Research On Matched Transmitting Antenna Technology With Non-Foster Circuits For Digital Broadcasting

Broadcasting plays an important role in social development,and the digitization of broadcasting has become an inevitable trend.At present,digital broadcasting is mainly used in shortwave and ultra-shortwave bands.Due to the low working frequency and long corresponding working wavelength of the antenna used in the digital broadcasting of shortwave and ultra-shortwave,the actual shortwave and ultra-shortwave antennas generally have the problem of large size.Therefore,electrically small antennas is a research hotspot in the band.The electrically small antenna is mainly characterized by small input resistance,large input reactance,low emission efficiency,narrow passband and high quality factor.Due to the constraint of bandwidth-gain-volume theory,the electrically small antenna cannot achieve broadband and high gain simultaneously by using passive matching technology.The non-Foster matching circuit can break through the gain-bandwidth theory,perfectly match the reactance of the antenna,and achieve frequency band matching and high gain.This paper focuses on the research and design of non-Forster circuit and electrically small antenna.The main work is to design an active monopole antenna based on non-Foster circuit.Firstly,the monopole antenna with the length of 0.0375 ?₀ and the inductance coil is designed and analyzed.The design frequency band is 2MHz?30MHz.The antenna has small input resistance and large input reactance,so it cannot work normally in the design frequency band.Secondly,the optimized non-Foster circuit is used to match the passive monopole antenna.The negative impedance converter structure in the circuit is used to offset the large reactance of the passive monopole.The transformer structure is used to improve the input resistance of the whole network.The current buffer structure improves the system gain and stability.In order to improve the performance of the circuit under high power input conditions,on the basis of the optimized non-Foster circuit,a low-pass filter structure is added between the circuit and the antenna to reduce the high-order harmonic power output by the circuit.The simulation results show that the S₁₁ of the active monopole antenna loaded with the filter structure is lower than-8d B in the frequency band of2MHz?30MHz,and the S₂₁ is higher than the monopole antenna in the frequency band and the peak gain value is greater than 16d B,when the input power is 30d Bm.The high-order harmonic suppression of the non-Foster circuit is higher than 40d Bc,which indicates that the active monopole antenna has good working performance at the input power of 30d Bm.Finally,the circuits and antennas are processed and tested.After the circuits and antennas are processed,their S parameters are tested.The results show that the impedance of the active monopole antenna loaded with the filter structure is well matched and the gain is also improved in the test frequency range,which verifies the design to a certain extent.The simulation and measured results are compared,and the error analysis is carried out.In view of the fact that the existing test equipment cannot directly test the active transmitting antenna with non-Foster circuit with high power input capacity,a high power test scheme of active antenna based on non-Foster matching circuit is designed.