A node microstrip architecture is proposed for designing a compact Butler Matrix (BM) that is integrated with a dual-polarized endfire antenna array. The node microstrip architecture can be used to form a variety of compact 2*2 port networks including, but not limited to, couplers and crossovers. The optimized compact BM is potentially suitable for use in 5G wireless communication handsets.

A design for a highly reconfigurable intelligent surface (RIS) that can provide three-dimensional 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, that are optimized to function over wide incident and reflected angles. In addition, the individual elements each have four RF switches, in a 5x5 sub-element structure, providing 16 different reflective phases, from 0 to 360 degrees relative to the incident waves. To quantify the performance of the RIS, the performance metric of phase entropy is defined and it is also utilized 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 4x4-element RIS, with a total size of 0.32x0.34 m2, is fabricated and an experimental setup for measuring the scattered pattern is described. It is shown that waves incident from various angles can be passively beam steered to any angle within 0-360 degrees azimuth and 70 degrees elevation angles. The high reconfigurability to manipulate incident waves makes the proposed RIS a promising surface for use in future high-capacity communication systems.

The development of an ambient radio frequency (RF) powered Internet of Things (IoT) wireless sensor system is reported. The system integrates all major components including multiple antennas, rectifiers, a power management unit (PMU), a microcontroller unit (MCU) with RF transceiver module and sensing unit. A novelty of this applied engineering innovation is the design and use of multi-band dual-polarized multiple antennas to handle the low ambient RF power density found in the everyday environment. Our prototype has demonstrated that it is able to sense temperature, pressure and humidity and wirelessly transmit these signals to a central server with a duty cycle of approximately 15 minutes, when the background ambient RF signals are as low as −28.6 dBm at 950 MHz. The proposed system can address the important issue of energy supply in the development of IoT providing an alternative energy source to batteries or solar cells. Ambient RF powered IoT devices do not require periodic replacement of their batteries or to be placed visible regions which makes them suitable for wall, ceiling and floor applications. Our ambient RF powered IoT wireless sensor system provides concrete proof, through demonstration, that harnessing ambient RF energy for powering IoT sensor systems is feasible.

Versatile configurable defected ground structures (CDGSs) for enhancing the performance of low profile antennas are introduced. It is shown that CDGS can significantly reduce mutual coupling (MC) between multiple antennas and suppress cross-polarization (XP) and enhance circular polarization (CP) excitation in single port low profile antennas for example. The key idea of CDGS is to construct defected ground structures (DGSs) from a grid of slots, which can be either opened or shorted with hardwires, so that they can be configured and optimized to enhance desired antenna performance characteristics. The importance and versatility of the CDGS approach is that it overcomes the issue of having to design bespoke DGS for each individual antenna design. Three design examples are provided to demonstrate the versatility of CDGSs for MC reduction, XP suppression and CP excitation. Experimental results demonstrate that MC can be reduced by up to 43 dB, XP can be suppressed by 15 dB and CP can be excited with 78 MHz (2.2%) 3-dB axial ratio (AR) bandwidth. The compactness and ease of fabrication also make the CDGS well suited to compact low profile internet of things (IoT) and wireless communication applications.