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.

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.

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.

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.

In this paper, a multiple input multiple output antenna which operates at 5.8 GHz for wireless local area network applications is proposed. The proposed antenna is composed of two sets of four elements antenna array (2 × 2) on the top and a novel metamaterial structure on the ground plane. Here, the ground plane, which includes a lattice of 2 × 5 unit cells of metamaterial structure, is utilized in order to improve parameters of the antenna. Thanks to the proposed metamaterial structure, not only gain and bandwidth of antenna are enhanced, but also mutual coupling is reduced. The final design, with an overall size of 137 × 77 × 3.048 mm3, resulted in a |S11| <−10 dB bandwidth of 1.78 GHz and a peak gain of 9.2 dBi. In addition, the isolation is higher than 18 dB although the close separation from edge to edge of the two antennas is only 2 mm and radiation efficiency of 73% at the operating frequency band. All is simulated based on CST Studio software and the simulated S-parameter results of the antenna are in good agreement with measurement results.

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.

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.

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.

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.

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.

This research investigates the MIMO antenna by using the Theory of Characteristics Mode (TCM) where 10 modes are subjected in designing. Also, 5 modes are the significant mode and 2 modes correspond to non-significant which defines the operating bandwidth and notched bands. The proposed 2 × 2 MIMO antenna configuration is designed for wideband applications with a size of 0.44 × 0.68 mm2. The two isolated 12-sided polygons radiating patches placed adjacent to each other share a common ground which is printed on an FR4 substrate. The measured impedance bandwidth covers bandwidth 3.11–11.98 GHz with two bands rejecting capability: Wireless Local Area Network (WLAN) and Downlink-Uplink Satellite (DUS) system. These two interfering bands are mitigated by etching a C-type slot on the radiating patch and an inverted U-type slot in the microstrip feed. The simulated and measured results are also compared in the far-field region (Normalized Radiation Efficiency (NRE), Peak Gain (PG), and 2-D/3-D radiation pattern). Proposed MIMO antenna also offers good diversity performance with ECC2×2 < 0.00001, DG2×2 > 9.999 dB, TARC2×2 < −15.0 dB, CCL2×2 < 0.001 b/s/Hz and MEG2×2 ≅ −3.0 dB.

Wireless sensor networks are an increasingly popular tool for monitoring various environmental parameters. They can also be used for monitoring the electromagnetic spectrum. Wireless sensors, due to their small size, typically have simplified radio receivers with reduced sensitivity and use small antennas. As a result, their effective performance area is similarly limited. This is especially important in urban areas where there are various kinds of adverse propagation phenomena related to area coverage. The aim of this paper is to present the phenomena in the wireless sensor networks and propose criteria and methods to optimize their deployment to ensure maximizing the probability of detection of emissions, minimization of unmonitored areas, and to provide the necessary hardware redundancy in the priority areas. Influence of detection parameters, number of sensors and range constraints between sensors on received outcomes are also presented.

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.

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.

The main implementation impairments degrading the performance of direct-conversion radio transmitters are in-phase/quadrature (I/Q) mismatch, local oscillator (LO) leakage, and power amplifier (PA) nonlinear distortion. In this article, we propose a recursive least-squares-based learning algorithm for joint digital predistortion (PD) of frequency-dependent PA and I/Q modulator impairments. The predistorter is composed of a parallel connection of two parallel Hammerstein (PH) predistorters and an LO leakage compensator, yielding a predistorter which as a whole is fully linear in the parameters. In the parameter estimation stage, proper feedback signal from the transmitter radio frequency (RF) stage back to the digital parts is deployed, combined with the indirect learning architecture and recursive least-squares training. The proposed structure is one of the first techniques to explicitly consider the joint estimation and mitigation of frequency-dependent PA and I/Q modulator impairments. Extensive simulation and measurement analysis is carried out to verify the operation and efficiency of the proposed PD technique. In general, the obtained results demonstrate linearization and I/Q modulator calibration performance clearly exceeding the performance of current state-of-the-art reference techniques.

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.

In this paper, combination of electromagnetic band gap (EBG) and split-ring resonator (SRR) loads with fractal formation for miniaturization of microstrip antenna is noticed. Here two different shapes of antenna have been studied with two well-known metamaterial structures as parasitic elements. A conventional microstrip antenna, which is surrounded by four EBG unit cells, is chosen as the first antenna. It has an effective resonance at 2.5. The Minkowski fractal method is applied to EBG unit cells in this stage. The Minkowski fractal structure is implemented for accession of effective capacitance in EBG unit cells. The second antenna frequencies are 2.5 and 5.9 GHz. It contains a slot structure with four SRRs, used for making parasitic elements and for achieving multi-band characteristic. The fractal method is used to improve the inductance of SRR structure by increasing the effective length of microstrip line. At this stage, the applied fractal structure has been modified, so that the frequency of wireless application could be achieved. In the last step, by some changes in feed line of the slot antenna, circular polarization (CP) is obtained for the second antenna, which shows that SRR load can be helpful for making the CP.