Linear Frequency Modulation (LFM) signals are widely used in radar and sonar technology. Many applications are interested in determining the source of an LFM signal. In recent years, the rapid development of machine learning has facilitated research in various fields, including signal recognition. The neural networks can extract the implicit features of the signals, which can help the system to sort and recognize the signal sources quickly and accurately. High performance of neural networks requires large amounts of high-quality labeled data. However, it is difficult and expensive to obtain a large amount of high-quality labeled data. Simultaneously, some features will be lost during data preprocessing, and feature extraction and classification tasks will be inefficient. The self supervised network is proposed in this paper for pre-training the signal waveform and fine-tuning the classification with a small amount of labeled data. The proposed method can extract more signal waveform features, save labeling costs, and has higher precision. This method can provide up to 99.7% recognition accuracy at 20 dB.
This paper presents the design and implementation of a C-Band Frequency Generator developed for Space-borne Synthetic Aperture Radar. This Frequency Generator subsystem generates stable and coherent reference signals for all the sub-systems of C-Band Synthetic Aperture Radar payload. Frequency Generator based on frequency multiplication technique generates various coherent signals namely 500 MHz signal for digital clock, local oscillator (LO) signals of 900 MHz and 4500 MHz needed for receivers and chirp signal of 5400±37.5 MHz. This chirp signal is generated by direct modulation of the full bandwidth baseband signal of DC-37.5 MHz at 4500 MHz and subsequently mixing with 900 MHz signal. Frequency generator unit is realized in a compact two-tier architecture, using novel concept of full chirp modulation, resulting in 6° rmsphase error in the transmit chirp signal along with in-band spurious rejection better than 20 dBc, whereas other coherent frequencies resulting in out of band spurious rejection better than 53 dBc against the specification of 40 dBc.
A metamaterial-inspired antenna is proposed that utilizes an artificial mu-negative (MNG) transmission line (TL) to incorporate the zeroth-order resonance (ZOR) into Wi-Fi 7 operation in the 2.4/5/6 GHz wireless local area network (WLAN) bands. The antenna comprises a meta-structured loop with periodically loaded series interdigital capacitors and a parasitic shorted strip, all formed on the same substrate layer in a coplanar structure. The 2.4 and 6 GHz bands are produced by the parasitic strip and the close-form loop strip, respectively, which are of typical right-handed antennas. The 5 GHz band caused by the ZOR mode, where the permeability is zero, can be adjusted by the series capacitance in the unit cell. The total antenna size is 5.4 mm × 19.6 mm only. In this work, the design applied to notebook computers for the upcoming Wi-Fi 7 operation is also demonstrated. Both numerical and experimental results validate our proof-of-concept design.
A 26 × 25 mm2 arbitrary-shaped antenna is constructed in this article, and it was expanded to 2 x 2 Multiple Input Multiple Output (MIMO) antenna. It has a range of 3.1 to 8.2 GHz. A T-shaped stub is employed in this instance to reduce the mutual coupling between the two ports. The effectiveness of the MIMO aerial is demonstrated using envelope correlation coefficient and radiation pattern. Additionally, it has been shown that simulated and measured results generally agree.
This paper focuses on designing and manufacturing a compact microstrip diplexer, which operates at 3.5 GHz and 5 GHz for 5G and Wi-Fi applications, respectively. Indeed, two bandpass filters are combined to create the proposed diplexer. For making bandpass filters compact, a hairpin resonator is suggested and developed into an E-shaped resonator. To attain the central frequencies, a short microstrip stub loading the E-shaped resonator is proposed. The filters were combined by a coupling junction to form the final diplexer. The proposed diplexer exhibits good isolation that is better than 40 dB in the whole operational frequency band. Additionally, the passband insertion losses are about 1 dB, and the return losses are about 20 dB and 26 dB at the two channels, respectively. Moreover, the final size of the manufactured diplexer is 30 × 25 mm2 (0.6λg x 0.52λg). These results confirm that the suggested diplexer is suitable for the demanded applications.
In this paper, we investigate the propagation behavior of electromagnetic waves through coaxial optical fiber bounded with DB-boundaries. For this purpose, an eigenvalue equation is derived by using suitable DB-boundary conditions to determine the allowed values of propagation constant β for each propagating mode. Moreover, we have analyzed the electric field and power distribution patterns through coaxial optical fiber for different propagating modes and dimensions, respectively. Our results show that small dimensional guide confinement remains maximum close to the lower interface of the guide, whereas, for larger dimensions, it shifts toward the upper interface. Investigations show that high power is confined by H12 mode compared to H11 mode, and, therefore, shows contrary behavior compared to commonly used fibers.
We designed a dielectric resonator antenna (DRA) that carries orbital angular momentum and has dual-band ultra-wideband characteristics based on the advantage of minor rain decay in L-band and C-band of microwave bands. The cavity of the antenna adopts an inner and outer nested spiral structure, and the material of resonant cavity shell is photosensitive resin. The internal medium is distilled water with a dielectric constant of 81, and the outer filling is saline with a concentration of 0.035 g/ml at room temperature for the dielectric constant. At the bottom of the cavity, we applied 2 feeds with phase difference of 90° to produce a circularly polarized beam in the DRA. Adjusting the size of the DRA and the height of the helical step surface to excite the OAM waves in higher order modes. The designed DRA generates resonance in 0.82-1.63 GHz and 3.35-7.27 GHz, and achieves ultra-wideband in both operating bands, furthermore, the antenna can generate OAM waves in l=±1 and l=±3 modes when operating at 1.51 GHz and 5.28 GHz, respectively. The simulation results match the measured results. The results show that the vortex wave generated by our designed antenna also has advantages such as high mode purity. Therefore, it can be effective in near-field communication and also provides a new solution for OAM near-field communication in 6G which is of great importance, and also for satellite communication and downlink signal transmission of communication satellites.
In this paper, a planar wideband antenna array with wide scanning angle in both E- and H-planes is proposed. The dipole antenna is used as an essential element of the array. To enlarge the scanning angle of the array, two layers of frequency selective surface (FSS) superstrates are loaded on the top of the antenna elements. A conducting-patch with shorting pins is loaded under the unit patch to enlarge the bandwidth of the array. Both simulated and measured results have confirmed that the proposed antenna array can scan up to 85° and 70° in the E- and H-planes from 8 GHz to 11 GHz, respectively.
In this paper, a method of designing a SIW (Substrate Integrated Waveguide) bandpass filter with high selectivity is proposed. Four resonant cavities of the proposed filter are arranged in straight line. The microstrip gradient line is directly fed into the cavities. Two U-shaped slots are etched on the top face of each cavity which will result in the resonant modes reduced and the high modes of SIW cavity pushed far away from the dominant resonant mode. Thus the filter will have both the features of compact size and wide stopband. The center frequency of the filter is designed at 5.2 GHz. The measured results are highly matched with the simulated ones.
In order to meet the requirements for the suppression of mirror frequencies in the 5G RF front end, this paper proposes a novel miniaturized image rejection bandpass filter by loading Stepped-Impedance Resonators (SIR). By analyzing the relationship between the impedance ratio of a half-wavelength SIR and its electrical length, we have designed an improved second-order bandpass filter, which reduces the size by 34.3% compared to traditional five-order hairpin filters. In order to further enhance the performance of the filter, the use of a radial stub, as opposed to the traditional rectangular open stub, allows for the generation of a wider band transmission zero, which can be analyzed using lumped equivalent circuits. This integration improves the stopband rejection of the filter. The results show that the passband range is 5.35 GHz-6.64 GHz; the rejection in the stopband range 8.10 GHz-11.98 GHz is over 45 dB; and the size is only 0.385λg×0.295λg.
In this paper, a wide harmonic suppression filtering antenna with high selectivity is designed. The filtering antenna adopts dual-layer structures. By introducing four parasitic patches around the top driven patch, the impedance bandwidth is widened. Moreover, the current directions on the driven patch and the parasitic patches are opposite in some frequency, so that the radiation null is introduced. In addition, a rectangular split ring DGS is etched in the middle of the ground plane, the lower sideband radiation null is introduced. Two sets of dumbbell-shaped defected ground structures are etched on the ground plane of the intermediate layer. The high-order harmonics are suppressed, and another radiation null is introduced. The experimental results show that the antenna operates at 2.46-2.66 GHz; the relative bandwidth is 7.8%; the peak gain is 3.8 dBi; and the S11 is more than -3 dB at 3-13 GHz.
A systematic technique for switching between horizontal and vertical polarizations is introduced. A fan-beam antenna array for base station applications employing a grounded reflector is implemented, and the proposed approach is implemented and validated on it. The antenna array is realized using planar monopole elementary elements against a non-parasitic reflector, which yields a desirable fan-beam pattern. The corresponding 3 dB H-plane beamwidth can be easily adjusted by changing the reflector height. Two versions of the antenna arrays are used to demonstrate suppression of unwanted asymmetrical modes in the current distribution yielding improved cross-polar isolation. The measured H-plane 3-dB beamwidth is approximately 127 degrees at 900 MHz and 124 degrees at 955 MHz. The corresponding side lobe level is almost -11.7 dB and -8.7 dB at 900 MHz, while the back lobe level of -9.3 dB and -11 dB at 955 MHz from measurements. The gain is within the acceptable level in both cases and compared with simulations that possess good agreement. By taking into account the antenna design and manufacturing aspects, such antennas will pave the way to be employed in OFDM reconfigurable antenna applications and Identification Friend or Foe (IFF).
A quad-element reconfigurable radiation pattern Multiple Input Multiple Output (MIMO) antenna is designed for WLAN and 5G applications suitable for indoor wireless communications. Antenna system consists of four radiating elements that operate over triband frequencies 2.4, 3.5 and 5.5 GHz. Moreover, the pattern diversity is obtained by introducing two diagonally crossed slots in the radiator to steer the main beams of the antenna in eight different angular directions using eight PIN diodes. The overall physical dimension of the proposed antenna is about 0.55λ0 × 0.55λ0. In addition, an Acrylonitrile Butadiene Styrene (ABS) enclosure is designed, and the performance of the proposed antenna is evaluated. The measurement results show that the proposed antenna has an impedance bandwidth of 4.18%, 14.13%, and 28.5% at the said frequencies, respectively.