Search

A printed and compact size antenna having functionality of frequency and pattern reconfigurability is presented in this work to be operated at 28 GHz for 5G communications. For the desired goal, antenna is incorporated with three PIN Diodes as a switch. The beam swapping of the antenna is guided by Switch 1 and Switch 2 and the frequency is controlled by Switch 3. Proposed work is validated for 28 GHz reconfiguration. When Switch 3 is on, the designed antenna operates at 26.8 GHz covering the 25.22–27.45 GHz band. When Switch 3 is off, it operates at 28.01 GHz, covering the 26.41–28.89 GHz band. The antenna is proposed to operate at the 5G mobile communication band having a center frequency at 28 GHz with a reflection coefficient of − 23.5 dB. RT Duroid 5880 with er of 2.33, tan δ of 0.0009 and thickness (h) of 0.509 mm with inset feeding to excite the antenna. With the deployment of Bended H-shaped stubs, a high gain was achieved. RLC circuit is used as PIN diode in the simulations in HFSS. Lastly the simulated and measured results have been compared for the authentication purposes.

Pockels cell is used for the processing of light in the field of optical communication and information processing. It is used for phase and amplitude modulation of light using polarized light as a carrier signal. A polarized incident light passes through electro-optic material, and by using the nonlinear property of the electro-optic material, the light is modulated as per the requirement. Here a study is done to show the massive reduction in the intensity of central frequency of the carrier light if multi-passing technique (multi-feedback) is adopted. In this paper, the authors show the significant number of passing (feedback) for such reduction in the intensity of central frequency and this number of passing (feedback) considerably increases the power of the sideband frequencies. The whole scheme is supported by MATLAB simulation. As the biasing signal information lies only in the sideband frequency, not in the carrier frequency, indirectly the increase in the power of the sideband frequencies strengthens the modulation information to be sent for communication by the carrier light wave having the central frequencies. This is the reason for increasing the sideband intensity by decreasing the intensity of the central frequency using multi-feedback mechanism.

We suggest a new graphene-based four-port circulator for THz applications that consists of two parallel graphene waveguides coupled to an elliptical graphene resonator between them. The graphene elements are deposited on a dielectric substrate. An external constant magnetic field is applied normal to the resonator. The frequency response of the circulator obtained from numerical simulations performed with COMSOL Multiphysics software is in good agreement with those obtained from the ad hoc temporal coupled-mode theory. The analysis shows that the bandwidth of the circulator is about 5.7% around the central frequency 5.03 THz with the applied constant magnetic field of 0.8 T.

We investigate the attenuation characteristics of high frequency seismic waves in the Kishtwar and its adjoining region of NW Himalaya using 161 local earthquakes (M 2.1–5.7), recorded by a local network of seven Broad Band Seismic (BBS) stations. The extended coda normalization technique and the single backscattering method are used to study the attenuation characteristics of body and coda waves, respectively. The study shows that the attenuation quality factors for P-wave (Qα), S-wave (Qβ) and Coda wave (Qc) are strongly dependent on frequency and increase with the increase in central frequency. The average frequency-dependent relationship for Qα, Qβand Qc is found to be as Qα = (44 ± 7)f(1..01±0.91), Qβ = (71 ± 6)f(0.91±0.01) and Qc = (60 ± 4)f(1.06±0.04). The sites located on the western part of the study area exhibit higher attenuation (Q) compared with those in eastern part, suggesting that the eastern part of the study area is more heterogeneous than the western part. Variation of Qc with increasing lapse time suggests that the lower lithosphere is less heterogeneous, compared with the upper crust. We infer that the heterogeneity in the upper crust of Kishtwar area is primarily, due to the presence of highly fractured strata, dense network of joints and local faults, which mainly include splays of regional faults.

A polyimide (PI)-based flexible bandpass filter is fabricated by self-metallization technology, which covers Wireless Local Area Network (WLAN) of 5.15—5.875 GHz. The measured characteristics indicate the flexible filter under flat state has the return loss of better than 20 dB, the minimum insertion loss of 0.83 dB, a 3 dB bandwidth of 0.725 GHz, and the central frequency of 5.5 GHz. At the same time, the designed filter is measured in different bending and folding conditions. Simulated and measured results are similar whether the filter is under flatting, bending, or folding conditions. Fatigue test and timeliness test are studied to confirm that the filter has stable chemical and mechanical properties. The formed silver layers fabricated by self-metallization technology have good mechanical and electrical flexibility. The designed flexible filter is promised for integration within future flexible electronics.

In this paper, we propose an acoustic block for widening the bandwidth and modulating center frequency of airborne transducers to improve the ultrasound imaging or metrology system. When acoustic block is attached, the characteristics of the ultrasonic transducer are changed by the squeeze film effect. Extra elastic and damping force are generated by squeeze film damping and can be changed according to parameters of acoustic block. For impedance matching, a CMUT vibrating in bending mode was used. The CMUT’s FBW is 3.18 % and the center frequency is 103.5 kHz. We changed the area ratio of the acoustic block and attached it to the CMUT. The FBW was changed to 7.14 to 9.14 % and the center frequency to 108.7 to 112.1 kHz. With acoustic block, conventional transducers can be transformed into transducers with better performance in areas such as non-destructive testing and ultrasonic imaging.

Continuous wavelet transform (CWT) has been proven to be an effective tool in feature extraction of non-stationary bio-signals. Therefore, hardware implementation of CWT has been widely investigated in wearable sensor integrated with local intelligence algorithm. To realize the feature extraction from low-frequency bio-signals, the design method of low-frequency Gm-C wavelet filter used in wearable sensor has been proposed in this paper. To alleviate the power constraint by wearable device, the Leap-Frog multiple-loop feedback filter structure is employed, which has low circuit complexity and sensitivity. Also, the transconductor consisting of simple differential pair is employed as Gm cell. By using low level bias current and deep weak inversion, low transconductance can be achieved to realize low frequency operation. A sixth-order Gaussian wavelet filter is designed in 0.18 $$\upmu$$ m CMOS process. Simulation results show that power consumption is only 392 pW at center frequency of 5.9 Hz, corresponding to dynamic range of 42.7 dB and figure-of-merit of 2.59 $$\times$$ 10 $$^{-13}$$ . Experiment result shows that the proposed wavelet filter can be used for accurate extraction of transient features in biomedical signal processing.

The present research work aims towards the design of a stepped impedance resonator (SIR) based dual band antenna having resonant frequencies at millimeter wave: V band (center frequency: 60 GHz) and W band (center frequency: 94 GHz). The structure comprises of stepped impedance resonator (SIR) patch, two stepped section impedance matching network and a microstrip feedline. The fractional bandwidth of the proposed dual band antenna is 2.9 GHz (4.8%) and 6.25 GHz (6.6%) at 60 and 94 GHz, respectively. The far field polar plots show broadside radiation pattern having gain of 7.9 dBi at 60 GHz and 4.2 dBi at 94 GHz. Further, as a testimony of this concept, scaling principle was used and accordingly microwave scaled antenna was devised. The prototype scaled hardware results matched closely with the designed mm-wave antenna. Further, the proposed dual frequency antenna finds enormous applications towards development of pioneering millimeter wave systems like; 60 GHz is focused on multi gigabit WPAN communication and 94 GHz frequency is currently extensively used for millimeter wave imaging applications. The proposed design is very simple, conformal and easily extendable as an array for MMIC applications for compact frontend design.

This article presents an analysis of spurious signals’ influence on automatic frequency control (AFC) in EPR spectrometers. The primary source of spurious signals is leakage across the circulator in the microwave bridge. Additionally, the signals reflected from connectors in the line between the circulator and the resonator modify that signal. Spurious signals may degrade the performance of AFC, significantly offsetting lock points from the center frequency of the resonator. The offset’s size depends on the parameters of the resonator and the amount of the circulator isolation. It can be minimized by the appropriate use of a phase shifter located in the line between the circulator and the resonator. Another way to avoid these problems is to introduce a leakage compensation arm to the microwave bridge.

This paper presents the design and simulation of a modified CMOS low noise amplifier (LNA) circuit in 180 nm CMOS standard technology. We modified a cascade LNA using π model of capacitor circuit. Impedance matching network at the input of proposed circuit provides low noise figure (NF) and suitable gain at the operating frequency of 6 GHz. Obtained simulation results after extracting post layout (with total chip size 2500*1600 μm2) provide higher gain (S21) of 19.75 dB and noise figure of 1.14 dB. The reverse isolation (S12) of the LNA is also achieved to − 30.8 dB. A comparison table confirms that the proposed LNA circuit has better performance than the other recent works.

In this work, broadband circularly polarized monopole antenna is proposed. The proposed antenna is designed by an FR4 substrate with a dielectric constant of 4.4 and thickness $$h = 1.6\;{\text{mm}}$$ . The size of the designed antenna is $$0.99\lambda_{0} \times 0.99\lambda_{0} \times 0.07\lambda_{0}$$ , where $$\lambda_{0}$$ is the free space wavelength at the center frequency of $$f_{0} = 12.36\;{\text{GHz}}$$ . A stub and a parasitic strip are loaded at the optimum positions on the ground plane to improve the results. The stub and parasitic strip helps to develop two orthogonal modes with the same amplitude for circular polarization. The proposed antenna offers − 10 dB simulated impedance bandwidth of 126% (4.55–20.16 GHz) and measured more than 129% (4.4–20.5 GHz). The 3-dB axial-ratio bandwidth (ARBW) of the monopole antenna is significantly enhanced by using a modified planar ground structure under the proposed patch. There are two 3-dB simulated and measured axial-ratio bandwidth (ARBW) of 86.5% (5.51–13.91 GHz), 16.7% (17.77–21 GHz) and 86.54% (5.5–13.89 GHz), more than 16.71% (17.76–21 GHz) achieved. The fabricated antenna is strongly desirable for WLAN (5.2–5.8 GHz), WiMAX (5.7–5.85 GHz), X-band (8–12 GHz), Ku-band (12–18 GHz) and fractional part of the K-band applications of wireless communication.

In this paper, a tunable, broadband metamaterial (MM) bandpass filter based on three-dimensional (3D) structure was designed. It improves the out-of-band attenuation problem of the traditional planar metamaterial filters. The filter has good out-of-band attenuation and produces two transmission zeros at low and high frequencies. The transmission rates at the two transmission zeros are − 20.412 dB and − 16.705 dB, respectively. The simulated results show that the 3 dB bandwidth is 46.156 THz. In addition, due to the symmetry of the structure, it is insensitive to electromagnetic (EM) waves with different polarization. It can also adjust the working bandwidth, the transmission zero and the center frequency. In the process of adjustment, the working bandwidth remains basically unchanged, while the transmission zeros and center frequency stay linear. The structure we designed provides a great possibility for the application of metamaterial filters in optical frequency devices.

In this article, a novel compact microstrip dual-narrowband bandpass filter (DNBPF) is presented with wide and high rejection levels in the stopbands. The location of each passband is independently controllable/tunable/selectable. The filter structure is made up of three-coupled-asymmetrical transmission lines, open-ended stubs and direct-transmission lines. Employing these lines can generate two narrowband passband filters. By combining these passband filters, the proposed DNBPF is configured. The proposed DNBPF is investigated. The center frequency of the first and second passband are 5.745 and 6.489 GHz, respectively. Also, the proposed DNBPF presents the fractional 3-dB bandwidth of the first and second passband 3.66 and 2.33%, respectively. It has the flattest group delay variations in comparison with previously published papers due to the design freedom. |S12

Ultrasound imaging through the intact skull is challenging because of the skull-induced aberrations and signal attenuation. We have designed an experimental ultrasound diagnostic system for noninvasive brain imaging through the intact skull. To overcome skull-induced aberrations and focus efficiently, the system implements the correction procedure based on a beacon approach. This approach is considered classical and highly accurate in comparison with other correction methods. Operation of the system requires two probes working at 3-4 MHz central frequency. The probes are attached coaxially on both sides of the head to the acoustic transparency windows.

In this paper, a metamaterial absorber based on graphene is proposed, designed and simulated numerically using multilayer structures. Before describing our work, the performance response of a three-layer structure is studied concerning one cylinder as a unit cell. Then, by varying the chemical potential of graphene (Fermi level of graphene) by applying external potential, the center frequency of this absorber can be adjusted. We will prove that by increasing the number of cylinders as fundamental elements in the unit cell, the bandwidth is also adjustable. Also, the center frequency can be affected by changing the dimensions of fundamental elements. Considering the above-mentioned items, the structure is investigated through increasing the graphene layers in which the absorber’s frequency response is wider respected to previous structures and the center frequency is adjustable as a result of variations in the chemical potential of graphene layers. It is shown that the proposed perfect absorber’s central frequency shift through graphene’s voltage variation is about 0.15 THz which can be increased to 0.3 THz by changing radius. In some of the introduced absorbers, the maximum value of the absorption has reached over 95%. The most important advantage of the proposed structure, which is the main purpose of designing terahertz metamaterial absorbers, is its adjustable bandwidth and center frequency, and simple fabrication.

In this paper concurrent design of Schottky diode based limiter and low noise amplifier (LNA), based on noise matching, is investigated to achieve minimum noise figure (NF) of the receiver chain. In design procedure of the LNA, the noise figure is minimum, gain at central frequency is 14.5 dB, and limiter structure tolerates up to 5 W continuous wave input power. In the proposed concurrent design, a pass-band filter is applied at the LNA output to attenuate undesired out-of-band signals. In the proposed design, the limiter-LNA is implemented with a 0.25 µm gate length AlGaAs/InGaAs pHEMT process. Measured noise figure of chain is 2.7 dB and average gain over 8.5–9.5 GHz frequency range and the gain at 9 GHz center frequency are 10 dB and 14.5 dB respectively. The performance results of proposed matching network are compared with traditional 50 Ω matching networks in limiter-LNA with identical circuit specifications.

This paper aims to improve the use of continuous wavelet transform (CWT) to identify the damping parameters from the free decay responses of structures. Numerical response functions (impulse response functions) were simulated with lower frequencies and higher damping parameters using the Hilbert Transform, and the damping parameters were estimated by extracting wavelet coefficients that corresponded to the frequency components of these numerical response functions. Numerical simulations were also performed on single-, separated- and closed-mode systems to analyze the effect of the center frequency of the mother wavelet on the estimation of system damping parameters. Experiments were performed on a two-span H-Beam. This study focuses on the damping parameter estimation errors for the center frequency setting of the mother wavelet function. The reliability of the estimated damping parameters can be improved by selecting the center frequencies of the mother wavelet function so that each corresponding scale is localized at half of the total scale.

Mechanical tuning of a 3D-printed, polymer-based one-dimensional photonic crystal was demonstrated in the terahertz spectral range. The investigated photonic crystal consists of 13 alternating compact and low-density layers and was fabricated through single-step stereolithography. While the compact layers are entirely polymethacrylate without any intentional internal structures, the low-density layers contain sub-wavelength sized slanted columnar inclusions to allow the mechanical compression in a direction normal to the layer interfaces of the photonic crystal. Terahertz transmission spectroscopy of the photonic crystal was performed in a spectral range from 83 to 124 GHz as a function of the compressive strain. The as-fabricated photonic crystal showed a distinct photonic bandgap centered at 109 GHz, which blue shifted under compressive stress. A maximum shift of 12 GHz in the bandgap center frequency was experimentally demonstrated. Stratified optical models incorporating simple homogeneous and inhomogeneous compression approximations were used to analyze the transmission data. A good agreement between the experimental and model-calculated transmission spectra was found.

This paper presents a two-stage tunable power amplifier (PA) fully-integrated in 130 nm CMOS process. This multi-band PA consists of reconfigurable input, interstage, and output matching networks in order to tune the center frequency in use. The proposed tunable power amplifier enables three different bands with center frequency of 900 MHz, 1450 MHz, and 1900 MHz. By switching these bands, the designed power amplifier covers frequency range of 700 MHz–2200 MHz known as Long-Term Evolution mobile network. As a result, the proposed tunable power amplifier obtains small-signal gain (S21) of 27.8 dB/29.4 dB/28.6 dB, saturated output power (Psat) of 22.4 dBm/23.0 dBm/23.2 dBm, and power added efficiency of 21.0%/23.7%/25.0% at three targeted frequency bands, respectively. The proposed fully-integrated triple-band power amplifier chip layout occupies an area of 2.25 mm2 including bond pads.

Two factors affecting the bandwidth of a reflectarray, the element phase error and the non-constant path delay phase error, have been investigated. A new solution is proposed to reduce the effect of the second factor. Using this method, without adding any particular complexity to the structure, the gain bandwidth of an array rises from 17 to 24%. This array is designed at the center frequency of 1.2 THz which can be used as a lens in the terahertz range. Since the dimensions of an array for such an application would be very large compared to the wavelength, the near-field to far-field transformation is used to accelerate the simulation time.

Two voltage-mode topologies single input multi-output universal fractional filters with high input impedance are proposed. The proposed analog filters consist of three DVCC+ blocks, two grounded capacitors and two resistors targeting the minimum passive elements. The proposed topologies provide a realization for all standard fractional filter functions (HP, LP, BP, AP and notch filter). The effect of Fractional order on filter responses in the range of $$\alpha$$ from 0.7 to 1.2 was studied. Fractional order has been investigated for different filter responses in terms of cutoff, gain, phase and noise. The central frequency was designed to be 110 KHz for the first topology, while that of the second topology is around 100 KHz. The proposed filters are simulated using Cadence TSMC 130nm with dual supply voltages $$\pm \,0.75V$$ . A performance comparison between the proposed topologies and the topologies in the literature shows that the proposed architecture gives an acceptable performance.

In this paper, a Mercedes-Benz logo antenna with a metal plate located at an optimized distance from the proposed antenna is introduced as a wearable antenna to operate in the industrial, scientific, and medical band with center frequency of 2.45 GHz. The metal plate is integrated with the antenna as an isolator and a reflector to improve the radiation performance of the proposed design, reduce the back radiation and reduce the specific absorption rate, when loaded on the human body. The front-to-back ratio improves by 18.2 dB, by adding a metal plate to the structure. The proposed antenna with coplanar waveguide-fed with dimensions of 35 mm × 35 mm × 0.508 mm is printed on a Rogers 4003C substrate, and has an impedance bandwidth from 2.20 to 2.56 GHz, the gain of 7.3 dBi at 2.45 GHz, and SAR levels is less than the criteria set by the FCC and ICNIRP. Nowadays, attention to health as product quality assurance factor along with other technical specifications is the requirements of industrial productions, especially in competition with superior brands. Based on comparisons made with similar works, the proposed wearable antenna structure can be used for wireless body area network.

A magnetron-injection gun able to provide very high ratio tj≈ 0.5 of the beam current to the Langmuir current has been designed, while maintaining good enough quality and stability of a formed helical electron beam. The specific feature of the gun is the shape of the cathode with two singular points of the electric field distribution which ensure close to uniform electric field profile within the emitter ring for wide range of operating currents. The gun provides the smoothed dependence of the beam parameters for currents up to 1.5–2 A and is suitable for wide (~ 10 GHz) frequency range gyrotron operation with the central frequency of 0.2 THz and output power ~ 1 kW within the whole tuning band. Such approach for the magnetron-injection gun design can be used for development of other promising high power sub-THz gyrotrons.

In the twenty-first century, graphene is widely used in wireless communication, especially in terahertz applications because of its amazing electrical, mechanical, and optical properties. This paper presents a graphene-based microstrip patch antenna at 0.72 THz resonant frequency for wireless communication. The proposed antenna shows 37.50% impedance bandwidth ranging from 0.53 to 0.84 THz at the center frequency of 0.72 THz. The result is demonstrated in terms of return loss (s11

In this paper, a fifth-order WR-3 band waveguide filter with two transmission zeros (TZs) is presented. The design process is described and manufacturing issues are addressed. The filter is designed to fulfill a center frequency of 237.9 GHz and a fractional bandwidth of 2.64%. Three identical filters are manufactured with the classical computerized numerical control (CNC) milling technique in order to obtain information about the manufacturing repeatability for filter structures in the WR-3 band. The comparison shows that even in very high frequency regions a good repeatability can be achieved, if modern high-speed cutting (HSC) CNC milling machines are used. A comprehensive tolerance analysis is accomplished to classify the obtained results. The filters were manufactured from brass to ensure a meaningful comparability and due to the good machining qualities in CNC machines. In order to reduce the losses, the filters are afterwards sputtered with different materials (gold, silver, copper) to evaluate the effect on the insertion loss at very high frequencies. In comparison with the literature, it is shown that even narrow-band filters, which show a high sensitivity to machining tolerances, can be manufactured with high reliability and manufacturing repeatability in modern CNC milling machines. One of the measured filters shows a return loss higher than 20 dB over the whole passband.

The resonant-mass gravitational wave detector SCHENBERG was designed by the Brazilian group Graviton to be sensitive to a central frequency nearing 3200 Hz and a bandwidth of 200 Hz. It has a spherical antenna weighing 1150 kg that is connected to the outer environment by a suspension system designed to attenuate local noise due to seism as well as other sources. Should a gravitational wave pass by the detector, the antenna is expected to vibrate. This motion will be monitored by six parametric transducers whose output signals will be digitally analyzed. In order to improve the sensitivity of the detector, it must be cooled down to the lowest possible temperature, and for this purpose a dilution refrigerator is planned to be implemented in the detector. It is known that such device produces vibration when operational, consequently introducing noise in the system. Using the finite elements method, this work investigates thermal connections between the dilution refrigerator and the sphere suspension that allow the detector to operate within its projected sensitivity. The finite elements method showed an attenuation of 240dB in the best-valued thermal connection.

A compact wideband multi frequency microstrip antenna for wireless communication is proposed in this paper. The antenna is designed by introducing meandered slot on the patch and a pair of spur lines along the triangular notch on the finite ground plane. The overall size of the fabricated antenna is very small and low profile as the total dimension is 20 × 16 mm2. The proposed antenna operates at 3.7 GHz, 4.27 GHz and 5.1 GHz which may be suitable for WiMAX and WLAN applications. In addition with multi frequency operation a wide bandwidth (VSWR ≤ 2) has been achieved from 6 to 13.7 GHz i.e. 78.2% bandwidth of center frequency, which is suitable for X-band communication and ITU band applications. The meandered slot on the patch causes multi frequency operation of the antenna with 60% compactness and the spur line along with triangular notch on finite ground plane cause bandwidth enhancement.

This research is focused on the design and realization of a low-cost conformal electromagnetic absorbing layer based on a composite of carbon nanotubes (CNTs) in polydimethylsiloxane (PDMS). It is experimentally demonstrated that the electromagnetic properties of the composite, i.e., its permittivity and loss tangent can be engineered. On that basis, composites with different concentrations of CNTs (and as a result different complex permittivities) are used for the design of a multi-layer absorber. In order to validate the design, a prototype of the absorber is fabricated and concept and the design are validated both numerically and experimentally. Experimental results show a measured absorption better than 96% at the central frequency of operation of the absorber. The proposed absorber benefits from a flexible shape that can be conformed to cover curved surfaces. Moreover, since the proposed absorber is initially in a semi-liquid state, it can be applied as a coating layer on almost any geometry. The absorber is waterproof and polarization independent. It is also shown that the operating frequency of the absorber can be pneumatically tuned.

The steady rise in the deployment of grid-connected inverters is driving a need for more efficient and accurate grid synchronization techniques. In this paper, digital implementation methods are proposed to increase grid synchronization accuracy when an integrated filter is used. First, a method to compensate for the computational delays in the implementation of integrated filters with numerical integrations is presented. Second, a simple method to estimate the grid frequency is introduced for updating the center frequency of integrated filters. The proposed methods have been implemented in a digital signal processor and tested with a real-time simulator. They achieve ripple errors of 0.14 mHz and 0.008° in the frequency and phase angle estimations, respectively.

Implementation and parametric analysis of single and dual band planar filtering antennas suitable for WLAN applications are described in this paper. The single band filtering antenna is designed using the filter synthesis approach in which the last resonator of the 5th order Chebyshev stub loaded bandpass filter is replaced by a monopole antenna. The dual band filtering antenna is designed by adding Electromagnetic Band Gap structures in the ground plane of stub fed patch antenna. The parameters of the two filtering antennas are analyzed and provide validation of the merits and demerits of the two design techniques used in the implementation of filtering antennas. Single band filtering antenna is designed at a center frequency of 2.4 GHz and has a gain of 3.1 dBi with less than − 16 dB reflection coefficient. The filter selectivity at the band edges is found to be 75/86 dB/GHz. The size of the single band filtering antenna is 0.68 λ0 × 0.216 λ0 (λ0 is the operating wavelength) and the structure is suitable for WLAN applications. Dual band filtering antenna is designed to have two operating bands at center frequency 1.875 GHz and 2.4 GHz. The reflection coefficient at the two operating bands is found to be less than – 20 dB and produces radiation nulls on either side of the two operating bands. The proposed dual band filtering antenna has dimension 0.57 λ0 × 0.714 λ0 and is suitable for LTE and WLAN applications as it has a gain of 5.8 dBi and 4.08 dBi at 1.875 GHz and 2.4 GHz respectively.

This paper proposes a higher-order fully passive N-path filter (HOFPNF) with better pass-band shape and higher out-of-band rejection compared with the conventional N-path filter. Two band-pass filters with slightly different center frequencies are constructed using two frequency mixers and two complex filters which are completely composed of switches and capacitors. The final output of the HOFPNF can be obtained by subtracting the outputs of these two filters. The input–output characteristic of the proposed filter is derived using the Fourier transform. Comparing the theoretical expressions with Spectre RF PSS-PAC simulation results verifies the correctness of the derived transfer function. The system is realized at TSMC 0.18 µm technology. There is no static power consumption, and the proposed filter represents high linearity, thanks to fully passive implementation. Based on post-layout simulations, the following results are obtained: the − 3 dB bandwidth of 20 MHz, center frequency tunability range of 0.2–1.2 GHz, maximum rejection of 61.8 dB (@ fLO = 500 MHz), 4.5–6.7 dB in-band loss, IIP3 > 17.5 dBm, P1dB > 7.9 dBm and the noise figure (NF) is 6.3–7.5 dB. The dynamic power consumption of the system increases from 2.95 to 19.4 mW by tuning the center frequency at the whole frequency band.

A polymer-based one-dimensional photonic crystal with a defect mode was demonstrated for the terahertz frequency range. The photonic crystal was designed to achieve a photonic bandgap centered around 100 GHz with a narrow defect mode at the center frequency. The defect mode allowed a narrow band transmission at the center of photonic bandgap, while the transmitted signal was suppressed in the rest of the bandgap. The photonic crystal incorporated two identical sets of alternating compact and low-density layer pairs symmetrically enclosing a defect layer. The compact layers consisted entirely of polymethacrylate with no intentional internal structures, while the low-density layers were composed of sub-wavelength-sized columns. The columnar structures had a volumetric fraction selected to provide a desired index contrast between the adjacent layers. The photonic crystal samples were fabricated in a single-step stereolithography using a commercial system. THz transmission spectroscopy measurements were carried out to determine the optical response of the sample in a range from 82 to 125 GHz. Stratified optical layer model calculations were used to evaluate the transmission data. A distinct photonic bandgap with a defect mode centered at 99 GHz was observed in the experimental transmission spectra. A good agreement between the relevant model parameters and the corresponding design parameters was found.

Nowadays, terahertz and sub-terahertz frequencies are experiencing a significant interest from both academic and industrial world, since they offer a wide and unused spectrum available for different applications, as high-throughput communications, efficient imaging systems and medical uses. In this work an innovative sub-THz voltage-controlled oscillator (VCO) realized with a 130-nm SiGe process is proposed and described in detail. The technology is the SG13G2 bipolar-complementary-metal-oxide-semiconductor (BiCMOS) provided by IHP foundry. The signal source is conceived for high-resolution THz imaging camera; at design level it has been defined with a push-push architecture and adopts an oscillator core based on a Colpitts topology. State-of-the-art performance has been obtained thanks to the proposed design choices that are uncommon at these frequencies, as for instance, the VCO output taken from the common base node, the use of varactors in anti-series connection and the possibility to define a double output at different harmonic frequencies. These, as well as other innovative expedients, allow to simplify the integration at system level and to achieve compact sizes, very low power consumption and almost constant output power level over the full tuning bandwidth. A relative tuning range of about 5.5% has been obtained around a central frequency of 330 GHz, while the output power is about − 8 dBm with a maximum variation of 0.4 dB. Also the phase noise of − 110 dBc/Hz at 10 MHz offset is very promising. Measurements over different chip samples demonstrate the robustness of the proposed solution and the reliability of the design.

In this paper, an enhanced voltage controlled oscillator (VCO) at center frequency 125 GHz with tuning rang of 24% is presented. The proposed idea is based on the tuning capacitance using MOS varactor. The structure is consisted of applying an MOS varactor capacitor to the drain and bulk (in parallel) of NMOS transistor in 65 nm CMOS standard technology. The obtained output of the proposed VCO at 2nd harmonic is tunable at 110–140 GHz frequency with applying ± 1.2 input tuning voltage. Simulation results of the proposed circuit are obtained after extracting post layout (with total chip size of 0.07 mm2) and confirm theoretical results. Compared to the resent designs, the obtained results indicate that the proposed circuit has high tuning range, low die area and a good figure of merit @ 1.2 power supply voltage.

In this paper, a broadband and compact oversized rectangular waveguide transition is proposed. Employing novel quadruple-ridged waveguide technology, two quadruple-ridged waveguides achieve an extreme compactness interconnection from a standard rectangular waveguide to an oversized rectangular waveguide. This design can be used as an alternative way to create a new oversized rectangular waveguide transition. The length of the transition is only 0.3λ, where λ is the TE10 mode wavelength at the center frequency. For verification purpose, a back-to-back transition was designed, fabricated, and measured. Measured results show that the return loss is greater than 20 dB and the insertion loss is less than 0.2 dB in the operating frequency band. Therefore, we can infer that the return loss and insertion loss of single transition are around 25 dB and 0.1 dB, respectively.

Compact, tunable and wide band stop filter (BSF) for wireless application is presented. The proposed filter is composed of compact rectangular microstrip open loop resonator with stub loaded resonator as building blocks of the filter. First, two vertical lumped capacitors are inserted in the open loop resonator from top to bottom of the substrate at the place which has maximum electric field to decrease the resonance frequency which in turn miniaturize the filter size. The resonance frequency of the fundamental mode is shifted from 5.5 to 4.2 GHz when lumped capacitors of 0.2 pF are added. Second, the capacitance of the open-ended stub can be changed to control the second resonance mode of the filter. Also, by inserting another vertical capacitor at the end of the open-ended stub, the second resonance mode can be controlled and reduced. Finally, by properly selecting the capacitance of the third lumped capacitor, the second resonance mode can be designed to be close to the fundamental mode and hence wide band stop filter can be achieved. The proposed BSF has some appropriate features such as compact size (its size has more than 40% size reduction), wide stopband and most importantly tunability of stopband. The band stop filter has a center frequency of 6.2 GHz, a stop band from 3.5 to 9 GHz, insertion loss lower than − 30 dB, and a return loss higher than 0.4 dB is accomplished inside the stop band. The measured results have good matching with the simulated results.

In this paper, a broadband and polarization-insensitive metamaterial absorber (MA) operating in the visible light band based on a cascade structure is proposed, and the main structure of MA consists of three metal resonator layers (MRLs), a metal reflector at the bottom, and a dielectric substrate between them. Each MRL consists of four different resonators. The similar resonator is proportional to the size of the top view in the different MRLs. Through the different absorption effects generated by different MRLs, a MA working in the visible light band is obtained, which can cover 490–825 nm. Absorption bandwidth can be expanded by adding different MRLs and placing different resonators near the same layer. The center frequency of the absorption spectrum can be controlled by changing the layer distance between different MRLs. To better understand the physical mechanism of absorption, the electric and magnetic field intensity distributions, the power flows, and the power loss densities also are investigated. We also found that the better permanence can be obtained with the lower incident angle.

A novel and miniaturized 4 × 4 butler matrix (BM) is proposed in this work. This proposed butler matrix is designed with four 3 dB quadrature (90°) forward wave coupled line coupler (FWCC) and two 45° Schiffman phase shifter. This BM is designed at center frequency of 2.4 GHz using FR4 substrate. The crossover of this BM has been replaced with a 0 dB FWCC. The performances of all couplers have been improved with the help of defected ground structures (DGS). Two C-shape and one I-shape DGSs are etched at the ground plane of each coupler, and two C-shape and one dumbbell shape DGSs are etched at the ground plane of 0 dB crossover which enhance the performance of the BM. This proposed BM provides a maximum bandwidth of 120 MHz at each port and occupies a total area of 0.677λ0 (84.74 mm) × 0.612λ0 (76.56 mm).

In this paper, a novel multiband coplanar waveguide-fed slotted transparent antenna is presented. The structural design of the radiating element is based on the semicircular curves in the form of slots on the patch to achieve multi-band characteristics with improved bandwidth. The overall structure having a size of λ0/2.67 × λ0/2.11 achieves transparency and a lightweight due to the presence of Plexiglas as a substrate material and AgHT-8 as a conductive material including the circular slotted patch and related CPW feeding line at the center frequency of the lowest operation band. The proposed antenna has the multiband operation characteristics with the center frequencies of 2.58 GHz, 3.67 GHz, 6.2 GHz having the impedance bandwidth of 19.84% (2.27—2.77 GHz), 1.76% (3.61—3.74 GHz) and 53.58% (4.50–7.79 GHz) respectively. The agreement between the numerical computation and measurement results of RF performance characteristics point out the technical potential of the proposed optically transparent antenna for short range multiband versatile wireless applications.

In this paper, we improved the error vector magnitude (EVM) performance of six-port receiver using a low noise amplifier (LNA) bias control algorithm based on analyzing the correlation between normalized output DC offset voltage and EVM relative to input radio frequency (RF) power variation. In contrast to the other works published in the literature, we consider test setup through which the software impairments of six-port receiver blocks are considered. Therefore, in this work to substantiate the EVM improvement, a designed 26–30 GHz CMOS six-port receiver is used which consists of LNA, coupled line bandpass filter, six-port correlator, diode power detectors and two instrumentation amplifiers for recovering the baseband I/Q data. The EVM improvement process is assessed in terms of 64QAM modulation, and according to obtained results, EVM is reduced from 61% when using constant DC bias to 22% achieved with an LNA bias control algorithm for low input power (− 60 dBm) at the center frequency of 28 GHz. Moreover, the EVM is become less sensitive to input RF power, and also the dynamic range is improved more than 20 dB.

This paper presents the applied pulsed radar signal processing which works in the C-band for imaging of walking human responses behind the wooden wall and foliage environment for military monitoring applications. The overall scenario of this work has been theoretically modelled to provide an insight into the interaction between the pulsed radar system and the surrounding environment. The experiment of this work has been performed under the (1) wooden wall and (2) foliage environment for the purpose of a preliminary study. Considering that there have been many types of research have been done utilizing UWB with a lower center frequency, this work mainly focuses on proposing a series of the pulsed radar signal processing worked in unique C-band for extracting the walking human response from other reflections associated with clutters. The three-dimensional images of walking human have been finally reconstructed in 20 dB scale under the wooden wall and foliage environment.

We propose and discuss a compact and tunable plasmonic terahertz (THz) metamaterial switch based on graphene microcavity. Due to the joint effect of graphene plasmon resonances and Fabry–Perot oscillations, this metamaterial structure can be switched from the ON state to OFF state with the maximum intensity attenuation larger than 95% (ON–OFF ratio larger than 30 dB). The central frequency of the switch could be tuned in a wide frequency range from 3.6 to 9.6 THz by tuning the Fermi energies of the graphene patterns. Moreover, the metamaterial structure is valid for a wide range of incident angles of both transverse electric (TE) and transverse magnetic (TM) polarizations with the highest Q factor of 15.5. This investigation promises the development of high-performance, widely tunable THz switch in chip integrated photonic circuits without reconstructing the physical structures.

A polymer-based one-dimensional photonic crystal with a photonic bandgap in terahertz frequency range was designed and fabricated through stereolithography and was characterized using THz spectroscopy. The photonic crystal studied here consists of alternating compact and low-density layers. The compact layers were fabricated from fully polymerized polymethacrylate without any intentional internal structure. The low-density layers consist of sub-wavelength sized columns, where the volume density was selected to provide sufficient contrast between the dielectric functions of adjacent layers. The photonic crystal samples were fabricated in a single step using a commercial stereolithography system and polymethacrylate compatible with the system. Transmission spectroscopy in a range from 82 to 125 GHz was used to determine the THz spectral response of the sample. The transmission data were analyzed using stratified optical layer model calculations. A distinct photonic bandgap with a center frequency of 111 GHz was observed in the experimental transmission spectra. Bruggeman effective medium approximation was found to accurately describe the dielectric function of the low-density layers. An excellent agreement between the relevant model parameters and the corresponding design parameters was found, indicating the versatility of the approach for the fabrication of photonic crystals for the THz spectral range.

A 3D band pass frequency selective surface structure with desired center frequency and bandwidth, designed by multi-objective optimization algorithms, is introduced in this paper. The ant colony optimization technique is used to achieve optimal design properties with the required characteristics. The performance of the manufactured structure using the 3D printing method is measured to verify the optimized structure for normal incidence. Come up with the results, the convenience of the optimization algorithm accordingly 3D printing can help in designing and constructing complex 3D structures.

A new design of graphene-based plasmonic waveguide is presented and its transmission properties are studied. The transmission channel is such designed that the chemical potential of graphene is periodically changed in two dimensions by application of voltage bias through a patterned substrate. Because of periodicity of structure, it shows a forbidden bandgap at terahertz (THz) frequencies similar to a conventional photonic crystal. The effect of different structure parameters on the rejection band frequency range is numerically studied and the switching function of the proposed waveguide is observed with rejection efficiency of more than 99%. The reported relation between center frequency of the rejection band and also FWHM with the related chemical potential of the 2D-GPC confirm the real-time tunability of the proposed structure employing an external bias voltage. According to the ultra-integrated size of the structure and its remarkable optical efficiency in THz range, such a realization can pave the way for further development in band rejection–based nanoplasmonic applications such as filtering and switching devices.

The objective of this work is to achieve a compact wideband band-stop filter using complementary split ring resonators (CSRR) as the fundamental element. The relation between the geometry and resonances of the CSRR were studied analytically along with their field distribution to determine the factors governing coupling between the rings of the CSRR. The effects of the inner-outer ring orientation on resonances of the CSRR has been studied and the resulting properties have been used to design the proposed compact wideband band-stop filter prototype operating with a center frequency of 2.5 GHz and a bandwidth of 1 GHz. The area of the proposed filter is 0.078 λg2 with a fractional bandwidth of 39.76%. This structure has following advantages: more compact, wide bandwidth and occupies less area. The fabricated prototype was tested and the results were promising representing this works potential.

This paper presents numerical quantification of depth-dependent free surface effect on ground motion characteristics for the earthquake-resistant design of underground structures. The SH-wave responses of homogeneous half-space model are computed on the vertical arrays using different central frequency in the Gabor wavelet for various angles of incidence. The analysis of simulated results reveals that the obtained free surface effect at the free surface as 2.0 is not affected by the angle of incidence and the magnitude of earthquake. On the other hand, depth-dependent free surface effect in homogeneous half-space depends on both the magnitude of the earthquake and the angle of incidence. However, in the case of layered earth model, it is conservatively concluded that the free surface effect almost linearly decreases from 2 at the free surface to 1 at a depth equal to one-eighth of wavelength of the corner frequency of earthquake. It is recommended to transfer the predicted peak ground acceleration at the free surface to the desired depth using a linear reduction factor from 1.0 at free surface to 2.0 at a depth equal to one-eighth of the wavelength of the corner frequency of the postulated earthquake for economical earthquake resistant design of the underground structures.

The development of sub-wavelength acoustic metamaterials such as local resonance phononic crystals is leading new research directions of elastic wavefront control as well as noise attenuation and vibration reduction. In this work, the low-frequency bandgap characteristics of a new three-dimensional local resonance phononic crystal model composed of lead sphere and multihole silicone rubber matrix are studied by finite element simulations. Compared with the reference model without matrix holes (Zhao et al. J. Sound Vib. 303:185, 2007), the first complete bandgap of the designed model possesses a lower starting frequency and a 133.68% relative bandwidth, that is the ratio of the bandwidth to the center frequency. The numerical results imply that the structure exists obvious transmission attenuation in the bandgap frequency range, and the effective mass density turns negative. It could be found that the excitation of torsional resonance mode as dominant mode for bandgap opening is attributed to the addition of the multiple holes, especially the cutting holes in the matrix, giving rise to the widening of bandgap. The effects of the component materials and the geometric parameters on the bandgap are further investigated.

In this article, we have proposed and demonstrated a new approach to implementing microwave photonic filter (MPF) with switchable, tunable and reconfigurable passbands based on a multi-wavelength fiber laser (MWFL) cooperating with a fiber Mach–Zehnder interferometer (FMZI). An EDFA and an SOA have been employed as a hybrid gain medium in the laser cavity, to suppress the homogeneous broadening of EDF. By inserting the FMZI in the fiber laser cavity, MWFL with tunable and switchable wavelength spacing has been achieved, which can be used as the multi-wavelength optical source to implement switchable, tunable and reconfigurable MPF together with a dispersive medium. By tuning the length of variable optical delay line (VODL), the wavelength spacing of the MWFL can be changed, and thus the passband’s central frequency of the MPF. By adjusting the polarization states, gain of EDFA or SOA of the laser cavity, the shape of the laser output can be adjustable, and as a result, shape-adjustable passbands of the MPF have been realized. By introducing the reflective FMZI structure as the wavelength selective component and carefully adjusting the polarization states, half number of the passband can be suppressed, which means the MPF can be switchable. The proposed MPF exhibits shape-adjustable and switchable passbands and enjoys more flexibility compared to previous methods.

We propose and experimentally demonstrate a multi-frequency optoelectronic oscillator (OEO) based on phase-modulation to intensity-modulation (PM-IM) conversion. A microwave photonic filter (MPF) incorporating an optical fiber Bragg grating Fabry-Perot (FBG-FP) filter and an electrical yttrium iron garnet (YIG) filter in two branches are used to select the oscillation modes of the OEO. By adjusting the wavelength of laser source or the central frequency of YIG filter, two frequencies can be tuned independently within a wide range. The single sideband (SSB) phase noises of the generated frequencies are measured experimentally. Moreover, the OEO shows potential ability to achieve more frequencies oscillation by multiplexing more optical and electrical filters.