Designing a 230-280 MHz Antenna: Simulation of Basic Parameters, Analysis of Broadband Matching Devices of Various Types

Abstract

Design of the antenna in the form of horizontally located broadband half-wave vibrator with an umbrella-type reflector creating the radiation directed up is considered. For work with the broad frequency range of 230-280 MHz options of matching devices are considered. Computer simulation of the antenna in a software package MMANA-Gal has shown nonsensitivity, sufficient for practice, to conditions of placement of the antenna concerning the earth. For synthesis of the matching device in a software package RFSim99 the antenna equivalent having close to the antenna input resistance in all frequency range of 230-280 MHz has been constructed. Among options of passive approval of the antenna path wide-band transformers of resistance with ratio 1:2 (ideal) and 1:2.5 (physically implemented), and also the matching device on reactive elements have been considered. Efficiency of broadband approval was estimated qualitatively according to Smith's chart in the RFSim99 program, and also quantitatively through calculation standing wave ratio (SWR) and reflection coefficient in the frequency range of 230-280 MHz. Research of efficiency of options of broadband approval on a feeder line of 50 Ohms showed that results of approval significantly did not differ in transformers 1:2 and 1:2.5, providing SWR  2. At the same time approval on reactive elements has allowed to reach SWR  1.5. The executed modeling has shown the high utilization properties of the broadband antenna with an umbrella-type reflector in the range of frequencies of 230-280 MHz reached using the offered schemes of broadband matching devices.