Simple Microwave Office Projects

These projects are aimed to give the novice an idea on how to lay out various simple type of circuit , the design criteria for your project will have already been decided for you , these projects are designed to show you the various PRACTICAL implementations of your project from the basic circuit which you would have used for lower frequency work ( as part of your course ) both for passive & active designs .

Simple Band pass filter for 7.5 GHz using Microstriplines

This project illustrates the use of transmission lines of variable widths being combined to produce a band pass filter this was used in a forward scatter radar transmitter by the MISL group . It also high lights the need for accurate modelling of ALL the relevant components , the differences between the two circuit's responses highlights the need to be fully aware of even the simplest of designs, the only difference being the addition of step transitions between the capacitive & inductive striplines , the lengths & widths of the actual striplines being the same in BOTH circuits , designing without these transitions results in a center frequency error of about 10% , this was born out by constructing the filter with the step transitions missing then testing it on a Network analyser , and comparing the real world design with both modelled results ! The use of the step transition is advisable when there is more than about a 25% variation in the width of adjoining striplines .

Basic MWO circuit ( microstrip elements )

S11 , S21 Responses for the MWO Basic circuit

Revised MWO circuit ( with simple microstrip & junctions)

S11 , S21 Responses for the revised circuit

Comparison of Basic & Revised circuits

MWO Artwork for the Revised filter

CAD generated Artwork ( Photo - negative )

VNA Plot of real filter

Dual MMIC Amplifier for 1 to 4 GHz

This project was conceived to provide a tried & tested amplifier for both my amateur radio projects and also to give to students as a basic building block to drive RF power devices to around about the 1 watt level ( from the tracking generators in the Spectrum & Vector Network Analysers ) for either Wlan or Wimax power amplifier projects. It was designed to be as flexible in nature so is two stages of SOT89 or MP86 package MMIC's with provision for attenuators to set the overall stage gain / allow some protection of the MMIC's in a research & teaching lab environment. Both Minicircuits & Hittite have a range of suitable MMIC amplifiers , the student just has to choose the suitable combination for Frequency response , Power output & Gain required for their project , the attenuators are made up using " Preferred Value " resistors so their attenuation is not " Whole dB's " the 1dB attenuator on the output ensures the following stage " see's a resistive source at all frequencies ", the use of twin resistors for the shunt element's improves the return loss of the attenuator as well as increasing the power dissipation at that point in the circuit.The circuit is modelled as usual using Microwave Office from AWR , but could just as easily be modelled using the Ansoft Designer SV package which is currently free or any other suitable RF modeling package.The circuit uses an attenuator on the input to ensure stability given the high gain of the MMIC and also to provide a resistive load to any preceding stage eg filter . The stages will be fed from a small voltage regulator to ensure the gain remains stable in a lab environment ( people rarely set bench top power supplies to the same value each time they use them ) the amplifier module was designed to fit in a standard commercial tinplate case measuring 50 x 25 x15 mm using a pair of SMA sockets for input / output connections with the upper & lower groundplanes soldered to the case to provide a low inductance grounding ,the earth planes nearer to the microstriplines were " Tied " together using my traditional technique of 0.5 mm holes with a single strand of 0.2 mm wire from ordinary instrument wire to suck the solder in by capillary action , the same is applied to the grounding of the tabs on the MMIC's to ensure a low thermal path as well as good RF earthing. The circuit was laid out with Microwave Office using the package's component libraries for ALL the parts as listed in the various supplier's catalogues to ensure that the parts chosen were freely available ( Preferably from more than one supplier ) with the full manufacturer's part no. checked in the Microwave Office Online component libraries or downloaded from the manufacturer's own websites , as a result of laying out the circuit with all the relevant tracks junctions & components it's quite easy to see ALL the elements involved in just a simple two stage amplifier ( It fills an A3 page ), the Voltage regulator circuit was added later in the CAD layout of the board after it had been generated in Microwave Office using the relevant layout tools this means that you can see the effects of the grounding you add as you create a full PCB artwork remembering to ADD all the relevant text to aid testing & inspection of the completed project. Having created the schematic in the modelling package the design is then transferred to a basic layout this only has components & microstrip on it the ground plane and board outline together with the relevant text to be etched on the Top copper layer are now added , this enables you to check that any grounding alongside microstripline does not turn into " Coplanar stripline " shold you need to extend tracks up to the edge of the board to fit it in a standard box then these can easily be re - modelled at this stage before committing the design to production . The stages in reaching the completed artwork ( including the " Mirroring " to produce a contact print ) are detailed in the modelling package but the instructions are often buried several layers down in the help files . This is a simple stage by stage set of instructions to enable anybody starting off using the modelling packages to get an artwork out ready for exposing a Photo - Sensitve PCB substrate .

The simple " Step by Step " instructions for using Microwave Office for these projects are listed below

Lay out your circuit using the relevant components & symbols from the MWO library or download them from the manufacturer's sites ,if your chosen component has to be loaded as a subcircuit using just the" S2P " data from the manufacturer's website then there is a work around to get the package , simply use the MWO website to find a device with the same package as the device you have only the " S2P" for simply add this to your drawing at schematic level as a " Floating " component then when you go to the layout place it where you require it , this is not perfect but will at least enable you to get an artwork with the right size component footprint , it will also show up correctly in the 3D visualisation .

Then add all the graphs you think you will need together with any text, when you have your desired amplifier completed at schematic level .

Then convert it to a layout using the relevant part of the program , you will end up with a " Rat's Nest " of all the parts don't forget if you have had to add a device for it's footprint to place it in the correct location at this stage .

Now lay these out as per your circuit diagram , the individual elements in the layout are highlighted as you move them ( if you wish to check back to the schematic you will see them highlighted accordingly in Green ). Then using the select all the items you wish to place , then from the tool bar using the " Snap Together " tool you can automatically place all the tracks & components that are highlighted , this saves a lot of time laying out the parts to join accurately , you may also use this tool if you modify the layout , for instance to fit a standard sized case , don't forget to go back to the schematic page & redo the simulation eg when you have bent a trace to fit ( eg when using " MTRACE2 " ) or you have added the top side groundplane which is not automatically generated by the package to enable decoupling capacitors to be grounded you may also need to add holes to make connections through the board to the main groundplane , the spacing of these holes in general should be less than L/4 to ensure no stray resonant currents build up in the top side ground plane with respect to the lower groundplane . With the microstripline used to go to the ports of the circuit it is advisable to allow for about 10 mm of system impedance ( 50 R ) for the legs of the edge transition SMA connectors , don't forget to buy the right type for the thickness & spacing to suit your board height & transmission line width !

An interesting point to remember when using these edge transition connectors is that the legs that fit over the PCB are in fact protruding from the groundplane ( Body of the SMA ) and at certain frequencies these may be coupled in to the transmission line causing problems when the are 1/4 wavelength long they become Monopole aerials this happened on a wideband aerial for 12 - 14 GHz !

Then add a shape for the housing you intend using using the " Layout editor " ( Toolbar at the bottom of the screen or drop down menu ) to " Add Shape " this will put a shape up coloured in as " Error " initially .

Then by using the " Shape Properties " command you can change it to " Board Outline ", then you can repeat the " Add shape " routine to ADD the groundplane as you require " Copper Layer " being chosen . By returning to the schematic part of the program you can see the effects on the circuit of adding the grounding areas changing line lengths to fit the board outline etc , Text can be added using the text editor on the taskbar ( The same way as you added text to you circuit & graphs earlier ).

Then when you have your completed design laid out copy the whole layout ( if more than one layer then check each one ) & mirror it and place it on the page below the " Normal " layout also you are advised to label the mirrored artwork with the relevant wording ( " Mirrored Artwork this side to copper " ) and in the case of a multi - layered design add a reference point " A " on ALL layers to ensure the correct aliginment , you are now ready to export your completed layout in to one of the CAD packages mentioned on this website , exporting it as a " Flat DXF " is the easiest option , this is then read in to the CAD package ( You will have to set the drawing defaults up at this stage see the relevant webpage ) .

Then you can finally colour the relevant areas of you layout in according to whether you require a photo positive or photo negative artwork you will need to choose the approriate colours for all the lines in the drawing otherwise the individual shapes drawn will be just that NOT joined up tracks !

The Circuit design and Graph of modelled results

The PCB Layouts are shown in stages ,the only difference between the artworks is the ground has been added using the Layout editor in MWO for the second PCB layout and the mirrored artwork has been added in the second layout.

The CAD artwork this is derived from second layout above , the DXF exported from MWO with the normal & mirrored layouts ready to fill to create the " Contact " print which can also be copied in to a word document .Note you may have to select the appropriate layer ( Top Copper ) during the exporting of the DXF as the view includes the component outlines .

Alternative attenuators for gain setting

The Finished module

Parts Listing for the Module ( Includes all gain setting values )

Single stage Amplifier for 3.4 - 3.8 GHz Wlan band using a GaN Fet

This module is designed to produce about +30 to +33dBm using the NPTB0004 for driving the output stage in a Doherty amplifier using a pair of NPT35015 GaN Fets , it uses the "Standard " GaN Fet bias power supply module Versatile Bias Regulator for GaN Fets mounted on the case of the amplifier module, although with a little effort it could be redrawn to fit on the main PCB on one of the large ground areas ( future work ? )

Circuit of 30dBm Wlan Amplifier

Graph of Amplifier responses ( S11, S21 & S22 )

Artwork of 30dBm Wlan Amplifier

Mirrored Artwork ( Photo - negative )

3D View of PCB ( MWO )

15 Watt Single stage Amplifier for 3.4 - 3.8 GHz Wlan band using a NPT35015 GaN Fet

When you design your circuit using a modelling package you should be aware of the needs of the physical implementation of your design so that to design this amplifier the starting point was the manufacturer's test circuit for the device ( LINK ) this technique applies to ALL circuit modelling packages but as I'm used to using Microwave office I'll give more detailed instructions for this package ( I've also tried it out on the free " Designer SV " package at home ) this is the design for a 15 - 20 Watt broadband amplifier using the GaN fets available from Nitronex together with it's 2 Watt driver the 10 Watt amplifier uses the NPTB35015 & the Driver uses the NPTB0004B the circuits are designed to be wide band with as flat a frequency response as practicable so the use of " Tunable components " is avoided ,the various elements are chosen from the library of the modelling package or the individual manufacturer's websites & inserted as sub-circuits using the software for the components which are not contained in the relevant libraries , Micro-strip elements & board parameters are usually in the manufacturer's libraries in the package ,but you often have to use " Online " libraries for upto date data for individual components .Some of the modelling packages have an in built optimisation tool to tune the design from your layout , whilst this may save time for some users it must be noted that this is NOT " Intelligent " it will only work within the parameters that you the designer specifies ( You can easily put one track down the middle of another ) .The way the lengths & widths of the individual elements are written will enable the software to do the optimisation but the designer will need to specify the ALL the relevant limits , so by carefully adding in ALL the elements needed to replicate the layout of the manufacturer's test board it is possible to reproduce it , however there are some " Tricks " to laying out the board such that the assembly can be done with minimum recourse to moving parts to obtain the required performance , for instance it is easy to model a shunt capacitor from a transmission line to earth but actually placing it to sub millimeter accuracy by HAND is another problem , so why not use the modelling software to help you , by using a microwave junction ( Tee or Cross ) you can add a short < 0.5mm track equal to the width of the shunt element , this will produce a definite location on the transmission line to locate it , ( the beauty of this is the software also knows it's here ! ) so you should get the results you expect . Also as you design the bias tee's ( Gate & Drain ) you should ensure that there are pads of fixed width equal to the transistors connection to ensure that the optimisation tool does not produce tracks that are too narrow to support the device or put them up the middle of the transmission line ( you have to specify the line lengths correctly just look at the circuits below to see how to do it ) the components in the bias tee's will require spacing to permit the soldering of individual components so tracks of a minimum length should be included in the design , again it is you the designer who knows the minimum spacing for your soldering skills . If you do not have the footprint / layout from the modelling package's library ,there is a work around whereby you can include a device with the footprint of your chosen device somewhere on the circuit ( BUT NOT connected to it ) this is to enable you to place the tracks at the correct spacing to enable the final layout to be produced before exporting it to generate the artwork , you could always learn how to create component layouts in an appropriate CAD program then import them as the program designer's intend you to ( but then that's another story !) . The circuit parts shown below have all the relevant information set in their parameters each limit is explained for each circuit together with the final layout of the completed board , this will just need mirroring in the layout editor to produce the contact print as most CAD packages do not mirror the text you have included on your design put it in the layout in your modelling package !

The Amplifier Input & Gate bias circuit

The layout of the input circuit

The circuit as initially modelled , before the added copper pads for the top groundplane which when added are shown in a different colour to the modelled microstripline , these will of course all end up the same colour when you do the CAD work , to complete the artwork according to whether it's photo - Positive or Negative artwork required .

The Amplifier output Circuit & Drain supply

The layout of the output circuit

The combined circuits are shown below ( note this was before the revised circuits for the bias networks were used to ease the placing of shunt components )

The Completed layout showing all the relevant features combined this is before any ( optional ) text has been added to identify the connections or " name " the board , this being done by removing the large areas of groundplane and replacing them with smaller areas around the text along with any fixing holes neccesary to secure the board to it's housing / heatsink .

The mirrored artwork is now ready to print out for a " Contact " printed PCB when exported via you CAD package ( Currently I use either Quickcad or it's replacement Autosketch )

The final " Mirrored " artwork ( with text ) from Microwave Office prior to exporting to the CAD package

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This page last updated 16th May 2013