Open Access
Access granted
Subscription Access
Vol 59, No 6 (2016)
- Year: 2016
- Articles: 7
- URL: https://journals.rcsi.science/0735-2727/issue/view/10874
Article
Designs of multi-bit sigma delta modulator
Abstract
This paper presents new design variants of third order multi-bit sigma delta modulator (SDM): low distortion SDM and cascaded SDM. The proposed modulator based on the conventional SDMsuch L-0MASH(Multi-stAge noise SHaping) and interstage feedback topology. TheMASHSDM is not a single loop system. One of the drawback is that performance is limited by uncancelled noise from the first modulator and interstage feedback topology only cancels nonlinear errors introducing by multi-bitDACin the final stage, but the rest stage still containsDACnonlinearity errors without any noise shaping which still degrade overall system performance. An improved version of cascaded multi-bit SDM is proposed to overcome these problems mentioned above. In addition a third order low distortion SDM is also proposed. Simulation results verify the superiority of the both proposed modulator.
237-243
Errors of target direction finding by radars with planar arrays under the influence of external noise radiations
Abstract
This paper describes the mathematical model, which allows to investigate both fluctuation and systematic errors of target angular coordinates measurement in a radar with planar phased antenna array under the influence of external sources of noise radiations. The results of mathematical simulations are presented.
244-250
Method of compensating the active component of combined interference in coherent pulse radar
Abstract
The combined impact of active and passive interferences on coherent pulse radar was investigated. A mathematical model was developed implementing a new method for compensating the active component of combined interference in coherent pulse radar employing spectral differences in the structure of active and passive interferences. The results of simulation reveal that the polarization-time signal processing involving the use of rejection filters for suppression of passive interferences in circuits of forming the weight coefficients of automatic compensator make it possible to significantly enhance the quality of active interference compensation under conditions of exposure to combined interferences. The rejection of passive interference in circuits of forming the weight coefficients is shown to eliminate the distortion of passive spectrum distortion at the output of adaptive polarization filter.
251-255
Necessity and possibility of taking into account of space and time domain parameters of interfering reflections from the underlying surface in the design of anti-interference airborne radar stations for air surveillance
Abstract
The development of anti-interference radar stations is impossible without the knowledge of interference parameters. The main difficulty of designing of anti-interference airborne radar stations for air surveillance is associated with the suppression of reflections from the underlying surface. In order to estimate the azimuthal-velocity parameters of reflections from the underlying surface in airborne surveillance stations with unambiguous distance measurement we implemented the simulation model of digital output signals of a coherent radar receiver. During the model development we used digital maps and an antenna with low side lobe level. With the help of simulations we have justified the necessity and possibility of development of anti-interference airborne radar stations with low-channel design and simultaneous application of direct inter-period and inter-channel correlation connections.
256-261
Frequency properties of electrical fields of cylindrical sonar antenna with a flat baffle in the diametral plane
Abstract
By means of method of coupled fields we obtain analytical relations describing electrical fields of cylindrical piezoceramic antennas with flat baffles in diametral plane. Numerical experiment results of frequency characteristics of antennas’ electrical fields dependently on parameters of antenna elements and embodiment are presented.
262-268
Design of compact bandpass filter for WiMAX and UWB application using asymmetric SIRs and DGS
Abstract
This paper considers a novel compact tri-band microstrip bandpass filter, the design of which employs asymmetric SIRs and DGS for achieving the characteristics of low insertion loss, high selectivity, wider range of bandwidth, and low group delay for 2.5/3.4 GHz (WiMAX) and 4.14–5.32 GHz (UWB) bands. The novel filter design implies the intentional selection of impedance ratio R and the length of the microstrip of asymmetric SIRs; in addition, DGS is used to improve the coupling strength of the last band. The scattering parameters of the three passbands have the following values: insertion losses S21 are–0.26/–0.07/–0.05 dB, and return losses S11 are–11.29/–19.25/–22.64 dB, respectively. The response of the filter was simulated using Ansoft HFSS simulator.
269-273
274-279