Circular polarized active integrated antenna for transmit and receive

Abstract

An active antenna with simultaneous transmit and receive function is of increasing interest, as system designers require more complex functions to be implemented in reduced space. This chapter discusses the integration of active antennas by combining both transmit and receive functions into one single antenna. Four main components in the design are circular polarized microstrip patch antenna, rat race coupler, power divider and amplifiers. The simulation of the circuit is done using the Agilent ADS. Each individual components was designed using Agilent ADS, before the components were fabricated. The optimization and the analysis have been done using the software. The circular polarized antenna resonates at 2.4 GHz. Two MESFET amplifiers have been used to transmit and receive the channel separately. The rat race coupler isolates the two channels and a Tee junction power divider is connected the two channels to the input and output port. The channels are of the same frequency. The simulation and measurement results of the microstrip patch antenna for S11 are lower than -10 dB at frequency of 2.4 GHz. The antenna polarization is confirmed as a circular polarized, as can be seen in the radiation pattern from the measured and simulated results. The amplifier biasing circuit is supplied by two power sources; one is the drain voltage (Vds) which is positive and the other is the gate voltage (Vgs), which is negative. When Vgs is fixed at a certain value, the current (Ids) from drain to source will vary while tuning Vds and when Vds is fixed at certain values, Ids will also change, while tuning Vgs. After integrating all of the components such as antenna, coupler, amplifier and divider together, the antenna is measured and implemented for both transmit and receive.