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RF và mạch lạc lò vi sóng P8

FILTER DESIGN A circuit designer frequently requires ®lters to extract the desired frequency spectrum from a wide variety of electrical signals. If a circuit passes all signals from dc through a frequency oc but stops the rest of the spectrum, then it is known as a low-pass ®lter. The frequency oc is called its cutoff frequency. Conversely, a high-pass ®lter stops all signals up to oc and passes those at higher frequencies. If a circuit passes only a ®nite frequency band that does not include zero (dc) and in®nite frequency, then it is called a band-pass ®lter. Similarly, a band-stop ®lter. | Radio-Frequency and Microwave Communication Circuits Analysis and Design Devendra K. Misra Copyright 2001 John Wiley Sons Inc. ISBNs 0-471-41253-8 Hardback 0-471-22435-9 Electronic 8 FILTER DESIGN A circuit designer frequently requires filters to extract the desired frequency spectrum from a wide variety of electrical signals. If a circuit passes all signals from de through a frequency fflc but stops the rest of the spectrum then it is known as a low-pass filter. The frequency fflc is called its cutoff frequency. Conversely a high-pass filter stops all signals up to fflc and passes those at higher frequencies. If a circuit passes only a finite frequency band that does not include zero de and infinite frequency then it is called a band-pass filter. Similarly a band-stop filter passes all signals except a finite band. Thus band-pass and band-stop filters are specified by two cutoff frequencies to set the frequency band. If a filter is designed to block a single frequency then it is called a notch-filter. The ratio of the power delivered by a source to a load with and without a two-port network inserted in between is known as the insertion loss of that two-port. It is generally expressed in dB. The fraction of the input power that is lost due to reflection at its input port is called the return loss. The ratio of the power delivered to a matched load to that supplied to it by a matched source is called the attenuation of that two-port network. Filters have been designed using active devices such as transistors and operational amplifiers as well as with only passive devices inductors and capacitors only . Therefore these circuits may be classified as active or passive filters. Unlike passive filters active filters can amplify the signal besides blocking the undesired frequencies. However passive filters are economical and easy to design. Further passive filters perform fairly well at higher frequencies. This chapter presents the design procedure of these passive .