GHz Center Frequency Research Articles

Reflector-Backed Antenna for UWB Medical Applications with On-Body Investigations

A recent reflector-backed antenna model is proposed in this paper for wireless capsule endoscopy localization. The antenna is designed to operate at the lowest 802.15.6 mandatory UWB (ultrawideband) channel, i.e., 4 GHz center frequency with 500 MHz bandwidth. The antenna achieves a good directivity and radiates well over the frequency band of interest. The proposed antenna was constructed within three successive steps. Initially, a planar omnidirectional antenna was designed of 3.15 dBi gain at 4 GHz. Since the antenna aims to operate as a receiving antenna, good directivity is preferred. Thus, an air-filled cavity was included backing the planar antenna to bolster the directivity toward the radiating element. The cavity-backed antenna has a measured gain of 6.4 dBi. The antenna was evaluated next to the homogenous and multilayer models. Then, the antenna design was optimized, by reducing its size, to a reflector-backed antenna structure reaching a maximum gain of 5.3 dBi, which is still promising for the regarded application. The body effect on the antenna matching was evaluated by means of multilayer and voxel models simulating the human body. This was followed by on-body measurements involving real subject. The depth of in-body propagation, from skin to small intestine, was studied using the multilayer and voxel models. Simulations were run using the CST Microwave Studio tool. While prototyping, free-space and on-body measurements took place at University of Oulu, Finland.

A PVT-Robust Super-Regenerative Receiver with Background Frequency Calibration and Concurrent Quenching Waveform

A process-voltage-temperature (PVT)-robust, low power, low noise, and high sensitivity, super-regenerative (SR) receiver is proposed in this paper. To enable high sensitivity and robust-PVT operation, a fast locking phase-locked-loop (PLL) with initial random phase error reduction is proposed to continuously adjust the center frequency deviations of the SR oscillator (SRO) without interrupting the input data stream. Additionally, a concurrent quenching waveform (CQW) technique is devised to improve the SRO sensitivity and its noise performance. The proposed SRO architecture is controlled by two separate biasing branches to extend the sensitivity accumulation (SA) phase and reduce its noise during the SR phase, compared to the conventional optimal quenching waveform (OQW). The proposed SR receiver is implemented at 2.46 GHz center frequency in 180 nm SMIC CMOS technology and achieves better sensitivity, power consumption, noise performance, and PVT immunity compared with existent SR receiver architectures.

Reinforced concrete mapping using full-waveform inversion of GPR data

Mapping the location and dimension of reinforcing bars in concrete can be critical for assessing the structure and state of reinforced concrete. Concrete structures, such as bridge pilings or cell phone tower foundations, are integral to modern life. Ground penetrating radar (GPR) is commonly used for mapping rebar grids, but traditional GPR data processing techniques fail to provide reliable information on the diameter of bars. Full-waveform inversion (FWI) of surface-coupled common-offset GPR B-scans (profiles) over reinforced concrete improves estimates of rebar diameters over more conventional ray-based methods. The method applies a sparse blind deconvolution (SBD) technique to obtain the optimized source wavelet and a sparse representation of the subsurface reflectivity series. A ray-based analysis is then performed on the estimated reflectivity model to define the initial geometry model to start the FWI. Applying this method to a synthetic data set and two real data cases with 1 and 2.6 GHz center frequency antennas results in errors in the rebar diameter estimates of less than 11% for rebars with concrete cover of 7.5 cm or less. These results compare favorably with those obtained from other methods that require cross-polarized antennas or ancillary equipment. The synthetic model demonstrates that the combination of SBD and FWI also improves ray-based estimates of the concrete permittivity and conductivity.

On-body Cavity-Backed Low-UWB Antenna for Capsule Localization

The paper presents a novel antenna operating at the lower UWB band (3.75–4.25 GHz), defined originally in IEEE 802.15.6 standard for Body Area Networks (BAN) applications. The proposed antenna is designed for biomedical application, wireless capsule endoscopy localization. In other words, the concerned application is dedicated to track a capsule, by means of an external device, swallowed by the patient to provide captured images of the Small Intestine (SI), essential part of the GastroIntestinal (GI) tract, and transfer them in real-time to the external device. In this context, antenna with and without cavity-backed structures, are presented and compared with the requirements for a receiving antenna in terms of directivity and bandwidth coverage in question. It was revealed that the cavity approach improved the antenna gain up to 8 dBi, at the 4 GHz center frequency, compared to 6 dBi without the cavity presence. Simulations were carried out using CST Microwave Studio, and the results were validated by measurements in proximity to human body. The antenna safety issue was assessed with CST SAR (Specific Absorption Rate) calculation, in compliance with IEEE/IEC 62704-1 standard. Results showed a maximum SAR of 0.112 W/kg and 0.005 W/kg at 4 mm and 30 mm antenna-skin distance, in the range of the SAR limit guidelines defined by safety standards. The cavity-backed antenna ability to penetrate the human tissues, to reach the small intestine layer was studied by means of CST voxel model and compared to a multi-layer model emulating the dielectric properties of the human tissues at 4 GHz. This analysis was conducted using power flow results and completed by the power field probes at the several tissue interfaces.

Studying the Construction of Floor Mosaics in the Roman Villa of Pisões (Portugal) Using Noninvasive Methods: High-Resolution 3D GPR and Photogrammetry

Over the past decade, high-resolution noninvasive sensors have been widely used in explorations of the first few meters underground at archaeological sites. However, remote sensing actions aimed at the study of structural elements that require a very high resolution are rare. In this study, layer characterization of the floor mosaic substrate of the Pisões Roman archaeological site was carried out. This work was performed with two noninvasive techniques: 3D ground penetrating radar (3D GPR) operating with a 1.6 GHz central frequency antenna, which is a very high-resolution geophysical method, and photogrammetry with imagery obtained by an unmanned aerial vehicle (UAV), which is a very high-resolution optical method. The first method allows penetration up to 30–40 cm depth and 3D models can be obtained, and with the second method, very high detail surface images and digital surface models can be obtained. In this study, we analyze a combination of data from both sensors to study a portion of the floor mosaic of the Pisões Roman Villa (Beja, Portugal) to obtain evidence of the inner structure. In this context, we have detected the main structural levels of the Roman mosaic and some internal characteristics, such as etched guides, internal cracking, and detection of higher humidity areas. The methodology that we introduce in this work can be referenced for the documentation of ancient pavements and may be used prior to carrying out preservation activities. Additionally, we intend to show that a Roman mosaic, understood as an archaeological structure, does not consist of only beautiful superficial drawings defined by the tesserae, but these mosaics are much more complex elements that must be considered in their entirety for preservation.

Design and simulate a doherty power amplifier using GaAs technology for telecommunication applications

<span>In this paper, a Doherty power amplifier was designed and simulated at 2.4 GHz central frequency which has high efficiency. A Doherty power amplifier is a way to increase the efficiency in the power amplifiers. OMMIC ED02AH technology and PHEMT transistors, which is made of gallium arsenide, have been used in this simulation. The Doherty power amplifier unique feature is its simple structure which is consisting of two parallel power amplifiers and transmission lines. In order to integrate the circuit, the Doherty power transmission amplifier lines were implemented using an inductor and capacitive components. Also, the Wilkinson power divider is used on the chip input. To improve the efficiency, the auxiliary amplifier dimensions is selected enlarge and the further input power is allocated it by the power divider. A parallel R-C circuit has been used at the input of transistors to improve their stability. Simulation results show that the Doherty power amplifier has 17.2 dB output power gain, 23 dBm maximum output power, and its output power P<sub>1dB</sub> =22.6dBm at compression point -1 dB, also, its maximum efficiency is 55.5%.</span>

A 0.34 mm2 1 Gb/s Non-Coherent UWB Receiver Architecture With Pulse Enhancement and Double PLL Clock/Data Packet Recovery

This paper presents a compact impulse-radio ultra-wide band non-coherent receiver architecture for high data rate wireless neural recordings from active high-density CMOS-probes. The system is capable of receiving, synchronizing, and demodulating a continuous on-off keying pulse stream at 1 Gb/s and 4 GHz center frequency using an active area of 0.34 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a single 31.25 MHz crystal reference. An asynchronous threshold energy detector, including a pulse enhancement baseband with an all-digital back-end, recovers incoming transmitter clock (CDR) and acquires packet synchronization based on a data-aided mechanism (DPR). Results shows that a prototype of the receiver integrated in a 130 nm CMOS process recovers synchronization in 30 ns. The system includes I/O output buffers and driver logic at 1.8 V supply operating at 1 GHz on a 50 $\Omega $ load and crystal oscillator. Overall, it consumes 115 pJ/pulse, while the receiver core only consumes 12 pJ/pulse. This paper presents the receiver architecture, and experimental results show a sensitivity of -38 dBm at 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> packet error ratio.

Compact high Q bandpass filter by using substrate integrated waveguide and split rings capacitive load post

A substrate integrated waveguide cavity filter is designed by loading with two split rings capacitive posts. Using these split rings posts results in high quality factor, low insertion loss (2.1 dB), very narrow bandwidth (2%) at 4.6 GHz centre frequency and compact (0.97×0.5 λ g 2 ) bandpass filter structure. The filter measured results are in good agreement with the simulation ones which prove the idea.

A Highly Selective Bandpass Filter Based on Suspended Substrate Resonators with a Two-Sided Stripline Pattern

New resonator design employing a hairpin stripline conductor with a stub situated on one side of a dielectric substrate and regular stripline conductors (connected to a screen) on the other side. Eigenfrequencies of the first three oscillation modes of this resonator can be made closer to each other, so that the resonances of two modes are involved in the formation of the passband while the third mode resonance forms a minimum of the transmission coefficient adjacent to the passband. A structure comprising four resonators of this type has the characteristic of an eighth-order bandpass filter arranged in a case with 45 × 16 × 6.25-mm internal dimensions possessing f0 = 0.52 GHz central frequency with a 14% relative bandwidth. The filter is highly selective due to the attenuation poles being close to the pass band and a wide high-frequency stopband extending above a fivefold f0 value at a level of –100 dB.

Quadruple-Mode Wideband Bandpass Filter with Improved Out-of-Band Rejection

This paper proposes a method for designing a quadruple-mode wideband bandpass filter using off-centered perturbed metallic cylinders in a rectangular waveguide cavity with compact size and improved out-of-band rejection. Two off-centered perturbation cylinders were placed at the bottom of the rectangular waveguide cavity along with a pair of perpendicularly-fed coaxial lines, which excited four quasi-transverse magnetic (TM) modes to realize the desired passband. The height of the waveguide cavity and the shape of the perturbation cylinders were exploited to achieve an all quasi-TM modes filter with good out-of-band rejection and sharp skirt selectivity. The proposed filter operates at 2.93 GHz center frequency with 38% wide fractional bandwidth (FBW). The proposed filter is fabricated using aluminum. The measured and simulated results are in good agreement with each other.

Switchable Bandpass/Bandstop Filter Using Liquid Metal Alloy as Fluidic Switch.

In this paper, we propose a switchable band-pass/band-stop filter using liquid metal alloy as a fluidic switch. The filter is designed based on the Chebyshev response and implemented using a three-stage quarter-wavelength resonant structure. The fluidic switch is realized by injecting eutectic gallium–indium (EGaIn) in the microfluidic stubs, engraved in the polydimethylsiloxane (PDMS) material. When the fluidic switch selects the short stub using a micro-pump and microprocessor for switching, the filter acts as a bandpass filter (BPF) with the short stubs. When the fluidic switch selects the open stub, the filter acts as the bandstop filter (BSF) with the open stubs. At the BPF mode, the center frequency is 2.5 GHz and the 1-dB bandwidth is 1.75–3.07 GHz. The insertion loss is 0.5-dB ± 0.4-dB. At the BSF mode, the 15-dB bandstop bandwidth is 2.4–2.65 GHz with 2.5 GHz center frequency.

Miniaturized dual‐band branch‐line coupler with enhanced bandwidth

AbstractIn this letter, a miniaturized hybrid dual‐band branch‐line coupler (BLC) with enhanced fractional bandwidths is proposed. Compact size and bandwidth enhancement are obtained using meandered transmission line sections with broken symmetry between cross‐coupling branches. The circuit is designed at a low numerical cost using surrogate‐assisted techniques. The optimized design features small size of only 0.25 λ g × 0.19 λ g (28% miniaturization with respect to conventional single‐band structure), as well as fractional bandwidths of 16% and 9% for 2.5 GHz and 5.4 GHz center frequencies, respectively. The proposed structure is compared against state‐of‐the‐art dual‐band couplers and validated experimentally.

A low noise stable radiometer front-end for passive microwave tissue thermometry

ABSTRACTA low noise, high gain, stable radiometer front-end is presented for non-invasive tissue thermometry using custom designed narrow band low noise amplifiers (LNAs) and band pass filter (BPF) with 1.3 GHz centre frequency and − 20 dB pass band of 332 MHz. The fabricated LNAs have >15 dB gain, unconditional gain stability and noise figure (NF) < 1.45 dB in the pass band. The maximum insertion loss of the BPF is <1 dB over 1.2–1.4 GHz with 50 dB suppression in the surrounding communication bands. The cascaded radiometer front-end has measured gain of 45–50 dB, NF < 1.75 dB in the pass band and > 30 dB suppression in the adjacent personal communication bands. The Allan deviation of the total power radiometer indicates long term system stability and presence of Gaussian thermal noise for integration time, . Radiometer measurements of a matched load at room temperature for indicate acceptably low influence of external electromagnetic interference (EMI) and system noise equivalent temperature of 145 K. The brightness temperature measured by the total power radiometer using a resonant slot antenna demonstrates the ability to detect a 0.3°C change in the test load temperature with better than 0.1°C accuracy.

Directive Low-Band UWB Antenna for In-body Medical Communications

A new antenna structure is presented in this paper. The antenna is operating at the Ultra-Wideband (UWB) band, 3.75-4.25 GHz, defined originally in Body Area Networks (BAN) part of IEEE 802.15.6 standard. The antenna size is 89 mm × 60 × 21 mm. The antenna is a directive with a measured gain of 8 dBi at 4 GHz center frequency. Since the proposed antenna is designed to meet the aspects of a receiving antenna for wireless capsule endoscopy localization, the antenna behavior in close proximity to a human body, in particular the small intestine area, is performed. For this end, initial on-body simulations were carried out by means of a tissue-layer model emulating the dielectric properties of the human body tissues at 4 GHz center frequency. This was followed by voxel model investigations. The human body impact on the antenna characteristics was analyzed firstly, followed by the examination of the power flow propagation inside the tissues. These analyses are consistent to evaluate the antenna ability to communicate with a capsule placed at the small intestine. Later, the antenna free-space propagation was assessed and validated by measurements. These results are followed by a measured on-body investigation conducted on male and female persons. Simulation results were obtained by CST Microwave Studio. Results were confirmed by measurements, conducted in an anechoic chamber at University of Oulu, Finland. The results were measured in frequency domain and later post-processed to a time domain. Consequently, measured results converge to the simulation ones. It is concluded that, the antenna could be used for Wireless Capsule Endoscopy communications with UWB signaling complying with IEEE 802.15.6 standard.

A Novel Fully Reconfigurable Non Foster Capacitance Using Distributed Negative Group Delay Networks

A novel reconfigurable non-Foster capacitance (NFC) using negative group delay (NGD) circuit is presented in this paper. The NGD circuit is based on a multi-order distributed amplifier which is used to achieve both NGD performance and gain compensation. By introducing shunt and series varactors next to trans-conductance transistors in the amplifier, the characteristic impedance, and electric length of transmission lines in the distributed amplifier can be flexibly tuned. As a result, the gain, phase shift, and negative group delay value of the proposed NGD circuit can be easily controlled as desired, and therefore, the scattering parameters S 21 can be adjusted to match with an ideal NFC, resulting in reconfigurable non-Foster capacitance. The working frequency ranges, equivalent negative capacitance value, and connection modes of the NFC be fully reconfigured by appropriately controlling the voltages applied to the varactors. Both simulation and measurement results were given, which agree well with each other. The experimental results show that the NFC value can be tuned from -1.1 to -2.5pF with 1 GHz center frequency and the working frequency can be tuned from 0.7 to 0.8 GHz with -10 pF shunt NFC.

Высокоселективный полосно-пропускающий фильтр на резонаторах с двухсторонним рисунком полосковых проводников на подвешенной подложке

AbstractNew resonator design employing a hairpin stripline conductor with a stub situated on one side of a dielectric substrate and regular stripline conductors (connected to a screen) on the other side. Eigenfrequencies of the first three oscillation modes of this resonator can be made closer to each other, so that the resonances of two modes are involved in the formation of the passband while the third mode resonance forms a minimum of the transmission coefficient adjacent to the passband. A structure comprising four resonators of this type has the characteristic of an eighth-order bandpass filter arranged in a case with 45 × 16 × 6.25-mm internal dimensions possessing f _0 = 0.52 GHz central frequency with a 14% relative bandwidth. The filter is highly selective due to the attenuation poles being close to the pass band and a wide high-frequency stopband extending above a fivefold f _0 value at a level of –100 dB.

Circularly Polarized Wideband-to-Narrowband Switchable Antenna

This paper presents a circularly polarized printed wideband-to-narrowband switchable monopole antenna for UWB/WiMAX applications. The proposed switching antenna consists of circularly polarized monopole antenna for the UWB mode with two bandpass filters integrated into the feeding network for the two 3.5/5.5 GHz center frequencies narrowband modes. The proposed antenna is utilized to operate at triple modes; 7.3 GHz, 3.5 GHz, and 5.5 GHz with wide impedance bandwidth (117.6%, 16.7%, and 7.3%), wide axial ratio bandwidth (89.2%, 16.7%, and 7.3 %), and the gain reaches (6.91 dBi, 5.5 dBi, and 4.2 dBi).

Path Loss Prediction Based on Machine Learning Methods for Aircraft Cabin Environments

Wireless communications in aircraft cabin environments have drawn widespread attention with the increase of application requirements. To ensure reliable and stable in-cabin communications, the investigation of channel parameters such as path loss is necessary. In this paper, four machine learning methods, including back propagation neural network (BPNN), support vector regression (SVR), random forest, and AdaBoost, are used to build path loss prediction models for an MD-82 aircraft cabin. Firstly, machine-learning-based models are designed to predict the path loss values at different locations at a fixed frequency. It is shown that these models fit the measured data well, e.g., at 2.4 GHz central frequency the root mean square errors (RMSEs) of BPNN, SVR, random forest, and AdaBoost predictors are 1.90 dB, 2.20 dB, 1.76 dB, and 2.12 dB. Subsequent research is engaged to forecast path loss at a new frequency based on available information at known frequencies. Additionally, to solve the data limitation problem at the new frequency, we propose a path loss prediction scheme combining empirical models and machine-learning-based models. This scheme uses estimated values generated by the empirical model according to prior information to expand the training set. To verify the performance of this scheme, measured samples at 2.4 GHz and 3.52 GHz, as well as samples generated by the empirical model are employed as the training set for the path loss prediction at 5.8 GHz. The RMSEs of BPNN, SVR, random forest, and AdaBoost models are 2.49 dB, 2.78 dB, 2.54 dB, and 3.76 dB. In contrast, without samples generated by the empirical model, the RMSEs of those models are 3.84 dB, 4.94 dB, 6.57 dB, and 6.77 dB. Results show that the proposed data expansion scheme improves prediction performance when there are few measurement samples at the new frequency.

Design of SIW Cavity Backed Triangular Slot Antenna Using Two Different Feeding Transitions

Abstract In this paper, a cavity backed triangular slot-antenna, which has novel feeding structures such as a substrate integrated waveguide (SIW) and two different feeding transitions, is investigated in terms of electrical performances, including reflection coefficients, gain and radiation patterns. In addition, in order to check the effects of feeding transition types on the electrical performances of the main radiator, two different feeding transitions, namely microstrip-to-SIW based on a taper and Grounded Coplanar Waveguide (GCPW)-to-SIW, have been studied by considering reflection coefficients, gain and radiation patterns. This antenna is designed with CST Microwave Studio. As a result, have been obtained a maximum gain more than 6dB has accomplished by using the proposed antenna with microstrip-to-SIW transition operating at k-band of 21 GHz center frequency.

A compact wideband circularly polarized SIW horn antenna for K band applications

In this manuscript, a compact wideband circularly polarized (CP) substrate integrated waveguide (SIW) horn antenna is presented. The proposed antenna is implemented on a substrate with a thickness of 3.1 mm (0.22 λ0 at 21 GHz central frequency). An antipodal tapered slotted structure is embedded inside the flared part of antenna to obtain a CP converter. The fabricated antenna occupies 36.2 × 27.6 × 3.1 mm3 (2.58 × 1.96 × 0.22 λ03) producing a maximum gain of 11.2 dBi. The measurements of presented antenna exhibit 40% (17–25.5 GHz) relative impedance bandwidth in which the reflection coefficient and axial ratio are below −10 dB and −2.6 dB, respectively. The simulation results are in good agreement with measurements.