Diffraction by Multiple Apertures

Stereoscopic occlusion and the aperture problem for motion: a new solution

To predict the multiples of a given trace, theoretically the wave-theory-based surface related multiple elimination technique requires all the traces in both the common shot gather and the common receiver gather corresponding to the given trace. However, according to Snell's law and ray theory it is not necessary to use all the traces, or the whole multiple contribution gather to predict multiples. That means it is necessary to optimize the multiple contribution gather aperture. Unfortunately, in practice, it is difficult to give an optimal multiple contribution gather aperture in terms of the simple formula and available parameters. In this paper, we present two simple formulae to determine the 2D optimal multiple contribution gather aperture by introducing the surface Fresnel zones of the water bottom reflection and diffraction multiples. A synthetic data example shows that the computational cost and the required computer memory to predict multiples can be significantly reduced with the proposed formulae.

Electromagnetic wave penetration into a rectangular cavity with multiple rectangular apertures is studied. The Fourier transform and the mode matching method are used to obtain simultaneous equations for the modal coefficients. The simultaneous equations are solved to represent the cavity field in series forms, which are suitable for numerical computations. Numerical computations are performed to investigate the field penetration into a cavity in terms of the shielding effectiveness for a various geometry.

We utilize aperture diversity combined with multiple-mode receivers and multiple-input-multiple-output (MIMO) digital signal processing (DSP) to demonstrate enhanced tolerance to atmospheric turbulence and spatial misalignment in a 10 Gbit/s quadrature-phase-shift-keyed (QPSK) free-space optical (FSO) link. Turbulence and misalignment could cause power coupling from the fundamental Gaussian mode into higher-order modes. Therefore, we detect power from multiple modes and use MIMO DSP to enhance the recovery of the original data. In our approach, (a) each of multiple transmitter apertures transmits a single fundamental Gaussian beam carrying the same data stream, (b) each of multiple receiver apertures detects the signals that are coupled from the fundamental Gaussian beams to multiple orbital angular momentum (OAM) modes, and (c) MIMO DSP is used to recover the data over multiple modes and receivers. Our simulation shows that the outage probability could be reduced from >0.1 to <0.01. Moreover, we experimentally demonstrate the scheme by transmitting two fundamental Gaussian beams carrying the same data stream and recovering the signals on OAM modes 0 and +1 at each receiver aperture. We measure an up to ∼10dB power-penalty reduction for a bit error rate (BER) at the 7% forward error correction limit for a 10 Gbit/s QPSK signal.

With two-order Taylor expansion formula and the equivalent transformation of the radical function, the double square rooted slant range history of multiple receiver synthetic aperture sonar (SAS) can be highly approximated. Based on that, system transfer function in two-dimensional frequency domain, which is required for fast imaging algorithms, is derived. Using the derived transfer functions, this paper presents a range-Doppler (R-D) algorithm for multiple receiver SAS based on our model. Then, simulated data is used to validate the presented method.

Motion compensation, referred to as micronavigation, is an unavoidable issue to obtain a high quality image for multiple receiver synthetic aperture sonar (SAS). A feasible micronavigation method based on the inertial navigation system (INS) data is presented in this paper. The INS data is obtained from some high-precision inertial navigation equipment, thus the accuracy of motion errors can be guaranteed. Using the back projection algorithm, some imaging results of experiment data are shown in the end of paper. Meanwhile, some imaging results focused by the conventional chirp scaling algorithm are also given, and the compared results show the effectiveness of the presented method.

The boundary-value problem of electromagnetic wave scattering from multiple circular apertures in a thick conducting plane is rigorously solved. The eigenfunction expansion, integral transform, and superposition principle are utilized to represent the scattered field in the discrete and continuous modes. The boundary conditions are enforced to obtain a set of simultaneous equations for the discrete modal coefficients. The transmission coefficient is represented in a fast convergent series. Computation is performed to illustrate the behavior of transmission and coupling through multiple circular apertures in terms of the aperture geometry.

850 nm vertical-cavity surface-emitting lasers with multiple thick oxide apertures suitable for temperature-insensitive error free transmission at 28 Gb s−1 are subjected to accelerated aging at high current densities and chip temperatures. The devices withstand a 20% power change test at a high current density () at an ambient temperature of for 2500 h. At 90– at this current density no degradation was observed up to 5000 h. We performed the studies at further elevated current densities and temperatures and define the acceleration factor as . The extrapolated lifetime for 20% power drop is estimated as 20 thousand years at 300 K at current density of which is sufficient for 28 Gb s−1 error-free temperature-insensitive data transmission.

The magnetostatic potential distribution through multiple rectangular apertures in a thick conducting plane is analysed. Series solutions are given for the transverse and longitudinal magnetic polarisability of multiple rectangular apertures with various depth and shapes. The differences between electric and magnetic cases are discussed.

The main drawback in communicating via the free-space optical channel is the detrimental effect the atmosphere has on a propagating laser beam. Atmospheric turbulence causes random fluctuations in the irradiance of the received laser beam, commonly referred to as scintillation. We investigate the mitigation of scintillation through the use of multiple lasers and multiple apertures, thereby creating a multiple-input multiple output (MIMO) channel. We adopt a quasi-static block fading model and study the outage probability of the channel under the assumption of orthogonal pulse-position modulation. Non-ideal photodetection is also assumed such that the combined shot noise and thermal noise are considered as signal-independent additive Gaussian white noise. Assuming perfect receiver channel state information (CSI), we compute the signal-to-noise ratio exponents for the cases when the scintillation is lognormal, exponential and gamma-gamma distributed, which cover a wide range of atmospheric turbulence conditions. Furthermore, we illustrate very large gains when CSI is also available at the transmitter.

Apertures in an rectangular enclosure can be the coupling path of EMI. An analytical formulation has been employed for the shielding effectiveness. Both the electric and magnetic shielding are calculated as a function of frequency, enclosure dimensions, aperture dimensions and position within the enclosure. The formulation is extended to calculate circular apertures and multiple apertures.

Abstract. Communication cables are used to transfer data between components of a system. As a part of the EMC analysis of complex systems, it is necessary to determine which level of interference can be expected at the input of connected devices due to the coupling into the irradiated cable. For electrically large systems consisting of several rooms with cables connecting components located in different rooms, an estimation of the coupled disturbances inside cables using commercial field computation software is often not feasible without several restrictions. In many cases, this is related to the non-availability of computing memory and processing power needed for the computation. In this paper, we are going to show that, starting from a topological analysis of the entire system, weak coupling paths within the system can be can be identified. By neglecting these coupling paths and using the transmission line approach, the original system will be simplified so that a simpler estimation is possible. Using the example of a system which is composed of two rooms, multiple apertures, and a network cable located in both chambers, it is shown that an estimation of the coupled disturbances due to external electromagnetic sources is feasible with this approach. Starting from an incident electromagnetic field, we determine transfer functions describing the coupling means (apertures, cables). Using these transfer functions and the knowledge of the weak coupling paths above, a decision is taken regarding the means for paths that can be neglected during the estimation. The estimation of the coupling into the cable is then made while taking only paths with strong coupling into account. The remaining part of the wiring harness in areas with weak coupling is represented by its input impedance. A comparison with the original network shows a good agreement.

The morphology of the brackish waterAmmoastuta salsa Cushman and Bronnimann, the type species ofAmmoastuta, is revised and the genus definition emended. In view of the early planispiral coil, the late uniserial development which tends toward rectilinear, the imperforate agglutinated wall, the multiple aperture and the simple interior, the Ammoastutinae Loeblich and Tappan 1984, are placed into the Lituolidae de Blainville 1827, emended herein, of the Lituolacea DE Blainville 1827, emended herein.

: This Final Report addresses key issues for development of a multiple aperture imaging system which could perform high resolution imaging at very long ranges for surveillance or discrimination. Multiple aperture systems can be used to realize extremely large optical apertures required for long-range, high- resolution systems. Our concept, which makes use of an array of intensity sensing subapertures (photon buckets), requires the simplest and potentially lowest cost hardware of any multiple aperture imaging system. The work described in this report is divided into three parts; a study of subaperture fill factors, a subaperture design, and a discussion of issues which relate to the performance of phase retrieval algorithms.

This paper presents the design, manufacturing, testing, and validation of the MASKARA (Multiple Apertures for high-resolution SAR based on Ka-band Reflectarray) Breadboard Model (BBM), a large Ka-band reflectarray antenna developed for Synthetic Aperture Radar (SAR) applications. The BBM features a dual-offset antenna configuration intended for a high-resolution, wide-swath SAR instrument. At the core of the system is a 1.5 m × 0.55 m reflectarray operating between 35.5–36.0 GHz in the Ka-band. To our knowledge, this is the first demonstration of a reflectarray antenna designed to support two distinct modes of operation, exploiting the inherent advantages of reflectarrays—such as reduced cost and compact stowage—over traditional solutions. The antenna provides a high-resolution mode requiring a higher-gain beam in one polarization and a low-resolution mode covering a larger swath with broader beam coverage in the orthogonal polarization. The design process follows a holistic, multidisciplinary approach, integrating RF and thermomechanical considerations through iterative and concurrent design reviews. The BBM has been successfully manufactured and experimentally tested, and the measurement results show good agreement with simulations, confirming the validity of the proposed concept and demonstrating its potential for future high-performance SAR missions.