A novel multiple-input and multiple-output (MIMO) fractal antenna excited by a coplanar waveguide was investigated in this study. A novel technique was used to improve the isolation of 20 dB between the dual radiating elements by inserting a strip line into the outer edges of the ground plane. A sunflower structure was used to configure the antenna in three steps. At each step, an additional sunflower structure was added with half the size of that used in the previous step to enhance the impedance bandwidth. The measured values of envelop correlation coefficient and total active reflection coefficient indicated that the proposed MIMO antenna has high-diversity performance between radiating elements. Wide dual operating bands of 2–2.9 and 5–10 GHz were obtained, which can support different wireless communications, such as 3G, LTE (2.6 GHz), WLAN (2.4 GHz/5 GHz), WiMAX (2.4 GHz/5GHz), ISM (2.4 GHz/5 GHz), 5G (5–6 GHz), and satellite communications (6–8 GHz). The MIMO fractal antenna with a small size achieved a maximum efficiency of 85% and a peak value gain of 6 dBi, low-channel capacity loss of 0.15–0.4 b/s/Hz, and high isolation between radiating elements is suitable for portable communication devices.

This paper describes a concept of stepped impedance resonators (SIR) built from two coaxial structures fitted inside one another. The resonator is built out of a succession of two coaxial sections in cascade, where the ground conductor of the first one is the central core of the next, or vice-versa. An advantageous property of SIR is that they allow a substantial reduction in size, while keeping away the first harmonic and without strongly degrading the quality factor. After describing the theoretical behavior of the resonator, we will then present the specific properties of this approach in second order filter, conceived, and realized in the UHF band. With this example, we will also address flexibility and tunability aspects, which are the other potentially useful properties of the structure. Measurements and simulations are presented and discussed. The architecture resembles a set of two Russian dolls that fit inside one another.

This article addresses the analysis and digital signal processing (DSP)-based mitigation of phase noise and sampling clock jitter in orthogonal frequency division multiplexing (OFDM) radios. In the phase noise studies, the basic direct-conversion receiver architecture case is assumed with noisy downconverting oscillator. In the sampling jitter case, on the other hand, the so-called direct-radio-frequency-sampling receiver architecture is deployed utilizing bandpass sub-sampling principle. The basis for the DSP-based impairment mitigation techniques is first formed using analytical receiver modeling with incoming OFDM waveform, where the effects of both oscillator phase noise and sampling clock jitter are mapped to certain type subcarrier cross-talk and distortion compared to ideal receiver case. Then iterative detection principles and interpolation techniques are developed to essentially estimate and cancel the subcarrier distortion. Also some related practical aspects, like channel estimation, are addressed. The performance of the proposed mitigation techniques is analyzed and verified with extensive computer simulations. In the simulations, realistic phase-locked-loop-based oscillator models are used for phase noise and sampling clock jitter. In addition, different received signal conditions like plain additive white Gaussian noise channel and extended ITU-R Vehicular A multipath channel are considered for practical purposes. Altogether the obtained results indicate that the effects of oscillator and sampling clock instabilities can be efficiently reduced using the developed signal processing techniques.

A novel compact multiple-input–multiple-output (MIMO) antenna system operating from 5 to 7.3 GHz is proposed for wireless applications. It comprises of two similar antennas with microstrip feeding and radiating patches developed on a reduced ground plane. The developed antenna system resonates at a dual-band of 5.4 and 6.8 GHz frequencies, giving an impedance bandwidth of 38% (based on S11 < −10 dB). The unique structure of the proposed MIMO system gives a reduced mutual coupling of −27 dB at 5.4 GHz resonant frequency and −19 dB at 6.8 GHz resonant frequency and in the entire operating band the coupling is maintained well below −16 dB. The envelope correlation coefficient of the proposed MIMO system is calculated and is found to be less than 0.05 in the operating band. The measured and simulation results are found in good agreement.

An ultra-wideband (UWB) frequency-selective surface (FSS) exhibiting band rejection characteristic is presented in this paper. The proposed unit cell has the size of 14 × 14 mm2 which is approximately 0.18 × 0.18 λo, where λo corresponds to free space wavelength at the lower cut-off frequency. The proposed UWB FSS consists of a single-layer substrate and provides 20 dB attenuation level for a wide bandwidth of 7.53 GHz at the normal incidence. The proposed FSS is polarization independent and also provides angular-independent operation for the EM wave incidences of 15°, 30° and 45° with 11.5 dB attenuation over a wide range from 4 to 14 GHz.

In this paper a new design of compact single layered triangular slotted microstrip patch antenna with spur lines and strip loading is proposed. It has been experimentally investigated that strip loading causes more size reduction where spur lines and triangular slot introduces multi frequency operation of microstrip patch antenna. The size reduction has been found to be 87% for the proposed antenna. In this article the effect of strip loading and spur lines over compactness are individually analyzed.

This paper presents the results of Doppler-polarimetric radar signal analysis, computer modeling, and real data processing that show the correlation between differential Doppler velocity (DDV), which is a difference between mean Doppler velocities measured at orthogonal polarizations of electromagnetic waves, and parameters of rain including both rain microstructure (parameters of drop-size distribution) and turbulence intensity in resolution volume. The reasonability to use DDV as one of the informative parameters in the recognition neural network system is checked.

In this paper, we show a second-order (four-resonator) absorptive bandstop filter circuit topology which gives a larger bandwidth compared to a first-order topology. Due to the absorptive characteristic, it creates a large attenuation at the center frequency using low-Q resonators. Since low-Q resonators can be used in generating a large attenuation, small-size resonators can be employed in bandstop filter design. Analytic design equations are provided so that a higher-order absorptive bandstop filter can be designed analytically. It is also shown that the second-order filter topology exhibits a better frequency selectivity having a same bandwidth. The proposed filter topology has been applied to a design of a miniaturized low-temperature co-fired ceramic bandstop filter with low-Q resonators. The Q-factor of the lumped-element resonators has been chosen to be 5 for demonstration.

A design of annular ring microstrip antenna with finite ground structure is proposed in this paper. The proposed geometry offers impedance bandwidth of 2.362 GHz and has stable radiation patterns for all resonant frequencies in the operational band. It is also found that shape and dimension of the finite ground plane is a key factor in improving the bandwidth of the proposed geometry. The geometry is low profile and has simple structure, therefore can be used for lower band of ultra-wideband applications.

In this paper, a 2.45-GHz wideband harmonic rejection rectenna for wireless power transfer is proposed. The rectenna comprises a microstrip-fed circular ring slot antenna (CRSA) and a series-parallel rectifier (SPR). A compact micro strip resonant cell is inserted into the CRSA so that the harmonic suppression over a wide bandwidth (3–8 GHz) can be obtained. The radio-frequency (RF)–DC conversion efficiency of the SPR is improved effectively by loading a proper compensating inductance, especially under the low input power levels. Furthermore, the proposed rectenna can easily achieve large-scale rectenna arrays using its simple structure. The adopted rectenna fabricated on a low cost Taconic RF-35 substrate has been measured. By up to 3rd-order harmonic rejection, the efficiency of the rectenna can achieve 70.2% with the optimum load resistance 1 kΩ. Good agreement among the calculated, simulated, and measured rectenna is observed.

This paper presents a broadband hybrid slot-dielectric resonator antenna for radiofrequency (RF) energy-harvesting application. The antenna geometry consists of a simple pentagon-shaped dielectric resonator antenna (PDRA) excited by a microstrip feed underlying rectangular slot with narrow notch. It is investigated that the bandwidth of the proposed PDRA is improved significantly owing to electromagnetic coupling between feeding slot and the dielectric resonator. The measured results demonstrate that the proposed PDRA achieves an impedance bandwidth of 110.8%, covering the frequency range from 0.86 to 3 GHz in addition of stable radiation pattern with peak gain of 6.8 dBi and more than 90% radiation efficiency throughout the band, showing its suitability for RF energy harvesting application. For this to be feasible, the developed antenna is matched with the rectifier at two public telecommunication bands of GSM-900 and GSM-1800 using a compact dual-band hybrid matching network. The measured result demonstrates that the proposed dual-band rectenna system provides the peak efficiency of 63 and 59% for a load impedance of 4.7 kΩ at 0.9 and 1.8 GHz, respectively.

Piezoelectric thin films have existing and promising new applications in microwave filter technologies. The final performance depends on many parameters, and very specifically on the materials properties of each involved material. In this article, materials and properties for thin-film bulk acoustic wave resonators are discussed on some selected issues: the piezoelectric coefficients and acoustic losses of AlN, the relation of the first one with microstructural parameters, the inclusion of parasitic elements, and the merits of and problems with ferroelectric materials.

ADS-B provides convenient means of air traffic control (ATC) for its low cost and simple ground station hardware. In a low percentage of cases, aircraft positions transmitted via ADS-B are error prone due to e.g. faulty wiring with onboard navigation systems. In the proposed approach, direction of arrival (DOA) estimation is used to verify ADS-B airborne positions. The potential positioning error of ADS-B is thereby evaluated by comparing DOA estimates to DOA values calculated from ADS-B references and the sensor position and orientation. To prove the accuracy of the applied DOA estimation sensor, an additional measurement campaign using a dedicated measurement aircraft has been conducted.

This paper discusses the determination of key electrical parameters of AlInN/(AlN)/GaN heterostructures from capacitance–voltage (CV) measurements. These heterostructures gained recently importance since they allow for high electron mobility transistor (HEMT) devices with several remarkable records: densities of the 2D electron gas (2DEG) of 2.6 × 1013 cm−2 for lattice-matched (LM) heterostructures and barrier thickness of 14 nm, beyond 2 A/mm saturation currents, above 100 GHz operation for heterostructures grown on Si (111) with gate length of 0.1 µm. Despite these striking experimental results, a consistent determination of the most important electrical parameters, namely polarization sheet charge density, surface potential, and dielectric constant of the alloy are still missing. By setting up the correct charge balance equation, these parameters can unambiguously be determined. For instance, in the case of nearly LM Al0.85In0.15N these parameters amount to σAl0.85In0.15N/GaN ~ 3.7 × 1017 m−2, eΦS ~ 3 eV and ɛAl0.85In0.15N ~11.2, for the charge density, the surface barrier potential, and the dielectric constant, respectively.

A study of the electrical performances of AlInN/GaN High Electron Mobility Transistors (HEMTs) on SiC substrates is presented in this paper. Four different wafers with different technological and epitaxial processes were characterized. Thanks to intensive characterizations as pulsed-IV, [S]-parameters, and load-pull measurements from S to Ku bands, it is demonstrated here that AlInN/GaN HEMTs show excellent power performances and constitute a particularly interesting alternative to AlGaN/GaN HEMTs, especially for high-frequency applications beyond the X band. The measured transistors with 250 nm gate lengths from different wafers delivered in continuous wave (cw): 10.8 W/mm with 60% associated power added efficiency (PAE) at 3,5 GHz, 6.6 W/mm with 39% associated PAE at 10.24 GHz, and 4.2 W/mm with 43% associated PAE at 18 GHz.

This paper describes a multiple-input multiple-output (MIMO) antenna for low millimeter (mm)-wave applications based on dielectric resonators. This is the first time that a filtering response is used in conjunction with an MIMO antenna operating at a low mm-wave frequency. The antenna is simulated using an asymmetrical U-shaped aperture and a microstrip line feed. The suggested filtenna has two distinguishing characteristics: (i) the diversity parameters of the proposed MIMO are increased by including pattern and spatial diversity, and (ii) the proposed feed mechanism of a dielectric resonator provides the filtering response. Between the two ports, a metallic plate tilts the radiation pattern by 45°. The anti-parallel locations of the ports increase the isolation value by >30 dB. To validate the performance of the suggested antenna, the proposed filtenna was built and confirmed. The proposed antenna operates between the frequencies 27.9 and 28.5 GHz. Within the operating frequency range, the observed gain is ~4.5 dBi. On the contrary, the gain suppression level beyond the operational frequency range is ~15 dB. The stable radiation properties and high diversity parameter values of the suggested filtenna make it an effective solution for 5G Internet of Things sensing applications.

A four-element wide-band octagonal ring-shaped antenna is proposed for human interface device and S-band applications. The isolation structure comprises a parasitic element and a T-shaped structure. The antenna has −10 dB impedance bandwidth 63% (2.1–4.0 GHz) with miniaturized dimension of 54.98 mm × 76 mm. The multiple input multiple output (MIMO) antenna gain is 2.83 dBi at the 2.4 GHz resonant frequency. The designed MIMO has envelop correlation coefficient of 0.026 in the 2:1 VSWR band. The −10 dB total active reflection coefficient bandwidth of 1.2 GHz has been achieved in the entire frequency band, and has MEG value of ≤−3 dB. The specific absorption rate has found below the safety limit near the human head, palm and wrist.

A compact planar ultra-wideband (UWB) antenna with WiMAX and WLAN notched band is presented in this paper. The presented antenna consists of a rectangular patch and slotted partial ground plane and fed by a microstrip feed line. The volumetric size of the antenna is 30 mm × 22 mm × 1.6 mm. Method of moment-based simulation technology is used to simulate and analyze the characteristics of the antenna. To generate two notch bands at WiMAX and WLAN, a pair of parasitic resonator is placed beneath the radiating patch. The presented antenna achieves an operating band (VSWR ≤2) ranging from 2.98 to 12 GHz with an average gain of 3.95 dBi along with considerable efficiency and symmetric radiation patterns. Moreover, the antenna exhibits two notch bands at 3.5 and 5.45 GHz and is able to avoid possible interference with pre-existing narrow band services. The proposed antenna is low cost and low profile and is modeled to be used as a transceiver in UWB communication applications.

We introduce an integrated design methodology for the optimization of RF-to-DC conversion efficiency of multi-band rectennas (rectifying antennas), with the aim of harvesting the RF energy available in humanized environments. Existing RF sources can either operate at known frequencies, power budgets, and locations, or can be ubiquitously available at different frequency bands, and with unknown directions of incidence and polarizations. In all cases, the RF link power budget may be extremely low. In order to harvest a significant quantity of energy, it is thus mandatory to place a very special care in the design of each part of the receiving/storing system. For this purpose, the receiving antenna must be optimized together with the rectifying circuit and the load. In our work, this is accomplished by a rigorous design tool based on the concurrent use of nonlinear/electromagnetic (EM) CAD tools and EM theory. The effectiveness of the method is demonstrated by comparing the computed and measured performance of single- and multi-band rectennas, both linearly and circularly polarized. Such antennas are designed to harvest RF energy from a variety of cellular and WiFi systems that are normally present in civil environments.

In this paper, we present several dielectric waveguide (DWG) setups that enable the transition between radar front ends and antennas in challenging, industrial environments. Apart from good propagation behavior, DWG provide a nearly dispersion free transmission over large distances. Furthermore, they can be used as an electrical insulator in places with critical creep distances, in high temperature environments, and for applications with limited installation space. Fundamentals concerning the ideal propagation mode and adequate waveguide–fiber transitions are presented. Results of electromagnetic simulations as well as measurements on manufactured DWG are discussed in detail. The presented excellent propagation behavior proves the effectiveness of the proposed setup.