Absorption properties of shoal-dominated waters in the Atchafalaya Shelf,Louisiana, USA

Spectral absorption coefficients of coloured dissolved organic matter (a _CDOM(λ)) and particulate matter (a _p(λ)) (phytoplankton (a _PHY(λ)) plus non-algal particles (a _NAP(λ)), measured on the shoal-dominated region off the Atchafalaya River (AR) Shelf, Louisiana, USA, are analysed, and their effect on chlorophyll-a retrievals from ocean-colour sensors examined. Compared to a _CDOM(λ) and a _NAP(λ), a _PHY(λ) is relatively constant, with a _CDOM(λ) and a _NAP(λ) varying by approximately 1.2 and 1.8 times as much as a _PHY(λ) at 443 nm, respectively. The specific a _PHY(λ) (a*_PHY(λ)) ranges from 0.006 to 0.0612 m^?2(mg chla)^?1 at 443 nm, which indicates a pigment-packaging effect or a variation in pigment composition. The a _NAP(λ) accounts for approximately 3–93% of a _p(λ) at 443 nm, with a higher contribution to a _p(λ) during an October 2007 cruise (62–93%) as compared to an August 2007 cruise (31–89%). Our results indicate that a _CDOM(λ) and a _NAP(λ) collectively dominate light absorption, even at higher wavelengths where their effect is expected to be minimal. In situ and satellite data match-up of chlorophyll-a yield root-mean square errors of 2.17 and 2.62 for the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the Medium Resolution Imaging Spectrometer (MERIS), respectively. The non-covarying a _CDOM(λ) and a _NAP(λ), along with variable a*_PHY(λ), greatly influenced the remote retrieval of biogeochemical variables using satellite ocean-colour algorithms in this region.     

Single-wavelength algorithms for in situ or remote sensing estimation of mean pigment concentration

The bio-optical relationships between inherent and apparent optical properties, and between optical properties and phytoplankton pigment concentration (C) averaged in a layer (ΔZ), were derived from analysis of data collected during the period 1996–1998 in the Gulf of Aqaba (Eilat). Parametrization of these relationships was based on radiative transfer theory, Gershun's equation, minimization of model errors by least-square fitting, and on known optical models relating underwater remote sensed reflectance (R _rsw) with the ratio of backscattering (b _b) to vertical attenuation coefficient (K _d) [or to absorption coefficient (a)]. These relationships explain a frequently used form of remote sensing algorithms for C estimation using ratio of water-leaving radiances measured at two or more wavelengths (λ). In this study, the possibility of using for this purpose a single wavelength in the blue range (λ=443?nm) within the framework of in situ and remote sensing algorithms for Case 1 waters was assessed.     

Spectral unmixing of multiple lichen species and underlying substrate

Cryptogamic covers are a wide range of photoautotrophic plants which synthesize their own food while using sunlight as an energy source. Globally, cryptogrammic covers (such as cyanobacteria, algae, fungi, lichens, and bryophytes) annually uptake about 7% of the net primary production of terrestrial vegetation and account for about half of annual biological terrestrial nitrogen fixation. On the basis of these contributions to global carbon and nitrogen cycling, it is crucial to be able to accurately monitor seasonal and regional patterns of cryptogamic cover distribution and abundance. However, lichen-encrusted rock seldom comprises 100% of the ground cover within a pixel of remote-sensed imagery, and thereby arise challenges in lichen mapping and monitoring. Here we explore spectroscopic methods and spectral mixture analysis (SMA) to overcome the challenges of reflectance spectroscopy-based optical remote sensing detection and characterization of crustose lichen species. One suite of discrete wavelengths (λ₁ = {400, 470, 520, 570, 680, 800, 1080, 1120, 1200, 1300, 1470, 1670, 1750, 2132, 2198, 2232 nm}) and two wavelength regions (λ₂ = {λ: 800 nm ≤ λ ≤ 1300 nm} and λ₃ = {λ: 2000 nm ≤ λ ≤ 2400 nm}) were investigated for their ability to discriminate between substrate and different lichen species. We found that the spectral region 800–1300 nm performed best at lichen-substrate differentiation and interspecial lichen differentiation. Furthermore, measures of central tendency from multiple wavelength regions are superior to most individual wavelength regions, particularly for lichen-rock unmixing.     

Cluster analysis of hyperspectral optical data for discriminating phytoplankton pigment assemblages in the open ocean

Optical measurements including remote sensing provide a potential tool for the identification of dominant phytoplankton groups and for monitoring spatial and temporal changes in biodiversity in the upper ocean. We examine the application of an unsupervised hierarchical cluster analysis to phytoplankton pigment data and spectra of the absorption coefficient and remote-sensing reflectance with the aim of discriminating different phytoplankton assemblages in open ocean environments under non-bloom conditions. This technique is applied to an optical and phytoplankton pigment data set collected at several stations within the eastern Atlantic Ocean, where the surface total chlorophyll-a concentration (TChla) ranged from 0.11 to 0.62 mg m^− 3. Stations were selected on the basis of significant differences in the ratios of the two most dominant accessory pigments relative to TChla, as derived from High Performance Liquid Chromatography (HPLC) analysis. The performance of cluster analysis applied to absorption and remote-sensing spectra is evaluated by comparisons with the cluster partitioning of the corresponding HPLC pigment data, in which the pigment-based clusters serve as a reference for identifying different phytoplankton assemblages. Two indices, cophenetic and Rand, are utilized in these comparisons to quantify the degree of similarity between pigment-based and optical-based clusters. The use of spectral derivative analysis for the optical data was also evaluated, and sensitivity tests were conducted to determine the influence of parameters used in these calculations (spectral range, smoothing filter size, and band separation). The results of our analyses indicate that the second derivative calculated from hyperspectral (1 nm resolution) data of the phytoplankton absorption coefficient, a_ph(λ), and remote-sensing reflectance, R_rs(λ), provide better discrimination of phytoplankton pigment assemblages than traditional multispectral band-ratios or ordinary (non-differentiated) hyperspectral data of absorption and remote-sensing reflectance. The most useful spectral region for this discrimination extends generally from wavelengths of about 425-435 nm to wavelengths within the 495-540 nm range, although in the case of phytoplankton absorption data a broader spectral region can also provide satisfactory results.     

Mapping aerosol optical thickness and water-leaving signals using an improved NIR/SWIR switching atmospheric correction model: A case study in the Bohai Sea

In this study, the performance of the near-infrared & short wave infrared switching atmospheric correction (NSSAC) model in estimating remote sensing reflectance (R_rs(λ)) and aerosol optical thickness at 869 nm (τ_a(869)) were assessed by field measurements taken in the Bohai Sea. It was found that the NSSAC model had approximately 30% uncertainty for retrievals of R_rs(λ) in the green regions but provided approximately 50% uncertainty for estimations of τ_a(869) and R_rs(λ) at all other moderate resolution imaging spectroradiometer (MODIS) visible wavelengths. Therefore, an optimised method is proposed for optimizing the retrieval results of the NSSAC model; it was validated using the field measurements collected from the Oujiang River estuary. The results show that the performance of the NSSAC model for τ_a(869) and R_rs(λ) at the blue, red, and near-infrared bands was greatly improved by using the optimised NSSAC model. Moreover, the study also finds that the τ_a(869) shows a large variation in the Bohai Sea, decreasing from coastal to offshore regions. The monthly average τ_a(869) has a maximum at February and August. Due to the imperfect atmospheric correction procedure, the NSSAC model-derived R_rs(λ) is always larger than those of the field measurements. Future work is needed to minimise the detected water-leaving signals in the short wave infrared (SWIR) images.     

Estimation of chlorophyll-a concentration in coastal waters with HJ-1A HSI data using a three-band bio-optical model and validation

Accurate assessment of phytoplankton chlorophyll-a (chl-a) concentration in turbid waters by means of remote sensing is challenging because of the optical complexity of case 2 waters. We applied a bio-optical model of the form [R^–1(λ₁) – R^–1(λ₂)](λ₃), where R(λ_i) is the remote-sensing reflectance at wavelength λ_i, to estimate chl-a concentration in coastal waters. The objectives of this article are (1) to validate the three-band bio-optical model using a data set collected in coastal waters, (2) to evaluate the extent to which the three-band bio-optical model could be applied to the spectral radiometer (SR) ISI921VF-512T data and the hyperspectral imager (HSI) data on board the Chinese HJ-1A satellite, (3) to evaluate the application prospects of HJ-1A HSI data in case 2 waters chl-a concentration mapping. The three-band model was calibrated using three SR spectral bands (λ₁ = 664.9 nm, λ₂ = 706.54 nm, and λ₃ = 737.33 nm) and three HJ-1A HSI spectral bands (λ₁ = 637.725 nm, λ₂ = 711.495 nm, and λ₃ = 753.750 nm). We assessed the accuracy of chl-a prediction with 21 in situ sample plots. Chl-a predicted by SR data was strongly correlated with observed chl-a (R² = 0.93, root mean square error (RMSE) = 0.48 mg m^–3, coefficient of variation (CV) (RMSE/mean(chl-a_mea)) = 3.72%). Chl-a predicted by HJ-1A HSI data was also closely correlated with observed chl-a (R² = 0.78, RMSE = 0.45 mg m^–3, CV (RMSE/mean(chl-a_mea)) = 7.51%). These findings demonstrate that the HJ-1A HSI data are promising for quantitative monitoring of chl-a in coastal case-2 waters.     

Optical closure for remote-sensing reflectance based on accurate radiative transfer approximations: the case of the Changjiang (Yangtze) River Estuary and its adjacent coastal area,China

Optical closure exercises are pivotal for evaluating the accuracy of water quality remote-sensing techniques. The agreement between radiometrically derived and inherent optical property (IOP)-derived above-water spectral remote-sensing reflectance R_rs(λ) is necessary for resolving IOPs, the diffuse attenuation coefficient, and biogeochemical parameters from space. We combined spectral radiometric and IOP measurements to perform an optical closure exercise for two optically contrasting Chinese waters – the Changjiang (Yangtze) River Estuary and its adjacent coastal area in the East China Sea. The final aim of our investigation was to compare two derivations of R_rs(λ): R_rs(λ), derived from radiometric measurements; and R_rs(λ), derived from simultaneous IOP measurements. Five subsequent steps have been taken to achieve this goal, including (1) estimation of the R_rs(λ) from radiometric measurements; (2) scattering correction for the non-water spectral absorption coefficient a_pd(λ); (3) estimation of the below-water spectral remote-sensing reflectance r_rs(λ) from IOPs measurements; (4) the estimation of the R_rs(λ) from the r_rs(λ) values; and (5) the comparison between the R_rs(λ) derived from radiometric and IOP measurements. All steps were realized by using both direct measurements and different models based on radiative transfer theory. Results demonstrated that the impact of the errors caused by the scattering correction procedure and conversion of radiometric quantities into R_rs(λ) may be rather significant, especially in the long-wavelength spectrum range. Nevertheless, spectral features were similar between these R_rs(λ) sets for all waters – from relatively clear to very turbid. Exploiting this fact allows use of the spectral reflectance ratios for remote sensing of the estuarine and coastal Chinese waters.     

A four-band semi-analytical model for estimating chlorophyll a in highly turbid lakes: The case of Taihu Lake, China

Accurate estimation of phytoplankton chlorophyll a (Chla) concentration from remotely sensed data is particularly challenging in turbid, productive waters. The objectives of this study are to validate the applicability of a semi-analytical three-band algorithm in estimating Chla concentration in the highly turbid, widely variable waters of Taihu Lake, China, and to improve the algorithm using a proposed four-band algorithm. The improved algorithm is expressed as [Rrs(λ₁)^− 1 − Rrs(λ₂)^− 1][Rrs(λ₄)^− 1 − Rrs(λ₃)^− 1]^− 1. The two semi-analytical algorithms are calibrated and evaluated against two independent datasets collected from 2007 and 2005 in Taihu Lake. Strong linear relationships were established between measured Chla concentration and that derived from the three-band algorithm of [Rrs^− 1(660) − Rrs^− 1(692)]Rrs(740) and the four-band algorithm of [Rrs^− 1(662) − Rrs^− 1(693)][Rrs^− 1(740) − Rrs^− 1(705)]^− 1. The first algorithm accounts for 87% and 80% variation in Chla concentration in the 2007 and 2005 datasets, respectively. The second algorithm accounts for 97% of variability in Chla concentration for the 2007 dataset and 87% of variation in the 2005 dataset. The three-band algorithm has a mean relative error (MRE) of 43.9% and 34.7% for the 2007 and 2005 datasets. The corresponding figures for the four-band algorithm are 26.7% and 28.4%. This study demonstrates the potential of the four-band model in estimating Chla even in highly turbid case 2 waters.     

A wideband circularly polarized crossed magneto‐electric dipole

A novel wideband crossed magneto‐electric (ME) dipole for circularly polarized (CP) radiation is proposed in this paper. The proposed antenna consists of a crossed dipole, four parasitic elements, and two pairs of folding metal plates (magnetic dipole). The parasitic elements and magnetic dipole are employed to enhance the axial ratio bandwidth (ARBW). The antenna size is 0.51λ₀ × 0.51λ₀ × 0.33λ₀, where λ₀ is the corresponding free‐space wavelength at the center frequency. A prototype antenna is fabricated and tested. The experiment results depict that the impedance bandwidth (IBW) for voltage standing wave ratio < 2 is 79.2% (2.5‐5.78 GHz) and the 3‐dB axial ratio bandwidth (ARBW) is 72.5% (2.7‐5.77 GHz). At the same time, good CP characteristics and stable symmetrical radiation patterns can be obtained across the operation bandwidth.     

A dual‐polarized cross‐dipole antenna with wide beam and high isolation for base station

In this paper, a dual‐polarized cross‐dipole antenna with wide beam and high isolation is designed and analyzed for base station. The proposed antenna consists of two planar cross dipoles with four square patches, two L‐shaped microstrip lines, two ground plates, four parasitic patches, and a reflector. The square patches are placed between the center of cross dipoles to couple with L‐shaped microstrip lines. By introducing the parasitic patches, the wide beam can be realized. The measured results show that the proposed antenna achieves an impedance bandwidth (|S₁₁| < ?10 dB) of about 18.7% (1.9‐2.35 GHz) and an isolation better than 30 dB. A measured gain of 5.7 dBi and a half‐power beamwidth over 120° at the center frequency are obtained. Furthermore, the size of the proposed antenna is only 0.5λ₀ × 0.5λ₀ × 0.22λ₀ (λ₀ is wavelength at the center frequency).     

An ultrawideband unidirectional modified foursquare antenna

This study introduces an ultrawideband unidirectional modified foursquare antenna. The antenna consists of two radiating loops and two truncated parasitic patches. A microstrip‐to‐stripline transition is used as a balun to feed the two radiating loops. A square cavity works as a reflector to realise a unidirectional radiation. This antenna has a total size of 0.56λ_L × 0.56λ_L × 0.15λ_L (λ_L: free space wavelength at lowest operating frequency). The measured results show that a broad operating bandwidth of 103.8% (2.67–8.44 GHz) for return loss being higher than 10 dB is achieved. Meanwhile, measured stable unidirectional radiation patterns with a gain (6.9–11.3 dBi) in +z direction, a front‐to‐back ratio better than 14.5 dB and low cross‐polarization level (相似文献   

New models for retrieving and partitioning the colored dissolved organic matter in the global ocean: Implications for remote sensing

Despite the importance of CDOM to upper ocean biogeochemical processes and optics, our current understanding of its spatial and temporal distributions and the factors controlling these distributions is very limited. This eventually prevents an understanding of its relationship to the pool of dissolved organic carbon in coastal and open oceans. This work aims to present a new approach for accurate modeling of absorption spectra of CDOM (a_cdom) and deriving information on its composition in global ocean waters. The modeling approach uses measurements (in situ) of the remote sensing reflectances at two wavelengths (denoted ₄₄₃⁵⁵⁵R_rs) to estimate a_cdom(350) and a_cdom(412), applies them to determine two spectral slopes of an exponential curve fit (S) and a hyperbolic curve fit (γ), derives an appropriate parameter (γ^o) for grading the CDOM compositional changes from a_cdom (350) and γ, and finally employs a_cdom(350), S, and γ^o in a modified exponential model to describe a_cdom(λ) as a function of wavelength. The robustness of this model was rigorously tested on three independent datasets, such as NOMAD in situ data, NOMAD SeaWiFS match-ups data and IOCCG simulated data (all of them contain a_cdom(λ) and R_rs(λ)), which represent a variety of waters within coastal and offshore regions around the world. Accuracy of the retrievals found with the new models was generally excellent, with MRE (mean relative error) and RMSE (root mean square error) of − 5.64-3.55% and 0.203-0.318 for the NOMAD in situ datasets, and − 5.63 to −0.98% and 0.136-0.241 for the NOMAD satellite datasets respectively (for λ₄₁₂ to λ₆₇₀). When used with SeaWiFS images collected over the regional and global waters, the new model showed the highest surface abundances of CDOM within the subpolar gyres and continental shelves dominated by terrestrial inputs (and perhaps local production) of colored dissolved materials, and the lowest surface abundances of CDOM in the central subtropical gyres and the open oceans presumably regulated by photobleaching phenomenon, bacterial activity and local processes. Significant interseasonal and interannual seasonal changes in the terrestrially-derived CDOM distributions were noticed from these new products that closely corresponded with the global mean runoff/river discharge induced by climate change/warming scenarios.     

Compact ultrathin conformal metamaterial dual‐band absorber for curved surfaces

A compact, ultrathin conformal metamaterial dual‐band absorber for curved surfaces has been presented in this article. The absorber unit cell composed of circular and split ring resonators which are connected with plus‐shaped structure. The proposed absorber unit cell is compact in size (0.22λ_o × 0.22λ_o) and as well as ultrathin thickness (0.006λ_o), where λ_o is the wavelength at 5.8 GHz. The designed absorber gives two absorption tips at 5.8 and 7.7 GHz with more than 90% absorptivity. The full width at half maximum bandwidths are 220 MHz (5.67‐5.89 GHz) and 250 MHz (7.58‐7.83 GHz). The proposed conformal absorber is sensitive to the polarization angle and has a stable absorptivity over a wide range of incident electromagnetic wave. The parametric analysis and equivalent transmission line model have been investigated. The surface current and electric field distribution also discussed for understanding the absorption mechanism. To analyze the performance of proposed absorber on the curved surfaces, it is wrapped on the different radius of cylindrical surface and measured the absorptivity. Simulated and measured results have good agreement between them.     

Compact dual‐ and triband bandpass filter using frequency selecting coupling structure loaded stepped‐impedance resonator

This article presents two novel resonators, that is, frequency selecting coupling structure loaded stepped‐impedance resonator (FSCSLSIR) and π‐section loaded FSCSLSIR. The resonator behaviors and guidelines are given to design FSCSLSIR dual‐band bandpass filter (BPF) and π‐section loaded FSCSLSIR triband BPF. The proposed dual‐ and triband BPF have very compact sizes of 0.13 λ_gd × 0.06 λ_gd and 0.115 λ_gt × 0.074 λ_gt, respectively. Moreover, good return loss, low insertion loss, and high band‐to‐band isolation can be observed, and the proposed FSCSLSIR dual‐band BPF has an ultrawide stopband from 5.79 to 36 GHz. The experimental results are in good agreement with the simulations. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:427–435, 2015.     

Low profile antenna based on a fractal shaped metasurface for public safety applications

In this article, design and analysis of a fractal shaped metasurface (FSMS) antenna for public safety applications is presented. It comprises of two layers, upper layer and lower layer. The upper layer has the metasurface (MS) and lower layer has the fractal inspired monopole antenna. MS is made up of Sierpinski Knopp fractal shaped unit cell, which is arranged in 4 × 6 layout to achieve miniaturization. Ansys Electronic Desktop tool is utilized for analyzing the performance of the MS antenna. The projected FSMS antenna is fabricated using FR4 dielectric material and experimented with the help of an anechoic chamber and Vector Network Analyzer (VNA). Results show that the FSMS antenna exhibits a bandwidth of 200 MHz and a gain of 1.56 dBi at 4.89 GHz. The results obtained in simulation and measurement are in good agreement. Consequently, the proposed antenna with a low profile of 0.43λ₀ × 0.43λ₀ × 0.03λ₀, where λ₀ is the free space wavelength at 4.89 GHz is well fit for public safety applications.     

Investigation on nanocrystalline copper-doped zirconia thin films for optical sensing of carbon monoxide at high temperature

Nanocrystalline copper-doped zirconia (CDZ; Cu:Zr = 16:84) thin films have been synthesized on long-period fiber gratings (CDZ-LPFG) by a polymeric precursor method. The CDZ-LPFG device was demonstrated to have high sensitivity and good reversibility for low-concentration CO sensing at high temperatures. The CDZ-LPFG responds with red shifts of its resonant wavelength (λ_R) to CO-containing gases and the λ_R shift reverses when it is exposed to air. The optical response of the CDZ-LPFG to CO is due primarily to the CDZ refractive index variations resulted from the reversible redox reactions (i.e. Cu²⁺ ⇔ Cu⁺) in reducing and oxidizing atmospheres. The magnitude of the λ_R shift exhibited a strong dependence on CO concentration in a range from 0 to 1000 ppm that is potentially useful for quantitative measurement.     

A dual‐band efficient circularly polarized rectenna for RF energy harvesting systems

A multilayered circularly polarized (CP), dual‐band, stacked slit‐/slotted‐patch antenna with compact size and with compact rectifier is offered for RF energy harvesting systems. The compact dual‐band CP antenna size is able to achieve by stacking slotted‐circular‐patch (SCP) on the substrate above the tapered‐slit‐octagon patch (TSOP). Dual‐band CP radiation is realized by stacking the SCP on the TSOP and the microstrip feedline with metallic‐via to SCP. Eight‐tapered‐slit with length difference of 6.25% are embedded along the octagonal directions symmetrically on the TSOP from the patch's center and two unequal size circular slots are embedded in diagonal axis onto SCP to produce dual‐orthogonal modes with almost equal magnitude for CP waves. The designed antenna is realized measured gain of greater than 5.2 dBic across the band (0.908‐0.922 GHz) with maximum gain of 5.41 dBic at 0.918 GHz and gain of greater than 6.14 dBic across the band (2.35‐2.50 GHz) with maximum gain of 7.94 dBic at 2.485 GHz. An overall antenna volume is 0.36λ _o × 0.36λ _o × 0.026λ _o (λ _o is free space wavelength at 0.9 GHz). A compact composite right‐/left‐handed (CRLH) based rectifier with dual‐band at 0.9 and 2.45 GHz is designed, prototyped, and measured. The right‐handed (RH) part of the CRLH transmission line (TL) is formed by a microstrip line. The left‐handed (LH) part of the CRLH‐TL is formed by lumped components. The measured RF‐DC conversion efficiency is 43% at 0.9 GHz and 39% at 2.45 GHz with rectifier size of 0.18λ _o × 0.075λ _o × 0.0002λ _o at 0.9 GHz.     

Bounds for sums of eigenvalues and applications

Let A be a matrix of order n × n with real spectrum λ₁ ≥ λ₂ ≥ ⋯ ≥ λ_n. Let 1 ≤ k ≤ n − 2. If λ_n or λ₁ is known, then we find an upper bound (respectively, lower bound) for the sum of the k-largest (respectively, k-smallest) remaining eigenvalues of A. Then, we obtain a majorization vector for (λ₁, λ₂,…, λ_n−1) when λ_n is known and a majorization vector for (λ₂, λ₃,…, λ_n) when λ₁ is known. We apply these results to the eigenvalues of the Laplacian matrix of a graph and, in particular, a sufficient condition for a graph to be connected is given. Also, we derive an upper bound for the coefficient of ergodicity of a nonnegative matrix with real spectrum.     

Spoof surface plasmon polariton‐fed circularly polarized leaky‐wave antenna with suppressed side‐lobe levels

A wide‐angle scanning circularly polarized (CP) leaky‐wave antenna (LWA) with suppressed side‐lobe levels (SLLs) is proposed, which can be a good candidate for future radar and wireless communication systems. The LWA consists of 12 cross slotted elliptical patch elements, which are fed by a microstrip spoof surface plasmon polariton (SSPP) line. Two fundamental modes of the patch array with two orthogonal polarizations can be excited by the electromagnetic coupling between the array and the SSPP line. By optimizing the elliptical eccentricity e and etching cross slots on the elliptical patch array, a 90° phase difference is introduced, and then, the CP radiation is realized. A tapered aperture field distribution is also realized by adjusting coupling intensities between the patch elements and the SSPP line, which is beneficial to reduce the SLLs. The electrical size of the LWA is 1.29λ₀ × 6.02λ₀ × 0.08λ₀, where λ₀ is air wavelength at 12.9 GHz (broadside direction). Both the simulated and measured results indicate that the CP operating band is 12.0 to 15.0 GHz. The proposed CP LWA scans continuously from ?14° to 38°. In the whole operating band, the axial ratios are less than 3 dB, and the SLLs are less than ?20 dB as well.