Far-field Pattern Measurements Research Articles

A 10 × 10 deep ultraviolet light-emitting micro-LED array

In this work, we design and fabricate a deep ultraviolet (DUV) light-emitting array consisting of 10 × 10 micro-LEDs (μ-LEDs) with each device having 20 μm in diameter. Strikingly, the array demonstrates a significant enhancement of total light output power by nearly 52% at the injection current of 100 mA, in comparison to a conventional large LED chip whose emitting area is the same as the array. A much higher (~22%) peak external quantum efficiency, as well as a smaller efficiency droop for μ-LED array, was also achieved. The numerical calculation reveals that the performance boost can be attributed to the higher light extraction efficiency at the edge of each μ-LED. Additionally, the far-field pattern measurement shows that the μ-LED array possesses a better forward directionality of emission. These findings shed light on the enhancement of the DUV LEDs performance and provide new insights in controlling the light behavior of the μ-LEDs.

Design of Multi-Functional Transmitarray with Active Linear Polarization Conversion and Beam Steering Capabilities

This study designed a multi-functional reconfigurable transmitarray with switchable polarization and beam steering capabilities using only a PIN diode having ON/OFF switching ability. The simulation confirmed that the proposed architecture is capable of 2D beam scanning of up to ±45° for elevation and azimuth while maintaining or converting linear polarization when operating within the X-band. The performance was verified through a far-field beam pattern measurement using the near-field antenna measurement system by producing a transmitarray with an 8 × 8 unit cell arrangement. The maximum level of gain of the proposed architecture was confirmed to be 14.5 dBi, the sidelobe level was below 14.5 dBc, the polarization converting loss was below 1.28 dB, and the polarization isolation level was above 14.7 dB. It can be utilized for the design technique of a radar system demanding small size, weight, power, and cost (SWaP-C) characteristics based on a simplified composition.

Experimental demonstration of mode selection in bridge-coupled metallo-dielectric nanolasers.

We experimentally demonstrate bridge-coupled metallo-dielectric nanolasers that can operate in the in-phase or out-of-phase locking modes at room temperature. By varying the length of the bridge, we show that the coupling coefficients can be realized in support of the stable operation of any of these two modes. Both coupled nanolaser designs have been fabricated and characterized for experimental validation. Their lasing behavior has been confirmed by the spectral evolution, light-in light-out characterizations, and emission linewidth narrowing. The operating mode is identified from the near-field and far-field emission pattern measurements. To the best of our knowledge, this is the first demonstration of mode selection in bridge-coupled metallo-dielectric nanolasers, which can serve as building blocks in nanolaser arrays for applications in imaging, virtual reality devices, and lidars.

Modal decomposition of fiber modes based on direct far-field measurements at two different distances with a multi-variable optimization algorithm.

We present a novel method for modal decomposition of a composite beam guided by a large-mode-area fiber by means of direct far-field pattern measurements with a multi-variable optimization algorithm. For reconstructing far-field patterns, we use finite-number bases of Hermite Gaussian modes that can be converted from all the guided modes in the given fiber and exploit a stochastic parallel gradient descent (SPGD)-based multi-variable optimization algorithm equipped with the D4σ technique in order for completing the modal decomposition with compensating the centroid mismatch between the measured and reconstructed beams. We measure the beam intensity profiles at two different distances, which justifies the uniqueness of the solution obtained by the SPGD algorithm. We verify the feasibility and effectiveness of the proposed method both numerically and experimentally. We have found that the fractional error tolerance in terms of the beam intensity overlap could be maintained below 1 × 10-7 and 3.5 × 10-3 in the numerical and experimental demonstrations, respectively. As the modal decomposition is made uniquely and reliably, such a level of the error tolerance could be maintained even for a beam intensity profile measured at a farther distance.

Fast Measurement of Single-Cut Far-Field Patterns at Quasi-Far-Field Distance for Linear Antenna Array of Any Polarization

Corrected method for fast measurement of single-cut Far-Field (FF) pattern at Quasi-Far-Field (QFF) distance for linear antenna array of any polarization by two orthogonal measurements has been proposed in this paper. The analytical equations were deduced based on cylindrical wave expansion (CWE). The required measurement distance of proposed method don’t need to satisfy the FF condition of the antenna under test (AUT), only need to satisfy the FF region of small dimension of the AUT, so it is in the Quasi-Far-Field (QFF) of another large dimension, which makes the process same as FF measurements. Therefore, the introduced method is especially applicable to arbitrary polarized antennas with one dimension large, and another dimension small. 45° linearly polarized and circularly polarized antenna array were simulated to prove the proposed method, the corrected results using the presented algorithm are consistent with the theoretical results.

Strategically constructed patterned sapphire with silica array to boost substrate performance in GaN-based flip-chip visible light-emitting diodes

A strategically constructed substrate, patterned sapphire with silica array (PSSA), was developed to boost the efficiency of patterned sapphire substrate (PSS) in GaN-based light-emitting diodes (LEDs) application. The light output power of a flip-chip LED on PSSA improved by 16.5% at 120 mA than that of device grown on PSS. The XRD and STEM measurements revealed that the GaN epilayer grown on PSSA had better crystalline quality compared to the epilayer grown on PSS, which was the result of decreased misfit at coalescence boundary in the PSSA case. Moreover, the light extraction efficiency of the flip-chip LED on PSSA was significantly enhanced, benefiting from the small refractive-index contrast between the patterned silica array and air. This small refractive-index contrast also contributed to a more convergent emission pattern for the flip-chip LED on PSSA, as demonstrated by the far-field radiation pattern measurements. The discovery that PSSA could excel at defect suppression and light extraction revealed a new substrate platform for III-nitride optoelectronic devices.

Reconstruction of Antenna Radiation Pattern Based on Compressed Sensing

The measurement of the far-field radiation pattern is an important factor in describing the characteristics of the antenna. The measurement process is time consuming and expensive. Therefore, this paper proposes a novel method to reduce the number of samples required for radiation pattern measurement by adopting compressed sensing theory. This method reconstructs the radiation pattern from data measured by a few sensors, and the positions of these sensors are generated via the m-sequence. Simulation results demonstrate that the proposed algorithm can effectively reconstruct the complete radiation pattern by using the 50% samples.

An effective numerical strategy for retrieving all characteristic parameters of an elastic scatterer from its FFP measurements

A new computational strategy is proposed for determining all elastic scatterer characteristics including the shape, the material properties (Lamé coefficients and density), and the location from the knowledge of far-field pattern (FFP) measurements. The proposed numerical approach is a multi-stage procedure in which a carefully designed regularized iterative method plays a central role. The adopted approach is critical for recognizing that the different nature and scales of the sought-after parameters as well as the frequency regime have different effects on the scattering observability. Identification results for two-dimensional elastic configurations highlight the performance of the designed solution methodology.

Design and analysis of a quad‐band substrate‐integrated‐waveguide cavity backed slot antenna for 5G applications

A planar and compact substrate integrated waveguide (SIW) cavity backed antenna and a 2 × 2 multi-input multi-output (MIMO) antenna are presented in this study. The proposed antenna is fed by a grounded coplanar waveguide (GCPW) to SIW type transition and planned to be used for millimeter-wave (mm-wave) fifth generation (5G) wireless communications that operates at 28, 38, 45, and 60 GHz frequency bands. Moreover, the measured impedance bandwidth (|S11| ≤ − 10 dB) of the antenna covers 27.55 to 29.36, 37.41 to 38.5, 44.14 to 46.19, and 57.57 to 62.32 GHz bands and confirms the quad-band characteristic. Omni-directional radiation characteristics are observed in the far-field radiation pattern measurements of the antenna over the entire operating frequency. The reported antenna is compact in size (9.7 × 13.3 × 0.6 mm3) and the gain values at each resonance frequency are measured as 3.26, 3.28, 3.34, and 4.51 dBi, respectively. Furthermore, the MIMO antenna performance is evaluated in terms of isolation, envelope correlation coefficient and diversity gain.

Ultrabroadband Three-Dimensional Printed Radial Perfectly Symmetric Gradient Honeycomb All-Dielectric Dual-Directional Lightweight Planar Luneburg Lens

An ultrabroadband all-dielectric planar Luneburg lens has been designed and fabricated in this study, which is in the form of a radial gradient lightweight honeycomb column. Because of the novel design of a radial symmetric honeycomb-like microstructure in the subwavelength dimension and the radial gradient configuration according to the refractive index distribution of Luneburg lens, the present lens can focus incident plane waves on the opposite side with high convergence, and its operating frequency range is rather broadband, spanning from 6 to 16 GHz. Besides, the all-dielectric honeycomb-like lens is lightweight with a mass density of 0.23 g/cm3, and its broadband transmittance is higher than the reported cases consisting of metallic metamaterial or gradient photonic crystal structures. A prototype of the lens is fabricated by using 3D printing techniques, on which the electric near-field distribution and far-field radiation pattern measurements have been carried out, and the aforementioned performances were demonstrated experimentally. It was also observed that for two point sources placed at the edge of the lens whose intersection angle with the center of the lens is 90°, the far-field radiation pattern was still kept highly directional, which means that the lens can generate two highly directional beams simultaneously, and is an efficient double input-double output device.

Gain Enhancement of Single-Mode Cr-Doped Core Fibers by Online Growth System

Gain enhancement of single-mode Cr-doped crystalline core fiber (SMCDCCF) with longer fiber length fabricated by online laser-heated pedestal growth (LHPG) technique is demonstrated. In comparison with the SMCDCCF fabricated without online growth, the online technique enables real-time monitoring and controlling small molten zone in the LHPG to achieve longer length with better uniformity and smaller core diameter of the SMCDCCFs. The SMCDCCF exhibits a length of 10.6 cm, a core diameter of 25 mu m, and a V-value of 2.40, which confirms the LP01 single-mode operation by the far-field pattern measurement. A 3.9-dB gross gain and a 1.9-dB net gain of the SMCDCCF at the wavelength of 1400 nm were obtained. The gross and net gains are the highest yet reported of the SMCDCCFs. Further development on higher gain of the SMCDCCF may be functioned the SMCDCCF as a broadband fiber amplifier for use in the next-generation fiber transmission systems.

Printed Slot Loaded Bow-Tie Antenna With Super Wideband Radiation Characteristics for Imaging Applications

A super wideband printed modified bow-tie antenna loaded with rounded-T shaped slots fed through a microstrip balun is proposed for microwave and millimeter-wave band imaging applications. The modified slot-loaded bow-tie pattern increases the electrical length of the bow-tie antenna reducing the lower band to 3.1 GHz. In addition, over the investigated frequency band up to 40 GHz, the proposed modified bow-tie pattern considerably flattens the input impedance response of the bow-tie resulting in a smooth impedance matching performance enhancing the reflection coefficient (S11) characteristics. The introduction of the modified ground plane printed underneath the bow-tie, on the other hand, yields to directional far-field radiation patterns with considerably enhanced gain performance. The S11 and E-plane/H-plane far-field radiation pattern measurements have been carried out and it is demonstrated that the fabricated bow-tie antenna operates across a measured frequency band of 3.1-40 GHz with an average broadband gain of 7.1 dBi.

New trends in antenna design: transformation optics approach

Transformation optics is an emerging field offering a powerful and unprecedented ability to manipulate and control electromagnetic waves. Using this tool, we demonstrate the design of novel antenna concepts by tailoring their radiation properties. The wave manipulation is enabled through the use of engineered dispersive composite metamaterials that realize a space coordinate transformation. Numerical simulations together with experimental measurements are performed in order to validate the coordinate transformation concept. Near-field cartography and far-field pattern measurements performed on fabricated prototypes agree qualitatively with Finite Element Method (FEM) simulations. It is shown that a particular radiation pattern can be tailored at ease into a desired one by modifying the electromagnetic properties of the space around the radiating element. This idea opens the way to novel antenna design techniques for various application domains such as aeronautical and transport fields.

Novel antenna concepts via coordinate transformation

Coordinate transformation is an emerging field which offers a powerful and unprecedented ability to manipulate and control electromagnetic waves. Using this tool, we demonstrate the design of novel antenna concepts by tailoring their radiation properties. The wave manipulation is enabled through the use of engineered dispersive composite metamaterials that realize the space coordinate transformation. Three types of antennas are considered for design: a directive, a beam steerable and a quasi-isotropic one. Numerical simulations together with experimental measurements are performed in order to validate the coordinate transformation concept. Near-field cartography and far-field pattern measurements performed on a fabricated prototype agree qualitatively with Finite Element Method (FEM) simulations. It is shown that a particular radiation pattern can be tailored at ease into a desired one by modifying the electromagnetic properties of the space around radiator. This idea opens the way to novel antenna design techniques for various application domains such as the aeronautical and transport fields.

Continuously Polarization Agile Antenna by Using Liquid Crystal-Based Tunable Variable Delay Lines

In this paper, a polarization agile planar antenna is presented by using tunable liquid crystal (LC) material. The antenna includes a 2 × 2 dual-fed microstrip patch array and two separate feeding networks for each feeding of the dual-fed antenna. The polarization state of the antenna can be controlled continuously between dual linear and dual circular polarizations depending on a differential phase shift between the antenna feedings. The feeding networks are implemented in inverted microstrip line topology with the liquid crystal material as a tunable dielectric. A desired differential phase shift is obtained between the feeding networks by tuning the LC material. Thus, no additional tunable components are required according to proposed antenna topology. Additionally, owing to the continuous tuning of the LC material, any polarization state between the circular and linear ones are achievable. The antenna prototype is designed at 13.75 GHz. The measured return losses are greater than 10 dB in a frequency range of 13.5 to 15 GHz for different polarization states. Far-field pattern measurements are performed, which confirm the continuous tuning of the antenna polarization. Specifically, the measured antenna patterns are presented for ±45° linear and right-handed circular polarizations. The prototype can be fabricated in a larger size with more radiating elements and can be efficiently scaled for higher operating frequencies at the Ka-or W-band since the LC material features even lower dielectric losses at higher frequencies.

Radiation Model for Terahertz Transmission-Line Metamaterial Quantum-Cascade Lasers

We present the use of the cavity antenna model in predicting the radiative loss, far-field polarization and far-field beam patterns of terahertz quantum-cascade (QC) lasers. Metal–metal waveguide QC-lasers, transmission-line metamaterial QC-lasers, and leaky-wave metamaterial antennas are considered. Comparison of the fundamental and first higher order lateral mode in a metal-metal waveguide QC-laser shows distinct differences in the radiation characteristics. Full-wave finite-element simulations, cavity model predictions and measurements of far-field beam patterns are compared for a one-dimensional leaky-wave antenna. Lastly, an active leaky-wave metamaterial antenna with full backward to forward wave beam steering is proposed and analyzed using the cavity antenna model.

합/차/부엽 억제 채널을 갖는 모노펄스 보조 감시 레이더(용) 안테나

본 논문에서는 레이더 표적의 피아 식별을 위해 일반적으로 사용되는 모노펄스 보조 감시 레이더용 안테나의 개발 방안 및 결과를 제시하였다. 개발된 안테나는 수동 선형 배열 안테나로서 횡급전기와 다수의 배열 소자로 구성된다. 횡급전기는 포트별로 전력 및 위상비가 최적화된 합, 차 및 부엽 억제 채널을 제공하며, 19개의 배열 소자와 1개의 후방 배열 소자와 연결되어 방위각 방향으로 빔 패턴을 형성한다. 합 채널 빔 패턴의 방위각 최대 부엽 수준은 -20 dBc 이하이며, 부엽 억제 채널 빔 패턴은 합 채널 빔 패턴의 주 빔 이외의 전 영역에서 부엽을 덮도록 한다. 그리고 차 채널 빔 패턴은 방위각 방향의 탐지 정확도를 높이기 위한 모노펄스 기능에 사용된다. 한편, 배열 소자는 고각 방향으로 성형 빔(shaped-beam)을 형성하여 지면으로부터의 강한 클러터 영향 및 다중경로 효과를 억제할 수 있도록 하였다. 개발된 안테나는 산란계수 측정 및 원전계 빔 패턴 시험을 통해 주어진 개발 규격을 모두 잘 만족하는 것을 확인하였다. In this paper, development of the monopulse secondary surveillance radar antenna which can be used for IFF system is presented. This antenna that is passive linear array is comprised of the row-feeder and several array-elements. The row-feeder provides sum, different and SLS(Sidelobe Supression) channels which are optimized the distribution of the power and phase ratio. The azimuthe sidelobe level of the sum channel beam pattern is -20 dBc or less. The SLS channel covers the sidelobe of the sum-chanel in the whole azimuth angle range. And the difference channel is used to perform the mono-pulse function, improves the detection accuracy in the azimuth direction. Meanwhile, the arrayelement makes shaped beam in the elevation angle, in order to eliminate the clutter and multipath effects from the ground. Performance of the antenna developed is verified by the measurement of S-parameters and far-field beam pattern, and satisfies all of the development specifications well.

Multi-frequency orthogonality sampling for inverse obstacle scattering problems

We discuss a simple non-iterative method to reconstruct the support of a collection of obstacles from the measurements of far-field patterns of acoustic or electromagnetic waves corresponding to plane-wave incident fields with one or few incident directions at several frequencies. The method is a variant of the orthogonality sampling algorithm recently studied by Potthast (2010 Inverse Problems 26 074015). Our theoretical analysis of the algorithm relies on an asymptotic expansion of the far-field pattern of the scattered field as the size of the scatterers tends to zero with respect to the wavelength of the incident field that holds not only at a single frequency, but also across appropriate frequency bands. This expansion suggests some modifications to the original orthogonality sampling algorithm and yields a theoretical motivation for its multi-frequency version. We illustrate the performance of the reconstruction method by numerical examples.

A multi-step procedure for enriching limited two-dimensional acoustic far-field pattern measurements

Abstract We propose a three-step solution methodology to increase the discrete set of acoustic far-field pattern (FFP) measurements, available in a small range of observation angles (small aperture). The first two steps of the proposed procedure allow the extension of the data to an aperture larger than π/2. They use a regularized Newton algorithm where the total variation of the FFP is incorporated as a regularization term. The third step consists in applying the standard Tikhonov regularization technique to recover the full aperture of the FFP from the previously extended field. Numerical results obtained using synthetic data illustrate the potential of the proposed procedure for reconstructing the full aperture of the FFP from data given in an aperture as small as backscattering measurements.

GaN Thickness Effect on Directional Light Enhancement from GaN-Based Film-Transferred Photonic Crystal Light-Emitting Diodes

Directional light enhancement behavior including collimated far-field patterns sensitively depending on both photonic crystal (PhC) lattice constant and GaN thickness from GaN film-transferred light-emitting diodes (FTLEDs) with a triangular PhC lattice has been experimentally studied. Far-field pattern measurement in the Γ–M and Γ–K directions of GaN PhC FTLEDs with various lattice constants and GaN thicknesses revealed different far-field profiles as detemined on the basis of guided mode extraction of Bragg's diffraction. Additionally, three-dimensional (3D) far-field measurement revealing the PhC diffraction patterns was also demonstrated. We also used the 3D finite-different time-domain method to confirm the experimental results.