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Biofouling on solid substrata was studied in the coastal waters of the Baltic with a photoacoustic spectroscopy (PA) technique. Several substrata biotic and abiotic of varying surface energy and bioaccumulation efficiency were deployed, for a certain length of time corresponding to the characteristic stages of biofilm development. Periphyton consists of algae, cyanobacteria, and heterotrophic microbes which stand for a photosynthetic system with a mixture of pigments. PA signal amplitude and phase were evaluated using the phase-sensitive method with a novel closed-cell type photoacoustic spectroscopy (PAS) system. Photosynthetic apparatus properties (photosynthetic energy storage (ES), PA amplitude and phase spectra) exhibited a seasonal variability. ES values were higher, for a season of high primary production. In addition, ES values were found to be higher by a factor of 1.5-2, for biofilm settled on biotic macroalgae. The peak values in PA signal amplitude spectra maximum at ~ 680 nm were highest for biotic substrata, lower for filtered planktonic phase, and lowest for abiotic surfaces. The photoacoustic parameters (ES and PA signal amplitude) turned out to be unequivocally related to the biofilm structural signatures (thickness, volume, number of cells, fractal dimension etc.) as learned from confocal microscopy and wettability techniques.

We present results of our investigation on the use of Fourier iteration techniques to determine the antenna boresight far field from limited Fresnel region measurements in one or two planes. Measurements on two planes are well-suited to antennas not characterized by planes, such as those enclosed by radomes. Fourier iteration between two near field measurement planes also has the potential to remove multiple reflections when measuring aperture antennas.

Summary form only given. The Gerchberg-Papoulis (G-P) iterative algorithm is a powerful method of extrapolating a band-limited time-domain function outside the time interval t in which it is known (Gerchberg, Optica Acta, 21, 9, pp. 709-720, 1974, Papoulis, IEEE Trans. Circuits and Systems, 22, 9, pp. 735-742, Sep. 1975). The method starts with the Fourier transform of the signal with zero padding outside the time interval t. The spectral data outside the known frequency band of the signal is deleted before performing inverse transform to obtain a new time domain signal. In this time-domain signal, the waveform in the time interval t is replaced by the original known time signal. Iterating the last three steps allows one to determine the entire time domain signal subject to numerical precision. Recently, this method has been employed successfully in constructing the front half space farfield antenna pattern using truncated planar near field data for a Gaussian tapered aperture distribution, uniform aperture distribution and a rectangular horn with no more than 50 iterations (Martini et al., IEEE Trans. Antennas Propagat., 56, 11, pp. 3485-3493, 2008). Martini et al. state that the G-P algorithm is suited to smoothly varying aperture distributions.The objective of this work is the application of the G-P technique for a wide range of aperture distributions to produce sum or difference patterns, and to understand the accuracy achievable as a function of the number of iterations, and the size of the truncated starting pattern. Initially we focus on one-dimensional aperture distributions since it may be easier to generalize the results. The contribution of the entire evanescent spectrum is incorporated using asymptotic evaluations. The effect of noise is investigated. The results will be applicable to the determination of the complete far-field pattern from the initial truncated near field data. Another application of this work is the determination of the far field at boresight from a small number of near field samples in a surface perpendicular to the axis. In this case it will be interesting to know how few near field samples are needed to reconstruct the far-field in the boresight direction. The results of our investigation will be presented at the symposium.

The characterization of wetting properties (by contact angles CA) of several undersea artificial (glass plates) and natural(stones, sand layers, soft-bottom structures, aquatic macrophytes, sediments) solid substrata in the Baltic Sea brackish water (Gulf of Gdansk) were performed. The apparent surface free energy γ SV and other interfacial interaction parameters: 2D film pressure Π, workof adhesion W A , and of spreading W S ; dispersive term γ SV d of γ SV were derived from CAH approach developed by Chibowski (2003)with only three measurable quantities: surface tension of the probe liquid γ LV and its advancing □ A and receding □ R contact anglehysteresis (CAH = □ A - □ R ). The most useful technique to measure in situ CAs giving reproducible and accurate values turned out acaptive bubble method, for fully hydrated interfacial layers of highly hydrophilic and porous nature met at seabed. Since the outermostsurface of the submerged substrate is sensed with the presented CA captive bubble technique (captive bubble syringe set-up + USBmicroscope system was assigned to field work), surface evolution of the formed biofilm structure can be monitored on-line and in-situ atdifferent stages of its formation from seconds (conditioning film) to weeks (macrofouling). In addition to surface free energy, otherfactors, including surface charge, surface roughness, temperature, contact time and fluid shear flow velocity turned out to havesignificant influence on the adhesion of biofouling. Views of the glass biofouled slides taken with confocal scanning laser microscopyallowed 3D biofilm architecture on glass to be visualized and quantified. The evolution of the wettability parameters allowed toindentify the particular biofilm states: best release properties, maximum organic matter accumulation, mature film dispersion. Thepresence of adsorbed organic matter layer lead to the surface hydrophobization (CA ↑, γ SV ↓, W A ↓, W S more negative).

We describe the design, fabrication, and testing of a seven element X-band coupled oscillator based phased array receiver. An array of seven mutually injection locked S-band voltage controlled oscillators provides seven local oscillator signals that are mixed with the signals received by each of seven microstrip patch elements in the aperture. Beam-steering of the receive array is accomplished by inducing the required phase shift in the local oscillator signal associated with each array element. The downconverted in-phase intermediate frequency signals are then summed in a UHF combining network. Frequency doubling of the oscillator signals is employed to extend the scan range.

This is a review of the work done at Caltech's Jet Propulsion Laboratory during the past decade on development of the coupled oscillator technology in phased array applications to spacecraft telecommunications. First, some historical background is provided to set the work in context. However, this is by no means intended to be a comprehensive review of all work in this area. Rather, the focus is on the JPL contribution with some mention of other work which provided either insight or motivation. In the mid 1990s, R. A. York, and collaborators proposed that an array of mutually injection locked electronic oscillators could provide appropriately phased signals to the radiating elements of an array antenna such that the radiated beam could be steered merely by tuning the end or perimeter oscillators of the array. York, et al. also proposed a receiving system based on such oscillator arrays in which the oscillators provide properly phased local oscillator signals to be mixed with the signals received by the array elements to remove the phase due to angle of arrival of the incident wave. These concepts were viewed as a promising simplification of the beam steering control system that could result in significant cost, mass, and prime power reduction and were therefore attractive for possible space application. The initial work at JPL was largely theoretical and, in collaboration with York and Maccarini, Pogorzelski developed a linearized formulation of the analysis of such arrays that provided considerable insight into the dynamic behavior of the aperture phase as a function of oscillator tuning. The key results (and limitations) of this theoretical work and their implications for array performance are reviewed here. Subsequently, several experimental arrays were designed, fabricated, and tested. These arrays are described and the salient experimental results are outlined. The body of work described has brought JPL from mere awareness of the concept a decade ago, through development of several experimental transmitters and receivers based on the concept, to the brink of a current effort to integrate the transmit and receive functions in a single unit to be developed for future fight application.

A five by five element array designed to operate at S-band was built and tested. The author reviews the array and diagnostic system designs, describes a few modifications of the diagnostic system and the addition of a radiating aperture using microstrip patch elements, and presents some of the results of an antenna range assessment of the fully assembled array.

Stephan (1986) proposed an approach to one dimensional (linear) phased array beam steering which requires only a single phase shifter. This involves the use of a linear array of voltage controlled electronic oscillators coupled to nearest neighbor. The oscillators are mutually injection locked by controlling their coupling and tuning appropriately. Stephan's approach consists of deriving two signals from a master oscillator, one signal phase shifted with respect to the other by means of a single phase shifter. These two signals are injected into the end oscillators of the array. The result is a linear phase progression across the oscillator array. Thus, if radiating elements are connected to each oscillator and spaced uniformly along a line, they will radiate a beam at an angle to that line determined by the phase gradient which is, in turn, determined by the phase difference between the injection signals. The beam direction is therefore controlled by adjusting this phase difference. Pogorzelski and York presented a formulation which facilitates theoretical analysis of the above beam steering technique. Using this formulation, the Stephan beam steering technique can be generalized to two-dimensional arrays in which the beam control signals are applied to the oscillators on the perimeter of the array. In this paper the continuum model for this two-dimensional case is developed and the dynamic solution for the corresponding aperture phase function is obtained The corresponding behavior of the resulting far-zone radiation pattern is displayed as well.

A method of moments (MM) solution for rotationally symmetric reflectors in the near field of a circular aperture is described. It is an extension of the Mautz and Harrington body of revolution code that has been modified to handle phase-scanned planar circular apertures. All three spherical electric field components (E/sub r/, E/sub theta/, E/sub /spl phi//) are considered in calculating the MM excitation vector. Thus, the reflector can be located in the near field of the feed. Calculated results are presented. >

Arrays of coupled oscillators have been proposed as means of realizing high power RF sources via coherent spatial power combining. In such applications, a uniform phase distribution over the aperture is usually desired. However, it has been shown that by detuning some of the oscillators away from the oscillation frequency of the ensemble of oscillators, one may achieve other useful aperture phase distributions. Of particular interest among those achievable are linear phase distributions because these result in steering of the output RF beam away from the broadside direction. The theory describing the behavior of such arrays of coupled oscillators is quite complicated since the phenomena involved are inherently nonlinear. However, a simplified theory has been developed which facilitates intuitive understanding. This simplified theory is based on a "continuum model" in which the aperture phase is represented by a continuous function of the aperture coordinates. A challenging aspect of the development of this theory is the derivation of appropriate boundary conditions at the edges or ends of the array.

Two Ka-band, half-meter diameter, circularly polarized microstrip reflectarrays have been developed. One has identical square patches with variable-length phase delay lines. The other uses identical square patches and delay lines with variable element rotation angles. Although both antennas demonstrated excellent efficiencies, adequate bandwidths, and low average sidelobe and cross-pol levels, the one with variable rotation angles achieved superior overall performance. It is believed that these are electrically the largest microstrip reflectarrays (6924 elements with 42 dB gain) ever developed. It is also the first time that circular polarization has been actually demonstrated using microstrip patch elements. It is known that, if a circularly polarized antenna element is rotated from its original position by /spl psi/ degrees, the phase of the element will be either advanced or delayed by the same /spl psi/ degrees. Hence, the technique of rotating circularly polarized elements to achieve the required phases for a conventional array to scan its beam has been previously demonstrated. This technique was also demonstrated for a spiraphase reflectarray where physically large spiral elements with discrete and limited switchable phase states were used to scan the beam. Here small and low-profile printed microstrip elements are used in a reflectarray with continuous variable angular rotations to achieve far-field phase coherence. It has been previously proposed that a controllable miniature or micro-machined motor can be placed under each patch element of a reflectarray to scan the beam to wide angular directions. By doing so, the high-cost/high-loss phase shifters, T/R modules, and beamformer are no longer needed in a beam scanning antenna.

Linear and planar arrays of coupled oscillators have been proposed as means of achieving high power rf sources through coherent spatial power combining (Mink, 1986 and York, 1993). In such-applications, a uniform phase distribution over the aperture is desired. However, it has been shown that by detuning some of the oscillators away from the oscillation frequency of the ensemble of oscillators, one may achieve other useful aperture phase distributions Liao and York, 1993). Notable among these are linear phase distributions resulting in the steering of the output rf beam away from the broadside direction. The theory describing the operation of such arrays of coupled oscillators is quite complicated since the phenomena involved are inherently nonlinear. This has made it difficult to develop an intuitive understanding of the impact of oscillator tuning on phase control and has thus impeded practical application. In this work a simplified theory is developed which facilitates intuitive understanding by establishing an analog of the phase control problem in terms of electrostatics.

Inflatable solar sails have been proposed which enable planetary missions employing solar power flux to provide thrust for the spacecraft thus decreasing the required additional propellant. To maximize the capture of solar flux, solar sails are required to have a large surface area (i.e. 100 m in diameter). A question has been raised if one can envision an antenna concept that can be readily integrated into the solar sail itself. Assuming that the inner portion of the sail has an acceptable level of flatness, one may then seek for concepts that provide required antenna gain. Applications of zone plate Fresnel antennas can be envisioned in solar sails. The zone plate (Fresnel) antenna is a type of reflector antenna in which strips of reflecting/nonreflecting materials are arranged on a flat surface to maximize the directivity of the plate. Having a lesser gain compared to parabolic antennas, they may be used in place of parabolic antennas where geometry may dictate a non-parabolic reflector surface. These sails can have a variety of shapes; however we focus on flat sails although most of the analysis can be easily extended to non-flat shapes. Our intention is to propose a comparable and alternative means of antenna design for deep space communication by taking advantage of solar sails' large surface area and by incorporating zone plate Fresnel antennas on the sail. In addition, for the purpose of developing clear insight into the performance of the antenna and to avoid unnecessary added complexity in the analysis, we propose a 2D MoM and PO analysis of the geometry in order to assess the computational accuracy of PO for the 3D structures.

In this paper, we describe the fabrication of the array of voltage controlled oscillators, the experimental determination of the behavior of this array, and comparison of the experimentally observed behavior with theoretical predictions. We further discuss the design of the microstrip patch radiating aperture and describe the experimental measurement of the antenna patterns under various scan conditions.

In many communications and radar applications, one is confronted with interfering signals originating in a predefined angular sector. In such a case, one would like to design the antenna to be insensitive to signals in that angular sector while maintaining high sensitivity in the direction of its main beam. Depending on the particular situation, one may desire that either or both the main beam and the suppressed angular sector be steerable. In treating this design problem, we consider initially the simple case of a one-dimensional linear array of 2N+1 discrete radiating elements. This case was treated in a patent disclosure by Michael A. Kott (1979) in which he described a method for sidelobe cancellation involving the use of an auxiliary interferometer consisting of two elements added to the array, one at each end. It can be shown that the uniform taper is, in a mathematical sense, the ideal taper for Kott's scheme. Extending his work, it is further shown that the entire concept is quite naturally generalized to a two dimensional array with a steerable pencil beam thus providing a suppression region which is independently steerable to any desired position outside the main beam regardless of the beam-steering angle.