This work presents the implementation of a synthetic aperture radar (SAR) at 77 GHz, for automotive applications. This implementation is unique in the sense that it is a radar-only solution for most use-cases. The set-up consists of two radar sensors, one to calculate the ego trajectory and the second for SAR measurements. Thus the need for expensive GNSS-based dead reckoning systems, which are in any case not accurate enough to fulfill the requirements for SAR, is eliminated. The results presented here have been obtained from a SAR implementation which is able to deliver processed images in a matter of seconds from the point where the targets were measured. This has been accomplished using radar sensors which will be commercially available in the near future. Hence the results are easily reproducible since the deployed radars are not special research prototypes. The successful widespread use of SAR in the automotive industry will be a large step forward toward developing automated parking functions which will be far superior to today's systems based on ultrasound sensors and radar (short range) beam-forming algorithms. The same short-range radar can be used for SAR, and the ultrasound sensors can thus be completely omitted from the vehicle.

This study provides an analytic method for the calculation of the cutoff frequencies and waveguide modes of a partially filled eccentric coaxial cable. The method is based on the expressions of the involved electromagnetic fields in bipolar coordinate systems and the validity range of the solution is discussed. It is shown how the waveguide geometry and dielectric parameters may be selected to engineer the lined waveguide's spectral response. Numerical results are included which show good agreement with the corresponding results from full-wave simulations by commercial software.

In this paper, a super-compact ultra-wideband (UWB) metamaterial absorber (MMA) is presented. The absorber design consists of an inverted L-shaped structure and a diagonal rectangular-shaped structure. The capacitive coupling between these two structures not only provides UWB nature but also provides a super-compact absorber design. The dimension of the unit cell arrangement is 5 × 5 mm2 and printed on a low-cost FR-4 substrate of thickness 1.54 mm (0.061λlowest). The design absorber provides more than 97% absorptivity from 12 to 21 GHz for normal incidence electromagnetic (EM) wave. However, the proposed MMA has a full width at half maximum absorption bandwidth of 11.71 GHz from 10.34 to 22.05 GHz. Moreover, the surface current distributions have been analyzed to understand the absorption mechanism of the MMA. The stability of the proposed design is validated with different incident angles (for TE and TM modes) and different polarization angles. Finally, the absorber design is fabricated and verified experimentally. Furthermore, the UWB frequency range, high absorption, ease in design and fabrication, and cost-effective make it suitable for different quality applications in stealth technology, thermal imaging, radar detection, antenna systems, and other EM devices.

The design of integrated systems requires the knowledge of the values of the effective permittivity of the substrate. Designing antenna using computer-aided design tools is a long process that necessitates doing iterative steps to find the correct dimensions that meet specific requirements at a certain operating frequency. The objective of this work is to propose an analytic model to reduce the time required for the design. By using electromagnetic simulation, the effect of the relative permittivity and the height of the substrate on the final effective permittivity have been studied. An analytic model that helps the designer in estimating the value of the effective permittivity has been proposed.

This research involves a compact wideband circularly-polarized antenna array, which consists of a sequential rotating phase feed network, 2 × 2 mushroom-type metamaterial (MTM) unit, and so on. Each antenna array unit contains a microstrip feedline, an L-shaped slot antenna, and so on. The MTM-based antennas were incorporated with a sequential-phase network of sequentially rotated series-parallel feed to achieve wideband operation. The operational bandwidth and the radiation model in the high-frequency area were improved through the adjustment of spacing between the L-shaped slots while maintaining the size and structure of the MTM. The proposed design had dimensions of 80 mm × 80 mm × 3.5 mm (~1.64 λ0 × 1.64 λ0 × 0.072 λ0 at 6.15 GHz), and it was simulated, fabricated, and tested.

A separately-designable diplexer with multiple transmission zeroes (TZs) using common stub-loaded stepped impedance resonator (SIR) is proposed. The common stub-loaded SIR operating in third harmonic (f3) and fifth harmonic (f5) is used for designing the two diplexer channels. The stub is loaded at the voltage-null point of f3 of the SIR. It can separately control f5 but has no effect on f3 so that the two channels can be separately designed. Meanwhile, the input port is tap-connected to the common stub-loaded SIR, which necessarily produces a TZ between f3 and f5, existing in both channel filtering responses. By properly choosing coupling schemes of the two channels, more TZs are realized at the desired locations. Thanks to the generation of the multiple TZs, both passband selectivity and isolation between the two channels are improved significantly. For demonstration, a diplexer operating at 2.22 and 2.95 GHz is designed, fabricated, and measured. The simulated and measured results are presented, showing good agreement.

An integral equation-fast Fourier transform (IE-FFT) algorithm is applied to the electromagnetic solutions of the combined field integral equation (CFIE) for scattering problems by an arbitrary-shaped three-dimensional perfect electric conducting object. The IE-FFT with CFIE uses a Cartesian grid for known Green's function to considerably reduce memory storage and speed up CPU time for both matrix fill-in and matrix vector multiplication when used with a generalized minimal residual method. The uniform interpolation of the Green's function on an equally spaced Cartesian grid allows a global FFT for field interaction terms. However, the near interaction terms do not take care for the singularity of the Green's function and should be adequately corrected. The IE-FFT with CFIE does not always require a suitable preconditioner for electrically large problems. It is shown that the complexity of the IE-FFT with CFIE is found to be approximately O(N1.5) and O(N1.5log N) for memory and CPU time, respectively.

This study presents an ultra-wideband receiver front-end, designed for a reconfigurable frequency modulated continuous wave radar in a 130 nm SiGe BiCMOS technology. A variety of innovative circuit components and design techniques were employed to achieve the ultra-wide bandwidth, low noise figure (NF), good linearity, and circuit ruggedness to high input power levels. The designed front-end is capable of achieving 1.5–40 GHz bandwidth, 30 dB conversion gain, a double sideband NF of 6–10.7 dB, input return loss better than 7.5 dB and an input referred 1 dB compression point of −23 dBm. The front-end withstands continuous wave power levels of at least 25 and 20 dBm at low band and high band inputs respectively. At 3 V supply voltage, the DC power consumption amounts to 302 mW when the low band is active and 352 mW for the high band case, whereas the total IC size is $3.08\, {\rm nm{^2}}$.

A significant excitation of toroidal moments in cylindrically arranged dogbone metallic inclusions is validated and presented in this paper. The antiparallel poloidal currents excited on the front and back faces of the proposed cylindrical dogbone inclusions create strong magnetic field confinement at the center generating intense toroidal moments on the structure. The significant excitation of toroidal dipole moment causes an improvement in the scattering cross-section from the resonant system. The resonant mechanism is analyzed using the multipole scattering theory, and we used the scattering measurement techniques to characterize the structure experimentally in the microwave regime.

A compact ultrawideband (UWB) bandpass filter (BPF) is designed by harnessing the efficacy of a Pythagorean tree fractal shape stub-loaded resonator. The design inherently provides the passband transmission poles, which make it convenient to be used in wide passband filtering circuits. The number and the position of the resonating modes can be controlled by increasing the iterations of the Pythagorean tree, as analyzed using odd- and even-mode analysis. Design steps of the BPF are detailed. The designed UWB BPF takes up a small circuit area of (12.13 × 9.59) mm2. The proposed design is fabricated and measured to verify the simulated results. The stopband is extended up to 17.5 GHz with a maximum attenuation of 15 dB.

This paper introduces a new maritime search and rescue system based on S-band illumination harmonic radar (HR). Passive and active tags have been developed and tested while attached to life jackets and a small boat. In this demonstration test carried out on the Baltic Sea, the system was able to detect and range the active tags up to a distance of 5800 m using an illumination signal transmit-power of 100 W. Special attention is given to the development, performance, and conceptual differences between passive and active tags used in the system. Guidelines for achieving a high HR dynamic range, including a system components description, are given and a comparison with other HR systems is performed. System integration with a commercial maritime X-band navigation radar is shown to demonstrate a solution for rapid search and rescue response and quick localization.

In this paper, a stacked microstrip patch antenna with polarization reconfigurable property has been proposed for worldwide interoperability for microwave access (WiMAX) application. The proposed antenna has two substrate layers: upper and lower layers with two radiating patches connected with the coaxial probe. Without the upper layer the lower square-shaped substrate layer having regular hexagonal radiating patch with probe fed acts as a linear polarized antenna with impedance bandwidth for (S11 ≤ −10 dB) is 370 MHz 10.56% (3.32–3.69 GHz) cover WiMAX (3.4–3.69 GHz) application band. The hexagonal radiating patch is perturbed with an optimum rectangular slot to enhance the impedance bandwidth of the antenna. The lower substrate layer having hexagonal patch with the same probe position is stacked with the upper square-shaped substrate layer with same sized square patch and the upper patch soldered with the coaxial probe. The overall stacked antenna generates a circularly polarized band when the opposite corner of the top square radiating patch of the upper layer is truncated with optimum size. In order to generate another circularly polarized band and to improve the input impedance matching of the stacked antenna, the top radiating patch is perturbed with two slots and a slit. The stacked circularly polarized antenna generates impedance bandwidth of 12.75% (3.23–3.67 GHz) for (S11 ≤ −10 dB) with two circularly polarized bands (3.34–3.37 GHz) and (3.66–3.70 GHz) as per (axial ratio ≤ 3 dB) for WiMAX application. Therefore, the proposed antenna can be used as linearly polarized or dual band circularly polarized according to requirement.

In this paper, a novel design of ultra-wide stop-band single-side single-layer frequency selective surface (FSS) is presented. The unit cell of the proposed FSS is designed using the combination of conventional square loop and cross (CSLC). To enhance the bandwidth of this structure, an additional cross is inserted in all the four quadrants of CSLC. The stop-band transmission bandwidth assuming −10 dB threshold is found to be 128.94% (2.16–10 GHz) which is 34.33% more as compared to the bandwidth of CSLC. The unit cell with a dimension of 16 × 16 mm2 is printed on one side of an FR4 substrate. The design is fabricated and the measured results are found to be in good agreement with the simulated results. The design provides excellent stability for both transverse magnetic and transverse electric polarizations. The design is very flexible, where any resonant frequency can be achieved by changing the length of unit cell. The design is useful in many applications such as antenna gain enhancement, electromagnetic wave shielding for Wi-Fi/5G systems, and other Internet of Things-based applications.

This paper presents a fully integrated three-way Doherty architecture to address the challenges of 5G applications using laterally-diffused metal-oxide semiconductor (LDMOS) technology. By using the so-called CDS cancelation method for the Doherty combiner design, a wideband impedance transformation is achieved, that combined with the three-way Doherty power amplifier (DPA) architecture allows for high efficiency in deep back-off, with a reduced load modulation for high bandwidth. Throughout this paper, the design approach and realization are described, while multiple critical design challenges will be addressed such as low frequency drain resonance optimization, impact of in-package coupling effects, and linearity versus efficiency tradeoff. Two state-of-the-art three-way fully integrated LDMOS DPA monolithic microwave integrated circuit (MMICs) are presented to demonstrate how these measures have been successfully applied to different power amplifier (PA) line-up components for 5G base station systems. First, a 60 W 1.8–2.2 GHz multi-stage device for driver application in true dual-band operation is presented. The circuit design pays special attention to extended PA video bandwidth thanks to integrated passive device. After digital pre-distortion (DPD) in dual-band operation, this highly linear device achieves an outstanding adjacent channel leakage ratio (ACLR) of −56 dBc for a 2cLTE 20 MHz 8 dB peak-to-average ratio signal spaced by 345 MHz, thus 385 MHz instantaneous bandwidth (IBW), with 29% efficiency at 35 dBm, 12 dB output back-off (OBO). Second, the simulation and measurement results of a 55 W 2.6 GHz multi-stage DPA for massive-MIMO final stage application are presented, which yields an excellent linearized efficiency of 49% using a 200 MHz 10cLTE signal with an ACLR lower than −47.5 dBc. For 8cLTE 20 MHz (160 MHz IBW), the device yields 50% efficiency with −50.7 dBc ACLR linearized after DPD. The achieved efficiency is well comparable to published GaN DPAs. These results were achieved by improved simulation techniques to minimize frequency dispersion and thus allow high efficiency operation over wide bandwidth. Both devices show that LDMOS is not only a mature technology which allows those PAs to be reliable and low-cost for mass production in very compact packages, but also provide best-in-class RF performance according to the needs of 5G base station systems.

This paper reports an integration of dual band microstrip antenna with thin film amorphous silicon solar cell which creates a wearable system to harvest microwave energy. The multiple layers in the encapsulation of the thin film solar cell are used as a substrate for microstrip antenna. The rectifier and matching circuit are designed on cotton jeans material and the whole system is mechanically supported by the foam of 5 mm thick. The performance of the antenna is studied for the mechanical bending condition. The device has maintained good power conversion efficiency. The efficiency of the voltage doubler is tested by varying radio frequency power levels from −30 to10 dBm. The voltage doubler conversion efficiency at 1.85 and 2.45 GHz are 58 and 43%, respectively, for a load of 7.5 kΩ for an input power level of −5 dBm.

Microstrip and stripline losses in Method of Moments (MOM) calculations have an error arising from the large current density at the strip edges, characterized by an integration limit (W/2-d) in the equation for current density in thin strips (width W), where d is a fitting parameter. It depends primarily on the width of the MOM subsection on the edge of the strip. By comparing with the integration limit (W/2-Δ) for an actual strip with finite thickness, a correction factor is estimated. The equations incorporating d are confirmed by comparing with MOM calculations of isolated stripline, uniformly spaced parallel strips, striplines and microstrips close to ground planes, and with a strip in a uniform, externally applied magnetic field. The results are also consistent with measurements with copper. This makes the accuracy of the loss estimates commensurate with the excellence of the other aspects of MOM simulations.

A frequency diverse array (FDA) radar has attracted wide attention, due to its capability to provide a range-angle dependent beampattern and to scan the spatial without phase shifters or rotating arrays. However, FDA systems will suffer from low echo signal energy or high sidelobe peaks when detecting targets by beamforming based on existing receivers. To reduce the sidelobe peak of detection results while increasing the echo signal energy, in this paper, we propose an FDA radar system based on diversity linear frequency modulation waveforms. Correspondingly, we propose a receiver architecture with a time-variant beamforming chain. The proposed system retains the ability of the FDA system to automatically spatial beam scanning, owing to the frequency increment across elements. By increasing the pulse duration of transmitted signals, we enhance the echo signal energy. By applying the artificial bee colony algorithm to design the bandwidth of each chirp signal, the proposed system reduces the sidelobe level of detection results while increasing pulse width. Numerical simulation results are presented to demonstrate the effectiveness of the proposed system.

A mode converter design using the concept of periodic substrates loading in a circular waveguide, to convert TM01 mode to TE11 mode is presented in this paper. The detailed design principle, simulation, and measurement results are included in this study. Simulation results show that the purity of output fundamental TE11 mode of the converter approaches 99.2% for an operating frequency of 3.2 GHz. The mode conversion efficiency is more than 90% over 3.07–3.25 GHz band and the relative bandwidth is 5.6% (180 MHz). The proposed TM01–TE11 mode converter has advantages, such as the compact, lightweight structure, high conversion efficiency, and proper bandwidth. The fabrication cost is relatively low and the structure is easy to fabricate. The power-handling capability is limited to 10 MW due to dielectric-based design. The compactness and portability of the system (e.g. Space applications, Accelerators, High Power Microwave) can be improved significantly using the proposed mode converter.

In this paper, a new empirical path loss model based on frequency, distance, and volumetric occupancy rate is generated at the 3.5 and 4.2 GHz in the scope of 5G frequency bands. This study aims to determine the effect of the volumetric occupancy rate on path loss depending on the foliage density of the trees in the pine forest area. Using 4.2 GHz and the effect of the volumetric occupancy rate contributes to the literature in terms of novelty. Both the reference measurements to generate a model and verification measurements to verify the proposed models are conducted in three different regions of the forest area with double ridged horn antennas. These regions of the artificial forest area consist of regularly sorted and identical pine trees. Root mean square error (RMSE) and R-squared values are calculated to evaluate the performance of the proposed model. For 3.5 and 4.2 GHz, while the RMSEs are 3.983 and 3.883, the values of R-squared are 0.967 and 0.963, respectively. Additionally, the results are compared with four path loss models which are commonly used in the forest area. The proposed one has the best performance among the other models with values 3.98 and 3.88 dB for 3.5 and 4.2 GHz.

This paper presents a rollable metamaterial screen for high-efficiency wireless power transfer (WPT) system based on magnetic resonance coupling, which operates at 4.5 MHz. The rollable metamaterial screen with a fully expanded area of 750 mm × 750 mm is located in the middle between transmitter and receiver coils and focuses the magnetic field and, by such a way, significantly improves power transfer efficiency (PTE). The metamaterial screen can be rolled up, e.g. onto the ceiling when it is not used, and thus does not require any designated space for the screen saving space. A WPT system with the rollable metamaterial screen is designed, fabricated, and characterized. Improved PTE is qualitatively and quantitatively verified by light bulb experiments and vector network analyzer measurements. The PTE of the WPT system with the metamaterial screen increases from 36 to 58.52% and 10.24 to 31.36% for the distances between the transmitter and receiver coils 100 and 150 cm, respectively. The effects of lateral and angular misalignments on the PTE of the WPT system are also studied. Obtained results show that the rollable metamaterial screen improves the PTE even at the misaligned condition.