Design of an Ultra Wideband Radio Front-End for Multi-band Communications
Application of multiband systems with a variety of frequency band combinations is accelerating since the communication capacity is increasing and new functions like GPS or Bluetooth are being added. It is expected, therefore, that all the handsets will probably become compatible with multibands in the near future. In such multiband systems, a multiband antenna is definitely one of the key devices since it is compatible with all the frequency bands without resort to multiple antennas as is usual in today´s practices. This project deals with design of a single antenna module for different standards, i.e., to design an ultra-wideband antenna together with frequency multiplexer. The thesis focuses on the wideband antenna design. In principle, the module must be able to work with GPS, GSM, UMTS, ZigBee, Bluetooth and Wi-Fi in the 1.5-2.5 GHz band. The antenna type chosen was the dipole antenna and it was implemented using a four metal layer PCB structure wich includes a flexible material. Two different shapes were used for the dipole, square and circular. The design process is mainly carried out in two steps. In the first step dimensions of the antennas were calculated and some results were verified in Linecalc. Then, in the second step, dimensions were experimentally tuned until simulation results fulfilled the demands of the design specifications. Evaluation was done by looking at impedance bandwidth and radiation characteristics. Simulation results showed that with perfect circular discs a correct adaptation could not be obtained in the specificated frequency band and because of this an improved circular discs antenna was designed. With this new design a good result was obtained, the voltage standing wave ratio was under 3 in the whole band. With the rectangular antenna a good result was also obtained, too. In both cases, the worst behaviour was in the middle of the bandwidth. The multiplexer structure came from a theorical design. Initial transmission line parameters were calculated in Linecalc and filters are implemented with the ADS tool. Finally, the design is experimentally tuned until good simulations results were obtained. The network insertion loss is under 2.3 dB between input port and all output ports and isolation behavior between all the different ports is satisfactory. In the end, the complete Multi-band Front-end was simulated using both antennas obtaining good behaviour for isolation and return loss parameters. In conclusion, a planar ultra wide-band front-end for GPS, GSM, UMTS, Bluetooth, WiFi, and ZigBee standards in the 1.5-2.5 GHz band using planar dipole antenna and microstrips has been designed with good simulation results.
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