Isn’t designing a microwave filter as simple as loading parameters into a computer-aided-engineering (CAE) program? In truth, many modern CAE software tools are quite good, and can provide accurate predictions of performance when fed sufficient input data. However, most do not account for all variables influencing a high frequency filter, including the effects of anisotropic printed-circuit-board (PCB) materials. When designing RF and microwave filters, it helps to choose your PCB material wisely.
High frequency filters come in many forms, based on lowpass, highpass, bandpass, and band-reject responses. As their names suggest, they are designed to operate at specific frequencies or bands of frequencies, to allow some signals to pass with minimal loss and stop other signals with high attenuation. Modern cellular telephones, for example, rely on filters to separate different cellular frequency bands within a handheld transceiver. Because of the growing integration of multiple functions in electronic devices, such as Bluetooth receivers and Global Positioning System (GPS) receivers in cellular telephones, filter designers are being asked to develop improved performance but in smaller circuits. As filters are made smaller and packed more closely together on a PCB, the choice of PCB material becomes a critical step in achieving acceptable filter performance.