Compact Hairpin Filter

Using Sonnet Software, I synthesized a five-section bandpass filter (BPF) on 20-mil-thick Rogers RO4350B laminate. The design began with a normalized low-pass Chebyshev prototype having 0.1 dB of ripple. The prototype was then transformed into a bandpass response, and the component values were converted into mutual coupling coefficients.

Once the coupling coefficients were established, Sonnet was used to determine the spacing between the resonators and the loaded Q required for the input and output resonators.

The fabricated PCB test hardware is shown below.

The measured response agrees closely with the simulated response.