Antenna array

Summary

An antenna array (or array antenna) is a set of multiple connected antennas which work together as a single antenna, to transmit or receive radio waves. The individual antennas (called elements) are usually connected to a single receiver or transmitter by feedlines that feed the power to the elements in a specific phase relationship. The radio waves radiated by each individual antenna combine and superpose, adding together (interfering constructively) to enhance the power radiated in desired directions, and cancelling (interfering destructively) to reduce the power radiated in other directions. Similarly, when used for receiving, the separate radio frequency currents from the individual antennas combine in the receiver with the correct phase relationship to enhance signals received from the desired directions and cancel signals from undesired directions. More sophisticated array antennas may have multiple transmitter or receiver modules, each connected to a separate antenna elem

Official source

https://en.wikipedia.org/wiki/Antenna_array

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Design of novel radiating elements for SATCOM phased arrays in Ku-Band

Baptiste Fernand Hornecker

The present thesis deals with the design of a planar antenna array for the communication between a civil aircraft (Dassault's Falcon) and an Inmarsat satellite. The final goal is to provide high speed Internet access in X/Ku-Band (8-12GHz / 12-18GHz), and possibly even in K/Ka- Band (18-27GHz / 17-40GHz). The study starts with the Ku-Band only, then evolves towards the transmission band and finishes with their Ka-Band counterparts. The main constraint of the thesis is that the final result should be a low profile antenna that will be easy to integrate below the fuselage of an aircraft. At the same time, the antenna has to provide a beam steering mechanism in order to track the position of the targetted satellite while the aircraft is moving. The usual way to achieve it is to implement some dedicated electronic chips below each radiating element of array. Dassault Aviation has its own alternate and more mechanical oriented solutions. Since the communication system is intended for top-notch business jets produced in small series, cost is not here a decisive criterion. This thesis assumes the existence of the beam-steering system and concentrates on a proof of concept and careful design of the antenna elements that will constitute the final array. They have to satisfy tight constraints in terms of size, return loss, mutual coupling with neighbors, efficiency, radiation pattern and dual circular polarization quality. Printed multilayer antennas have been retained as the best candidates, and themain parts of the thesis have been dedicated to their study. The thesis concludes with the presentation of an apparently completely unrelated and independant topic, namely the simulation of nanoscale 2D planar structures based on Graphene. The rationale for this last chapter is to provide a prospective study of the use of Graphene to create a variable capacitance. This component is always needed in the beamforming network of reconfigurable and scanning arrays. Our laboratory is developing a deep knowledge of the electromagnetic properties of Graphene-based devices and these varicaps could lead to very interesting applications in high frequencies, once the Graphene technology has definitely progressed. Thanks to electrostatics Green's functions, a variable capacitor based on Graphene has been simulated, and a Quantumeffect -the Quantum capacitance of Graphene- has been successfully tackled from a numerical point of view.

EPFL2016

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A single GNSS antenna moving along a known trajectory can be used to synthesize a virtual array in order to apply spatial diversity techniques, e.g. beamforming. With these techniques, referred as synthetic aperture (SA) techniques, the receiver can mitigate interfering signals, including multipath. The use of a single antenna element, instead of an antenna array, significantly reduces the hardware complexity, and there is no longer need for precise calibration and system synchronization. Before SA techniques can be used to process the GNSS signal, a critical practical issue must be addressed: the carrier Doppler frequency caused by the antenna motion only, that we have called “relative” Doppler, must be isolated from any other carrier frequency contribution. We have called the sum of all these possible contributions “reference” Doppler. In this paper, we propose two new techniques making use of the so-called extended Kalman filter (EKF), in order to compensate the reference Doppler at the correlation output. The first method, named EKF1, tracks the carrier frequency using a conventional FLL, and then uses its output to feed an EKF responsible for the reference Doppler estimation. The second method, named EKF2, is an ultra-tight integration solution in charge of the carrier tracking, while simultaneously estimating the reference Doppler component from the correlators output. A comparison of these new methods with two previously existing techniques, in terms of their impact on direction-of-arrival estimation techniques, is presented. Synthetic and real GPS L1 C/A signals are used in this comparison.Real signal measurements were obtained using a GPS antenna mounted on a mechanical rotating arm –built in-house– to implement an approximately uniform circular movement.

2017

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We describe the experimental framework that we have developed to study the use of synthetic aperture in GNSS receivers to estimate and mitigate multipath interference. By combining the signal received by a single moving antenna during different time instants along a known trajectory, it is possible to per-form spatial filtering on the received signal. Our framework is divided in two parts. First, we modified a software GNSS receiver to implement beamforming and direction of arrival (DoA) algorithms, which have been adapted to work with synthetic aperture, instead of with a fixed antenna array. Second, we built a rotating arm supporting an antenna in order to implement circular trajectories of 0.5 to 1 m radius, and adjustable rotating speeds of up to 1.5 rev/s. Finally, we present an analysis of the performance of the algorithms implemented using real data obtained with our rotating antenna.

2017

Design of novel radiating elements for SATCOM phased arrays in Ku-Band

Baptiste Fernand Hornecker

EPFL2016