The Terminal Matching Of The Spherical Dipole Antennas And Frequency Range Extension

Spherical dipole antennas with signal generator embedded is a new kind of small broadband antenna. It is only 100 mm in diameter, and built-in source without external feeder,so it is widely applied to shielding effectiveness tests of cabinets and subracks, site attenuation measurements, etc.This paper, base on the results of laboratory early, improves the existing spherical dipole antennas of fundamental frequency 30 MHz, and developes the fundamental frequency 5 MHz and 100 MHz spherical dipole antennas to expand the application of frequency band.This paper firstly does the research on the relevant information about the research progress of related products across the world to provide guidance for the design, in particular the level of overseas'research and research methods. This paper firstly calculates the radiation efficiency of the existing antennas,the antennas have more space for improvement.This paper mainly adopts two research methods to enhance the radiation efficiency.On one hand,this paper further analyzes the comb generator working mechanism to improve the output power, including replacing the better transistors to improve the high frequency power gain, adjusting the working current to reduce the unwanted signals, designing the bias circuit to reduce the coupling between the DC circuit and the high-frequency signal, capacitor filter to suppress unwanted energy, redesigning four-layer PCB to replace the original PCB,etc.On the other hand, in order to provide guidance for design, this paper analyzes the model parameters of the spherical dipole antennas, testes its radiation pattern in the darkroom and measures the input impedance of the antennas with double coaxial lines method. Compared with the HFSS simulation results, the test results is more accurate than the traditional physical Balun method/The test results can be used for the terminal matching design.The real frequency method and the genetic algorithm are employed to design the terminal matching network of the antennas of three different fundamental frequencies to reduce the reflection loss.The measurement results show that the electric field strength of the fundamental frequency 30 MHz spherical dipole antennas is more than 60 dBuV/m in the frequency range of 100MHz?1GHz,most of the points especially high frequency range of 700MHz?1GHz are over 70 dBuV/m.The electric field strength of the fundamental frequency 5MHz spherical dipole antennas reaches 50 dBuV/m in the frequency range of 30MHz-100MHz. The electric field strength of the fundamental frequency 100 MHz spherical dipole antennas is more than 70 dBuV/m in the frequency range of 1GHz?1.8GHz and is over 60 dBuV/m in the frequency range of 1.8GHz-3GHz.This article also analyzes the factors of the output dynamic range of the spherical dipole antennas in the shielding performance tests for cabinets and subracks. The spherical dipole antennas of three different fundamental frequencies can meet the shielding performance tests requirements of different levels of cabinets and subracks in different test conditions.