Natasa Males-Ilic

MESFET noise modeling based on noise wave temperatures

A simple procedure for the extraction of intrinsic noise wave temperatures in the wave representations of microwave transistors is presented in this paper. A set of equations describing the noise parameters as a function of three equivalent noise temperatures is implemented within the circuit simulator Libra. After that, the wave noise model is defined as a new user-defined element of the Libra program library. Good agreement between modeled and measured noise parameters is observed.

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.

Amplifiers with Improved IMD Performance for Multi-Channel Wireless Systems

A linearization technique for reducing spectral regrowth caused by the third-order non-linearity, that uses the injection of the fundamental signal second harmonic together with the fundamental signal at the amplifier input has been applied in this paper. The second harmonic is led from the output to the amplifier input trough the feedback loop. Designed amplifier with additional components at feedback loop (phase shifter, attenuator, bandpass filter, power divider and combiner) has been tested for OQPSK modulation at 2.5 GHz carrier frequency. Optimising phase shift and attenuation of the feedback loop signals 16 dB improvement in the adjacent channel power ratio (ACPR) for ±900 KHz offset from carrier frequency over 30 KHz bandwidth was obtained in simulation by program ADS. The measured results for the amplifier with second harmonics feedback referring to output powers for seven fundamental signal frequencies at the amplifier input and the higher order IMD signals are shown as well.

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 (Advanced Design System). The phase and amplitude of the loop signals are the adjustable parameters. Therefore, a voltage that controls the phase shift of the phase shifter and the 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 fist and 18 dB for the second kind of the third-order intermodulation product levels was achieved.

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 input.

Application of neural networks in microwave FET transistor noise modeling

An application of neural networks in microwave FET transistor (MESFET) noise modeling is presented. A multilayer perceptron neural network is implemented to model four transistor noise parameters. Inputs for the neural models include small-signal intrinsic equivalent circuit elements, two equivalent temperatures and frequency, while outputs are noise parameters. Pospieszalskis approach is employed to characterize the noise parameters.

Design of Low Intermodulation Amplifiers for Wireless Multichannel Applications

A novel linearisation technique for reduction in the third-order intermodulation distortion products, with the injection of the second harmonics through a feedback loop of a power amplifier was applied in this paper. The power amplifier including the feedback loop components (band pass filter, phase shifter, attenuator) was designed as a hybrid microwave integrated circuit. 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 15 dB for the case of the two fundamental signals at the power amplifier input.

Linearization of broadband doherty amplifier

The linearization of broadband two-way Doherty amplifier for application in the frequency range 0.85-1.15GHz is considered in this paper. The carrier and peaking amplifiers in Doherty configuration comprise Freescales transistor MRF281S LDMOSFET characterized by the maximum output power 4W and the broadband lumped element matching circuits. The linearization of the amplifier is carried out by the second harmonics and fourth-order nonlinear signals that are extracted at the output of the peaking cell, adjusted in amplitude and phase and injected at the input and output of the carrier cell in Doherty amplifier. The effects of linearization are considered for two tones separated in frequency by 10MHz, 20MHz, 40MHz and 80MHz at different input power levels of 0dBm, 5dBm, 10dBm and 15dBm, as well as for WCDMA digitally modulated signal.

An amplifier design for MMDS application at 12 GHz using neural network transistor noise model

The modeling procedure of a single-stage amplifier for MMDS application at 11.7-12.5 GHz is presented in this paper. A neural network noise model for the Hewlett Packard pseudomorphic HEMT ATF-36163 is used for simulation purposes. Designing results at a center frequency of the required frequency range 12.1 GHz obtained by using standard microwave circuit simulator Libra are: gain 10.9 dB, noise figure 1.23 dB, input return loss -12.8 dB and output return loss -12 dB. Noise parameter characteristics (F/sub min/, r/sub n/, /spl Gamma//sub opt/) of the amplifier simulated for neural network transistor noise model are compared with the ones obtained for transistors S and noise parameters available in the manufacturers catalog. Good agreement can be seen for all characteristics.

MESFET Noise Model based on Three Equivalent Temperatures

A completed model for the prediction of MESFET noise parameters by using the standard microwave circuit simulator is proposed in this paper. Starting from the noise model with two noise sources and two corresponding equivalent temperatures, the correlation between the noise sources in the model is taken into account in a new way, by assigning an additional complex parameter named equivalent correlation temperature. A set of equation describing the noise parameters as the function of equivalent circuit elements as well as three equivalent temperatures is derived. The proposed procedure is implemented within the circuit simulator Libra and applied to a number of commercially available MESFETs. The simulated noise parameters agree very well with referent data.