employed both as a resonant antenna for receiving the RF signal and for constructing the balanced mixer. In order to further minimize the complexity of the circuit, the receiving Part ofthe mansponder was designed using only one as a single ended SOM. A new planar transponder integrating a self-oscillating mixer (SOM) and active antennas is presented. The receiving active antenna combines a FET SOM with a patch antenna and the transmitting antenna is combined with the IF amplifier. The transponder was successfully operated up to 2 m. The design concept and the experimental result are discussed.

This thesis was carried out in the DIEMAG Group and TSC department of ETSI y Sistemas de Telecomunicacion from Universidad Politecnica de Madrid. Its title is “Contributions and Reflections to the Study of Stability and Oscillation of Active Antennas” and it has been developed by Angel Parra Cerrada, Electrical Engineer MSc, under the supervision of Prof. Vicente Gonzalez Posadas, PhD and Prof. Jose Luis Jimenez Martin, PhD. The current interest on active antennas is very important, mainly on small antennas and integrated antennas. The patch antennas are maybe the type of integrated antennas more used at present designs. The design of active patch antennas must always include a study of stability, because they must be stable for amplifier function or because they must oscillate in a proper way for TX-oscillator, mixing-oscillator, etc. The fundamental aspects of analysis of patches and their modes are covered in a general review. The modes and internal fields of the patches are fundamental for the proper understanding of the radiation diagram, impedance at the feed point, interaction with active elements and compatibility with the feeding uses for active functions. The main problem to study the stability of any circuit is as several authors have pointed out that “there is not a compact formulation of an oscillation criterion that is both necessary and sufficient”. The linear methods for the study of the stability of the RF circuits are reviewed and the conditions for their proper use, limitations and problems are exposed and summarized. The presentation of a new method based on the NDF for the linear stability analysis is a significant contribution of this work. This proposed method is used for several designs of active antennas and compared with classic linear methods, non-linear simulations and measurements. These comparatives state the NDF Method as correct predictor of stability, but not the classic linear methods. The new proposed NDF Method is a compact procedure that is necessary and sufficient criterion on the study stability. There are multiple elements that can be used to tune or control the impedance of the patches. Two of these elements are the metamaterials (passive) and the Negative Impedance Converters, NIC (active). The inclusion of these elements on active patches and their implications on the stability of active patches are studied using the NDF Method and the classic methods. The results outcome that the use of NICs built with discrete transistors is a high risk for the stability. The proposed NDF Method opens a new way for the research of new oscillators, active antennas and low phase noise oscillator topologies. The lack of additional conditions (proviso) for the use of the NDF Method provides it the advantage of being a universal method for studying the linear stability of any topology of oscillator or active antenna. The thesis covers in detail the field of the stability of integrated active patch antennas. This study of the stability is disseminated with multiple publications as it is detailed in the contributions section. RESUMEN Esta tesis ha sido realizada en el Grupo DIEMAG y en el Departamento TSC de la ETSIS y Sistemas de Telecomunicacion de la Universidad Politecnica de Madrid. Su titulo es “Contributions and Reflections to the Study of Stability and Oscillation of Active Antennas” (Contribuciones y Reflexiones al Estudio de la Estabilidad y Oscilacion de Antenas Activas) y ha sido realizada por Angel Parra Cerrada, Ingeniero de Telecomunicacion (MSc), bajo la direccion de el Prof. Dr. Vicente Gonzalez Posadas y el Prof. Dr. Jose Luis Jimenez Martin. Hoy en dia existe un gran interes en el campo de las antenas activas, especialmente en las antenas integradas y de pequeno tamano. Posiblemente, las antenas de parche sean, al dia de hoy, las antenas mas utilizadas en los nuevos disenos. El diseno de antenas activas siempre debe incluir un analisis de su estabilidad, ya que esta debe ser estable para aplicaciones como la amplificacion e inestable de forma controlada para otras como oscilador, mezclador-oscilador, etc. Los principales aspectos del analisis de los parches y de sus modos se cubren en una presentacion general de estos. Conocer los campos internos de los parches es imprescindible para poder tener un correcto entendimiento de los diagramas de radiacion, impedancia de entrada, interaccion con los elementos activos y compatibilidad con puntos de acoplo al parche usados por los elementos activos. El mayor problema para el estudio de la estabilidad de cualquier circuito es, como declaran diversos autores, “no existe una formulacion compacta del criterio de oscilacion que sea condicion necesaria y suficiente” . Se realiza una revision de los metodos clasicos de analisis lineal de la estabilidad de circuitos de RF y se enumeran y resumen sus condiciones para un uso apropiado, limitaciones y problemas. Una importante aportacion de esta tesis es la presentacion de nuevo metodo lineal de analisis de estabilidad basado en la NDF. El metodo propuesto es utilizado en el diseno de varias antenas activas; y los resultados de este analisis, de los analisis con los metodos clasicos, de los analisis no lineales y de las medidas son comparados. Estas comparaciones demuestran que el metodo basado en la NDF es una herramienta correcta para el analisis de estabilidad, mientras que los metodos clasicos no lo son. Este nuevo metodo basado en la NDF es un metodo compacto que es un predictor necesario y suficiente para el estudio de la estabilidad. Existen multiples elementos que pueden ser utilizados para ajustar y controlar la impedancia de los parches. Dos de estos elementos son los metamateriales (pasivos) y los Conversores de Impedancia Negativa, NIC (activo). Las implicaciones y efectos de incluir estos elementos en parches activos se han estudiado utilizando el metodo basado en la NDF y los metodos clasicos. Los resultados demuestran que los NICs realizados con transistores discretos presentan un elevado riesgo de inestabilidad. El metodo basado en la NDF que se ha propuesto posibilita nuevos caminos para la busqueda de nuevas topologias de osciladores, antenas activas y osciladores de bajo ruido. El no requerir ninguna condicion previa (proviso) para utilizar el metodo basado en la NDF, le confiere a este la ventaja de ser un metodo universal para el estudio de la estabilidad valido para cualquier topologia de osciladores y antenas activas. En esta tesis se desarrolla en detalle el estudio de la estabilidad y antenas activas. Este estudio de la estabilidad se ha difundido ampliamente con multiples publicaciones, tal como se detalla en el capitulo de Contribuciones.

Self-oscillating mixer and active antenna

Contributions and reflections to the study of stability and oscillation of active antennas

http://ieeexplore.ieee.org/iel5/1100/7886/00335423.pdf

Planar quasi-optical receivers that compactly integrate a coupled slot antenna and a HEMT or MESFET balanced self-oscillating mixer and on the same substrate for applications in microwave and millimeter-wave receiver arrays are discussed. Both the HEMT and the MESFET circuit are designed and demonstrated at X-band. The HEMT circuit exhibits an isotropic conversion gain of 4.5 dB and a noise figure of 6.5 dB. The isotropic conversion gain of the HEMT circuit is 7.5 dB higher than the mixer diode circuit previously reported. >

Self-oscillating mixer and active antenna

Citations

Contributions and reflections to the study of stability and oscillation of active antennas

References

Quasi-optical HEMT and MESFET self-oscillating mixers

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