This thesis deals with the design and characterization of antennas and antenna arrays used for directional of arrival (DoA) application in the Bluetooth Low Energy (BLE) standard. The research aims to address several key challenges in DoA estimation, from the definition of the required antenna key performance indicators (KPI) to the evaluation of the various factors affecting DoA accuracy. The problem has been addressed by modeling the non-ideal behavior of the hardware as well as the multipath propagation and noise that significantly influence the system performance, especially in indoor environments. The use of circularly polarized signals is suggested and adopted in this thesis since it has several advantages. In particular, the use of circular polarized antennas does not require a relative orientation between the transmitter and receiver, known respectively as tag and locator and moreover, it makes possible the natural rejection of odd reflections enabled by circular polarization. Mitigating the influence of reflected signals is a desired characteristic, especially in complex indoor scenarios. The design of several antennas and antenna arrays with enhanced impedance and axial ratio bandwidth has been carried out. In particular novel configurations for single antennas and antenna systems have been analyzed to optimize the antenna KPIs. The study also investigates the impact of fabrication tolerances as well as the array geometries and feeding techniques. A grounded coplanar-fed circularly polarized antenna is proposed as it outperforms other monolithic antennas ensuring a percentage bandwidth BW%=3.1. A novel patch antenna fed by a branch line coupler is also developed to improve the axial ratio bandwidth and the overall circular polarization purity. The antennas studied are intended for mass production thus a low-cost substrate is adopted, for this reason, a sensitivity study has been carried out. The study confirms that slight variations of the dielectric constant of the substrate εr with respect to its nominal value have a significant effect. This circumstance was confirmed by the experimental characterization of the antenna array since a detuning of the resonance frequency was observed. To deal with this problem a direct approach has been conceived introducing a way to tune the antenna's resonance frequency after fabrication (i.e., by cutting the edges of each radiating patch). Moving to the direction of arrival algorithms an analytical model for multipath environments has been developed. The method allows us to consider a real scenario; since the different reflections are modeled and considered together with the noise. Evaluation of DoA estimation performances has been carried out by using standard algorithms (i.e., Music and Bartlett). A new approach called Embedded Radiation Pattern (ERP) is adopted to take into account the non-idealities of the real antenna system. The embedded patterns are used both to model amplitude and phase information measured at each port of the BLE locator and also to retrieve the direction of arrival in the newly developed direction-finding method. A comparison of this newly developed method with the Conventional Steering Vector (CSV) method, for different parameters confirms that ERP outperforms CSV in all cases. The ability to accurately retrieve the DoA of the incoming signals is a crucial task of this thesis, In this regard for "quantitative" evaluations, it is important to define a reliable error metric to assess the performance of various choices. In 1D and 2D scenarios, different error definitions are adopted in the literature and these definitions are not always meaningful from both physical and mathematical points of view. A new metric based on direction cosine has been therefore proposed. It well behaves in the 2D direction of arrival detection problems by considering the real angular distance between the target and the estimated DoA. We show that the new metric is superior since its definition takes into account the 3D nature of the 2D DoA estimation. The thesis is organized as follows: Chapter 1 briefly describes the main features of Bluetooth technology in location-based services, highlighting its advantages and drawbacks, the chapter also introduces the research objectives of the thesis. Chapter 2 describes the fundamentals of Direction of Arrival estimation and the Bluetooth Low Energy standard. Chapter 3 summarizes the design principles of microstrip patch antennas and a self-contained treatment that briefly recalls the widespread models of the design: the transmission line model and cavity model. Chapter 4 is focused on the design and experimental characterization of circular polarized antennas and antenna systems. Since low-cost substrates are used, sensitivity studies have been carried out as well as various performance comparisons between the proposed antenna typologies. In Chapter 5 a mathematical model takes into account multipath reflections is defined. Finally, a new approach to the DoA estimation is proposed. The new method, based on the use of Embedded Radiation Pattern (ERP), is described in detail. An extensive evaluation of its performance is carried out also in comparison with the standard approach of conventional steering vector. Finally, Chapter 6 reviews the different figures of merits (FoM) for error evaluation in DoA estimation introducing a new FoM based on direction cosines. Conclusions follow in Chapter 7
Questa tesi tratta la progettazione e la caratterizzazione di antenne ed array di antenne utilizzate per applicazioni di DoA (Direzione di Arrivo) nello standard Bluetooth Low Energy (BLE). La ricerca mira ad affrontare diverse sfide chiave nella stima del DoA, dalla definizione dei principali indicatori di prestazione (KPI) dell'antenna richiesti fino alla valutazione dei vari fattori che influenzano l'accuratezza della DoA. Il problema è stato affrontato modellando il comportamento non ideale dell'hardware, nonché la propagazione multipath e il rumore che influenzano significativamente le prestazioni del sistema, soprattutto in ambienti indoor. L'uso di segnali a polarizzazione circolare è suggerito e adottato in questa tesi poiché presenta diversi vantaggi. In particolare, l'utilizzo di antenne a polarizzazione circolare non richiede un orientamento relativo tra trasmettitore e ricevitore, noti rispettivamente come tag e locator, e inoltre rende possibile il rigetto naturale delle riflessioni dispari, reso possibile dalla polarizzazione circolare. La mitigazione dell'influenza dei segnali riflessi è una caratteristica auspicabile, soprattutto in scenari indoor complessi. Sono state progettate diverse antenne ed array di antenne con prestazioni elevate in termini di banda di impedenza e rapporto assiale. In particolare, sono state analizzate nuove configurazioni per antenne singole e sistemi di antenne per ottimizzare i KPI dell'antenna. Lo studio analizza anche l'impatto delle tolleranze di fabbricazione, delle geometrie dell'array e delle tecniche di alimentazione. Viene proposta un'antenna polarizzata circolarmente con alimentazione grounded coplanar, che supera le prestazioni di altre antenne monolitiche garantendo una percentuale di larghezza di banda BW% = 3,1%. È stata inoltre sviluppata una nuova antenna patch alimentata da un branch line coupler per migliorare la larghezza di banda in termini di rapporto assiale e purezza complessiva della polarizzazione circolare. Le antenne studiate sono destinate alla produzione di massa, pertanto viene utilizzato un substrato a basso costo; per questo motivo è stato condotto uno studio di sensibilità. Lo studio conferma che lievi variazioni della costante dielettrica del substrato εr rispetto al suo valore nominale hanno un effetto significativo. Questa circostanza è stata confermata dalla caratterizzazione sperimentale dell'array di antenne, poiché è stato osservato un detuning della frequenza di risonanza. Per affrontare questo problema, è stato utlizzato un approccio diretto che introduce un metodo per sintonizzare la frequenza di risonanza dell'antenna dopo la fabbricazione (ovvero, tagliando i bordi di ciascuna patch radiante). Passando agli algoritmi di DoA, è stato sviluppato un modello analitico per ambienti multipath. Il metodo considera uno scenario reale, tenendo in considerazione le diverse riflessioni che vengono modellate e considerate insieme al rumore. La valutazione dell’accuratezza in termini di DoA è stata effettuata utilizzando algoritmi standard (ovvero, Music e Bartlett). Un nuovo approccio chiamato Embedded Radiation Pattern (ERP) è stato adottato per tenere conto delle non idealità del sistema di antenne reali. I pattern embedded vengono utilizzati sia per modellare le informazioni di ampiezza e fase misurate su ciascuna porta del localor BLE, sia per ricavare la direzione di arrivo nel nuovo metodo di direction-finding. Un confronto tra questo nuovo metodo e il metodo Conventional Steering Vector (CSV), per diversi parametri, conferma che l'ERP supera il CSV in tutti i casi. La capacità di calcolare con precisione la DoA dei segnali in ingresso è un obiettivo cruciale di questa tesi. A tal proposito, per le valutazioni "quantitative", è importante definire una metrica di errore affidabile per valutare le prestazioni di diverse opzioni. In letteratura vengono adottate diverse definizioni di errore negli scenari 1D e 2D, non sempre significative sia dal punto di vista fisico che matematico. È stata quindi proposta una nuova metrica basata sul coseno direzionale. Essa si comporta bene nei problemi di rilevamento della direzione di arrivo bidimensionale, considerando la distanza angolare reale tra il target e la DoA stimata. Dimostriamo che la nuova metrica è superiore poiché la sua definizione tiene conto della natura tridimensionale della stima della DoA bidimensionale. La tesi è organizzata come segue: il Capitolo 1 descrive brevemente le caratteristiche principali della tecnologia Bluetooth nei servizi basati sulla localizzazione, evidenziandone vantaggi e svantaggi; il capitolo introduce inoltre gli obiettivi di ricerca della tesi. Il Capitolo 2 descrive i fondamenti della stima della direzione di arrivo e lo standard Bluetooth Low Energy. Il Capitolo 3 riassume i principi di progettazione delle antenne patch a microstrip e presenta una trattazione completa che richiama brevemente i modelli di progettazione più diffusi: il modello a linea di trasmissione e il modello a cavità. Il Capitolo 4 si concentra sulla progettazione e la caratterizzazione sperimentale di antenne e sistemi di antenne a polarizzazione circolare. Poiché vengono utilizzati substrati a basso costo, sono stati condotti studi di sensibilità e diversi confronti prestazionali tra le tipologie di antenna proposte. Nel Capitolo 5, un modello matematico tiene conto delle riflessioni multipath. Infine, il Capitolo 6 esamina le diverse figure di merito (FoM) per la valutazione dell'errore nella stima della DoA, introducendo una nuova FoM basata sui coseni direzionali. Le conclusioni seguono nel Capitolo 7
DESIGN AND CHARACTERIZATION OF ANTENNAS AND ANTENNAS ARRAY FOR DIRECTION OF ARRIVAL APPLICATIONS
CRISAFULLI, OTTAVIO
2025
Abstract
This thesis deals with the design and characterization of antennas and antenna arrays used for directional of arrival (DoA) application in the Bluetooth Low Energy (BLE) standard. The research aims to address several key challenges in DoA estimation, from the definition of the required antenna key performance indicators (KPI) to the evaluation of the various factors affecting DoA accuracy. The problem has been addressed by modeling the non-ideal behavior of the hardware as well as the multipath propagation and noise that significantly influence the system performance, especially in indoor environments. The use of circularly polarized signals is suggested and adopted in this thesis since it has several advantages. In particular, the use of circular polarized antennas does not require a relative orientation between the transmitter and receiver, known respectively as tag and locator and moreover, it makes possible the natural rejection of odd reflections enabled by circular polarization. Mitigating the influence of reflected signals is a desired characteristic, especially in complex indoor scenarios. The design of several antennas and antenna arrays with enhanced impedance and axial ratio bandwidth has been carried out. In particular novel configurations for single antennas and antenna systems have been analyzed to optimize the antenna KPIs. The study also investigates the impact of fabrication tolerances as well as the array geometries and feeding techniques. A grounded coplanar-fed circularly polarized antenna is proposed as it outperforms other monolithic antennas ensuring a percentage bandwidth BW%=3.1. A novel patch antenna fed by a branch line coupler is also developed to improve the axial ratio bandwidth and the overall circular polarization purity. The antennas studied are intended for mass production thus a low-cost substrate is adopted, for this reason, a sensitivity study has been carried out. The study confirms that slight variations of the dielectric constant of the substrate εr with respect to its nominal value have a significant effect. This circumstance was confirmed by the experimental characterization of the antenna array since a detuning of the resonance frequency was observed. To deal with this problem a direct approach has been conceived introducing a way to tune the antenna's resonance frequency after fabrication (i.e., by cutting the edges of each radiating patch). Moving to the direction of arrival algorithms an analytical model for multipath environments has been developed. The method allows us to consider a real scenario; since the different reflections are modeled and considered together with the noise. Evaluation of DoA estimation performances has been carried out by using standard algorithms (i.e., Music and Bartlett). A new approach called Embedded Radiation Pattern (ERP) is adopted to take into account the non-idealities of the real antenna system. The embedded patterns are used both to model amplitude and phase information measured at each port of the BLE locator and also to retrieve the direction of arrival in the newly developed direction-finding method. A comparison of this newly developed method with the Conventional Steering Vector (CSV) method, for different parameters confirms that ERP outperforms CSV in all cases. The ability to accurately retrieve the DoA of the incoming signals is a crucial task of this thesis, In this regard for "quantitative" evaluations, it is important to define a reliable error metric to assess the performance of various choices. In 1D and 2D scenarios, different error definitions are adopted in the literature and these definitions are not always meaningful from both physical and mathematical points of view. A new metric based on direction cosine has been therefore proposed. It well behaves in the 2D direction of arrival detection problems by considering the real angular distance between the target and the estimated DoA. We show that the new metric is superior since its definition takes into account the 3D nature of the 2D DoA estimation. The thesis is organized as follows: Chapter 1 briefly describes the main features of Bluetooth technology in location-based services, highlighting its advantages and drawbacks, the chapter also introduces the research objectives of the thesis. Chapter 2 describes the fundamentals of Direction of Arrival estimation and the Bluetooth Low Energy standard. Chapter 3 summarizes the design principles of microstrip patch antennas and a self-contained treatment that briefly recalls the widespread models of the design: the transmission line model and cavity model. Chapter 4 is focused on the design and experimental characterization of circular polarized antennas and antenna systems. Since low-cost substrates are used, sensitivity studies have been carried out as well as various performance comparisons between the proposed antenna typologies. In Chapter 5 a mathematical model takes into account multipath reflections is defined. Finally, a new approach to the DoA estimation is proposed. The new method, based on the use of Embedded Radiation Pattern (ERP), is described in detail. An extensive evaluation of its performance is carried out also in comparison with the standard approach of conventional steering vector. Finally, Chapter 6 reviews the different figures of merits (FoM) for error evaluation in DoA estimation introducing a new FoM based on direction cosines. Conclusions follow in Chapter 7File | Dimensione | Formato | |
---|---|---|---|
PhD Thesis_Crisafulli Ottavio_XXXVII ciclo.pdf
accesso aperto
Dimensione
27.16 MB
Formato
Adobe PDF
|
27.16 MB | Adobe PDF | Visualizza/Apri |
I documenti in UNITESI sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/20.500.14242/210223
URN:NBN:IT:UNIRC-210223