A reconfigurable antenna (RA) capable of steering its beam into the hemisphere corresponding to θ ∈ {-40°, 0°, 40°}, φ ∈ {0°, 45°, 90°, -45°}, and of changing 3 dB beamwidth, where θ ₃ dB ∈ (40°, 100°), φ ∈ {45°, 90°, -45°} for broadside direction is presented. The RA operating in 5 GHz band consists of a driven patch antenna with a parasitic layer placed above it. The upper surface of the parasitic layer has two pixelated metallic strips, where each strip has four pixels. The pixels connected via p-i-n diode switches enable to change the current distribution on the antenna providing the desired modes of operation. A prototype RA was characterized indicating an average gain of 8 dB. Measured and simulated impedance and radiation patterns agreed well. The proposed RA offers an efficient solution by using less number of switches compared to other RAs. The system level simulations for a 5G orthogonal frequency division multiple access system show that the RA improves capacity/coverage tradeoff significantly, where the RA modes and users are jointly determined to create proper beamwidth and directivity at the access point antennas. For a hotspot scenario, the presented RA provided 29% coverage and 16% capacity gain concurrently.

The design, prototyping, and characterization of a radiation pattern reconfigurable antenna (RA) targeting 5G communications are presented. The RA is based on a reconfigurable parasitic layer technique in which a driven dipole antenna is located along the central axis of a 3-D parasitic layer structure enclosing it. The reconfigurable parasitic structure is similar to a hexagonal prism, where the top/bottom bases are formed by a hexagonal domed structure. The surfaces of the parasitic structure house electrically small metallic pixels with various geometries. The adjacent pixels are connected by PIN diode switches to change the geometry of the parasitic surface, thus providing reconfigurability in the radiation pattern. This RA is designed to operate over a 4.8–5.2 GHz frequency band, producing various radiation patterns with a beam-steering capability in both the azimuth ( $0 {^{\circ }} <\phi < 360 {^{\circ }}$ ) and elevation planes ( $-18 {^{\circ }} <\theta < 18 {^{\circ }}$ ). Small-cell access points equipped with RAs are used to investigate the system level performances for 5G heterogeneous networks. The results show that using distributed mode optimization, RA equipped small-cell systems could provide up to 29% capacity gains and 13% coverage improvements as compared to legacy omnidirectional antenna equipped systems.

MU-MIMO transmission relies on exploiting multi-user diversity among a multitude of users. In this paper, to enhance MU-MIMO transmission, techniques for designing and exploiting reconfigurable antennas (RAs) are developed. A single-element RA is capable of generating modes with different radiation pattern and polarization states resulting in multiple different channel states for each user. This capability expands the search space for user-pairing optimization. To reduce complexity, an iterative user and antenna mode selection algorithm is proposed. Based on parasitic tuning, an RA optimized for MU-MIMO transmission and capable of creating four pattern types is designed using a genetic algorithm and full-wave electromagnetic analyses. Pattern- and channel-aware mode-set generation methods are developed, where mode groups are determined to reduce channel estimation overhead and mode selection complexity while achieving superior performance. Simulation results indicate that the proposed schemes need a lower number of users and/or relax user selection requirements to benefit from MU-MIMO transmissions. It is also seen that more legacy antennas are needed to achieve similar MU-MIMO performance provided by the RA system. Simulations show up to 16-dB signal-to-noise ratio gains for a single cell with 12 users, where the base station has four RAs and four single-antenna users are simultaneously served via MU-MIMO transmission.

In this letter, a reconfigurable dual-polarized broadband antenna with beam-steering capabilities using a parasitic layer is proposed for 5G new radio (NR) frequency range 1 (FR-1) applications. The antenna is a dual-port aperture-stacked patch structure with symmetrical orthogonal (horizontal and vertical) currents. The beam-steering is achieved by a pair of reconfigurable cross-shaped parasitic strips, which bestow the antenna three main beam directions θ = { ~ -25 ^° ,0 ^° , ~ 25 ^° }, Ψ = {0 ^° } with pointing and gain ($ 7$ dB) stability across a 30% impedance bandwidth (S ₁₁ , S ₂₂ <; -10 dB) from 3.2 - 4.3 GHz for both ports/polarizations. A prototype of the antenna is manufactured and measured demonstrating results in accordance with simulation expectations.

We present a novel antenna reconfiguration mechanism relying on electrowetting based digital microfluidics to implement a frequency reconfigurable antenna operating in the X-band. The antenna built on a quartz substrate (ε_r = 3.9, tan δ = 0.0002) is a coplanar waveguide fed annular slot antenna, which is monolithically integrated with a microfluidic chip. This chip establishes an electrowetting on dielectric platform with a mercury droplet placed in it. The base contact area of the mercury droplet can be spread out by electrostatic actuation resulting in a change of loading capacitance. This in turn changes the resonant frequency of the antenna enabling a reversible reconfigurable impedance property. This reconfigurable antenna has been designed, fabricated and measured. The frequency of operation is tuned from around 11 GHz to 13 GHz as demonstrated by simulations and measurements. The design methodology, fabrication processes and the experimental results are given and discussed.

Physical layer message integrity protection and authentication by countering signal-cancellation has been shown as a promising alternative to traditional pure cryptographic message authentication protocols, due to the non-necessity of neither pre-shared secrets nor secure channels. However, the security of such an approach remained an open problem due to the lack of systematic security modeling and quantitative analysis. In this paper, we frst establish a novel signal cancellation attack framework to study the optimal signal-cancellation attacker's behavior and utility using game-theory, which precisely captures the attacker's knowledge using its correlated channel estimates in various channel environments as well as the online nature of the attack. Based on theoretical results, we propose a practical channel randomization approach to defend against signal cancellation attack, which exploits state diversity and swift reconfigurability of reconfigurable antenna to increase randomness and meanwhile reduce correlation of channel state information. We show that by proactively mimicking the attacker and placing restrictions on the attacker's location, we can bound the attacker's knowledge of channel state information, thereby achieving a guaranteed level of message integrity protection in practice. Besides, we conduct extensive experiments and simulations to show the security and performance of the proposed approach.