A Ku-band electronic 2-dimensional (2-D) beam-scanning transmitarray employing a new reconfigurable dual-layer Huygens element is developed in this article. The Huygens element consists of two metallic crosses printed on two layers of a dielectric substrate, which enables a near nonreflection Huygens resonance. A 1 bit phase compensation with low transmission loss is realized by controlling two p-i-n diodes on the element. Compared with many other reconfigurable transmitarray elements using multilayer structures with metallic vias, the proposed reconfigurable Huygens element has a much simpler configuration with a simpler biasing network, and it is not affected by multilayer alignment errors. This particularly facilitates large aperture array development at higher frequencies. To validate the design concept, an electronically reconfigurable transmitarray with the proposed element is fabricated at 13 GHz. Good agreement between the measured and simulated results is found, showing 2-D scanning beams within ±50° in the E-plane and ±40° in the H-plane with a maximum realized gain of 18.4 dBi.

Self-interference (SI) cancellation for full-duplex (FD) multiple input multiple output (MIMO) systems is challenging due to both hardware and signal processing complexity. In this paper, a beam-based adaptive filter structure with analog least mean square (ALMS) loops is proposed to significantly reduce the complexity of SI cancellation for FD MIMO systems. With this structure, the number of adaptive filters required for SI cancellation scales linearly with the number of transmit beams rather than quadratically with the number of antennas. Furthermore, to avoid additional transmit chains used to up-convert the beam signals to generate reference signals for the ALMS loops, a novel method is proposed to select the optimized reference signals from all transmitted signals. In addition, our stationary analysis shows that the proposed structure for FD MIMO systems outperforms the ALMS loop employed for an FD single input single output system. Simulations are conducted to confirm the theoretical analyses.

The performance of transmit beamforming for both optimized precoding and self-interference cancellation (SIC) in full duplex multiple input multiple output (MIMO) transceivers is analysed in this paper. With sub-space dimension larger than that of the null-space of the self-interference channels, the precoding error is reduced but the interference suppression ratio (ISR) is degraded, resulting in a trade-off between multibeam communication and MIMO SIC. An analytical approach for the ISR evaluation is proposed assuming known eigenvalue distribution of the self-interference channels, and a closed-form ISR expression is derived after applying a uniform distribution approximation. The ISR and precoding error trade-off curves are also formulated. Joint SIC by transmit beamforming and beam-based analog adaptive filters over both propagation and analog domains is proposed to achieve better SIC performance and enable more flexible receive antenna selection. Simulation results verify the theoretical analyses.

Source positioning using hybrid angle-of-arrival (AOA) estimation and received signal strength indicator (RSSI) is attractive because no synchronization is required among unknown nodes and anchors. Conventionally, hybrid AOA/RSSI localization combines the same number of these measurements to estimate the agents’ locations. However, since AOA estimation requires anchors to be equipped with large antenna arrays and complicated signal processing, this conventional combination makes the wireless sensor network (WSN) complicated. This paper proposes an unbalanced integration of the two measurements, called 1AOA/nRSSI, to simplify the WSN. Instead of using many anchors with large antenna arrays, the proposed method only requires one master anchor to provide one AOA estimation, while other anchors are simple single-antenna transceivers. By simply transforming the 1AOA/1RSSI information into two corresponding virtual anchors, the problem of integrating one AOA and N RSSI measurements is solved using the least square and subspace methods. The solutions are then evaluated to characterize the impact of angular and distance measurement errors. Simulation results show that the proposed network achieves the same level of precision as in a fully hybrid nAOA/nRSSI network with a slightly higher number of simple anchors.

In-band full-duplex (IBFD) technology has been extensively researched over the last decade, and numerous techniques have been proposed to cancel self-interference (SI) caused by the simultaneously transmitted local in-band signal. Although some prototypes for SI cancellation (SIC) have been published, there are limited works demonstrating the communication performance of the IBFD system. The noise enhancement caused by analog and/or digital SIC is mostly ignored in the literature. This article presents a prototype for an IBFD system with solutions in three domains of SI mitigation. A practical structure for joint analog and digital SIC is proposed and implemented using off-the-shelf components. The transmit data frame is designed to align with the track/hold control signaling so that the irreducible noise caused by the analog SIC can be avoided. By combining a full-duplex antenna, an analog SIC filter, and a field-programmable gate array (FPGA) platform, this prototype successfully demonstrates the performance of the desired IBFD communications. Experiments on the prototype with 50-MHz bandwidth signaling show that under a certain hardware condition, the proposed SIC solution can sufficiently mitigate the SI with 75 dB of cancellation, and a low bit error rate (BER $< $ $10^{-4}$ ) is demonstrated to allow practical applications.

High transmit power in-band full-duplex (IBFD) systems are promising due to their tremendous advantages in both civilian and military applications. However, mitigating self-interference (SI) in such a high transmit power condition is significantly challenging. A two-stage analog filtering structure is proposed in this letter to tackle this problem successfully. The first stage is based on a vector modulator and a balun to cancel the direct leakage SI component. The second stage is constructed from an analog least mean square (ALMS) loop to adaptively cancel the residual SI. The performance of the second stage with nonlinear transmit signals is investigated analytically. Simulation results show that a total 75 dB of SI cancellation can be achieved by the proposed structure, ensuring the residual SI falls into the linear range of the analog-to-digital converter.