RF and Microwave Filter Modeling

Receivers, transmitters, and frequency synthesizers use RF and microwave filters to select or reject signals with a particular band of frequency. Filtering a signal modifies its phase and magnitude components. RF receiver systems use filters such as the RF preselector filter, image rejection filter, and IF filter. You can design filters suited to your application using the rffilter object from RF Toolbox™ or the Filter blocks from RF Blockset™. For example, you can design an RF preselector filter in Chebyshev configurations using an rffilter object or the Circuit Envelope Filter (RF Blockset) block and filter undesired frequency bands causing spurious emissions and intermodulation distortions in mixers [1].

You can also use the rffilter object to create a Butterworth or inverse Chebyshev filter. The rffilter object also supports implementing a transfer function. For more information, see Design Data for Transfer Function Implementation. In addition to the three configurations, you can also design an ideal filter in Simulink^® environment using the Circuit Envelope Filter block. Ideal filters perfectly allow frequencies in the passband and completely reject frequencies in the stopband.

Microstrip filters play an important role in microwave applications. Almost all communication systems contain an RF front end that performs signal processing using RF and microwave filters. You can design coupled-line, hairpin, and stepped-impedance lowpass filters in the microstrip form. These filters have very low insertion loss and are easy to fabricate in compact sizes. Design these filters in a printed circuit board (PCB) using RF PCB Toolbox™ filter objects.

Design Workflows

Design RF and microwave filters using these workflows:

Design, Visualize and Explore Inverse Chebyshev Filter - I — This workflow shows how to determine the transfer function for a fifth-order inverse Chebyshev lowpass filter with 1 dB passband attenuation, cutoff frequency of 1 rad/sec, and a minimum attenuation of 50 dB in the stopband.
Frequency Response of RF Transmit/Receive Duplex Filter (RF Blockset) — This workflow shows how to use RF Blockset Circuit Envelope blocks to simulate a transmit/receive duplex filter and calculate the frequency response curves from a broadband white-noise input.
Stepped Impedance Maximally Flat Lowpass Filter for Microwave Applications (RF PCB Toolbox) — This workflow shows you how to design a stepped-impedance lowpass filter for X-band applications.
Model RF Filter Using Circuit Envelope (RF Blockset) — This workflow shows how to model an RF filter using the Circuit Envelope library and compare the input and output signal amplitudes to study signal attenuation.
Design and Analyze HighPass Filter Using pcbComponent (RF PCB Toolbox) — This example shows how to design and analyze a microstrip highpass filter. The filter design is based on a three-pole Chebyshev highpass prototype with 0.1 dB passband ripple and a cutoff frequency of 1.5 GHz.

References

[1] Besser, Les, and Rowan Gilmore. Practical RF Circuit Design for Modern Wireless Systems. 1: Passive Circuits and Systems. Boston, Mass.: Artech House, 2003.