PHASE MEASUREMENTS ACCURACY UNDER CONDITIONS OF INTERFERENCE WITH NON-IDEAL CHARACTERISTICS OF PHASE MEASUREMENT ELEMENTS

A Mathematical Method for Detecting LPI Signals

The unique characteristics of Low Probability of Intercept (LPI) waveforms, which are based on wideband specialized modulation techniques, LPI signals not only provide high resistance against electronic jamming but also significantly reduce the detectability of these signals, thereby establishing LPI signals as an effective electronic countermeasure. The Chirp Spread Spectrum (CSS) waveforms used in the LoRa protocol are a current example of signals possessing LPI characteristics. In complex electromagnetic environments where spectral density is high and the signal-to-noise ratio (SNR) drops to critical levels, the detection of these signals and the separation of their sub-characteristics remain an ongoing challenge in the literature. This study presents an original time-frequency analysis approach that enables the detection of CSS signals and parameter estimation with high accuracy under the aforementioned challenging environmental conditions. In tests conducted to validate the method’s performance, CSS signals with unknown parameters were subjected to different channel scenarios by generating spectral density in a laboratory environment. The proposed method was tested on IQ (In-Phase Quadrature) signal data recorded on a Software-Defined Radio (SDR) platform; using the developed algorithm, CSS signal parameters are extracted with high accuracy even under low SNR conditions where the signal power fell below the noise floor in some cases.

Algorithm for eliminating parasitic angular modulation in electromagnetic sensors

Electromagnetic sensors of the inductive type are widely used in industrial systems, scientific research, and measuring equipment. However, during their operation, parasitic angular modulation may occur, leading to distortion of measurement results and a decrease in the accuracy of useful signal extraction. Therefore, the development of methods for compensating or eliminating the influence of such modulation is an important scientific and practical task. The paper proposes an algorithm for eliminating parasitic angular modulation in electromagnetic sensors based on extracting the central carrier frequency from an amplitude-modulated oscillation and generating a reference signal for synchronous detection. The proposed approach involves the use of an amplifier-limiter, a narrowband filter, an analog multiplier, and a low-pass filter, which together provide suppression of parasitic angular modulation and extraction of a useful low-frequency signal proportional to the parameters of the object under investigation. A structural diagram of the device implementing the proposed algorithm is presented, and spectral transformations of the signal in the main functional blocks are analyzed. It is shown that the developed approach makes it possible to reduce the influence of parasitic phase distortions and improve the quality of information extraction from the sensor output signal. The proposed algorithm has a general character and can be adapted for various types of electromagnetic measuring systems. Further development of the method is associated with its implementation using digital signal processing technologies and quadrature signal processing, which will provide additional information about the investigated object and improve measurement accuracy under low signal-to-noise ratio conditions.

Radiation phase control system for a WIFI and BLUETOOTH antenna array using phase shifters

This article presents a system for controlling the angle of sound and rapidly changing the radiation patterns of WiFi and Bluetooth antennas by modifying the phase shift in a patch antenna array. The system incorporates a phase shifting process to achieve beamforming, which improves signal strength in desired locations and reduces noise in undesired areas. This involves designing patch antennas with precise measurements, installing a control unit to adjust the phase shift, and testing their operation in both real and simulated environments. Measurements were made in a circular pattern, covering a 180- degree area with 30 points, at 6-degree intervals, in an anechoic chamber. A voltage of 3 V was used to determine the phase shift between measurements without a phase shifter. The results showed that without a phase shifter, a minimum value of -25.25 dB was found, while with the different voltages, a value of -25.29 dB was obtained at 3 V, indicating an approximate phase shift of 12 degrees compared to measurements without a phase shifter. The data show significant changes in signal coverage, power utilization, and an improvement in system performance. The findings highlight the potential of this approach for use in smart homes, IoT devices, and other wireless communication systems that require flexible radiation patterns.

On the Precision of Impedance Argument Estimation in the Presence of Additive Noise

Estimating the argument of an electrical impedance is an important task in many engineering fields. Modern systems usually employ data acquisition systems to sample and digitize the voltage and current signals obtained by stimulating the unknown impedance with a sinusoidal signal. The presence of nonideal phenomena in signal generation or signal measurement inevitably leads to an increased uncertainty in impedance argument estimation. This work focuses on the effect of additive noise and proposes an analytical expression that can be easily used to compute the impedance argument standard deviation as a function of additive noise precision, number of samples, stimulus signal amplitude, current sampling resistance value, and nominal impedance modulus value. It specifically considers the presence of additive noise on both the voltage and current measuring channels. The analytical expression given is important when designing the measurement system to determine the minimum number of samples that should be acquired as well as in computing the confidence intervals for the estimations made using this method.

SOME PRACTICAL ISSUES OF THE TRACKING PROCESS IN GNSS RECEIVERS

Accuracy and intolerance to interference of GNSS receivers depend on the efficiency of tracking modules. To achieve better characteristics, designers should implement various issues, affecting the process of tracking in these modules: integration interval, spacing and configuration parameters of PLL and DLL. The article discusses practical issues concerning implementation of tracking modules. Using the obtained results, it is possible to improve transient characteristics of tracking modules. These issues were tested in an experimental navigation receiver. The results were obtained using the simulation software, developed by the authors, as well as Vivado simulator and experimental testing.

ADVANCED STUDY OF VIDEO SIGNAL PROCESSING IN LOW SIGNAL TO NOISE ENVIRONMENTS