TRL Offset Stripline Transmission Line

Synthesis and Analysis

• To synthesize offset stripline transmission lines, the parameters Z0, B, BL, and ER must be entered prior to clicking Synthesis. The width, W, is computed.
• For analysis, the parameters W, B, BL, and ER must be entered prior to clicking Analysis. The impedance, Z0, is computed. The frequency is used if entered; otherwise, 0 Hz is used in the calculation.
• Conversion from electrical length, E, to physical length, P, can be performed by entering values for E and Frequency. Click Synthesis to compute P. Similarly, to convert from physical length to electrical length, enter values for P and Frequency, and click Analysis to compute E.

Dielectric Substrates

A dielectric substrate is defined by the parameters B, BL, ER, and TAND. The substrate is assumed to be lossless unless TAND is specified and greater than zero.

Conductor Metalization

• Conductor specification is performed in the Metalization control group. If the conductor is not specified, the conductor loss is zero and no thickness corrections are made to the structure’s propagation characteristics. Up to three conductors of different metals and thicknesses can be selected.
• Metalization rms surface roughness, RGH, can be specified for additional conductor losses due to imperfect metal surfaces. RGH is specified in terms of rms variation from an ideal flat surface.

Sweep Options

Parameters that can be swept for the offset stripline transmission line are:

Frequency
Width, W

The order shown is the order used to generate output data when multiple parameters are swept simultaneously. See the Sweep Entries topic for further information.

Limitations

Error less than 0.5% for W /B < 10.

Example

To select the stripline medium, select TRL on the Product menu, select Stripline, and click OSL. Set the units to mm and GHz. Enter the following parameters to synthesize an offset stripline:

Impedance, Z0: 50 ohms

Dielectric constant, ER: 2.2

Substrate thickness, B: 2 mm

Offset Spacing, BL: 0.5mm

Click Synthesis to determine the width, W, of the transmission line:

Width, W: 1.1982 mm

Since offset stripline is a TEM structure and does not vary with frequency, perform a sweep analysis on the width of the strip instead. Type (0.5, 3.0, 0.5) into the W field to sweep the width from 0.5 mm to 3.0 mm in steps of 0.5 mm. Be sure to supply metal and loss information:

Metal: Cu 0.01 mm

TAND: 0.001

Click Analysis. The following warning message appears:

W/(B-T-BL) >0.7

Clicking Yes yields the following results:

Offset Stripline

B = 2.000mm BL = 0.500mm ER = 2.20 TAND =0.00100 T/B =0.0050

Freq Width W/B Z0 D Loss C Loss T Loss

ghz mm Ohms dB/mm dB/mm dB/mm

0.0 0.500 0.250 79.93 0.0000 0.0004 0.0004

0.0 1.000 0.500 55.40 0.0000 0.0002 0.0002

0.0 1.500 0.750 42.74 0.0000 0.0002 0.0002

0.0 2.000 1.000 34.86 0.0000 0.0001 0.0001

0.0 2.500 1.250 29.45 0.0000 0.0001 0.0001

0.0 3.000 1.500 25.50 0.0000 0.0001 0.0001

Change the frequency to 10 GHz and click analysis again:

Offset Stripline

B = 2.000mm BL = 0.500mm ER = 2.20 TAND =0.00100 T/B =0.0050

Freq Width W/B Z0 D Loss C Loss T Loss

ghz mm Ohms dB/mm dB/mm dB/mm

10.0 0.500 0.250 79.93 0.0014 0.0062 0.0076

10.0 1.000 0.500 55.40 0.0014 0.0035 0.0048

10.0 1.500 0.750 42.74 0.0014 0.0025 0.0039

10.0 2.000 1.000 34.86 0.0014 0.0021 0.0034

10.0 2.500 1.250 29.45 0.0014 0.0018 0.0031

10.0 3.000 1.500 25.50 0.0014 0.0016 0.0030

Notice that the impedances are the same for DC or 10 GHz, but the conductor loss calculations differ significantly due to the skin effect.