Study and Application of Microwave Active Circuits with Negative Group Delay

This chapter is available on the following open access link: http://www.intechopen.com/books/microwave-and-millimeter-wave-technologies-modern-uwb-antennas-and-equipment/study-and-application-of-microwave-active-circuits-with-negative-group-delayA simple topology of an NGD active circuit consisting of a FET terminated by a shunt RLC-resonant network and dedicated to the microwave signals was proposed and extensively studied. To our knowledge, in this chapter, the first experimental time-domain demonstration of a circuit able to exhibit simultaneously gain and NGD in microwave domain is proposed. By injecting in the NGD circuit a sufficiently smoothed input short-pulse modulating a sine carrier, one gets an output having an envelop peak in advance compared with the input one. Of course, this phenomenon does not contradict the causality principle. It is also worth emphasizing that the tested circuit respects all required criteria of classical active microwave devices such as gain, matching and stability. As predicted in theory (Ravelo et al., 2007a, 2007b, 2007c and 2008a), for a prototype implemented in planar technology, we have measured in time-domain a pulse peak advance of about -2 ns or 24% of the 1/e-input pulse half-width without attenuation. It is also interesting to note that through this experimentation, the input noise contribution did not destroy the occurrence of time-domain advance induced by the NGD active circuit. Moreover, in this chapter, thanks to the S21-magnitude form, the understudied NGD circuit is able to exhibit a pulse compression phenomenon with a possibility of amplification. Then, it should be worth using the presented NGD active topology to compensate for dispersion effects and especially to reduce the intersymbol interference in certain telecommunication channels. As a potential application of this NGD circuit, a new principle of frequency independent phase shifter is proposed. By cascading a classical transmission line with this NGD circuit, a constant phase value is obtained. The efficiency of this principle was demonstrated by measurement. Indeed, a constant phase value of 90°±5° was obtained within a 76% relative frequency band centred at about 1.5 GHz. The impacts of the PS parameter variations and sensitivity analysis are stated. The main benefits of this NGD active PS concerns its compactness and also the facility to generate very low group delay, and the broad band characteristics. Besides, a two-stage NGD PS was also designed; the simulation results showed a bandwidth enhancement of the constant phase up to 125%. Some fields of applications such as the design of broadband active balun for RF front end architectures are discussed. As ongoing research, design of reconfigurable devices dedicated to telecommunication applications is envisaged. Future investigations will be devoted to the design of NGD devices able to operate at higher frequencies through the use of distributed elements. In this optic, the implementation of MMIC devices based on distributed elements is envisaged

Synthese et realisations d'amplificateurs micro-ondes par la methode des frequences reelles

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

A New Technique of Interconnect Effects Equalization by Using Negative Group Delay Active Circuits

Non

Miniature Antenna for Breast Tumor Detection

International audienceMicrowave imaging is recognized as a potential candidate for biomedical applications, such as breast cancer detection. In this context a miniature antenna is used for quantitative imaging of inhomogeneous tissues. Microwave breast imaging (MBI) uses low power and longer wavelength signals to obtain information about breast tissues, and promises a safer and more accurate modality for regular breast scanning. This paper presents a miniature microstrip antenna that can be placed in contact with the breast model to investigate the presence of malignant tissues. A miniature antenna has been designed, and placed toward a breast phantom model with inhomogeneous tissues. Images are successfully obtained by using scattering electromagnetic waves (S11) from the designed model. The antenna was then manufactured and tested.In this paper the design of a miniature antenna for microwave imaging has been presented. This antenna aims to overcome the limitation of the conventional solutions by detecting breast tumors regardless its evolution stages. The simulation results show that the response of the antenna is affected in terms of frequency and return loss when it’s implanted on the heterogeneous model. Indeed, comparing to the normal breast model simulated response, the frequency was down shifted of around 100 MHz and the S11 parameter was improved. The antenna has been fabricated using plexyglass substrate and the measured results confirm the resonance frequency shift from 2.63 GHz to 2.54 GHz and the S11 improvement from -12 dB to -18 dB These results are respectively obtained when the antenna is implemented on two different mediums: clean serum representing a human body with absence of tumor and serum with steel balls representing human body with presence of tumor. After this first proof-of-concept, it’s intended to design the antenna using a flexible substrate and to perform real tests using samples representing tumors in human body which would be given by the research team of CHRU (Centre Hospitalier Régional et Universitaire de Brest) in Brest - France.