Wideband Frequency Modulation Research Articles

Wide-band frequency modulation of a terahertz intrinsic Josephson junction emitter of a cuprate superconductor

Wide-band frequency modulation of a terahertz intrinsic Josephson junction emitter of a cuprate superconductor

Ultralinear 140-GHz FMCW signal generation with optical parametric wideband frequency modulation enabling 1-mm range resolution.

We demonstrate ultralinear and ultrawideband frequency-modulated continuous-wave (FMCW) signal generation using an optical parametric wideband frequency modulation (OPWBFM) method. The OPWBFM method optically expands the bandwidths of FMCW signals beyond the electrical bandwidths of optical modulators via a cascaded four-wave mixing (FWM) process. Compared to the conventional direct modulation approach, the OPWBFM method simultaneously achieves high linearity and a short measurement time of the frequency sweep. On the other hand, it is also known that the OPWBFM method expands the phase noise of idlers as well as their bandwidths if an input conjugate pair has different phase noise. To avoid this phase noise expansion, it is crucial to synchronize the phase of an input complex conjugate pair of an FMCW signal using an optical frequency comb. For demonstration, we successfully generated an ultralinear 140-GHz FMCW signal by using the OPWBFM method. Moreover, we employ a frequency comb in the conjugate pair generation process, leading to the mitigation of phase noise expansion. By using a 140-GHz FMCW signal, we achieve a range resolution of ∼1 mm through fiber-based distance measurement. The results show the feasibility of an ultralinear and ultrawideband FMCW system with a sufficiently short measurement time.

Narrowband and wideband frequency modulation spectral characterization and bandwidth calculation

Frequency modulation (FM) is a class of analog modulation techniques that rely on varying the instantaneous frequency of a radio-frequency (RF) carrier in accordance with the baseband signal. The amplitude of the FM signal is constant, while its instantaneous frequency is time variant; therefore, the zero crossing rate (ZCR) of the carrier differs at a rate proportional to the Nyquist rate of the baseband signal. Unlike amplitude modulation (AM), FM is a nonlinear modulation technique; therefore, the calculation of the spectrum of an FM signal is expected to be a tedious mathematical problem.

Wideband current modulation of diode lasers for frequency stabilization.

We present a current modulation technique for diode laser systems, which is specifically designed for high-bandwidth laser frequency stabilization and wideband frequency modulation with a flat transfer function. It consists of a dedicated current source and an impedance matching circuit both placed close to the laser diode. The transfer behavior of the system is analyzed under realistic conditions employing an external cavity diode laser (ECDL) system. We achieve a phase lag smaller than 90° up to 25 MHz and a gain flatness of ±3 dB in the frequency range of DC to 100 MHz, while the passive stability of the laser system is not impaired. The potential of the current modulation scheme is demonstrated in an optical phase-locked loop between two ECDL systems with a phase noise of 42 mradrms. The design files are available as an open-source project.

Simulation and Analysis of Frequency Modulation System in MATLAB as Practical Assessment Method for Communication Engineering Course

COVID-19 pandemic hit has raised new challenges for Outcome-Based Education (OBE) system since the normalization of the online education delivery. Still, this era of endemic imposes challenges in satisfying OBE requirements, especially the students’ practical assessments. As an essential part of Communication Engineering, Frequency Modulation (FM) fundamental can be theoretically and mathematically explained during the online classes. However, its practical assessment needs to be done experimentally. Since buying the real devices and tools needed to create a complete FM system consumes high cost, software simulation is the best solution to accommodate the learning processes for all students. Hence, aided by the MATLAB simulation and analysis approaches, this paper presents the implementation of FM practical assessment at Universiti Teknologi MARA (UiTM) as an institute of higher education. For this task, students have built the FM system by using both mathematical and Simulink model. The model also emphasized students on the association between FM’s important parameters: modulating frequency, modulation index, frequency deviation, and bandwidth, with the type of FM, Narrow Band FM (NBFM) or Wide Band FM (WBFM). Results for all model configurations are recorded and analyzed accordingly. From this practical activity, students have demonstrated a better attainment for this course’s Program Outcome (PO) as compared to the conventional assessment methods.

A Method Against Interrupted Sampling Repeater Jamming Based on Genetic Algorithm and Compressed Sensing Reconstruction

By analyzing the discontinuous character in time domain, a jamming suppression method is propose to counter Interrupted sampling reperter jamming(ISRJ, which is an effective coherent jamming to wide-band linear frequency modulation signal. The discontinuous character of ISRJ and the instantaneous frequency change rule after stretch is firstly analyzed. Secondly, by controlling the adjustment parameters, the generalized S transform is utilized to obtain the time-frequency grayscale image of received signal. Then, the grayscale image can be segmented by using genetic algorithm to construct a time-domain filter, and the time-domain filter can be used to extract the echo band without jamming signal. Finally, the extracted signal is used as compressed data to construct a compressed sensing minimization model, and the compressed sampling matching pursuit algorithm is used to reconstruct the target echo signal. Simulation shows that this method has good jamming suppression performance.

Determination of Fast-Moving Objects’ Speed and Range with Linear Frequency Modulation Continuous Wave Radar Using Autocorrelation Scheme

Introduction. A hardware basis of modern Advanced Driver Assistance Systems (ADAS) consists of millimeterrange radars, characterized by a relatively short range (meters – tens of meters). At the same time, improving of traffic safety requires to increase the range at least to several hundred meters. The one way to achieve such values is to increase wavelength of a probing signal, to use the centimeter range of wavelengths, for example. The paper represents a detailed description of main steps of signal processing algorithm in the model of the ADAS low-power centimeter range radar, which provides fast-moving objects speed and range definition.Aim. Development of an algorithm for estimating the range and the speed of targets by an autocorrelation radar with a wide-band continuous linear frequency modulation (linear FM) signal in order to increase the rate of the ADAS system estimates formation.Materials and methods. The proposed algorithm is based on the methods of primary and secondary digital processing of radar signals. The model of a centimeter-range autocorrelation radar with a broadband continuous linear FM probing signal was used for practical researches. MATLAB software was used to process the received signal samples.Results. The algorithm has been developed to determine the speed and the range of fast-moving objects in conditions when their movement during the evaluation interval significantly exceeds the radar range resolution. The use of simplified Kalman filtering for inter-period secondary signal processing allowed to increase significantly the stability of the algorithm. In a full-scale experiment using the low-power radar model with continuous radiation of the centimeter range, it was shown that a stable assessment of a real car speed and range was provided at a distance of at least about one kilometer.Conclusion. The results of the field experiment make it possible to draw conclusions that the proposed algorithm is highly robust even in the absence of inter-period secondary processing. Its usage allows one to improve the stability of the algorithm without considerable additional computational costs. It is possible because near-linear dynamics of the observation object and of the radar carrier makes it sufficient to use a simplified implementation of Kalman filter in the form α-β-algorithm.

Photonic-Assisted Leakage Cancellation for Wideband Frequency Modulation Continuous-Wave Radar Transceiver

Frequency modulated continuous-wave (FMCW) radar systems suffer from permanent leakage from the transmitted signal into the receiver, which will reduce the dynamic range of the system and degrade the receiver sensitivity. Herein, a photonic-assisted leakage cancellation method for a wideband FMCW radar transceiver is proposed and experimentally demonstrated. At the remote antenna unit (RAU), a local oscillator (LO) signal, and a leakage signal are converted to optical signals with orthogonally polarization states by using a polarization-division-multiplexed Mach–Zehnder modulator (PDM-MZM). After the transmission of 10 km single mode fiber (SMF), the leakage signal is cancelled by using a variable optical attenuator (VOA), a variable optical delay line (VODL), and a balanced photodetector (BPD) at central office (CO). Compared with other analog cancellation methods, the proposed one has wider sweeping bandwidth and simpler structure. In the experiment, the LO signal and leakage signal are emulated by using an arbitrary waveform generator (AWG), a power divider, and two different length radio frequency lines. Then, experimental results show that a leakage cancellation depth of 17.5 dB at the carrier frequency of 15 GHz with a sweeping rate of 2 GHz/4 us is achieved.

The Influence of Wide-Band Frequency Modulation on the Competition of Orthogonally Polarized Modes in a Two-Mode Laser

Competitive interaction of orthogonally polarized modes in a two-mode laser operating in a regime of wide-band frequency modulation has been numerically simulated. This modulation was implemented by means of the corresponding variation of the laser cavity length. Parameters of the active medium adopted in the numerical model were characteristic of He–Ne lasers with an inhomogeneously broadened gain line. It is established that negative consequences of the mode competition can be significantly reduced at certain values of the modulation frequency and frequency deviation.

A Dual-Loop Synthesizer With Fast Frequency Modulation Ability for 77/79 GHz FMCW Automotive Radar Applications

The implementation of wideband mm-wave radars for automotive applications necessitates wideband, fast, and precise linear frequency modulation generation. In this paper, we propose to use dual-loop phase-locked loop (PLL) architecture for this task. The frequency modulation dynamics are analyzed for this architecture. The results are employed to implement a SiGe BiCMOS fully integrated 75–83 GHz frequency-modulated continuous-wave synthesizer. Performance enhancements were achieved by utilizing the bulk-drain parasitic variable capacitance of P-channel transistors, embedded in a gm-boosted Colpitts VCO, for frequency control. This mechanism together with the dual-loop PLL architecture provides low loop bandwidth variation over the whole output frequency range, −97 dBc/Hz phase noise at 1-MHz offset, and maximal modulation rate of 100 GHz/ms.

Laser Frequency Analysis Aided by Electronic Frequency Dividers

Conventional laser spectral analysis relies on direct measurement of power spectral density (PSD), which is not able to distinguish certain types of phase and frequency modulations without ambiguity. In this paper, we propose and demonstrate a modified scheme aimed at improving the specificity in laser frequency analysis. Our method is based on PSD measurement of the downshifted laser spectrum in the radio-frequency range but introduces an electronic frequency divider (EFD) prior to the spectrum analyzer. By monitoring the spectral changes caused by the EFD, we show, both theoretically and experimentally, that common scenarios of phase and frequency modulations, such as wideband frequency modulation (FM) and broadband phase modulation, can be differentiated without ambiguity. Moreover, the new method allows for quantitative assessment of wideband FM parameters such as modulation frequency, modulation index, and frequency deviation, which is not possible with any conventional spectral analysis methods. This technique may find potential applications in laser frequency metrology, microwave photonics, optical sensing, and radar/lidar technologies.

Dispersion compensation method based on focus definition evaluation functions for high-resolution laser frequency scanning interference measurement

We study dispersion mismatches and compensation in high-resolution frequency scanning interference measurements. Compared to semiconductor lasers, external cavity lasers can, in theory, provide wideband frequency modulation and high-resolution measurements. However, experiments indicate that the dispersion mismatch cannot be ignored in measurement systems containing wideband tuning lasers. Fibre auxiliary interferometer external clock sampling results indicate that the beat frequency of measurement signals exhibits linear chirp. In turn, the frequency spectrum of the measurement signal broadens, thus lowering the measurement resolution and limiting the measurement distance. We present a dispersion mismatch model and analyse the associated measurement effects. We also propose a dispersion compensation method based on a focused definition evaluation function. By studying the relationship between the compensation coefficient and evaluation function, the optimal compensation coefficient can be determined quickly and accurately. Our experiments demonstrate that within a tuning bandwidth of 40nm, the peak full width at half maximum (FWHM) after dispersion compensation is 32.2µm at a distance of 3.8931671m, which is close to the theoretical resolution. Our method provides a technical approach to realizing large, high-resolution distance measurements for broadband laser frequency scanning interferometers.

Atmospheric and Fog Effects on Ultra-Wide Band Radar Operating at Extremely High Frequencies.

The wide band at extremely high frequencies (EHF) above 30 GHz is applicable for high resolution directive radars, resolving the lack of free frequency bands within the lower part of the electromagnetic spectrum. Utilization of ultra-wideband signals in this EHF band is of interest, since it covers a relatively large spectrum, which is free of users, resulting in better resolution in both the longitudinal and transverse dimensions. Noting that frequencies in the millimeter band are subjected to high atmospheric attenuation and dispersion effects, a study of the degradation in the accuracy and resolution is presented. The fact that solid-state millimeter and sub-millimeter radiation sources are producing low power, the method of continuous-wave wideband frequency modulation becomes the natural technique for remote sensing and detection. Millimeter wave radars are used as complementary sensors for the detection of small radar cross-section objects under bad weather conditions, when small objects cannot be seen by optical cameras and infrared detectors. Theoretical analysis for the propagation of a wide “chirped” Frequency-Modulated Continuous-Wave (FMCW) radar signal in a dielectric medium is presented. It is shown that the frequency-dependent (complex) refractivity of the atmospheric medium causes distortions in the phase of the reflected signal, introducing noticeable errors in the longitudinal distance estimations, and at some frequencies may also degrade the resolution.

A 56.4-to-63.4 GHz Multi-Rate All-Digital Fractional-N PLL for FMCW Radar Applications in 65 nm CMOS

A mm-wave digital transmitter based on a 60 GHz all-digital phase-locked loop (ADPLL) with wideband frequency modulation (FM) for FMCW radar applications is proposed. The fractional-N ADPLL employs a high-resolution 60 GHz digitally-controlled oscillator (DCO) and is capable of multi-rate two-point FM. It achieves a measured rms jitter of 590.2 fs, while the loop settles within 3 μs. The measured reference spur is only -74 dBc, the fractional spurs are below -62 dBc, with no other significant spurs. A closed-loop DCO gain linearization scheme realizes a GHz-level triangular chirp across multiple DCO tuning banks with a measured frequency error (i.e., nonlinearity) in the FMCW ramp of only 117 kHz rms for a 62 GHz carrier with 1.22 GHz bandwidth. The synthesizer is transformer-coupled to a 3-stage neutralized power amplifier (PA) that delivers +5 dBm to a 50 Ω load. Implemented in 65 nm CMOS, the transmitter prototype (including PA) consumes 89 mW from a 1.2 V supply.

Wideband laser locking to an atomic reference with modulation transfer spectroscopy

We demonstrate that conventional modulated spectroscopy apparatus, used for laser frequency stabilization in many atomic physics laboratories, can be enhanced to provide a wideband lock delivering deep suppression of frequency noise across the acoustic range. Using an acousto-optic modulator driven with an agile oscillator, we show that wideband frequency modulation of the pump laser in modulation transfer spectroscopy produces the unique single lock-point spectrum previously demonstrated with electro-optic phase modulation. We achieve a laser lock with 100 kHz feedback bandwidth, limited by our laser control electronics. This bandwidth is sufficient to reduce frequency noise by 30 dB across the acoustic range and narrows the imputed linewidth by a factor of five.

UWB systems for body area networks

The paper describes a survey of the UWB physical layer for body area networks currently in development by the IEEE Standardisation 802.15.6 Task Group. Such UWB PHY consists of impulse radio-based UWB technology as well as CP-2FSK and wideband frequency modulation (FM-UWB) technology. IR-UWB systems employ on-off signalling modulation and FM-UWB modulation for medical and non-medical applications, while differentially encoded PSK modulation for high QoS medical applications. Such systems are optimised for low power consumption and reliable operation, especially in medical applications. Furthermore, the UWB signal power levels are in the order of those used in the MICS band (implant devices like pacemakers), therefore providing safety power levels for the human body and low interference to other systems’ devices.

Medical applications adapting ultra wideband: a system study

In order to find the best solution of physical layer for medical wireless body area network (WBAN), two single-band ultra wideband (UWB) systems are studied, i.e., direct sequence ultra wideband (DS-UWB) and ultra wideband frequency modulation (UWB-FM). UWB is considered to be one of the most feasible techniques among those that can be applied to medical WBAN since it provides low power consumption, simple transceiver structure and good coexistence characteristics due to a low power spectral density. The simulation results indicate that UWB-FM has better performance than non-coherent DS-UWB in overall. It was expected that coherent DS-UWB with multiple rake fingers gives the best results, and this was justified by the simulation results.

Armstrong's invention of noise-suppressing FM [History of Communications

Edwin H. Armstrong is well known as the inventor of wide-deviation or wideband FM. His patent on this invention was granted December 26, 1933, followed soon thereafter by demonstrations of his system before engineers, papers on the subject of wideband frequency modulation (FM) and its noise-suppression property, and eventually, of course, after World War II, widespread acceptance of FM by the radio industry and the public at large. The years in between were devoted to a bitter court fight between Armstrong and RCA, leading eventually to Armstrong's tragic suicide in 1954. This is well documented in the book by Lessing devoted to Armstrong's life (1969). What is not clear is precisely how and when Armstrong had the intuitive leap, his Eureka! moment, that led to this truly momentous invention. Armstrong was notorious for leaving very little documentation on his inventions. Lessing does note that Armstrong was fully occupied with his FM work, carrying out thousands of experiments, from 1928 to 1933, but no attempt to further narrow this interval of time down or discuss how he came to develop the wide-deviation FM concept is offered. We try, in this brief note, using documentation available in the Armstrong papers housed at Columbia University, to come to grips with these questions.

LMS-based calibration of an RF digitally controlled oscillator for mobile phones

We propose a least-mean square based gain calibration technique of an RF digitally controlled oscillator (DCO) in an all-digital phase-locked loop (ADPLL). The DCO gain of about 12-kHz/least significant bit is subject to process, voltage and temperature variations, but is tracked and compensated in real time. Precise setting of the inverse DCO gain in the ADPLL modulating path allows direct wide-band frequency modulation that is independent from the ADPLL loop bandwidth. The technique is part of a single-chip fully compliant Global System for Mobile Communications (GSM)/EDGE transceiver in 90-nm digital CMOS.

SoC with an integrated DSP and a 2.4-GHz RF transmitter

We present a system-on-chip (SoC) that integrates a TMS320C54x digital signal processor (DSP), which is commonly used in cellular phones, with a multigigahertz digital RF transmitter that meets the Bluetooth specifications. The RF transmitter is tightly coupled with the DSP and is directly mapped to its address space. The transmitter architecture is based on an all-digital phase-locked loop (ADPLL), which is built from the ground up using digital techniques and digital creation flow that exploit high speed and high density of a deep-submicrometer CMOS process while avoiding its weaker handling of voltage. The frequency synthesizer features a wideband frequency modulation capability. As part of the digital flow, the digitally controlled oscillator (DCO) and a class-E power-amplifier are created as ASIC cells with digital I/Os. All digital blocks, including the 2.4-GHz logic, are synthesized from VHDL and auto routed. The use of VHDL allows for a tight and seamless integration of RF with the DSP. To take advantage of the direct DSP-RF coupling and to demonstrate a software-defined radio (SDR) capability, a DSP program is written to perform modulation of the GSM standard. The chip is fabricated in a baseline 130-nm CMOS process with no analog extensions and features high logic gate density of 150 kgates per mm/sup 2/. The RF transmitter area occupies only 0.54 mm/sup 2/, and the current consumption (including the companion DSP) is 49 mA at 1.5-V supply and 4 mW of RF output. This proves attractiveness and competitiveness of the "digital RF" approach, whose goal is to replace RF functions with high-speed digital logic gates.