Roberto Vincenti Gatti

Design of large mm-wave beam-scanning reflectarrays

Beam scanning reflectarrays represent an attractive alternative to MMIC-based phased array antennas, particularly at mm-wave frequencies, thanks to their potential low costs and high performance. In this paper a simple but effective reconfigurable reflecting element is presented and the design procedure is described. An architecture for 2-D electronic beam steering with reduced number of control signals, suitable for large reflectarray antennas, is presented. To demonstrate the feasibility of the proposed solution a prototypal reflectarray antenna operating at 25 GHz has been designed and fabricated. Comparison with measured results shows very good agreement and confirms the capability to electronically steer the antenna beam

A novel rotman lens in SIW technology

This paper presents a novel Rotman lens in low-cost substrate integrated waveguide (SIW) technology. An original solution is proposed for the design of the adsorbing load at the sidewalls of the lens and for the phase-shifters at the output ports. A three beam prototype feeding an 8-element array working at Ku band has been fabricated and tested.

Electronic steerable MEMS antennas

Recent advances in the technology of radiofrequency (RF) circuits, such as RF-microelectromechanical systems (MEMS) make it possible to practically implement electronically reconfigurable antenna arrays paving the way to innovative communication systems including applications such as next generation mobile communications, radar applications, remote sensing and imaging. This paper reviews the basic implementations of such antenna systems, namely phased arrays and reflectarrays, as well as the algorithms allowing for beam shaping, beam steering, null placing etc., as well as the typical RF-MEMS circuitry for both amplitude and phase control.

A Novel Compact Dual Band Reconfigurable Power Divider for Smart Antenna Systems

This paper presents a novel compact dual band reconfigurable power divider for smart antenna systems. The circuit employs two cascaded dual band hybrid couplers connected through two dual band discontinuities. The dual band discontinuities, consisting of a diplexer and two varactor diodes, can be tuned through two different biasing voltages thus allowing an independent and arbitrary choice of the power ratio in the two frequency bands. A prototype has been designed to operate in the dual band WLAN frequency range, and fabricated in microstrip technology on a 25 mils CER10 substrate. Measured scattering parameters exhibit good performance in terms of return loss, insertion loss and isolation in both WLAN bands, confirming the feasibility of the proposed architecture. The compactness of the circuit makes it suitable for employment in array configurations.

Equivalent circuit of radiating longitudinal slots in dielectric filled rectangular waveguides obtained with FDTD method

A rigorous FDTD characterization of a longitudinal radiating slot in a dielectric filled rectangular waveguide in terms of an equivalent shunt admittance is presented. The FDTD method allows one to account for a number of details that affect the antenna performance, such as the waveguide wall thickness, the presence of a finite or infinite flange, a dielectric layer over the slot. High numerical efficiency has been obtained by using Stegens factorization of the slot admittance. Comparison with other methods (MoM) and with experimental results have shown very good agreement with FDTD simulations even in the computation of the resonant length, which is the most critical parameter. The proposed equivalent circuit allows for a fast and accurate analysis of a radiating slot in a frequency range of the order of 15%.

A novel phase-only method for shaped beam synthesis and adaptive nulling

A new method for phase-only synthesis of linear array antennas is proposed. The phase distribution of the array excitation can be described by a weighted sum of proper basis functions. By optimizing the weights of this sum, rather than the phase of each element, the problem becomes almost independent of the size of the array. The present work shows that with this method both beam shaping and interference nulling can be achieved. The very fast convergence of the optimization makes it suitable even for real-time applications.

Fast and accurate analysis of scanning slotted waveguide arrays

An iterative procedure is presented for a fast and accurate analysis of scanning slotted waveguide arrays including the effects of mutual couplings and their dependence on the scanning angle. The analysis takes also into account the input transitions from the feeding network; each slotted waveguide being excited either at one end or at the centre. The procedure is applied to the simple case of a linear array of four slots, for which a full-wave analysis could be carried out for comparison. The proposed method is shown to provide excellent agreement with the full-wave computation still requiring extremely short computation times.

Flat Array Antennas for Ku-Band Mobile Satellite Terminals

This work presents the advances in the development of an innovative flat array antenna for Ku-band mobile satellite terminals. The antenna is conceived to allow a bi-directional high data rate satellite link. The available circular surface (diameter 110 cm) integrates both a transmitting and a receiving section, operating in orthogonal linear polarizations. The TX frequency range is fully covered while the RX bandwidth is around 300 MHz arbitrarily allocated on the DVB range depending on requirements. The beam is steered in elevation through a phased array architecture not employing costly phase shifters, while the steering in azimuth is mechanical. Active BFNs in printed circuit technology allow excellent performance in terms of EIRP (42 dBW/1MHz, ITU-R S.728.1) and G/T (13 dB/°K at 40° in elevation), maintaining extremely low profile (< 5 cm, radome included). Gain as high as 32 dBi is achieved thanks to the use of slotted waveguide technology, while low fabrication costs are ensured by the employment of innovative SIW (substrate integrated waveguide) structures. In the design fabrication cost is considered as a driving factor, yet providing high performance with a flat profile and thus resulting in a great commercial potentiality.

Computation of gain, noise figure, and third-order intercept of active array antennas

In this work a general formulation for the computation of gain, noise figure and third-order intercept of the parallel of a number of branches is presented. These formulas are particularly useful for the characterization of active weighted array antennas, thus for the design of the relevant beam-forming networks.

A Transportable Reflectarray Antenna for Satellite Ku-band Emergency Communications

The design of a Ku-band reconfigurable reflectarray antenna for emergency satellite communications is presented. Bidirectional high data rate satellite links are needed in emergency conditions where other telecommunication infrastructures are not available. In order to operate in this type of scenario, an antenna should be deployable, transportable, and easily repointable. The need of an automatic and fast satellite location and pointing system leads to a completely electronic reconfigurable antenna. The operative bandwidth is from 10.7 to 12.5 GHz for reception and from 14 up to 14.5 GHz for transmission (30% of relative bandwidth). The selected antenna architecture is based on a dual reflectarray system comprising a passive subreflectarray and an active main reflectarray made of reconfigurable 1-bit elementary cells based on PIN diodes.