Design Of Low-profile Multi-frequency Coaperture Antennas

The functions of modern wireless communication systems are increasingly complex,which means that more and more frequency bands need to be covered,but the systems'sizes are limited.Therefore,it is of great significance to study antennas with multi-band coverage,low profile,compact structure,and wide bandwidth in each band.The conical-beam antenna with these characteristics is suitable for a variety of practical application scenarios of the new generation of mobile communication.However,there is relatively little research on this type of antenna at present.In the existing works,there are still problems with a high profile or a narrow bandwidth,which cannot meet the needs of practical applications well.To tackle the problems above,this paper mainly studies low-profile,multi-band,compact conical-beam antennas.The major works of this paper include the following three parts:First,a low-profile dual-band co-aperture monopolar antenna based on crossed-layer folded structure is investigated.A novel cross-layer folded structure is proposed to construct a single-band monopolar antenna in the lower band.It can provide enough space for another higher-band section to be integrated together without extra profile.Meanwhile,by adding a high frequency radiation element to the reserved space,a dual-band co-aperture antenna with independent frequency control is obtained.Moreover,by exciting TM₀₁ and TM₀₂modes in both two bands,the proposed antenna can achieve a relatively large impedance bandwidth of 10.9%in the lower band and 14.6%in the upper band with a thickness of 3.14mm.Stable monopole-like radiation patterns are achieved within the two bands and the gains in the lower and upper bands are 5.2–5.8 and 3.7–5 dBi,respectively.Compared with other works,the proposed antenna features its low profile and independent band performance.Second,a compact low-profile tri-band co-aperture monopolar patch antenna is investigated.A cross-layer folded structure(C1)is designed to excited TM_01L and TM_02Lmodes in the first band.It can provide enough space for other higher-band sections to be integrated together without extra profile.Then,by adding a smaller cross-layer folded structure(C2)to the reserved space,TM_01M and TM_02M modes could be excitd in the second band.Finally,by adding a via-loaded circular patch to the reserved space of C2,TM_03M and TM_03S modes,which bring the third band,could be excited.In these bands,the electromagnetic waves are radiated from different radiation slots respectively.By making full use of the antenna space,the antenna achieves impedance bandwidths of 2.3%(2.56-2.62 GHz)in the first band,12.3%(5.50-6.22 GHz)in the second band and 5.7%(8.92-9.44 GHz)in the third band with a very low profile(0.025?₀).The simulated gain ranges are 3.1-4.0 dBi,4.9-5.7 dBi and 7.6-8.5 dBi,respectively.To the best of our knowledge,there is little tri-frequencies conical-beam patch antenna that simultaneously excites 6 modes with consistent patterns through single-probe feeding.Third,a low-profile dual-band omnidirectional circularly polarized antenna is proposed.Compared to linearly polarized antennas,circularly polarized antennas can better eliminate polarization mismatch and suppress multipath interference.In order to make the proposed low-profile dual-band antenna more advantageous,it will be converted into a circularly polarized antenna by loading an Alford loop and a dielectric polarizer on it.The simulated results show that this method can achieve omnidirectional circular polarization in the two bands.