A biquad is a second order IIR (Infinite Impulse Response) filter. It is used as the basic building blocks for complex filters due to the sensitivity of the biquad. biquad1, b0=1, b1=0, b2=0, a1=0, a2=0, biquad2, b0=1, b1=0, b2=0, a1=0, a2=0, biquad3, b0=1, b1=0, b2=0, a1=0, a2=0, biquad4, b0=1, b1=0, b2=0, a1=0. How to Build Your Own Double BiQuad Antenna for internet. Home made Homemade . See more. Build Your Own Antenna: BiQuad Antenna Calculator.