An optimal microstrip filter design method based on Advanced Design System for satellite receiver

The alias interference is the most troublesome signal which can produce the same intermediate frequency as the useful signal does when we carry out mixing in the RF (radio front) stage, thus it would degrade the SNR(signal to noise ratio) greatly of the signal and raise the error rate of demodulation. The only way to reduce this effect is to restrain the alias frequency with a filter before mixing. Usually a band-pass filter is installed in front of the LNA (low noise amplifier) to choose the specified band radio signal and reduce the energy in the alias frequency in a receiver RF.For the signal is usually very weak after receiving by the antenna in the RF so extra strict requests are needed on the indexes of the preselect filter such as SWR(stand wave ratio), insert loss and alias frequency attenuation. Microstrip filter which features smart structure, high frequency as well as good frequency response is favorable in microwave field. To realize a S band coupled microstrip Chebyshev band-pass filter, an optimal design method is introduced in this paper based on ADS(advanced design system) with the process as follows: at first we decide the number of the stages of the coupled microstrip in the attenuation curve by the decibel attenuation needed to suppress the alias interference, then we get the unitary parameters of a low pass filter by table reference, after that the simulation is carried out after the actual width and gap are figured out by ADS LineCalc tool to affirm the design. To amend the deviation and distortion of the response curve and meet the demand bitterly, the OPTIM controller is adopted to adjust the parameters of the coupled micristrip and the simulation shows the goal is well realized after the optimization.