A Classic RF Component in a High Power Megahertz Implementation

Abstract

This paper describes a magnetic core based balun, designed to work at 4 MHz frequency and capable of transferring up to 4 kW of power. For the magnetic core a high frequency material in a E and I shape had been chosen. The windings are realized in a planar form, each of them being a separate Printed Circuit Board (PCB). Impedance transformation ratio is meant to be as close to 1:1 as possible, since the sole purpose of using the balun is to adapt a power amplifier balanced output to an unbalanced load. The challenging aspect of the design is estimating the required physical dimensions of the cores and windings according to the losses. There are three sources of power dissipation: copper windings, PCB laminate and cores. Magnetic material characteristics, such as losses and temperature dependance of its permeability, were taken into account since they affect transformer linearity and pulse response. In order to deliver an optimal solution, an electromagnetic model was put under analysis using a Finite Element Analysis (FEA) tool. Thus, a precise estimate of the electrical properties had been derived what effectively shortened the project timeline.