Security in wireless networks has traditionally been addressed above the physical layer. With the expected proliferation of applications in 5G, the mm-wave spectrum and new network architectures, traditional methods of data encryption may not be scalable for energy-constrained applications. Thus, there has been a surge of interest in physical layer security that aims to impart confidentiality by exploiting the physics of the wireless communication channel without the need for exchanging secret cryptographic keys [1], [2]. The idea of a secure directional wireless link between a TX/RX pair is to preserve the signal information within a secure cone where the intended receiver is located while scrambling signals everywhere else to prevent eavesdropping. In a phased array, the same temporal digital information is fed to all the TX elements, transmitting the same information to all directions albeit at different power levels. This information can be recovered (especially at the side lobes) with a sensitive enough receiver. Spatial modulation with I, Q radiated out through separate antennas, and modulation of parasitic elements can distort the constellation in other directions [3], [4]. However, this one-to-one (bijective) mapping allows potential decoding by the eavesdropper, particularly using various signal processing and machine-learning-based classification techniques. Time modulation in an antenna array can incorporate such physical layer security through careful mapping of symbols to antennas in a time-modulated fashion.

Circulator is a key component in full-duplex wireless and radar detection systems. In this letter, a dual interference-canceling active quasi-circulator is proposed to enhance the isolation capability over the range of 1-7 GHz. The circulator is fabricated in the standard 0.18-μm CMOS process occupying 1.03 mm x 0.55 mm including the pads. Measurement results demonstrate more than 36-dB isolation from the Tx to the Rx within 6-GHz bandwidth. The designed circulator is a good candidate for duplexers to allow the integrated transmitter and receiver to share a single antenna in the certain short-range wideband wireless communication systems, where noise figure (NF) is not strictly demanded but low cost and high integration are urgently required.

Physical layer security incorporates security features embedded in the communication channels without the need to exchange cryptographic keys. Interest in exploiting such mechanisms has been increasing rapidly for 5G and beyond, due to the low overhead and low-latency properties of such encoding. Although phased arrays, by their nature of the focused beams to users, introduce secrecy, they are still vulnerable to eavesdropping at the sidelobes. In this article, we present a class of spatio-temporal modulated arrays (STMAs) with custom CMOS integrated circuits (ICs) and packaged antennas operating in the 71–76-GHz range that creates secure cones in space by preserving signal fidelity in the intended direction while emulating a time-varying channel outside the secure cone. At unintended directions, the architecture intentionally spectrally aliases signals to create noise-like features and scrambles constellations with a one-to-many mapping (including infinite constellation splitting), making it challenging to invert the mapping by eavesdroppers. Through the architecture, the secure cone can be reconfigured in space on demand and narrowed when we increase the number of elements. We also show how reconfigurable time modulation (such as through frequency chirping) can create a non-repetitive mapping of the constellation to protect against colluding attacks.

The effects of supply-induced frequency variations on single-ended tuning LC voltage-controlled oscillator (VCO) which degrade the jitter performance of the clock are investigated. The first-order impact on the supply sensitivity is that the varactor's effective capacitance varies with the supply voltage, with other second-order impacts attributed to commonly used capacitive bank and cross-coupled pairs. A compensation technique based on complementary varactors to improve the supply sensitivity of single-ended tuning LC VCO is proposed with no extra power dissipation, nor phase noise degradation within the relative frequency band of interest, along with the discussion on the operating principle of the compensation technique. Both the NMOS cross-coupled and complementary cross-coupled LC VCOs have been designed, demonstrating robust supply-insensitive performance over process, voltage, and temperature (PVT) variations. Prototyped oscillators were fabricated in a 0.18-μm CMOS process to verify both the theoretical analysis and the effectiveness of the proposed technique. Measurement results show that the compensated topologies exhibit more than 93% reduction in periodic jitter versus the noncompensated counterparts, with the figures of merit (FoMs) among the best compared with previous supply insensitive works.

Based on the dual-path cancellation methodology, a noise cancellation technique and an insertion loss (IL) mitigation technique are presented to improve the properties of the active quasi-circulators. The proposed circulator is fabricated with a standard 0.18-μm CMOS process, occupying an area of 0.91 mm x 0.49 mm including the pads. The measurement results show that 34-dB isolation is obtained over a wide frequency range from 1 to 8 GHz, while the IL is below 2.5 dB and the noise figure (NF) is less than 10 dB.