We study the surface enhanced Raman scattering (SERS) from bimetallic core-shell nanoparticles by taking into account the nonlocal effect. The Gersten-Nitzan model is applied to investigate SERS from a molecule adsorbed on the nonlocal bimetallic nanoparticle. Numerical results show that there are two enhanced SERS peaks for bimetallic coated nanoparticles, and nonlocal effects will lead to less enhancement and blue-shift of SERS peaks. In addition, unusual resonant electric-field patterns are found in the nonlocal gold core in comparison with those in the local case. Our investigation is helpful for understanding some details of SERS schemes in nano-optics and plasmonics when nonlocal effects are considered.
Retinal prosthesis system is currently being developed in various places around the world. This system involved data transfer between an implanted antenna inside an eyeball and an external camera that is located just in front of the eyeball. While there are plenty of publications about the stimulating electrodes or the processing unit of the system itself, very limited amount has been published regarding the wireless communication link between the two antennas despite the fact that the electromagnetic wave will propagate through a complex medium in the form of Vitreous Humor. This paper will discuss about the constraints associated with implanting an antenna into an eyeball. An antenna design and simulation was performed with the aid of High Frequency Structure Simulator (HFSS) and its Finite Element Method (FEM) mathematical solver in the operating frequency of 402-405 MHz. The antenna, which was a 4 layer microstrip antenna, was positioned at the centre of a spherical model filled with homogeneous Vitreous Humor material. Antenna performances that include return loss, bandwidth, gain, radiation pattern, and SAR value are analysed and compared against those of other implantable antennas operating in Medical Implant Communication Service (MICS) band. Free space and simulating fluid measurements were also conducted on the fabricated antenna to validate the simulation results. It was concluded that the fabricated antenna was able to produce the similar performance to the simulation results and hence at the same level as the other antennas operating in material with lower dielectric constants and conductivities.
In this paper, a compact and high isolation microstrip diplexer is designed for broadband and wireless local area network (WLAN) application, simultaneously. The bandpass filter (BPF) for broadband channel is formed by three-coupled-line structure and two short stubs with different size loaded in 50 feed lines, and the BPF for WLAN channel consists of two coupling quarter-wavelength resonators (QWR) and one open stub loaded in short parallel-coupling feed structure. Multiple transmission zeros can be generated due to their intrinsic characteristics, so the broadband BPF with sharp skirt and wide upper-stopband performance and the WLAN BPF with sharp roll-off and lower-stopband characteristic can be realized. The tapped stub not only can generate transmission zeros to deepen the stopband, but also can connect other BPF as an its part without deterioration of in-band performance. Hence, a compact microstrip diplexer combines of two BPFs without the extra junction matching network. The mutual loading effect approximately equivalent to a coupled short QWR can also generate new transmission zero at the passband edge to improve the isolation. A microstrip diplexer with the 3 dB fractional bandwidth (FBW) of 80% for broadband channel and 5% for WLAN channel is designed and fabricated. Good agreement between the simulated and measured results is observed.
The physiological parameters monitoring of human target are considered to be a meaningful and challenging task in non-line-of-sight (NLOS) scenes such as rescue of trapped survivors in post-disaster. In this paper, a new method based on developed adaptive line enhancer (DALE) is proposed to monitor vital signs via ultra-wideband (UWB) radar with centre frequency of 400 MHz. The validity of this new method is proved by means of two experiments with different positions of human target. The good results demonstrate that this new method can be used for vital sign monitoring including respiration and heartbeat through the obstacle. Furthermore, the motion responses due to respiration and heartbeat in different body positions are also discussed.
The Modified Winding Function Theory (MWFTh), regarded as a very powerful and general theory, has been extensively used for the last 15 years. This paper performs an in-depth review of the mathematical and physical framework on which the MWFTh is based, showing that it is indeed very well suited to analyse machines with small air gaps of arbitrary shape. However, contrary to what is usually stated in the literature, it is also proved that its general formulae fail when applied to large air gaps. This major finding is deduced from two different approaches, both of which are later reinforced by numerical examples. In spite of that, there is an important industrial field (diagnosis techniques of salient-pole synchronous machines eccentricities) in which very good theoretical results are reported by applying the MWFTh to these large air-gap machines. This issue is addressed and clarified in the paper.
Presently, wireless capsule endoscopy (WCE) is the sole technology for inspecting the human gastrointestinal (GI) tract for diseases painlessly and in a non-invasive way. For the further development of WCE, the main concern is the development of a high-speed telemetry system that is capable of transmitting high-resolution images at a higher frame rate, which is also a concern in the use of conventional endoscopy. A vital task for such a high-speed telemetry system is to be able to determine the path loss and how it varies in a radio channel in order to calculate the proper link budget. The hostile nature of the human body's channel and the complex anatomical structure of the GI tract cause remarkable variations in path loss at different frequencies of the system as well as at capsule locations that have high impacts on the calculation of the link budget. This paper presents the path loss and its variation in terms of system frequency and location of the capsule. Along with the guideline about the optimum system frequency for WCE, we present the difference between the maximum and minimum path loss at different anatomical regions, which is the most important information in the link-margin setup for highly efficient telemetry systems in next-generation capsules. In order to investigate the path loss in the body's channel, a heterogeneous human body model was used, which is more comparable to the human body than a homogenous model. The finite integration technique (FIT) in Computer Simulation Technology's (CST's) Microwave Studio was used in the simulation. The path loss was analyzed in the frequency range of 100 MHz to 2450 MHz. The path loss was found to be saliently lower at frequencies below 900 MHz. The smallest loss was found around the frequency of 450 MHz, where the variation of path loss throughout the GI tract was 29 dB, with a minimum of -9 dB and a maximum of -38 dB. However, at 900 MHz, this variation was observed to be 38 dB, with a minimum of -10 dB and a maximum of -48 dB. For most positions of the capsule, the path loss increased rapidly after 900 MHz, reaching its peak at frequencies in the range of 1800 MHz to 2100 MHz. During examination of the lower esophageal region, the maximum peak observed was -84 dB at a frequency of 1760 MHz. The path loss was comparatively higher during examination of anatomically-complex regions, such as the upper intestine and the lower esophagus as compared to the less complex stomach and upper esophagus areas.
Although many directive antennas operating in a narrow band of millimeter (mm) waves were reported, e.g., antennas for 60-GHz wireless local area network (WLAN), their wideband counterparts are still unpopular. Cavity-backed antennas (CBAs) are widely developed and reported in microwave frequency bands, but few literatures can be found about mm-wave CBAs in spite that their many properties are quite suitable for mm-wave applications. This paper presents a wideband unidirectional CBA with a bowtie exciter, operating in a frequency band of 40 ~ over 75 GHz, and it is carefully analyzed in terms of influences of all antenna components on radiation patterns, broadside gains, and reflection coefficients. Then, the antenna prototype is built by generic printed circuit board (PCB) technologies, and measurements prove the validity of simulations.
Low-frequency ultra-wideband synthetic aperture radar is a promising technology for landmine detection. According to the scattering characteristics of body-of-revolution (BOR) along with azimuth angles, a discriminator based on Bayesian decision rule is proposed, which uses sequential features, i.e. double-hump distance. First, the algorithm estimates the target scatterings in all azimuth angles based on regions of interest. Second, sequential aspect features are extracted by sparse time-frequency representation. Third, the distributions of features are obtained by training samples, and then the posterior probability of landmine class is computed as an input to the classifier adopting Mahalanobis distance. The experimental results indicate that the proposed algorithm is effective in BOR target discrimination.
Design and 3-D numerical simulation of a 140 GHz spatialharmonic magnetron (SHM) are presented. The effect of geometrical parameters of the side resonators of the anode block on the output power are considered using the results of a theory based on a single harmonic approximation approach. This theory enables the determination of the optimum geometrical parameters of the side resonators. SHM design evaluation is carried out via numerical simulations performed with a 3-D particle-in-cell (PIC) code embedded in CST-Particle Studio. Simulations of the SHM are performed without artificial RF priming and without assuming restrictive assumptions on the mode of operation or on the number of harmonics to be considered. Thus in our simulations the electromagnetic oscillations grow naturally from noise. The results of time evolved electron flow simulations and gradual formation of a single frequency RF oscillation are presented. The presented SHM shows stable operation in the π /2-1-mode at 140 GHz over a range of DC anode voltages extending from 11.3 kV to 11.5 kV and for an axial magnetic flux density equal to 0.79 T. RF Output power of the SHM varies from 2 kW to 11 kW over these voltages with a maximum efficiency of around 6.8%.
In this paper, a one-dimensional nonlinear fractal sea surface model has been established based on the narrow-band Lagrange model, which takes into account the vertical and horizontal skewnesses for the sea surface. By using the method of second-order small-slope approximation (SSA-II), the normalized radar cross section (NRCS) and Doppler spectrum of linear and nonlinear fractal sea surface are calculated. The calculated NRCS of the nonlinear fractal sea surface is larger than the linear surface for backscattering, especially for large incidence angles, which indicates the nonlinear surface has stronger scattering echoes. And the result of nonlinear fractal sea surface is also larger than the linear fractal sea surface for bistatic case, which is characterized as the discrepancies being small near specular direction, while the discrepancies becoming larger as the scattering angles departing from the specular direction. For the Doppler spectrum of sea surface, the nonlinearity of sea surface effects greatly enhances the Doppler shift and the Doppler spectrum bandwidth at large incidence angles, which are attributed the fact that the nonlinear-wave components propagate faster than the linear-wave components and the nonlinear fractal sea surface corrects the phase velocities by adding the horizontal and vertical skewness. And also, all the results can indicate the validity of this nonlinear model.
It is generally believed genetic algorithm (GA) is superior to particle swarm optimization (PSO) while dealing with the discrete optimization problems. In this paper, a suitable mapping method is adopted and the modified PSO can effectively deal with the discrete optimization problems of line array pattern synthesis. This strategy has been applied in thinned linear array pattern synthesis with minimum sidelobe level, 4-bit digital phase shifter linear array pattern synthesis and unequally spaced thinned array pattern synthesis with minimum sidelobe level. The obtained results are all superior to those in existing literatures with GA, iterative FFT and different versions of binary PSO, that show the effectiveness of this strategy and its potential application to other discrete electromagnetic optimization problems.
In this paper, a compact ultra-wideband microstrip-fed annular ring antenna with band notch characteristics for wireless local area network (WLAN) and dedicated short-range communication (DSRC) is proposed. The proposed antenna comprises an annular ring patch and a partial ground plane with a rectangular slot. The notched frequency band is achieved by etching a partial annular slot in the lower portion of the ring radiator. The centre frequency and bandwidth of the notched band can be controlled by adjusting the width and position of the annular slot. Measured results show that the proposed antenna achieved an impedance bandwidth of 3-10.6 GHz with a notched frequency band cantered at 5.5 GHz. Compared to the recently reported band-notched UWB antennas, the proposed antenna has a simple configuration to realize the band notch characteristics to mitigate the possible interference between UWB and existing WLAN & DSRC systems. Furthermore, a symmetric radiation patterns, satisfactory gain and good time domain behaviour, except at the notched frequency band, makes the proposed antenna a suitable candidate for practical UWB applications.
In this paper, we investigate the impact of beamforming (BF) on a multi-antenna two hop amplify-and-forward (AF) fixed gain relay network over Rician-Rayleigh and Rayleigh-Rician asymmetric fading channels, respectively. The network consists of a relay with single antenna used to assist the signal transmission from the source to the destination, both of which are equipped with multiple antennas. By using the channel state information (CSI), the maximal output signal-to-noise ratio (SNR) with optimal beamforming is first obtained. Then, the novel analytical expressions for the outage probability (OP), probability density function (PDF) and generalized moments of the maximal output SNR are derived. Moreover, the theoretical formulas of the Ergodic capacity and average symbol error rates (ASERs) with various modulation formats are also developed. To gain further insights, the asymptotic ASERs at high SNR are presented to reveal the diversity order and array gain of the multi-antenna relay network. Finally, computer simulations confirm the validity of the theoretical analysis and indicate the influence of antenna number and Rican factor on the system performance.
An extrinsic Fabry-Perot cavity in optical fiber is used to achieve surface imaging at infrared wavelengths. The micro-cavity is realized by approaching a single mode fiber optic with a numerical aperture NA to a sample and it is fed by a low-coherence source. The measurement of the reflected optical intensity provides a map of the sample reflectivity, whereas from the analysis of the reflected spectrum in the time/spatial domain, we disentangle the topography and contrast phase information, in the limit of nearly homogeneous sample with complex permittivity having Im(ε) << Real(ε). The transverse resolution is not defined by the numerical aperture NA of the fiber and consequently by the conventional Rayleigh limit (about 0.6λ/NA), but it is a function of the transverse field behavior of the electromagnetic field inside the micro-cavity. Differently, the resolution in the normal direction is limited mainly by the source bandwidth and demodulation algorithm. The system shows a compact and simple architecture. An analytical model for data interpretation is also introduced.
Surface plasmon resonance effects on a system consisting of the double-chain silver nanorings are numerically investigated by means of the finite element method with three-dimensional calculations. The numerical results for resonant wavelengths corresponding to different light polarizations, pair numbers, illumination wavelengths, charge distribution and the permittivities filled inside the dielectric holes are reported as well. Results show that the double-chain silver nanorings exhibit tunable plasmon resonances in the near field zone that are not observed for the silver nanodisks of the same volume. The resonance wavelength is redshifted as the filling medium in dielectric holes increases, which is attributed to a longer effective optical path. It can be verified that the proposed structure (e.g., twelve pairs or more pairs) is pertinent to the functionality of long range of wave guiding and also show promise for applications in nanooptical devices, sensing, and surface-enhanced spectroscopy, due to their strong and tunable plasmon resonance.
We experimentally demonstrate a low-cost hardware technique for synthesizing a specific electromagnetic pulse shape to improve a time-domain microwave breast imaging system. A synthesized broadband reflector (SBR) filter structure is used to reshape a generic impulse to create an ad-hoc pulse with a specifically chosen frequency spectrum that improves the detection and imaging capabilities of our experimental system. The tailored pulse shape benefits the system by improving the level of signal detection after transmission through the breast and thus permits higher-resolution images. We report on our ability to use this technique to detect the presence of tumours in realistic breast phantoms composed of varying quantities of glandular tissue. Additionally, we provide a set of images based on this experimental data that demonstrates the increased effectiveness of the system using the SBR-shaped pulse in the localisation and identification of the embedded tumour.
During the experimental data processing, we find that corner reflectors cannot be focused properly using 3-D SAR with a moving transmitter due to the phase reversal phenomenon based on the phase history analysis, i.e. the phases at different observation angles might shift rad, and the echoes cancel, rather than accumulate, to each other. To overcome this defect, 3-D SAR with fixed transmitter is designed. Since the geometry of the transmitter and targets remains unchanged during the observation session, the coherence of echoes is well preserved. The mechanism of 3-D SAR with fixed transmitter can accurately be explained using the Stratton-Chu equation. For perfect conductor, the 3-D image is related to the electric current density. For general dielectric medium, the 3-D image is related to the electric current density, magnetic current density and directional vector of scatterer. Experimental results show that one can focus corner reflectors and cavity-shaped objects by fixing the transmitter, which might fail for the traditional 3-D SAR because of the phase reversal phenomenon.
We introduce and discuss a parallel SAR backprojection algorithm using a Non-Uniform FFT (NUFFT) routine implemented on a GPU in CUDA language. The details of a convenient GPU implementation of the NUFFT-based SAR backprojection algorithm, amenable to further generalizations to a multi-GPU architecture, are also given. The performance of the approach is analyzed in terms of accuracy and computational speed by comparisons to a ``standard", parallel version of the backprojection algorithm exploiting FFT+interpolation instead of the NUFFT. Different interpolators have been considered for the latter processing scheme. The NUFFT-based backprojection has proven significantly more accurate than all the compared approach, with a computing time of the same order. An analysis of the computational burden of all the different steps involved in both the considered approaches (i.e., standard and NUFFT backprojections) has been also reported. Experimental results against the Air Force Research Laboratory (AFRL) airborne data delivered under the ``challenge problem for SAR-based Ground Moving Target Identification (GMTI) in urban environments" and collected over circular flight paths are also shown.
Recently, the limited-angle TOF-PET system has become an active research topic due to the considerable reduction of hardware cost and potential applicability for performing needle biopsy on patients while in the scanner. This undersampling measurement configuration oftentimes suffers from the deteriorated reconstructed images. However, the established theory of Compressed Sampling (CS) provides a potential framework for undertaking this problem, given that the imaged object can be sparse in some transformed domain. In here, we studied using numerical simulations the application of sparsity-promoted framework to TOF-PET imaging for two undersampling configurations. From these simulations, a relationship was obtained between the number of detectors (or the range of angle) and TOF time resolution, which provided an empirical guide of designing a low-cost TOF-PET systems while ensuring good reconstruction quality. Another contribution is the exploration of p-TV regularization, which showed that RMSE (Root of Mean Square Error) and SSIM (Structural Similarity) were optimized when p = 0.5. Several sets of representative numerical experiments were executed to validate the proposed methodology, which demonstrates the promising applicability of undersampling TOF-PET imaging.
This paper evaluates the mode-stirring efficiency in terms of uncorrelated positions of a mechanical stirrer operating inside a reverberation chamber (RC). The actual RC is simulated and viewed as a multivariate random process: the chamber field is sampled in a lattice of spatial points distributed uniformly over a volume of arbitrary dimensions. By adopting such a grid, the stirrer efficiency is then computed through the correlation matrix, accounting for the residual correlation between stirrer positions. The second-order statistics are calculated averaging over the sampling volume. Results are presented for two stirrers that move in both synchronous and interleaved mode. A comparison with the traditional circular correlation (CC) method, for the determination of the uncorrelated positions, is done showing how CC overestimates stirrer efficiency.
Traditional synthetic aperture radar (SAR) utilizes Shannon-Nyquist theorem for high bandwidth signal sampling, which induces the complicated system, and it is difficult to transmit and process a huge amount of data caused by high A/D rate. Compressive sensing (CS) indicates that the compressible signal using a few measurements can be reconstructed by solving a convex optimization problem. A novel SAR based on CS theory, named as parallel frequencies SAR (PFSAR), is proposed in this paper. PFSAR transmits a set of narrow bandwidth signals which compose the large total bandwidth. Therefore PFSAR only uses much less data to obtain the same resolution SAR image compared with a traditional SAR system. The data acquisition mode of PFSAR is developed and an algorithm of target scene reconstruction in pursuance of compressive sensing applied to PFSAR is proposed. The azimuth imaging of PFSAR is carried out based on Doppler Effect, and then, the range imaging is performed by using compressive sensing of parallel frequencies signal. Several simulations demonstrate the feasibility and superiority of PFSAR via compressive sensing.
With the advent of magnetic gears, researchers have developed a new breed of permanent-magnet machines. These magnetic-geared permanent-magnet machines artfully incorporate the concept of magnetic gearing into the permanent-magnet machines, leading to achieve low-speed high-torque direct-drive operation. In this paper, a quantitative comparison of three viable magnetic-geared permanent-magnet machines is firstly performed, hence revealing their key features, merits, demerits and applications. Initially, the development of the magnetic gears, including the converted topologies and field-modulated topologies, is reviewed. Then, three viable magnetic-geared permanent-magnet machines are identified and discussed. Consequently, the corresponding performances are analyzed and quantitatively compared. The results and discussions form an important foundation for research in low-speed high-torque direct-drive systems.
This paper presents a circular ring antenna fed by two perpendicular probes, both of which are placed above the square reflector. The antenna is employed to radiate unidirectional beam for polarization diversity reception. A linear isolator is added to improve the isolation between the two probes. The antenna is proposed for the point-to-point communication of Wireless Local Area Network (WLAN) system according to the IEEE 802.11a standard in which the allocated frequency band ranges from 5.150 GHz to 5.825 GHz. The proposed antenna is compact and suitable for mass production. Without the dielectric material, the antenna is free of dielectric loss and capable of high power handling. The prototype antenna was fabricated and measured to verify the theoretical predictions. At the center frequency, the unidirectional pattern with the measured half-power beamwidths in two principal planes of 65 and 75 degrees is achieved. The front-to-back ratio is 31 dB, and the antenna gain is 7.42 dBi. The |S11| and |S21| are respectively -23.09 dB and -33.99 dB; the obtained bandwidth is 23.64%. Based on the aforementioned characteristics, the antenna is a potential candidate for polarization diversity of WLAN applications.
The relationship between the reflection phase curve and the dispersion curve of a H-shaped slot fractal uniplanar compact electromagnetic bandgap (HSF-UC-EBG) structure is investigated in this paper. It is demonstrated numerically and theoretically that the pole (located at phi = 180 degrees) of the reflection phase curve is related to the EBG location of the dispersion curve. More specifically, the pole is always located in the bandgap and the frequency shift characteristics of the pole and the EBG location are the same. Therefore, locations of the artificial magnetic conductor (AMC) and EBG can match with the AMC point and the pole, respectively. By realizing and making appropriate use of this, we can tailor the AMC and EBG locations to coincide in the frequency region only by reducing the spectral distance (d) between the AMC point and the pole. This method can improve the computational efficiency significantly. Parametric studies have been performed to obtain guidelines for reducing d. Finally, an example to design HSF-UC-EBG structure with simultaneous AMC and EBG properties by using this technique is presented with detail steps.
A new hybrid method of moments (MoM)/finite-difference time-domain (FDTD), with a sub-gridded finite-difference time-domain (SGFDTD) approach is presented. The method overcomes the drawbacks of homogeneous MoM and FDTD simulations, and so permits accurate analysis of realistic applications. As a demonstration, it is applied to the short-range interaction between an inhomogeneous human body and a small UHF RFID antenna tag, operating at 900 MHz. Near-field and far-field performance for the antenna are assessed for different placements over the body. The cumulative distribution function of the radiation efficiency and the absorbed power are presented and analyzed. The algorithm has a five-fold speed advantage over fine-gridded FDTD.
In this paper, a novel technique to develop multifrequency microstrip patch antennas with polarization diversity or circular polarization is presented. The proposed approach consists of exciting modes with orthogonal polarizations in microstrip patches partially filled with Composite Right/Left-Handed (CRLH) cells. Two different kinds of quad-frequency single-layer patch antennas are proposed. The first one has two orthogonal ports with high isolation between them. The second kind of quad-frequency patch antennas consists of exciting the four modes with two orthogonal polarizations through only one port. Finally, the proposed approach is used to develop dualfrequency circularly-polarized (CP) patch antennas by exciting the modes with orthogonal polarizations in quadrature phase. Prototypes of all the designs are manufactured and measured, showing good performance.
A phase-only power pattern synthesis technique for at (aperiodic) microstrip reflectarrays with elements arranged on a nonregular lattice is presented. The approach mitigates the typical design issues of reflectarray antennas related to the computational burden and to the possible occurrence of suboptimal solutions which are here even more significant due to the non-regular element lattice. This is done by a convenient two-stage procedure for choosing the starting point of the iterations and by proper representations of the unknowns of the problem. Design constraints on the element positions are also imposed to avoid overlapping as well as too large spacings. The algorithm, accelerated by parallel programming on Graphics Processing Units, has been analyzed against the cases of a pencil-beam and of a shaped-beam involving a typical South America coverage. In order to properly characterize the performance of the synthesis algorithm, it has been applied also to the design of reflectarrays with elements located on a non-regular lattice. The results show that in the case of non-regular lattice better directivities, better coverage behavior and better side-lobe levels are achievable as compared to reflectarrays characterized by a regular lattice.
A new scheme for overcoming losses with incoherent optical gain in a quantum-coherent left-handed atomic vapor is suggested. In order to obtain low-loss, lossless or active left-handed media (LHM), a pump field, which aims at realizing population inversion of atomic levels, is introduced into a four-level atomic system. Both analytical and numerical results are given to illustrate that such an atomic vapor can exhibit intriguing electric and magnetic responses required for achieving simultaneously negative permittivity and permeability (and hence a gain-assisted quantum-coherent negative refractive index would emerge). The quantum-coherent left-handed atomic vapor presented here could have four fascinating characteristics: i) three-dimensionally isotropic negative refractive index, ii) doublenegative atomic medium at visible and infrared wavelengths, iii) high-gain optical amplification, and iv) tunable negative refractive index based on quantum coherent control. Such a three-dimensionally isotropic gain medium with negative refractive index at visible and infrared frequencies would have a potential application in design of new quantum optical and photonic devices, including superlenses for perfect imaging and subwavelength focusing.
The Modal Method by Gegenbauer polynomials Expansion (MMGE) has been recently introduced for lamellar gratings by Edee [J. Opt. Soc. Am. 28, (2011)]. This method shows a promising potential of outstanding convergence but still suffers from instabilities when the number of polynomials is increased. In this work, we identify the origin of these instabilities and propose a way to remove them.
Microstrip reflectarrays consisting of rectangular patches are investigated for application in space-based dual-polarized dual-beam radar interferometers. For nadir looking beams the angle of incidence of feed radiation in each patch is nominally 45˚. In such an application, square-patch reflectarrays can be designed for only one polarization with a sacrifice in performance in the other whereas reflectarrays consisting of rectangular patches may be designed for both polarizations, thereby improving their radiation performance. Piecewise planar parabolic reflectarrays consisting of square patches exhibit poor scan performance in tilted configuration. It is shown that with the use of rectangular patches in such a reflectarray one can design two beams of different polarizations for two offset feeds, thereby providing significant improvement in bandwidth and radiation performance.