Research And Design Of Broadband Electrically Small Antennas By Non-foster Circuits

With the rapid development of modern electronic information technology,people put forward more requirements on the antenna in a wireless communication system,such as achieving the requirements of miniaturization and broadband as much as possible which make the broadband electrically small antenna to become one of the hotspots in the field of wireless communication.Generally,due to the small size and large input reactance,the electrically small antenna has a high quality factor,and the frequency band is narrow.Non-Foster circuit can realize the negative impedance which offset the large reactance of the electrically small antenna and reduce the quality factor,thus expanding the frequency band and improving the performance of the antenna.An intensive research on non-Foster circuit matching electrically small antennas to achieve broadband was conducted and furthermore,a conclusion on encountered problems of devising was drawn in this article.The main contents are as follows:1.In the simulation and measurement study on the non-Foster circuit matching electrically small monopole antenna,firstly,a monopole antenna was fabricated and its input characteristic parameters were measured,and secondly,obtain the equivalent capacitance of the antenna.Based on the equivalent capacitance,the non-Foster circuit was devised.The port characteristics S1P file of the measured antenna importing into the circuit simulation software and non-Foster matching circuit were connected as a whole,firstly,the input impedance and S₁₁ parameter of the whole circuit were simulated and optimized and secondly,fabricate and test the non-Foster circuit to meet design requirements,finally,realized broadband electrically small monopole antenna matching and obtained the relative bandwidth up to 64.8%.2.In the intensive simulation study and test analysis on the non-Foster circuit loading electrically small loop antenna,the input impedance characteristics of the single loop electrically small antenna in the 2MHz-30MHz band were simulated,and the condition of the non-Foster circuit realizing the negative impedance element was analyzed by using the equivalent circuit of the antenna.The simulation results show that the multiplier circuit composed of two stage non-Foster circuit can match the equivalent circuit of the antenna to the pure resistance of the 50 ohms.Multi-loop electrically small antennas as target antenna,single stage non-Foster circuit and two stage non-Foster multiplier circuit were devised respectively,through simulating and optimizing,achieved 50 ohms matching,and fabricated the single stage non-Foster circuit.The test results show that the performance of the antenna was greatly improved in the short wave and ultrashort wave,and realized antenna broadband in the whole research band.3.In the simulation study on the operational amplifier floating type non-Foster circuit matching loop monopole antenna,through scanning the load of the non-Foster circuit,found the minimum load components to achieve negative impedance,and simulation verified the operational amplifier floating type non-Foster circuit can realize antenna broadband.