Showing papers in "Radioengineering in 2014"

Near Sea-Surface Mobile Radiowave Propagation at 5 GHz: Measurements and Modeling

Abstract: Near sea-surface line-of-sight (LoS) radiowave propagation at 5 GHz was investigated through narrowband measurements in this paper. Results of the received signal strength with a transmission distance of up to 10 km were examined against free space loss model and 2-ray path loss model. The experimental results have good agreement with the predicted values using the 2-ray model. However, the prediction ability of 2-ray model becomes poor when the propagation distance increases. Our results and analysis show that an evaporation duct layer exists and therefore, a 3-ray path loss model, taking into consideration both the reflection from sea surface and the refraction caused by evaporation duct could predict well the trend of LoS signal strength variations at relatively large propagation distances in a tropical maritime environment.

An Efficient Framework For Fast Computer Aided Design of Microwave Circuits Based on the Higher-Order 3D Finite-Element Method

Abstract: In this paper, an efficient computational framework for the full-wave design by optimization of complex microwave passive devices, such as antennas, filters, and multiplexers, is described. The framework consists of a computational engine, a 3D object modeler, and a graphical user interface. The computational engine, which is based on a finite element method with curvilinear higher-order tetrahedral elements, is coupled with built-in or external gradient-based optimization procedures. For speed, a model order reduction technique is used and the gradient computation is achieved by perturbation with geometry deformation, processed on the level of the individual mesh nodes. To maximize performance, the framework is targeted to multicore CPU architectures and its extended version can also use multiple GPUs. To illustrate the accuracy and high efficiency of the framework, we provide examples of simulations of a dielectric resonator antenna and full-wave design by optimization of two diplexers involving tens of unknowns, and show that the design can be completed within the duration of a few simulations using industry-standard FEM solvers. The accuracy of the design is confirmed by measurements.

The Impact of Interference on GNSS Receiver Observables – A Running Digital Sum Based Simple Jammer Detector

Abstract: A GNSS-based navigation system relies on externally received information via a space-based Radio Frequency (RF) link. This poses susceptibility to RF Interference (RFI) and may initiate failure states ranging from degraded navigation accuracy to a complete signal loss condition. To guarantee the integrity of the received GNSS signal, the receiver should either be able to function in the presence of RFI without generating misleading information (i.e., offering a navigation solution within an accuracy limit), or the receiver must detect RFI so that some other means could be used as a countermeasure in order to ensure robust and accurate navigation. Therefore, it is of utmost importance to identify an interference occurrence and not to confuse it with other signal conditions, for example, indoor or deep urban canyon, both of which have somewhat similar impact on the navigation performance. Hence, in this paper, the objective is to investigate the effect of interference on different GNSS receiver observables in two different environments: i. an interference scenario with an inexpensive car jammer, and ii. an outdoorindoor scenario without any intentional interference. The investigated observables include the Automatic Gain Control (AGC) measurements, the digitized IF (Intermediate Frequency) signal levels, the Delay Locked Loop and the Phase Locked Loop discriminator variances, and the Carrier-to-noise density ratio (C/N0) measurements. The behavioral pattern of these receiver observables is perceived in these two different scenarios in order to comprehend which of those observables would be able to separate an interference situation from an indoor scenario, since in both the cases, the resulting positioning accuracy and/or availability are affected somewhat similarly. A new Running Digital Sum (RDS) -based interference detection method is also proposed herein that can be used as an alternate to AGC-based interference detection. It is shown in this paper that it is not at all wise to consider certain receiver observables for interference detection (i.e., C/N0); rather it is beneficial to utilize certain specific observables, such as the RDS of raw digitized signal levels or the AGC-based observables that can uniquely identify a critical malicious interference occurrence.

Analysis of Radar Doppler Signature from Human Data

Abstract: This paper presents the results of time (autocor- relation) and time-frequency (spectrogram) analyses of radar signals returned from the moving human targets. When a radar signal falls on the human target which is moving toward or from the radar, the signals reflected from different parts of his body produce a Doppler shift that is proportional to the velocity of those parts. Moving parts of the body causes the characteristic Doppler signa- ture. The main contribution comes from the torso which causes the central Doppler frequency of target. The motion of arms and legs induces modulation on the returned radar signal and generates sidebands around the central Dop- pler frequency, referred to as micro-Doppler signatures. It was demonstrated that the human motion signature extrac- tion is better using spectrogram analysis. While the central Doppler frequency can be determined using the autocor- relation and the spectrogram, the extraction of the funda- mental cadence frequency using the autocorrelation is unreliable when the target is in the clutter presence. It was demonstrated that the value of the fundamental cadence frequency increases with increasing dynamic movement of people and simultaneously the possibility of its extraction is proportional to the degree of synchronization movements of persons in the group.

Single-, dual- and triple-band frequency reconfigurable antenna

Abstract: The paper presents a frequency reconfigurable slot dipole antenna. The antenna is capable of being switched between single-band, dual-band or triple-band operation. The antenna incorporates three pairs of pindiodes which are located within the dipole arms. The antenna was designed to operate at 2.4 GHz, 3.5 GHz and 5.2 GHz using the aid of CST Microwave Studio. The average measured gains are 1.54, 2.92 and 1.89 dBi for low, mid and high band respectively. A prototype was then constructed in order to verify the performance of the device. A good level of agreement was observed between simulation and measurement.

Low-Voltage High-Linearity Wideband Current Differencing Transconductance Amplifier and Its Application on Current-Mode Active Filter

Abstract: A low-voltage high-linearity wideband current differencing transconductance amplifier (CDTA) is presented in this paper. The CDTA consists of a current differencing circuit and a cross-coupling transconductance circuit. The PSPICE simulations of the proposed CDTA show a good performance: -3dB frequency bandwidth is about 900 MHz, low power consumption is 2.48 mW, input current linear range is ±100 μA and low current-input resistance is less than 20 Ω, high current-output resistance is more than 3 MΩ. PSpice simulations for a current-mode universal filter and a proposed high-order filter are also conducted, and the results verify the validity of the proposed CDTA.

Maximum Bandwidth Enhancement of Current Mirror using Series-Resistor and Dynamic Body Bias Technique

Abstract: This paper introduces a new approach for enhancing the bandwidth of a low voltage CMOS current mirror. The proposed approach is based on utilizing body effect in a MOS transistor by connecting its gate and bulk terminals together for signal input. This results in boosting the effective transconductance of MOS transistor along with reduction of the threshold voltage. The proposed approach does not affect the DC gain of the current mirror. We demonstrate that the proposed approach features compatibility with widely used series-resistor technique for enhancing the current mirror bandwidth and both techniques have been employed simultaneously for maximum bandwidth enhancement. An important consequence of using both techniques simultaneously is the reduction of the series-resistor value for achieving the same bandwidth. This reduction in value is very attractive because a smaller resistor results in smaller chip area and less noise. PSpice simulation results using 180 nm CMOS technology from TSMC are included to prove the unique results. The proposed current mirror operates at 1 Volt consuming only 102 μW and maximum bandwidth extension ratio of 1.85 has been obtained using the proposed approach. Simulation results are in good agreement with analytical predictions.

Backscatter Transponder Based on Frequency Selective Surface for FMCW Radar Applications

Abstract: This paper describes an actively-controlled frequency selective surface (FSS) to implement a backscatter transponder. The FSS is composed by dipoles loaded with switching PIN diodes. The transponder exploits the change in the radar cross section (RCS) of the FSS with the bias of the diodes to modulate the backscattered response of the tag to the FMCW radar. The basic operation theory of the system is explained here. An experimental setup based on a commercial X-band FMCW radar working as a reader is proposed to measure the transponders. The transponder response can be distinguished from the interference of non-modulated clutter, modulating the transponder’s RCS. Some FSS with different number of dipoles are studied, as a proof of concept. Experimental results at several distances are provided.

Motion Capture System for Finger Movement Measurement in Parkinson Disease

Abstract: Parkinson's disease (PD) is a chronic neurode- generative disorder that affects almost 1% of the popula- tion in the age group above 60 years. The key symptom in PD is the restriction of mobility. The progress of PD is typically documented using the Unified Parkinson's Dis- ease Rating Scale (UPDRS), which includes a finger-tap- ping test. We created a measurement tool and a methodol- ogy for the objective measurement of the finger-tapping test. We built a contactless three-dimensional (3D) capture system using two cameras and light-passive (wireless) reflexive markers. We proposed and implemented an algo- rithm for extracting, matching, and tracing markers. The system provides the 3D position of spherical or hemi- spherical markers in real time. The system's functionality was verified with the commercial motion capture system OptiTrack. Our motion capture system is easy to use, saves space, is transportable, and needs only a personal com- puter for data processing - the ideal solution for an outpa- tient clinic. Its features were successfully tested on 22 patients with PD and 22 healthy control subjects.

Robust Detection of Moving Human Target in Foliage-Penetration Environment Based on Hough Transform

Abstract: Attention has been focused on the robust moving human target detection in foliage-penetration environment, which presents a formidable task in a radar system because foliage is a rich scattering environment with complex multipath propagation and time-varying clutter. Generally, multiple-bounce returns and clutter are additionally superposed to direct-scatter echoes. They obscure true target echo and lead to poor visual quality time-range image, making target detection particular difficult. Consequently, an innovative approach is proposed to suppress clutter and mitigate multipath effects. In particular, a clutter suppression technique based on range alignment is firstly applied to suppress the time-varying clutter and the instable antenna coupling. Then entropy weighted coherent integration (EWCI) algorithm is adopted to mitigate the multipath effects. In consequence, the proposed method effectively reduces the clutter and ghosting artifacts considerably. Based on the high visual quality image, the target trajectory is detected robustly and the radial velocity is estimated accurately with the Hough transform (HT). Real data used in the experimental results are provided to verify the proposed method.

A Broadband UHF Tag Antenna For Near-Field and Far-Field RFID Communications

Abstract: The paper deals with the design of passive broadband tag antenna for Ultra-High Frequency (UHF) band. The antenna is intended for both near and far fields Radio Frequency Identification (RFID) applications. The meander dipole tag antenna geometry modification is designed for frequency bandwidth increasing. The measured bandwidth of the proposed broadband tag antenna is more than 140 MHz (820–960 MHz), which can cover the entire UHF RFID band. A comparison between chip impedance of datasheet and the measured chip impedance has been used in our simulations. The proposed progressive meandered antenna structure, with an overall size of 77 × 14 × 0.787 mm, produces strong and uniform magnetic field distribution in the near-field zone. The antenna impedance is matched to common UHF chips in market simply by tuning its capacitive and inductive values since a perfect matching is required in the antenna design in order to enhance the near and the far field communications. Measurements confirm that the designed antenna exhibits good performance of Tag identification for both near-field and far-field UHF RFID applications.

Multi-Feature Based Multiple Landmine Detection Using Ground Penetration Radar

Abstract: This paper presents a novel method for detection of multiple landmines using a ground penetrating radar (GPR). Conventional algorithms mainly focus on detection of a single landmine, which cannot linearly extend to the multiple landmine case. The proposed algorithm is composed of four steps; estimation of the number of multiple objects buried in the ground, isolation of each object, feature extraction and detection of landmines. The number of objects in the GPR signal is estimated by using the energy projection method. Then signals for the objects are extracted by using the symmetry filtering method. Each signal is then processed for features, which are given as input to the support vector machine (SVM) for landmine detection. Three landmines buried in various ground conditions are considered for the test of the proposed method. They demonstrate that the proposed method can successfully detect multiple landmines.

An Improved NSGA-II and its Application for Reconfigurable Pixel Antenna Design

Abstract: Based on the elitist non-dominated sorting ge- netic algorithm (NSGA-II) for multi-objective optimization problems, an improved scheme with self-adaptive cross- over and mutation operators is proposed to obtain good optimization performance in this paper. The performance of the improved NSGA-II is demonstrated with a set of test functions and metrics taken from the standard literature on multi-objective optimization. Combined with the HFSS solver, one pixel antenna with reconfigurable radiation patterns, which can steer its beam into six different direc- tions (θDOA = ± 15°, ± 30°, ± 50°) with a 5 % overlapping impedance bandwidth (S11 < -10 dB) and a realized gain over 6 dB, is designed by the proposed self-adaptive NSGA-II.

Wavelet Features for Recognition of First Episode of Schizophrenia from MRI Brain Images

Abstract: Machine learning methods are increasingly used in various fields of medicine, contributing to early diagnosis and better quality of care. These outputs are particularly desirable in case of neuropsychiatric disorders, such as schizophrenia, due to the inherent potential for creating a new gold standard in the diagnosis and differentiation of particular disorders. This paper presents a scheme for automated classification from magnetic resonance images based on multiresolution representation in the wavelet domain. Implementation of the proposed algorithm, utilizing support vector machines classifier, is introduced and tested on a dataset containing 104 patients with first episode schizophrenia and healthy volunteers. Optimal parameters of different phases of the algorithm are sought and the quality of classification is estimated by robust cross validation techniques. Values of accuracy, sensitivity and specificity over 71% are achieved.

Double-layer Perfect Metamaterial Absorber and Its Application for RCS Reduction of Antenna

Abstract: To reduce the radar cross section (RCS) of a circularly polarized (CP) tilted beam antenna, a doublelayer perfect metamaterial absorber (DLPMA) in the microwave frequency is proposed. The DLPMA exhibits a wider band by reducing the distance between the three absorption peaks. Absorbing characteristics are analyzed and the experimental results demonstrate that the proposed absorber works well from 5.95 GHz to 6.86 GHz (relative bandwidth 14.1%) with the thickness of 0.5 mm. Then, the main part of perfect electric conductor ground plane of the CP tilted beam antenna is covered by the DLPMA. Simulated and experimental results reveal that the novel antenna performs well from 5.5 GHz to 7 GHz, and its monostatic RCS is reduced significantly from 5.8 GHz to 7 GHz. The agreement between measured and simulated data validates the present design.

Estimation of Most Favorable Optical Window Position Subject to Achieve Finest Optical Control of Lateral DDR IMPATT Diode Designed to Operate at W-Band

Abstract: The optimum position of the optical window (OW) of illuminated lateral double-drift region (DDR) impact avalanche transit time (IMPATT) device has been determined subject to achieve the finest optical control of both DC and RF properties of the device. The OW is a tiny hole that has to be created on the oxide layer through which the light energy of appropriate wavelength can be coupled to the space charge region of the device. A non- sinusoidal voltage is assumed to be applied across the diode and the corresponding terminal current response is obtained from a two-dimensional (2-D) large-signal (L-S) simulation technique developed by the authors for illumi- nated lateral DDR IMPATT diode. Both the DC and L-S properties of the illuminated device based on Si, designed to operate at W-band frequencies (75-110 GHz) are ob- tained from the said L-S simulation. Simulation is carried out for different incident optical power levels of different wavelengths (600-1000 nm) by varying the position of the fixed sized OW on the oxide layer along the direction of electrical conduction of the device. Results show that, the most favorable optical tuning can be achieved when the OW is entirely created over the p-type depletion layer, i.e. when the photocurrent is purely electron dominated. Also the 700 nm wavelength is found to be most suitable wave- length for obtaining the maximum optical modulation of both DC and RF properties of the device.

A New Wideband Circularly Polarized Dielectric Resonator Antenna

Abstract: A wideband and compact circularly polarized (CP) C-shaped dielectric resonator antenna (DRA) is pre- sented and investigated. The proposed C-shaped DR is excited by a simple stripe line connected to a coplanar waveguide (CPW) feeding line. The C-shaped DRA is cir- cularly polarized with 19% axial ratio (AR) bandwidth. It is found that the CP bandwidth can be expanded by using a narrow short circuit strip. The final design achieves CP with 50% AR bandwidth. The proposed circularly polar- ized DRA (CPDRA) with good radiation characteristics offers an impedance bandwidth of 58% between 3.45 and 6.26 GHz for VSWR ≤ 2. The proposed DRA is fabricated and tested. Very good agreement between simulated and measured results is obtained.

Curved Track Analysis of FSO Link for Ground-to-Train Communications

Abstract: In this work, a free space optical (FSO) link for the ground-to-train (G2T-FSO) communications is proposed. Analytical analysis is carried out for the curved rail tracks. We show that the transmitter divergence angle, the transmit power and the size of the concentration lens need to increase for the curved section of the rail track compared to the straight track. We derive the analytical expression for the received power level based on the link geometry for the case of the curved track In the worst case scenario when the curvature radius is 120 m, the transmit power at the optical base station (BS) needs to increase by over 2 dB when the concentration lens radius is increased by 5 times. Analyses also show that the received power along the track increases with the curvature radius for the same transmit power and receiver optics illustrating the effect due to link geometry. Additionally, the signal-to-noise ratio (SNR) and the bit error rate (BER) performance of the system for the curved track with different curvature radii is analysed at data rates of 10 Mbps and 100 Mbps for an additive white Gaussian noise (AWGN) channel showing a good agreement between the theoretical and the simulated BER. Finally, effect of scintillations on the G2T-FSO link performance is discussed.

An FPGA Based Implementation of a CFAR Processor Applied to a Pulse-Compression Radar System

Abstract: A hardware architecture that implements a CFAR processor including six variants of the CFAR algorithm based on linear and nonlinear operations for radar applications is presented. Since some implemented CFAR algorithms require sorting the input samples, the two sorting solutions are investigated. The first one is iterative, and it is suitable when incoming data clock is several times less than sorting clock. The second sorter is very fast by exploiting a high degree of parallelism. The architecture is on-line reconfigurable both in terms of CFAR method and in terms of the number of reference and guard cells. The architecture was developed for coherent radar with pulse compression. Besides dealing with sur- face clutter and multiple target situations, such radar de- tector is often faced with high side-lobes at the compres- sion filter output when strong target presents in his sight. The results of implementing the architecture on a Field Programmable Gate Array (FPGA) are presented and discussed.

On Amplify-and-Forward Relaying Over Hyper-Rayleigh Fading Channels

Abstract: Relayed transmission holds promise for the next generation of wireless communication systems due to the performance gains it can provide over non-cooperative systems. Recently hyper-Rayleigh fading, which represents fading conditions more severe than Rayleigh fading, has received attention in the context of many practical communication scenarios. Though power allocation for Amplify-andForward (AF) relaying networks has been studied in the literature, a theoretical analysis of the power allocation problem for hyper-Rayleigh fading channels is a novel contribution of this work. We develop an optimal power allocation (OPA) strategy for a dual-hop AF relaying network in which the relay-destination link experiences hyper-Rayleigh fading. A new closed-form expression for the average signalto-noise ratio (SNR) at destination is derived and it is shown to provide a new upper-bound on the average SNR at destination, which outperforms a previously proposed upperbound based on the well-known harmonic-geometric mean inequality. An OPA across the source and relay nodes, subject to a sum-power constraint, is proposed and it is shown to provide measurable performance gains in average SNR and SNR outage at the destination relative to the case of equal power allocation.

Analysis of Topological Impact on Wireless Channel Performance on Intelligent Street Lighting System

Abstract: In this work, an analysis of the physical radio channel propagation for the deployment of a wireless sensor network for intelligent street lighting is presented based on an in house implemented deterministic 3D ray launching code. Simulation as well as measurement results from a deployed wireless sensor network, based on ZigBee motes for an intelligent street light control system confirm the topological and morphological dependence of the considered scenario, given to diffraction and scattering from the street lights in which the sensor are located. Received power levels as well as performance metrics given by Packet Error Ratio values are presented in order to validate radioplanning estimations. The results can be applied to the optimal radioplanning of the wireless systems prior to deployment phase, in order to achieve maximum system performance while minimizing power consumption.

Monthly and diurnal variability of rain rate and rain attenuation during the monsoon period in Malaysia

Abstract: Rain is the major source of attenuation for microwave propagation above 10 GHz. In tropical and equatorial regions where the rain intensity is higher, designing a terrestrial and earth-to-satellite microwave links is very critical and challenging at these frequencies. This paper presents the preliminary results of rain effects in a 23 GHz terrestrial point-to-point communication link 1.3 km long. The experimental test bed had been set up at Skudai, Johor Bahru, Malaysia. In this area, a monsoon equatorial climate prevails and the rainfall rate can reach values well above 100 mm/h with significant monthly and diurnal variability. Hence, it is necessary to implement a mitigation technique for maintaining an adequate radio link performance for the action of very heavy rain. Since we now know that the ULPC (Up Link Power Control) cannot guarantee the desired performance, a solution based on frequency band diversity is proposed in this paper. Here, a secondary radio link operating in a frequency not affected by rain (C band for instance) is placed parallel with the main link. Under no rain or light rain conditions, the secondary link carries without priority radio signals. When there is an outage of the main link due to rain, the secondary link assumes the priority traffic. The outcome of the research shows a solution for higher operating frequencies during rainy events.

Filtenna integration achieving ideal chebyshev return losses

Abstract: This paper demonstrates that it is possible to find an ideal filter response (Chebyshev, Butterworth,..) considering the antenna as the last resonator of a filter under certain circumstances related with the antenna performance and the bandwidth of the filtenna device. If these circumstances are not accomplished, we can achieve excellent performance as well, by means of an iterative process the goal of which is defined by either a filter mask or a classical filter function itself. The methodology is based on the conventional coupling matrix technique for filter design and has been validated by fabricating a microstrip prototype using hairpin resonators and a rectangular patch antenna.

Multistatic Wireless Fidelity Network Based Radar – Results of the Chrcynno Experiment

Abstract: This paper presents the theory and experimental result of passive radar using WIFI transmitters as illuminators of opportunity. As a result of experiments conducted on 17th August 2013 at airfield Chrcynno a Cessna C208 airplane was detected using multistatic passive radar system based on low power signal from WIFI network nodes, which were acting as non-cooperative illuminators of opportunity. In the experiment the 3 wireless access points (AP) were communicating with each other and illuminating the radar scene (airfield). The direct reference and reflected (surveillance) signals have been acquired and processed using specially developed algorithm presented in the paper. After signal processing using Passive Coherent Location methods the target has been detected. This paper describes in details the algorithms and the results of the experiment for the multistatic passive radar based on the WIFI signal.

Design of Dual-Band Two-Branch-Line Couplers with Arbitrary Coupling Coefficients in Bands

Abstract: A new approach to design dual-band two- branch couplers with arbitrary coupling coefficients at two operating frequency bands is proposed in this article. The method is based on the usage of equivalent subcircuits input reactances of the even-mode and odd-mode excita- tions. The exact design formulas for three options of the dual-band coupler with different location and number of stubs are received. These formulas permit to obtain the different variants for each structure in order to select the physically realizable solution and can be used in broad range of frequency ratio and power division ratio. For verification, three different dual-band couplers, which are operating at 2.4/3.9 GHz with different coupling coeffi- cients (one with 3/6 dB, and 10/3 dB two others) are de- signed, simulated, fabricated and tested. The measured results are in good agreement with the simulated ones.

Concentrated Ground Plane Booster Antenna Technology for Multiband Operation in Handset Devices

Abstract: The current demand in the handset antenna field requires multiband antennas due to the existence of multi- ple communication standards and the emergence of new ones. At the same time, antennas with reduced dimensions are strongly required in order to be easily integrated. In this sense, the paper proposes a compact radiating system that uses two non-resonant elements to properly excite the ground plane to solve the abovementioned shortcomings by minimizing the required Printed Circuit Board (PCB) area while ensuring a multiband performance. These non-reso- nant elements are called here ground plane boosters since they excite an efficient mode of the ground plane. The pro- posed radiating system comprises two ground plane boost- ers of small dimensions of 5 mm x 5 mm x 5 mm. One is in charge of the low frequency region (from 0.824 GHz to 0.960 GHz) and the other is in charge of the high frequency region (1.710 GHz-2.170 GHz). With the aim of achieving a compact configuration, the two boosters are placed close to each other in a corner of the ground plane of a handset device (concentrated architecture). Several experiments related to the coupling between boosters have been carried out in two different platforms (barphone and smartphone), and the best position and the required matching network are presented. The novel proposal achieves multiband performance at GSM850/900/1800/1900 and UMTS.

Fundamental Behavior Analysis of Single-Frequency Sine Wave Forced Oscillator Based on Linear Model and Multi-Time Technique

Abstract: In this article, an excited oscillator which is analyzed by using a multi-time linear analytical model is proposed. An obtained closed-form solution can be ex- ploited not only to explain phenomena in the beat and locked states that are mostly studied in literature but also in an additional state called the non-locked state. With the proposed analysis, it is found that the non-locked state of the oscillator behaves similarly to the up-conversion proc- ess. It provides a new point-of-view to the phase noise oscillator. Moreover, our principle indicates that the im- portant factor defining the behavior in each state and state transition is the transfer function of the system. The pro- posed mathematical model is verified by the experimental and numerical results.

Modelling and Measuring Dielectric Constants for Very Thin Materials Using a Coaxial Probe

Abstract: This paper is focused on the non-destructive measurement of the dielectric constants (relative permittivities) of thin dielectric material (0.1-0.5 mm) using an open-ended coaxial probe with an outer diameter of 4.1 mm. Normalized de-embedding and network error calibration procedures were applied to the coaxial probe. The measured reflection coefficients for the thin samples were taken with a vector network analyzer up to 7 GHz, and the calibrated reflection coefficients were converted to relative dielectric constants using an empirical reflection coefficient model. The empirical model was created using the regression method and expressed as a polynomial model, and the coefficients of the model were obtained by fitting the data using the Finite Element Method (FEM).