Lightweight Design of Spaceborne CFRP Rigid Antenna Reflector

ZHOU Tao，LIANG Yanmin，WU Wenping，WU Xinrui，YE Zhoujun，DONG Bin

（1.Shanghai Composite Technology Co.，Ltd.，Shanghai 201112，China；2.Shanghai Engineering Research Center of Aerospace Resin Based Composite，Shanghai 201112，China；3.Shanghai Spaceflight Precision Machinery Institute，Shanghai 201600，China）

Abstract:In order to overcome the shortcoming of space-borne rigid antenna reflector made of carbon fiber reinforced plastic（CFRP）skins with aluminum honeycomb sandwich（SAHS）structure，a new type of full CFRP skin plus rib（SPR）structure ring-focused parabolic surface antenna reflector with the size of 2.5 m×1.9 m is designed.Under the condition that the original caliber，surface type，and interface remain unchanged，the main influence factors are designed and controlled.First，from the perspective of high stiffness，lightweight，and easy to form，a finite element simulation software is used to analyze and optimize the layout of the rib，the cross-sectional shape of the rib，the size of the rib，and the matching of the size and the coefficients of thermal expansion（CTEs）of the rib and the skin.Second，two structures are prepared by the autoclave molding process.Third，the weight and the surface precision root mean square（RMS）value are measured.The results show that the fundamental frequency of the SPR structure is 142.2 Hz，which is 3.5 Hz higher；the number of the new structural parts is reduced by 40%，and the forming process is greatly simplified.The total weight of the new structure is 11.9 kg，lighter 42.5%，indicating that the weight loss is obvious.The RMS value is 0.15 mm，which is slightly lower 0.01 mm but satisfies the accuracy requirement not greater than 0.3 mm.It is proved that the SPR structure reflector is a superior structure of the lightweight spaceborne antenna reflector.

Key words:antenna reflector；skin plus ribs structure；carbon fiber reinforced plastic（CFRP）；finite element；lightweight

0 Introduction

Rigid reflector antenna is one of the most widely used high-gain antenna forms on satellites.With the deepening of human exploration of the universe，the rigid reflector gradually develops to the direction of large aperture，high frequency band，and high gain，and the requirements for the accuracy of the reflector are also increasing.

Moreover，the mutual influence and mutual re‑striction between the electromagnetic and mechanical structural factors of the antenna become more and more prominent.The antenna must have enough high surface accuracy and anti-deformation ability.In the early stage，the antenna was mostly made of met‑al materials，and its biggest disadvantage was large weight.It has been shown that if the antenna weight is reduced by 1 kg，it is possible to reduce the weight of the high-frequency box by 1 kg，and the weight of the drive system can be reduced by 2 kg.The light‑weight of the antenna will bring considerable econom‑ic benefits.

In recent years，in order to reduce the weight and deformation of the antenna，carbon fiber rein‑forced plastic（CFRP）with high strength and good heat resistance is used to replace metal materials to manufacture antenna reflectors.CFRP possesses high specific modulus and strength，low thermal expan‑sion coefficient（CTE），and strong designability.At present，the rigid reflection surface of CFRP used in the aerospace field is mainly the carbon fiber skin with aluminum honeycomb sandwich（SAHS）structure，which has low design difficulty，high process maturi‑ty，and convenient manufacturing and processing.

However，owing to the low stiffness and high CTE of the core material aluminum honeycomb，this kind of reflector has large thermal deformation and poor thermal stability，which is mainly at the sub-mil‑limeter level，and cannot meet the needs of high-pre‑cision and high-stability micron-level reflector.For the large-diameter sandwich structure，the hon‑eycomb cores are spliced with foaming adhesive.The panel of honeycomb sandwich structure is bonded to the honeycomb core with a film.The use of film and foaming adhesive increases the weight.At the same time，in order to improve stiffness，honeycomb cores with larger height，thicker honeycomb wall，and smaller honeycomb lattice are needed，which will al‑so increase the weight.Sometimes，in order to re‑duce the on-orbit temperature gradient at different parts of the reflector，thermal control measures must be adopted，and the use of thermal control materials also increases the weight.To improve the short‑comings of traditional SAHS structure reflectors，more advanced light reflectors and ultra-light reflec‑tors have been developed，e.g.，2.5 m light reflec‑tors.LIANG et al.proposed an optimal design scheme for high-precision reflectors with low thermal deformation，and concluded that the honeycomb joints of a reflector should be less and be symmetri‑cally distributed，and the ribs，made of honeycomb sandwich plates，with symmetrical structure and qua‑si-homogeneity carbon fiber layer have minor thermal deformation.PACE et al.developed a lightweight dimensionally stable carbon fiber composite deploy‑able antenna reflector structure utilizing a rib stiff‑ened thin shell design.REZNIK et al.presents the results of selecting a thin-walled CFRP shell reflector structure with a ribbed convex surface，which was ra‑tional in terms of the mass and shape stability.

Based on this，in this paper，a 2.5 m×1.9 m ap‑erture ring-focus parabolic solid-surface reflector is taken as an example.Through the design and control of the main influencing factors and under the condi‑tion of ensuring the original aperture，surface shape，and interface unchanged，the finite element analysis is used to design a new type of full CFRP skin plus rib（SPR）structure from the perspectives of high stiffness，lightweight，and easy forming.The layout of the ribs，the cross-sectional shape of the reinforce‑ment，the size of the ribs，and the matching of the size and the CTEs of the rib and the skin are opti‑mized.The comparison of the fundamental frequen‑cy，weight，and surface accuracy shows that the new designed SPR reflector has the characteristics of light weight and high precision，and is an excellent struc‑ture for lightweight spaceborne antenna reflectors.

1 Reflector surface and boundary conditions

The boundary conditions are as follows：

1）The working temperature of the main reflec‑tor ranges from -180 °C to +100 °C.

2）The overall constraint of the reflector is the four support points（pyrotechnics）and central sup‑port points，and all degrees of freedom are con‑strained.

2 Material properties

The skin，back reinforcement，and feed brack‑ets are made of CFRP.The sandwich core material is hexagonal porous and durable honeycomb.The adhe‑sive layer is 2051 epoxy resin，and the connecting parts are titanium alloy.

Carbon fiber composite parts are prepared from the dip woven fabric and unidirectional fabric prepared by M55J carbon fiber and cyanate ester produced by Toray Corporation，Japan.The properties of the two materials are shown in Tab.1.

Tab.1 Material properties of the skins

The selected honeycomb is a hexagonal honey‑comb with a size of 4 mm×0.03 mm，which is pro‑duced by Hirsch，USA.The material properties are shown in Tab.2.

Tab.2 Material properties of aluminum honeycomb

The adhesive layer is 2051 epoxy resin adhesive produced by Japan Axson Company，and its material properties are shown in Tab.3.

Tab.3 Material properties of 2051 epoxy resin adhesive

The titanium alloy used is TC4 titanium alloy bar produced by Northwest Institute for Non-ferrous Metal Research，and its material properties are shown in Tab.4.

Tab.4 Material properties of TC4 titanium alloy

3 Honeycomb sandwich structure model and simulation analysis

The infrastructure is a reflection surface of SAHS.The reflector consists of a main reflector，a secondary reflector，four carbon fiber struts，and a feed support.The total height is 828.5 mm，the di‑ameter of the main reflector is2 500 mm，and the tangential width is 1 900 mm.The three-dimensional（3D）model of the reflector is shown in Fig.1.

Fig.1 3D model of the reflector

The main reflector is composed of three parts，i.e.，inner skin，aluminum honeycomb，and outer skin.The inner skin surface is the working face.The total thickness of the honeycomb sandwich structure is 23 mm，the inner and outer skin thicknesses are 0.5 mm.The back is strengthened by CFRP rein‑forcement，and the thickness is 1 mm.The adhesive layer is between different parts，and the thickness is 0.15 mm.

The mesh finite element model is established based on the geometric model.To effectively improve the modeling accuracy and modeling efficiency，the model is appropriately simplified.The model details such as holes，chamfers，and connecting screws that do not affect the mechanical properties of the reflector are removed.According to the characteristics of the reflector，the honeycomb sandwich and adhesive layers are simulated by C3D8R hexahedral solid elements，and the inner skin，outer skin，back ribs，carbon fiber strut，and feed bracket are simulated by SC8R continuous shell elements.The strut and the primary are fixed by titanium alloy joints through bonding and screwing，so do the strut and secondary reflectors.The bonding can be basically covered by the screw thread pressing area，owing to the large stiffness of the connection area，the connection areas are bounded by ties.The rib，the honeycomb sandwich panel，and the feed support，the reflection panel are also fixed by bonding and screwing.Since the connection area and the bonding area are large while the area of screwing is relatively small，the connection interface has a great effect on the overall mechanical properties.Therefore，the grid connection in the form of fusion is adopted to ensure the accuracy of the model and the validity of the simulation results.The finite element model is shown in Fig.2.

Fig.2 Finite element model of the reflector

According to the analysis of the vibration mode，the overall fundamental frequency of the antenna re‑flector is considered to be 173.7 Hz.Based on the temperature requirements，the temperature field is applied to the antenna reflector，and the deformation and surface accuracy of the antenna reflector in the temperature range from -180 °C to +100 °C are simulated and analyzed.From 20 °C to -180 °C，the maximum displacement of the reflector working face is 0.58 mm，and the root mean square（RMS）of the surface accuracy of thermal deformation is 47.5 μm.As shown in Fig.3，under the ambient temperature from 20 °C to 100 °C，the maximum displacement of the reflector working face is 0.23 mm，and the RMS value of the surface accuracy of thermal deformation is 19.0 μm.

Fig.3 Thermal deformation cloud of the reflector working face

4 Design and optimization of SPR structure

Under the condition of guaranteeing the original caliber，surface type，and interface unchanged，the SPR structure is designed by using the finite element analysis from the perspective of high stiffness，light‑weight，and easy forming.The layout of the rib，the cross section shape，and the matching of the size and the CTEs of the rib and the skin are optimized.

4.1 Layout design of back ribs

The role of back ribs is to increase the stiffness of the structure，ensure that the surface is not easy to deform，and then match the CTE of the skin to re‑duce the internal thermal stress of the structure，thereby reducing the thermal deformation.

The layout design of ribs can be divided into three steps.First，divide the reflector into small ar‑eas of similar size，and distribute the ribs on the boundary of each area.Second，distribute the ribs along the radial and circumferential directions accord‑ing to the characteristics of the reflector.Third，set the main ribs along the reflector skin contours with the assist of auxiliary ribs，forming a combination of the main and auxiliary rib layouts.

The rib layout of symmetrical structure is de‑signed with the basic frequency as the criterion of stiffness.The auxiliary rib is added to the weak position of stiffness through simulation analysis.At the same time，according to the RMS of the surface thermal deformation of the structure at the ambient temperature from 20 °C to 100 °C or 20 °C to-180 °C，the effect of the increase in the ribs on the thermal deformation is judged.The rib in the weak position can improve the fundamental frequency，im‑prove the stiffness of the structure，and improve the thermal deformation.However，the thermal deforma‑tion does not decrease with the increase in the stiff‑ness，and the rib that increases the thermal deforma‑tion caused by the increase in the stiffness belongs to the unreasonable layout.Moreover，the thermal de‑formation is relatively large in the position where the ribs are relatively concentrated.This is mainly be‑cause the local stiffness and CTE of the bars and the skin do not match each other，leading to thermal stress concentration.

According to the results of the above analysis and the summarized rules，the overall layout of the fi‑nal optimized rib is shown in Fig.4.The fundamen‑tal frequency of the obtained structure is 152.3 Hz，and the thermal deformation cloud diagrams of the profile surface at the ambient temperature ranging from 20 °C to 100 ℃and 20 °C to -180 ℃are shown in Fig.4（b）and Fig.4（c），respectively.The distri‑bution of thermal deformation is relatively uniform，mainly concentrating around the center，the joint of the counter strut，and the radial ribs on both sides of the long axis.The RMS values of thermal deforma‑tion are 22 μm and 55.1 μm，respectively，which are larger than those of honeycomb sandwich structure.Therefore，the structure is further optimized.

Fig.4 Configuration diagram and thermal deformation cloud diagrams of the rib layout

Several typical optimal layout structures of back ribs are shown in Fig.5.According to the calculation of thermal deformation，weight，and overall stiffness，the tendon layout shown in Fig.5（c）is selected through comprehensive analysis and comparison.

Fig.5 Typical layout of rib configuration optimization

4.2 Geometric design of skin and back ribs

After the selection of the overall layout of the ribs，the thickness of the skin，the height of the ribs，and the thickness and section shape of the ribs are optimized.

4.2.1 Design of the rib height

In view of the limitation of the position of the ex‑ternal interface，the height of the rib does not exceed 77 mm.For the layout of the rib structure shown in Fig.5（c），the height of the rib is set to 15 mm，30 mm，45 mm，60 mm and 75 mm，respectively.The other sizes and stacking methods remain the same.The fundamental frequencies of Structure 3 with different reinforcement heights are calculated，and the results are shown in Fig.6.

Fig.6 Fundamental frequencies of Structure 3 with different rib heights

It can be seen that in the range of designable height，the fundamental frequency of Structure 3 in‑creases with the increase in the reinforcement，but the increase tends to be slower with the continuous increase in the reinforcement.This is consistent with the actual situation，but is not good for the increase in the height of the reinforcement all the time.With the increase in the height of the reinforcement，insta‑bility may occur，and the weight of the structure will increase，which needs comprehensive investigation.

4.2.2 Design of the skin thickness

First，the matching effects of the skin thickness and ribs height are investigated.According to the thickness of the existing single layer prepreg，the skin is still laid 8 layers with a total thickness in the range from 0.24 mm to 3 mm，a total of 12 groups of values.The fundamental frequencies corresponding to 12 groups of different skin thicknesses and 6 groups of different rib heights are calculated，and the results are shown in Fig.7.It shows that when the skin thickness is constant，the higher the height of the reinforcement is，the higher the fundamental fre‑quency is，and the existence of the reinforcement can greatly improve the stiffness of the structure.Howev‑er，when the rib height is constant，the fundamental frequency of the structure does not have the same trend with the increase in the skin thickness.When the rib height is small，the structural stiffness increas‑es with the increase in the skin thickness，but the in‑crease rate decreases with the increase.When the rib height is high，the stiffness of the structure increases to a maximum value first and then decreases with the increase in the skin thickness，and the higher of the rib height is，the thinner the skin thickness corre‑sponding to the peak value is.This is mainly because the skin stiffness at the peak position matches well with the rib stiffness.

Fig.7 Fundamental frequencies corresponding to different skin and rib heights

Furthermore，the frequencies of the first 15 or‑der structures with different skin thicknesses and dif‑ferent rib heights are analyzed，and the results are shown in Fig.8.It can be seen that the rib thicknesses at 75 mm height and lower order fre‑quencies are higher，while the rib thicknesses at 60 mm height and higher order frequencies are the highest.From the vibration mode nephogram of high-order frequency，it can be seen that the highorder frequency will involve the large deformation vibration of some edge ribs，indicating that the height of edge ribs is too high，and the effect of mass load on the stiffness reduction is greater than the effect of the rib height increase on the stiffness improvement.Therefore，the edge ribs should not be too high，and the height of 60 mm is the overall optimal.At this time，the optimal skin thickness ranges from 0.6 mm to 1.6 mm.

Fig.8 First 15 order frequencies corresponding to different rib heights

4.2.3 Shape design of the rib section

In the above design，the ribs are directly com‑bined with the skin.Considering that the actual back ribs need to be bonded with the skin，the back ribs need to provide a bonding surface.In this way，the cross-section shapes of the back ribs can be various，including I-shaped，T-shaped，L-shaped，Capshaped，W-shaped，and so on.For the designed stiffeners，I-shaped，T-shaped，and cap-shaped sec‑tions are selected（see Fig.9）to ensure that the heights of stiffeners with different cross-section shapes and the areas of the adhesive interfaces are equal and the stiffeners at different positions are paved according to quasi-isotropy.The skin thick‑ness is still 0.8 mm.

Fig.9 Cross-section shapes of the rib

The fundamental frequencies of the overall struc‑ture of the skin-reinforced reflector and the thermal deformation of the reflector surface at the ambient temperature in the ranges from 20 °C to 100 °C and from 20 °C to -180 °C are calculated，respectively.The results are shown in Tab.5.

Tab.5 Fundamental frequency and thermal deformation of different section shapes

From the results，it can be seen that the struc‑tural stiffness and thermal deformation of the capshaped rib are better than those of the I-shaped and T-shaped ribs，which is related to the structure itself.For the SPR structure，the skin panel mainly bears the surface internal force.When there is no rib，the thin skin cannot bear shear force，and the existence of back ribs can enhance the bending and shear capaci‑ty of the structure.In bending and shear resistance，the cap-shaped rib and I-shaped rib have certain ad‑vantages.The stiffness of the cap-shaped or I-shaped stiffened skin reflector is the same as or better than that of the honeycomb sandwich structure，but the thermal deformation is larger than that of the honey‑comb sandwich structure.This is mainly because the thickness of the reinforcement is too thick and does not match the CTE of the skin.Considering that the skin is a rotating parabolic surface and the curvatures are different，the rib is more suitable for the overall molding，and the molding of the cap-shaped rib is rela‑tively difficult.The stiffness and thermal deformation values of the cap-shaped rib and the I-shaped rib are basically the same.From the weight of the rib per unit length，the I-shaped rib is more advantageous.There‑fore，the back rib of the I-shaped section is adopted.

4.2.4 Design of the I-shaped rib flange width

In view of the low shear strength of the compos‑ite material and the poor shear capacity between lay‑ers，the shear deformation of the thin-walled beam structure will cause the change of the normal stress and produce additional normal stress，which will af‑fect the distribution of the normal stress and the de‑formation of cross section，so that the cross section is no longer maintained as a plane.When the I-beam is subjected to bending load，the shear stress on the flanges of the upper and lower panels of the I-beam presents a triangular distribution，with the maximum value in the middle and zero at the free edges of both ends，the flanges of the upper and lower panels are compressed or tensioned.Therefore，the 0° layer should be laid along the beam axis direction.The shear stress is distributed in a parabolic form along the height on the web and is maximal at the midpoint of the web.The flange may appear local instability.Therefore，it is necessary to lay ±45° layers along the beam axis direction.The beam web is mainly subjected to the shear force，and the pavement should be given priority to ±45°，which can be auxil‑iary laid 0° or 90° layer，in order to bear the tensile or compressive stress of the web owing to bending.

According to the calculation，keep the web height of I-shaped ribs 60 mm and the web and flange thicknesses 2 mm.Set the flange width as 5 mm，10 mm，15 mm，20 mm，and 25 mm，respectively.The fundamental frequencies of the structure with the 5 groups of flange width are calculated.The ther‑mal deformation of the profile is also calculated at the ambient temperature in the ranges from 20 °C to 100°C and from 20 °C to -180 °C.The results are shown in Fig.10

Fig.10 Fundamental frequencies and thermal deformation of I-shaped rib reflectors with different flange widths

From Fig.10，it can be seen that the fundamen‑tal frequency of the reflector increases with the in‑crease in the width of the flange in the design range，but the thermal deformation of the reflector increases first，then decreases，and finally increases again.This is mainly because with the increase in the flange width，the overall stiffness of the I-shaped rib increas‑es.When it reaches a certain range，the stiffness and CTE of the skin match with the rib，and the thermal deformation of the structure is small.When the width of the flange increases continuously，the stiffness of the I-shaped rib increases slowly，while the thermal deformation of the structure increases rapidly.This is caused by the excessive width of the I-shaped rib flange.The large upper and lower panels are，and the lower the shear stress of the web under the ther‑mal stress state of the structure is.With comprehen‑sive consideration，the flange width is set as 15 mm.

4.2.5 Design of the I-shaped rib thickness

Furthermore，the thickness of the web and pan‑el of the back ribs are optimally designed.According to the calculation of the layout part of the back ribs，when the back ribs are thin-walled rectangular sections，the stiffness and thermal deformation are better.Therefore，the thicknesses of the upper and lower panels of the I-shaped ribs are reduced to 0.8 mm，and the stiffness，thermal deformation，and weight are calculated.The results are shown in Tab.6.

From Tab.6，it can be seen that the stiffness changes little，but the thermal deformation and weight loss effect is obvious.The mass decreases with the decrease in the thickness of the web.The fundamental frequency has small difference，but a fluctuating state indicates that the thermal deforma‑tion becomes worse in the process of mutual balance between the structural weight reduction and structur‑al stiffness improvement.Obviously，this is because of the mismatch between the stiffness and the CTEs of skin and back ribs.

Tab.6 Finite element analysis results of different thicknesses

From the effect point of view，although the ther‑mal deformation of Group 7 is better，the advantage of mass reduction of Group 6 is more prominent，and the structure is self-symmetric along the height direc‑tion of the web，which can make the skin and the back ribs symmetrical，respectively，and have less influ‑ence on each other.Therefore，the design parameters of Group 6 are the optimal values.The first-ordermodal shapes of the structure obtained from Group 6 of design values and the thermal deformation cloud diagram of the structure at the ambient temperature in the ranges from 20 °C to 100 °C and from 20 °C to-180 °C are shown in Fig.11.From the perspective of the vibration mode，the long axis direction of the reflector surface between the external support constraints on the side feet vibrates first.It is the first vibration in the long axis direction of the reflection surface between the external support constraints on the side foot.In terms of the distribution of thermal deformation，the distribution is relatively uniform，and the protruding points are in the positions of the metal embedded parts.

Fig.11 Fundamental frequency and surface thermal deformation of the reflector structure corresponding to the optimized values

In summary，the design of the geometric size of the SPR structure reflector is basically determined，the rib structure is shown in Fig.12.It can be seen that the section shape of the back rib is I-shaped，and the skin thickness is 0.6 mm，the height of the Ishaped rib is 60 mm，the thicknesses of web，upper，and lower panels are 0.8 mm，and the width of the flange is 15 mm.

Fig.12 Rib diagram of the SPR structure reflector

5 Strength check of the SPR reflector

The analysis parameters are set according to the sinusoidal vibration test conditions of the antenna re‑flector.In the analysis，the acceleration excitation signal is applied to the position of the initiating explo‑sive device and the center support position at the bot‑tom of the back ribs to imitate the acceleration input of the vibration table.The damping of the composite material is 5%，and the damping of the metal struc‑ture is 2%.The strength criterion values of the struc‑ture under the maximum response acceleration load in the，，and-axial directions are obtained based on the Cai-Wu criterion.The strength distribu‑tion under the，，and-axial loads is shown in Fig.13.The area marked by the red ellipse is the place where the strength is weak.The-direction is concentrated in the connection between the carbon fi‑ber strut and the vice anti-joint.The weak positions in the-and-directions are all in the connection be‑tween the reflector and the carbon fiber strut joint.These places are metal parts，which are prone to stress concentration and are prone to damage.How‑ever，the simulation structure shows that theval‑ues of the Cai-Wu failure criterion are 0.178，0.016，and 0.013，respectively，and thevalues are all less than 1，indicating that these weak areas do not have strength failure，and there is a large margin，i.e.，the designed skin stiffened structure reflector meets the strength requirements.

Fig.13 Strength distribution of the SPR reflector

6 Preparation and test of the reflector

Since only the main reflector is designed to be lightweight，the secondary reflector and the strut components are unchanged.Therefore，only the main reflector is prepared and tested.The main reflector of honeycomb sandwich structure and the main reflector of SPR structure are prepared by the hot pressing tank molding process.The physical objects of the two main reflectors are shown in Fig.14.

Fig.14 Physical objects of the two main reflectors

6.1 Comparison of the reflector weight

The total weight of the SPR structure reflector is 11.9 kg.Under the same condition，the weight of the honeycomb sandwich structure reflector is 20.72 kg.The new structure reflector is reduced by 8.82 kg，and the weight loss is 42.5%.The weight reduction advantage is obvious.

6.2 Precision test of the reflector surface

The test targets are evenly pasted on the reflec‑tor surface，and the RMS value of the profile accura‑cy is tested by the three-dimensional（3D）closerange photogrammetry method.The equipment used is the MPS/FP single camera photogrammetry sys‑tem.The test state of the molding reflector after the target is affixed as shown in Fig.15（a）.The surface precision is calculated by the computer assistant design（CAD）surface conversion method.The CAD surface of the reflection surface is put into the program，and the measured data are displayed in a window.Through the conversion of common points，the initial value of the coordinate conversion parame‑ter is given，and the program can carry out the fitting calculation until the square sum of the distance from all discrete points to the surface is the smallest.The distribution of the calculated needle error（normal de‑viation）of actual measurement points relative to the CAD surface is shown in Fig.15（b）.

Fig.15 Precision test

The results show that the actual shape is convex in the middle of the theoretical surface and sinks at both ends，which is related to the position of the re‑flector，mainly owing to the influence of self-weight deformation.The manufacturing accuracy of the mid‑dle part of the surface is higher，and the manufactur‑ing accuracy of the edge part is lower.In general，the RMS of the profile accuracy of the SAHS reflector is 0.14 mm，and that of SPR structure is 0.15 mm，which is slightly lower 0.01 mm but satisfied the ac‑curacy requirements of RMS ≤0.3 mm.

6.3 Modal correction of the reflector

According to the actual state and weight of the formed product，the finite element simulation analy‑sis model is revised.The calculated fundamental fre‑quency of the SPR structure reflector is 142.2 Hz.The calculated fundamental frequency of the SAHS structure reflector is 138.7 Hz.The simulation re‑sults show that the stiffness of the SPR structure re‑flector is better than that of the SAHS structure reflector in the actual state.

7 Conclusions

The SPR structure antenna reflector is a high performance composite reflector made of carbon fiber composites.It only needs the reflective surface skin，and no longer needs the double skin structure，i.e.，the traditional structure with the inner and outer skins made of sandwich materials.The design of the back ribs is also more flexible and controllable.The skin and the back ribs can be designed to match the stiff‑ness and CTE.The design and experimental verifica‑tion of this paper can be concluded as follows.

1）The fundamental frequency of the new struc‑ture is 142.2 Hz，3.5 Hz higher than the original structure.The number of the new structure parts is reduced by 40%，and the molding process is greatly simplified.

2）The total weight of the new structure is 11.9 kg，which is 8.82 kg less than the original struc‑ture，and the weight loss proportion is 42.5%.

3）The measured RMS value of the profile accuracy is 0.15 mm，which is slightly lower than the 0.14 mm of the original structure，but it meets the ac‑curacy requirements of RMS，i.e.，not greater than 0.3 mm.

Overall，the reflector with single SPR structure has the characteristics of light weight and high preci‑sion，which is an excellent structure for lightweight spaceborne antenna reflector.In the future，variable height or weight reducing holes in the web can be considered for further lightweight as needed.