Research On Ultra-wideband Large-angle Scanning Planar Tightly-coupled Phased Array Antennas

With the development of electronic systems,the bandwidths and the scanning angles of phased array antennas are required to be wider and larger,respectively.Although the broadband planar phased array antennas have achieved a ±60° scanning,they cannot meet the requirements of modern electronic systems.The technology of the tightly-coupled dipole array(TCDA)is an effective means to achieve an ultra-bandwidth,but the problems of the ultra-bandwidth impedance matching and the large-angle scanning are needed to be solved.In this dissertation,the theory of the large-angle scanning,the ultra-wideband impedance transformer,the large-angle scanning method in the H plane and wide-beam antenna element are deeply studied with the TCDAs.The main contents of this dissertation include the following four parts.Firstly,it is clarified that the directivity of a finite planar array does not satisfy the cosine rule when scanning in the near end-fire region and the directivity is not zero when scanning at the end-fire.In view of this,the idea of using the element pattern to compensate the directivity of the array factor is proposed to realize an ultra-large angle scanning.Based on the strict formula of the array factor,the change rules of the directivity at different array sizes are analyzed,which are compared with the cosine rule.The analyses show that the directivity of a finite planar array does not satisfy the cosine rule near end-fire region,and the directivity is not zero at the end-fire.Based on this conclusion,the idea of using the element pattern to compensate the reduced directivity of the array factor when scanning at a large angle is proposed.Then,a hypothetical reconfigurable element pattern with seven complex states is applied to an 8?×8? array(element spacing d=0.5?,where ? is the wavelength in free space)array without considering coupling,which can achieve a ±90° scanning with 3d B directivity fluctuation.This part points out the direction for the planar phased array antenna to realize the ultra-large angle scanning.Secondly,a compact and easy-to-integrate microstrip-to-slot structure is used as the ultra-wideband impedance transformer for the TCDA,which significantly reduced the size,weight,cost,and complexity of the antenna.The impedance transformer,TCDA,and wide-angle scanning matching layer are all on a PCB.Using the impedance transformer,a TCDA with bandwidths of 5.13:1(0.75-3.85 GHz)is obtained,which can realize 70°,60°,and 70° scanning in the E,H,and D planes,respectively.The profile of the TCDA is only 0.12? at the lowest frequency.In this part,the proposed ultra-wideband impedance transformer solves the problems of large volume,complex structure,high cost,and difficulty in integration.Thirdly,a wide-band and wide-angle impedance conjugate matching(WWICM)method and a WWICM structure when scanning in the H plane are proposed.For an ultra-wideband phased array antenna when scanning at large angles in the H plane,the problem that the impedance transformer is difficult to match input impedance that changes drastically is well solved.The Floquet impedances at the upper surface of the antenna gradually decrease to zero ? as the scanning angle increases in the H plane and the imaginary parts are inductive.Then,a new WWICM method and a WWICM structure are proposed.The impedances at the lower surface of the WWICM can be well conjugated with the impedances at the upper surface of the antenna when scanning at large angles in the H plane.Finally,a single-polarization array with a bandwidth of1.02-5.15 GHz is presented,which can scan up to 70° in all azimuth planes.The profile of the proposed array is 0.2? at the lowest working frequency.Fourthly,a self-complementary array of the tightly-coupled electric dipole array is proposed,the element of which is a wide-band magnetic current antenna with a nearly180° 3 d B beamwidth in the E Plane.Theorefore,the proposed phased array antenna can realize ±80° scanning in the E plane.Because the TCDA with the electric dipole has a narrow 3 d B beamwidth in the E plane,it is difficult to achieve a large-angle scanning.However,when a magnetic current antenna is parallel to a metal ground,it can produce a nearly 180° 3 d B beamwidth in the E plane,which can provide a wide-beam element for wide-angle scanning.Therefore,this dissertation proposes a self-complementary array of the tightly-coupled electric dipole array to achieve a wide-band magnetic current antenna,which has a wide-angle scanning range in the E plane.Finnally,the proposed phased array with bandwidths of 2.7:1(2.2-5.95 GHz)is obtained.The scanning angles reach up to ±80°,±40°,and ±70° in the E,H,and D planes,respectively.The profile of the proposed phased array is only 0.14? at the lowest frequency.