Research On Wideband Wide-scanning Phased Array Antenna

Active electronic scanned array(AESA)has advantages of flexible beam scanning,fast beam switching,and high-precision beam scanning.It is widely used in the modern wireless communication and radar systems.With the increasing requirements of high-speed communication,high-resolution radar,multi-beam and multi-function electronic platforms,wideband wide-scanning phased array antennas are in urgent demand.Besides,in an antenna array,the performance of the elements are different from the isolated ones.The mutual coupling among the elements affects the bandwidth of the array,and the scan blindness phenomenon can be seen in phased array designs,which restricts the performance of the array essentially.This dissertation is focused on broadening the bandwidth and scanning angle of the two-dimensional phased arrays.The methods studied in this dissertation include reducing the mutual coupling among the elements,adjusting the impedance matching at the ports,eliminating the scan blindness phenomenon.The main contributions and contents of this dissertation are listed as follows.1.A novel wideband wide-scanning microstrip antenna array with substrate-integrated cavity(SIC)-backed U-slot patches is proposed.Firstly,the U-slot patch is used as the antenna element for its wideband performance among the microstrip antenna types.The elements are arranged in a triangular lattice for mutual coupling reduction since the element spacing is enlarged.This U-slot patch array achieves 20% bandwidth under ±60° scanning range.Based on this original array design,the scan blindness phenomenon in the array is analyzed from the aspect of surface wave propagation.With this mechanism,the SIC structure is introduced in the antenna elements.As a result,the scan blindness is effectively shifted out of the operation band as the SIC structure obstructs the surface wave and eliminate the mutual coupling.The simulated and the measured results show that the X-band array provides a bandwidth of over34% frequency range under ±60° scanning in all azimuth planes.2.A compact extended-matching type Vivaldi antenna array with a low profile is proposed.The transition structures of the Vivaldi antenna,including the feedline to the slotline,the slotline to the tapered slot and the aperture to the freespace transistion,are analyzed and designed.The parameters of the Vivaldi antenna are optimized.Based on the design of the original Vivaldi antenna array,the antenna flare is extended with a part of a constant-width taper.This extened part adjusts the impedance matching between the antenna aperture and the free space.The implemented array is able to work over 4 GHz with scanning over ±60°,with a profile of only 0.72 wavelength at the highest frequency3.Focused on the scan blindness problem in the low-profile Vivaldi array in a triangular lattice,a mushroom-type reactive impedance surface(RIS)is introduced on the same PCB as the antenna.The metasurfaces used in phased array designs are classified by its characteristics,including reflection phase,transimission characteristic,and surface wave propagation supported characteristic.Based on these analyses,the RIS is introduced in this design.The equivalent model of the RIS is built so that the trasmmission ability and the impedance of the RIS are extracted.The reactance of the RIS structure compensates for the scan impedance variation of the antenna during the beam scanning.A superior scanning performance in all azimuth planes is achieved with a profile of 0.712 wavelength at the highst frequency.The C/X-band array is capable of operating over a 1.8:1 bandwidth with at least ±60° scanning range.4.With the scan blindess problem in the low-profile rectangular-lattice Vivaldi array considered,a patch-type RIS structure is introduced as a wide-angle impedance matching(WAIM)layer.With the analysis of the equivalent transmission-line model,the patch-like RIS is proved to provide capacitive reactiance for the impedance matching at the antenna port.The performance of the original Vivaldi array,the dielectric superstrate loaded Vivaldi array,and the mushroom-type RIS loaded Vivaldi array are compared together for illustration of the effectiveness of this method.Metal walls are placed at the edges of the array for further performance enhancement as elimination of edge effects.The proposed C/X-band array achieves a scanning volume more than ±65° during a bandwidth of 6.4 GHz in all azimuth planes.