Research On Omni-directional Antennas And Monopulse Antenna Arrays

With the rapid development of wireless communication,antenna plays an important role in wireless devices.Nowadays,the demands of the antennas in wireless communication systems become more and more strictly.In this background,this paper focuses on omni-directional linearly polarized(LP)antennas,omni-directional circularly polarized(CP)antennas,multi-mode circular patch antennas and monopulse antenna arrays.This paper does deep research on several types of antennas based on scientific research topics.The major contributions of this paper can be summarized as follows.1.Research on the omni-directional LP antennas.Based on the printed dipoles and the microstrip antennas,three types of antennas are designed in this section.(1)A handheld broadband omni-directional antenna is designed.The parallel strip line is used to feed the dipoles.The bandwidth of the antenna is 30%.In the working band,the roundness of the radiation patterns of the antenna is less than 3dB and the minimum gain is larger than 1dBi.The antenna is simple in structure,good in performance,small in size and light in weight.(2)An omni-directional LP dipoles array with high gain property is presented.The proper input impedances of elements and the proper feeding network are chosen for high gain in azimuthal plane in a quite limited space.Besides,the gain of the antenna beyond 130deg in elevation plane is small.(3)A controlled omni-directional microstrip antenna array for four surfaces is designed.The antenna in each surface is a four elements array.The array is fed by series combined parallel feeding method.By loading the shorted metal pin in the bottom element,the antenna can achieve a better high-gain property in the whole range of Odeg to 90deg in elevation plane.The minimum gain can achieve-12dBi in the whole range of Odeg to 90deg in elevation plane.The maximum gain of the proposed antenna is 13dBi and the mimimum gain is larger than 7dBi in azimuthal plane.The front to back ratio is larger than 25dB.2.Research on omni-directional CP antennas.Based on the theory of electric monopoles and magnetic monopoles,three types of omni-directional CP antennas are designed.(1)A compact omni-directional CP antenna is presented.Four L-shaped patches are printed on both upper and lower surfaces of two stacked substrates.Four L-shaped patches and shorted pins are connected to provide horizontal polarization while the center fed circular patch provides vertical polarization.By adjusting the parameters of this antenna,the desired omni-directional CP property can be achieved.The antenna is good in omni-directional CP property and compact in size.(2)A bottom-fed omni-directional CP antenna array is proposed.The antenna array consists of four elements.Two dipoles provide vertical polarization and two ZPS line loops provide horizontal polarization.The lto4 T-shaped parallel strip line power divider is used to ensure that four outputs are same in phase and amplitude.The structure which transferred parallel strip line to microstrip line is used in the bottom to make the antenna more suitable for practical use.(3)A compact omni-directional CP antenna with high gain property is proposed.Based on the antenna proposed in(2),the positions of two ZPS line loops and two dipoles are different.The loops and the dipoles are fed by T-shaped parallel strip line power divider and the omni-directional CP property is formed in far field.The antenna is more compact in size.3.Research on multi-mode of patch antennas with omni-directional radiation patterns.Based on multi-mode of circular and circular loop patches,two types of multi-mode antennas with omni-directional patterns are proposed.(1)A dual-band dual-polarized antenna with omni-directional patterns is presented.The antenna is loaded with eight shorted pins to get different working modes.In lower band,the TM01 mode of the circular patch is excited to provide vertical polarization while eight open slots in the circular patch provide horizontal polarization.Omni-directional CP pattern is formed.In higher band,the TM02 mode of the circular patch is excited to provide omni-directional LP pattern.(2)The wideband circular loop antenna based on the TM11 and the TM21 modes is presented.Different ports of this antenna can excite different modes of the circular loops.The broad beam can be achieved with the TM11 mode excited and the conical beam can be achieved with the TM21 mode excited.The circular loops working in both TM11 and TM21 modes have parasitic patches to broaden the impedance bandwidths.4.Research on monopulse antenna arrays.Two types of monopulse antenna arrays are proposed.(1)The wideband monopulse linear antenna array with shaped beam is presented.The antenna has a zero-filled shaped pattern in elevation plane while a sum and a difference patterns in azimuthal plane.The element of the antenna array consists of two double layer metal patches with T-shaped power divider.The element can be used to shape the beam in elevation plane and broaden the impedance bandwidth.Hybrid coupler and Wilkinson power dividers are used to feed eight elements.The maximum gain of the sum beam is larger than 20dBi and the sidelobe of the sum beam is less than-18dB.The null depth of difference beam is less than-25dB.(2)A monopulse planar antenna array based on SIW technology is presented.The center fed H-slots antennas are used to form an antenna array with 8x8 elements.Hybrid coupler with SIW technology is used to form the feeding network to get the sum and the difference beams in both azimuthal and elevation planes.The antenna can radiate the sum and the difference beams in both planes and the null depth is less than-25dB.