ZZFilter (Zig-Zag Coupled-Line Filter)

Symbol

Parameters

Name	Description	Unit	Default
Subst	Microstrip substrate name	None	MSub1
Fs1	Lower stopband edge frequency	GHz	1.8
Fp1	Lower passband edge frequency	GHz	2
Fp2	Upper passband edge frequency	GHz	2.2
Ap	Passband edge attenuation (or ripple for Chebyshev)	dB	2.4
As	Stopband edge attenuation	dB	3
N	Number of filter sections (or 0 to compute N)	None	20
ResponseType	Type of frequency response (maximally flat or Chebyshev)	None	0
Zo	Desired input/output impedance	Ohm	Maximally Flat
Delta	Length added to coupled sections for tuning performance	mil	0

Notes

1. A zig-zag coupled-line filter provides a bandpass frequency response between the input and output ports. The design uses a coupled-line filter topology but includes 90 degree bend between each coupled section so that the layout is more compact.
2. Because of the heavy computational burden in determining the line parameters, a brief delay will occur for the design.
3. For a Chebyshev (equal ripple) frequency response, ripple levels greater than about 1 dB are not recommended. Exceeding this value will typically deform the shape of the passband characteristics.
4. If N is zero, the number of filter sections will be computed from the frequency/attenuation information. If N is non-zero, the design will use the frequency/attenuation parameters only for determining the design center frequency.
5. The optimization minimizes the absolute difference between S21 and the specified passband edge attenuation (which equals the ripple for Chebyshev response) at the passband edge frequencies. Because only the line lengths are changed, this tuning will typically center the response within the specified passband. More advanced shaping of the passband response can be accomplished by manually tuning the widths and spacings of the coupled filter sections.
6. A SmartComponent subnetwork is empty until the Design Assistant is used to generate the design. Refer to Design Assistant.

For a more detailed discussion of this device, see: D. M. Pozar, Microwave Engineering, 2nd Edition, John Wiley & Sons: New York, 1998, pp. 477-485.

Example

A zig-zag coupled-line filter was designed for a maximally flat response with the 3 dB passband edge frequencies at 2 GHz and 2.4 GHz respectively. The design required 4 coupled-line sections. Tuning using the Optimization Assistant yielded a value of Delta = -6.233 mil.

Passive Circuit DG - Matching