The Design and Optimization of Dual-slot corrugated horn antenna on Ka-band-3.doc

The Design and Optimization of Dual-slot corrugated horn antenna on Ka-bandAbstract- A novel corrugated horn antenna on Ka-band is designed. It combines by axial slots and straight slots. Based on the structure, the size of the antenna can be miniaturized by reducing the number of axial slots and straight slots. The model is tested in the software HFSS and the simulation result shows that the antenna not only has good radiation characteristic and Voltage Standing Wave Ratio (VSWR) performance, the size and the structure of the antenna also加上 has been optimized. Key words- Ka-band; Corrugated horn antennas; Axial slot; Straight slot; Dual-slot.I. INTRODUCTIONWith the rapid development of (Aerospace Measurement and control)spaceflighttestcontrol and deep-space exploration, corrugated horn antenna has a very good performance, such as good radiation performance and return loss performance, smaller cross-polarization and smaller sidelobes level. Corrugated horn antenna is widely used in radar surveying, satellite communications, target detection and other fields. It is a kind of gold antenna among all the feed antennas 1. Reference 2 describes the development of corrugated horn antenna in the radio astronomy, national security and satellite communications. Reference 3 describes the application of corrugated horn antenna in the microwave remote sensing and reflector antenna. A traditional corrugated horn antenna can be divided into small angle antenna and large angle antenna. The slots in a small angle corrugated horn antenna areper-pendicularto the antenna axis. The slots in a large angle corrugated horn antenna are perpendicularto the horn wall. In this paper, firstly，加上a novel small angle corrugated horn antenna works in the Ka-band is designed at first.去掉 It has dual-slot structure with axial slots and straight slots. Based on the antenna structure, the size is optimized by reducing the number of axial slots and straight slots. The model is tested in the software HFSS and the result shows that the antenna has a good performance and a miniaturization structure.II. WORKING PRINCIPLEThe corrugated horn antenna structure can be seen in the walls of the conical horn carving a group of ring-slot. The electric field lines in the antenna output surface is straight. These electric field lines doesDo not resulted from transverse-electric (TE) or transverse-magnetic (TH), but from two mixed with a certain percentage 4. The mixed-model isexpressed by HE11. The far fielddistribution of HE11 model is expressed by (1) to (4). (1) (2) (3) (4)Among these parameters, J0(kr) and J2(kr) are the first kind后面加of Bessel function. k means transverse wave number and k0 means free space wave number. B1 and B2 are amplitude coefficients. X and Y are impedance and admittance when 改为whiler=a. Z0 means the free- space impedance. Entrance to the corrugated horn antenna is connected to a smooth circular waveguide. It mainly transmits TE11 mode. The mode-transformation section achieves to turn TE11 mode to HE11 mode, and the radiation section transfers HE11 mode.III. BASIC STRUCTURE AND INITIAL DESIGNTwo kinds of structures when we designed corrugated horn antenna, two-part structure and four-part structure. The two-part structure includes mode-conversion section and radiant section, and four-part structure increasing taper section and transition section. Now, corrugated horn antenna for literature in the structural design is noNot clear distinction, it always uses two-part structure, shown in Fig.1. The circular waveguide section, the mode-conversion section and the radiant section of corrugated horn are expressed by A0, A1 and A2. The length of A1 add A2 is the total length of corrugated and the length of A0 is expressed by M. ai, means the input radius of the corrugated horn, ao means the input radius of it, and means the halfangle of the corrugated horn. A1 section consists of several slots. The Figure 1. Corrugatedhornantennastructureslotsdepthofstructure is variable from c/2 to c/4. The depthof the first slot is expressed by h. So h=c/2 and c=c/fc is the centerwavelength. The depthof the slots in A0 section keeps c/4. Theaircolumn widthisexpressed by w in the section A1 and A0. The metal corrugated widthis expressed byt.The frequencyrange of the corrugated horn is 30GHz-40GHz, is 15, VSWR1.2 and the sidelobelevel is less than -30dB. These are the goals of corrugated horn antenna in this paper. Because of 去掉fmax fmin, f0 could becalculate by (5), is 34.64GHz. In order toensure thatthereturnloss of the corrugated horn antenna isless than 15dB, ai could be calculate by (6). Assuming =w/(w+t), the value of could affectthecross-polarization levels. Usually 0.7 0.9, here =0.8 intheinitial design, so it means w=4t. The total length of the corrugated horn can affect the sidelobelevelandthe phasestabilityof thecenter, usually it 去掉is 5c 10c. In this paper, the length is 8c and the mode-conversion section has 6 slots. The length of slots are 9h/10，4h/5，7h/10，3h/5，h/2. (5) (6)IV. OPTIMIZATION DESIGNA. SlotsdesignandoptimizationIntheory, the antenna will has Havebetter performance if the relative length of the antenna longer and slot period greater. But moreslots willmakeitdifficulttoprocess. So the number of slotsshould bedesignedtoapplyto thesatellite applications whilereducingcostandweight 5.We take 3,4 and 5 slots number eachwave-length tofindtherightslotnumbers. Theinitial value of the para-metersareshowed inTable1.TABLE I. Corrugated horn antenna parameters (mm)Slots numberTotal number of slotsMhwt3244.334.332.3090.5774324.334.331.7320.4335404.334.331.3840.346(a) 3 slots(b) 4 slots(c) 5 slots(d) VSWRFigure2. Simulationresults when changing the slots numberSimulationresultsareshowed inFig.2. Fig. 2 (a),(b) and(c)are E and H polarization radiationpattern when theslots numberis 3,4 and 5. These figures show that the planes have good performance. E-planeandH-plane coincide in the main directions of polarization, andthe average sidelobe isless than-30dB. Fig.2 (d) is the result of VSWR. The figure shows when the slot number is 3, the performance of VSWR is better that the others, and the flanessand radiantperformancecan meetrequirements well. Takentogether,thecorrugated hornshouldselect3 slots number.To further optimize the structure of the corrugated horn antennas, the values of M, h and w are done parameter sweeping and optimization in HFSS. The ranges are 去掉like this: M=(h/2-c/4, h/2+c/4), h=(h/2-c/8, h/2+c/8), w/(w+t)=(0.7,0.9). The result shows that the performance of the antenna is the best when M=4.185mm, h=4.539mm, w=2.26mm. The gain is 22.131dB, the axial dimension of the antenna is 69.28mm, and the longitudinal dimension 51.888mm. Simulation results of pattern and VSWR are showed in Fig.3.(a) Pattern(b)VSWRFigure 3. The optimization results of the corrugated horn antenna parameter B. Miniaturizationdesign The corrugated horn usually has straight slots, axial slots and skewed slots. The surfacesdiameter of axial slots is smaller among these 6. Usually, theaxialslots arerarelyusedin the smallangleofcorrugatedhornantenna but suitableforthe largeangle corrugatedhorn antenna. In this paper, theaxialslotsandstraightslots are combined to achievethegoalofminiaturization.Dual-slotstructureofthe corrugated horn antenna is showed in Fig.4. The number of axial slots diminishingfrom5 to 2 when 改为 whilethe number of slots in theradiationsection keeping no change. The axial slotsdepthareIslineardecrease from c/2 to c/4. Simulationresults are showed inFig.5.Fig.5 (a) shows E-plane and Fig.5 (b) shows H-plane. When the number of slots are 3, 4,and 5, the primary polarization pattern has good symmetry but the sidelobe level is bigger. When the number of slots is 2, the radiation characteristic is better than the other. So we design the slots number are two. The first slot depth is c/2 and the second slot depth is c/4.Figure 4. The structureofthe double-slotcorrugated horn(a) E-plane (b) H-plane Figure 5. The radiation characteristic when the number of slots changing(a) Pattern(b)VSWRFigure 6. The results of the double-slotstructure antennaThe straight slots will affect the longitudinal dimension of the antenna. The number of the straight slots areIs reduced in turn from 18. The result of simulation shows that the number of the straight slots can be reducedto 16. The corrugated horn antenna with 2 axial slots and 16 straight slots are modeled in HFSS. The result of polarization radiationpattern and VSWR are showed in Fig.6.The result shows that the patter of E-plane and H-plane have good symmetry and basically coincident from -25 to 25. The antenna can meet the needs of the irradiation level and maintain a good equalization. The VSWR is less than1.18 within the target frequency band. Based on optimizing design, the gain of theantennais20.492dB. The axialdimension of antenna was 55.169mm, 87.56% sizefor initial design and thelongitudinal dimension was45.432mm, 79.63% sizefor initial design. The designmethodcould achieve theaims of miniaturization.V. CONCLUSIONIn this paper, we combine axialslotsandstraightslots to design a novel corrugatedhorn antenna which works in Ka-band. Onthisbasis,the corrugatedhornantenna structureis optimized. Simulationresults show that the corrugatedhornantenna has good radiati