Measured Reflection Coefficient Research Articles

A Sidelobe-Reduced, Four-Beam Array Antenna Fed by a Modified $4\times4$ Butler Matrix for 5G Applications

A sidelobe-reduced, four-beam array antenna fed by a modified 4 × 4 Butler matrix (BM) is proposed for 5G applications. Two attenuators are utilized in two external channels of the BM to realize a tapered amplitude distribution. In addition, three H-slots are employed as decoupling structures to enhance the isolation between the input ports. The modified BM is then cascaded with a 4 × 7 microstrip comb-line array antenna to establish four steering beams with high gains and reduced sidelobe levels. A prototype of the proposed four-beam array antenna is fabricated and experimentally demonstrated. The overall dimensions of the fabricated prototype are 95 × 32 × 0.254 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The total area of the modified BM is only 30 × 32 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The measured reflection coefficients and coupling levels between the input ports are less than -15 dB over the target frequency range of 27.525-28.325 GHz. At the center frequency of 27.925 GHz, the measured four beams point toward -16.2°, +40.8°, -39.4°, and +12.6° with corresponding measured peak gains of 17.52, 16.55, 15.74, and 17.87 dBi. The measured peak sidelobe levels for each beam are -16.7, -10.3, -10.9, and -14.5 dB, respectively. Radiation patterns are also presented and discussed.

Ka-Band 8 × 8 Low-Sidelobe Slot Antenna Array Using a 1-to-64 High-Efficiency Network Designed by New Printed RGW Technology

This letter proposes an 8 × 8 high-efficiency low-sidelobe slot antenna array operating at Ka -band frequencies with a feeding network designed by a new printed ridge gap waveguide (PRGW). The device consists of a slot antenna element, a PRGW unequal feeding network, and a stripline-to-PRGW transition. The substrate integrated waveguide slot antenna element fed by the PRGW through a coupling aperture has a wide bandwidth, and the isolation is also increased by adding metallized holes to the array. Compared with other gap waveguide antenna arrays, our work realizes an antenna element fed separately due to the use of a PRGW with a compact mushroom cell size, which helps improve the properties of the unequal feeding network. In addition, the transition between the PRGW and stripline is also designed with a wide band and low insertion loss. The measured reflection coefficient is less than –10 dB over a 6 GHz bandwidth (16%), the gain is more than 23.5 dBi in the working band, and the sidelobe level is –18 dB. In addition, the measured radiation efficiency of the array with a two-dimensional Taylor distribution is 41.69%.

Asynchronous Optical Sampling for Laser-Based Vector Network Analysis on Coplanar Waveguides

We employ asynchronous optical sampling to realize a laser-based vector network analyzer for the measurement of complex electrical reflection coefficients. This sampling method utilizes two separate femtosecond lasers for the generation and detection of ultrashort voltage pulses on a waveguide structure and does not require any optical delay lines. The scheme allows us to increase the measurement epoch, enabling a frequency resolution of 76 MHz while simultaneously covering a broad frequency range up to approximately 500GHz. Our analysis comprises a direct comparison with measurements from a conventional synchronous optical sampling technique. We obtain a very good agreement between the two measurement methods. However, asynchronous sampling reveals a four times higher frequency resolution and shows a reduced residual systematic error. In addition, we investigate different laser stabilization methods utilizing laser-pulse-cross-correlation measurements. Our analysis reveals a temporal jitter of better than 46 fs with the possibility to use one free-running laser oscillator.

Subminiature Panel (SMA-P) Coaxial Sensor for the Determination of Moisture Content of Mango cv. Chok Anan

The research describes the development of a simple, cheap and efficient open-ended coaxial sensor for the determination of moisture content of Chok Anan mango during fruit ripening from week 5 to week 17. The sensor was a modification of a standard subminiature panel (SMA-P). The finite element method was used to calculate the numerical values of the reflection coefficient. The reflection coefficient of the sensor was measured using a Microwave Network Analyzer in the frequency range from 1 to 4 GHz. The actual moisture content was obtained using standard oven drying method. A calibration equation was obtained to predict moisture content from the measured reflection coefficient at 1 GHz with accuracy within 1.5%. The results indicate that the amount of m.c. in Chok Anan mango can be determined with excellent accuracy using a SMA-P coaxial sensor as an OEC sensor.

Characterization of Electromagnetic Properties of In Situ Soils for the Design of Landmine Detection Sensors: Application in Donbass, Ukraine

To design holographic and impulse ground penetrating radar (GPR) sensors suitable for humanitarian de-mining in the Donbass (Ukraine) conflict zone, we measured critical electromagnetic parameters of typical local soils using simple methods that could be adapted to any geologic setting. Measurements were recorded along six profiles, each crossing at least two mapped soil types. The parameters selected to evaluate GPR and metal detector sensor performance were magnetic permeability, electrical conductivity, and dielectric permittivity. Magnetic permeability measurements indicated that local soils would be conducive to metal detector performance. Electrical conductivity measurements indicated that local soils would be medium to high loss materials for GPR. Calculation of the expected attenuation as a function of signal frequency suggested that 1 GHz may have optimized the trade-off between resolution and penetration and matched the impulse GPR system power budget. Dielectric permittivity was measured using both time domain reflectometry and impulse GPR. For the latter, a calibration procedure based on an in-situ measurement of reflection coefficient was proposed and the data were analyzed to show that soil conditions were suitable for the reliable use of impulse GPR. A distinct difference between the results of these two suggested a dry (low dielectric) soil surface, grading downward into more moist (higher dielectric) soils. This gradation may provide a matching layer to reduce ground surface reflections that often obscure shallow subsurface targets. In addition, the relatively high dielectric deeper (10 cm–20 cm) subsurface soils should provide a strong contrast with plastic-cased mines.

Wideband circularly polarized hybrid dielectric resonator antenna with bi‐directional radiation characteristics for various wireless applications

In this article, a wideband circularly polarized (CP) dielectric resonator (DR) over an asymmetric-slot radiator based hybrid-DR antenna is proposed with bi-directional radiation characteristics. Bi-directional CP radiation of the dual sense is obtained using a rectangular-DR over asymmetric-rectangular-slot radiator with L-shaped feed line. The asymmetric-slot radiator feed by L-shaped stub with the coplanar waveguide is used for generating two orthogonal modes, namely TE x δ11 and TEy1δ1 in the combined (rectangular-DR and asymmetric-slot radiator) hybrid-DR antenna, which is verified by the distribution of electric field inside the rectangular DRA. The measured reflection coefficient bandwidth (S11 < −10 dB) and axial ratio (AR) bandwidth (AR < 3 dB) of the hybrid-DR antenna are 80.5% (1.87-4.39 GHz) and 43.8% (1.75-2.73 GHz), respectively. The antenna radiation is in the broadside (θ = 0°, ϕ = 0°) direction as well as in the backside (θ = 180°, φ = 0°) direction with equal magnitudes in both the directions. Right-handed and left-handed CP waves are achieved respectively, in the boresight (+Z) and the backside (−Z) directions. The proposed CP hybrid-DR antenna gives an average gain of 3.55 dBic and radiation efficiency of 95.0% in both directions. The proposed antenna covers various wireless useful bands such as ISM 2400 band, Wi-Fi, Bluetooth, and Wi-MAX (2.5-2.7 GHz).

A Compact Circular Polarization Antenna Using Folded Ground Elements

This communication presents a new antenna structure using a folded ground element (FGE) for a compact antenna implementation. The proposed FGE is analyzed with an equivalent circuit model where equivalent capacitances and inductances of the proposed antenna are included. Also, slot patterns are integrated into a radiation patch element, resulting in a further reduction in the overall antenna size. To verify the proposed antenna with FGEs, an RFID antenna module with a right-handed circular polarization (RHCP) feed network was implemented and tested. The fabricated antenna size was $100\times 100\times 12\,\,{\mathrm{ mm}}^{3}$ ( $0.29\,\,\lambda _{0} \times 0.29\,\,\lambda _{0} \times 0.03\,\,\lambda _{0}$ at 868 MHz), showing a significant reduction in size compared to the conventional structures. The measured reflection coefficient for the feed network was better than 10 dB from 610 to 950 MHz, and 3 dB axial ratio (AR) bandwidth was about 137 MHz (817–954 MHz). Also, the measured peak gain and AR at 868 MHz were 4.6 dBic and 0.6 dB, respectively.

Combined Thickness and Permittivity Measurement of Thin Layers with Open-Ended Coaxial Probes.

This paper presents a method to simultaneously determine the thickness and permittivity of thin layers from multi-frequency reflection coefficient measurements using an open-ended coaxial probe. This is achieved by exploiting that the probe becomes radiating at frequencies higher than the probe’s typical operating range. Permittivity information is extracted from measurements in the typical frequency range, whereas thickness information is obtained from high frequency measurements by exploiting resonances that occur when the radiated waves are reflected at the layer boundary. A finite element model of the measurement set-up is made in COMSOL MultiphysicsTM, and a matrix of simulations spanning the relevant layer thicknesses and permittivity range is generated. The measured permittivity spectra of unknown samples are compared to the simulation matrix to estimate layer thickness and permittivity. The method is verified by measurements of water–ethanol mixtures. An application example where the water fraction and layer thickness of a gas hydrate deposition layer is estimated from permittivity measurements in a multiphase flow loop is also presented.

Method for low frequency sound reflection coefficient measurements in a compact space

Here, we present a method to measure the quasi-normal reflection coefficients of sound absorbing materials in a compact space. A short incident sound pulse (length < 3ms) is generated by a deconvolution method with the source speaker. Then, a stage-mounted microphone moves across the material surface and records the total (incident + scattered) sound field. By comparing the sound field with and without the presence of the sound absorbing material, the frequency-dependent reflection coefficients can be derived by extracting the corresponding frequency components from the sound pulse. Using this method, we can calculate the reflection coefficients of a 2 ft. by2 ft acoustic panel from 300 Hz to 2500 Hz within a 2 m by2 m by3 m lab space without anechoic coatings. Moreover, this method enables us to investigate the spatial inhomogeneity of the sound absorbing material by studying the amplitude/phase variation of reflection coefficients across the material surface. Compared with conventional measurement techniques for reflection/absorption coefficients, our method has the advantages of low cost, minimal requirements for the measurement environment and the ability to measure the reflection coefficients at different locations. The proposed method can be favorable for measuring reflection coefficients of two-dimensional acoustic panels/metamaterials at low frequencies.

Circularly polarised antenna with wide harmonics suppression by two angled C‐shaped structures

In this Letter, a circularly polarised (CP) antenna is proposed. The proposed antenna is realised by combining two angled C-shaped structures. By setting different widths ( W L and W R ) for the left and right angled C-shaped structures, respectively, an asymmetric structure is obtained. Therefore, the proposed antenna exhibits CP characteristics. From repeated simulation results, the authors find that the optimum ratio W L : W R to make the proposed structure operate as a CP antenna is 5: 8. Moreover, the measured reflection coefficient is lower than -2.4 dB within a stopband up to 12 GHz. This means that wide harmonics suppression (up to the fifth harmonic) is successfully achieved.

Multi-Walled Carbon Nanotubes Composites for Microwave Absorbing Applications

The response of materials to impinging electromagnetic waves is mainly determined by their dielectric (complex permittivity) and magnetic (complex permeability). In particular, radar absorbing materials are characterized by high complex permittivity (and eventually large values of magnetic permeability), Indeed, energy dissipation by dielectric relaxation and carrier conduction are principally responsible for diminishing microwave radiation reflection and transmission in non-magnetic materials. Therefore, the scientific and technological community has been investigating lightweight composites with high dielectric permittivity in order to improve the microwave absorption (i.e., radar cross-section reduction) in structural materials for the aerospace industry. Multiwalled carbon nanotubes films and their composites with different kind of polymeric resins are regarded as promising materials for radar absorbing applications because of their high permittivity. Nanocomposites based on commercial multi-wall carbon nano-tube (MWCNT) fillers dispersed in an epoxy resin matrix were fabricated. The morphology of the filler was analyzed by Field emission scanning electron microscopy (FESEM) and Raman spectroscopy, while the complex permittivity and the radiation reflection coefficient of the composites was measured in the radio frequency range. The reflection coefficient of a single-layer structure backed by a metallic plate was simulated based on the measured permittivity. Simulation achievements were compared to the measured reflection coefficient. Besides, the influence of morphological MWCNT parameters (i.e., aspect ratio and specific surface area) on the reflection coefficient was evaluated. Results verify that relatively low weight percent of MWCNTs are suitable for microwave absorption applications when incorporated into polymer matrixes (i.e., epoxy resin).

Quadrature Block for UHF Reflection Coefficient Measurements Using a Directional Coupler and Injection Locking

The measurement of the radio frequency reflection coefficient is widely used in characterizing various materials nondestructively. Generally, the measurement is done using a one port vector network analyzer together with some sort of probe. Here, the design theory of a new, low-cost replacement for such a network analyzer is explained. The proposed Cartesian reflection coefficient measurement block is outlined as well as the results of computer simulations and measurements on a printed circuit board (PCB) setup. Unlike previous approaches, it explores the use of injection locking to enhance the performance of quadrature amplitude demodulation of both the forward and the reflected waves as sampled from the output path of an ultrahigh-frequency power amplifier by a bidirectional coupler. Computer simulations at 400 MHz resulted in an average error of 3.4% full scale on the reflection coefficient, including extreme impedance values as well as various parasitic effects of the circuit measurements on a simplified PCB setup, also at 400 MHz.

Antenna for humidity sensor using split ring resonator

&lt;span&gt;This paper presents an antenna as a humidity sensor application to control and monitor the quality of humidity. A passive sensor tag with low cost solution is suggested where it implemented on a low-cost substrate, FR4. A capacitive sensor that works from 0 to 1.5 GHz is implemented in the design. The capacitive sensor is designed based on a small antenna loaded with a Split ring resonator (SRR). To sense the humidity, the SRR resonator is coated with Kapton, placed on the top of the resonator. To validate the proposed method, a prototype was fabricated. The comparison between simulated and measured reflection coefficient is presented.&lt;/span&gt;

Microwave polarization characteristics of snow at 6.9 and 18.7 GHz: Estimating the water content of the snow layers

ABSTRACT Theoretical and empirical tools for the exploration of the radio-thermal radiation of the snow cover in C and K-bands are developed taking into account the method of polarization measurements of the integral reflection coefficient of a snow layer. In addition, experimental in-situ measurements were performed at 6.9 and 18.7 GHz using a new portable optical system. The analyses of the measurements showed that the difference in polarization increases by increasing the thickness of the snow layer according to its physical characteristics. The study of reflection coefficient of the snow layer includes volumetric diffusion and coherent components determined by effective dielectric conductivity and volumetric scattering. The results showed that the value of the effective dielectric conductivity depends on the correlations between the roughness parameter and the wavelength, and increases with the growth of crystal size, as shown by the increase in the polarization difference when the size of the snow grains is increased. Moreover, the reflection coefficient was found to depend weakly on the polarization irradiance. The calculated snow depths and snow water equivalents are in a very good agreement with the observations made.

A Wideband-to-Narrowband Rectangular Dielectric Resonator Antenna Integrated With Tunable Bandpass Filter

A compact, frequency-reconfigurable dielectric resonator antenna (DRA) with wideband and continuously tunable narrowband states is presented. It is intended for the application scenario in the cognitive radio system. The wideband state is the sensing state and operationally covers 3.82-8.94 GHz. The narrowband states are intended to cover communications within the 5.14-5.98 GHz range, which completely covers the WLAN frequency bands. Three p-i-n diodes are employed to switch between wide and some narrowband operational states by selecting the corresponding path. A varactor diode is used to shift the operational frequencies continuously among the narrowband states. The proposed DRA consists of a rectangular dielectric resonator excited by microstrip feedline with a reconfigurable filter; it has a compact dimension: 0.31λ L × 0.41λ L × 0.06λ L , where the wavelength λL corresponds to the lower bound of its operating frequencies. The measured reflection coefficients, far-field radiation patterns, and realized gains for both operation states are in good consistent with their simulated values.

A 3D-Printed Tapered Cavity-Backed Flush-Mountable Ultra-Wideband Antenna for UAV

A tapered cavity-backed flush-mountable dual mono-cone antenna is proposed. The proposed antenna consists of four main sections: a lower mono-cone, an upper mono-cone, novel feeding structures, and an exponentially tapered cavity. To obtain high-frequency band operation, the upper mono-cone excited by the feeding structures is located inside the lower mono-cone. The circular cavity used in the proposed antenna has a tapered wall for mitigating the deterioration of radiation performance. The proposed antenna has overall dimensions of 200 mm × 200 mm × 30 mm. The measured reflection coefficients (S-parameters) are below -10 dB from 1.43 GHz to 39.05 GHz (1:27.3). The measured radiation pattern has a quasi- omnidirectional characteristic in the operating frequency band.

Millimeter waveband dielectric properties of nanocomposite 3d and rare-earth titanates

The transmission and reflection coefficients were measured in frequency range from 17 to 38 GHz for ceramic and nanocomposite titanates. The real and imaginary parts of complex dielectric permittivity were determined from measurements of transmission and reflection coefficients.

Benchmarking a High-End Smartphone’s Antenna Efficiencies

In an effort to create a benchmark for antenna designs for mobile applications, the total and radiation efficiencies of a modern high-end smartphone’s antennas are measured. To this end, an adapter board is designed that facilitates the connection to a calibrated measurement system. Its shape is chosen to closely resemble the original phone’s dimensions while allowing connection of the antennas via spring fingers to a coaxial measurement system. The characterization of this mock-up is performed in a reverberation chamber, which offers the advantage of an on-average isotropic environment, making it ideal for antenna reflection coefficient and efficiency measurements. The reflection coefficients, total efficiencies, and radiation efficiencies of the mock-up are then measured from 0.75 to 6 GHz. The total antenna efficiencies, not accounting for a possible improvement due to adaptive matching networks, are found to be below 15% up to 4 GHz and up to 25% below 6 GHz. Meanwhile, the radiation efficiencies are up to 15% below 2.5 GHz and up to 40% below 6 GHz. Such antenna efficiency measurements are the first and serve well as a benchmark for future designs and concepts.

Ridge Gap Waveguide Multilevel Sequential Feeding Network for High-Gain Circularly Polarized Array Antenna

This paper proposed a wideband, efficient, and high gain circularly polarized (CP) array antenna based on the gap waveguide technology for 30 GHz frequency band applications. The antenna subarray is a $2 \times 2$ slot groove gap waveguide-based cavity-backed antenna. The antenna is fed by a ridge gap waveguide (RGW). Two corners of the radiating slots are truncated to obtain CP radiation, and some corrugations are introduced to the radiating layer to suppress the surface waves between neighbor subarrays. The planar 16-way feeding network based on RGW is utilized to feed the subarrays. The feeding network is multilevel sequential phased with a quadrature phase shift. To validate the array antenna performance, a prototype of the antenna has been manufactured using standard milling technology. The measured reflection coefficient bandwidth is about 22% covering from 28.3 to 35.3 GHz, and a measured 3 dB axial ratio bandwidth of about 21.8% is achieved from 27.8 to 34.6 GHz. The maximum measured gain is 23.5 dBi which is occurred at 30.75 GHz.

Smartphone-Based Blood Lipid Data Acquisition for Cardiovascular Disease Management in Internet of Medical Things

With the ubiquitous deployment of smartphones worldwide recently, biomedical diagnostic devices based on smartphones are potential to be widely used for smart health management on the Internet of Medical Things (IoMT) applications under point-of-care (PoC) settings. Therefore, this paper introduces one smartphone-based blood lipid data acquisition dongle to monitor blood lipid level, including total cholesterol (TC), triglycerides (TG), and high-density lipoprotein cholesterol (HDL-C), using only a fingertip blood drop for cardiovascular disease management. During detection, a thin photochemical test strip that consists of LEDs and detectors is plugged into the compact dongle, where changed color intensities will indicate the lipid determinant concentration from the measured reflection coefficient of the chromogenic product. Such smartphone-based photochemical blood lipid data acquisition dongle was validated by comparing with a clinical analyzer, and reached a correlation coefficient over 0.903 and averaged coefficient of variation (CV)% of 4.575% for blood lipid measurement of 115 patients. The photochemical dongle is, therefore, promising for the future chronic disease management in the IoMT.