# some questions about using hfss

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#### sanders

##### Member level 3
i have two questions to ask:

(1) how to excite two ports at the same time in hfss, what can i do to realize it?

(2) how to set high-resistivity line or plane?assign it impedance boundary?

more quations:
(1) a paper mentioned: sheet resistence is around Rs=10κΩ/sq and each resistive line was designed to be at least 20 squares long. my question is how long a square is ? a square=(? )m.

(2) "the bias line conclude in dc pads of 150 and 400 pitch", so what is pitch?

(3) the loss tangent of high-resistivity Si?

That is all, any help will be appreciated!

#### asdfaaa

##### Full Member level 4
sanders said:
i have two questions to ask:

(1) how to excite two ports at the same time in hfss, what can i do to realize it?

HFSS-> Fields-> Edit Sources...

(2) how to set high-resistivity line or plane?assign it impedance boundary?

Yes,

more quations:
(1) a paper mentioned: sheet resistence is around Rs=10κΩ/sq and each resistive line was designed to be at least 20 squares long. my question is how long a square is ? a square=(? )m.

Square is arbitray unit, please refer to sheet resistence definition.

(2) "the bias line conclude in dc pads of 150 and 400 pitch", so what is pitch?

(3) the loss tangent of high-resistivity Si?

ρ=1/σ, for accurate simulation, you need the bulk conductivity versus frequency, which is quite difficult to get.

That is all, any help will be appreciated!

#### sanders

##### Member level 3
thank you ,asdfaaa.then i want to ask:

1 i want the bulk conductivity of high-resistivity Si in X-band (8-12GHz),can anybody tell me ,thank you!

2 "square " is often used, i want to know it represents which unit in general.

3 the last,"pitch" is what?

#### asdfaaa

##### Full Member level 4
sanders said:
thank you ,asdfaaa.then i want to ask:

1 i want the bulk conductivity of high-resistivity Si in X-band (8-12GHz),can anybody tell me ,thank you!

I dont have those data, maybe you can consult your vendor.

2 "square " is often used, i want to know it represents which unit in general.

It is arbitray unit,
In a regular three-dimensional conductor, the resistance can be written as
R=ρ×L/A=ρ×L/Wt

where ρ is the resistivity, A is the cross-sectional area and L is the length. The cross-sectional area can be split into the width W and the sheet thickness t.

By grouping the resistivity with the thickness, the resistance can then be written as

R=(ρ/t)×(L/W)=Rs×(L/W)
Rs is then the sheet resistance. Because it is multiplied by a dimensionless quantity, the units are technically ohms. The term ohms/square is used because it gives the resistance in ohms of current passing from one side of a square region to the opposite side, regardless of the size of the square.

3 the last,"pitch" is what?