Impedance Matching Circuit for 30-88MHz Monopole Antenna with Automatic Matching

This paper presents an impedance matching circuit for monopole antenna in the frequency range 30-88MHz which is integrated by microcontroller with tuning algorithm as an automation component. An impedance matching type L is used for the circuit, while for the realization some trimmer capacitors and SMD inductors are employed. To get an input voltage for the microcontroller, some supporting circuits are designed including VSWR meter, comparator and amplifier with 2 levels. It shows that the circuit is successfully tested by replacing values of load impedance with Z(A) = 75 + 14.6952j and Z(B) = 75 + 25.6224j, and tuning frequency values in frequency range of 41-45MHz. When impedance matching circuit is active, VSWR values for load impedance ZA = 75 + 14.6952j in the frequency 41MHz, 43MHz, and 45MHz are 1.34, 1.35 and 1.5, respectively and for load impedance ZB = 75 + 25.6224j are 1.37, 1.373 and 1.5.