Research On Wide-angle Wideband Scanning Phased Array Antennas

Phased array antennas have broad applications,from radar to communications,due to their unique electronically controlled beam agility.A phased array antenna with wide-angle wideband scanning capability is the key component in relevant systems to ensure high performance.It is also the hot and difficult issue in phased array research field.The interaction between array elements,i.e.,mutual coupling,changes the distributions of the current magnitude and phase on each element,then results in a different impedance and radiation characteristic compared with a single element and thus affects the array scanning performance.Therefore,the mutual coupling is the main reason to make it difficult to design a wide-angle wideband scanning phased array antenna.From the key perspective of mutual coupling control,an in-depth research on wide-angle wideband scanning phased array antenna is conducted in this dissertation.The main contributions are summarized as follows:1.From the view of compensating the mutual coupling,a coupling compensation network based on overlapped feed structure is studied.By analyzing its work mechanism,it is found that the overlapped feed network introduces a compensation signal varies with scan angle.Then,by combining the circuit model and full-wave simulation,the design process of the overlapped feed network is detailed.We find that the phase adjustment provided by the output arms of power dividers is the key to achieve coupling compensation for wide-angle scanning.A 1×16 phased array prototype using overlapped feed network has been designed and fabricated for experimental verification.Due to the improved wide-angle impedance matching,simulation and experimental results show that the array can scan to ±60° with gain decrease lower than 3 dB.2.From the view of compensating the mutual coupling,two kind of coupling compensation networks based on connected couplers are studied.The two kind of networks are used to intentionally introduce an indirect coupling to cancel the direct coupling from the array aperture,thus compensating the variation of the active input impedance of the array element with beam steering.The couplers are employed to control the magnitude of the indirect coupling.The transmission lines are used to connected adjacent couplers and provide the phase adjustment.Scattering matrix theory is used to analyze the working principle of the two networks.Then,general design procedures of the two networks are given.In the first kind of coupling compensation network,lossy resistors are used.To avoid the use of resistors,the second kind of coupling compensation network is proposed.A two-element microstrip antenna array with the second kind of network is built to demonstrate the method.Simulated and measured results show that the isolation between the feed ports of adjacent elements is greatly improved due to the cancelation of indirect and direct coupling.Furthermore,the coupling compensation bandwidths of the two networks are analyzed and a solution is provided to improve the coupling compensation bandwidth of the first kind of network.3.Based on the theoretical analysis and experimental validation above,the application of the two networks to wide-angle wideband phased array antennas is studied.Firstly,the second kind of coupling compensation network is applied to a 16-elment microstrip linear array.Due to the effective compensation to the mutual coupling between adjacent elements,wide-angle impedance matching is achieved,which avoids the gain reduction caused by the impedance mismatch at large scan angles.The simulated-10 dB bandwidth is about 5.5% over the scan range of 0°~60°.The array can experimentally scan to 66° with a gain reduction of only 3.04 dB.Secondly,the first kind of coupling compensation network is improved to have wide coupling compensation bandwidth and high efficiency,and then applied to a 16-elment stacked patch array.The simulated-10 dB bandwidth is about 13.2% over the scan range of 0°~60°.When the array scans from 0° to 60°,the measured gain decreases by 1.2 and 2.4 dB at 6.6 and 7.5 GHz,respectively,which shows wideband wide-angle scanning capability.4.A novel wideband antenna is proposed,which is backed by an open metal cavity and uses microstrip feed line and parasitic metal strips to radiate energy.It has advantages of compact size and simple feed structure.From the view of using the mutual coupling,the proposed antenna elements are connected to each other,thus constituting a novel kind of array antenna based on connected backed cavities.Since adjacent elements in the H-plane are electrically connected,the mutual coupling is intentionally enhanced.The infinite array unit cell achieves in simulations about 43.4% bandwidth(7.4~11.5 GHz)with VSWR?2 when scanning to ±60°,and nearly 44% bandwidth(7.45~11.65 GHz)with VSWR?2.5 when scanning to ±70° in all azimuth planes.The measured results of a 2×18 finite array show that the array experimentally achieves over 50% bandwidth(7.2~12.1 GHz)with VSWR ?2.3 at 60° scan,and more than 54% bandwidth(7.2~12.5 GHz)with VSWR ? 3.2 at 70° in the H-plane.Measured results show that the coupling coefficient between feed ports of adjacent elements in the H-plane is above-15 dB in most of the band,which proves that the wide-angle wideband performance is attributed to the effective use of mutual coupling.5.Based on the above research on the array of connected backed cavities,more applications of the proposed design are developed.Firstly,a triangular grid array is investigated for some practical applications that require large element spacing.The element spacing of the proposed array with equilateral triangular grid is 14.5mm,which equals 0.58?h(?h is the wavelength at the highest operating frequency of 12 GHz).The scan blindness appears when scanning to large angles in the E-and H-planes,which is analyzed and then suppressed.The infinite array unit cell achieves in simulations 41.8% bandwidth(7.85-12 GHz)with VSWR?3 when scanning to ±70° in the E-and H-planes.Secondly,for radar and communication systems that demands dual-polarization,a second orthogonal set of element is added into original single polarized element to radiate two polarizations.The dual-polarized element achieves in simulations 41.2% bandwidth(7.7-11.7 GHz)with VSWR?2.5 when scanning to ±70° in all azimuth planes.The port-to-port coupling between the orthogonal elements is below-16.5 dB when scanning in the E-and H-planes and below-9.4 dB when scanning in the D-plane within the operating bandwidth.