77 GHZ MILLIMETER WAVE ANTENNA ARRAY WITH WILKINSON DIVIDER FEEDING NETWORK

The spatially variant apodization (SVA) algorithm, a classic super-resolution method for synthetic aperture radar (SAR) images, can suppress side lobes while maintain the resolution of the main lobe. To address the problem of residual side lobes or loss of main lobe energy in improved SVA algorithms, the article proposes a new side lobe suppression method combining the bidirectional recurrent neural network (BiRNN) and the SVA algorithm, employing BiRNN to extract the main lobe and side lobe features of radar data to achieve side lobe suppression at any Nyquist sampling rate. The land flight experiment data of the fully polarized microwave scatterometer is used to quantitatively evaluate the side lobe suppression performance and the main lobe energy in order to verify the effectiveness of the BiRNN-SVA method. The experimental results demonstrate that the BiRNN-SVA method can be applied to data at any Nyquist sampling rate and has superior peak side lobe ratio and ISLR compared to the GSVA algorithm and MSVA algorithm. The image processed with the proposed method retains more fine details and edge features. In comparison to the GSVA algorithm and MSVA algorithm, the image contrast and focus have increased by 31.6% and 3.6%, respectively, and by 4.4% and 1.1%.

We discuss the optimization and design of a single-layer, single-patch antenna element for base station array antennas. Such an element should have a minimum of 10% bandwidth and preferably a return loss of 20 dB or more. The antennas used in base stations for mobile communications usually consists of linear arrays of radiating elements in order to achieve the desired pattern: narrow beamwidth in the vertical plane and a broad beam in the horizontal plane. Other aspects of the pattern are also important: constant beam peak angle over the frequency band (i.e. no beam squint), suppression of sidelobes above the main beam and null-fill below the main beam to ensure coverage close to the base station site. For the array to meet these requirements over the frequency bandwidth, it is important to maintain good control over the phase and amplitude distribution to the elements. Furthermore, due to the high power used and the increasing demand for low intermodulation levels, the use of power dividers which provide isolation between the output ports, such as the Wilkinson divider or the 90/spl deg/ hybrid, is very limited. Therefore, any impedance mismatch at the elements will disturb the power distribution of the array and degrade the pattern. The above considerations means that the usual patch antenna designs presented, where a VSWR<2 over the band, are inadequate for use in a base station antenna array. In fact, even if an input VSWR of 1.5 (14 dB return loss) is acceptable for the array, the elements should preferably be matched to a 20 dB return loss to ensure pattern stability.

Sidelobe suppression is of particular importance in the SAR image quality improvement. However, the range and azimuth sidelobes are coupled and non-orthogonal in squinted SAR images, which makes traditional methods ineffective. This letter presents a sidelobe suppression method for squinted SAR complex data based on the SAR convolution model and minimum image sharpness. First, the convolution model of SAR images is revised with the subpixel offset. Then, the sidelobe suppression is achieved by deconvolution pixel by pixel. Innovatively, a convex optimization based on minimum image sharpness is built and solved to estimate the unknown and variant subpixel offset of each target. In addition, a new factor based on integrated side lobe ratio (ISLR) is applied for efficiency improvement. Finally, results on the squinted spaceborne SAR real data verify the effectiveness of the proposed method both in sidelobe suppression and the maintenance of amplitude-phase characteristics.

In a practical space-borne active phased antenna array (APAA), main beam scanning angle (MBSA)-dependent low side lobe level (SLL) and taper loss are the ultimate and most critical performances. At some MBSA, extremely SLL in some local space is needed. The harsh limitation on APAA taper loss further complicates the problem seriously. In this paper, the main beam scanning space (MBSS) was divided into several subspaces. Instead of applying a single set of weights regardless of the MBSA, a separate set of weights is implemented independently in each subspace. This transforms the nearly unsolvable problem into multiple solvable problems. An array-decomposition approach is proposed to further reduce the number of synthesis parameters for each subspace. The entire array is simplified as an assembly of multiple sub-arrays. Each and every sub-array shares the same set of weights. The number of synthesis parameters is therefore reduced to the order of the subarray that the synthesis is much easier to solve without sacrificing too much synthesis performance. The proposed approach has been applied to solve concerned practical problem successfully.

The performance parameters of an acousto-optic tunable filter (AOTF) determine its application range. In order to further expand the application field of the AOTF, a system is built based on a single crystal. In this system, the difference between single filtering and double filtering with a single crystal tellurium dioxide (TeO2), including spectral bandwidth and side lobe, is studied using a broadband light source. The experimental results indicate that single crystal double filtering has the advantages of a narrow spectral bandwidth and side lobe suppression. In addition, the diffraction efficiency of single crystal double filtering is measured experimentally.

To overcome the competition between the side lobe suppression and the main lobe spread in radar imaging, we introduce a super-resolution imaging algorithm based on the iterative processes of the reshaped window function. The side lobes of the target imaging are sensitively dependent on the structures of reshaped window function, and the main lobes, however, are not changed. One could obtain a super-resolution image by using the iterative process, which minimizes the energy between the radar images constructed from the different reshaped window functions. The experimental results of two cylinders agree with the analysis of electromagnetic theory, which verifies the new algorithm.

Enhancing signal quality, minimizing interference, allowing high-speed data transmission, and beam steering in phased array antennas are pivotal in today's wireless communication systems.In terms of global optimality, low side lobe levels, and fast convergence, conventional optimization methods often fail to deliver.The ease and adaptability of metaheuristic algorithms, such as the Whale Optimization Algorithm (WOA), have rendered them desirable solutions for managing such complex optimization problems.However, traditional WOA may still suffer from premature convergence and failure to exploit the search space fully.This study proposes a Chaos-Enhanced Whale Optimization Algorithm (CWOA) in intelligent beam steering for phased array antennas.A significant enhancement is that the algorithm can now escape local optima more effectively and attain higher global convergence due to the integration of chaos theory into the WOA framework.Chaotic maps such as the logistic and tent maps generate dynamic control parameters that guide the search for a more balanced exploration-exploitation trade-off.To reduce side lobe levels and give accurate main lobe steering, the proposed CWOA is employed to enhance phase excitation of the antenna elements in a uniform linear array (ULA).Beam direction accuracy, side lobe suppression, and convergence speed are three domains where the CWOA performs better in simulations than normal WOA, PSO, and GA.By comparing various approaches, we realize that chaotic integration significantly enhances the performance of WOA in adaptive beamforming and real-time applications.Innovative and self-adaptive beam steering in dynamic environments like 5G, radar, and satellite communications can be built on this research's efficient and resilient optimization framework for next-generation antenna systems.

An unconventional, yet quasi‐modular base station phased array architecture synthesis technique is proposed for multiuser fifth‐generation applications. By keeping uniform amplitudes and linearly progressing phases at the elements of an optimal irregular array, power‐efficient side lobe suppression is achieved for effective inter‐user interference mitigation. The layout irregularity is achieved within a slice of an array, which is repeated rotationally. The sequential rotation technique is applied to obtain modularity and improve the circular polarization characteristics. A modified k‐means clustering algorithm is used to form the optimal subarrays. The simulation results indicate that the proposed quasi‐modular topologies provide a good compromise between the side lobe performance and integrated array design complexity.

A novel multilayer Frequency Selective Surface (FSS) is proposed for the suppression of far side lobes of radiating elements. Based on the affinity of the proposed structure with a Fabry-Perot resonator, a method is developed for its analysis and design. A double layer filter is designed, fabricated, and used in conjunction with several radiating elements that suppressed side lobes in the angular range of 40° - 50° by 15dB.

In this paper, we consider out-of-band radiations caused by high sidelobes in orthogonal frequency division multiplexing (OFDM) system. Suppression of sidelobes in OFDM system allows higher spectral efficiency and less interference with existing legacy systems in OFDM based overlay system. We combine different sidelobe suppression techniques to suppress the sidelobes in OFDM system. The multiple-choice sequence (MCS) is combined with cancellation carriers (CCs) and also MCS is combined with subcarrier weighting (SW) technique. MCS is applied prior to CCs or SW techniques. Simulation results show that combining MCS with CCs and MCS with SW techniques the sidelobes in OFDM system can be significantly reduced, which allow a successful co-existance between OFDM overlay system and an existing legacy system.

In circular tomosyntesis obtained from a sufficient number of radiographs with projection directions forming a single cone, object detail at a distance from the plane of interest is blurred according to the zero order Bessel function. The main lobe of this window function defines slice thickness, while its ringing side lobes are undesirable because they permit further outlying structures to “leak” through. Using the orthogonality of Bessel functions, a sampling scheme consistmg of multiple, concentric projection cones was designed to synthesize by a finite FourierBessel series a slice window with superior side lobe suppression. The window that concentrates the most “energy” within a finite slice, and can be realized by a limited number of sampling cones, is the zero order circular prolate spheroidal function. Its application to tomosynthesis of 3 mm thick slices with a characteristic detail size of 0.5 mm, concentrated 95% of the total series expansion to only 3 concentric circular scans, yielding a theoretical suppression of the first side lobe of − 38 dB, to be compared to − 8 dB achieved with the Bessel function. Experimental implementation of this optimal sampling scheme using 3, 8, and 14 projection views, distributed over cones with opening half‐anges of 1.92, 4.39, and 6.88°, respectively, resulted in a side‐lobe attenuation of at least − 20 dB. This attenuation reduced significantly artifacts arising from out‐of‐plane detail of high spatial frequency (e.g., edges) in tomosynthetic images of clinical interest in dentistry.

Increasing congestion has spurred investigations into more efficient utilization of the radio frequency (RF) spectrum while minimizing the volume and weight of the RF equipment. Considering the similarity of radar and communication in both software and hardware, this paper presents a co-design integrated waveform of radar and communication based on the multiantenna system. In this paper, communication data is first transported by utilizing space-frequency modulation on a fixed transmitting frequency set. By using digital beamforming technology in the subarray level, directional communication with cooperative targets in the main lobe can be achieved. However, modulation in space-frequency domain results in high sidelobes in the autocorrelation function. Thus, to acquire an acceptable radar performance, the mismatched filter (MMF) is proposed to realize information defusion and sidelobe suppression. Aiming at reducing the signal-to-noise ratio loss of the MMF process, the filter response is further modified. Finally, numerical simulations assess the effectiveness of the proposed MMF and the Doppler coherency between pulses for clutter cancellation. Simulation results demonstrate the capability and potential of the proposed co-design signal for radar-communication system.

In the receive focusing in an ultrasound imaging system, we calculate the magnitude of the main and side lobe spectrum of received channel data using a two-dimensional Fourier transform. During the ultrasound receive focusing process, if signals coming from outside the imaging point are not completely removed, side lobe occurs in the image. Because the time signal of the side lobe is difficult to distinguish from the time signal of the imaging point, it is hard to remove it using time domain filter processing. However, if the received channel-time data is transformed by a two-dimensional Fourier transform, the spectrum of the main lobe and side lobe can be separated in the spectral domain. Therefore, the magnitude of the main lobe and side lobe spectra and the distance between the centroid of the two spectra were used to design a time domain side lobe suppression filter weight. We suppress the side lobe by multiplying the ultrasound image by spectral weights. To assess the filter performance, ultrasound RF data from the human organs were synthesized on a computer at the 5 MHz and 64-channel linear array transducer. We compared the conventional focusing image, weights applied image, Hamming apodization image, and the main lobe only image. Computer simulations showed a significant increase in the contrast of the lesion while maintaining resolution.

Adaptive array beamforming achieves high resolution and sidelobe suppression by producing sharp nulls in the adaptive beampattern when using sample matrix inversion (SMI). In the presence of source motion, the adaptive processor often cannot provide sufficient nulling of the interferer, given the number of snapshots available, and this results in a masking of the desired target signal. The null broadening approach, originally developed to improve the robustness of adaptive beamforming for a stationary problem, is extended to the snapshot-deficient problem arising from the nonstationarity of the background interference. Null broadening allows strong interferers to move through resolution cells and increases the number of degrees of freedom, thereby improving the detection of weak stationary signals. Numerical simulations demonstrate the robustness of the null broadening approach.

Lamb waves are considered a promising tool for the monitoring of plate structures. Large areas of plate structures can be monitored using active arrays employing beamforming techniques. Dispersion and multiple propagating modes are issues that need to be addressed when working with Lamb waves. Previous work has mainly focused on standard delay-and-sum (DAS) beamforming while reducing the effects of multiple modes through frequency selectivity and transducer design. This paper presents a minimum variance distortionless response (MVDR) approach for Lamb waves using a uniform rectangular array (URA) and a single transmitter. Theoretically calculated dispersion curves are used to compensate for dispersion. The combination of the MVDR approach and the two-dimensional array improves the suppression of interfering Lamb modes. The proposed approach is evaluated on simulated and experimental data and compared with the standard DAS beamformer. It is shown that the MVDR algorithm performs better in terms of higher resolution and better side lobe and mode suppression capabilities. Known issues of the MVDR approach, such as signal cancellation in highly correlated environments and poor robustness, are addressed using methods that have proven effective for the purpose in other fields of active imaging.