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Synthetic aperture radar (SAR) inter-pulse parameter agility technology involves dynamically adjusting parameters such as the pulse width, chirp rate, carrier frequency, and pulse repetition interval within a certain range; this effectively increases the complexity and uncertainty of radar waveforms, thereby countering active deceptive interference signals from multiple dimensions. With the development of active deceptive interference technology, single-parameter agility can no longer meet the requirements, making multi-parameter joint agility one of the main research directions. However, inter-pulse carrier frequency agility can cause azimuth Doppler chirp rate variation, making azimuth compression difficult and compensation computationally intensive, thus hindering imaging. Additionally, pulse repetition interval (PRI) agility leads to non-uniform azimuth sampling, severely deteriorating image quality. To address these issues, this paper proposes a multi-parameter agile SAR imaging scheme based on traditional frequency domain imaging algorithms. This scheme can handle joint agility of pulse width, chirp rate polarity, carrier frequency, and PRI, with relatively low computational complexity, making it feasible for engineering implementation. By inverting SAR images, the echoes with multi-parameter joint agility are obtained, and active deceptive interference signals are added for processing. The interference-suppressed imaging results verify the effectiveness of the proposed method. Furthermore, simulation results of point targets with multiple parameters under the proposed processing algorithm show that the peak sidelobe ratio (PSLR) and integrated sidelobe ratio (ISLR) are improved by 12 dB and 10 dB, respectively, compared to the traditional fixed waveform scheme. [ABSTRACT FROM AUTHOR]

Emerging millimeter‐wave wireless communication systems require high‐performance radio frequency switches to support advanced functionality such as frequency agility, circuit reconfigurability, and beamforming. Ferroelectric (FE)‐gated AlGaN/GaN high‐electron‐mobility transistors (HEMTs) (FeHEMTs) are developed and demonstrated as a technology option for this important role. AlGaN/GaN HEMT heterostructures grown by metal‐organic chemical vapor deposition are augmented with a FE gate stack comprising atomic layer deposition‐grown HfZrO2. In addition, highly doped regrown source and drain Ohmic contacts are integrated into an improved fabrication process flow. This improved process leads to contact resistances of 0.105 Ω mm and a reduction in switch on‐resistance as compared to prior reports, as well as drain current densities of 1 A mm−1 and measured ft = 54 GHz for gate lengths of 0.1 μm. The improved contact and gate length scaling makes FeHEMTs a promising candidate for mm‐wave switch applications achieving a reported switch figure of merit of fCO = 1.55 THz. [ABSTRACT FROM AUTHOR]

Frequency agility refers to the rapid variation of the carrier frequency of adjacent pulses, which is an effective radar active antijamming method against frequency spot jamming. Variation patterns of traditional pseudo-random frequency hopping methods are susceptible to analysis and decryption, rendering them ineffective against increasingly sophisticated jamming strategies. Although existing reinforcement learning-based methods can adaptively optimize frequency hopping strategies, they are limited in adapting to the diversity and dynamics of jamming strategies, resulting in poor performance in the face of complex unknown jamming strategies. This paper proposes an AK-MADDPG (Adaptive K-th order history-based Multi-Agent Deep Deterministic Policy Gradient) method for designing frequency hopping strategies in frequency agile radar. Signal pulses within a coherent processing interval are treated as agents, learning to optimize their hopping strategies in the case of unknown jamming strategies. Agents dynamically adjust their carrier frequencies to evade jamming and collaborate with others to enhance antijamming efficacy. This approach exploits cooperative relationships among the pulses, providing additional information for optimized frequency hopping strategies. In addition, an adaptive K-th order history method has been introduced into the algorithm to capture long-term dependencies in sequential data. Simulation results demonstrate the superior performance of the proposed method. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

For hybrid direct sequence/frequency hopping (DS/FH) spread spectrum signals, even if the relative motion speed between the transmitter and receiver remains constant, the Doppler frequency will vary due to the continuous hopping of the carrier frequency. Under high dynamic conditions, the first-order and second-order change rates of the Doppler frequency attached to the received signal further increase the Doppler frequency agility, making it difficult for the carrier tracking loop to maintain steady-state tracking. To address these issues, a high dynamic velocity locked loop (HD-VLL) is proposed in this paper. Specifically, the accumulated phase tracking error caused by acceleration and jerk is first analyzed. Subsequently, to compensate for this phase tracking error with the system clock, the proposed loop adds an acceleration compensation module and a jerk compensation module. However, this results in the output of the high dynamic loop filter being updated with the system clock, which contradicts the multiplexing design of a traditional loop filter for parallel signal processing, making the hardware implementation of an HD-VLL impractical. Therefore, this contradiction leads us to design an HD-VLL-based multi-carrier NCO (HD-VLL-NCO). The HD-VLL and HD-VLL-NCO are simulated, revealing the HD-VLL's superior dynamic adaptability and steady-state tracking, while the HD-VLL-NCO achieves comparable accuracy with the appropriate truncation bit width. [ABSTRACT FROM AUTHOR]

Interrupted-sampling repeater jamming (ISRJ) is a type of intra-pulse coherent jamming that poses a significant threat to radar detection and tracking of targets. This paper proposes an ISRJ suppression method based on frequency agile waveform and sparse recovery, starting from the temporal discontinuity and modulation characteristics of ISRJ. This method is particularly suitable for scenarios with high jamming duty ratio (JDR) and high jammer sampling duty ratio (SDR). By dividing the transmitted waveform into sub-pulses with different carrier frequencies and applying a two-round block sparse algorithm, the method accurately recovers three parameters of ISRJ, achieving effective jamming identification, reconstruction, and cancellation. Additionally, a target detection technique based on robust sparse recovery is proposed, significantly improving the stability and accuracy of target detection. Comparative experimental results conducted in three scenarios confirm the effectiveness and superiority of this method under high JDR and SDR conditions. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Optimizing jamming strategies is crucial for enhancing the performance of cognitive jamming systems in dynamic electromagnetic environments. The emergence of frequency-agile radars, capable of changing the carrier frequency within or between pulses, poses significant challenges for the jammer to make intelligent decisions and adapt to the dynamic environment. This paper focuses on researching intelligent jamming decision-making algorithms for Intra-Pulse Frequency Agile Radar using deep reinforcement learning. Intra-Pulse Frequency Agile Radar achieves frequency agility at the sub-pulse level, creating a significant frequency agility space. This presents challenges for traditional jamming decision-making methods to rapidly learn its changing patterns through interactions. By employing Gated Recurrent Units (GRU) to capture long-term dependencies in sequence data, together with the attention mechanism, this paper proposes a GA-Dueling DQN (GRU-Attention-based Dueling Deep Q Network) method for jamming frequency selection. Simulation results indicate that the proposed method outperforms traditional Q-learning, DQN, and Dueling DQN methods in terms of jamming effectiveness. It exhibits the fastest convergence speed and reduced reliance on prior knowledge, highlighting its significant advantages in jamming the subpulse-level frequency-agile radar. [ABSTRACT FROM AUTHOR]

This study is the first to examine the associations between the occurrence, frequency, and adaptivity of children's subtraction by addition strategy use (SBA; e.g., 712 − 346 = ?; 346 + 54 = 400, 400 + 300 = 700, 700 + 12 = 712, and 54 + 300 + 12 = 366) and their underlying conceptual knowledge. Specifically, we focused on two rarely studied components of conceptual knowledge: children's knowledge of the addition/subtraction complement principle (i.e., if a + b = c, then c − b = a and c − a = b) and their knowledge of different conceptual subtraction models (i.e., understanding that subtraction can be conceived not only as "taking away" but also as "determining the difference"). SBA occurrence was examined using a variability on demand task, in which children had to use multiple strategies to solve a subtraction. SBA frequency and strategy adaptivity were investigated with a task in which children could freely choose between SBA and direct subtraction (e.g., 712 − 346 = ?; 712 − 300 = 412, 412 − 40 = 372, and 372 − 6 = 366) to solve 15 subtractions. We measured both children's knowledge of the addition/subtraction complement principle, and whether they understood subtraction also as "determining the difference." SBA occurrence and frequency were not related to conceptual knowledge. However, strategy adaptivity was related to children's knowledge of the addition/subtraction complement principle. Our findings highlight the importance of attention to conceptual knowledge when teaching multi-digit subtraction and expand the literature about the relation between procedural and conceptual knowledge. [ABSTRACT FROM AUTHOR]

Frequency agile technology provides full play to the advantage of radars for adopting electronic countermeasures actively, which can effectively enhance the antinoise suppression jamming performance of radars. However, with the increasing complexity of the interference environment, developing an online decision-making method for frequency-agile radar with dynamic adaptability and without foresight of the nature of the environment is a demanding task. According to the features of the jamming strategy, suppression jamming scenarios are divided into three categories, and an online decision-making method for frequency-agile radar based on Multi-Armed Bandit (MAB) is developed to maximize the radar’s detection probability. This approach is an online learning algorithm that does not need to interfere with the foresight of the environment and offline training process and realizes remarkable learning performance from noninterference scenarios to adaptive interference scenarios. The simulation results and theoretical analysis demonstrate that compared with the classical algorithm and stochastic agile strategy, the proposed method has stronger flexibility and can effectively improve the antijamming and target detection performances of the frequency-agile radar for various jamming scenarios.

Dielectric resonators (DRs) are widely investigated and applied due to the high Q‐factor feature. Their frequency agility is desperately needed in modern communication systems. In this letter, we propose a novel tuning method for DRs using top‐loaded rotatable anisotropic metasurface, instead of the traditional mechanical tuning structures or electrical switches. The effective permittivity of the anisotropic metasurface varies with the E‐field direction of the incident wave. We can tune the resonate frequency by rotating the metasurface placed on the top of the DR. To demonstrate the feasibility of this method, a tunable DR with the anisotropic metasurface printed on a thin substrate is designed, fabricated, and measured. With a compact profile, the prototype provides a wide tuning range of 8.4% from 4.80 to 5.22 GHz and a Q‐factor higher than 1098. The good tuning performance makes the proposed method highly potential for tunable filters and frequency‐reconfigurable antennas. [ABSTRACT FROM AUTHOR]

Interrupted sampling repeater jamming can produce numerous active false targets with high fidelity, which is a significant challenge for coherent pulse radar. This poses a threat to the effectiveness of anti‐jamming technology, such as time‐frequency analysis and frequency agility for conventional constant pulse repetition interval (PRI) radar, which will render the radar inoperable to detect and track the actual target. A random PRI and intra‐pulse frequency agile radar waveform with low interception properties is proposed, which can effectively restrict the acquisition of radar waveform parameters by the jammer, destroy the coherence of jamming signals, and capture the range‐dimensional centroid feature of the echo. Accordingly, a jamming identification method based on the scale constrained Gaussian mixture model and an entity radar target energe recovery algorithm based on the neighbourhood weighted maximum entropy are proposed for target detection. Theoretical analysis and simulation experiments demonstrate the effectiveness of the proposal. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the rapid growth of wireless communication systems, there is a rising demand for multi-input multi-output (MIMO) antenna systems capable of adapting to various frequency bands and operating conditions. This paper presents an integrated design for MIMO antennas based on a varactor diode as a promising component for achieving frequency agility in the proposed system. A dual-polarized system is achieved by employing a combination of two antennas. One antenna is situated on the exterior surface of the side-edge frame, while the other is positioned on the substrate surface. The spatial configuration enables the creation of orthogonal polarization orientations, specifically vertical and horizontal polarizations. In each element, varactor diodes are positioned to provide reactive loading. By incorporating varactor diodes with a variable bias voltage (0.5-10 V) into the antenna design, the resonant frequency can be dynamically adjusted, allowing the antenna to operate across a wide range of frequencies (4.3 to 6.5 GHz) with more than 18 dB of mutual coupling in the working band. The presented reconfigurable antennas are printed on compact dimensions of 15 × 25 × 0:8mm³ using a Rogers RT5880 material with a relative dielectric constant 2.2. Because of its exible frequency range, extensive tuning range, small size, and planar structure, it is well-suited for various current and future wireless communication applications, including cognitive radio, software-defined radio, and next-generation wireless networks. [ABSTRACT FROM AUTHOR]

Frequency agility refers to the rapid variation of the carrier frequency of adjacent pulses, which is an effective radar active antijamming method against frequency spot jamming. Variation patterns of traditional pseudo-random frequency hopping methods are susceptible to analysis and decryption, rendering them ineffective against increasingly sophisticated jamming strategies. Although existing reinforcement learning-based methods can adaptively optimize frequency hopping strategies, they are limited in adapting to the diversity and dynamics of jamming strategies, resulting in poor performance in the face of complex unknown jamming strategies. This paper proposes an AK-MADDPG (Adaptive K-th order history-based Multi-Agent Deep Deterministic Policy Gradient) method for designing frequency hopping strategies in frequency agile radar. Signal pulses within a coherent processing interval are treated as agents, learning to optimize their hopping strategies in the case of unknown jamming strategies. Agents dynamically adjust their carrier frequencies to evade jamming and collaborate with others to enhance antijamming efficacy. This approach exploits cooperative relationships among the pulses, providing additional information for optimized frequency hopping strategies. In addition, an adaptive K-th order history method has been introduced into the algorithm to capture long-term dependencies in sequential data. Simulation results demonstrate the superior performance of the proposed method.

This study investigated the teachers 'challenges in implementing expanded face-to-face classes and school standards and procedures in the Division of Nueva Ecija. This utilized descriptive research in describing the socio-demographic profile of the respondents as well as their perceived student attitudes towards learning Araling Panlipunan, challenges on the implementation of face-to-faces and perception of school standards and procedures. A total of 48 teachers were selected purposively as respondents to the study. They were teachers in Carranglan District handling Araling Panlipunan subjects in the Schools Division of Nueva Ecija. The survey questionnaire was administered. Data gathered were analyzed using frequency, mean and percentage. Meanwhile, Chi-square was used to establish relationships among variables. The study shows that regular monitoring of students' performance through their assessments and performance tasks ranks first as issues and challenges that Araling Panlipunan teachers experienced during the pandemic, and resiliency and flexibility were the traits that the respondents described. With the study's findings, an intervention plan is proposed to help Araling Panlipunan teachers overcome the challenges in teaching and attain their full potential. This will become the basis for educators and administrators to help them enhance their competencies in the field. [ABSTRACT FROM AUTHOR]

Path loss models estimate the average path loss a signal experiences at a particular distance from a transmitter. However, each type of existing path loss propagation model is designed to predict path loss in a particular environment that may be inaccurate in other different; hence selecting the best path loss model and optimizing it will minimize that inaccuracy. This work presents a comparative analysis of five empirical path loss models, COST- 231, ECC-33, Hata, SUI, and Ericsson model, with respect to the measured data from the 14 selected sites in Hawassa city, Ethiopia at 1800 MHz frequency bands. A drive test methodology was adopted for data collection and Nemo Handy and Nemo Outdoor were used as measuring tools for the test. Error measuring tools such as root mean square error, mean absolute error, standard deviation, and mean absolute percentage error were used to select the terrain type of each site and the path loss model that best fits that site. The results show that not only Hawassa city consists of urban and sub-urban terrains but also ECC-33 and Hata are better estimators for Hawassa urban and sub-urban areas with RMSE of 4.18 and 7.86 respectively. The model tuning using the least square method reduced the RMSE of ECC-33 and Hata to 2.46 and 5.18 respectively. The reduction in RMSE shows that the tuned versions are close to the environment. Hence, using the tuned versions of the selected models will result in good cellular network design and enhance the service quality. [ABSTRACT FROM AUTHOR]

A reconfigurable antenna with frequency agility and pattern-switching ability is presented in this paper. The proposed design comprises a planar and compact frequency reconfigurable monopole antenna and an active frequency selective surface (AFSS) with reconfigurable transmission and reflection properties in dual bands. The AFSS screen is divided into four sections and each section is composed of four FSS elements with only one PIN diode in each unit cell. The monopole antenna, which is situated at the center of the box-shaped AFSS to illuminate , can reconfigure its resonating frequency between 2.5 and 3.6 GHz with the help of only one PIN diode. With the help of this transformation ability of AFSS behavior electronically, the pattern can be steered across the entire X–Z plane in eight steps at two different operating frequencies independently. This antenna can be very useful in various wireless applications such as drones, small base stations, etc. [ABSTRACT FROM AUTHOR]

Copyright of Computer Measurement & Control is the property of Magazine Agency of Computer Measurement & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This research investigates a frequency-switchable, multi-mode operation antenna contingent on ground structure slots and suitable for 4G, 5G/sub 6 GHz and other modern systems. In earlier research work, researchers used the approach of putting slots on the radiator or ground to create frequency-reconfigurable antenna designs. This antenna acquired benefits, in particular compactness, wide-bandwidth, and a consistent far-field pattern due to the amalgamation of slots on the patch and defects in the ground. The proposed antenna used various slots on the substrate's top and a π shaped DGS on the bottom layer. The pin-diodes embedded in the defects of the ground ensured the frequency agility and permitted the design to tune to various resonances. Data observed from experiment is used to demonstrate the antenna's performance. The modelling approach and analytical values manifest that this antenna could indeed reconfiguration between different operating bands, encompassing the frequency range from 2.2 to 8.9 GHz, by switching between four operating modes. The antenna can operate in a wide range of commercial bands, including WLAN, Bluetooth (2.4 to 2.5 GHz), 4G-LTE (2.3 to 2.7 GHz), S-band (2 to 4 GHz), Radio-Navigation (2.7 to 2.9 GHz), and 5G-sub6GHz (3.2 to 4.7 GHz). The antenna presented has narrowband to wideband characteristics, an omnidirectional radiation, fair gain (1.6 dB to 5.9), and an efficiency from 87 to 93%. [ABSTRACT FROM AUTHOR]

In this article, a polarization reconfigurable concentric circle microstrip antenna with simultaneous frequency agility has presented. The frequency agility and polarization reconfigurability have been controlled by open stub cascaded branch-line coupler (OSCBLC) feed network configuration. The −10 dB tunable impedance bandwidth of 2.0 GHz to 3.0 GHz (40%) is achieved by varying the capacitance of four varactor diodes from 4.15pF (0 V) to 0.84pF (7.5 V). These varactor diodes are fixed between the circular patch and ring. The polarization is reconfigured by directing the input RF through a single pole 4 throw (SP4 T) and routed to a single pole double throw (SPDT) switch in the feed network configuration. The right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP) are realized in the antenna by exciting the feed ports with a time phase difference of ± 90°. Similarly, the vertical linear polarization (V-LP) and horizontal linear polarization (H-LP) are attained in the antenna by excited any one port through the feed network. The impedance bandwidth (1.5 GHz to 3.5 GHz) of OSCBLC feed network configuration is well-matched with the agile wide impedance bandwidth of the designed antenna. The proposed designed antenna shows good agreement between simulated and measurement results for polarization reconfigurability and frequency agility. [ABSTRACT FROM AUTHOR]

The low power wide area networks (LPWANs) based on the LoRaWAN standard are suitable for Internet of Things (IoT) applications that involve a large number of low-power devices distributed over large areas. The LoRaWAN standard imposes some limitations on end-device configuration, such as the medium access strategies to be adopted, which depend on the region in which the network operates. In particular, in Europe, according to the ETSI regulations, a LoRaWAN end-device can use either a pure ALOHA medium access control (MAC) protocol or a polite medium access technique based on Listen Before Talk (LBT) Adaptive Frequency Agility (AFA). The aim of this work is to investigate the combined use of the two MAC protocols in the same LoRaWAN network. In particular, the work presents a simulative assessment of a LoRaWAN network that combines the use of Pure ALOHA and LBT AFA in realistic scenarios, under different workloads, when they work in compliance with the ETSI regulations. The work provides quantitative information that can help the network designer choose which protocol is more suitable for achieving the desired performance. [ABSTRACT FROM AUTHOR]

In this paper, a frequency reconfigurable multiband multiple-input-multiple-output (MIMO) antenna is developed for 5G communication systems. The presented MIMO antenna element consists of a 50 Ω microstrip line, a rectangular monopole divided into two patches, and a partial ground plane. A split-ring resonator (SRR) is introduced into the upper patch to cover multiple 5G application bands, and an RF PIN diode is embedded between the upper and lower patches to enable the frequency diversity feature. In order to design a MIMO antenna with improved inter-element isolation, four antenna elements are orthogonally located with ground planes connected to each other. The antenna design covers the n41/n46/n48/n79 5G application bands. The prototype MIMO antenna is developed on the FR-4 substrate, and the measured results match with the simulated outcomes. The overall footprint of the prototype antenna is 70 × 70 × 1.6 mm3. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of Nanjing University of Aeronautics & Astronautics is the property of Editorial Department of Journal of Nanjing University of Aeronautics & Astronautics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents the prototype demonstration where an integrated transmitter circuit drives a mobile handset terminal antenna in order to provide frequency tunability and multiple input multiple output (MIMO) operation across the 0.5–4.5 GHz frequency range. The transmitter implementation incorporates on-chip weighted signal generation, i.e. amplitude and phase scaling to provide sufficient MIMO performance in the low band (700–960 MHz) and in the high band (1.5–4.5 GHz). In the transmitter, two antenna elements are used for MIMO operation in the low band and another two in the high band. The transmitter integrated circuit (IC) is fabricated in a 28 nm bulk CMOS technology with an active on-chip area of 0.2 mm $^2$. A custom antenna measurement procedure is proposed here in order to support and verify active antenna measurements with transmitter IC. A measurement procedure for the transmitter system comprising the transmitter IC and four antenna clusters is developed and discussed in comparison with traditional passive antenna measurements. The measurement results demonstrate that the transmitter IC driving the antenna clusters provides total antenna efficiency of $-6.5$ dB to $-1.5$ dB, and envelope correlation coefficient below 0.4 across the designated frequency bands. The results indicate that the implemented transmitter IC successfully tunes frequency response of the antenna clusters, and enhances the MIMO operation of such mobile antennas. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The article discusses a research study in which researchers demonstrate experimentally that reflectionless scattering modes (RSMs) can be functionalized to perform reflectionless programmable signal routing. Topics discussed include versatile programmability both in terms of operating frequencies and routing functionality, how damping rates of scattering singularities broadens under strong absorption and reflectionless excitations of arbitrarily complex linear scattering systems.

In this study, a compact reconfigurable dielectric resonator antenna (DRA) array is proposed to operate in the band IEEE 802.11 WLAN. The main goal of this design is to propose an array feeding topology to avoid radiated beam squinting due to frequency alteration and acquire some gain enhancement with miniaturized array size. For that, the parallel–series geometry is used to layout a microstrip feeder with four output ports on the front plane. Each output port coupled with a rectangular slot (RS) at the bottom plane, and a rectangular dielectric resonator (RDR) mounted above the RS. The frequency reconfigurability is attained by employing PIN diodes that are integrated with the four output ports to operate as switches. Moreover, an impedance equivalent circuit model of the proposed array is postulated for studying the resonance behavior to ensure the validity of the proposed design prior to simulation and fabrication. The prototype 64 × 18 mm2 achieves frequency agility in the range of 5.8 to 5.17 GHz. Also, the realized gain ranges from 12.2 to 10. 5 dBi. The array specifications make it a decent potential candidate to be used for WLAN wireless systems. [ABSTRACT FROM AUTHOR]

Frequency agility has been extensively used in military and commercial-communication applications due to its inherent transmission security features. This paper proposes algorithms and system-level design to intercept as well as monitor of frequency-agile signal in real-time by receiver. Receiver is assumed to have no prior knowledge of spread spectrum hopping sequence used by the frequency agile transmitter. Novelty of design is capability of simultaneously & reliably intercepting multiple frequency-agile transmissions with signal-to-noise ratio (SNR) requirement of 15dB, whereas other interceptor needs minimum SNR of 30 dB Pan et al. (IEEE Transactions on Signal Processing, 23(5):1113–1122, 1) and monitoring of intercepted transmitter upto message bits/audio level in real time. Unlike the conventional approach, this technique is independent of number of transmitters and is designed to achieve higher throughput. Additionally, it mitigates the storage requirement or memory for recording the entire spread bandwidth while intercepting and monitoring the frequency-agile signal off-the-shelf. The proposed system has been designed to process frequency-agile signal with instantaneous frequency-band ranging from 13 MHz to 31 MHz with the hop-rate of 100 hops/second. Hardware prototype of this system has been implemented on a Virtex-7 FPGA platform with 22% resource occupancy and 1.667 W of total power consumption. Subsequently, we have tested this FPGA prototype using the real-world signals with the aid of 16-bit on-board ADC, digital oscilloscope, spectrum analyzer and signal generator that produce signals of 10 hopping frequencies (21, 30, 15, 25, 31, 18, 19, 17, 29 & 13 MHz) with a hopping time of 10 msec. Finally, the performance analysis of this system has been carried out to observe the variations of the parameters like processing latency, tracker resolution and percentage of correct hop-estimation with respect to the BER. [ABSTRACT FROM AUTHOR]

This paper presents the design of a co-located sub-1 GHz long-term evolution (LTE) and sub-6 GHz 5G band antennas implemented in multiple-input-multiple-output (MIMO) configuration. In addition, it demonstrates the integration of the millimetrewave (mm-wave) 5G band antenna arrays. Using the characteristic mode analysis (CMA), these antenna elements have been designed for the user equipment's (UEs) where they share the common ground plane of 150 mm × 70 mm size. Using the varactor and PIN diodes, band switching and frequency agility of the MIMO elements have been achieved to cover the 0.69–1.19 GHz, 2.29–3.29 GHz, 3.93–4.6 GHz, and 5.52–6.45 GHz bands with the S11 = −6.0 dB criterion. At each side of the structure, two 1 × 8 elements patch array antennas with the individual element fractional bandwidth (FBW) of 20.56% to cover 24.0–29.5 GHz band with the beam scanning angle of ±30° have been integrated. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Signal Processing is the property of Journal of Signal Processing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We propose and demonstrate a widely tunable microwave photonic filter with controlled frequency agility, bandwidth reconfigurability and flexible switching functions. It is based on the self-interference microring aided by an asymmetric Mach–Zehnder interferometer, breaking the fundamental microring footprint limit and achieving a doubled free spectral range (123.2 GHz) with a strong out-of-band rejection. Simulation results show that a bandpass microwave photonic filter can be tuned across a 60 GHz frequency range with a varied 3-dB bandwidth from 2.13 GHz to 40.7 GHz in a cascaded dual-ring topology. Its RF out-of-band rejection ratio is improved by more than 60 dB in the high frequency region due to a perfect residual phase cancellation. A dual-band notch microwave photonic filter with an extinction ratio of about 50 dB and a frequency tunable range of about 27.7 GHz is also demonstrated, showing its broadly applicability. Our method highlights its suitability to improve chip-scale wideband and high-performance RF receiver systems. • Our design breaks the fundamental microring footprint limit and achieves a doubled FSR using dissipative tuning. • A bandpass MPF can be tuned across a 60 GHz frequency range with a varied 3-dB bandwidth from 2.13 GHz to 40.7 GHz. • Our design enables an RF out-of-band rejection ratio of more than 60 dB due to a perfect residual phase cancellation. [ABSTRACT FROM AUTHOR]

Abstract Frequency agile radar (FAR) systems have been demonstrated to have outstanding performance in electronic counter‐countermeasures (ECCM). With increased bandwidth in which FAR can switch carrier frequency, the phase errorswill appear at the corresponding frequency point, resulting in the decrease of coherence of the system. To accomplish phase error correction and range and velocity information extraction of the target simultaneously, a joint phase error estimation and sparse scene restoration algorithm based on sparse recovery (JPSA‐SR) is proposed here. To further reduce the computational complexity of the algorithm, a joint phase error estimation and sparse scene restoration algorithm based on alternating direction method of multipliers (JPSA‐ADMM) is also proposed. Numerical examples show the effectiveness of the proposed algorithms.

In the proposed research paper, a novel compact, ultra-wideband electronically switchable dual-band omnidirectional to directional radiation pattern microstrip planar printed rectangular monopole antenna (PRMA) has been presented. The proposed antenna system has an optimum size of 0.26 λ0 × 0.28 λ0. A combination of radiators, reflectors, and two symmetrical grounds does place on the same layer of the rectangular microstrip PRMA. The frequency agility and the radiation pattern from omnidirectional to directional are achieved using two SMD PIN diodes (SMP1340-04LF). The directional radiation patterns with 180° phase shifts are achieved at the C-band frequency spectrum. The parametric study of the proposed antenna system was performed for different design parameters, and the antenna characteristics were analyzed. An antenna prototype is fabricated using the printed circuit board etching method by using RMI UV laser etching and cutting tools. The measurements of the proposed antenna are conducted in an anechoic chamber to validate the simulations. There are three states of operations due to two SMD PIN diodes being used in switching circuits. In state-I, the proposed antenna radiates at 6.185 GHz (5.275–6.6 75 GHz) in the Ф = 270° direction with a gain of 2.1 dBi, whereas in state-II, it radiates at 5.715 GHz (5.05–6.8 GHz) in the Ф = 90° direction with a gain of 2.1 dBi. In state-III, the antenna exhibits the X-band frequency with center frequency at 9.93 GHz (8.845–10.49 GHz), and the omnidirectional pattern offers a gain of 4.1 dBi. The features of the proposed antenna are suitable for high-speed wireless sensor network communication in industries such as chemical reactors in oil and gas and pharmaceuticals. It is also well suited for IoT and 5G-sub-6-GHz applications. [ABSTRACT FROM AUTHOR]

Smart home is a building, network, communication, automation, set management, and service, as one of the efficient, comfortable, safe, and environmental protection of the living environment, and can provide personalized living space according to the needs of different users. Due to the advantages of wireless sensor network (WSN), such as strong expansion ability, strong communication ability, and strong self-organization ability, the smart home system based on WSN has become the main development direction in the field of smart home. This paper analyzes the different functions and features of wireless sensor network routing protocol and use scope, aiming at the application layer, using the MQ queue enhance server concurrent processing capacity and system scalability and design based on application layer gateway and terminal node "data matching list," which are introduced in the design of smart home system based on geographic information location energy-efficient routing protocols. The solution of routing void problem is improved by using information feedback mechanism and alternate nodes. Simulation results show that this method can improve the energy saving of energy-efficient routing protocol. Finally, the intelligent home system experiment platform was built to verify the overall function of the system, and the communication function of the WiFi network and ZigBee network was tested. Based on the analysis of the interference between ZigBee and WiFi network, frequency agility algorithm is used to solve the problem of the same frequency interference, so as to ensure the performance of the system to meet the needs of the smart home system. [ABSTRACT FROM AUTHOR]

A multiple-frequency continuous-wave (MFCW) agile radar system has the ability to cope with various physiological conditions of a human subject. Following the mathematic model, a favorable carrier frequency for detection is pursued by analyzing the amplitude and composition of the baseband signal. In Experiment-1, a CMOS dual-band transceiver prototype emulate searching a subject from a distance. The frequencies of the dual-band system are 4.26–4.95 GHz and 17.06–19.79 GHz. During the experiment, the respiratory signal could be detected up to 12 m, and the heartbeat signal up to 6 m. Even with a wooden or a brick barrier in the path, the vital-sign detection remained satisfactory. Later, a concurrent MFCW detection is performed in Experiment-2 for more precise analyses. From the concurrent results, the breathing status can be inferred, and by cross-correlating the results after the ensemble empirical mode decomposition (EEMD) and principal component analysis (PCA), the nonlinear effects of respiratory harmonics or intermodulation tones are reduced, resulting in an accurate heart rate extraction. The receiver front-end and the signal source are manufactured using a 180-nm CMOS process, both packaged on an RO4003C printed-circuit board (PCB). [ABSTRACT FROM AUTHOR]

The design of an agile 5° irregular ring metamaterial for a 24-cavity relativistic magnetron with diffraction output (MDO) using single-stepped cavities for frequency switching is presented. By inserting six pieces of 5° irregular ring metamaterials in place of the traditional 5° vanes of a slow wave structure, the operating frequency can be tuned. When U = 400 kV high voltage is applied, with an applied magnetic field B = 0.36 T, the operating mode can be switched from the TE41 mode with a frequency of 2.585 GHz to the TE31 mode with a frequency of 2.282 GHz. The 24-cavity anode block is an electromagnetic medium which can support the operating mode working under its cutoff frequency, and the insertion of the irregular ring metamaterials alters its dispersion relation. The results suggest a new technique to achieve frequency agility by changing the dispersion relation of the electromagnetic system using a metamaterial unit cell. This work seeks to design a compact high power microwave source for a narrowband directed microwave wave beam that is suitable for frequency agility. [ABSTRACT FROM AUTHOR]

In this paper, the initial condition independence property of Grünwald-Letnikov fractional difference is revealed for the first time. For example, the solution x(k) of equation Ga..., cannot be calculated with initial condition x(a). First, the initial condition independence property is carefully investigated in both time domain and frequency domain. Afterwards, some possible schemes are formulated to make the considered system connect to initial condition. Armed with this information, the concerned property is examined on three modified Grünwald-Letnikov definitions. Finally, results from illustrative examples demonstrate that the developed schemes are sharp. [ABSTRACT FROM AUTHOR]

This article aims to inspect the pulsating hydromagnetic slip flow of Casson fluid in a vertical porous channel with heat and mass transfer. The fluid is injected into the channel from the left wall and removed at the opposite wall with the same velocity. The impact of non-Darcy, Soret, and Dufour effects are taken under consideration. The governing partial differential equations (PDEs) are converted to ordinary differential equations (ODEs) using perturbation method and solved by utilizing 4th-order Runge-Kutta (R-K) technique together with shooting method. The impact of dissimilar parameters on flow, heat and mass transfer characteristics are displayed and discussed. [ABSTRACT FROM AUTHOR]

Olive harvesting machine by shaking was developed and fabricated using local materials with required specifications. The developed elements were frame and hitch, gear assembly, input and transmission shafts, vibrating unit, connecting rod, limb clamp, and transmission system. This research work aimed to evaluate the developed olive harvester capable to perform harvesting operation in the proper time using the tractor as the available economic source of power. Measurements covered the properties of olive fruit, stem, and limb for five olive varieties: Agizi, Manzanillo, Picholine, Kalamata and Arbiquen. The developed harvester was tested at three levels of frequency; 3.3, 6.7, and 10 Hz, four levels of stroke; 40, 80, 120, and 160 mm, and three levels of shaking time 60, 120 and 180 s. Results indicated that the effective range to attach the clamp on the olive limb were 30 to 40% of limb length. The average value of the maximum bending stress affecting the limb and limb deflection were 16.5 MPa and 196.6 mm respectively. In addition, results have provided the suitability of the developed shaker to harvest olive fruit. The suitability of the developed machine was judged through the fruit removal percentage. The values of performance parameters of olive harvester were 10 Hz optimum shaking frequency, 120 mm of stroke, and 120 s of shaking time. [ABSTRACT FROM AUTHOR]

Sparse frequency agile linear frequency modulation-orthogonal frequency division multiplexing (LFM-OFDM) radar can improve anti-interference ability as well as reduce the sampling rate of the radar system. However, the frequency agility makes it difficult to realize coherent processing by using the fast Fourier transform. To overcome this problem, a signal processing scheme for the sparse frequency agile LFM-OFDM radar is proposed to obtain the high range and Doppler resolution in this study. The subcarriers are synthesised to an LFM signal in the time domain at first. Then, within the framework of the compressed sensing theory, an improved orthogonal matching pursuit algorithm is proposed to obtain the high-resolution range-velocity profile while reducing the computation complexity. Finally, several numerical simulations are provided to verify the effectiveness of the proposed method for moving targets. [ABSTRACT FROM AUTHOR]

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Laser frequency comb generators on photonic chips open up the exciting prospect of integrated dual-comb microspectrometers. Amongst all nanophotonic platforms, the technology of low-loss thin-film lithium-niobate-on-insulator shows distinguishing features, such as the possibility to combine various optoelectronic and nonlinear optical functionalities that harness second- and third-order nonlinearities, and thus promises the fabrication of a fully on-chip instrument. Here, a critical step towards such achievement is demonstrated with an electro-optic microring-based dual-comb interferometer. Spectra centered at 191.5 THz and spanning 1.6 THz (53 cm−1) at a resolution of 10 GHz (0.33 cm−1) are obtained in a single measurement without requiring frequency scanning or moving parts. The frequency agility of the system enables spectrally-tailored multiplexed sensing, which allows for interrogation of non-adjacent spectral regions, here separated by 6.6 THz (220 cm−1), without compromising the signal-to-noise ratio. Our studies show that electro-optic-based nanophotonic technology holds much promise for new strategies of molecular sensing over broad spectral bandwidths. Thin-film lithium niobate is a promising photonic platform owing to its strong optical nonlinearity and low losses. Here, the utility of this platform is demonstrated as a tunable dual frequency comb spectrometer based on second-order nonlinearities in a proof-of-principle experiment. [ABSTRACT FROM AUTHOR]

Low phase noise lasers based on the combination of III–V semiconductors and silicon photonics are well established in the near-infrared spectral regime. Recent advances in the development of low-loss silicon nitride-based photonic integrated resonators have allowed them to outperform bulk external diode and fiber lasers in both phase noise and frequency agility in the 1550 nm-telecommunication window. Here, we demonstrate for the first time a hybrid integrated laser composed of a gallium nitride-based laser diode and a silicon nitride photonic chip-based microresonator operating at record low wavelengths as low as 410 nm in the near-ultraviolet wavelength region suitable for addressing atomic transitions of atoms and ions used in atomic clocks, quantum computing, or for underwater LiDAR. By self-injection locking of the Fabry–Pérot diode laser to a high-Q (0.4 × 106) photonic integrated microresonator, we reduce the optical phase noise at 461 nm by a factor greater than 100×, limited by the device quality factor and back-reflection. [ABSTRACT FROM AUTHOR]

Frequency agile radar has excellent low intercept and electronic countermeasures performance. In this paper, the research results of anti-main-lobes deceptive jamming of radar seeker are briefly reviewed, and the basic concepts and technical characteristics of frequency agile radar seeker are described. Then, the research results of frequency agile radar seeker at home and abroad are introduced, and the advantages and disadvantages of three frequency agile waveforms and the research progress of each signal processing technology are summarized. Finally, the development of adaptive frequency agility and multi-parameter combined agility radar seeker technology is prospected based on the future battlefield complex electromagnetic environment and seeker development trend.

The broadband agile frequency technology is used in pulse-to-pulse random frequency agility pulse Doppler fuze to make tracking or copying fuze signal with difficulty for jammer. It can resolve target detection problem of radio fuze that is in the environment of deceptive jamming based on DRFM, and can reduce the influence of suppression jamming to fuze. This paper introduces the working principle and the composition of the pulse-to-pulse random frequency agility pulse Doppler fuze, then makes the simulation analysis for anti-jamming performance of the fuze, and analyzes and optimizes the effect of pulse-to-pulse random frequency agility on target detection. The simulation results show that the fuze based on pulse-to-pulse random frequency agility technology has good anti-jamming performance.