dB Sidelobe Level Research Articles

Design of Microstrip Antenna Array with Suppressed Back Lobe

A practical procedure to reduce the back lobe level of microstrip antenna arrays is presented in this paper. The novel concept consists in the design of the radiators asymmetrically positioned with respect to the ground plane. In order to validate this technique, a four-element linearly-polarized array is designed in the HFSS software and a prototype is manufactured. Furthermore, the design of beamforming circuit to achieve broadside radiation and -20 dB side lobe level is detailed. Very good agreement between simulated and experimental results is obtained. Although the technique is presented for linearly polarized arrays, it is general and can also be applied in the circularly polarized ones.

Substrate Integrated Horn Antenna With Uniform Aperture Distribution

A new substrate integrated horn antenna with hard side walls combined with a couple of soft surfaces is introduced. The horn takes advantage of the air medium for propagation inside, while having a thickness of dielectric on the walls to realize hard conditions. The covering layers of the air-filled horn are equipped with strip-via arrays, which act as soft surfaces around the horn aperture to reduce the back radiations. The uniform amplitude distribution of the aperture resulting from the hard conditions and the phase correction combined with the profiled horn walls provided a narrow beamwidth and -13 dB sidelobe levels in the frequency of the hard condition, which is validated by the simulated and measured results.

Ka-Band Low-Sidelobe-Level Slot Array Leaky-Wave Antenna Based on Substrate Integrated Nonradiative Dielectric Waveguide

This letter presents a leaky-wave antenna array in the substrate integrated nonradiative dielectric (SINRD) waveguide technology. Several radiating slots are etched on the copper foil of the SINRD guide and placed with opposing tilt angles to achieve a compact configuration. After investigating the characteristic of the complex propagation constant of an SINRD guide with slots, the low sidelobe level (SLL) of a leaky-wave antenna can be synthesized. Besides, this kind of antenna can be fabricated directly on the printed circuit board substrate, which means that it can be easily integrated with other kinds of planar circuits in the millimeter-wave band. As an example, a Ka-band prototype is designed and experimented, which has –18.1 dB SLL and 12.7 dBi gain at 29.4 GHz.

SLL reduction of slot array antenna by artificial magnetic conductor side walls

A new waveguide slot array antenna with two artificial magnetic conductor (AMC) side walls is proposed. The AMC layers reflect the wave with different phase delays through the waveguide side walls which compensate the requirement of slots offset and improve the antenna gain and sidelobe level (SLL). A five slots array antenna with AMC layers is designed and measured which shows 9 dB SLL reduction and 1.5 dB gain enhancement with compact size compared with the conventional Elliot one. These results clarify the ability and capability of the proposed design approach.

Square loop slots loaded substrate integrated waveguide based horn antenna

This article represented the effective approach to improve the bandwidth and gain response of substrate integrated waveguide antenna (SIW) using novel defected microstrip structure (DMS) technique for Ku band applications. First of all, Horn antenna was designed using SIW technique and it provided gain around 6 dB. Single square loop slots and multiple square loop slots were introduced in SIW based horn antenna and performance analysis have been carried out. Their responses proved that they were not only responding the fundamental mode but also at different high order modes. Creation of multiple square loop slots not only increased bandwidth but also it increased gains more than 8.5 dB. Moreover, the proposed antennas also responding dual frequencies with more than 500 MHz bandwidth, −2 dB side-lobe levels and VSWR was around 1.35. All the structures were simulated using Ansoft high frequency structure simulator. Comparison between results verified the effectiveness of the proposed idea. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1577–1582, 2016

Omnidirectional Wideband E-Shaped Cylindrical Patch Antennas

Two novel wideband cylindrical microstrip array antennas (CMAAs) are proposed. They involve two symmetrically located probe-fed E-shaped radiating elements mounted on a cylindrical ground platform. The first design consists of two E-shaped patches located on a textile circular dielectric substrate. The second design involves a radiating element consisting of four strongly coupled E-shaped patches. For both CMAAs, the design has been performed using CST Microwave Studio. In both cases, an omnidirectional radiation pattern (ORP) in the horizontal plane with a deviation of less than 3 dB (maximum over minimum) is obtained. The two antennas are operational at 3.4 and 3.3 GHz with realized bandwidths of 33% and 21% and peak gain values of 2.98 and 4.56 dBi, respectively. A - 10 dB sidelobe level is reached in the vertical plane for the second antenna. The CMAA with the higher gain has been fabricated and measured. Above the - 10 db Breflection level, simulations and measurements are in good agreement.

Synthesis of Linear Concentric Ring Arrays with High Directivity and Low Sidelobe Levels

In this paper, intensive investigations are carried out to produce directional patterns from linear concentric ring arrays using isotropic radiators . A ring array which produces about ?8 dB sidelobe level creates a lot of Electromagnetic Interference problems. To overcome this, the concentric ring arrays are used and these produce about ?17.6 dB sidelobe level. However, these sidelobes are still high in some applications such as satellite communications, wireless communications, and broadband applications. Therefore, a linear concentric ring array is a concept introduced for optimization of the radiation patterns are found in. Using the new concept, the directional patterns are numerically evaluated for linear concentric ring arrays for different concentric rings. The data presented here found that the first sidelobe level is reduced by ?36.33 dB, null-to-null beamwidth is decreased to 6.78 degrees, and directivity is increased to 90.72 dB.

High-contrast and low-computational complexity medical ultrasound imaging using beamspace capon method.

Several adaptive beamforming techniques have been proposed to improve the quality of medical ultrasound images. The beamspace (BS) Capon method is one common method used to depict high-resolution images with low computational complexity. However, the complexity is not low enough for real-time imaging in clinical situations because the conventional BS Capon method employs a time-delay process and a transition process from elementspace signal processing to BS signal processing at all points of interest. Thus, we propose a technique that replaces the time-delay process using a steering vector. In addition, the Capon method employs a spatial averaging (SA) technique to stabilize the estimation in intensity. However, when the averaging size is not adequate, the estimated intensity might be smaller than that given by the delay-and-sum (DAS) method. Because most medical diagnoses are presented based on the estimation of intensity acquired by the DAS beamformer, accurate estimation of intensity is also required. Therefore, we propose a compensation technique that uses both small and large sizes for SA. In an experiment, the -6 dB beam width, sidelobe level, and estimation error in the intensity of the proposed method were 0.17 mm, -27 dB, and 0.92 dB, respectively, where those of the conventional BS Capon method were 0.29 mm, -22 dB, and 8.1 dB. The complexity of the proposed method is one-fourteenth that of the conventional method. Compared with conventional methods, the proposed method succeeded in depicting a higher-contrast image with accurate intensity estimation and lower computational complexity.

Design of a Bifocal Single Reflectarray Antenna with Improving Beam Scanning Performance

A novel scheme is introduced to design the high gain beam scanning reflectarray antennas for limited scan range application. At first, various existing schemes for beam scanning reflectarray antennas design are reviewed and it is concluded that as a convenient design scheme, the feed displacement technique is preferred for limited scan range applications. In order to improve the scan range, a bifocal single reflector aperture phase is introduced for reflectarray aperture phase design, and in order to further improve the performance, a circular path for feed displacement is introduced to take the place of the conventional lateral path. Based on the introduced scheme, a Ku band bifocal single reflectarray antenna is designed for limited scan range application. The scan performances of the designed reflectarray are analyzed numerically and compared with conventional parabolic design. Numerical results show that the bifocal design shows significant improved scan performance with less 0.8 dB gain loss and lower than -13 dB side lobe level over entire scan range -30° to +30°, which illustrates that the bifocal design for limited field of view beam scanning reflectarray is a promising attempt.

A Switched Beam Antenna With Shaped Radiation Pattern and Interleaving Array Architecture

A six-beam switched beam antenna (SBA), whose beam patterns are shaped in the azimuth plane, is designed and fabricated. A synthesis method, which is based on a four-elements array and can generate a flat-top beam pattern with 46° flat gain region (gain fluctuation within ±0.5 dB), 60° 3-dB beam width, and less than -20.1 dB side lobe level (SSL), is proposed. By combining six of those beams together, the proposed SBA can provide near consistent gain and good interference rejection in the azimuth plane. Meanwhile, an interleaving array architecture, which minimizes the size of the proposed array, is also implemented. To extend the beam coverage, a series-fed in-phase array with tapered amplitude distribution is introduced in the elevation plane. The peak gain of the beam reaches 16.6 dB, and the SLL is controlled under -23.2 dB in this plane.

Switched‐beam array of dielectric rod antenna with RF‐MEMS switch for millimeter‐wave applications

AbstractA conformal dielectric rod antenna array with operating frequency of 11.2 GHz is investigated, designed, and measured. This antenna array is combined with a single pole double throw radio frequency microelectromechanical systems (RF‐MEMS) switch to realize switched‐beam performance. Moreover, this antenna array exhibits uniform radiation performance for different scan angles with no grating lobes. The characterization and measurement of the antenna system have been performed. The measured radiation pattern of the antenna in the anechoic chamber is in good agreement with the simulated antenna pattern. The measured antenna with the RF‐MEMS switch has 13.5 dBi realized gain, −15 dB sidelobe level, 22° half‐power beamwidth, and 7.3% (fractional) bandwidth (or 800 MHz) at 11.2 GHz.

An Opportunistic Array Beamforming Technique Based on Binary Multiobjective Wind Driven Optimization Method

We present a novel binary version of multiobjective wind driven optimization (WDO) for emitted beamforming of opportunistic array radar, which is assumed as a multiobjective optimization problem. Firstly, the emitted signal model and objective functions of optimization are presented. Then the algorithm proposes a new definition of the position vector of air parcel, and brings a good discretization interpretation of continuous WDO. For multiobjective optimization, the grey relational grade (GRG) is then used to measure the similarity between the best two solutions for these two objectives. The best pressure locations with the maximum GRG will be recorded as the best two candidate solutions to the problem, and a final optimization result will be selected according to the importance of the two objectives. Finally, the proposed improved WDO has been applied for the optimal design of beamforming of the opportunistic antenna array, which needs a trade-off between the 3 dB main beam width and sidelobe level. The simulation results show that the proposed method outperforms conventional particle swarm optimization (PSO) in the optimal beamforming by achieving more reduction in the sidelobe level and saving more runtime.

High-Isolation X-Band Marine Radar Antenna Design

This paper presents a high-isolation printed antenna array for marine radar applications. The antenna array is composed of 32 identical square microstrip patches operated at a center frequency of 9.35 GHz and includes a 100-MHz bandwidth (subject to a 1.5:1 voltage standing wave ratio [VSWR]). The patch antennas are arranged in four arms, each of which contains eight elements and is series-fed using Chebyshev tapering (25 dB side-lobe level). To apply the antenna in marine radar applications, an antenna with horizontal polarization was employed because, in comparison with vertical polarization, it can relatively reduce the sea clutter reflectivity. Therefore, a slit was carved on each patch element to change the current path, thereby enabling horizontal polarization. The antenna gain, 3-dB beamwidth, side-lobe level, and front-to-back ratio were 22 dBi, 5.3 °, 26.4 dB, and 38.5 dB, respectively. Additionally, metallic baffles were introduced for increasing the isolation between the transmitting and receiving antennas to 60 dB .

Excitation Control Method for a Low Sidelobe SIW Series Slot Array Antenna With 45$^{\circ}$ Linear Polarization

A sidelobe suppression method for a series slot array antenna which radiates 45° -inclined linear polarization is proposed. Axial displacements are employed to create arbitrary excitation coefficients for individual centered-inclined radiating slots along the center line of a broad wall. To verify the proposed design method, we design two types of center-fed linear slot array antennas with a Dolph-Chebyshev distribution for -20 dB and -26 dB sidelobe levels (SLLs) in the Ka band. Furthermore, a cross-validation process involving an equivalent circuit model analysis and electromagnetic full-wave simulation using CST MWS is utilized. The entire structure of the proposed series slot array antenna is fabricated on printed circuit boards (PCBs), including drilling and chemical etching, to secure advantages of miniaturization and cost reduction. The measured realized gains are 15.17 and 15.95 dBi and SLLs are -18.7 and -22.5 dB respectively for two types of fabricated antennas. It demonstrates the validity of the proposed sidelobe suppression method.

Millimeter-Wave Shaped-Beam Substrate Integrated Conformal Array Antenna

A millimeter-wave shaped-beam substrate integrated conformal array antenna is demonstrated in this paper. After discussing the influence of conformal shape on the characteristics of a substrate integrated waveguide (SIW) and a radiating slot, an array mounted on a cylindrical surface with a radius of 20 mm, i.e., 2.3 λ, is synthesized at the center frequency of 35 GHz. All components, including a 1-to-8 divider, a phase compensated network and an 8 × 8 slot array are fabricated in a single dielectric substrate together. In measurement, it has a - 27.4 dB sidelobe level (SLL) beam in H-plane and a flat-topped fan beam with -38 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> ~ 37 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> 3 dB beamwidth in E-plane at the center frequency of 35 GHz. The cross polarization is lower than -41.7 dB at the beam direction. Experimental results agree well with simulations, thus validating our design. This SIW scheme is able to solve the difficulty of integration between conformal array elements and a feed network in millimeter-wave frequency band, while avoid radiation leakage and element-to-element parasitic cross-coupling from the feed network.

High-Efficiency Periodic Sparse Microstrip Array Based on Mutual Coupling

In this paper, a novel idea to reduce the number of active elements in a large periodic array is presented and demonstrated firstly by an $E$ -plane microstrip array. High aperture efficiency can be achieved by making use of mutual coupling between array elements, and then the total production cost of the array is greatly decreased by reducing the number of active array elements and associated components. A simple way to control the mutual coupling of the microstrip array is given as an example in this paper. Simulations and measurements show that when the active element spacing is as large as $1.6\lambda_{0}$ ( $\lambda_{0}$ is the free-space wavelength at the operating frequency), a $-$ 18.3 dB side lobe level (SLL) and an approximately equal aperture efficiency can be achieved. No obvious performance degradations are found compared to a conventional array with half the element spacing $(0.8\lambda_{0})$ and an identical total size. Then, simulations and measurements of an $H$ -plane sparse array are given based on the same idea, followed by the simulated results of a planar two-dimensional (2-D) one.

Compact Wideband Corrugated Feedhorns With Ultra-Low Sidelobes for Very High Performance Antennas and Quasi-Optical Systems

The corrugated or scalar feedhorn has found many applications in millimeter wave and sub-millimeter wave systems due to its high beam symmetry, relatively low sidelobe levels and strong coupling to the fundamental mode Gaussian beam. However, for applications such as millimeter wave cosmology, space-based experiments, or even high performance imaging, there is a generic requirement to reduce the size of horns whilst maintaining very high levels of performance. In this paper we describe a general analytic methodology for the design of compact dual-profiled corrugated horns with extremely low sidelobe levels. We demonstrate that it is possible to achieve -50 dB sidelobe levels, over wide bandwidths with short horns, which we believe represents state-of-the-art performance. We also demonstrate experimentally a simple scalar design that operates over wide bandwidths and can achieve sidelobes of better than -40 dB, whilst maintaining a frequency independent phase center. This design methodology has been validated experimentally by the successful manufacture and characterization of feedhorns at 94 GHz and 340 GHz for both radar and quasi-optical instrumentation applications.

An X-Band Reflectarray With Novel Elements and Enhanced Bandwidth

A novel single-layer reflectarray element with an I-shaped dipole encompassed by a circular ring, showing smooth phase-frequency response, is proposed in this letter. Based on this element, an optimization method is adopted to match the desired phase delays at two edge frequencies so as to get fixed phase difference between two adjacent elements in the optimized band. A low-profile X-band 6 × 10-element reflectarray with a scattering angle of 30° for normal incidence of plane waves is designed and fabricated. Simulations and measurements show that a bandwidth of 22.3% for 3 dB directivity dropping and 15.2% for -10 dB sidelobe level (SLL) can be achieved.

도파관 슬롯 배열 안테나용 리지가 장하된 끝이 둥근 소형 슬롯

본 논문에서는 도파관 슬롯 배열 안테나의 요소로서 구형 도파관 광벽에 위치하고 이중 리지가 장하된 끝이 둥근 소형 슬롯을 제안하였다. 리지 치수를 적절히 조절하면 원하는 주파수에서 슬롯의 공진을 얻을 수 있다. 제안된 슬롯의 공진 길이는 공진 주파수에서 약 <TEX>$0.26{\lambda}_0$</TEX>(자유 공간 파장)이다. 제안된 공진 슬롯은 소형이고, 작은 공진 컨덕턴스 그리고 짧으면서도 안정된 공진 길이 등의 장점을 가진다. 부가적으로 슬롯을 도파관 슬롯 배열에 적용할 때 각 슬롯의 특성들이 인접한 슬롯에 의해서 영향을 적게 받는다. 부엽 준위 -20 dB를 가지는 <TEX>$4{\times}1$</TEX> 도파관 슬롯 배열 안테나를 설계, 제작한 후 실험하였다. 측정결과들이 시뮬레이션 결과들과 잘 일치하고, 주파수 9.41 GHz에서 부엽 준위 -15.9 dB, E-평면 반치각 <TEX>$110.2^{\circ}$</TEX>, H-평면 반치각 <TEX>$21.2^{\circ}$</TEX>이다. In this paper, a small round-ended slot loaded by double ridges on the broad wall of a rectangular waveguide is presented as an element for a waveguide slot-array antenna(WSAA). By properly adjusting the ridge dimension, a resonance of the slot at a desired frequency can be achieved. The resonant length of the proposed slot is about <TEX>$0.26{\lambda}_0$</TEX>(free space wave length) at the resonance frequency. The proposed resonant slot has some advantageous properties, such as small size, small resonant conductance, and short and stable resonant slot length. In addition, the characteristics of the slots are slightly affected by the adjacent elements when the slots are arrayed for a waveguide slot antenna. A <TEX>$4{\times}1$</TEX> WSAA with -20 dB side-lobe level(SLL) is designed, fabricated, and tested experimentally. The measured results are well agreed with the simulated ones and have an SLL of -15.9 dB and a half-power beam width of <TEX>$110.2^{\circ}$</TEX> in the E-plane and <TEX>$21.2^{\circ}$</TEX> in the H-plane, respectively, at 9.41 GHz.

Gain Improvement in Time-Modulated Linear Arrays Using SPDT Switches

Time-modulated linear arrays (TMLAs) based on single-pole-single-throw (SPST) switches usually have higher reduction in gain due to the sideband radiation and power absorption of the off-state absorptive switches. In this letter, a novel approach is proposed to improve the gain of TMLAs using single-pole-double-throw (SPDT) switches. The gain of the proposed TMLA can be improved significantly by controlling two array elements with each SPDT switch. Moreover, the proposed TMLA has a constant instantaneous directivity, which is favorable for some applications. Numerical results are presented to illustrate the proposed approach by considering a 16-element linear array with a -30 dB sidelobe level.