Conformal Load-Bearing Microstrip Antenna Arrays Integrated Into 3D Orthogonal Woven Composites

Antenna, known as the acceptor and transmitter, is wildly used in many important field. However, traditional antenna also famous for their well-marked shape and poor aerodynamics performance, which are deadly drawbacks for the advanced aircraft and warship. With the novel concept, such as to embed the active element into the structures like the wings and airframes, technic as smart skin is introduced to enhance the structure efficiency. Meanwhile, in responses to the demand of aerodynamic, invisibility and mechanic properties, a combination of microstrip antennas and sandwich core composites or laminated composites is highlighted. The combination of microstrip antennas and sandwich core composites or laminated composites is to be conformal with the airframe, which overcome the shortcomings of traditional antennas from the structure point of view, with improved anti-damage capabilities and aerodynamic properties. However, element antenna is usually insufficient in gain to reach the demand of long distance communication. To obtain high gain means increasing the electrical size of the antenna. Thus, there are mainly two way to reach desired electrical size of the antenna: enlarging the dimensions of single elements and assemble the radiation element in certain configuration. The single antenna size is limited due to the aircraft shape and manufacture but the array has no such limit, what’s more, array could phased scan and keep working even with some elements are totally destroyed. The 3D woven composite, unlike the taditional laminates or sandwich core composites, has good anti-delamination capabilities thanks to the bind yarns in the thickness direction. Thus, it is especially important to combine 3D woven composite and array antenna for the design of advanced airspace crafts, hidden technology for warships.E-glass fiber and vinyl ester are selected as reinforced fiber and matrix to fabricate the composite as dielectric substrate. Two kind of microstrip array antenna and feed network are designed and simulated with the simulation soft (Ansoft hfss). For 1×2 array, the characteristic impendance is obtained though the simulation and calculation and then to be used in the design of the array and feed network. For the 2×2 array three kinds of impedance network, one to average the characteristic impedance of the transmission line another to average the widths of the transmission line while the last is to possibly minimize the total area of the transmission line, has been proposed and discussed. The simulation result shows that the impedance network will influence the radiation pattern of array antenna. However, narrow feed line will bring in extra energy loss and possibility of mis-match or even unable to be fabricated due to the limit of weaving machine. The method with the principle that to average the characteristic impedance of the transmission line perform best that VSWR (Voltage Standing Wave Ratio) reachs 1.1 to 1.4 and with Gain in value 3 to 4dB, less distortion on radiation pattern. Meanwhile, all four samples present a frequence shift to left from 1.5Ghz and 2×2 array shift to 1.2Ghz. This may be because the design error is amplified though the array structure.Part of first layer and total bottom layer of glass fiber are replaced with conductive wire. Conformal array antenna preform is fabricated, strictly follows the requirement and design, though our unique methods. The whole antenna array structure includes radiation patch, feeding network and ground. Due to the bind yarns in the thickness direction, the integrated structure has no shortcoming of delamination that is familiar in the traditional laminates and sandwich core composites. Three 1×2 array and a 2×2 array samples have been fabricated with edge excited and back excited respectively and then curdled though VRATM method. Antenna performance test result shows that all samples resonant at near 1.5Ghz, two of 1×2 array present VSWR to 1.1 and a good match of radiaiton pattern with simulation. The front lobe of 1×2 array is concentrated and back lobe is small while the gain reache to 2dB, which is good enough to meet the design requirement. However, the other two samples are disappointing. Although the 2×2 shows the best front lobe concentration in radiation pattern, the gain value of those two samples are far below zero to about -8dB, which is weird. We believe that the degenerative resin should take the responsibility for the zoom in dielectric loss and decrease in gain. Meanwhile, all four samples shows a trend that the radiation pattern performance of E plane is better than that of H plane. This may be due to the fact that the diameter of conductive weft yarns and warp yarns are differentm, which are fabricated as the radiation patch and ground structure.