CPW dimensions design

[ihcarp]

Hi,
I am a student and designing a branchline coupler using CPWs at 18GHz for my final year project.

In one of the threads i read that width of CPW is limited by excitation of a higher order mode whose cutoff frequency is given by the formula:

lambda_0/(a*sqrt(epsilon_r))=(2*G+W)

Can nyone give me some refernce or paper where this formula is proved/derived or used??

It would be a great help!!

 

[Manjunatha_hv]

Hello,

Here you go
[1] **broken link removed**

[2] Compact CPW Rat-Race and Branch-Line HybridsUtilizing Slow-Wave Structure
by Takao FUJII, Yoshihiro KOKUBO, and Isao OHTA

[3] **broken link removed**

Also use AWR TXLINE -Free transmissionline Calculator for CPW dimensions...
https://web.awrcorp.com/content/Downloads/TXLine.zip


---manju---

 

[ihcarp]

thanx a lot!!
i also wanted to ask if these effects are taken into account in ADS schematic simulation like if my dimensions increase beyond what is prescribed what kind of effects should this have on my schematic simulation?and how do i observe it?

 

[Manjunatha_hv]

Hello,

You may get warning messages in ADS schematic simulator as cirtain boundry conditions applied to these CPW closed form circuit elements...If so then you need to use Electromagnetic simulator Momentum to see the effects of these parameters....
By the way what are your CPW dimentions calculated..?

---manju---

 

[ihcarp]

basically in branchline coupler for Z0=50 ohm, my dimesnsions are
conductor width=598um
gap width=296.77um
length=1.744mm
This, W+2G=1.17mm

for 18GHz, lambda=16.66mm
If i use the given formula then W+2G<0.24mm else higher order modes will exist in the CPW and affect circuit performance

But i am not seeing any negative effects/warnings in my circuit s-parameter simulation. In fact, i get better values as i increase W.....so on what grounds should i limit W??

The CPW i am using is without backside metallization..

 

[Manjunatha_hv]

hello,

So you are using CPW withoud Ground right...
Also mention the substrate Dilectric Constant & the Height values to calculate & plot the effects...
Did you try TxLine?

---manju---

 

[eoncu]

Hi Manjunatha,i am trying to design 2-way conventional cpw(ungrounded) wilkinson power divider.How can it possible to define the ground plane that is between the arms of the divider?The two side grounds are touching the enclosure.But i couldnt find a way to define the middle ground planes as grounds.If you help,i will be very glad.
Thnx in advance.

 

[Manjunatha_hv]

hello eoncu,

Yes it is possible to design the ground plane between the arms...
I suggest & recommend you to read the following article, which addresses the required details....

Uniplanar power dividers using coupled CPW and asymmetrical CPS for MICs and MMICs
by Lu Fan Kai Chang Dept. of Electr. Eng., Texas A&M Univ., College Station, TX

IEEE Xplore - Denial

ABSTRACT

Uniplanar coplanar waveguide (CPW), coplanar strip (CPS), and slotline on dielectric substrates have many applications in microwave integrated circuit (MIC) and monolithic microwave/millimeter wave integrated circuit (MMIC) designs. New power dividers using one-section and two-section coupled CPW have been developed. These circuits provide substantially improved performance over a wider bandwidth than conventional microstrip power dividers. Measured results show that the one-section CPW power divider has greater than 20-dB isolation, less than 0.3-dB insertion loss, a 0.2-dB power dividing imbalance, and a 20 phase imbalance over a bandwidth of more than 30% centered at 3 GHz. The two-section CPW power divider has greater than 24-dB isolation, less than 0.5-dB insertion loss, a 0.1 dB power dividing imbalance, and a 1.6° phase imbalance over a bandwidth of more than 66% centered at 3 GHz. Experimental results agree well with calculated ones. In-phase and 180° out-of-phase power dividers constructed by the circuit configuration method are described in this paper. The even-odd mode excited method is used to analyze the power dividers. Also two other power dividers using asymmetrical coplanar strip (ACPS) have been developed with good performance. A 180° out-of-phase power divider is demonstrated with an amplitude imbalance of 0.4 dB and a phase difference of 180°±1° over a wide bandwidth


&

**broken link removed**

---manju---

 

[eoncu]

Thank you very much Manjunatha...