| The appearance of wireless communication systems changes every aspect of our daily life tremendously.Antenna,as the important part of communication system,is responsible for radiating and receiving radio waves.The performance of antenna has a great impact on the whole wireless communication system.For different scenarios,the shapes and performance of antennas are different.In this dissertation,we have studied compact multiband antenna for WLAN(Wireless Local Area Network)/WiMAX(Worldwide Interoperability)application,compact ultra-wideband(UWB)Multiple-Input Multiple-Output(MIMO)with band-notched characteristic,mobile phone antenna with metal rim,shark-fin antenna for automotive application.The main content of this dissertation is presented as follow: 1.A compact tri-band wide slot antenna monopole antenna with dual-ring resonator is presented.First,a resonant frequency at 5 GHz is produced by the traditional monopole antenna.Then,by replacing the ground with a wide-slot ground,a new resonance at 2.58 GHz is yielded.Finally,with the addition of a dual-ring resonator underneath the fork-like monopole,the third resonance at 3.7 GHz is generated with the unchanged antenna structure.The proposed antenna with a compact size of 32 mm×28 mm has the 10 dB impedance bandwidth can completely cover WLAN 2.4/5.2/5.8 GHz and WiMAX 2.5/3.5/5.5 GHz bands.A prototype of the proposed antenna is fabricated and tested.Consequently,these features make the proposed antenna a good candidate for the modern communication applications.2.A compact UWB MIMO antenna with band-notched characteristic is presented.First,by cutting the half structure of the conventional circle-slot antenna,a compact element structure is obtained.Second,two same antenna elements employ the back-to-back placement to get the original UWB MIMO antenna.To improve the isolation of the proposed UWB MIMO antenna,a rectangular slot between the two antenna elements is introduced.To produce band-notched operation without changing the structure and performance of the antenna,two T-shaped open slots are etched on the ground.In addition,the placement of two antenna elements is also studied.The proposed antenna with a compact size of 33 mm×26 mm has a-10 dB impedance bandwidth varying from 3 to 11 GHz except rejection band of 4.5-5.5 GHz and has a port isolation of more than 15 dB.In addition,the acceptable gain and omnidirectional radiation pattern and the ECC(Envelope Correlation Coefficient)of less than 0.03 are also realized.3.Two kinds of mobile phone antenna with metal rim are proposed.By utilizing the metal rim as a part of antennas,the antenna performance would not be degraded and a compact structure can be received.The first kind is hepta-band mobile phone antenna with metal rim.Firstly,different from the traditional loop antennas with the half wavelength resonant modes,the proposed antenna has two fundamental quarter-wavelength loop modes,which can reduce the electrical length.Secondly,to lower the upper band without changing the antenna structure,a distributed inductor is introduced.A matching circuit as a useful bandwidth-enhancement technique is introduced to improve the bandwidth of the lower band.Finally,the proposed antenna with a simple structure has a clearance of 8 mm.The measured impedance bandwidth can cover GSM850,GSM900,DCS1800,PCS1900,UMTS2100,and LTE2300/2500 bands.The second kind is tri-band mobile phone antenna with metal rim.Three bands are generated by three slots.For two lower working bands,two slots,which are formed by the intrinsic slots between the metal rim and the system circuit board,are employed.To reduce the electrical length,the two slots are open.To adapt the perpendicular location of two monopole slots,an L-shaped feed network is employed.The proposed antenna occupying a small size of 8.9 mm × 2 mm can cover WLAN 2.4/5.8GHz and WiMAX 2.5/3.5GHz bands.4.A shark-fin antenna for automotive application,which includes four antennas,is proposed.Under the premise of ensuring the good performance of every antenna,four antennas are placed reasonably under the shark-fin structure.For 4G main antenna,to realize wide bands,coupled-fed grounded branch and parasitic branch are utilized.And other antennas are employed to improve the antenna impedance.Finally,the 4G main antenna with a compact size of 55 mm × 25 mm can produce two wide bands covering LTE700,GSM850,GSM900,DCS1800,PCS1900,UMTS2100 and LTE2300/2500.In addition,the 4G main antenna has omnidirectional radiation patterns for several elevation angles.The proposed FM(Frequency Modulation)antenna is perpendicular to 4G main antenna to get a compact whole structure.FM antenna structure is printed on three surfaces of two substrates to obtain a compact antenna size.For the lower band of 4G diversity antenna,the coupled-fed grounded branch is employed and the band is lowered by the addition of a lumped inductor.The higher band of 4G diversity antenna is attained by the higher-order mode of coupled-fed grounded branch along with the quarter-wavelength mode of the monopole.In addition,a matching network consisting of lumped elements is used to improve the antenna impedance.Finally,the 4G diversity antenna produce two wide bands,which can cover 728-960 MHz and 1808-2690 MHz bands.And it has omnidirectional radiation patterns for several elevation angles.Besides,the isolation between 4G main antenna and 4G diversity antenna is also considered.The measure results show that the isolation is between 6 and 10 dB for the lower band,and the isolation is more than 10 dB for the higher band,which is reasonable under the consideration of the limited space of shark-fin structure.For navigation antenna,a substrate with a high permittivity is used to achieve a compact size.To obtain a circular polarization wide band,dual-fed technology is employed.The design process of 90 phase shifter with individual power is also presented,and then is integrated with the patch antenna.The measured results show that the impedance bandwidth can cover 1559-1560 MHz.The axial ratio is less than 3dB in the working band.Besides,the navigation antenna has stable gain and radiation patterns. |
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