Analysis Of Cavities By FE-BI And Study On Circularly Polarized Antennas

Antenna is one of the key components of wireless communication systems. With the development of electronic technique and advancement of space technique, the communication systems are developing towards wideband and miniaturization direction, which makes the design and manufacture of waveguide slots array antennas and wideband and compact circularly polarized antennas to be an urgent and important issue. Being associated with the demands of the wireless communication systems, this dissertation makes deeply insight to waveguide slots array antennas, wideband and circularly polarized antennas for GPS, reconfigurable wideband and circularly polarized antennas, wideband and broad beamwidth circularly polarized antenna, Inductively-Loaded and Magnetically-Coupled Small Antenna and "buried-on-wall" antenna for indoor applications. The author's major contributions are as follows:1. A new method for analyzing waveguide slots array is investigated. The Finite element-boundary integral (FE-BI) method is introduced to analyze waveguide slots array antennas. The numerical model based on FE-BI is established. Then by obtaining the equivalent magnetic current on the surfaces of the slots, far field radiation characteristics of the waveguide slots array can be acquired. Also simulated and measured results are compared to verify the efficiency and accuracy of the presented method. The good agreement shows that FE-BI can be utilized as an efficient method for analyzing waveguide slots array.2. Two wideband and circularly polarized antennas for GPS are studied. With a suspended structure and a T-shaped feeding probe, wideband and circularly polarization are implemented. By incorporating a long probe inside a high substantial cavity (～0.16λ), a circularly polarized (CP) antenna in broadside direction is achieved. The horizontal arm of the probe is implemented by means of a printed monopole that is diagonally coupled to a small special shaped copper plate. The two CP antennas feature a wide operating bandwidth and good bore sight axial-ratios during the GPS band. The maximum gains of these two antennas are recorded as no less than 7.2 dBc across the bandwidth. The measured results are presented.3. A polarization reconfigurable microstrip antenna without orthogonal feeding network is proposed. The antenna is composed of a suspended patch, two printed probes and a simple switch circuit. Reconfigurable polarization, i.e. right-hand circular polarization (RHCP) or left-hand circular polarization (LHCP) or linear polarization (LP), is produced by controlling the states of the switch circuit. A prototype is designed and tested. The simulation and measured results show that the proposed antenna demonstrates wide impedance bandwidth, and a good axial ratio in the circularly polarized states.4. A novel printed crossed dipole with broad axial ratio (AR) bandwidth and enhanced beamwidth is proposed. The proposed antenna consists of two dipoles crossed through a 90°phase delay line, which produces one minimum AR point due to the sequentially rotated configuration and 4 parasitic ring loops, which generate one additional minimum AR point. By combining these two minimum AR points, the proposed dipole achieves a broadband circularly polarized (CP) performance. Behind the dipoles are 8 erect parasitical monopoles and a reflector, which are placed to broaden the beamwidth. The proposed antenna has not only a broad 3 dB AR bandwidth with respect to the CP center frequency 1.575 GHz, but also a broad 3 dB beamwidth of about 180°. The computed and measured results show the high practicality of this method.5. Two kinds of inductively-loaded and magnetically-coupled small antennas with circular polarization are presented. The electronically small size is implemented by employing a new inductively-loaded technique. This technique consists of adding short circuited cylindrical covers to extremes of the structure, making the elements be inductively loaded, and as a result, increases the electronic length. Two antenna prototypes are proposed to verify this method. This method may have some guiding significance for the minimization antennas with circular polarization properties.6. Two wideband antennas for indoor communication applications are proposed. One is dual band for GSM/UMTS/WLAN applications, the other has impedance bandwidth of about 116% ranging from 800 MHz to 3 GHz (VSWR<2), making it easy to cover the GSM/DCS/PCS/UMTS/IMT/Wibro/CDMA/WiMAX bands. The wall effects to the antennas are also studied. The computed and measured results show that these two antennas feature good performances in their operating bands.