Electrothermal Analyses of Bandpass NGD RLC-Network Topologies

This paper develops an original study of temperature effect on the unfamiliar bandpass (BP) negative group delay (NGD) lumped passive circuits. The paper presents the first study of electrothermal analysis of electronic circuits classified as BP-NGD topologies. The considered BP-NGD passive cells are mainly constituted by RLC-resonant networks. The equivalence between two basic BP-NGD topologies constituted by RLC-series and RLC-parallel networks is elaborated via the voltage transfer function (VTF) analogy. Then, the theoretical demonstrations are introduced to define the main specifications as the NGD center frequency, NGD value, attenuation and NGD bandwidth. The electrothermal innovative study is developed based on the temperature coefficient resistor (TCR) of elements constituting the BP-NGD circuits. With proofs of concept of RLC-series and RLC-parallel circuits operating with -500 ns NGD value at 13.56 MHz, calculated and simulated results showing are in excellent agreement. The sensitivity analyses of BP-NGD specifications in function of ambient temperature variation from 0°C to 100°C are investigated. The BP-NGD response variations versus frequency and temperature are characterized with thermo-frequency cartographies and discussed

Active negative group delay circuits and applications

The design of a low profile antenna operating over wide bandwidth with enhanced radiation performance is the objective of this work. The methods to improve the operational bandwidth, reduce the size and enhance the radiation properties such as directivity and gain, while minimising the beam squint for an antenna are presented. Two antennas are designed: an electrically small antenna (ESA) integrated with an active circulator for simultaneous signal transmission and reception (duplex operation) operating over a wide bandwidth and a Fabry-Perot cavity antenna having high directivity and gain with reduced beam squint. A negative group delay (NGD) concept is used in lumped element implementation and in frequency selective surface implementation for achieving the objectives of this work. A detailed study is carried out on the filter based NGD network design. The NGD network impact is clearly demonstrated: in adjusting the impedance characteristics for the design of an ESA; in achieving wideband signal cancellation for the active circulator and in optimising the phase characteristics of a high impedance surface (HIS) for the design of a wideband Fabry-Perot cavity antenna with reduced beam squint. A low profile ESA is designed using a NGD matching network. The passive NGD network offers wide bandwidth impedance matching for an antenna over the frequency band, far lower than the quarter wavelength resonance frequency associated with the physical length of the antenna. The inevitable transmission loss of the NGD based matching network is compensated using an active circulator. This enables the ESA to be used in duplex mode. An active quasi-circulator operating over a wide bandwidth, working on a signal cancellation principle is designed using NGD networks. The employment of the NGD network achieved signal cancellation over a wide bandwidth. This network also offered extra design flexibility in terms of optimisation and selection of gain blocks. The ESA is integrated with an active circulator of 14% bandwidth operating at 1.8GHz. The average 5dB gains in the transmission and reception paths are used to compensate the losses of the matching network. This novel antenna is suitable for duplex operation over a wide bandwidth. The prototypes of the ESA and the active circulator are fabricated and tested separately. An ESA operating at 1.08GHz ( =0.98/2) of 50% bandwidth with a physical length of 43mm is designed and tested. This method is more stable and effective than those that are reported in the literature. The performance parameters of the ESA are discussed in detail. A three-port active circulator (clockwise: transmitter, antenna, receiver) operating at 1.5GHz with 200MHz (14%) bandwidth offering 20dB isolation between the transmitter and the receiver is fabricated and tested. Between any pair of ports the average gain in the clockwise direction is 5dB and the isolation in the anti-clockwise direction is greater than 20dB. The noise figure is less than 5dB from the antenna to the receiver. Using the proposed method the bandwidth of the circulator is improved almost 30 times compared to a similar design reported in the literature. A Fabry-Perot cavity antenna operating at 10GHz is designed with a partially reflective surface (PRS) and a high impedance negative group delay surface. The HIS with NGD characteristics enabled the establishment of the resonance phase condition over a 0.75GHz bandwidth resulting in a wideband cavity antenna with reduced beam squint. The signal absorption along the HIS and the possible loss compensation techniques are also discussed. A lossy design has exhibited only 0.20 per 100MHz beam squint over 1.5GHz bandwidth with degraded directivity and gain. A loss compensated model has exhibited 1.30 per 100MHz beam squint over 0.75GHz with improved directivity and gain of 19dBi and 5.6dBi respectively

Good Research Practice in Non-Clinical Pharmacology and Biomedicine

This open access book, published under a CC BY 4.0 license in the Pubmed indexed book series Handbook of Experimental Pharmacology, provides up-to-date information on best practice to improve experimental design and quality of research in non-clinical pharmacology and biomedicine

THE IMPACT OF MERGERS AND ACQUISITIONS ON THE ECONOMIC PERFORMANCES

This paper aims to measure the extent to which banking systems from Central and Eastern Europe have been characterized by banking consolidation through mergers and acquisitions and the extent to which this process led to the concentration of the banking activity. Also, we measure the impact of mergers and acquisitions on the economic performance of the targeted banks. The conclusions show that the banking system from Central and Eastern Europe was subject to numerous acquisitions from Western banks that chose to enter aggressively into these markets with high growth potential. The effect of the acquisitions on the economic indicators is not obvious in the first years because of the strategy aiming larger market shares.mergers; acquisitions; consolidation; financial repression; economic performances.