Research On Electrically Small Omni-Directional Antenna In Short-Wave Communication

Short-wave and ultra-short-wave communication play an important role in the field of long-distance communication.Due to the band limitation,short-wave and ultra-short-wave antennas are generally too large in size.Therefore,broadband electrically small antennas have become the focus of research in the field of short-wave and ultra-short-wave communication.In general,electrically small antennas hasve smaller size and larger input reactance,so they have higher quality factors,narrow bandwidth.But passive matching technology is constrained by bandwidth-gain theory,it is difficult to achieve the design requires of broadband and high gain.However,non-Foster circuits can generate negative reactance.It can convert large reactance of electrically small antennas,achieve broadband matching,and improve antenna gain.In this paper,the non-Foster circuit and electrically small antennas are studied in depth,and the design of small active antenna is completed.The main contents include:1.An active disc-cone antenna based on non-Forster circuit is designed.Firstly,the miniaturization technology of the disc-cone antenna is studied.The scheme of using sawtooth structure of reference slow wave structure to replace the cone metal straight rod under the disc-cone antenna is used to miniaturize the antenna.The input impedance characteristics,S11 parameters and S21 parameters of the disc-cone antenna in the frequency band from 150 MHz to 250 MHz are simulated.Then,according to the non-Forster circuit theory,the non-Forster circuit is designed and simulated using the circuit simulation software ADS.The antenna's scattering parameters are imported into the ADS to connect with the circuit.The S11 and S21 parameters of the active disc-cone antenna loaded with non-Forster circuit are simulated.The simulation results show that the S11 parameter of the active disc-cone antenna is lower than-15 d B in the range of 150 MHz to 250 MHz,and the S21 parameters is higher than that of the disc-cone antenna by more than 10 d B in the whole band.Finally,an active disc-cone antenna is processed,and the results of physical test are in agreement with the simulation results.2.An active monopole antenna based on a non-Forster circuit is designed.The antenna is designed with the single-pole antenna with inductance coil loaded.The operating band is from 2MHz to 30 MHz,covering the short-wave band.The non-Forster circuit uses the circuit structure in the active disc-cone antenna,and a band-pass filter is inserted between the circuit and the antenna to suppress the high-order harmonics of the non-Forster circuit,so as to improve the performance of the circuit under large signal conditions.The simulation results show that when the input power is 30 d Bm,the S11 parameter of the active monopole antenna is lower than-10 d B in the frequency band from 2 MHz to 30 MHz,the S21 parameter is higher than that of the monopole antenna by 5 d B in the whole band,and the harmonic suppression of the non-Forster circuit is higher than-50 d Bc.This shows that the designed active monopole antenna works well at the input power of 30 d Bm.