SRFilter (Stepped Impedance Resonator 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
Fs2	Lower stopband edge frequency	GHz	2.4
Ap	Passband edge attenuation (or ripple for Chebyshev)	dB	3
As	Stopband edge attenuation	dB	20
N	Number of filter sections (or 0 to compute N)	None	0
ResponseType	Type of frequency response (maximally flat or Chebyshev)	None	Maximally Flat
Zo	Desired input/output impedance	Ohm	50
Fsp	Center frequency of first spurious passband	GHz	4.1
Delta	Length added to filter sections for tuning performance	mil	0

Notes

1. A stepped impedance resonator filter provides a bandpass frequency response between the input and output ports. N coupled-line sections produce an N−1 order filter response. Additional numbers of sections can be used to steepen the transition band roll off or widen the pass bandwidth. The use on non-uniform impedance for each resonator moves the second pass band center frequency away from the second harmonic of the fundamental frequency.
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 center frequency of the first spurious passband should be on the order of twice the fundamental passband center frequency.
6. The optimization minimizes the absolute difference between S21 in dB 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.
7. 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, refer to: Makimoto and Yamashita, "Bandpass filters using parallel coupled stripline stepped impedance resonators," IEEE Trans. Microwave Theory and Techniques , vol MTT-28, pp. 1413-1417, 1980.

Example

A stepped impedance resonator filter was designed for a maximally flat response with the 3 dB passband edge frequencies at 2 GHz and 2.2 GHz respectively. The second passband was set to 4.1 GHz. The design required 4 coupled lines. Tuning using the Optimization Assistant yielded a value of Delta = 0.785 mil.