International Telemetering Conference Proceedings / October 13-16, 1986 / Riviera Hotel, Las Vegas, Nevada / A digital frequency discriminator (DFD) of the delay-correlator type is described. The device is shown to have an instantaneous frequency measurement capability on very short pulses. The theoretical performance of the DFD in a noisy background is derived and shown to compare favorably with measured results.

With the rapid and ongoing developments in telecommunication and electronic warfare technology, faster and more flexible systems are in demand. Wideband signal processing is thus needed to implement such systems. Microwave photonics has been introduced as a tool for achieving such ultra broadband signal processing. Instantaneous Frequency Measurement (IFM) receivers play an important role in electronic warfare. They have been developed as a means of obtaining a rapid indication of the presence of a threat and to roughly identify the frequency of the threat signals. They also have the advantages of low-cost, compactness and moderate to good sorting capability in an interference-free environment. The main limitation of the traditional RF IFM receivers is constrained bandwidth. Microwave Photonic IFMs have been considered, but the main disadvantages of photonic realization of the recent IFM receiver is cost. This work aims to propose and demonstrate low-cost photonic IFM receivers with a broad frequency measurement range. The proposed methods are based on the use of photonic mixing to down-convert the RF modulated optical signals to DC. In a RADAR warning receiver, usually a bank of IFMs is required. Increasing the numbers of IFMs requires an increase in the number of photo-detectors. Thus if low-frequency, low-cost detectors can be used, then the net system cost will be reduced significantly. The concept is proven and the issues arising are analyzed. In the proof of concept system, measurement of the RF frequency required advance knowledge of the RF power. Secondly, the use of co-axial RF cables as delay elements limited the bandwidth and increased bulk. Using a photonic hybrid approach to achieve orthogonal measurements was demonstrated as a means of dentifying both RF frequency and power simultaneously and independently. Employing all optical mixing removed the need for co-axial RF cables delays using non-linear optical devices such as Semiconductor Optical Amplifier (SOA) and Highly Non-Linear Fiber (HLNF). The last investigation is to improve the sensitivity of the implemented IFM system. The sensitivity of the implemented system is characterized first and a lock-in technique is employed to improve the sensitivity of the system. The final system achieves a sensitivity of -41 dBm which is comparable with the traditional RF IFM receivers.

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In this thesis, RF sections of a multi tier instantaneous frequency measurement (IFM) receiver which can operate in 2 &ndash / 18 GHz frequency band is designed, simulated and partially realized. The designed structure uses one coarse tier, three medium tiers and one fine tier for frequency discrimination. A novel reflective phase shifting technique is developed which enables the design of very wideband phase shifters using stepped cascaded transmission lines. Compared to the classical phase shifters using coupled transmission lines, the new approach came out to be much easier to design and fabricate with much better responses. This phase shifting technique is used in coarse and medium tiers. In fine frequency measurement tier, I/Q discriminator approach is used because reflective phase shifters would necessitate unacceptably long delay lines. Two I/Q discriminators are designed and fabricated using Lange directional couplers that operate in 2-6 GHz and 6-18 GHz, resulting in satisfactory response. Additionally, 6 GHz HP and 6 GHz LP distributed filters are designed and fabricated to be used for these I/Q discriminators in fine tier. In order to eliminate possible ambiguities in coarse tier, a distributed element LP-HP diplexer with 10 GHz crossover frequency is designed and fabricated successfully to be used for splitting the frequency spectrum into 2-10 GHz and 10-18 GHz to ease the design and realization problems. Three power dividers operating in the ranges 2-18 GHz, 2-6 GHz and 6-18 GHz are designed for splitting incoming signals into different branches. All of these dividers are also fabricated with satisfactory response. The fabricated components are all compact and highly reproducible. The designed IFM can tolerate 48 degrees phase margin for resolving ambiguity in the tiers while special precautions are taken in fine tier to help ambiguity resolving process also. The resulting IFM provides a frequency resolution below 1 MHz in case of using an 8-bit sampler with a frequency accuracy of 0.28 MHz rms for 0 dB input SNR and 20 MHz video bandwidth.

Microwave limiting amplifiers are the key components of Instantaneous Frequency Measurement (IFM) systems. Limiting amplifiers provide constant output power level in a wide input dynamic range and over a broad frequency band. Moreover, limiting amplifiers are high gain devices that are used to bring very low input power levels to a constant output power level. Besides, limiting amplifiers are required to provide minimum small signal gain ripple in order not to reduce the sensitivity of the IFM system over the operating frequency band. In this thesis work, a high gain, medium power, 2-18 GHz limiting amplifier module is designed, simulated, fabricated and measured. First, a 3-stage cascaded amplifier with 27 dB small signal gain is designed and fabricated. The 3-stage amplifier is composed of a novel cascaded combination of negative feedback and distributed amplifiers that provides the minimum small signal gain ripple and satisfactory input and output return losses inside 2-18 GHz frequency band. Then, the designed two 3-stage amplifiers and one 4-stage amplifier are cascaded to constitute a limiting amplifier module with minimum 80 dB small signal gain. The designed 10-stage limiting amplifier module also includes an analog voltage controllable attenuator to be used for compensating the gain variations resulting from temperature changes. The fabricated 10-stage limiting amplifier module provides 20 +/- 1.2 dBm output power level and excellent small signal gain flatness, +/- 2.2 dB, over 2-18 GHz frequency range.

[EN] Microwave photonics (MWP) is a well-established research field that investigates the use of photonic technologies to generate, distribute, process and analyze RF waveforms in the optical domain. Despite its great potential to solve long-standing problems faced by both the microwave and electronics industries, MWP systems are bulky, expensive and consume a lot of power. Integrated microwave photonics (IMWP) is an emerging area of research that promises to alleviate most of these drawbacks through the use of photonic integrated circuits (PIC). In this work, we have aimed at further closing the gap between the worlds of MWP and integrated optics. In particular, we have focused on the design and experimental characterization of PICs with reconfigurable, ring-assisted Mach-Zehnder interferometer filters (RAMZI), and demonstrated its potential use in different IMWP applications. These filters consist of a symmetric MZI loaded with ring resonators, which are coupled to the MZI branches by different optical couplers. The contributions of this thesis can be split into two sections. In the first one, we demonstrate integrated optical couplers and reflectors with variable power splitting and reflections ratios. These exploit the well-known properties of tapered multimode interference couplers (MMI), and their inherent robustness makes them highly suitable for the implementation of both RAMZI and reflective filters. Besides, we study in detail the impact of manufacturing deviations in the performance of a 4x4 MMI-based 90º hybrid, which is a fundamental building block in coherent optical communication systems. In the second section, we demonstrate the use of integrated RAMZI filters for three different IMWP applications, including instantaneous frequency measurement (IFM), direct detection of frequency-modulated signals in a MWP link, as well as in tunable, coherent MWP filters. A theoretical analysis of the limits and trade-offs that exist in photonics-based IFM systems is also provided. Even though these are early proof-of-concept experiments, we hope that further technological developments in the field will finally turn MWP into a commercial reality. / [ES] La fotónica de microondas (MWP) es un campo de investigación que estudia el uso de tecnologías ópticas para generar, distribuir, procesar y analizar señales de RF. A pesar de su gran potencial para resolver algunos de los problemas a los que se enfrentan las industrias electrónica y de microondas, estos sistemas son voluminosos, caros y consumen mucha potencia. La fotónica de microondas integrada (IMWP) es un área emergente que promete solucionar todos estos inconvenientes a través de la utilización de circuitos ópticos integrados (PIC). En esta tesis, hemos pretendido avanzar un poco más en el acercamiento entre estas dos disciplinas. En concreto, nos hemos centrado en el diseño y caracterización experimental de PICs con filtros reconfigurables basados en interferómetros Mach-Zehnder cargados con anillos (RAMZI), y demostrado su potencial uso en diferentes aplicaciones de IMWP. Los filtros RAMZI están hecho básicamente de un MZI simétrico cargado con anillos, los cuales a su vez se acoplan a las ramas del interferómetro a través de distintos acopladores ópticos. Las contribuciones de este trabajo se pueden dividir en dos partes. En la primera, hemos demostrado acopladores y reflectores ópticos integrados con coeficientes de acoplo y reflexión variables. Éstos explotan las propiedades de los acopladores por interferencia multimodal (MMI), y su robustez les hace muy atractivos para la implementación de filtros RAMZI y de tipo reflectivo. Además, hemos analizado el impacto que las tolerancias de fabricación tienen en el rendimiento de un híbrido óptico de 90º basado en un MMI 4x4, el cual es un elemento fundamental en los sistemas de comunicaciones ópticas coherentes. En la segunda parte, hemos demostrado el uso de filtros RAMZI en tres aplicaciones distintas de IMWP. En concreto, hemos utilizado dichos filtros para implementar sistemas de medida de frecuencia instantánea (IFM), detección directa de señales moduladas en frecuencia para enlaces fotónicos, así como en filtros coherentes y sintonizables de MWP. También hemos desarrollado un análisis teórico de las limitaciones y problemas que existen en los sistemas IFM. A pesar de que todos los experimentos realizados han consistido en prototipos para una prueba de concepto, esperamos que futuros avances tecnológicos permitan que la fotónica de microondas se convierta algún día en una realidad comercial. / [CA] La fotònica de microones (MWP) és un camp d'investigació que estudia l'ús de tecnologies òptiques per a generar, distribuir, processar y analitzar senyals de radiofreqüència. A pesar del seu gran potencial per a resoldre alguns dels problemes als que s'enfronten les indústries electrònica i de microones, estos sistemes son voluminosos, cars i consumixen molta potència. La fotònica de microones integrada (IMWP) és un àrea emergent que promet solucionar tots estos inconvenients a través de la utilització de circuits òptics integrats (PIC). En esta tesi, hem pretés avançar un poc més en l'acostament entre estes dos disciplines. En concret, ens hem centrat en el disseny i caracterització experimental de PICs amb filtres reconfigurables basats en interferòmetres Mach-Zehnder carregats amb anells (RAMZI), i demostrat el seu potencial en diferents aplicacions d' IMWP. Els filtres RAMZI estan fets bàsicament d'un MZI simètric carregat amb anells, els quals, al seu torn, s'acoblen a les branques del interferòmetre a través de distints acobladors òptics. Les contribucions d'este treball es poden dividir en dos parts. En la primera, hem demostrat acobladors i reflectors òptics integrats amb coeficients de transmissió i reflexió variables. Estos exploten les propietats dels acobladors per interferència multimodal (MMI), i la seua robustesa els fa molt atractius per a la implementació de filtres RAMZI i de tipo reflectiu. A més a més, hem analitzat l'impacte que les toleràncies de fabricació tenen en el rendiment d'un híbrid òptic de 90 graus basat en un MMI 4x4, el qual és un element fonamental en els sistemes de comunicacions òptiques coherents. En la segona part, hem demostrat l'ús de filtres RAMZI en tres aplicacions diferents de IMWP. En concret, hem utilitzat estos filtres per a implementar sistemes de mesura de freqüència instantània (IFM), detecció directa de senyals modulades en freqüència per a enllaços fotònics, així com en filtres coherents i sintonitzables de MWP. També hem desenvolupat una anàlisi teòrica de les limitacions i problemes que existixen en els sistemes IFM. A pesar de que tots els experiments realitzats han consistit en prototips per a una prova de concepte, esperem que futurs avanços tecnològics permeten que la fotònica de microones es convertisca algun dia en una realitat comercial. / Sánchez Fandiño, JA. (2016). Integrated Optical Filters for Microwave Photonic Applications [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/67690