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Transmission Line Designer >
Transmission Lines >
Edge-Coupled Stripline Transmission Lines

Edge-Coupled Stripline Transmission Lines

Keyword	Default	Unit	Description
W	Req (Phys)	m	Conductor width
S	Req (Phys)	m	Spacing between conductors
P	0	m	Physical length of transmission line
Z0	Req (Elec,Opt 1)	ohm	Impedance of the coupled lines
K	Req (Elec,Opt 1)	dB	Coupling coefficient (positive)
Zo	Req (Elec,Opt 2)	ohm	Odd-mode impedance of the coupled lines
Ze	Req (Elec,Opt 2)	ohm	Even-mode impedance of the coupled lines
E	0	deg	Electrical length of the coupled lines
Frequency	0	Hz	Analysis frequency
ER	Required		Relative dielectric constant
B	Required	m	Substrate thickness
TAND	0		Dielectric loss tangent
RGH	0	m	Rms surface roughness

Synthesis and Analysis

Two options exist for synthesis of edge-coupled stripline transmission lines:

— Specify impedance, Z0, and the coupling coefficient, K.

— Specify the even-mode impedance, Ze, and the odd-mode impedance, Zo.

• The substrate parameters B, and ER must be entered prior to clicking the Synthesis button. The width of the striplines, W, and the spacing between them, S, will be computed. Also, the alternate electrical option set will be computed (e.g., if Z0 and K are entered, Ze and Zo will be computed).

• For analysis, the parameters W, S, B, and ER must be entered prior to clicking the Analysis button. The electrical properties, Z0, K, Zo, and Ze will be computed. The frequency will be used if entered; otherwise, 0 Hz will be 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, ER, and TAND. The substrate is assumed to be lossless unless TAND is specified and greater than zero.

Conductor Metallization

• Conductor specification is performed in the Metallization control group. If the conductor is not specified, the conductor loss is zero and no thickness corrections are made to the propagation characteristics. Up to three conductors of different metals and thicknesses can be specified.

• Metallization 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 edge-coupled stripline are:

Frequency
Width, W
Spacing, S

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

Limitations

To maintain accuracy, the following limitation should be followed:

T/B < 0.1, where T is the metal thickness

Example

To select the edge-coupled stripline medium, select TRL on the Product menu, click Stripline, and click CPL. Set the units to mm and GHz. We will use the following parameters to synthesize a 6-dB coupler at 10 GHz:

Impedance, Z0: 50 ohms

Coupling, K: 6 dB

Frequency: 10 GHz

Substrate thickness, B: 1.27 mm

Dielectric constant, ER: 2.2

Metal: Cu 0.01 mm

Click the Synthesis button to determine the coupled line parameters:

Width, W: 0.625 mm

Spacing, S: 0.019 mm

Odd-mode impedance, Zo: 28.82 ohms

Even-mode impedance, Ze: 86.74 ohms

To specify a 1/4 wavelength line, enter:

Electrical length, E: 90

Click Synthesis again to determine the physical length:

Physical length, P: 5.05 mm

A sweep analysis can be performed on W, S, or Frequency. To perform a sweep analysis on W, type 0.3,0.7,0.05 in the W field to specify a sweep from 0.3 mm to 0.7 mm in steps of 0.05 mm. Clicking Analysis then yields the following results:

Coplanar Coupled Strip Lines

B = 1.270mm ER = 2.20 TAND = 0.00000 T/B = 0.0079

Freq S/B W/B ZE ZO Cond + Diel Loss (dB/mm )

ghz Ohms Ohms Even Mode Odd Mode

10.0 0.015 0.236 134.5 33.7 0.0028 0.0108

10.0 0.015 0.276 123.9 32.7 0.0027 0.0105

10.0 0.015 0.315 114.9 31.8 0.0026 0.0102

10.0 0.015 0.354 107.2 31.1 0.0025 0.0100

10.0 0.015 0.394 100.4 30.4 0.0024 0.0098

10.0 0.015 0.433 94.5 29.7 0.0024 0.0096

10.0 0.015 0.472 89.2 29.1 0.0023 0.0095

10.0 0.015 0.512 84.5 28.5 0.0023 0.0093