An analytic design-oriented model of phase and frequency modulated microwave optical links has been developed. The
models are suitable for design of broadband high dynamic range optical links for antenna remoting and optical
beamforming, where noise and linearity of the subsystems are a concern Digital filter design techniques have been
applied to the design of optical filters working as frequency discriminator, that are the bottleneck in terms of linearity for
these systems. The models of frequency modulated, phase modulated, and coherent I/Q link have been used to compare
performance of the different architectures in terms of linearity and SFDR.
In this paper we present a methodology to calibrate and correct frequency-dependent errors in phased-array antennas with large signal bandwidth and large size. If the receivers are not narrow-band, the hypotheses of constant gain and group delay are not valid. If the frequency responses of the receivers are affected by mismatches, this will also impact directivity. Standard Amplitude and Phase Correction (APC) algorithms will not be effective in this case, and a more advanced complex FIR filtering algorithm is used. A transmitted signal is assumed to be known in order to provide a reference and estimate the optimal calibration coefficients of the FIR filters.
The paper deals with the opportunity to introduce “Not strictly TEM waves” Synthetic detection Method (NTSM), consisting in a Three Axis Digital Beam Processing (3ADBP), to enhance the performances of radio telescope and sensor systems. Current Radio Telescopes generally use the classic 3D “TEM waves” approximation Detection Method, which consists in a linear tomography process (Single or Dual axis beam forming processing) neglecting the small z component. The Synthetic FEED ARRAY three axis Sensor SYSTEM is an innovative technique using a synthetic detection of the generic “NOT strictly TEM Waves radiation coming from the Cosmo, which processes longitudinal component of Angular Momentum too. Than the simultaneous extraction from radiation of both the linear and quadratic information component, may reduce the complexity to reconstruct the Early Universe in the different requested scales. This next order approximation detection of the observed cosmologic processes, may improve the efficacy of the statistical numerical model used to elaborate the same information acquired.
The present work focuses on detection of such waves at carrier frequencies in the bands ranging from LF to MMW. The work shows in further detail the new generation of on line programmable and reconfigurable Mixed Signal ASIC technology that made possible the innovative Synthetic Sensor. Furthermore the paper shows the ability of such technique to increase the Radio Telescope Array Antenna performances.
The paper deals with a possible use of the feed array present in a large antenna system, as a layer for measuring the antenna performance with a self-test procedure and a possible way to correct residual errors of the Antenna geometry and of the antenna distortions. Focus has been concentrated on a few key critical elements of a possible feed array metrology program. In particular, a preliminary contribution to the design and development of the feed array from one side, and the subsystem dedicated to antenna distortion monitoring and control from the other, have been chosen as the first areas of investigation. Scalability and flexibility principles and synergic approach with other coexistent technologies have been assumed of paramount importance to ensure ease of integrated operation and therefore allowing in principle increased performance and efficiency. The concept is based on the use of an existing feed array grid to measure antenna distortion with respect to the nominal configuration. Measured data are then processed to develop a multilayer strategy to control the mechanical movable devices (when existing) and to adjust the residual fine errors through a software controlled phase adjustment of the existing phase shifter The signal from the feed array is converted passing through a FPGA/ASIC level to digital data channels. The kind of those typically used for the scientific experiments. One additional channel is used for monitoring the antenna distortion status. These data are processed to define the best correction strategy, based on a software managed control system capable of operating at three different levels of the antenna system: reflector rotation layer, sub reflector rotation and translation layer (assuming the possibility of controlling a Stewart machine), phase shifter of the phased array layer. The project is at present in the design phase, a few elements necessary for a sound software design of the control subsystem have been developed at a technological demonstrator level while the ASIC board for generating the digital data stream has been fully developed. A prototype for control accurately the position of the sub-reflector up to a diameter of 5 meters (similar to the sub reflector size of a large antenna) using a Stewart mechanism is being planned. The selection strategy of the correction modes will depend on the dynamics of the phased array (i.e. the available bits of the A/D conversion). The reaction time allowed for the correction, depending on the error type and the inertia of the sub systems. Typically, the compensation can be divided among all the adjusting elements.
Phase noise models that describe the near-carrier spectrum in an accurate but insightful way are needed, to better optimize the oscillator design. In this paper we present a model to describe the effect of flicker noise sources on the phase noise of an oscillator, that can be applied both to linear oscillators and to nonlinear structures like relaxation and ring oscillators, so extending previous works that considered only the effect of the flicker noise superimposed to the control voltage of a VCO. In the phase noise of an oscillator we can separate the effect of high frequency noise sources, that can be described by a short-time-constant system, and the effect of low frequency noises (mostly flicker sources), described by a system with time constants much slower than the oscillation period. Flicker noise has been considered to cause a change in the circuit bias point; this bias point change can be mapped in a shift of the oscillation frequency by exploiting Barkhausen conditions (for linear oscillators) or obtaining this link by simulations. The power spectral density of the oscillator can then be obtained as the probability distribution of the oscillation frequency, starting from the flicker noise probability distribution. If the effect of high frequency noise sources is also taken into account, the overall oscillator spectrum can be obtained as a convolution of the spectrum due to flicker sources with the Lorentzian-shaped spectrum due to white noise sources, in analogy with the description of inhomogeneous broadening of laser linewidth.