Development and investigation of the D-band balance mixer
Authors: Bilinsky K.V. , Kuleshov G.E. , Badiin A.V. , Dorozhkin K.V. 
Published: February 2025

In this article the methodology of mathematical modeling of waveguide-microstrip design of D-band balance mixer on the basis of calculation model of nonlinear element taking into account volt-ampere and dynamic characteristics of SBD produced by NIIPP JSC enterprise is considered. The methods of investigation of the characteristics of the manufactured balanced mixer are described. The analysis of the obtained results is given.

Introduction. Electromagnetic waves of the EHF band are widely used in many industries and spheres of human activity. EHF receiving and transmitting devices, due to the peculiarities of the propagation of EHF radio waves, have a number of advantages over microwave, IR, VHF, HF. The main disadvantage is the significant attenuation of EHF radio waves during transmission in a humid environment. The balanced mixer is well suited for converting EHF frequencies, as it has a relatively low level of conversion losses and noise factor, high values of interchanges. Goal. Mathematical calculation and practical implementation of a balanced mixer of the D-band comparable in characteristics with existing analogues. The tasks to be solved are necessary to achieve the goal. Conducting linear electromagnetic calculation and nonlinear analysis based on equivalent parameters and a nonlinear SBD model. Investigation of the conversion and noise characteristics of the created EHF converter.

The device and the principle of operation. The balanced mixer performs the operation of adding (subtracting) the first harmonics of the radio signal and the heterodyne with the allocation of an intermediate frequency. The implemented passive D-band mixer has a waveguide-microstrip design. The nonlinear element on which the frequency conversion takes place is a sequential pair of SBD, which is made on a GaAs-substrate with beam terminals. Mathematical modeling consists in the initial implementation of the electromagnetic calculation of the nodes of a balanced mixer with the replacement of a nonlinear element by a calculation model based on equivalent parameters of the SBD. This is followed by a nonlinear analysis using a nonlinear SBD model.

Measurement methodology. The measurement of the converter characteristics of the D-band mixer was carried out using a spectrum analyzer and EHF signal generators. The noise characteristics were measured using a noise coefficient meter. The interchanges between the heterodyne and radio signal paths were measured using a panoramic VSWR and attenuation meter.

Analysis of the results. For the implemented balanced D-band mixer, the conversion loss in the radio signal band does not exceed 15 dB. In the frequency band 110…145 GHz, the conversion loss is 10±1 dB. Optimal parameters for operation: a constant bias current of 500…1200 µA, a heterodyne power of 7…12 dBm. The noise factor does not exceed 15 dB. The isolation between the paths of the heterodyne and the radio signal is at least 24 dB, between the IF line and the lines of the heterodyne and the radio signal is at least 50 dB. There is a certain correlation between the mathematical calculation data and experimental results using the example of the conversion loss spectrum and decoupling of the LO-RF, RF-LO, IF-LO, IF-RF mixer. A significant discrepancy in the results of nonlinear analysis and experiment at frequencies above 140 GHz is due to the assumptions of the computational model of the nonlinear element, which excludes the dependence of the differential resistance of the barrier contact BDS on the frequency of the heterodyne, and the influence of the frequency of the radio signal on the surface resistance of the GaAs volume, approximation of the differential capacitance by a constant.

Conclusions. The developed balanced mixer of the D-band has characteristics comparable to analogues. A comparative analysis of the results of mathematical calculation and experiment confirms the applicability of the mathematical calculation methodology, especially at frequencies below 145 GHz. The resulting balanced D-band mixer is in demand as a frequency converter in receiving and transmitting devices.