Daniele Petrolati

Steps towards the preparation of a Wavemill mission

Wavemill is a microwave instrument designed to retrieve ocean surface currents in two dimensions. After initial internal investigations and the successful results of a feasibility study, the European Space Agency (ESA) is pursuing a programme of steps aimed towards the development of a Wavemill-based mission. This includes a proof-of-concept campaign, scientific assessment of the product validity, end-to-end simulator development, mission (Phase 0) study and hardware risk retirement for the antenna and on-board processing sub-systems. This paper briefly covers all these activities and establishes a notional timeline for their completion. The end goal of a Wavemill mission is dependent not only on a successful conclusion to these activities but also on the interest and enthusiasm of the oceanographie community as well as the validity and applicability of the products such a mission could provide.

New Piecewise Linear Polyphase Sequences Based on a Spectral Domain Synthesis

A new class of piecewise linear polyphase codes of perfect square length, named PAT codes, is introduced. PAT codes derive from an innovative design procedure and present excellent performance in terms of both merit factor and peak to side-peak ratio with respect to previously proposed sequences such as Frank, P1, P2, and Px codes. In particular, for odd lengths, the merit factor of PAT codes is larger than that of all other polyphase sequences under analysis, and the peak to side-peak ratio is as large as that of the best of these sequences (namely the Frank and P1 codes). For even lengths, the merit factor and the peak to side-peak ratio performance of PAT codes coincide with those of Px and P2 codes, which are the best polyphase sequences under analysis. PAT code synthesis is based on a rigorous analytical method in the code spectral domain and leads to a simple recursive formula for the generation of sequences of arbitrary length.

A novel phase only excitation law for omnidirectional arrays

A new class of excitation sequences (PAT Codes) for feeding large linear omnidirectional arrays is presented. The use of PAT Codes succeeds in overcoming the problem, typical of previously proposed excitations (e.g., Kuttruff-Quadt, Huffman-Type, Huffman Codes), which consists in obtaining Radiation Patterns with excellent omnidirectional characteristics avoiding, at the same time, power utilization inefficiencies due to amplitude tapering. This attractive feature derives from the innovative PAT Code generation method named Spectral Domain Synthesis (SDS) which acts directly on Code Spectrum and leads to define a simple code generation formula. Thanks to SDS, PAT Code-fed arrays succeed in controlling Radiation Pattern omnidirectionality both on average and locally, avoiding the presence of deep dips or peaks typical of other feeding sequences (e.g., Frank Codes). PAT Codes, deriving from a systematic algorithm, may be easily employed in large array applications and represent also an optimum starting point for numerical optimization techniques aiming at different performance improvements.

Sidelobe optimization of Skobelev Networks

A new optimization method for computing the coupling coefficients of the directional couplers constituting a Skobelev Network is presented in this paper. Skobelev Networks (also known as chessboard networks), typically used in Limited Field Of View (LFOV) applications, present a modular structure composed by N stages feeding linear arrays partitioned into several overlapped sub-arrays. Each network stage is made up of directional couplers whose coupling coefficients are determined through a constrained optimization routine based on deformed polyhedron methods. In this work an alternative optimization is proposed. The new procedure consists in two steps: 1) computation of the Skobelev Network Scattering Matrix, 2) constrained optimization of directional coupler coefficients adopting a Sequential Quadratic Programming (SQP) method. The results obtained employing this new routine show a remarkable reduction in the sub-array radiation pattern sidelobe level (from 4.7 dB for N = 1 up to 6.49 dB for N = 4) with negligible effects on the main beam.

A new class of equi-amplitude omnidirectional linear arrays

Nowadays arrays exhibiting omnidirectional patterns, initially developed in Acoustics, have assumed relevant importance in a wide number of different fields and are employed in several applications such as active array systems and quasi-optical power combining networks at mm wavelength.

Spectral synthesis of piecewise linear polyphase codes for good aperiodic autocorrelation performance

In performing the synthesis of the code, the attention is naturally focused on the code domain. Turning the attention toward the Fourier dual domain (i.e. the code spectrum) casted light on the reasons for performance limitations of previously known linear polyphase codes and allowed the authors to develop a new family of sequences, named PAT codes, with excellent performance in terms of both Merit Factor (MF) and Peak to Side-Peak Ratio (PSPR) [10]. It is worth noting that, while in the code domain the interest is in the sharpness of the AAF, in the code spectrum domain the interest is on the spectrum flatness.