To fulfil the need for finer resolution automotive radar imaging, in this paper, a SAR demonstrator and processing algorithm at 77 GHz are shown which represent a realistic low cost implementation for automotive applications. In the measurement setup section, the demonstrator is described along with how the strict requirements of synchronous radar measurements and trajectory information are fulfiled. A processing algorithm is also presented that is modelled for automotive applications, such that the measurements are processed in blocks, which represent sub-apertures, as they become available from the radar. This results in a faster processing time. Additionally the effect of the missing signals in azimuth, which occur because of hardware restrictions, is clarified and minimised using compressed sensing by recovering the missing signals. To verify the results delivered from the developed algorithm, the processed images are compared with those obtained from the time domain backprojection algorithm and the results were found to be in good agreement.
This work describes how indirect holography which has previously been applied to the determination of antenna radiation patterns can be adapted for the imaging of passive objects. It provides details of how complex scattered field values can be obtained in a simple and inexpensive manner from sampled scalar intensity measurements taken over a single scanning aperture. This work uses indirect holographic techniques to image a number of simple objects including a rectangular metallic plate, a small metal plate covered by a dielectric sheet and a small metallic circular annulus. This work demonstrates that good quality images can be reconstructed from simple scalar intensity patterns. It demonstrates that clear outlines can be obtained in particular from reconstructed phase patterns and that good images can be obtained from objects with dimensions of the order of a half wavelength. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.
The present work proposes a digital Doherty power amplifier (PA) with improved efficiency performance. The efficiency enhancement is achieved by using a digital adaptive phase alignment mechanism that is implemented to address the problem of power-dependent phase imbalance between the carrier and peaking cells of gallium-nitride (GaN) Doherty PAs following the turn-on of the peaking cell. An average efficiency of 57% has been measured using a one-carrier Worldwide Interoperability for Microwave Access (WiMAX) signal with a peak-to-average power ratio of 7 dB. This corresponds to an improvement of 7% in average efficiency with no linearity degradation compared to a conventional single-input fully analog Doherty PA.
Wireless body area networks (WBANs) technology is now recognized as a promising candidate for various potential applications in the domains of health, surveillance, monitoring, sport, multimedia, entertainment, etc. As the devices are implanted or embedded in the human body, the design constraints are particularly stringent: low power consumption is required for applications demanding autonomy (e.g., medical surveillance), security and safety are mandatory for vital applications, radiations are subject to regulatory limits for public health and coexistence in addition to other constrains like size, aspect ratio, and weight.
In this paper, we present the study of a printed Vivaldi- type antenna, simulated using two software: “LINpar” to ensure the adaptation of the input of the antenna with the coaxial line and “ANSOFT Designer” for the analysis of the adjusted line and the antenna. This tool has helped us to obtain simulation results in the form of S-parameters and allowed us to obtain a gain of about 10dB, a bandwidth from 500 MHz at 6 GHz and an input impedance of 50 Ohms from the reflection coefficient S11. Finally, to validate the simulations, carried out, the realised antenna has been characterized using a network analyzer. The radiation pattern and S parameter values obtained are very satisfactory.
We describe the design of wide band printed dipole. We obtain with this technique more than 50% bandwidth around the frequency of 2.5 GHz. We obtain very flat gain (around 5dBi) over the entire bandwidth. This antenna is low profile, low cost and with a very simple feeding.
An efficient proximity coupled microstrip patch antenna has been designed at 2.45 GHz. The length of the feeding line penetration and a simple rectangular slot etched in radiation element are used to reject the 2 nd and the 3 rd harmonic frequencies. The proposed antenna is well suitable for microwave wireless transmission because no input low pass filter and no via-hole connections are required, resulting in simpler and compact structures. An electromagnetic simulation has been used to optimise the antenna. The antenna gain is 6.37 dB at 2.45 GHz operating frequency. The return losses at the 2 nd and 3 rd harmonic frequencies are -0.4 dB and -0.8 dB, respectively.
The considerable evolution of microelectronics has highlighted the need for new dielectric materials of high permittivity (high-k).
In this paper, we present a method based on Neural Network (NN) technique and accompanied with MMSE (Minimum Mean Square Error), which corrects at the receiver level, the Non-Linear (NL) distortions due to the HPA (High Power Amplifier). The neural network consists on a feed-forward Multi-Layer Perceptron (MLP) associated with Levenberg-Marquardt learning algorithm. The results show that the neural network compensator brings perceptible in a complete VBLAST MIMO OFDM (Vertical Bell Laboratories Layered Space-Time Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing) system running under a Rayleigh fading channel.
The past decade has seen phenomenal advances in portable electronics technology like mobile phones, RFID tags and MP3 players. This has led to the development of System in Package (SiP) which combines all the necessary components into a single package. Miniaturization of RF circuit technology has resulted in the need for miniaturized antennas. Meander line antennas are widely used in applications where compactness and miniaturization are key objectives. Although this antenna has been widely used, yet no simple analytical model except those using complicated numerical techniques is available. In this paper, we present a simple analytical model to calculate the resonant frequency of the antenna employing a lumped equivalent circuit model. Circuit response of a typical meander line antenna using our model has been compared with simulated antenna response using Method of Moments based simulator IE3D with good agreement, thereby validating our approach.
We propose a computer-aided design tool of complex passive microwave devices in rectangular waveguide technology by hybridizing the finite element method and a modified multimodal variational formulation. The finite element method characterizes waves in the arbitrarily shaped discontinuities and the total response of the circuit is obtained by applying the modified multimodal variational formulation. The size of the scattering matrix of the total circuit depends only on the number of accessible modes in the beginning and the end of the overall structure. This feature makes the computation time of our hybrid method independent from distances between discontinuities of the circuit. The proposed hybrid method is successfully applied to the full-wave analysis of filters with great practical interest (i.e., multimode filters), thus improving computation time and memory storage against several full-wave finite element method based computer aided design tools.
A RF amplifier based on compact tunable MEMS impedance matching network was designed for sub-2GHz frequency applications. The amplifier uses a PHEMT transistor fabricated in GaAs technology while the MEMS circuits is fabricated using a dedicated UW-MEMS process. The performance of the amplifier is controlled for the PCS1900 frequency band while the gain is kept around the maximum available stable gain.
In this paper, we propose a study of performance of the channel estimation using LS, MMSE, LMMSE and Lr-LMMSE algorithms in OFDM (Orthogonal Frequency Division Multiplexing) system which, as known suffers from the time variation of the channel under high mobility conditions, using block pilot insertion. The loss of sub channel orthogonality leads to inter-carrier interference (ICI). Using many algorithms for channel estimation, we will show that, for a 16- QAM modulation, the LMMSE algorithm performs well to achieve this estimation but when the SNR (Signal Noise Rate) is high, the four algorithms (LS, MMSE, LMMSE and Lr-LMMSE) perform similarly, this is not always the case for another scheme of modulation. We will improve also the mean squared error for these algorithms. It will be illustrious in this paper that the LMMSE algorithm performs well with the block- pilot insertion as well as its low rank version which behave very good even when the size of FFT is very high.
FP/EBG antennas have received intensive attention and large investigations during the last decade. The development of such structure opened the field for real industrial applications in the microwave domain, especially for the antenna design. In this paper we present an FP/EBG antenna operating around 2GHz. The structure consists of a Fabry-Perot Cavity composed of a ground plane, an air cavity and a Partially Reflecting Surface (PRS) made of SRR cells (Slot Ring Resonator). The simulation results show a directivity enhancement of about 4 dB. This structure can be used as directive antenna in communication systems.
This paper describes a new method for adaptive beamforming for a phased antenna arrays using genetic algorithm. The algorithm can determinate the values of phase excitation for each antenna to steer the main beam in specific direction. Various results are presented with -10 dB side lobes level. To improve these results, a Chebyshev model was proposed in order to decrease the level of side lobes which consists in amplitude synthesis.
An effective method is proposed to design a matching circuit for a microwave rectifier in order to manage the frequency bandwidth and the power bandwidth. Although the input impedance is affected by the nonlinear behavior of diodes with the variation of input power levels, the analysis on a variety of matching circuit configuration brings more evidence to improve the performance of rectifiers. This method has been applied in a low cost, zero-bias Schottky diode rectifier having RF-DC conversion efficiency of 55 %. The nonlinear simulation of rectifier circuit and an analytic description of multiple dimensional parameters are the key to study the relation between the nonlinear performance of a rectifier and its matching circuit.
Reflection from a stratified medium, backed by a perfect electromagnetic conductor (PEMC) due to an oblique incident plane wave is calculated analytically and numerically. Applying the PEMC boundary condition, the analytic reflection dyad is computed by the notion of propagators and wave-splitting technique and the numerical implementation is carried out using the FDTD method. FDTD modeling is achieved by implementation of PEMC boundary condition in the FDTD technique. Simulation results are provided for verification.
We present a reliable solution for service data exchange provided by various nodes of a wireless adhoc networks without bothering the routing protocol mechanism. A service is defined as the entity invoked either by a software, a host or a user. In recent works, the mechanism of service-discovery has been already implemented at application layer. The main idea of this work is to implement new service discovery mechanism at the network layer without disturbing the routing protocol machine in order to cut down latency and also energy consumption.
In this paper, an accurate and numerically robust singularity correction technique for transmission line matrix method (TLM) algorithm is proposed. The impedance of the adjacent cells to the singularity is corrected by a scalar correction factor, which amounts to a quasi-static correction of the electric and magnetic energy stored in the TLM cells at the singularity. The effectiveness of this method in accurate modeling of structures with metallic strips (sharp edges) been clearly validated against published measurement and common TLM simulation data.
