A multicarrier amplifier design linearized trough second harmonics and second-order IM feedback

A novel linearisation technique for reduction in the first and second kind of the third-order intermodulation products was applied in this paper. The second harmonics and second-order intermodulation products are led from the output to the input of a power amplifier through a feedback loop. The power amplifier including the feedback loop components (bandpass filter, phase shifter and attenuator) was designed as a hybrid microwave integrated circuit by using program ADS. The phase and amplitude of the loop signals are the adjustable parameters. Therefore, a voltage that controls a phase shift of the phase shifter and a control current of a PIN diode in the attenuator circuit were optimised to obtain a reduction in the third-order intermodulation distortion. For three fundamental signals at the power amplifier input, the lowest improvement of 13 dB for the first and 18 dB for the second kind of the third order intermodulation product levels was achieved

Miniaturized Quadrature Hybrid Couplers based on Novel U-shaped Transmission Lines

In this paper, a miniaturized microstrip quadrature hybrid coupler (QHC) using U-shaped transmission lines (USTLs) is presented. The proposed approach replaces all arms of the conventional QHC with its equivalent USTL to achieve compactness. The proposed coupler structure is designed to operate in the 1.5 GHz (1427-1518 [MHz]) band which is one of the 5G bands of interest. At such low RF/microwave bands below 3-4 GHz, the size of the conventional coupler is considerably very large which raises a concern for the next generation networks. The pro- posed coupler is designed, simulated and fabricated using Rogers 5880 with thickness of 0.79 mm, dielectric con- stant (εr) of 2.2 and loss tangent of 0.0021. The proposed QHC size is 70% smaller in circuit area (30% relative area) than the conventional equivalent. Simulation and mea- sured results are presented and good matching between the results is observed, confirming the outstanding coupler performance properties. The proposed miniaturized QHC structure will play a vital role for next generation 4G and 5G wireless communication systems operating below 6 GHz

Linearization of multichannel amplifiers with the injection of second harmonics into the amplifier and predistortion circuit

A linearization technique that uses the injection of the fundamental signal second harmonics together with the fundamental signals at the amplifier input has been extended in this paper by introducing the injection the second harmonics into nonlinear microwave amplifier and so-called predistortion circuit. Predistortion circuit produces the third-order intermodulation signals that are injected at the amplifier input together with the second harmonics making the linearization procedure more independent on the phase variation of the second harmonics. In addition, a considerably better improvement is attained for the power of fundamental signals close to 1-dB compression point by applying the linearization technique proposed in this paper in comparison to the linearization with the injection of the second harmonics merely in the nonlinear amplifier

Doherty Amplifier Linearization in Experiments by Digital Injection Methods

In this paper, the experimental verification of two linearization methods applied on a broadband two-way microstrip Doherty amplifier is performed. The laboratory set-ups are formed to generate the baseband nonlinear linearization signals of the second-order. After being tuned in magnitude and phase in the digital domain the linearization signals modulate the second harmonics of fundamental carrier. In the first method, adequately processed signals are then inserted at the input and output of the main Doherty amplifier transistor, whereas in the second method, they are injected at the outputs of the Doherty main and auxiliary amplifier transistors. The experimental results are obtained for 16QAM and 64QAM digitally modulated signals

Experimental Verification of the Impact of the 2nd Order Injected Signals on Doherty Amplifiers Nonlinear Distortion

In this paper, an asymmetrical Doherty amplifier fabricated in microstrip technology is tested in the experiments to verify the impact of the 2nd order signal for the linearization prepared in baseband. The measurement set-up consists of three USRPs programmed by LabVIEW to generate the useful 64QAM signal and the signals for linearization that are set in amplitude and phase and modulate the 2nd harmonic of fundamental carrier. The USRPs instruments should be synchronized for performing measurements for two scenarios: the signals for linearization are injected at input of the transistor within the main Doherty amplifier or are injected at its output

Low intermodulation amplifiers for RF and microwave wireless systems

A novel linearisation technique for reduction in the third-order intermodulation distortion products, with injection of second harmonics through a feedback loop of a power amplifier, was applied in this paper. The power amplifier including the feedback loop components (bandpass filter, phase shifter, attenuator) was designed as a hybrid microwave integrated circuit by using the program Libra. The adjustable parameters are the phase and amplitude of the loop signals. Therefore, a voltage that controls a phase shift of the phase shifter and a control current of a PIN diode in the attenuator circuit were optimised to obtain a reduction in the third-order intermodulation distortion. The achievable improvement was found to be 21 dB for the case of two fundamental signals at the power amplifier inpu

An In Vitro Synergistic Interaction of Combinations of Thymus glabrescens Essential Oil and Its Main Constituents with Chloramphenicol

The chemical composition and antibacterial activity of Thymus glabrescens Willd. (Lamiaceae) essential oil were examined, as well as the association between it and chloramphenicol. The antibacterial activities of geraniol and thymol, the main constituents of T. glabrescens oil, individually and in combination with chloramphenicol, were also determined. The interactions of the essential oil, geraniol, and thymol with chloramphenicol toward five selected strains were evaluated using the microdilution checkerboard assay in combination with chemometric methods. Oxygenated monoterpenes were the most abundant compound class in the oil, with geraniol (22.33%) as the major compound. The essential oil exhibited in vitro antibacterial activity against all tested bacterial strains, but the activities were lower than those of the standard antibiotic and thymol. A combination of T. glabrescens oil and chloramphenicol produced a strong synergistic interaction (FIC indices in the range 0.21-0.87) and a substantial reduction of the MIC value of chloramphenicol, thus minimizing its adverse side effects. The combinations geraniol-chloramphenicol and thymol-chloramphenicol produced synergistic interaction to a greater extent, compared with essential oil-chloramphenicol association, which may indicate that the activity of the thyme oil could be attributed to the presence of significant concentrations of geraniol and thymol

Antioxidative responses to seasonal changes and chemiluminescence assay of Astragalus onobrychis leaves extract

The aim of this study was to research the seasonal changes of antioxidant enzyme activity and total antioxidant capacity in leaves of Astragalus onobrychis L. subsp. chlorocarpus (Griseb.) S. Kozuharov et D.K. Pavlova. Leaves of A. onobrychis were collected during the different stages of growth and analyzed for antioxidant enzyme activity: superoxide dismutase, catalase, guaiacol peroxidase, glutathione peroxidase. Quantities of malonyldialdehyde, superoxide radicals, and hydroxyl radicals were measured as well as the content of soluble proteins. Furthermore, total antioxidant capacity was determined by the inhibition of chemiluminescence activity of blood phagocytes by leaf extracts. Stages of vegetation significantly affected the accumulation of superoxide radicals, but there were no significant differences in hydroxyl radical quantity and lipid peroxidation levels during vegetation. Soluble proteins vary greatly between different stages of growth. Seasonal changes were found to have an effect on enzymatic activities. During the spring season, guaiacol peroxidase showed the highest levels. Catalase and glutathione peroxidase increased their activities in summer, while, during the autumn season, superoxide dismutase showed maximum activity. On the basis of chemiluminescence assay, it can be concluded that leaf extract of A. onobrychis possesses a significant antioxidant capacity thus protecting plants during environmental stress