In this paper, an orthogonal frequency-division multiplexing (OFDM) waveform radar sensing approach is demonstrated based on field measurements at C-band. We demonstrate a concept that is based on the exploitation of typical wireless communication transmissions to perform passive, distributed radar sensing. Our concept is based on an OFDM radar that operates in the modulation symbol domain and can be well integrated into existing OFDM receivers. The measurement setup and the signal processing steps for the OFDM radar are described. The results show that the passive, distributed radar sensing approach can be used to detect and localize moving cars and even pedestrians in automotive intersection scenarios.

In this paper, a sandwiched type frequency selective surface (FSS) is designed and analyzed. The design procedure and operating principle is given based on the equivalent circuit model. The proposed FSS includes two identical layers of periodic metallic arrays, which are separated by a foam layer. In each layer of the periodic array, the unit cell is composed of a gridded-triple square loop structure. The FSS provides three pass-bands, in which a flat band response is presented. Three bands are separated by one or two transmission zeros, which leads to a sharp rejection on both sides of each pass-band. The central frequencies of the three pass-bands are 7.0, 10.9 and 14.0 GHz. To verify the simulated results, a prototype of the FSS is fabricated and measured. The simulated results agree well with the measured ones. This work can be used in area of a radar stealth or satellite communication system.

In this paper, a microstrip lowpass filter adopting two main resonators with steep transition band and wide rejection band has been introduced. The first main resonance cell consists of meandered transmission lines which are loaded by modified T-shaped patches. The second main resonator is composed of high-impedance lines loaded by polygon patches. To obtain a steep skirt performance, the first and second resonators have been combined. Moreover, employing eight high–low impedance folded stubs and two rectangular open-stubs as suppressing cells has resulted in improving the stopband features. To comprehend the frequency behavior of the employed resonators and also their combination, the formulas of the transmission coefficient, reflection coefficient, and the transmission zeros of their equivalent LC circuits have been extracted, separately. According to the measurement results, the −3 dB operating frequency of this filter is 1.65 GHz. Moreover, a relative stopband bandwidth equal to 166% with a corresponding attenuation level of 23 dB and a sharp roll-off rate (393.61 dB/GHz) have been achieved. In the passband region from DC to 1.632 GHz, the insertion loss and return loss are better than 0.0763 and 15.85 dB, respectively, proving an acceptable in-band performance. Finally, the implemented structure brings about a high figure-of-merit equal to 81 672.

A compact transition between conductor-backed coplanar waveguide (CBCPW) and substrate integrated suspended line (SISL) is presented. Compared to the reported transitions from CBCPW to SISL, performance and compactness are improved. For demonstration purpose, a multilayer transition is designed and fabricated for operation up to 46 GHz. Experimental results, based on an electronic calibration and thru–reflect–line calibration allowing measurement in the 0.01–50 GHz frequency range, demonstrate an insertion loss of 0.59 ± 0.51 dB with a return loss of better than 10 dB in the 10 MHz to 46 GHz frequency range.

This paper discusses the design of chip-less RFID tags of a standard pocket size of 69 mm by 156 mm. These tags are based on lumped elements of copper metal traces constructed on a thin polyamide flexible substrate. Moreover, a low-cost single-chip Bluetooth detector circuit system is demonstrated. Two different detection methods: variable coil load coupling and optical light intensity detection were combined to yield 256 unique ID codes. In the first method, by utilizing simple 4 MHz digital drivers and an integrated analog to digital converter (ADC) in the reader controller; various inductively coupled resonant loads corresponding to multiple distinct tags could be differentiated, yielding eight different (3-bit) ID codes. The additional via-based hole pattern reflectometer method creates additional 32 distinct levels (5-bit) utilizing 650 nm visible light-emitting diode and a simple trans-impedance operational along with the same analog ADC pins of a Bluetooth controller. The printed circuit board trace coil on the two-layer low-cost FR-4 waterproof sealed detector unit is simultaneously used as a Qi wireless power receiver to charge the120 mAh 2450 Lithium Polymer (LiR) battery. The device could remain operational for more than a month with a single charge; remaining connected with a mobile device and enabling 10 readouts daily.

The design, simulations, and optimized results for a novel low specific absorption rate (SAR) monopole antenna on a single artificial magnetic conductor (AMC) cell are described in this paper. Simulated results show a reduction close to 70% in the 1 g ps SAR for the developed monopole antenna with the AMC in comparison to the monopole antenna without AMC. This allows higher radiation efficiency, battery drain reduction as well as mobile terminal user health risks reduction.

The spectral and energy characteristics of the tunable thin planar dielectric resonator with the movable metal mirror are researched. It is found that the high-Q HE-polarized whispering gallery modes (WGMs) are effectively excited in such a resonator by the dielectric waveguide. A mode set of the tunable thin planar dielectric resonator depends on the presence of an air gap in its design. Changing the height of the air gap affects the energy characteristics of the tunable thin planar dielectric resonators (DR). Shifting the resonant fields of WGMs from the dielectric disk to the air gap is the reason for this effect. It is shown that at certain heights of the air gap, increasing the unloaded Q-factor of the tunable thin planar DR and improving the excitation efficiency of WGMs in it is achieved.

The implementation of advanced multi-level modulation schemes such as quadrature phase-shift keying (QPSK) in contrast to the conventional on–off keying is crucial to further boost the terahertz (THz) communications speed. Thereby, carrier phase noise reduction in the THz range is one of the key goals that need to be urgently achieved. In this paper, the photonic-based THz sources and the phase noise problem are briefly summarized. Then, a low phase-noise photonic source based on the stimulated Brillouin scattering (SBS) optical fiber cavity is first applied for a 300-GHz-band QPSK wireless communication link. The highest data rate at forward-error-correction limited condition was 15 Gbaud utilizing the SBS-based photonic source with a small transmit power of ~ −36 dBm. Its transmission characteristics are evaluated and compared with the conventional optical frequency comb generator (OFCG)-based source at 5 Gbaud. The proposed SBS-based photonic source has been proven to offer better performances than the OFCG-based source with respect to the phase noise, optical carrier to noise ratio, and bit error rate in communications.

This paper presents center frequency and bandwidth switchable substrate integrated waveguide filters loaded with PIN diodes. The diodes are added in the slot on the surface of the resonators to switch the resonant frequencies and the coupling coefficients. Although the introduction of the slot causes extra radiation loss, it is small and acceptable. The proposed center frequency switchable filter has four center frequency switchable states of 1.78, 1.82, 1.88, and 1.91 GHz, while the bandwidth only changes ±0.64%. The bandwidth switchable filter has two states with 3 dB bandwidths of 70 and 103 MHz at a center frequency of 2.08/2.09 GHz. The measured performance of the fabricated filters shows good agreement with the simulation.

Near-field to far-field transformations constitute a powerful antenna characterization technique for near-field measurement scenarios. In this paper, a near-field to far-field transformation technique based on multiple spherical wave expansions (SWEs) is presented. Thanks to its iterative matrix inversion nature, the approach performs the transformation of fields measured on arbitrary surfaces. Also, irregular sampling schemes can be incorporated. The proposed algorithm is based on modeling the antenna fields with not one, but several SWEs distributed over its geometry. Due to the high number of SWEs, their truncation number can be arbitrarily reduced. Working with expansions of low order allows us to incorporate the probe correction in the transformation in a very simple way, accepting any type of probe and orientation. Only the probe far-field pattern is used, thus working with its full SWE is avoided. The algorithm is validated using simulated field data as well as measurements of real antennas.

Structures of tunneling nanotubes (TNTs) of the circular cross-section of 50 and 200 nm and length up to 1 mm form a communication system between cells. While transport of material such as endocytic vesicles, mitochondria, proteins, cytoplasmic molecules, etc., is experimentally proven, a possible transfer of electric and electromagnetic energy across TNTs corresponding to electrotechnical processes of excitation, propagation, and amplification in cavity systems is yet in a beginning stage of research. The ideas presented in this paper are based on technical mechanisms applied to submicroscopic systems. Main features of corrugated periodic structures, electromagnetic circular waveguides, the Manley–Rowe amplification, the Fröhlich non-linear interaction of coherent electric polar vibrations, and description of cut-off frequency propagating limits in the waveguide and cavities and along periodic structures are discussed. We suggest that cell-to-cell connection with TNTs may form a unified coherent cavity system which enables simultaneity and mutual cooperation in multicellular organisms.

In this paper, an electromagnetic band gap (EBG) metasurface (MS) superstrate-based circularly polarized antenna for the WiMAX (3.5 GHz) band is proposed. The proposed structure comprises a 2 × 2 slot-loaded rectangular patch MS array that can be perceived as a polarization-dependent EBG MS superstrate. Furthermore, to achieve circular polarization, the proposed antenna has an inclined coupling slot onto the ground with a conventional coplanar waveguide feed line. The proposed antenna has a compact structure with a low profile of 0.037λ0 (λ0 stands for the free-space wavelength at 3.48 GHz) and a ground size of 30 × 30 mm2. The measured results show that the −10 dB impedance bandwidth for the proposed antenna is 34.6% and the 3-dB axial ratio (AR) bandwidth is 6.8% with a peak gain of 3.91 dBi in the desired operating band. Good agreement between the simulated and the measured results verifies the performance of the proposed antenna.

A high-isolation diplexer based on a dual-mode substrate integrated waveguide (SIW) resonator is proposed in this paper. Based on the theory of the dual-mode resonator, the miniaturized diplexers are designed by using the SIW dual-mode resonators. The superior isolation of the diplexers is obtained because the two operating modes of the dual-mode SIW resonators are not directly coupled and there is no interference with each other. In order to further improve the isolation of the circuit, the number of the order of the diplexer is added. Equivalent circuits are given to analyze and design the dual-mode high-isolation diplexers. Detailed analyses are given according to the equivalent circuits. The dual-mode third-order and fourth-order diplexers are designed and fabricated. The measured results agree well with the simulated ones. The total sizes of the fabricated third-order and fourth-order diplexers are 1.78λg × 2.64λg and 1.79λg × 3.63λg, respectively.

Electromagnetic waves in the microwave and millimeter-wave frequency range are used in non-destructive testing and structural health monitoring applications to detect material defects such as delaminations, cracks, or inclusions. This work presents a sensing concept based on guided electromagnetic waves (GEW), in which the waveguide forms a union with the structure to be inspected. Exploiting ultra-wideband signals a surface defect in the area under the waveguide can be detected and accurately localized. This paper presents numerical and experimental GEW results for a straight waveguide focusing on the detection of through holes and cracks with different orientation. It was found that the numerical model qualitatively replicates the experimental S-parameter measurements for holes of different diameters. A parametric numerical study indicates that the crack parameters such as its orientation and width has a significant influence on the interaction of the incident wave with the structural defect. On top, a numerical study is performed for complex-shaped rectangular waveguides including several waveguide bends. Besides a successful damage detection, the damage position can also be precisely determined with a maximum localization error of less than 3%.

A growing interest in dielectric waveguides (DWGs) as an alternative to commonly used waveguides (like coaxial or twisted-pair cables) for high data rate interconnects could be observed in the last few years. Especially in the mm-wave frequency range (30–300 GHz) applications with these waveguides benefit from low losses and low dispersion. Moreover, using both polarizations of the fundamental mode in such waveguides could theoretically double the data rate without the need of higher bandwidth or additional fibers. The connection between DWGs and commonly available transceiver chips requires broadband transitions from planar waveguides like microstrip lines to DWGs. In this paper, an overview of the current developments of such transitions is given and a novel low-complexity design is presented that reduces the space consumption by 35% related to recently published works. This allows an easy integration into a printed circuit board layout or a chip package. Furthermore, an extensive sensitivity analysis is presented to prove the robustness toward manufacturing tolerances. The transition is realized at W-band frequencies (75–110 GHz) and achieves a relative 10 dB-bandwidth of more than 25% with a minimum insertion loss of 1.2 dB. It is shown that these properties even hold for manufacturing tolerances of nowadays manufacturing processes.

In this paper, different techniques for the generation of additional transmission zeros (TZs) in planar waveguide filters are investigated. In the classical theory, TZs are generated only by destructive interference of non-adjacent cavities, limiting the available number of TZs to the filter order itself. However, more approaches for the generation of TZs are known, including bypass-coupling in oversized cavities, frequency-dependent coupling apertures as well as dispersive/resonant TZs which can be realized by the direct source to load cross-coupling. The aim of this paper is to combine several of the strategies in one physical filter set-up to increase the maximal number of TZs beyond the filter order. Different Ku-band fourth-order filter set-ups are presented, showing in total between six and eight real as well as complex TZs. Three filters are manufactured as a proof of concept and compared with the simulation, showing very good agreement.

A novel flexible radio frequency (RF) sensor is designed to facilitate the accurate testing of various samples used in the biomedical industry at the industrial, scientific and medical (ISM) frequency band. The proposed RF biosensor comprises a liquid channel-loaded interdigitated capacitor, which is integrated on a coplanar waveguide structure. The prototype of the sensor is fabricated on a 0.13 mm thin biodegradable polyethylene terephthalate polyester film to perform the testing of various bio-graded samples by recording the corresponding resonant frequency. It is observed that there is a noticeable change between the measured resonant frequencies of these samples, which primarily occurs due to the difference in their dielectric properties. The designed sensor was used to monitor and investigate the quality of glycerol, which is the most commonly used raw ingredient in the biomedical and food industry. The determination of glucose concentration in base fluids is considered to ease the challenges faced by doctors and biochemists regarding the monitoring of glucose concentration. It is found that the proposed sensor can quantify the glycerol purity up to the minimum specified adulteration level of 2 and 1% corresponding to toxic contaminants diethylene glycol and ethylene glycol, respectively, and the glucose concentration of 0.5 mg/ml.

We present details of on-wafer-level 16-term error model calibration kits used for the characterization of W-band circuits based on a grounded coplanar waveguide (GCPW). These circuits were fabricated on a thin gallium arsenide (GaAs) substrate, and via holes, were utilized to ensure single mode propagation (i.e., eliminating the parallel-plate mode or surface mode). To ensure the accuracy of the definition for the calibration kits, multi-line thru-reflect-line (MTRL) assistant standards were also fabricated on the same wafer and measured. The same wafer also contained passive and active devices, which were measured subject to both 16-term and conventional line-reflect-reflect-match calibrations. Measurement results show that 16-term calibration kits are capable of determining the cross-talk more accurately. Other typical calibration techniques were also implemented using the standards on the GCPW calibration kits, and were compared with the MTRL calibration using a passive device under test. This revealed that the proposed GCPW GaAs calibration substrate could be a feasible alternative to conventional CPW impedance standard substrates, for on-wafer measurements at W-band and above.

This article proposes a bandpass filter with three controllable transmission zeros (TZs) using three inductive-coupled stub-loaded resonators (SLRs). Different from other works, the proposed SLR can create one transmission pole and one TZ. With the TZs above the passband, high stopband rejection level is achieved. Moreover, the K-inverters are realized by short-circuit stubs between two adjacent SLRs. A general synthesis method for this kind of filter is described. For verification, a filter centered at 2.44 GHz with 0.18 GHz bandwidth is designed. The measured results show that the filter has three TZs at 3.1, 3.9, and 5 GHz. With those TZs, the filter's stopband rejection level is greatly improved.

The problem of the plane H-polarized electromagnetic wave scattering by flat pre-fractal impedance strips' gratings is examined. For this purpose, a mathematical model in the form of the first kind singular integral equation system is modified for correct usage. Considerable attention is focused on the asymptotic model of the H-polarized electromagnetic wave scattering by sparsely filled grating, which has an explicit solution. The scattered electromagnetic field in the far-zone is considered in details. Dependences of scattering integral characteristics on values of the strip impedance and angles of the plane H-polarized electromagnetic wave incidence upon the grating are studied.