A new computer analysis method is presented by which the noise contributions of the various noise sources within a MESFET mixer can be determined and its overall single sideband and double sideband noise figure and noise temperature calculated. The method extends Kerr's work on diode type mixers and utilises a frequency conversion matrix of a MESFET mixer which was described previously. The simulation program was run for a mixer circuit based on an NEC720 transistor, and the results for the noise sources and noise figure behaviour as functions of the LO power are presented and compared to measured values with good agreement. An optimal operating point from the standpoint of minimum noise figure can thus be determined for transistor biasing conditions and the LO input power.
An analysis method for a microwave mixer, based on an active nonlinear device, is developed. The method is a two-port extension of Kerr's work on a one-port (diode)-type mixer and utilizes the harmonic balance approach for the large-signal analysis portion. It results in a relatively fast and efficient program, the use of which is demonstrated by simulating the operation of a mixer based on a NEC MESFET for a range of local oscillator available power and frequency conditions.
A new computer analysis method is presented by which the noise contributions of the various noise sources within a MESFET mixer can be determined and its overall single side-band and double sideband noise figure and noise temperature calculated. The method utilizes a frequency conversion matrix of a MESFET mixer which was described previously. The simulation program was run for a mixer circuit based on NEC720 transistor and the results for the noise sources and noise figure behaviour as functions of the LO power are presented and compared to measured values. An optimal operating point, from the standpoint of minimum noise figure, can thus be determined for transistor biasing conditions and the LO input power.
This paper presents a microwave large-signal model for the dual-gate MESFET. The model enables prediction of device performance in small-signal and large-signal circuits. The model is an extension of a previously developed model for the ordinary MESFET. It relies on basic principles, thus correlating the device geometry and physical parameters to its performance. The speed and accuracy of the model are demonstrated by calculating three types of device performance: dc curves smell-signal scattering parameters, and huge-signal simulation of an amplifier. Good agreement was achieved between calculated and measured perfomance. The computed results are presented for comparison only, and no attempt was made to present a comprehensive analysis of the device performance.
A method for the analysis of a microwave mixer based on a dual-gate MESFET is presented. The method extends a previously published analysis technique for a single-gate MESFET mixer by treating the circuit as a threeport network. The device is described by a complete mathematical model and the harmonic balance technique is utilised for the large-signal analysis stage. This results in a relatively fast program. The method is demonstrated by applying it to the simulation of a mixer based on a Raytheon transistor RDX832 for which device data was available. The mixer was constructed and its experimentally obtained performance results show good agreement between the simulated and the measured conversion gain values through a wide range of local-oscillator input power.
MESFET microwave oscillators and dual gate mixers are analyzed by applying the harmonic balance method to the complete large signal device model combined with the external circuit. The combination results in a single port structure for the case of the oscillator and a three-port structure in the case of the mixer. Accurate prediction of the power efficiency and harmonic content of the oscillator and the conversion gain of the mixer is obtained. The technique is quite general and a change of the active device type requires only a change of the subroutine that handles its model.
The waveform balance (WB) approach is combined with a modified form of the almost periodic Fourier transform (APFT) algorithm, resulting in an approach in which the number of randomly selected sampling points is increased, the overall computation accuracy is enhanced, the spread among results is reduced, and the computation time is practically unchanged. This approach is applied to the evaluation of large-signal S-parameters of a MESFET and to the calculation of its 1-dB compression power, the intermodulation distortion products, and the third-order intercept points (IP/sub 3/) for a range of frequencies. The results are in excellent agreement with those parameters that are available from the manufacturer's measurements. The conversion gain of a MESFET mixer is calculated, and the reduced spread among the results is compared with that obtained by use of the original APFT algorithm.< >
A new approach is used for the analysis of active microwave mixers which combine mixing and amplification, e.g. mixers based on single and dual-gate FETs (DGFETs). The normally used assumption that the LO signal alone is large while all the other signals present can be considered small is no longer valid when amplification is combined with the mixing process using a device with non-linear characteristics like a DGFET. In this case all the signals at all the device ports should be assumed large. A new algorithm, based on the modified harmonic balance (MHB) technique is developed and applied to the simulation of a mixer based on a Raytheon RDX832 DGFET for which device data was available. The simulation results are compared with the experimentally obtained mixer performance results of gain vs LO power and gain vs RF input power and show good agreement.
