Low Sidelobe Level Research Articles

Improving the Sidelobe Level, Return Loss and Bandwidth of Notch-Loaded TM30 Mode Patch via Fractal-Slot

This paper presents a method for sidelobe level (SLL) reduction, return loss improvement, and bandwidth enhancement in notch-loaded TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sub> mode rectangular patch antennas. In this method, a fractal-slot is introduced in the center of notch-loaded patch to remove the unwanted out-of-phase current regions. It is shown that a combination of the fractal-slot and notch loading technique can achieve significant improvement in SLL, return loss, and bandwidth of notch-loaded TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sub> mode without compromising gain or symmetry of radiation patterns. Moreover, the method also gives an additional degree of freedom to improve the impedance matching without changing the feed location. A prototype of the antenna is fabricated to verify the proposed method. The proposed antenna shows a measured gain of 13 dBi with a low SLL of −16 dB. Furthermore, it shows symmetrical patterns in both planes with cross-polarization (X-pol) levels of less than 35 dB. An under-sampled <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> array of the proposed antenna is also presented by utilizing its low SLL property to simplify the complexity of feed networks in high gain array antennas. The array offers the same directivity and SLL as that of an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times 8$ </tex-math></inline-formula> array of fundamental mode rectangular patch elements in the same area.

Light-weight wideband antenna array with low sidelobes for SAR applications

PurposeThe purpose of this study is to achieve the low-cost, light-weight and compact antenna array with wide bandwidth and low side lobe levels for synthetic aperture radar (SAR) applications in Ku frequency band.Design/methodology/approachA compact design of a rectangular microstrip patch antenna array using multilayered dielectric structure is presented in Ku-band for advanced broadband SAR systems. In this design, stepped pins are used to connect the microstrip feed lines to the radiating patches.FindingsThe simulation and fabrication results of the multilayered antenna and a 1×16-element linear array of the antenna with Taylor amplitude distribution in the feeding network are presented. The antenna element has a 10-dB impedance bandwidth of more than 26%, and the linear array shows reduction in bandwidth percentage (about 15.4%). Thanks to Taylor amplitude tapering, the side lobe level (SLL) of the array is lower than −24 dB. The maximum measured gains of the antenna element and the linear array are 7 and 19.2 dBi at the center frequency, respectively.Originality/valueIn the communication systems, a high gain narrow beamwidth radiation pattern achieved by an array of multiple antenna elements with optimized spacing is a solution to overcome the path loss, atmospheric loss, polarization loss, etc. Also, wideband characteristics and compact size are desirable in satellite and SAR systems. This paper provides the combination of these features by microstrip structures.

Design and Evaluation of Transmitting Antennas for Solar Power Satellite Systems

This study attempts to identify, design, and evaluate transmitting antennas for Solar Power Satellite (SPS) systems. The design approach aimed at meeting the SPS operational requirements at ISM bands, namely 2.4-2.5GHz for the NASA and 5.725-5.875GHz for the JAXA models. The primary attributes of SPS antennas for transmitting Beamed High-Power Microwaves (BHPMs) are high power handling capability, efficiency, and directivity with narrow beamwidth and lower sidelobe levels. Using a planar end-fed 20×20 SWA module, the whole planar Slotted Waveguide Antenna Arrays (SWAAs) were designed for both the NASA and JAXA reference models having 1km diameter antenna aperture, peak power level over 1GW, directivity over 80dBi, Side Lobe Level (SLL) less than 20dB, and pencil beam with HPBW less than 0.01°. The proposed slotted waveguide transmitting antenna arrays fulfilled the operational requirements for both the NASA and JAXA SPS reference models. Due to the higher operating frequency, the results showed that the proposed planar SWA array performs better on the JAXA than on the NASA SPS model.

W‐band ridge gap waveguide slot array antenna with low sidelobe and high‐gain characteristics

AbstractIn this letter, a W‐band slot array antenna based on ridge gap waveguide (RGW) with low sidelobe and high‐gain characteristics has been proposed. It adopts a series and parallel hybrid feeding network to realize low sidelobe levels in E‐ and H‐plane, respectively. The tunable pins and large power ratio dividers are introduced in the distribution network, which improves the phase consistency and brings flexibility to amplitude‐tapering. The proposed antenna overcomes the shortcomings of grating lobes caused by quasi‐Taylor distribution of conventional slot array with backed cavities. The prototype of a 16 × 18 slot array is fabricated and measured. The measured impedance bandwidth is from 81.2 to 86 GHz, and the peak gain is higher than 29.4 dBi with the sidelobe levels (SLLs) of −19.7 dB and −30 dB on E‐ and H‐plane, respectively.

Optimization of optical waveguide antennas for directive emission of light

Optical traveling wave antennas offer unique opportunities to control and selectively guide light into a specific direction, which renders them excellent candidates for optical communication and sensing. These applications require state-of-the-art engineering to reach optimized functionalities such as high directivity and radiation efficiency, low sidelobe levels, broadband and tunable capabilities, and compact design. In this work, we report on the numerical optimization of the directivity of optical traveling wave antennas made from low-loss dielectric materials using full-wave numerical simulations in conjunction with the particle swarm optimization algorithm. The antennas are composed of a reflector and a director deposited on a glass substrate, and an emitter placed in the feed gap between them serves as an internal source of excitation. In particular, we analyze antennas with rectangular- and horn-shaped directors made of either hafnium dioxide or silicon. The optimized antennas produce highly directional emissions due to the presence of two dominant guided TE modes in the director in addition to leaky modes. These guided modes dominate the far-field emission pattern and govern the direction of the main lobe emission, which predominately originates from the end facet of the director. Our work also provides a comprehensive analysis of the modes, radiation patterns, parametric influences, and bandwidths of the antennas, which highlights their robust nature.

Planar Broadband Higher-Order Mode Millimeter-Wave Microstrip Patch Antenna Array With Low Sidelobe Level

AbstractIn this letter, a planar broadband higher-order mode millimeter wave (MMW) microstrip patch antenna array with low sidelobe level (SLL) is presented. For the antenna element, antiphase-TM30 mode is excited by unequally etching the radiating patch with two transverse slots. Meanwhile an SIW-based pin-loaded slot coupling feeding structure is introduced to achieve merits of broadband, low cross polarization and low backward radiation. Then a one-eight power divider with in-phase unequally tapered amplitude distribution is adopted to excite an eight-element array with SLL. The GCPW-SIW transition structure is also selected to achieve broadband impedance matching. Finally, both element and array antenna are optimized and fabricated for verification. For the antenna array, the measured -10 dB impedance bandwidth is from 25.1 to 31.3 GHz (22%) with a maximum gain of 14.6 dBi at 29.5 GHz and a 3dB gain bandwidth of 27.9%. And the measured SLL at 26, 28 and 30 GHz are all less than 20 dB. Index TermsMillimeter-wave (MMW), broadband, higher-order mode, low sidelobe level (SLL).

Near-Field Bessel-Gauss Antenna for Nonmetal Internal Defects Detection

A radial line slot array (RLSA) is proposed for Bessel-Gauss beam generation with a narrow main beamwidth and low sidelobe characteristics for nonmetallic internal defects detection. Owing to the radial attenuation factor of Gaussian function, the sidelobe level of Bessel-Gauss beam can be suppressed. By accurately adjusting the slot position and size of the RLSA, the optimum aperture field distribution can be synthesized to generate the near-field Bessel-Gauss beam based on the projection method. The simulated/measured results have shown that the maximum nondiffraction distance of 70 mm/70 mm and the null-null beam width of the Bessel-Gauss main beam of 30 mm/30 mm are achieved at the operating frequency of 12.5 GHz/12.5 GHz, while low sidelobe levels (<−18.14 dB/−18.07 dB) are generated. Compared to other antennas for microwave nondestructive testing, the proposed RLSA has merits of low sidelobes, large E-field depth and narrow main beam; therefore, it can improve the detection performance in terms of sensitivity and depth, which can be widely, used for nonmetal internal defects detection applications.

The optical system of the Tenerife Microwave Spectrometer: a window for observing the 10–20 GHz sky spectra

The TMS optical system is based on a decentered dual-reflector system in a Gregorian configuration to observe with an angular resolution of less than 2°. The primary goal of the present study is to evaluate the final design and verify that it satisfies the design requirements. We aim for low cross-polarization (-30 dB), low sidelobe (-25 dB) levels, and a stable beam in terms of shape (low ellipticity) and size over a full octave bandwidth (10–20 GHz). We performed both ray-tracing and full-wave simulations using the CST Studio software in order to investigate the system behaviour. We gave special attention to the beam frequency variation and polarization leakage. We have characterized the effects on the radiation pattern produced by the cryostat window. We present the final design of the TMS optical system, as well as a complete study of the system's performance in terms of cross-polarization, sidelobes, ellipticity and beamwidth. We discuss the effects of sidelobes and study the need for a baffle.

Joint design of mismatched filter and unimodular transmit waveform

To improve the receiver performance, unimodular transmit waveform and mismatched filter are jointly designed by using the alternating direction method of multipliers (ADMM). A series of auxiliary variables are introduced to decouple the variables in objective function and additional constrains. Denominator normalization(fractional programming technology) and step function are applied to obtain optimal solution from some subproblems. For given transmit waveform, same-length mismatched filter is designed in receiver. The low sidelobe level performance of the present methods are illustrated with the simulation results.

X-Band Low-Probability Intercept Marine Radar Antenna Design With Improved Bandwidth and High Isolation

A series-parallel hybrid-fed microstrip array antenna design is presented for X-band low-probability intercept (LPI) marine radars. Contrary to traditional counterparts, the proposed antenna has improved impedance and radiation bandwidth from 9.1 to 9.6 GHz to accommodate pulse compression and frequency diversity for LPI radars. The antenna structure consists of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$24\times4$ </tex-math></inline-formula> patch elements with horizontal polarization. The two halves of the structure are fed in parallel and each arm is fed in a series-series feed network to achieve low sidelobe level (SLL) of −26.5 dB. The manufactured antenna has a gain of 24.0 dBi with half-power beamwidth (HPBW) of 4.5° and 21.5° in azimuth and elevation, respectively. The measured gain flatness is ±0.3 dB over the radionavigation band and ±1.0 dB over the entire band. A novel grid baffle structure with capacitive surface impedance is proposed and implemented to provide high isolation over the target bandwidth. The maximum and average isolations between transmit and receive antennas are measured as 65 and 62 dB, respectively. The proposed antenna is very suitable for dual-mode pulsed and continuous-mode LPI marine radars.

Design of 2 × 8 Filtering Butler Matrix With Arbitrary Power Distribution

This paper reports a novel 2 × 8 filtering Butler matrix with arbitrary power distribution. The filtering Butler matrix, composed of coupled resonators, provides arbitrary power division and 0∘ and 180∘ phase differences as well as a fifth-order bandpass filtering characteristic. The detailed design process and synthesis method for the 2 × 8 filtering Butler matrix are reported. To validate the analysis, a 2 × 8 filtering Butler matrix with unequal power division, operating at 2.4 GHz, is devised, manufactured, and measured. The results of the simulation and experimentation are matched very well. According to the measurement results, the array factors have been calculated to further verify the performance of the Butler matrix, which show a lower sidelobe level.

Design of A Ka-Band 3D-Printed Dual-Polarization Magnetoelectric Dipole Antenna Array with Low Sidelobe

A Ka-band dual-polarization magnetoelectric (ME) dipole antenna array based on three-dimensional (3D)-printed technology with low sidelobe level (SLL) is proposed in this paper. The metal posts and cross-slots are explored to build a novel subarray with 2 × 2-unit ME-dipoles as the basic element. Creatively, a square waveguide to cross-slots transition with a pyramid horn cavity structure is investigated to feed the ME-dipole subarray. Furthermore, two types of power-tapering corporate-feed networks with laminated structures are used to design an 8 × 8-unit low-SLL array. The fabricated array has a relative bandwidth (VSWR &lt; 2) of 14.3% and 17.1%, with a realized gain higher than 25.8 dBi and 26.1 dBi for the H-pol. and V-pol., respectively. The maximum radiation efficiency for both arrays is 73.2%. The measured first sidelobe levels are less than –17.5 dB for both polarizations. With competitive performance and low fabrication cost, the proposed dual-polarization ME-dipole antenna array would be valuable for polarization-agile radar and communication systems.

Hybrid FSK-PSK Waveform Optimization for Radar Based on Alternating Direction Method of Multiplier (ADMM).

In this paper, a new radar signal modulated with a hybrid of the frequency shift keying (FSK) and the phase shift keying (PSK) signal—i.e., the FSK-PSK signal—is studied. Different phase encoding sequences are used to modulate the sub-pulses to obtain lower sidelobe levels and ensure signal orthogonality. In addition, to counter intra-pulse slice repeater jamming of specific length generated by the enemy jammer, an orthogonal waveform made of sub-pulses of equal length based on the FSK-PSK modulation scheme is designed. The simulation results show that the optimized discrete phase encoding sequence can significantly enhance the orthogonality of the sub-pulse in the FSK-PSK signal and effectively suppress the slice repeater jamming. Two algorithms are proposed: (1) the low sidelobe waveform optimization algorithm based on ADMM (LSW-ADMM); and (2) the anti-slice-repeater-jamming algorithm based on ADMM (ASRJ-ADMM). Both algorithms exhibit fast convergence speed and low computational complexity.

Synthesis of low sidelobe level antenna arrays through only main lobe assumption

An analytic method is proposed to design uniformly spaced arrays so that have as low as possible sidelobe level and having directivity as close as to that of uniformly excited arrays. The ideal array factor of arrays is assumed to have only one main lobe. The actual synthesized array would have sidelobe levels which can be controlled by a parameter. Some examples are given to verify the effectiveness of the presented method.

Double Meander Dipole Antenna Array with Enhanced Bandwidth and Gain

In this paper, a new design of high gain and wide bandwidth microstrip patch antenna array containing double meander dipole structure is proposed. Two in-phase resonant frequencies in the Ku-band (12–18 GHz) could be achieved in the double meander dipole array structure, which lead to enhance impedance bandwidth without costing extra design section. Besides, further enhanced gain of 2 dBi of the array over the entire operating frequency range has been achieved by introducing a double-layer substrate technique. The proposed antenna has been fabricated using the E33 model LPKF prototyping PCB machine. The measurement results have been performed, and they are in very good agreement with the simulation results. The measured –10 dB impedance bandwidth indicates that the array provides a very wide bandwidth which is around 30% at the center frequency of 15.5 GHz. A stable gain with a peak value of 10 dBi is achieved over the operating frequency range. The E- and H-plane radiation patterns are simulated, and a very low sidelobe level is predicted. The proposed antenna is simple and has relatively low-profile, and it could be a good candidate for millimeter wave communications.

Radial Basis Function Neural Network Optimal Modeling for Phase-Only Array Pattern Nulling

Phase-only nulling with low sidelobe level is a problem of interest in array synthesis which is a tedious problem without an analytical solution. In this communication, a novel framework for the phase-only nulling based on radial basis function neural network (RBFNN) is proposed to predict the phase adjustment for the array pattern nulling with sidelobe control. In the process of network training, the parameters of the RBFNN are optimized simultaneously based on the self-adaptive differential evolution (SADE) algorithm, which aims to improve the approximation ability and reduce the complexity of the network. Simulation results of the optimized RBFNN models show compact network structure and form the array pattern under desired performance with good generalization capability.

Reflectarray Antenna Concept for a Snow Mass Measurement SAR Mission in Ku-Band on a Nanosatellite Platform

The design of a 1 × 0.33 m dual-polarized reflectarray antenna (RA) operating in Ku-Band (17.2 GHz) for a synthetic aperture radar (SAR) mission using a 12 U CubeSat is presented. The SAR RA has larger electrical size, larger aspect ratio, and smaller focal to aperture length ratio (F/L) compared to existing CubeSat RAs designed for communication payloads. Electrically small unit cells accounting for large incidence angle variations, improving phase resolution, and preventing grating lobes are designed. To illuminate the RA with the desired elliptical beam, a compact aperture-coupled microstrip patch array antenna was designed. Tests done on a CubeSat mockup integrating the dual-polarization feed source and a five-panel reflectarray showed good agreement between the simulated and the measured beamwidths, with low sidelobe and cross polarizations levels.

W-Band Low-SLL Size-Reduction Microwaveguide Array Antenna Using TE120-Mode-Cavity Dual-Layer Power Divider

In this letter a W -band small-size low sidelobe level (SLL) 6 × 16 microwaveguide slot array antenna is proposed based on the silicon micromachining technology. The feeding network within the limited available area consists of several stages of equal T-junctions and TE120-mode-cavity dual-layer power dividers able to build the desired tapering power distribution over a relatively wide bandwidth. The TE120-mode-cavity dual-layer power divider is at the end of the feeding network, which can implement the layer-to-layer transition and the power division simultaneously. Thus, the whole size of the array antenna can be reduced by about 25% compared with the conventional five-stage tree-like feeding network. The overall antenna size is 60 mm × 20 mm × 1.85 mm. The measured maximum gain is 26.1 dBi at 94 GHz, and the corresponding radiation efficiency is 69.2%. The measured SLL in E -plane is below than −18.5 dB within the frequency band from 92 to 96 GHz.

Performance evaluation of Non-Uniform circular antenna array using integrated harmony search with Differential Evolution based Naked Mole Rat algorithm

In many wireless applications, circular antenna arrays are commonly used but managing the lower side lobe with high directivity is still challenging. Many typical methods could be used to synthesize the array in real time but lag behind to retain high directivity and the low sidelobe level. This study formulates an optimization problem to obtain the desired main lobe direction, suppress the subsidiary lobe, and maximizes the directivity. A modified optimization algorithm is proposed called Integrated Harmony Search with Differential Evolution based Naked Mole Rat Algorithm (IHDN) to rapidly and reliably refine control parameters. Simulations are performed, and results are compared to other traditional algorithms. The findings show that the proposed algorithm results in excellent side lobe minimization with good directivity. The size analysis indicates that good directivity values with low sidelobe levels can be obtained for a smaller number of antenna elements.

Negative refractive index-shaped lens antenna with straight line condition for wide angle beam scanning

For a base station antenna in 5G mobile communications, lens antennas have been proposed for excellent multiple beam performances. In this paper, the negative refractive index (NRI) lens is selected for thinning the lens thickness. By applying lens shaping method, straight-line condition lens is designed. Multi beam radiation characteristics are compared with the conventional hyperbolic shape lens and Abbe's sine condition lens. In order to determine the feed positions for multi beam performances, the focal region ray tracing is performed. The best feed positions are obtained. For calculating multi beam radiation characteristics, ANSYS HFSS software is employed. Multi beam radiation patterns in the wide angle scanning up to 45° are obtained. The results show that the proposed straight-line condition lens achieves higher gain and lower sidelobe level compared to the other two structures. The usefulness of the proposed lens antenna is ensured.