dB Sidelobe Level Research Articles

Very-low-sidelobe printed tapered arc-shaped wide-slot antenna array

This study proposes two unique techniques to increase the impedance bandwidth and reduce the sidelobe level (SLL) of printed antenna arrays. In the first, a printed tapered wide-slot antenna array fed by an array of printed patch elements placed above a metal reflector is introduced. The impedance bandwidth of this antenna array is 10.3–23.1 GHz, that is, 76.6%. By tapering the width of each of the slot elements, a very low SLL of −33.5 dB is obtained. The proposed antenna has a stable radiation pattern over the range 14.7–17 GHz, that is, the 3 dB gain bandwidth is 14.5% and has a front-to-back ratio (F/B) level of 40 dB and a low cross-polar component <−45 dB at broadside and <−35 dB off-broadside direction. In the second technique, to achieve further improvement in the SLL of the antenna array the length of each of the slot array elements is tapered, in the form of an arc-shape, leading to an antenna array with very low SLL of −35 dB at a centre frequency of 16.26 GHz, a wide bandwidth of 78.8%, 20 dB SLL bandwidth of 8.8%, and high F/B of 38 dB. A prototype of the antenna array is fabricated and the simulated and measured results are presented and discussed.

Design of a Planar Slotted Waveguide Array Antenna for X-band Radar Applications

A planar slotted waveguide array antenna has been designed at 9.37 GHz for X-band radar applications. The antenna consists of multiple branchline waveguides with broadwall radiating shunt slots and a main waveguide to feed the branch waveguides through a series of inclined coupling slots. The antenna feed point is located at the center of the main waveguide. Element weights in the array have been calculated bysampling a continuous circular Taylor aperture distribution at the 25 dB sidelobe level in both the E and Hplanes. A commercially available electromagnetic (EM) simulation tool has been used to characterize the individual isolated slot and that data hassubsequently been used to design the planar array. The array is finally analyzed in a CST Microwave studio and the measured and simulated results have been found to be in good agreement.

W-band prototype of platelet feed-horn array for CMB polarisation measurements

We present the design and performance of a 2x2 prototype arrayof corrugated feed-horns in W-band. The module is fabricated using a so-called ``platelet'' technique by milling Aluminum plates. This technique is suitable for low-cost and scalable high performance applications. Room temperature Return Loss measurements show a low ( < −30 dB) reflection over a 30% bandwidth with a maximum matching of -42 dB at 100 GHz for all four antennas. Beam pattern measurements indicate good repeatability and a low (-25 dB) sidelobe and crosspolarisation levels. This work is particularly relevant for future Cosmic Microwave Background polarisation measurements, which require large microwave cryogenic detector arrays coupled to high performance corrugated feed horns.

Pareto Optimization of Thinned Planar Arrays With Elliptical Mainbeams and Low Sidelobe Levels

A multi-objective Pareto genetic algorithm design methodology is applied to thinned planar arrays to simultaneously minimize peak side-lobe levels and target an elliptical mainbeam with specific minimum and maximum half-power beamwidths. This new radiation pattern synthesis technique for thinned planar arrays provides antenna engineers with a set of tradeoffs between low side-lobe levels and close adherence to mainbeam design objectives (i.e., the specified half-power beamwidths corresponding to the major and minor axes of an elliptical mainbeam). One Pareto optimization example is presented for a thinned low side-lobe planar array with a desired minimum and maximum beamwidth of 8.4° and 12° respectively. Two designs from the Pareto front are discussed, one with a -20.92 dB side-lobe level and beamwidths between 11.5° and 7.5° and a second with a -18.97 dB side-lobe level with beamwidths between 12° and 7.93°.

Influence of the Aperture Edge Diffraction Effects on the Mutual Coupling Compensation Technique in Small Planar Antenna Arrays

Influence of the Aperture Edge Diffraction Effects on the Mutual Coupling Compensation Technique in Small Planar Antenna Arrays In this paper the quality of a technique to compensate for mutual coupling (and other phenomena) in small linear antenna arrays is investigated. The technique consists in calculation of a coupling matrix, which is than used to determine corrected antenna array excitation coefficients. Although the technique is known for more than 20 years, there is still very little information about how different phenomena existing in a real antenna arrays influence its performance. In this paper two models of antenna arrays are used. In the first model the effect of mutual coupling is separated from the aperture edge diffraction. In the second model antenna both mutual coupling and aperture edge diffraction effects are included. It is shown that mutual coupling itself can be compensated very well and an ultralow sidelobe level (i.e. -50 dB) could be achieved in practice. In the presence of diffraction effects -46.3 dB sidelobe level has been attained, but radiation pattern can be controled only in narrow angle range (i.e. up to ±60°).

Modified antipodal Fermi antenna with piecewise-linear approximation and shaped-comb corrugation for ranging applications

The authors propose the dual-tapered structure consisting of piecewise-linear inner taper and outer shaped-comb corrugation and the antipodal feeding section to present a modified antipodal Fermi antenna. This antenna exhibits the performance with wider band (3.6–15 GHz) in return loss responses, moderately high gain (5.1–14.5 dBi), high front-to-back ratio (24.8–38.9 dB) and available end-fire (29.8° beamwidth and −18.7 dB side lobe level) in radiation patterns. The current distributions demonstrate the characteristics of leakage, transverse waves among dual-taper and transition on balun. The proposed antenna presents the longitudinal conformation for mounting application and evaluate the pulse responses with linearity test for ultra-wideband (UWB) ranging and imaging applications.

LARGE APERTURE LOW ABERRATION ASPHERIC DIELECTRIC LENS ANTENNA FOR W-BAND QUASI-OPTICS

An advanced aspheric and asymmetric large aperture dielectric lens antenna is proposed flrstly here for high resolution at W- band frequency. Large aperture and aspheric lens provides minimum focusing error and high resolution in millimeter wave quasi-optics application. To the best of the authors' knowledge we design flrst time 500mm large aperture lens for W-band quasi optics application. Near fleld radiation pattern, beam size and focal length of the lens are obtained theoretically and experimentally as well. Dielectric rod waveguide antenna is also designed and employed as a source antenna for the lens. The measured and simulated results of the DRW antenna also show very good performance at W-band frequency, and it has 15.3dB gain with i22.5dB sidelobe levels at 94GHz.

Time-Domain Design of UWB Vivaldi Antenna Array Using Multiobjective Particle Swarm Optimization

A method to obtain optimum tradeoffs (Pareto front) between sidelobe level (SLL) and beamwidth (BW) in time domain for ultrawideband (UWB) antenna arrays is presented. Multiobjective particle swarm optimization (MOPSO) is used to deal with these two conflicting objectives. In the optimization process, mutual coupling effects between elements are not considered. However, the multiple solutions obtained from MOPSO enable the designer to consider the mutual coupling effect as an additional constraint. Each element of the array is an antipodal Vivaldi antenna. The optimization template is applied for three different time-domain pattern descriptors. In comparison to arrays with the same number of elements reported in literature, the Pareto fronts obtained in this study provide lower BW and SLL. A four-element sample from resultant Pareto fronts was simulated by using CST Microwave Studio software. This array shows a 13.7-17.2 dBi gain over the whole frequency band from 3-11 GHz, 7.2° BW, and -12 dB SLL for energy pattern.

A Substrate Integrated Waveguide Circular Polarized Slot Radiator and Its Linear Array

A top-wall substrate integrated waveguide (SIW) slot radiator for generating circular polarized (CP) field is proposed and characterized in this letter. The reflection of the slot radiator is extremely weak, which simplifies the linear traveling wave array design. Based on such a structure, a 16-element CP SIW traveling wave antenna array is designed, fabricated, and measured at 16 GHz. A -23 dB side lobe level (SLL) with an axial ratio (AR) of 1.95 dB is experimentally achieved. The size of the proposed SIW CP linear array antenna is 285 mm times 22 mm. The measured gain is 18.9 dB, and the usable bandwidth is 2.5%.

Coded excitation using biphase-coded pulse with mismatched filters for high-frequency ultrasound imaging

A scheme of using phase-coded excitation and mismatched filter compression for high-frequency ultrasound imaging is presented in this paper. Biphase-coded pulses were constructed to excite the transducer. Received signals were compressed with mismatched filters optimized by minimizing peak-sidelobe-level (PSL). Both simulation and experiments were carried out to demonstrate the advantage of this technique. The simulation results demonstrated a possible sidelobe reduction (<−90 dB) with a slightly decrease of the signal-to-noise ratio of less than 1 dB compared with the compression using matched filters alone. The experimental results showed about 14 dB SNR improvement as well as −40 dB sidelobe level when the Barker-13 code excitation with 3-cycle sinusoidal wave carrier was used.

Mutual coupling compensation in time modulated linear antenna arrays

A practical approach to compensate for the mutual coupling effect in low sidelobe time modulated linear antenna arrays is proposed. Taking into account the measured complex embedded element patterns, the compensated element weights and time sequences are optimized by the differential evolution (DE) algorithm. The proposed approach is experimentally verified by the successful realization of a -30 dB sidelobe level discrete Taylor pattern from a 16-element time modulated linear array. Numerical results are compared with measured data and good agreement is reported.

A NRD Guide Fed Dielectric Lens Antenna with High Gain and Low Sidelobe Characteristics

A NRD guide fed dielectric lens antenna with high gain and low sidelobe characteristics is proposed for millimeter wave applications. The measured results showed very good performance at 60 GHz. It exhibited a gain of 24.9 dBi, 27 dB sidelobe level suppression.

Beamforming for circular and semicircular array antennas for low-cost wireless LAN data communications systems

An investigation into beam synthesis for small circular and semicircular arrays is presented. Array antennas of this type are likely to become a core component in future wireless LAN systems architecture. They offer additional spatial diversity as a means for combating multipath interference, necessary for high speed data communications, and user mobility. Beams are synthesised using cophasal and adaptive algorithms. Beamwidths of 19° and –20 dB sidelobe levels are attainable from an array of three wavelengths diameter. A semicircular array of this type can maintain a gain of approximately 10 dBi over a look direction angular range of ±50°.

Ultrasound imaging based on multiple beamforming with coded excitation

Phased-array ultrasound imaging employing multiple receive beamforming with coded excitation is investigated. The approach is based on simultaneous excitation of transducer array elements with coded signals, and multiple receive beamforming. It involves only a single transmit-receive step for reconstruction of each image frame. The excitation signals are chosen as decorrelated binary pseudo-noise sequences. Performance of the coded excitation imaging is tested through simulations for code sequences with various lengths and different decoding filters. The simulation results show that the ultrasound scanner with the coded excitation can produce up to —15 dB side lobe level at the transmit beam profile with sufficiently long codes, whereas very short codes result in about —7 dB side lobe level. The coded excitation imaging improves the signal-to-noise ratio and minimizes the signal firings, and hence provides increased penetration depth and frame rates.

Phase correcting zonal reflector incorporating rings

An array of conducting elements printed on a grounded dielectric substrate functions as an electromagnetic phase shifter. With a fixed substrate and a given operating frequency, the phase shift is determined by the array parameters. In the paper, the spectral domain moment method model for analyzing homogeneous reflective phase shifters with conducting rings as elements is presented, and numerical and experimental results are given. A novel phase correcting Fresnel zonal reflector based on this model is reported. A 43% maximum antenna efficiency and -22 dB sidelobe level were measured in X-band. The bandwidth of the reflector is estimated to be greater than 10%.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Short-range sea clutter in horizon search radar systems: antenna pattern effects

Short-range clutter can limit the performance of radar systems using high pulse repetition frequency (PRF) waveforms. The paper evaluates the antenna pattern effects of short-range sea clutter for an example horizon search system. Clutter-to-noise ratio (C/N) and signal-to-noise ratios (S/N) are evaluated for several antenna designs, in which aperture illumination weighting can be achieved on either transmit or receive. Three antenna effects are studied: illumination function (pattern), elevation of the pattern with respect to horizontal (‘upspot’), and aperture diameter. Of several cases examined, one with uniform weighting on transmit and Taylor weighting on receive gives the most desirable clutter response. With reference to the case of uniform transmit and receive patterns with no upspot, a Taylor receive pattern with −42 dB sidelobe level in combination with an optimal upspot angle reduces worst-case clutter by ≈14.7 dB at the expense of ≈10.25 dB increase in the transmit power required to equalise S/N to that of the reference. Doubling the aperture diameter further reduces worst-case clutter by ≈13.2 dB, with required transmit power actually decreasing (≈12.41 dB) over the previous case. Here, the cost is a larger antenna. Antenna considerations are shown to have a considerable impact on clutter and to be perhaps the best method of reducing radar dynamic range requirements.

High aperture efficiency symmetric reflector antennas with up to 60 degrees field of view

A microwave single-reflector scanning antenna derived from an ellipse (rather than the usual parabola) which gives a much greater field of view is presented. This reflector combines reasonable scanning in one plane with good focusing in the other, and its scanning ability is superior to the torus and other single reflectors because it has much greater aperture efficiency and is thus smaller while having the same performance. The reflector surface is derived in two steps: a fourth-order even polynomial profile curve in the scan plane is found using least squares to minimize the scanned ray errors; then even polynomial terms in x and y that minimize astigmatism for both the unscanned and maximally scanned beams are added to form the three-dimensional surface. Numerical simulations of radiation patterns for a variety of antenna diameter and field-of-view cases give excellent results. The 60 degrees scan case with 30- lambda -diameter aperture has only 0.2-dB peak gain deviation from ideal and first sidelobe levels below 14 dB down from peak gain. The 17 degrees , 500- lambda case has only 0.8-dB gain variation and -14 to -11 dB sidelobe levels for approximately +or-68 beamwidths of scan, with focal length to aperture diameter ratio equal to about one. >

Low-loss SAW filters with 70 dB sidelobes using cascaded and weighted single-phase unidirectional transducers

Close-in sidelobe suppression was attained in low-loss SAW filters with single-phase unidirectional transducers (SPUDTs), by Dolph-Chebyshev weighting of the SPUDT rungs. Two such structures electrically cascaded in a 1.5% bandwidth filter yielded an overall 70 dB sidelobe level, with an insertion loss of only 8.5 dB.

Pulse compression filter for ultrasonotomography utilizing L(0,3) mode of the elastic wave in a fused quartz rod

AbstractTo introduce the pulse compression technique into ultrasonotomography, a pulse compression filter with a large delay time difference of 100 μs at a bandwidth of 1 to 2 MHz is needed. In this paper, it is clarified that a pulse compression filter with the forementioned capacity is realized by utilizing the L (0, 3) mode of elastic waves propagating in a fused quartz rod approximately 1 mm in diameter and 1 to 2 m in length. In using the L (0, 3) mode, the L (0, 2) mode causes deterioration in the S/N ratio after pulse compression because it is an unwanted spurious vibration. Therefore, the unwanted signal caused by the L (0, 2) mode is eliminated by the difference in vibration patterns between the L (0, 2) mode and the L (0, 3) mode. In addition, a pulse compression ratio of 100 with ‐32 dB sidelobe level has been obtained in a pulse compression system using the filter proposed herein.

Improved design of series-fed circularly polarised printed linear arrays

In a previous paper, a practical design method was presented for a circularly polarised printed array antenna composed of strip dipoles and slots (CP-PASS). Although the design method was useful for linear-array type CP-PASS with medium sidelobe levels, the determination procedure for the dimensions of the radiating elements was rather complicated. The paper describes an improved design method for CP-PASS to realise the lower sidelobe levels specified and to provide a much clearer determination procedure for the element dimensions. Some improved points in the array design are described and a generalised design procedure for lineararray type CP-PASS is presented. Finally, a Cheb$$$chev-array CP-PASS with a −20 dB sidelobe level is designed and measured at S-band. Experimental results demonstrate the validity of the improved design method.