Search for: All records

A reconfigurable substrate integrated waveguide (SIW) filtenna operating in the 5G millimeter Wave (mmWave) band is presented, where varactors are integrated into the filtering-antenna structure to change the resonant frequency and coupling between the SIW resonators. The proposed structure allows for the reconfigurability of the antenna radiation frequency band in the range of 24-27 GHz, covering most of the 3GPP n258 band, with a constant bandwidth of 400 MHz and broadside radiation pattern. A prototype of the proposed mmWave filtenna is designed and fabricated, where the measurement results are in good agreement with the simulation. The proposed cost-effective and scalable filtenna is an ideal candidate for deployment in 5G wireless networks, with the ability to reduce adjacent channel interference (ACI) and enable passive spectrum coexistence with weather sensors in the 23.8 GHz band. 

The allocation of the 5G mmWave spectrum in the 26 GHz range, known as 3GPP band n258, has raised wide concern among the remote sensing and weather forecast communities due to the adjacency of this band with a frequency band used by passive sensors in Earth Exploration-Satellite Service (EESS). The concern stems from the potential radio frequency interference (RFI) caused by transmissions in the n258 band into the 23.8 GHz frequency, one of the key frequencies employed by weather satellite passive sensing instruments, such as AMSUA and ATMS, to measure atmospheric water vapor using its emission spectrum. Such RFI can bias satellite observations and compromise weather forecasting. In this paper, we develop a modeling and numerical framework to evaluate the potential effect of the 5G mmWave n258 band’s commercial deployment on numerical weather forecast accuracy. We first estimate and map the spatio-temporal distribution of 5G mmWave base stations at the county-level throughout the contiguous United States (US) using a model for technology adoption prediction. Then, the interference power received by the AMSU-A radiometer is estimated for a single base station based on models for signal transmission, out-of-band radiation, and radio propagation. Then, the aggregate interference power for each satellite observation footprint is calculated. Using the contaminated microwave observations, a series of simulations using a numerical weather prediction (NWP) model are conducted to study the impact of 5G-induced contamination on weather forecasting accuracy. For example, our results show that when the interference power at the radiometer from a single base station is at a level of −175 dBW for a network of base stations with spectral efficiency of 15 bit/s/Hz/BS, the aggregate interference power has limited impact in the year 2025 but can result in an induced noise in brightness temperature (contamination) of up to 17 K in the year 2040. Furthermore, that level of RFI can significantly impact the 12-hour forecast of a severe weather event such as the Super Tuesday Tornado Outbreak with forecasting errors of up to 10 mm in precipitation or a mean absolute error of 12.5%. It is also estimated that when the level of interference power received by the radiometer from a single base station is −200 dBW, then there is no impact on forecasting errors even in 2040. 

Abstract Recent advancement in digital coding metasurfaces incorporating spatial and temporal modulation has enabled simultaneous control of electromagnetic (EM) waves in both space and frequency domains by manipulating incident EM waves in a transmissive or reflective fashion, resulting in time-reversal asymmetry. Here we show in theory and experiment that a digitally space-time-coded metamaterial (MTM) antenna with spatiotemporal modulation at its unit cell level can be regarded as a radiating counterpart of such digital metasurface, which will enable nonreciprocal EM wave transmission and reception via surface-to-leaky-wave transformation and harmonic frequency generation. Operating in the fast wave (radiation) region, the space-time-coded MTM antenna is tailored in a way such that the propagation constant of each programmable unit cell embedded with varactor diodes can toggle between positive and negative phases, which is done through providing digital sequences by using a field-programmable gate array (FPGA). Owing to the time-varying coding sequence, harmonic frequencies are generated with different main beam directions. Furthermore, the space time modulation of the digitally coded MTM antenna allows for nonreciprocal transmission and reception of EM waves by breaking the time-reversal symmetry, which may enable many applications, such as simultaneous transmitting and receiving, unidirectional transmission, radar sensing, and multiple-input and multiple-output (MIMO) beamformer. 

The utilization of newer spectrum bands such as in 5G and 6G networks, has the potential to inadvertently cause interference to passive sensing applications operating in the adjacent portions of spectrum. One such application that has received a lot of attention has been passive weather sensing where leakage from 5G mmWave band transmissions in the 26 GHz spectrum could potentially impact the observations of passive sensors on weather prediction satellites. To mitigate problems such as the above, we present a design framework that can be employed in mmWave networks by using filtennas (or filtering antennas) at the transmitter along with integrated resource allocation to minimize leakage into adjacent channels. Specifically, we propose an Iterative Leakage Aware Water Filling solution to allocate power and bandwidth in a system employing filtennas that guarantees performance requirements while reducing the leakage. In addition, a key contribution of this work is the characterization of the leakage function based on the order of filtennas which is incorporated in our resource allocation framework. 

Novel transmission schemes, enabled by recent advances in the fields of metamaterial (MTM), leaky-wave antenna (LWA) and directional modulation, are proposed for enhancing the physical layer (PHY) security. MTM-LWAs, which offer compact, integrated, and cost-effective alternatives to the classic phased-array architectures, are particularly of interest for emerging wireless communication systems including Internet-of-Things (IoT). The proposed secure schemes are devised to accomplish the functionalities of directional modulation (DM) transmitters for orthogonal frequency-division multiplexing (OFDM) and non-contiguous (NC) OFDM transmissions, while enjoying the implementation benefits of MTM-LWAs. Specifically, transmitter architectures based on the idea of time-modulated MTM-LWA have been put forth as a promising solution for PHY security for the first time. The PHY security for the proposed schemes are investigated from the point of view of both passive and active attacks where an adversary aims to decode secret information and feed spurious data to the legitimate receiver, respectively. Numerical simulations reveal that even when the adversary employs sophisticated state-of-the-art deep learning based attacks, the proposed transmission schemes are resistant to these attacks and reliably guarantee system security.