Design Of Dual-Band Antenna With Large Frequency Ratio

The rapid development of wireless communication system has brought about the rapid growth of data traffic.At the same time,the available spectrum resources of the microwave band are increasingly scarce,and the millimeter-wave applications have attracted much attention.The antenna which can only work in a single frequency band cannot meet the needs of future communication systems.And it is more practical to design a multi-frequency antenna that can work both in microwave and millimeter wave bands.In this thesis,the research background,design principle and development trend of multi-frequency antenna with large frequency ratio are investigated.Based on the research above,four dual-band antennas which can cover both microwave and millimeter-wave bands are proposed.The main content of this thesis is summarized as follows:1.A compact singly-fed dual-band antenna which covers 3.5 GHz and 28 GHz bands is investigated in this thesis.The presented antenna,is realized by the loading of low-pass filter and the utilization of tapered slot.At microwave band,the antenna operates as a dipole antenna and the tapered slot works as a portion of feeding structure,while at millimetrewave band,the tapered slot works as a radiator.Signals in different bands can be separated by integrating a compact microstrip resonance cell(CMRC)low-pass filter into microstrip line,which is used to transmit the corresponding signals to feed different antennas.The antenna has measured impedance bandwidths of 28.3% and 24.2% for microwave and millimetre-wave bands,respectively.And the frequency ratio of the dual-band antenna can be flexibly adjusted.2.A singly-fed dual-band antenna integrating a 3.5 GHz monopole and a 28 GHz series-fed angled dipole array is presented.An interdigital coupling structure with different transmission characteristics at different bands is introduced into the lower-side of the parallel stripline,which enables the double-side parallel stripline to have two functions.It can operate as a monopole antenna at microwave band and as a feeding structure for dipole elements at millimeter-wave band.The operating bands of the two antennas can be adjusted without affecting the other,and the frequency ratio of the antenna can be changed according to the demand.3.Based on the utilization of dual-mode coplanar waveguide(CPW)transmission line,a dual-band antenna with large frequency ratio for microwave and millimeter-wave applications is proposed in this thesis.The dual mode operation of the transmission line is obtained by introducing a rectangular stub to traditional CPW.At millimeter-wave band,the dual-mode transmission line(DMTL)can support odd mode while it supports even mode at microwave band.Based on this,the dual-band antenna which operate as monopole antenna at microwave band and Vivaldi antenna at millimeter-wave band is realized using the same aperture.Furthermore,the proposed antenna aperture is completely reused in both bands because of the application of dual-function structures.The monopole serves as a radiation structure in low-frequency band and is used to enhance the radiation performance in highfrequency band,while the Vivaldi works as a feeding structure and as an end-fire radiation antenna respectively in different bands.4.A dual-band shared-aperture antenna operating at both microwave and millimeter-wave band is presented based on the concept of structure reuse.The antenna is composed of a printed monopole working 3.5 GHz and a slotted SIW cavity antenna operating 28.5 GHz.The high-frequency antenna is loaded on the monopole rectangular patch and thus,the two antennas realize aperture sharing.The feeding structure of microstrip-coplanar waveguide enables the ground plane and the radiation part of the monopole to be connected.The arrangement of high-frequency antenna slots makes the polarization modes of the two bands antenna orthogonal to each other,so the proposed antenna can achieve high isolation at dual bands.The frequency range covered by the antenna can be adjusted and the frequency ratio can be changed.