considered.

A design for a highly reconfigurable intelligent surface (RIS) that can provide 3-D passive reflective beamforming suitable for sub-6-GHz frequency bands is proposed. The RIS is based on a novel double-layer structure consisting of independently controllable and highly reconfigurable elements on top of a ground plane. The novelty of the structure is the use of reconfigurable RIS elements, whose size is of the order of a wavelength, which are optimized to function over wide incident and reflected angles. In addition, the individual elements each have four RF switches, in a $5$ $\times$ $5$ subelement structure, providing 16 different reflective phases, from $0^{\circ}$ to $360^{\circ}$ relative to the incident waves. To quantify the performance of RIS, the performance metric of phase entropy is defined and it is also used as an objective function for optimizing the design. An efficient analytical method for predicting the reflected waves from the RIS elements, as well as phase entropy, is also provided. For verification, a prototype of a $4$ $\times$ $4$ -element RIS, with a total size of $0.32~\textrm{m}$ $\times$ $0.34~\textrm{m}$ , is fabricated and an experimental setup for mea

The channel estimation overhead of reconfigurable intelligent surface (RIS) assisted communication systems can be prohibitive. Prior works have demonstrated via simulations that an adaptive transmission scheme where neighbouring RIS elements are grouped together can help to reduce the pilot overhead and improve achievable rate. In this paper, we present an analytical study of RIS element grouping. We derive a tight closed-form upper bound for the achievable rate and then maximize it with respect to the group size. Our analysis reveals that more coarse-grained grouping is important when the channel coherence time is low (high mobility scenarios) or the transmit power is large. We also demonstrate that optimal grouping can yield significant performance improvements over simple ‘On-Off’ RIS element switching schemes that have been recently considered.

In this article, a reconfigurable surface in reflecting mode is proposed to achieve linearly polarized (LP) conversion. Based on grid defected ground structures, a PIN diode is utilized as the an RF switch to provide the reconfigurability. The surface is analyzed based on internal multiport method (IMPM) which is over 80x faster than the simulation software. When the diode is in ON state, the surface can reflect the incident wave in copolarization mode. When the diode is in OFF state, the surface will work in polarization conversion mode, which can reflect the incident wave in cross-polarization state. And the surface can realized more than 70% polarization conversion ratio (PCR) from 3.33GHz to 3.56GHz.

The channel estimation overhead of reconfigurable intelligent surface (RIS) assisted communication systems can be prohibitive. Prior works have demonstrated via simulations that grouping neighbouring RIS elements can help to reduce the pilot overhead and improve achievable rate. In this paper, we present an analytical study of RIS element grouping. We derive a tight closed-form upper bound for the achievable rate and then maximize it with respect to the group size. Our analysis reveals that more coarse-grained grouping is important-when the channel coherence time is low (high mobility scenarios) or the transmit power is large. We also demonstrate that optimal grouping can yield significant performance improvements over simple `On-Off' RIS element switching schemes that have been recently considered., Comment: Submitted to IEEE Wireless Communications Letters

In this article, a reconfigurable surface in reflecting mode is proposed to achieve linearly polarized (LP) conversion. Based on grid defected ground structures, a PIN diode is utilized as the an RF switch to provide the reconfigurability. The surface is analyzed based on internal multiport method (IMPM) which is over 80x faster than the simulation software. When the diode is in ON state, the surface can reflect the incident wave in copolarization mode. When the diode is in OFF state, the surface will work in polarization conversion mode, which can reflect the incident wave in cross-polarization state. And the surface can realized more than 70% polarization conversion ratio (PCR) from 3.33GHz to 3.56GHz.