RFMW design: Comparing the leading CAD tools, ADS ( Keysight) and Microwave office ( NI) for RFPA design.

Recently evaluation verisons of ADS and Microwave Office were used to evaluate an existing 10W Class F RFPA design. The active device was a CREE 40010 packagedĀ  part. Here are my the insights at first blush. ( Other users will probably have a vastly different experience). Both tools are very good and provide excellent solutions to a difficult problem. However,

( 1 ) Technical support on MWO was excellent. Questions were answered and much more. ADS technical support was sluggish and difficult to get to.

(2) Model installation in ADS was extremely easy while that in MWO was a little messy and took a long time.

(3) License file installation was very easy in ADS and fairly involved and difficult in MWO.

(4) LineCalc on ADS was very good and provided accurate results. TXLINE in MWO was less so and needs some improvement.

(5) Running two tone simulations was very easy on ADS and quite difficult on MWO. However MWO provided a more flexible interface and experienced MWO users will probably like it more. ADS has a somewhat more limited tool.

(6) Help on ADS was marginally better than MWO, and provided more explicit answers than in MWO.

(7) Up and running time was short on ADS and long on MWO.

(8) Examples on ADS were marginally better than in MWO and provided more details and help.

(9) MWO marketing/sales support was simply superb and very obliging. ADS sales support was very slow and in some cases non-existent.

(10) MWO has a much better stable of CAD tool routines than ADS. This allows a more flexible approach to analysis.

(11) ADS has a better user interface for output results that includes both textual and graphic output accesses with ease.

(12) Not enough evaluation time was provide to go into EM and layout eval so these are not addressed in this post.

To conclude: For someone getting into RFMW analysis tools ADS may be a better choice initially but much less flexible and somewhat limited CAD tools. MWO is for the more experienced user, but its limitations are compensated by the level of and quality of the technical and sales/business support. Please use our website at www.signalpro.biz for contact or for comments or for more information about our services.

 

Double stub impedance matching for RF and Microwave design

 

Its interesting how many techniques exist today for impedance matching of complex loads to transmission lines. A really interesting one is the technique of double stub matching which is a popular one. Its simpler cousin is single stub matching which can be used but runs out of steam under some circumstances

Double stub impedance matching is more involved than single stub matching. First of all we need to discuss the rationale for using double stub matching. In order to understand all this, consider the points below:

1.0 A single stub match involves the use of a stub of fixed length placed at a fixed position on the transmission line from the load for a specific load.

2.0 If the value of the load changes then the length of the stub and the position at which it is placed must also change.

3.0 A better technique would be where we could fix the positions of the stubs in relation to each other and only change the lengths of the stubs to match varying loads. This is done using the techniques of double and triple stub matching.

4.0 Both analytic and graphical techniques are available to do double stub matching. The graphical method is usually the Smith Chart method and that is what we have focused on. However analytical techniques can be enlightening as well, and are recommended if you are mathematically minded.

5.0 In order to further understand the technique of double stub matching you need a reasonable amount of the understanding of how the Smith Chart works.

6.0 There are some loads that cannot be matched using double stub matching by simply altering the length of the stubs. However if we are willing and able, to move the stubs together a distance away (or towards the load) from the load then we can accommodate the load. This can be discussed and illustrated using the Smith Chart method. These loads form an area of the Smith Chart collectively known as the forbidden zone for double stub matching.

7.0 Additional techniques can be used to overcome the limitations of double stub matching if needed. Similar techniques to that of double stub matching are used for triple stub matching.

The interesting situation as far as learning about double stub matching is that there are very few articles available that really discuss the technique for the newbie. We know as we did a web search and came up with very few articles that deal with this.

A forthcoming book from Ain Rehman of Signal Processing Group Inc, addresses these techniques in some detail with a minimum of math. The title is VSWR and Impedance matching techniques. This book will be available on Amazon both as a paperback and as a Kindle book shortly for interested readers.

Please visit our website www.signalpro.biz for more information and other articles of interest.

Signal Processing Group Inc., delivers RF Design, RF IC design, rf circuit design, ic design, analog design, rf technology, analog circuit design, asic chip, integrated circuit design and various rf devices

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