The development of a millimeter-wave transparent antenna integrated inside a headlamp for automotive radar application is presented. The antenna consists of two radiating elements: the primary and secondary ones. The primary antenna is the one that is fabricated on RF PCB material (e.g., patch, slot, sectoral horn) and connected directly to the transceiver chip, while the secondary antenna is made of optically transparent materials such as glass, but with a optical transparent electrically conductive coating, well known as transparent conductive oxide (TCO). This antenna is realized as a planar offset reflector to collimate and shape the incoming wave from the primary antenna. This reflector is designed based on the Fresnel theory and the reflectarray concept. The division of the primary and secondary antenna enables the placement of the radar module (that contains the primary antenna) at the base of the headlamp, and therefore it is concealed from the surroundings and hidden from the optical path of the light. The secondary antenna is inserted in the space between the headlamp cover and the light unit. The main challenge here is to provide a maximum on transparency in the visible range of the spectrum with a specially designed and laser-based generated microstructure for the resonant reflection of the radar wavelength. An antenna demonstrator has been fabricated, and together with the headlamp cover, the radiation pattern and realized gain are measured. We reported here the measurement results for several reflector designs and concluded that the headlamp cover gives minimal influence on the antenna performance.

Large truncated spherical near-field systems with conductive or absorbing floors are typically used in the measurement of the performances of vehicle-installed antennas. The main advantage of conductive floor systems is the ease of accommodation of the vehicle under test, but their performances are affected by the interaction with the reflecting ground floor. Instead, absorbing-based systems emulating free-space conditions minimize the effect of the interaction with the floor, but generally require longer setup times, especially at lower frequencies (70–400 MHz), where bulky absorbers are typically used to improve reflectivity levels. Considering scaled measurements of a vehicle model, the performances of these two typical implementations are analyzed in the 84–1500 MHz range and compared to free-space measurements. Absorbers with different dimensions and reflectivity have been installed in the scaled measurement setup, and measured data have been investigated with proper post-processing to verify the applicability to realistic systems. Figures of merit of interest for automotive applications, like gain and partial radiated powers, have been compared to free-space to evaluate the impact of different scenarios.

Wireless connectivity has been realized for multiple environments and different frequency bands. However, little research exists about mmWave communication in industrial environments. This paper presents the 60 GHz double-directional radio channel for mmWave communication in a ship hull for Line-of-Sight (LOS) and non-Line-of-Sight (NLOS) conditions. We performed channel measurements using the Terragraph channel sounder at different locations in the ship hull and fitted LOS path loss to a one-slope path loss model. Path loss and root-mean-square delay spread of the LOS path is compared to the reflected path with lowest path loss. NLOS communication via this first-order reflected path is modeled by calculating the path distance and determining the reflection loss. The reflection losses have a considerable contribution to the signal attenuation of the reflected path. The channel models are implemented in an indoor coverage prediction tool, which was extended with a ray launching algorithm and validated by comparison with an analytical electromagnetic solver. The results show that the mmWave radio channel allows high-throughput communication within a ship hull compartment, even when no LOS path between the transmitter and receiver is present.

A cost-effective millimeter-wave measurement setup for narrowband path loss and angle-of-arrival measurements is presented in this paper. The setup consists of ubiquitous radio-frequency lab equipment and additional low-cost components. An algorithm is developed, which improves the measurement accuracy and reduces the required measurement time. An uncertainty analysis is performed, including a noise analysis, amplifier linearity, antenna misalignment and general system impairments. A theoretical model of the received signal plus noise is developed, which is used in Monte Carlo simulations to show the impact of snapshot averaging on the uncertainty. The estimated combined uncertainty with a 95.45% confidence level is 1.1 dB at the maximum measurable path loss and 0.3 dB in the case of low path loss, where the uncertainty due to receiver noise is negligible. The measurement setup is used in outdoor specular building reflection measurements at 24.00–24.25 GHz. The measured single-building reflections show a 1–9 dB excess loss compared to the free-space path loss. The measured excess loss is 9–20 dB for double-building reflections. These results indicate that buildings could potentially be used as effective millimeter-wave specular reflectors to extend millimeter-wave coverage.

We present the design steps of a coaxial dipole antenna for telemetry applications under extreme conditions of accelerations and centrifugal forces. Both, electromagnetic and mechanical designs are explained, as well as performance compromises that have to be made between both domains. The experimental results are given in the following part of the article, before some details on the instrumented firings and the receiving station; at last a few examples of projectiles equipped with such antennas are presented.

Precise characterization of concealed person-worn objects will speed up the passenger screening process by reducing the rate of nuisance alarms, while also enhancing the airport security imaging systems. This paper presents an automatic, real-time method for wideband millimeter-wave radar identification of the nominal surface contours of the human body – even with affixed foreign objects or when a segment of the body cross-section is not captured by the radar – without relying on the body's bilateral symmetry. The developed method is verified experimentally when applied to the actual images generated by a laboratory airport scanning prototype developed recently by the US Department of Homeland Security (DHS). Our method uses the noisy collection of radar cross-section reflectivity data to extract the main contours and estimates the nominal body surface cross-sections through fitting a small-term Fourier series of circumferential variation. This is a necessary step for accurate characterizing of concealed terrorist threat objects affixed to the body.

Compressed sensing allows recovery of image signals using a portion of data – a technique that has drastically revolutionized the field of through-the-wall radar imaging (TWRI). This technique can be accomplished through nonlinear methods, including convex programming and greedy iterative algorithms. However, such (nonlinear) methods increase the computational cost at the sensing and reconstruction stages, thus limiting the application of TWRI in delicate practical tasks (e.g. military operations and rescue missions) that demand fast response times. Motivated by this limitation, the current work introduces the use of a numerical optimization algorithm, called Limited Memory Broyden–Fletcher–Goldfarb–Shanno (LBFGS), to the TWRI framework to lower image reconstruction time. LBFGS, a well-known Quasi-Newton algorithm, has traditionally been applied to solve large scale optimization problems. Despite its potential applications, this algorithm has not been extensively applied in TWRI. Therefore, guided by LBFGS and using the Euclidean norm, we employed the regularized least square method to solve the cost function of the TWRI problem. Simulation results show that our method reduces the computational time by 87% relative to the classical method, even under situations of increased number of targets or large data volume. Moreover, the results show that the proposed method remains robust when applied to noisy environment.

Advanced telecommunication systems are moving toward a high data transfer rate and wider bandwidth. The 5G communication network has recently been implemented for such aims. However, 5G networks operating with high operating frequency (typically above 20 GHz) could lead to impairments because of the atmospheric phenomena mainly precipitation and especially heavy rain. To address this, an optimum rain fade margin for the 5G network in Peninsular Malaysia is proposed using 77 sites of the rain-gauge network, which convert 1-h rain data to 1-min rain data by means of the international telecommunication union recommendation (ITU-R) P.837-7 model. Long-term rain attenuation statistics are obtained from ITU-R P.530-17 and the synthetic storm technique. The predicted rain attenuation is also presented in monthly statistics and in rain attenuation contour maps. The analysis showed that at 99.99% of link availability, the optimum rain fade margin operating at 26 GHz link should be in the range of 6.50 to 10 dB and 7 to 11 dB at 28 GHz link for a 5G network. Such information is useful for network operators and system engineers for the operation of 5G terrestrial microwave links in heavy rain regions.

The paper presents a numerical simulation of the propagation characteristics of symmetric E-type and H-type waves in microwave circular shielded waveguide with radially inhomogeneous dielectric filling. Using the modified Galerkin method, the calculation of a circular two-layer shielded waveguide was carried out, as a result of which the distribution of the electromagnetic field of the waveguide with linear and parabolic distribution of permeability was determined. The results obtained using the modified Galerkin method were compared with the results obtained using the classical partial domain method, which agree well enough.

An efficient analysis of time-modulated array (TMA) toward realizing less-attenuating radiation patterns with simultaneously suppressed sidelobe and sidebands is presented in this paper. In this framework, an optimal outer element-controlled time sequence is derived. The proposed time scheme, along with optimized array excitations, is profitably applied for the desired solution. TMAs are considered unconventional alternatives to the phased arrays. The desired array radiation features can be attained by periodically enabling and disabling the array elements through high-speed switches. Despite the advantages of architectural simplicity and real-time reconfigurability of periodic time sequences, time-domain antenna arrays inherently generate unavoidable sideband radiations (SRs). The undesired SRs obtained at multiple harmonics around the carrier frequency of the array resembles power loss in unintended directions. This paper aims to minimize the SRs as well as the sidelobe level (SLL) for an efficient analysis of time-modulated linear array (TMLA) with high-directive radiation patterns. The starting instants and the period of on-times are optimized to generate a unique shifted time scheme for the edge elements of the TMLA to reduce the sideband levels (SBLs). The array excitations and the uniform spacing between the elements are also optimized together with the shifted time scheme for the coveted solution. Other methods of suppressing SLLs and SBLs with shifted pulse schemes and sub-sectioned pulse schemes are also presented for a fair comparison. Modified versions of the particle swarm optimization algorithm (PSO) are applied for the desired solutions. The optimal results attained by wavelet mutation-based novel PSO is compared with the conventional PSO and the modified novel PSO-based results. The representative results are reported, and the superior performance abilities of the proposed method compared to other published studies are assessed.

In this article a compact circular monopole antenna is represented with dimensions of 38.87 × 24.00 × 1.60 mm3 applicable for WLAN/Wi-MAX and satellite band rejection characteristics. The impedance bandwidth is 9.42 GHz (3.12–12.54 GHz) for the final antenna with an equivalent fractional bandwidth of about 120.31%, producing triple notched bands centered at 3.95, 5.20 and 8.90 GHz with assistance of Archimedean spiral slot and incorporation of defected ground structure allowing WLAN (5.2 GHz), WiMAX (3.5 GHz) and higher satellite X-band (8.5 GHz) filtering abilities. Simulations of the antenna are performed to attain preferable return loss properties as well as gain and omni-directional radiation patterns. The suggested antenna yields a peak gain of about 7.46 dBi at 11.30 GHz and experimental values are in good obedience with simulated ones.

To design a low radar cross section (RCS) antenna, the major concern is not only to reduce scattering, but also to maintain its radiation parameters, viz. gain, voltage standing wave ratio (VSWR), etc. This paper presents a simple configuration of low RCS microstrip patch array with a periodic structure-based superstrate. The ground of the array is designed as reduced ground plane with high impedance surface elements, viz. rectangular patch and Jerusalem cross. The configuration of superstrate consists of multilayered, viz., two-layered and three-layered structures having partially absorbing and reflecting surfaces. In both the proposed configurations, the array gain of 12.5 dB is maintained with reduced structural RCS over the entire in-band frequency range. The reflection coefficient (~ −20 dB) and VSWR (~ 1.1) of the array are maintained. It is shown that the proposed superstrate-based patch array design has significantly reduced in-band RCS (−18 dBsm) at its resonant frequency.

The paper has proposed a multilayer, polarization rotation featured, low radar cross-section (RCS) antenna using electromagnetic band-gap (EBG)-based frequency selective surface (FSS) at 8.25 GHz. Cross-shaped EBG unit cells offer zero reflection phase and −25 dB reflection magnitude at 8.25 GHz. The FSS layer consists of eight cross-shaped EBG unit cells sandwiched between two substrates to offer high absorptivity at the desired band. The circular patch antenna resonating at 8.25 GHz is placed on the top substrate having a lower dielectric constant. Four circular-shaped patches are etched at the four corners of the top layer and are coupled with two feed lines which are aligned 90° to each other at the bottom layer and interconnected diagonally to achieve polarization rotation. The proposed antenna offers a gain of 6.72 dB and an in-band RCS of −21.4 dBsm. Incident energy is backscattered into eight directions separated by angle ϕ = 45°. The proposed antenna has the RCS reduction band of 7.7–9.4 GHz. It offers normalized polarization rotation ratio more than 0.8 within the −40° to 40° angular region at the frequency band 8–8.5 GHz. The measured result using the fabricated prototype agrees well with the simulated one.