Research On The Ka-band Fixed-frequency Beam-scanning Leaky-wave Antenna

Antennas always plays an important role in the modern wireless communication system,and different scenes have different requirements for various antennas.In remote sensing and satellite communication systems,especially in Ka-band moving-in-communication system,the beam-scanning characteristics of antenna have attracted much attention.In general,beam-scanning antennas can be divided into mechanical-scanning antennas and electronically-controlled beam-scanning antennas.The mechanical-scanning antennas have several disadvantages such as large volume,slow scanning speed and poor stability,and the traditional electronically-controlled beam-scanning antennas mainly include phased array antenna and reconfigurable planar reflection or transmit array antennas.Phased array antennas usually need a large number of T/R components,which are expensive and difficult for large-scale applications.On the other hand,reconfigurable planar reflection or transmit array antennas often require additional sources and hence own a higher profile,which also limits their integration and potentials for the systems.As a result,the leaky-wave antenna（LWA）with low profile,low cost,easy integration and frequency scanning features has been a hotpot.Since it was proposed in 1940s,it has been applied in microwave and millimeter wave bands for a long time.However,the realization of the beam-scanning property for LWA needs the change of frequency,which is difficult to meet the requirements of communication systems usually operating in a specific frequency band,and limits its application more or less.Therefore,it is of great value to explore the LWA with fixed-frequency beam-scanning property.Most of the existing fixed-frequency beam-scanning LWAs are performing in low-frequency bands such as C-and S-band,and in this paper,LWAs combined with PIN diodes or liquid crystal materials are designed aiming at the Ka-band fixed-frequency beam-scanning ability.A series of new LWAs with circular polarization,positive-harmonic radiation,polarization reconfiguration,dual-band property,wide-band ability and open-stop band suppression have been presented.The main innovations of this thesis are stated as follows:1.Two types of single-polarization fixed-frequency beam-scanning LWAs operating in Ka-band are presented.1)The first one is a fixed-frequency beam-scanning LWA with circularly-polarized property,and a groove gap waveguide（GGW）is adopted as the transmission structure.The corner-cut patch is used as the radiation element for circular-polarization radiation.The PIN diodes are soldered below each radiation unit,and the working state of the unit is controlled by the PIN diode,corresponding with the 1-bit principle.The coding“0”means that the patch unit is not in operation,while“1”means that the patch is functioning.Based on the period-reconfigurable method,a variety of period lengths can be achieved with different coding arrangements,and a beam-scanning range more than 83°is realized within the operating band from 30 to 33 GHz.Meanwhile,a peak gain up to 17 d Bic is realized in the practical experiment with a circular-polarization radiation.2)Another one is a fixed-frequency beam-scanning LWA with vertical polarization,and a similar GGW structure is utilized as the transmission structure.The rectangular patch is adopted as the radiating element,which is coupled by the longitudinal gap excited within a TE₁₀ mode,and each patch is also switched by the PIN diode.In addition,a concept of equivalent transmission constant is proposed,and the radiation principle of positive-harmonic radiation is stuided.On this basis,a beam-scanning range of 70°and a peak gain of 16.5 d Bi at 29 GHz is realized.2.Two kinds of polarization-reconfigurable fixed-frequency beam-scanning LWAs operating in Ka band are presented.1)The first one is a circular-polarization reconfigurable fixed-frequency beam-scanning LWA.A GGW structure and the corner-cut patches are acting as the transmission structure and the radiating elements respectively.By using the PIN diodes to change the cross-shaped coupling slots,the polarization states can be switched between left-handed circular polarization（LHCP）and right-handed circular polarization（RHCP）,and the hologram can be adjusted as well.As a result,based on the holographic theory,a beam-scanning range of 100°at both of LHCP and RHCP is realized at 28 GHz in the presented LWA.2)The other one is a quad-polarization reconfigurable fixed-frequency beam-scanning LWA.A GGW structure and the±45°inclined slots are performing as the transmission structure and the radiating elements respectively.In addition,a modified holographic method is presented,and on this basis,when the phase difference in the two rows of objective waves are 0°,90°,180°and 270°,the polarization states of a horizontal polarization（HP）,an LHCP,an vertical polarization（VP）and an RHCP can be achieved respectively,and a beam-scanning range of 100°is realized at 30 GHz in all of the four different polarization states.Besides,peak gains of11.3 d Bi,11.5 d Bic,13.0 d Bi and 11.8 d Bic are achieved as well in the practical measurement.3.A large-frequency-ratio dual-band fixed-frequency beam-scanning LWA is presented,which is consisting of a low-band array and a high-band array.The upper microstrip transmission line and the lower slow-wave GGW are employed as the feeding and transmission structures of the low-band and high-band arrays respectively.Based on the holographic principle,a beam-scanning range of 100°can be realized at both 5 GHz and 27 GHz.4.A wideband fixed-frequency beam-scanning LWA is presented.A GGW with TE₀₁-mode excitation is introduced as the transmission structure,and two rows of longitudinal slots are utilized as the radiation elements.Based on the period-reconfigurable method,a beam-scanning range of more than 70°within the frequency band between 23 and 29 GHz is realized.In addition,the peak gain reaches at 16.8 d Bi in the practical experiment.5.A Ka-band fixed-frequency beam-scanning LWA is presented by using the liquid crystal（LC）material.A series of periodic-perturbation stubs are introduced as the radiating elements.Owing to the tunable property of the LC,the relative permittivity of the LC will get changed when there is an extra biasing filed,and hence the phase constant of the LWA will be changed as well,leading to a fixed-frequency beam-scanning ability from 26 to 30 GHz.In addition,a new method is presented to eliminate the open-stop band（OSB）effect in the LWA.By using this method,the OSB can be eliminated effectively and the attenuation is suppressed.As a result,a stable broadside beam is realized at 26 GHz.