In this research study, a compact dual-polarized co-radiator ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with improved impedance bandwidth and isolation is proposed for wireless applications. The designed co-radiator has an overall area of 0.3λo × 0.3λo mm2 (where, λo is free space wavelength corresponding to the lower cut-off frequency, i.e., 3.1 GHz). The proposed resonator comprises of a hybrid geometry which is created with the combinations of a circular-shaped patch, a square, and two rectangular stubs. It is centrally aligned between two 50 Ω micro-strip feed lines that are positioned orthogonal to each other. Further, the modified ground plane is attached with the end-loaded line which provides broadband isolation over entire UWB frequency band. The simulated results of the proposed antenna exhibit wideband characteristics with impedance bandwidth of 3.1–16.9 GHz with minimum isolation of −15 dB. Moreover, all the radiation performance parameters are analyzed and discussed. Some important diversity parameters such as envelope correlation coefficient, mean effective gain, effective diversity gain, and channel capacity loss have also been evaluated. Furthermore, all the measured results of proposed antenna agree well with the simulated results which make the proposed antenna a suitable candidate for UWB-MIMO wireless applications.

This paper presents the design of all dielectric non-absorptive phase gradient reflective surfaces that can be used to manipulate the reflected electromagnetic waves at millimeter-wave regime. Compared with a bare perfect electrical conductor reflector which obeys the classical Snell's law of reflection, the presented design can effectively alter both the shape and level of the backscattered energy and thus radar cross section (RCS) reduction is achieved in the specular direction. One- and two-dimensional phase gradient reflective dielectric surfaces of phase change about 72° across their apertures are designed and their ability to manipulate the reflected waves under normal incidence are investigated both by means of full-wave simulations and experimentally tested for validation. More than 6 dB of specular RCS reduction is achieved from about 66.5–78.2 GHz.

A circularly polarized high-power antenna with higher-order mode excitation (TM01) is presented in this paper. The proposed structure consists of metal plates placed on the conical horn antenna's aperture for achieving TM01 to circular polarized TE11 mode conversion at the output. The structure is simulated on CST Microwave Studio. The designed antenna exhibits high gain and a directive radiation pattern. The axial ratio of the proposed structure is below 3 dB. The simulated and measured reflection coefficient for TM01 mode excitation is below −10 dB over a frequency range of 2.95–3.13 GHz. The structure is purely metallic, and the calculated high-power microwave (HPM) capability is up to the MW level. The proposed antenna is helpful for portable HPM systems.

Radar sensors are key components of modern driver assistance systems. The application of such systems in urban environments for safety applications is the primary goal of the project “Radar on Chip for Cars” (RoCC). Major outcomes of this project will be presented and discussed in this contribution. These outcomes include the specification of radar sensors for future driver assistance systems, radar concepts, and integration technologies for silicon-germanium (SiGe) MMICs, as well as the development and evaluation of a system demonstrator. A radar architecture utilizing planar antennas and highly integrated components will be proposed and discussed with respect to system specifications. The developed system demonstrator will be evaluated in terms of key parameters such as field of view, distance, and angular separability. Finally, as an outlook a new mid range radar (MRR) will be introduced incorporating several concepts and technologies developed in this project.

A new Ku-band reflectarray with an artificial anisotropic slab that consists of periodic holes, backed by a planar artificial magnetic conductor (AMC) is proposed. The unit-cell of the reflectarray is a two-layered structure that consists of a dielectric with a hole on a grounded patch. The phase diagram of the proposed unit-cell is calculated by a full-wave computational technique, which uses the dyadic Green's function evaluated by an equivalent transmission line modeling in the spectral domain. The obtained dyadic Green's function is used in an integral equation formulated for the surface current densities on the metallic grating. The resultant integral equation is then solved using the method of moments. The required phase shift at Ku-band is obtained by changing the radius of holes in the artificial slab. The introduced unit cell has linear phase range between 13.95 and 14.95 GHz. It is shown that this frequency band is the usable bandwidth of AMC structure. Finally, the designed reflectarray is analyzed using a full-wave electromagnetic solver. The numerical results show a maximum gain of 27.4 dBi, and 48.09% efficiency, at 14.45 GHz with 4.15% 1-dB gain bandwidth for the designed 21 × 21 cm2 reflectarray.

Delay time measurements are a commonly used technique for the characterization of dielectric materials. Especially with regard to the characterization of water–solid mixtures like soil or grain delay time measurements, e.g., time domain reflectometry offers a powerful method. However, the accuracy of reflection measurements is limited due to multiple reflections caused by inhomogenities of the environmental material of the sensor. This contribution deals with an improved sensor design based on time domain transmission (TDT) measurements. Thus, the first received impulse includes the necessary information. Multiple reflections are received at later time steps and their influence on the measurement accuracy is nearly negligible. To improve the performance and the applicability of the designed sensor, a cost–efficient TDT system is designed, which is integrated in the sensor. Additionally, a so-called “concentric reversion coupler” is used, which offers the possibility to perform TDT measurements without the necessity of external measuring ports.

A compact, two-element textile MIMO antenna is designed with enhanced isolation by using modification in the ground, open-ended slots along with shorting pins. Maximum 27.8 dB isolation is achieved in two-element antennae, where the edge-to-edge distance is kept at 0.19 λ0 which is less than the conventional half wavelength. The Y-shaped decoupling and shorting pins improve the isolation up to 14 dB and can mitigate the current moment between the two ports effectively. The open slots in the ground are enhancing the mutual impedance and shift the operating band of the antenna toward the lower frequency band and thus size miniaturization is also achieved. The textile antenna achieves a 10 dB impedance bandwidth from 4.24 to 5.38 GHz with more than 21.1 dB isolation in the entire band. The phantom wrist model and bending analysis are carried out with the textile antenna to validate the on-body effects of the antenna in wearable and 5G applications.

A microwave design for an industrial scale applicator of a continuous microwave assisted depolymerization of polyethylene terephthalate (PET) has been developed. The cavity is designed for use in combination with an Archimedean screw pump to transport the reaction material, surrounded by a cylindrical pipe with a diameter of 250 mm and a length of 250 mm at the 2.45 GHz ISM band. The proposed design is modular and can be easily expanded for the heating of longer reactor tubes. Simulation results show that a homogeneous heating of the process material along the screw axis can be achieved by using a novel cavity design which is based on the TE1,0,x– rectangular waveguide cavity mode. The achieved design provides high energy efficiency with a reflected power of less than 10%. It is robust against changes in the permittivity of the reactants. The electromagnetic design is based on the dielectric properties of the solvolytic reaction mixture measured in the relevant temperature range. It is verified over the full range of the expected permittivities.

In this research article, a compact wideband stack patch antenna array integrated with compact stack electromagnetic band gap (EBG) structure for multiple input multiple output (MIMO) application is proposed. The wide resonance bandwidth is achieved at 2.45 GHz band by stack arrangement of compact meander line slot driven and parasitic patch elements. The isolation bandwidth is matched with resonance bandwidth with the design of a compact stack L slot EBG structure. The polarization diversity and three-layer EBG structure ensure an enhancement in isolation level. To validate the performance of the proposed stack antenna array, a prototype was fabricated and tested for different MIMO parameters. The measured result confirms the effectiveness of the proposed antenna array in a diverse MIMO environment.

This paper of lettering reveals about a modified Koch snowflake fractal multiband antenna for cognitive radio applications. Multiband antennas can be employed for spectrum sensing in cognitive radio. This new microstrip-modified Koch fractal antenna exhibits multiple actions in four dissimilar resonant frequencies at 3.2, 5.2, 6, and 9.5 GHz correspondingly that covers the frequency bands such as S, C, and X bands. Its multiband behavior was analyzed by designing and simulating in ADS EMDS software. Three iterations were carried out to study the performance of modified Koch snowflake fractal antenna. The outer ring and a small rectangular slot in the center of the antenna are used for 50 Ω impedance matching and to increase the number of resonant frequencies. The fractal antenna parameters such as gain, directivity, and its radiation pattern are also analyzed in this paper. The measured results show good agreement with the simulated results.

This paper presents the analysis and design of a wideband asymmetrical Doherty amplifier. The frequency response of the output combining network of the Doherty amplifier with arbitrary back-off level configuration is analyzed. Other bandwidth-limiting factors were discussed and analyzed as well. A number of performance enhancement techniques were taken into consideration to obtain high and flat back-off efficiency over the amplifier design band of 1.7–2.25 GHz. The designed Doherty amplifier had, at 8.0–9.9 dB output back-off, a minimum efficiency of η = 50% [power-added efficiency of 45%], measured near 40 dBm of output power, and over 28% bandwidth. Using digital predistortion (DPD) linearization, an adjacent-channel leakage ratio (ACLR) of −43 dBc was obtained for a single-carrier W-CDMA signal, at 40.9 dBm and 46% of average output power and drain efficiency, respectively. The designed amplifier represents the first wideband Doherty amplifier reported over extended power back-off range.

In this report, a compact antenna system with dual-band-notched characteristics is proposed for ultra-wideband (UWB) multiple-input multiple-output (MIMO) applications. Two antenna elements are placed side by side and fed with matched microstrip lines on a substrate with an area of 35 × 30 mm2. Notched characteristics at WiMAX (3.4–3.6 GHz) and WLAN (5.725–5.825 GHz) have been achieved using complementary split ring resonator (SRR) slots etched in both the antenna elements. Electromagnetic isolation between the two elements close to each other is achieved using a ground T-stub and slots etched in the ground plane. Antenna system has been tested and measured results are close to the desired ones. Measured isolation >20 dB is obtained in most of the UWB bands. The proposed antenna system meets the requirements well for MIMO applications.

The design and measurement of reconfigurable circularly polarized capacitive fed microstrip antenna are presented. Small isosceles right angle triangular sections are removed from diagonally opposite corners for the generation of circular polarization (CP) of axial ratio bandwidth of 11.1%. Horizontal slits of different lengths are inserted at the edges of the truncated patch to provide the dual-band CP and by switching PIN diodes across the slits ON and OFF, reconfigurable circularly polarized antenna is realized. The antenna shows dual-band behavior with reconfigurable CP. In order to enhance the operation bandwidth of the antenna, an inclined slot was embedded on the patch along with PIN diodes across the horizontal slits. This proposed antenna gave an impedance bandwidth of 66.61% (ON state) ranging from 4.42 to 8.80 GHz and 68.42% (OFF state) ranging from 4.12 to 8.91 GHz and exhibits dual-frequency CP with PIN diode in OFF state and single-frequency CP with PIN diode in ON state with good axial ratio bandwidth. The axial ratio bandwidth of 4.42, 2.35, and 2.72% is obtained from the antenna. The antenna has a similar radiation pattern in all the three different CP bands and almost constant gain within the bands of CP operation.

In this paper, a novel ultra-wide-band antenna backed by a suspended ground for an enhancement of bandwidth and a frequency selective surface (FSS) reflector for the enhancement of gain is proposed in order to meet the specific coverage requirements for broadband applications. The impedance bandwidth of the proposed antenna is 13.4 GHz (1.8–15.2 GHz). To enhance the gain of the antenna, a FSS reflector is employed below the suggested ultra wide-band antenna. A novel FSS, which consists of 5 × 5 array of elements, located at a distance of 1.01 λ (36.14 mm) below the proposed antenna. There is 4–5 dBi improvement in antenna gain after application of the FSS. In order to observe the signal correlation of the proposed antenna, the time domain analysis using similar antennas in face-to-face and side-to-side scenarios has been performed using the EM simulation tool CST-STUDIO. The simulated results of the proposed antenna exhibit good agreement with the experimental results of the prototype model antenna.

Self-protection deceptive jammers create at the radar receiver output multiple-false targets that are impossible to isolate in both time and frequency domains. In this paper, we introduce a novel technique based on fractional Fourier transform (FrFT) to discriminate between the true target echo and those false targets in the case of frequency-shifting jammers. In fact, we exploit the capability of the FrFT to resolve, in a matched manner, spectra that are overlapping in time and frequency. This is a property that cannot be achieved using a standard matched filter. The theoretical analysis of this technique is presented and its effectiveness is verified by simulation.

The field of short- and mid-range radar sensors for automotive comfort and safety systems is a fast-growing market. The frequency regulation provides a new 76–81 GHz frequency band, which will be mandatory in the EU for ultra-wideband sensors from 2018. In the “radar-on-chip for cars” (RoCC) project funded by the German Ministry of Research (BMBF), a new technology was developed based on SiGe components with the objective to make the sensors affordable for all car platforms. This paper reports on the contribution of Continental A.D.C. GmbH to the joint “RoCC” project. The aim of the project was to exploit the cost-reduction potential of the SiGe technology by a further integration of the individual components and to show that the reliability and the functionality of the new sensors can meet the current requirements of the market. For this purpose, we evaluated the new eWLB package technology of Infineon. The Institute of Microwave Techniques of the University of Ulm supported us in designing a substrate integrated slotted waveguide antenna array. Demonstration sensors for short- and mid-range applications were built up and tested in the laboratory. To show the ability of the sensors to deal with real scenarios on the road, they were integrated into an experimental vehicle.

This paper presents the results of direct rain attenuation measurements carried out on four experimental microwave links, installed at UTM, Malaysia. The links operate at frequencies of 15, 22, 26, and 38 GHz and the cumulative distribution function for different rain rates have been generated from the measured 4-year rain gauge data. The experimentally measured attenuation data have been compared with International Telecommunication Unior-R rain attenuation predictions; and it has been found that the latter have underestimated the measured values, especially at higher rain rates. The deviations have been modeled as a function of rain rate exceedances R%p. It is hoped that the study will provide useful information for estimation of rainfall attenuation on microwave links in tropical regions that have similar situation to Malaysia.

A compact reconfigurable filtering ultra-wideband (UWB) antenna with switchable band-notched functions is proposed. The basic structure of the proposed design is a filtering slot antenna with good band-edge selectivity using stepped impedance resonator feeding line. The reconfigurability is achieved by using two microstrip lines paralleling to the feeding line and two PIN diodes. The reconfigurable structure and bias circuit of the antenna are relatively simple and are not connected to the radiation structure, so they have little negative influence on the radiation characteristics of the antenna. Total four states could be achieved by using two PIN diodes to short the microstrip lines and ground. To verify the performance of the final design, multiple measured and simulated results in frequency and time domain are studied and analyzed. The measured results agreed very well with simulation. Compared with the traditional UWB antenna, the proposed antenna has advantages in size, filtering function in-band and out-of-band, and tunable states for multiple UWB applications.

In this paper, a novel miniaturized implantable circular antenna is presented. It supports both wireless information communication and wireless energy transmission at the Medical Device Radiocommunication band (MedRadio 402–405 MHz) and the industrial, scientific, and medical bands (ISM 902.8–928 MHz). The antenna is circular to avoid sharp edges while miniaturization is achieved by adding two circular slots to the patch. The main scenario includes embedding into the muscle layer of a cylindrical three-layer model of a human arm for which several parameters are analyzed (resonance, radiation pattern, and specific absorption rate). Power transmission efficiency and interaction distance limits to ensure connections are also evaluated. Finally, the design is validated by an experimental measurement in an anechoic chamber, and some new improvements are proposed.

This paper presents a miniature monopole reader antenna for tri-band radio frequency identification (RFID) portable devices. The proposed antenna operates at the main RFID frequencies and can alleviate and compensate for the shortcomings of a single-band antenna. An additional rectangular stub couples with the bent monopole antenna, allowing the latter to resonate at the RFID bands at 902–928 MHz, 2.4–2.48 GHz, and 5.725–5.875 GHz. By bending the feedline, the dimensions of the miniature antenna are reduced to 115.5 × 20 × 1.6 mm3, facilitating its integration into portable devices. The measured bandwidths(return loss < −10 dB) of the proposed antenna are 677, 580, and 250 MHz in the three operating bands, 883–1560 MHz, 2.31–2.89 GHz, and 5.65–5.9 GHz, respectively, with high-gain characteristics. An experimental study of a fabricated prototype of the optimized antenna is performed, and the results verify its good performance.