DESIGN AND ANALYSIS OF PREPOST SELECTOR FROM 30MHz TO 3000MHz

Abstract

A prepost selector improves the performance of any receiver. Typically it is tuned to have a narrow bandwidth centered on the operating frequency of the receiver .the signal which passes through the prepost selector is declined slightly ,but attenuates other signals reducing unwanted signals. A prepost selector may be designed so that in addition to mitigating the unwanted signals ,it protect the receiver from damage caused by the input voltage spikes. In this research the idea is to design a prepost selector whiach can handle any signal within the frequency range 30MHz to 3000Mhz .which is realized using a set of tunable bandpass filters with constant fractional bandwidth(7.5%). Depending on the frequency of interest to be passed through the filter switches are used to select between the available filters . Each filter can handle a band of frequencies to pass through. Filters are made tunable by using reverse biased varactor diodes. Total 8 filters are used to cover the frequency range 30MHz to 3000MHz. First filter is a high pass filter remaining all filters are bandpass filters. Within the bandpass filters first 5 filters are lumped element structures and two of them are microstripline structures, since lumped elements will not give good response at high frequencies. All filters are simulated and verified before fabricating. Finally module is fabricated and tested. All the results of simulation and testing results are given in detail.