Researches On Novel Planar Multi-band And Broadband Filtering Antennas

With the rapid development of wireless communication technology,communication systems constantly give more and more stringent requirement on the RF devices.Systems tend to be more portable,smaller,more cost-efficient and more powerful.Antenna,working as one of the most indispensable part of communication system,are also facing some new challenges.They are supposed to be smaller,possessing higher gain and wider bandwidth and so on.Facing these challenges,reseachers tried to intergrate antenna and bandpass filter into one modual,making it possible to function simultaneously as a filter and an antenna.However,most of the presented arts are concentrate on the single band filtering antenna and some of them also suffer from limited impedance bandwidth.In this thesis,some novel design methods of multi-band and broadband filtering antennas will be proposed and demonstrated.The thesis is arranged as follow?.Synthesis of filtering antennas with cross-coupling.First,the detailed synthesis procedure of filtering antenna is provided.Then the investigation looks at a patch antenna-filter with a third order filtering response.The first stage of the filtering circuit is two cross-coupled microstrip resonators which are then coupled to the radiating patch which acts as the last resonator of the filter.However,the structure is configured to emulate a cascaded triplet?CT?bandpass filter.Such a filter introduces zero gain on either the high side or the low side of the passband,depending on the configuration.To get an insight of the working mechanism of such a structure,the phase relationships is studied.In addition,a cascaded quadruplet?CQ?antenna-filter is also proposed.As we expected the CQ structure shows two radiating frequency attenuation poles on the either side of the passband.A detailed synthesis procedure is presented for the design of these antennas,including a new method for the extraction of the radiating quality factor.?.Design of broadband filtering patch antenna.Unlike conventional gap coupled patch antennas,the electric and magnetic coupling between adjacent patches is considered and studied.Also,for improved understanding of the broadband nature of the proposed configuration,the phase relationships between patch elements are studied.Considerable selectivity is observed in the results of the three-patch antenna because of the radiation nulls introduced by the electric and magnetic coupling.Based on this a stub loaded resonator fed structure is introduced showing a good filtering performance.Apart from the broadband operation,the proposed antenna elements show promise for application in high isolation MIMO systems due to their inherent band reject characteristic when they are closely placed.?.Design of tri-band filtering patch antenna.A tri-band patch antenna utilizing the TM₁₀mode together with modified TM₂₀ and TM₃₀ modes of a single patch is proposed in this paper.Through asymmetrically loading a stub on one radiating edge of the patch and cutting a rectangular slot offset from the other one,the current distributions of the TM₂₀ and TM₃₀ modes are perturbed,resulting in broadside radiation for all the first three modes of a single patch.Each operational frequency can be effectively controlled through varying the dimensions of the patch,slot,loading stub.Good impedance matching is achieved simultaneously in three operational bands through aperture coupling.Based on this tri-band antenna,a new tri-band filtering antenna is further developed showing good selectivity and broadside radiation characteristic.?.Design of multi-band slot antennas and their integration with bandpass filter.An approach for designing multi-band microstrip slot antennas is proposed.Multiple resonators are loaded on a conventional microstrip slot antenna to introduce multiple resonances.The number of the operational bands of the antenna can be easily controlled by varying the number of the loading resonators.The locations of each resonance can be adjusted by varying the positions and lengths of the loading resonators together with the geometry of the slot if necessary.The proposed antenna features low profile,small radiating slot and easy fabrication,showing promising application prospect for modern communication system.A tri-band filtering slot antenna is achieved by using a multi-mode resonator to feed a tri-band slot antenna,showing satisfying filtering and radiating performance.