Low Sidelobe Level Research Articles

Ultra-low SLL slotted waveguide antenna array using Chebyshev aperture distribution function for MM-wave tracking radar applications

A non-uniform aperture distribution slotted waveguide antenna is presented. The slotted waveguide antenna array is chosen for its ease for aperture distribution control and the flexibility of gain adjustment. Multiple aperture distribution functions, including uniform, binominal, Chebyshev, and Blackman, have been extensively investigated to achieve the best possible side lobe suppression. These distribution functions have been converted to slot displacement from the center line of the antenna. Number of slots in the proposed array is chosen to be eight to satisfy the required gain for mm-wave radar tracking application. The proposed antenna is simulated and optimized using the full wave simulator package (CSTMWS). Rounded edge slots are adapted instead of the sharp ones, as they are more applicable for the CNC fabrication process. An eight-slot waveguide antenna is fabricated and gold-plated, considering the Chebyshev distribution approach. The proposed design achieves very stable radiation characteristics and performance over the operating bandwidth, which extends from 33.6 GHz up to 35.9 GHz. At 35 GHz, the total realized gain of the overall antenna is found to be 13.4 dBi, with an overall radiation efficiency of 95.21 %. An obvious low SLL of −30 dB is obtained at the frequency of 35 GHz. The low side lobe level parameter is very crucial for radar applications as it enhances the overall target SNR and reduces false target observations. The pre-stated antenna characteristics make it a good candidate for mm-wave radar applications and point-to-point communications (P2P).

An Effective Array Beamforming Scheme Based on Branch-and-Bound Algorithm

In this paper, we propose an effective full array and sparse array adaptive beamforming scheme that can be applied for multiple desired signals based on the branch-and-bound algorithm. Adaptive beamforming for the multiple desired signals is realized by the improved Capon method. At the same time, the sidelobe constraint is added to reduce the sidelobe level. To reduce the pointing errors of multiple desired signals, the array response phase of the desired signal is firstly optimized by using auxilary variables while keeping the response amplitude unchanged. The whole design is formulated as a convex optimization problem solved by the branch-and-bound algorithm. In addition, the beamformer weight vector is penalized with the modified reweighted ℓ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> -norm to achieve sparsity. Theoretical analysis and simulation results show that the proposed algorithm has lower sidelobe level, higher SINR, and less pointing error than the state-of-the-art methods in the case of a single expected signal and multiple desired signals.

LMS and RLS beamforming algorithms based linear antenna array with known mutual coupling

This study explores the application of LMS and RLS algorithms in adaptive beamforming for a linear array of half wavelength dipole (HWD) antennas with known mutual coupling. The research initiates by deriving analytical expressions for the covariance matrix of signal impinging on an HWD antenna array, accounting for mutual coupling effects. Leveraging these expressions, we calculate the weights for both LMS and RLS algorithms, enabling the evaluation of the overall far-field radiation patterns of the HWD antenna array. The results demonstrate that these algorithms effectively steer the main lobe of the radiation pattern towards the desired user while creating nulls in the direction of undesired users. Notably, simulations indicate that the proposed compensation method enhances the performance of beamforming algorithms, particularly when considering mutual coupling effects. Specifically, the LMS algorithm outperforms the RLS algorithm in reducing interference, resulting in lower side lobe levels (SLL) in the radiation pattern.

Directive Millimeter-Wave End-Fire Diplexing Antenna for IoT Applications

Millions of passengers use High-speed trains (HSTs) daily, in the world. The roofs of HSTs can be equipped with a variety of transmitting and receiving antennas to accommodate high-data-rate Internet services with reliable radio access for passengers. The design of commercial antenna systems is a compromise between cost, size, manufacturability, and performance. This paper proposes a new, compact and low-cost two-port millimeter-wave diplexing directive end-fire antenna, which is designed, fabricated and tested. The proposed antenna is made of a tapered slot antenna and a diplexing structure based on transitions in stacked Printed Circuit Boards (PCBs). The ports of the antenna cover the frequency band 25.9-32.4 GHz (6.5 GHz) and 34.6-37.1 GHz (2.5 GHz). In all operating frequency bands, measured isolation between input ports exceeds 24 dB. Furthermore, symmetric directive end-fire radiation patterns are obtained experimentally, with low side lobe level and low front-to-back ratio. All these features make the proposed diplexing antenna suitable for high-speed railway wireless networks.

Effective reduction of sidelobes in pulse compression radars using NLFM signal processing approaches

Pulse compression techniques are widely used in modern radar systems to enhance range resolution and detection capability. As signal design is one of the basic factors of an efficient radar system, the problem of designing a radar signal with good characteristics using pulse compression is addressed in this paper. A linear frequency modulated (LFM) waveform has been widely used for conventional radars. However, it has a higher sidelobe level which makes the detection of weak targets very difficult in presence of strong targets returns and as a result the problem of masking occurs. In order to get suppressed sidelobes of radar matched filter output as well as preserve the main lobe resolution and level to overcome the problem of masking, nonlinear frequency modulated (NLFM) signals are used in modern radars. In this paper, we will introduce two different approaches to design an optimized NLFM signal which is characterized by optimized sidelobe level (SLL). The first is the exponential piecewise linear function (EPWL) which is the modification of piecewise linear (PWL) functions relying on an exponential predistortioning function. The second is the odd-term polynomial approximation (OTPA) in which the generation of NLFM signal depends only on odd-powered terms of the polynomial function. Furthermore, the simulation results of autocorrelation functions (ACF) of the proposed signals show its superiority over the traditional LFM signals and significantly enhancement compared to the recent background work. The Doppler sensitivity of the designed signals has been evaluated, revealing that the first approach offers Doppler tolerance and is suitable for surveillance radar systems, while the second approach with a lower sidelobe level is used in applications such as Synthetic Aperture Radar (SAR). Finally, the ambiguity function of the designed signals has been measured to illustrate the effect of the Doppler effect relative to different velocities.

Cosecant-squared pattern synthesis of leaky-wave antenna using ridge waveguide

Antennas with a cosecant-squared pattern play a significant role in air-surveillance radar systems. In this article, a cosecant-squared pattern leaky-wave antenna (LWA) is synthesized using a ridge waveguide. The LWA consists of periodic shunt slots located at the broad wall of a ridge waveguide. To obtain the desired cosecant-squared pattern, the attenuation and the phase constant must be controlled properly along the antenna length. To this end, the slots offset and the ridge profile are properly tapered along the antenna. This adjustment is performed through an optimization algorithm such as a genetic algorithm (GA) optimization. Through the proposed antenna configuration, a cosecant-squared pattern LWA with a wide range of 10° to 40° together with low ripples (≤2 dB) in the shaped region and a low level of sidelobes (≤−18 dB) is synthesized, fabricated and measured. Apart from the good agreement between the simulation and the measurement results, such a design indicates a size reduction (about 47%) compared with the previous published work.

Non-linear least squares optimization for the design of low side lobe level bidirectional holographic antennas

In this manuscript, an analytical framework aimed at optimizing the performance of double-sided modulated metasurface antennas featuring independent beams is introduced. To synthesize the aperture field distribution, the proposed framework employs the adiabatic Floquet-wave expansion technique as the analysis strategy and the aperture field estimation method as the synthesis technique. For the modulation index, the nonuniform distribution with unknown coefficients is chosen to improve the side lobe level. The ideal values for each of these unknown coefficients are obtained using a non-linear least squares approach. The obtained results demonstrate the efficiency of the proposed methodology for both vortex and pencil beams. To illustrate its feasibility, a double-sided hologram is designed, radiating a pencil beam and a vortex beam on each side.

Quasi-binomial series-fed array for performance improvement of millimeter-wave antenna for 5G MIMO applications

A quad-port MIMO antenna based on a quasi-binomial series-fed array is presented in this paper for n257 and n258 millimeter-wave applications with an investigation of additional loaded patches on performance enhancement of the conventional binomial series-fed array. The single element of the proposed MIMO is a 3 × 3 element planar binomial series-fed array whose width of the radiating elements is tapered to achieve the binomial distribution. From both simulated and tested results, it is observed that a wider bandwidth (S11 < –10 dB of 21.78 %), high peak gain (12.4 dBi), and high radiation efficiency (92 %) with side lobe level (SLL) reduction of more than 9 dB are achieved by additional loaded patches. This design approach does not only offer wider bandwidth, low SLL, and gain increment, but also ensures the excellent diversity performances of the very closely spaced (0.116λ) MIMO antenna, without utilizing any additional decoupling structure. The proposed MIMO antenna system offers impedance bandwidth (S11 < − 10 dB) from 24.6 GHz to 30.59 GHz, isolation > 27 dB, envelope correlation coefficient < 0.0002, diversity gain > 9.99 dB, and mean effective gain between –4 dB and –8 dB. Owing to its performance attributes, the proposed antenna is an excellent choice for 5G millimeter-wave communication devices, including but not limited to enormous IoT, smart cities, and virtual reality.

Thinned planar antenna array synthesis using a hybrid approach combining almost difference sets and weighted total least squares method

This paper introduces a hybrid approach for designing thinned planar antenna arrays with low peak sidelobe levels (PSLLs). The standard almost difference set (ADS) approach allows the analytical determination of the turned-on element positions within the array configuration, but it provides suboptimal performance in PSLL reduction. To address this limitation, a hybrid method is presented by integrating the ADS approach with the weighted total least squares (WTLS) method. Simulation results from various case studies demonstrate the effectiveness of the hybrid ADS-WTLS method in designing thinned planar antenna arrays with low PSLLs. Additionally, the performance of the synthesized designs obtained through the hybrid method is validated using electromagnetic (EM) simulations.

A split-ring resonator full/sparse planar array based on Chebyshev polynomial

A planar split-ring resonator (SRR) antenna full/sparse array, fed by a Chebyshev distribution, is proposed in this paper. Following the Yagi principle, the antenna element consists of SRRs and an I-shaped resonator. The inclusion of the I-shaped resonator enhances coupling, resulting in high gain. Additionally, a 14 × 13 Chebyshev planar antenna array, based on corporate feed, allows for a non-uniform amplitude distribution to suppress side lobes. The proposed Chebyshev planar array exhibits high gain characteristics and low side lobe levels (SLL) in both the E- and H-planes. For sidelobes suppression further, by utilizing a genetic algorithm, a planar sparse array is constructed based on the proposed Chebyshev array. The measured gain of the array at 10.1 GHz is 22.4 dBi, with SLL values of −20.4 dB and −17.5 dB in the E- and H-planes, respectively. These results meet the requirements for wireless communication.

Wide-Angle Scanning Microstrip Patch Antenna Array for mmWave Applications with High Gain

This paper presents a modified rectangular microstrip patch antenna (MRMPA) array conforming to the hemisphere for wide-angle beam scanning. Two different conformal antenna array designs are presented in this work. The first of these designs, a 13-element MRMPA array conformal to the surface of a circular arc, and the second one, a 9-element array conformal to the surface of a hemisphere, are designed and optimized. The geometrical approach of calculating the phase value is used to calculate the phase value of each antenna. The simulated results show that the 13-element conformal MRMPA array is achieving a beam scanning angle of ±84° with a gain of 13.89 dBi with low side lobe levels, and further, the gain of the array is enhanced by a dielectric superstrate that improved the gain by ∼2 dBi at all the scanning angles. Second, an MRMPA array conformal to a hemisphere with nine elements is designed with beam scanning ability from φ = 0°−360° and θ = ±30° with a gain of 15.69 dBi, and further, the gain is enhanced by ∼3 dBi with the dielectric superstrate. Full-wave simulations have proven both designs to be accurate and aligned with theoretical calculations.

Design of a Wideband, High Steering Angle and Low Side-Lobes Levels Matrix Antenna

This paper presents the use of pixel-type radiating elements in the context of broadband beam steering. The elements are composed of a resonant cavity topped by a frequency selective surface, fed via a patch antenna and filled with dielectric substrates. This pixel antenna has a wide -10 dB matching band from 1.22 to 1.61 GHz, which corresponds to a 27% fractional bandwidth. It has an angular aperture greater than 124° and a realized gain between 3.3 and 3.8 dBi over the whole matching band. An array composed of 5 elements has been simulated and allows a steering on a range of ±60° in the E plane while keeping the gain variation below 3 dB. A prototype has been manufactured and presents a steering capacity between -56 and 53° on the whole band with side-lobes levels lower than -8.1 dB whatever the angle.

Direct printable X-band low profile broadband reflectarray antenna using copper foils

This work reports on a compact and broadband reflectarray antenna that can be directly applied to the exterior surface of a nanosatellite. The design is composed of an annular ring with a wheel-shaped concentric structure loaded with two circular stubs acting as delay lines for maximum phase angle coverage. The design offers a phase variation of 576° in the X-band along with a peak measured gain of 26.6 dBi and an aperture efficiency of 49.24%. The design also offers low side lobe levels of −13 dB and −18 dB in both E- and H-planes at 11 GHz, respectively. Cross-polarization discrimination is also sufficiently large and is better than −32 dB and −36 dB for E- and H-planes, respectively. Moreover, the proposed printable reflectarray exhibited a 1-dB gain Bandwidth (BW) of 31.5 %. The design is produced by applying copper foils on float glass with a thickness of 2 mm as a proof of concept.

Two-Bit Planar Coding Reconfigurable Array Antenna for Dual-Polarized Wide-Angle Beam Scanning

In this communication, a dual-polarized coding reconfigurable array antenna with the characteristics of being low-profile, low-cost, relatively low-sidelobe and wide-angle beam scanning is proposed. By exciting the array via different feeding ports, horizontal and vertical polarized scanning beams can be generated. By adjusting the PIN diodes integrated on the feeding lines, the element presents four different phase states of -270°, -180°, -90°, and 0°, labeled as “00”, “01”, “10”, and “11”. An eight elements array antenna is designed based on the element. With the introduction of elaborately designed two groups of fixed phase delay, the sidelobe level at different scanning angles can be effectively reduced in two polarized directions and the gain are also improved. The simulated and measured results of the fabricated prototype indicate that dual-polarized ±60° wide-angle beam scanning, moderate array gain, relatively low sidelobe level, and low cross polarization level can be achieved. The proposed array antenna, which according to our best knowledge, is the first dual linear polarized wide angle beam scanning coding reconfigurable array without the feeding horn, might have good applications in base station and fully polarimetric radar.

A Single Plane Low profile Patch Antenna π-Shaped Slots and Low Side Lobe Level for Directive Wireless Communications

The patch antenna was used recently for ISM band (5.725 – 5.875) GHz, the patch antenna suffers of being an antenna with low gain as well as narrow operating bandwidth with high side lobe level (SSL) radiation pattern. A single plane with low profile and easy fabrication microstrip patch antenna has been proposed in this work was presented for directive communications and operates in Industrial, Scientific, and Medical (ISM) band 5.8 GHz with low SLL radiation pattern and gain of 5.20 dB for pint to point (directive). The gain of antenna has been increased while SLL decreased due to shifting the radiating patch and feeder of antenna with specific distance toward –ve side of the X-axis without any need for using techniques which would increase overall dimensions of antenna. The antenna has been printed on Arlon AD 250 substrate. The simulated results of antenna’s gain, operating frequency, bandwidth, return loss, and radiation pattern are presented. CST Microwave studio software was used in this design simulation.

A dual-band dual-polarized low-side-lobe transmitarray using independent amplitude and phase controllable elements

In this paper, a novel transmitarray (TA) element with independent control capability of amplitude and phase under dual-band dual-polarized operation is proposed. By changing the physical size of the TA element, the phase variation of the element can cover 360° at two bands. Moreover, the phase change of the frequency band is less than 30° when the phase of the other band is changed. Meanwhile, a higher maximal transmission amplitude can be maintained when varying the phase. Amplitude modulation is achieved by rotating the TA element. Utilizing the proposed TA element, a dual-band dual-linear polarization (LP) TA with low side lobe level (SLL) operating at 12.5 GHz and 14.25 GHz is designed. The SLL can be decreased by amplitude modulation of the elements. The measured peak gains of the proposed TA are 25.96 dBi and 25.89 dBi at 12.5 GHz and 14.25 GHz. In addition, the measured SLLs of the yoz/xoz planes are −22.4 dB/−22.4 dB and −22.5dB/−22.3 dB at 12.5 GHz and 14.25 GHz, respectively. The proposed TA shows good SLL performances and great application potential in satellite communication systems.

All-plasmonic optical leaky-wave antenna with a low sidelobe level

Optical antennas have received considerable attention in recent years due to their unique ability to convert localized energy to freely propagating radiation and vice versa. Sidelobe level (SLL) is one of the most crucial parameters in antenna design. A low SLL is beneficial to minimize the antenna interference with other optical components. Here a plasmonic optical leaky-wave antenna with low SLL is reported. Shifting spatial frequency by periodically modulating the electric-field amplitude in a plasmonic gap waveguide enables a free-space coupled wave out of the antenna. At the same time, precise control of the aperture fields by the modulation depth allows for reducing SLL. Simulation results indicate that the proposed design can achieve a high directivity of 15.8 dB and a low SLL of −20 dB at the wavelength of 1550 nm. A low SLL below −15 dB is experimentally demonstrated within the wavelength range from 1527 to 1570 nm. In addition, the low-SLL property is further verified by comparing it with a uniformly modulated antenna. By modulating the guided waves in the plasmonic gap waveguide in different forms, the aperture fields can be flexibly arranged to achieve arbitrary wavefront shaping. It bridges the gap between guided and free-space waves and empowers plasmonic integrated devices to control free-space light, thus enabling various free-space functions.

Supervised Reciprocal Filter for OFDM Radar Signal Processing

In this paper, we address the problem of the range-Doppler map evaluation in continuous wave radar exploiting OFDM signals. This stage is usually implemented by resorting to a suboptimal batches algorithm and a typical choice is to fragment the signal in batches with length equal to the OFDM symbol length and to apply at each batch an appropriate range compression strategy: typically, either Matched Filter (MF) or Reciprocal Filter (RF). The former provides the best performance against noise-limited scenarios, whereas the latter against clutter-limited scenarios, thanks to its high Peak SideLobe Level (PSL). Using “OFDM fragmentation” requires symbol synchronization and sets constraints on the coherent processing chain; moreover, we show that it provides a Signal-to-Noise Ratio (SNR) loss both when using MF and RF. Therefore, we investigate the case of “non-OFDM fragmentation”, which does not require synchronization and avoids setting constraints on the processing chain. Specifically, we address the case of batch lengths longer than a single OFDM symbol that can potentially reduce the SNR loss at long ranges. We find that this is effective for the MF, but causes an even higher SNR loss for the direct application of the RF filter, which still provides a low level of sidelobes. Aiming at preserving the potential benefits of the RF over the MF against the clutter-limited scenarios, we propose some modified versions of the RF for the non-OFDM fragmentation case, which are shown to offer a trade-off between SNR losses and sidelobes level control. The effectiveness of the proposed approaches is demonstrated both by providing theoretical performance prediction expressions and by using simulated analyses. To this purpose, a case study is considered for a passive radar exploiting DVB-T transmissions

Low-Sidelobe Microstrip Patch Filtenna Array Fed by Higher Order Mode SIW Cavity

In this letter, a 1 × 3 microstrip patch (MP) filtenna array with low sidelobe level fed by TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">410</sub> -mode substrate integrated waveguide (SIW) cavity is investigated. Benefiting from the fact that the magnetic field amplitude at the adjacent region of the two central quasi-TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">110</sub> modes of the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">410</sub> -mode SIW cavity is twice that of the single quasi-TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">110</sub> mode on either side of the edge, it enables the filtenna array to obtain a binomial power distribution and then achieve low sidelobe level. In the fusion design of filtering power divider (FPD), the SIW cavity and the patch radiators are regarded as first and second resonators of filter respectively, meanwhile, the power dividing function is fulfilled by the coupling process between them. For demonstration, a filtenna array prototype centered at 13.2 GHz is designed, fabricated and measured. The measured results show that a peak gain of 11.6 dBi and a maximum efficiency of 85%. The measured sidelobe levels in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -planes are both below than -19.1 dB at 13.06 GHz and 13.32 GHz. Good agreement between the simulation and measurement can be observed.

High-resolution frequency-difference beamforming for a short linear array.

Conventional beamforming (CBF) is a commonly employed approach for detecting and estimating the direction-of-arrival (DOA) of acoustic signals in underwater environments. However, CBF becomes ambiguous due to spatial aliasing when the received signal's half wavelength is smaller than the array spacing. Frequency-difference beamforming (FDB) allows for processing data in the lower frequency Δf without encountering spatial aliasing by utilizing the product of array data at frequency f with its complex conjugate at frequency f+Δf. However, lower frequency results in a wider mainlobe, which can lead to poorer DOA performance for short arrays. In this paper, a fourth-order cumulants FDB method and a conjugate augmented FDB method are proposed to extend an M-element uniform linear array to 2M-1 and 4M-3 elements. The proposed methods generate narrower beams and lower sidelobe levels than the original FDB for short arrays with large spacing. And by setting the signal subspace dimension reasonably, the proposed methods can improve the weak target detection ability under strong interference compared with FDB. Last, we verify the excellent performance of the proposed methods through simulations and experimental data.