Abstract : Utilizing the output characteristics of a bipolar transistor, an S-band resistive upconverter primarily applied in 2.4GHz wireless LANs was designed. S-parameter and harmonic balance simulations were performed using Agilem's RF circuit design software ADS2003, achieving a good result with a conversion gain of 8.17dB, RF-intermediate oscillator port isolation of 14dB, and RF-IF port isolation of 36dB. After final debugging, the circuit achieved a conversion gain of 6.28dB, RF-intermediate oscillator port isolation of 18dB, and RF-IF port isolation of 16dB. The results show that the simulation results are very close to the test results. Keywords : Upconverter; Harmonic balance method; Conversion gain Introduction Upconverters play a crucial role in wireless communication systems, and their specifications directly affect the performance of the entire system. Therefore, the design of upconverters is key to the design of many microwave transceiver systems. The continuous emergence of various microwave CAD software allows us to simulate and optimize circuits to achieve better performance. Practical engineering demonstrates that skillfully applying these software programs to product development can shorten the development cycle, reduce production costs, and improve product performance. Agilent's ADS2003 (Advanced Design System 2003) was used for design and simulation, yielding good results. 1. Up-converter Overview The essence of an up-converter is to utilize the nonlinear characteristics of devices to generate the sum or difference frequency of the input signal and the local oscillator signal, and then use filters to remove unwanted frequency components. Up-converters can be classified into resistive and capacitive mixers based on their generation mechanisms. We use a resistive mixer; the time-varying transconductance under local oscillator control can be expressed by the following formula: [b][align=center]For more details, please click: Design of S-band Resistive Up-converter[/align][/b]