CW Signal Research Articles

A 100 W SiC MESFET Amplifier for L-band T/R Module of APAR

A 100 W SiC MESFET Amplifier for L-band T/R Module of APAR In the paper, a 100W SiC MESFET amplifier design dedicated for a L-band T/R module of APAR is presented. The output power higher than 100 W has been achieved by combining in a balanced configuration two single stages with Cree's 60 W CRF24060 SiC MESFETs. The amplifier design methodology is based on the small-signal model and DC characteristics of SiC MESFET. The model is extracted using the transistor S-parameters at three operating points for On-state, Off-state and normally biased. The measurements and simulations prove usefulness of the proposed design method. The amplifier was excited with pulsed and cw signals for the case temperature ranging from 60°C to 140°C. As a result of the case temperature changes the output power drop was lower than 0.5 dB at the level of 150 W.

Application of kernel methods in signals modulation classification

A new approach to common signals classification of relevance vector machine (RVM) was presented and two signal classifiers based on kernel methods of support vector machine (SVM) and RVM were compared and analyzed. First several robust features of signals were extracted as the input of classifiers, then the kernel thought was used to map feature vectors impliedly to the high dimensional feature space, and multi-class RVM and SVM classifiers were designed to complete AM, CW, SSB, MFSK and MPSK signals recognition. Simulation result showed that when chose proper parameter, RVM and SVM had comparable accuracy but RVM had less learning time and basis functions. The classification speed of RVM is much faster than SVM.

Depth and Rate of Fading on Fixed Wireless Channels Between 200 MHz and 2 GHz in Suburban Macrocell Environments

Various bands between 200 MHz and 2 GHz have recently been reallocated to multipoint fixed wireless services. The links in such systems are usually obstructed by buildings and foliage and are susceptible to fading caused by windblown trees and foliage. To date, there have been relatively few efforts to characterize either the depth of fading in bands below 1.9 GHz or the rate of fading in any of these bands. We transmitted CW signals in the 220, 850 and 1900 MHz bands from a transmitter located 80 m above ground level in a typical suburban macrocell environment and collected time-series of received signal strength at distances between 1 and 4 km from the site. We reduced the data to show how the depth and rate of fading depend on the frequency band, time-averaged wind speed and distance in such an environment. Our most significant finding is that the rate of signal fading is very similar in all three bands. In particular, it is not proportional to carrier frequency, as a simplistic model involving moving scatterers might suggest. These results will provide useful guidance to those who seek to simulate, or develop detailed physical models of, fade dynamics in such environments.

A high-power solid-state RF source driven by a doubly-differential signal

This letter presents a new solid-state RF source generating kW-level output power at HF band.Four power transistors are driven in a doubly-differential way, operated in a switching mode, and combined together to produce high output power. A multilayered input feed network is carefully designed, such that an accurate doubly-differential signal is provided to the transistors. The output matching and combining circuitry is optimized toward a high efficiency. The implemented RF source produces a CW signal of 1.5 kW at 29 MHz with a drain efficiency of 85%. The measured high efficiency is attributed to the well-balanced and symmetric switching-mode operation of each transistor, which is verified experimentally by a thermal image. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1489–1492, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25230

Impact of the third-order dispersion on the modulation instability gain of pulsed signals

We demonstrate that modulation instability gain of time-localized signals (i.e., pulsed signals) depends strongly on the third-order dispersion, contrary to the well-known case of time-extended signals (cw signals). This surprising contribution of an odd dispersion term on this four-photon-mixing process is established analytically and confirmed by numerical simulations.

Study of weak high-frequency CW signal detection based on stochastic resonance

CW telegraph has been largely used for high-frequency tactical communication. But there exists serious decline in high-frequency channel, which presents great difficulties to the detection and identification of CW telegraph signals. The traditional detection method based on time-frequency transformation has a poor performance in strong noise environment. An advanced detection method that combines non-linear bi-stable stochastic resonance model and time frequency analysis is proposed in this paper. Firstly, the received CW signal was modulated to a certain low frequency, and filtered by stochastic resonance model to restore its waveform from strong noise environment. Secondly, the WVD transformation and Hough transformation were utilised to extract its time domain features of the restored waveform. Thus, the detection of CW telegraph signal was easily implemented by detecting the peak values in parameters space. The simulation studies and results showed that the new method performs very well in the detection of CW signal with low signal noise ratio.

All-fiber joint-transform correlator for time-multiplexed signals

We present the temporal counterpart of a spatial joint-transform correlator. This system optically measures the rf spectrum of a real-time spectral interferogram achieved by stretching a sequence of two time-multiplexed pulses. The optical rf analyzer makes use of the cross-phase modulation on a cw probe in a highly nonlinear fiber. We show that the optical spectrum appearing on the cw signal contains the information of the electric-field cross correlation of the signals under test. This device offers potential applications for all-optical pattern recognition of ultrashort pulses.

All-optical signal gating using ytterbium-doped fiber and a pair of thermally expanded core fibers

We report all-optical signal gating using ytterbium-doped fiber (YDF) and a pair of thermally expanded core fibers (TECFs). Splicing the YDF with two TECFs at their expanded-core ends, we obtained an interference pattern in the transmission spectrum of the device. When pumped by a laser diode at 980 nm, the interference fringes shift to longer wavelength due mainly to the resonantly enhanced nonlinearity of the YDF. Consequently, signals within the interference pattern can be gated or blocked all optically. Full gating of cw signals at 1564.21 and 1564.54 nm were obtained using a pump power of about 38.44 mW.

Modal Inversion Analysis for Geoacoustic Properties of the New Jersey Continental Shelf in the SWAT Experiments

In this paper, inversion for bottom sediment properties at a site on the New Jersey continental shelf is studied as part of the Shallow Water Acoustic Technology (SWAT) project. A source towed at a constant water depth over a range of some tens of kilometers transmitted low-frequency continuous wave (cw) signals, which were measured on a bottom-moored vertical line array of receivers. For the along-shelf geometry, the zeroth-order asymptotic Hankel transform is then applied to the acoustic field at 50 Hz measured on the resulting synthetic aperture horizontal array created at each receiver depth. The resulting horizontal wave number spectra, which have peaks corresponding to the mode eigenvalues, are observed to have slightly different values at different receiver depths, and therefore, stochastic mode inversion is exploited to utilize all of the observed peak position information. The estimated sound-speed profile (SSP) for the upper 10 m of sediment is then compared with an inversion result obtained using midfrequency (2-16 kHz) chirp sonar pulses reflected at normal incidence from the sediment. Although obtained using totally different inversion techniques, both estimated profiles are shown to be in good agreement in the top 10 m of sediment. The acoustic field simulated using the inverted SSP also agrees well with the measured acoustic field at each receiver depth. Furthermore, simulated sound fields which use this profile as input data are shown to be effective in predicting the measurements obtained at a different frequency (125 Hz) and for a different (cross-shelf) geometry.

A highly efficient class‐F power amplifier for wideband linear power amplifier applications

AbstractIn this letter, a highly efficient class‐F power amplifier (PA) is developed as a new main block of the wideband base‐station linear power amplifier. The class‐F PA is implemented using Eudyna EGN010MK GaN HEMT with a 10‐W peak envelop power. The nonlinearity and memory effects of class‐F PA are explored to apply the wideband application. The maximum power‐added efficiency of the implemented PA is 68% at a saturated output power of 40 dBm for the 2.14‐GHz CW signal. The PA delivers a good efficiency of 35% at an average output power of 32.3 dBm for wide‐band code division multiple access 3FA signal with 15‐MHz bandwidth, and the linearity can be improved to about −48 dBc using the digital feedback predistortion linearization technique. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2323–2326, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24631

Extinction Ratio Improvement Due to a Bogatov-Like Effect in Ultralong Semiconductor Optical Amplifiers

Theoretical results on the extinction ratio (ER) improvement in ultralong semiconductor optical amplifiers (UL-SOAs) are presented indicating a Bogatov-like effect in the saturated section. Starting from general nonlinear gain equations, an analytic description of the Bogatov-like effect is derived in terms of gain coefficients. These equations are used to explain the results of fully numerical simulations. The data signal's ER improves because of a two-step process. First, the data signal cross-gain modulates the additionally injected CW signal. Second, due to this inverse modulation, the data signal's states are differently amplified via the Bogatov-like effect. Since the ER improvement is caused by the fast intraband effects, this simple scheme has the potential for high-speed regeneration.

Development of 16 μm continuous-wave modulation hard-target differential absorption lidar system for CO_2 sensing

We have demonstrated the 1.6 mum cw modulation hard-target differential absorption lidar system for CO(2) sensing. In this system, ON and OFF wavelength laser lights are intensity modulated with cw signals. Received lights of the two wavelengths from the hard target are discriminated by modulation frequencies in the electrical signal domain. The optical circuit is fiber based, and this makes the system compact and reliable. It is shown that a stable CO(2) concentration measurement corresponding to a fluctuation of 4 ppm (rms) (ppm is parts per million) has been achieved in 32 s measurement intervals and the 1 km path.

Low-power 1×2 all-optical switching in a silicon double coupler microring resonator

Low-power 1×2 optical switching in a double coupler ring resonator (DCRR) made by a silicon nanoscale waveguide based on two photon absorption (TPA) is analyzed theoretically. The TPA originates from a femtosecond pump light at 400 nm, which enters the DCRR together with a CW signal light at 1.55 μm through the input port. TPA makes the silicon free-carrier concentration change, which is proportional to the change of reflective index. Our numerical simulation shows that when average pump power reaches 2 mW, it will induce the 10. 3 refractive-index change and the π-phase shift of signal light, after which 1×2 all-optical switching can be realized.

Phase-Coded Interrupted CW Signals and Processors

High resolution radars require signals with large time-bandwidth product such as CW signal and coherent pulse train (CPT). We discuss a phase-coded interrupted CW (ICW) signal which is the combination of CW signal and CPT. Phase codes used here are with perfect periodic autocorrelation. The periodic ambiguity function of ICW signals is studied including single-carrier signal and multi-carrier signal. It is interesting that the gate function has different effects on two signals and contributes to a multi-carrier ICW signal which yields nearly perfect autocorrelation. Meanwhile we also suggest an efficient receiver approach to ICW signals, which can reduce the computational burden of the processor and utilize the good properties of P3 and P4 codes.

6-단자 위상 상관기를 이용한 PSK 반송파 신호 복원 회로 해석

The PSK carrier signal recovery circuit using a six-port phase correlator was analyzed and the circuit structure is proposed in this paper. The proposed carrier signal recovery circuit that is made of reflection element and six-port phase correlator, which is comprised of a power divider and three hybrid branch line couplers, give a simple structure and can be fabricated without no difficulty. The circuit recovers the carrier signal of BPSK and QPSK modulation signal. The proposed scheme can be utilized as a basis structure for high-mode PSK carrier signal recovery. By simulation results, the recovered signal by the proposed circuit shows a good carrier signal characteristic with CW signal of a constant phase() and phase error due to glitch conditions.

Quality enhancement of image generated with bistatic ground based noise waveform SAR

A new method for quality enhancement in a noise synthetic aperture radar (SAR) image and the first results of its application to the SAR image generated with the use of a bistatic Ka-band ground-based noise waveform SAR (GB NW-SAR) are presented. A SAR image generated with a noise SAR suffers from the masking effect which is tied to residual random fluctuations in noise radar response from bright scatterers in the scene. This is similar to the masking effect present in the deterministic waveform SAR when the signal sidelobes of echoes from bright scatterers may mask the main response from a weaker target. The procedure presented is a variation of the CLEAN algorithm. Knowing precisely the emitted signal and finding positions of the strongest scatterers one may model the echo signal originated from a selected scatterer. Extraction of the modelled signal from the received one reduces the residual fluctuations and makes it possible to clean the image and increase its dynamic range. The final image is constructed from the cleaned signal and the previously removed strongest scatterers. A theoretical background is provided to the proposed procedure and its application to enhance the SAR image using simulated data as well as data generated by the Ka-band bistatic GB NW-SAR is demonstrated. The GB NW-SAR, recently developed and tested in LNDES IRE NASU, may operate in CW and pulse random signal regimes for short range applications.

Three-Wave Trapponic Solitons for Tunable High-Repetition Rate Pulse Train Generation

We demonstrate that the parametric mixing of an ultrashort Zakharov-Manakov (ZM) soliton pulse with a quasi-continuous-wave (CW) signal in a weakly quadratic nonlinear and dispersive medium may lead to the generation of a three-wave soliton with variable speed, or trappon. We show that trappons may provide a novel mechanism of cavityless ultrashort pulse train generation. The timewidth, the amplitude and the repetition rate of the generated pulse trains may be controlled in a stable manner by adjusting the intensity level of the CW signal and/or the ZM short soliton pulse.

INVESTIGATION OF 3D ACOUSTICAL EFFECTS USING A MULTIPROCESSING PARABOLIC EQUATION BASED ALGORITHM

A parallelized algorithm based on an existing 3D wide-angle parabolic equation model is developed to perform numerical simulations of underwater acoustic propagation on a massively parallel computer. The parallelization method used is a suitable two-level procedure: A frequency decomposition and a spatial decomposition of the calculations, which are respectively dedicated to reduce CPU times for broadband and cw signal propagation. The high-performance of the parallelized algorithm is examined for the 3D extension of the classical ASA wedge benchmark. CPU times are reported and both speedup and efficiency are analyzed. An investigation of significant 3D effects at higher frequencies and at longer propagation ranges than in earlier works [F. Sturm, J. Acoust. Soc. Am.117(3) (2005) 1058–1079] is performed with reasonable CPU times by using the new parallel algorithm. Further, the feasability of the procedure applied to a realistic oceanic environment problem involving both real sound speed profiles and bathymetry data sets is also illustrated.

Hybrid discriminative/class-specific classifiers for narrowband signals

The class-specific (CS) method of signal classification operates by computing low-dimensional feature sets defined for each signal class of interest. By computing separate feature sets tailored to each class, i.e., CS features, the CS method avoids estimating probability distributions in a high-dimension feature space common to all classes. Building a CS classifier amounts to designing feature extraction modules for each class of interest. In this paper we present the design of three CS modules used to form a CS classifier for narrowband signals of finite duration. A general module for narrowband signals based on a narrowband tracker is described. The only assumptions this module makes regarding the time evolution of the signal spectrum are: (1) one or more narrowband lines are present, and (2) the lines wandered either not at all, e.g., CW signal, or with a purpose, e.g., swept FM signal. The other two modules are suited for specific classes of waveforms and assume some a priori knowledge of the signal is available from training data. For in situ training, the tracker-based module can be used to detect as yet unobserved waveforms and classify them into general categories, for example short CW, long CW, fast FM, slow FM, etc. Waveform-specific class-models can then be designed using these waveforms for training. Classification results are presented comparing the performance of a probabilistic conventional classifier with that of a CS classifier built from general modules and a CS classifier built from waveform-specific modules. Results are also presented for hybrid discriminative/generative versions of the classifiers to illustrate the performance gains attainable in using a hybrid over a generative classifier alone.

Directly modulated laser diode in the nonlinear regime for low‐cost digital frequency up‐conversion

AbstractThe purpose of this article is to demonstrate the extension of the modulation bandwidth of single mode laser sources to reach the RF frequency range of wireless access networks such as ultra‐wide band systems with low‐cost solutions. In this article, we have studied optical microwave mixing using nonlinear direct modulation of a distributed feedback (DFB) laser diode. First, the nonlinear behavior of the DFB laser diode near the threshold current has been analyzed and explained based on frequency mixing measurements made with CW signals. Then, we have experimentally demonstrated frequency up‐conversion of a QPSK signal. These results were compared to eye‐diagram simulations based on the laser static and dynamic characteristics. Subsequently, the frequency up‐conversion of a WLAN IEEE 802.11a signal was experimentally demonstrated. Best conditions in terms of DFB bias current and RF input power signals have been studied. Good conversion loss and EVM results have been obtained. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1214–1219, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23329