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Innovating passive and chipless coded landmarks have recently emerged for high accuracy self-localization systems. Existing landmarks make use of the combination of retro-directive devices, corner reflectors and lenses, with a coding particle in order to give a high RCS response over a wide angle. In this paper, with a consideration of important practical parameters unappreciated in existing designs, we propose a wide-angle retro-directive frequency-coded lens based on a curved one-dimensional Photonic Crystal (PhC) resonator. The proposed frequency-coded lens is made of two parts: a homogenous lens and a curved PhC resonator where the resonator is located along the lens focal line. A frequency coding is used, where the presence or absence of a notch frequency in a specified information channel encodes an information bit. A PhC resonator provides unique advantages over existing coding particles due to its continuity along the lens focal line which creates a stable ID appearance over wide-angle. In addition, the potential of coding in its volume, rather than on the surface, allows for a high coding capacity. Two frequency-coded lenses with single and dual defect resonators are EM simulated, fabricated, and experimentally validated in the W-band (75 GHz-110 GHz). Simulated results show that a wide detection angle of 170° can be achieved where the tag ID is maintained over all angles. A wide retro-directivity of 80° and 60° is experimentally demonstrated for frequency-coded lenses by a single defect (single notch) and a dual defect (double notch) PhC resonator, respectively. CA Alhaj Abbas

This paper reports the far-distance achievable reflected paths of indoor material groups such as glass, wood, paper , and plastic at frequencies ranging from 270 GHz to 330 GHz. A VNA equipped with ~ 25.45 dBi horn antenna as transceiver is employed to retrieve and evaluate these reflections. The beam spot size illuminated by the horn antenna from a distance of interest to the material under test (MUT) is aforethought and considered during the channel sounding. Thus, approximately 14.4 m long reflections are detected. The knowledge of the reflective properties of indoor building materials is virtuous in terms of facilitating propagation modeling and design of efficient future indoor wireless systems at terahertz (THz) frequencies. The results obtained taking into account the beam spot size are the first ever published.

One-dimensional Photonic Crystal (1D PhC) resonator is recently introduced as a good nominee to replace conventional tags at mm-wave and THz bands. For a use of such tags as landmarks in mm-wave indoor self-localization systems, an augmentation of their RCS is required to improve the reading range. As a solution, we propose the integration of a 1D PhC resonator with a dielectric lens (i.e. frequency coded lenses). This concept is demonstrated by locating a 1D PhC resonator in the focal area of a spherical dielectric lens made of PolyPropylene (PP) material with a relative permittivity of 2.0. On the other hand, the PhC resonator is designed by introducing a defect layer between two quarter-wave Bragg mirrors in order to produce a notch signature in the backscattering. Two frequency coded lenses of 24 mm and 40 mm diameter are simulated, fabricated, and experimentally examined. Results show that these coded lenses can achieve 9 dB and 14 dB improvement in RCS, respectively.

The problem of wave propagation and scattering at terahertz (THz) frequencies has become increasingly important, in particular for accurate modeling of future indoor wireless communication channels. The reflective properties of indoor materials with different surface roughness and dielectric constants are important to explore diffuse scattering for accurate channel modeling. First and foremost, a terahertz Swissto12 system is adopted to obtain the first ever transmission measurements for a wide choice of indoor material groups, such as wood, plastic , and brick at frequencies from 750 GHz to 1.1 THz using up-conversion (frequency-domain) method. Both the reflection ( $S_{11}$ , $S_{22}$ ) and transmission coefficients ( $S_{12}$ , $S_{21}$ ) are measured using this novel and noninvasive electromagnetic technique. The inversion method based on Kramers–Kronig (K-K) relations is then applied to convert the calibrated scatter data into intrinsic material properties (i.e., refractive index, permittivity, absorption coefficient). Then, the surface topography of rough material samples is acquired using surface measurement instruments. Further, the optically smooth $(\sigma _{h} /\lambda \ll 1)$ materials are assorted as most to least rough based on Rayleigh roughness factor. Lastly, the ray tracer considering the Rayleigh-Rice (R-R) scattering model is employed to obtain the maximum achievable reflected paths of the above-mentioned indoor material samples at 300 GHz followed by their experimental validation.

To achieve 1 Tb/s wireless links considering simplified modulation schemes, that are in short-range and at terahertz (THz) frequencies, the quest for overwhelming extreme bandwidths is self-evident. In this paper, we analyze the channel performance and limitations of THz communication systems at 300 GHz carrier frequency due to the horn-antenna beam misalignment in line-of-sight (LoS) scenario. Firstly, a ray-tracer is employed to examine the implications of beam spot size for varied distances. Then, these effects are studied in terms of link coverage and the achievable data rates when altering the antenna positions horizontally and vertically. A VNA-based 300 GHz transmission system is used to experimentally validate the above mentioned implications in terms of distance and antenna positions. Finally, the impact of beam spot size is studied by rotating the antennas. To the best of our knowledge, this work reports the first ever recorded implications of beam spot size on the THz wireless links.

In radar systems, the frequency range is being extended to high frequencies such as THz for sub-mm resolution. The spectrum offers high resolution but on the contrary, propagation distance and penetration depth are limited because of smaller wavelength. It suffers from higher atmospheric absorption in comparison to sub-GHz systems. In comparison to optical technology, the radar technique majorly benefits with respect to the penetration property such as cloud/smoke cover penetration and detection of concealed objects. However, the THz range and synthetic aperture radar (SAR) imaging of concealed objects are not very well established. Therefore, this paper examines this property at THz. A testbed has been set up with a bandwidth of 110 GHz at a carrier frequency of 275 GHz. The imaging is performed of a very small metal object. Firstly, the sub-mm resolution is validated with the experiment after that the range and SAR imaging are performed in which this object is covered with different types of materials. The backscattered data is processed with the image reconstruction algorithms and the results are presented in this paper with respect to sub-mm resolution and detection. © 2020 IEEE.

Full-Duplex (FD) is an emerging technology that allows the communication device to use the same frequency to simultaneously transmit and receive. The cancellation of the high power Self-Interference (SI) is the main challenge in FD systems. Hybrid SI mitigation and cancellation schemes in propagation, analog, and digital domains, have to be used in order to mitigate the SI. Antenna selection (AS) can be employed to select the best antenna, or set of antennas, that guarantees jointly the maximization of the desired signal, and the minimization of SI. In this paper, we aim to experimentally enable FD transmission in an indoor femto base-station (BS) with antenna selection. Receive antenna selection is combined with cross-polarization and antennas conditional placement in order to achieve the required SI cancellation. Half-duplex (HD) Uplink (UL) user-equipments (UE) are used to measure the effect of downlink (DL) SI on the UL reception at the FD BS receiver. Different scenarios are experimented in the testbed such as, changing the number of antennas, the type of isolation (vertical/horizontal), and the type of antennas (Omnidirectional/directional). Three AS criteria are used, and the performance of the system is evaluated in terms of bit-error-rate, sum-rate, residual SI, and FD/HD sum-rate enhancement ratio. The measurement results show that the proposed hybrid solution is feasible to enable FD transmission in the considered scenario. OA Förderung 2019

Channel measurements across 300 GHz to 310 GHz spectrum are performed to realize the ultra-broadband wireless communication channel behaviour for various channel configurations in lecture room environment. At terahertz (THz) frequencies, it is believed that high directional antenna based line-of-sight (LoS) communication possibly achieves terabitper-second (Tbps) links. Thereupon, the VNA-based channel measurements are performed using 26 dBi horn antennas at both the transmitter (TX) and receiver (RX) sides for retrieving the channel parameters (i.e., path loss exponent, shadowing factor) to derive the single-slope path loss model in LoS scenario for distances up to 5 m. Moreover, the results are also evaluated with waveguide antenna (open) for horn-open, and open-open configurations to estimate the propagation losses for different antenna directivities. So far, the results from such a long-distance channel measurement campaign are not recorded yet.