Study On Radiation Pattern Reconfigurable Electrically Small Endfire Antenna And Broadband Electrically Small Antenna

Radiation pattern reconfigurable directional antenna can not only concentrate the energy in the required direction,but also adjust the main-beam radiation direction in real time to meet the complex communication requirements.At the same time,electrically small antenna can make the communication system highly integrated,so the research on electrically small radiation pattern reconfigurable directional antenna becomes more and more important.In addition,electrically small antennas have large quality factor and narrow bandwidth,while broadband antennas can increase the system capacity and improve the transmission rate.Therefore,the research of broadband electrically small antenna has important theoretical and practical application value.In this paper,the radiation pattern reconfigurable electrically small directional antenna and broadband electrically small antenna are studied.It mainly includes the following contents:(1)A low-profile radiation pattern reconfigurable electrically small endfire antenna with three beams is designed.According to the principle of complementary antenna to realize the end-fire radiation pattern,the electrically small equivalent electric dipole and the magnetic dipole are placed orthogonally on a single dielectric substrate,and the two are excited through equal amplitude and in phase,the endfire radiation pattern is obtained.Furthermore,loading the diode on the feed network to obtain three beam reconfigurable states,the beams in the three states can completely cover the azimuth plane.The designed antenna also has the advantages of electrically small,ultra-low-profile,high gain,high radiation efficiency and high front-toback ratio.(2)A low-profile radiation pattern reconfigurable electrically small endfire antenna with six beams is designed.Also based on the working principle of complementary antennas,the Alford loop and the slotted ground loaded with six circular arc stubs are designed on a single dielectric substrate,and a coaxial cable is used to feed from the center.The Alford loop and the loaded six circular arc stubs form a compact in-phase current loop,which is equivalent to a magnetic dipole,and etching a rectangular slot can change the current distribution on the ground and introduce an equivalent electric dipole.The two are organically combined,and excited by the equal amplitude and antiphase to obtain end-fire radiation pattern.In addition,the mutual coupling between the Alford loop and the loaded six circular arc stubs reduces the electrical size of the equivalent magnetic dipole,while the Alford loop arms and the loaded circular arc stubs extend the current path of the equivalent electric dipole,thereby electrically small characteristics is obtained.Furthermore,six symmetrical rectangular slots are etched on the ground plane and diodes are introduced to realize six reconfigurable radiation patterns.The designed antenna has excellent endfire radiation performance,and the front-to-back ratio is as high as 35.6d B.(3)A broadband electrically small antenna with stable gain is designed.The halfwavelength dipole is designed on a single-layer dielectric substrate,and then two arms of the dipole are widened,and the length remains unchanged to broaden the bandwidth.Four L-shaped grooves are etched on the widened half-wavelength dipole,and loading stubs at the ends of its arms to achieve miniaturization of the antenna.Furthermore,an I-shaped coupling feed structure is designed on the lower layer of the dielectric substrate,which strongly coupling with the wide dipole loaded with four L-shaped grooves to generate another adjacent resonance mode,thereby broadening the antenna bandwidth.The antenna has electrically small characteristics,ka=0.94,and its impedance bandwidth reaches 31.9%,and at the same time has a stable gain in the passband...