Research On The Possibility Of Helical Array Antenna Used As High Power Microwave Feed

With the development of high-power microwave(HPM) technology, more attention has been progressively paid to the function of HPM antenna as the terminal of HPM system. An important form of HPM antenna is the reflector antenna illuminated by a HPM feed, it can produce high gain and is widely used in the high-gain and high-power occasion. HPM feed is the critical part in this technology. The high power feeds for reflector antenna usually are single-mode horn feed, multi-mode horn feed, multi-mode coxial feed and array horn feed. They are subject to some disadvantages more or less, although now used in the related field. High power radial line helical array antenna adopts short helical antenna as radiation unit, uses radial line as feeding waveguide, the existing researches show that it has some advantages, such as it has high power capacity, low pofile and rotationally symmetrical beam, It also can realize beam shaping by adjusting the excitation of its radiation cell, which can increase the aperture efficiency of a reflector by producing proper beam. So the helical array antenna owns its specific advantages applied in the HPM feed. Based on the forsaid backgroung, the possibility of helical array antenna used as the HPM feed is studied in this paper.A unique phase center in the feed is one requirement of the reflector, in order to demonstrate the possibility of helical array antenna used as HPM feed, it is necessary to calculate its phase center. At first, a helical array antenna with eighteen radiation cells is taken as an example, its phase center is theoretically calculated by the method of moving reference point, then numerical simulation is put forward. The simulation result is consistent with the theoretical result mostly. The result shows that the phase deviation is less than 5 degree during its 15dB beamwidth, so the helical array antenna has a unique phase center which satisfies the requirement of the reflector. This method can also be used to multi-circle helical array antenna and antenna which excitation are adjusted.Basing on the pre-research, a helical array antenna working at X-band is designed. In order to make good use of the property of helical array antenna that it can realize beam shaping by adjusting the excitation, meanwhile, consideing the advantages of the flat-top beam which can reduce the electric field at the proper height in the radiatin region and can increase the aperture efficiency of the reflector compared with the pencil beam which has the same beamwidth, research on the beam shaping is carried out using particle swarm optimization(PSO) method, a helical array antenna which radiates a flat-top beam with 38 degree beamwidth is obtained. Then its amplitude, phase pattern and the electric distribution in the radiation region are simulated, research on the beam shape, phase center and power capacity are made. The result shows that the helical array antenna can produce a rotationally symmetrical beam with flat-top shape, its side lobe is low in each principle plane, it has a unique phase center.The comparison with the multi-mode conical horn are made, both feed have a unique phase center in the range of the illuminated beamwidth, The helical array antenna bear the advantage as follows:1) The longitudinal dimension and axial demension are more less than the multi-mode conical horn feed; 2)the beam rotation symmetry property of this antenna is better than multi-mode conical horn feed; 3)The aperture efficiency of a reflector illuminated by flat-top beam radiated by the helical array antenna is higher than the pencil beam radiated by the multi-mode conical horn.In this paper, the side lobe of the helical array antenna designed is higher than the multi-mode conical horn feed, and the amplitude taper is large. These remain further study.