Introduction

The input network of the power amplifier will be designed in the example. The network synthesized will be expanded to allow for biasing of the transistor gate.

Some of the stubs in the network will be replaced with stepped main-line sections. A thin-film resistor will also be added to the network to stabilize the transistor. The performance will be restored by optimizing the network.

The discontinuity effects of the steps will also be reduced by adding extra steps in the network. The effects of these steps on the performance will also be eliminated by optimization.

The amplifier as designed previously. The length of the input line selected has been increased to allow the matching network to be synthesized to start with a shunt element.

The specifications for the required matching network will be set up by using one of the wizards provided in a Schematic View.

The Impedance-Matching Wizard shown will be selected.

The network required will be inserted to the right of the selected component.

The position at which the network will be inserted is high-lighted.

The Impedance-Matching Wizard has been launched.

The passband can be changed on this page.

A default name and title were assigned to the matching problem.

The default option to control the gain/VSWRs associated with the input network will be used.

The impedances to be matched are listed in the table.

The option to display the impedances to be matched graphically was selected.

The steps provided by the wizard were completed. The Impedance-Matching Module will be launched next.

The impedance-matching document has been opened. The original circuit file is still open too.

The option to synthesize non-commensurate microstrip networks has been selected.

The terminations page will be selected in order to change the gain specified.

The terminations and the gain specified. Note that the default gain values were set to level the gain response of the amplifier.

The Gain Slope Command has been selected to change all the gain values to 0 dB (best match instead of lowest gain ripple).

The gain values were adjusted to 0 dB.

Some of the Topology Settings will be changed.

Five-element lowpass solutions, with the first element (load side) shunt, will be synthesized.

The default settings for Gain Window and the Q-range are displayed.

The lumped element values will not be constrained.

The Distributed Networks Wizard will be launched.

The first page of the wizard is displayed.

The same substrate will be used.

The specifications for the vias allowed. By setting a large step size only one via size is allowed.

Double stubs will be allowed in the networks to be synthesized.

The line widths and the stub separation to be used.

A rendering of the specifications made is displayed. The blue box shown represents the height of the substrate.

The parasitics associated with the junctions in the networks to be synthesized. The range allowed for the main-line should also be checked.

The last page of the wizard is displayed.

The changes made are saved.

The Synthesis Command will be selected.

The best solutions obtained with the specifications made. Note that Q3 is outside the search range specified (-4.4, 4.4).

The artwork of the first solution.

The command to display the next solution will be selected.

The second solution obtained.

The third solution obtained.

The Q-range will be extended to see if better solutions are available.

The Search Parameters Command will be selected.

The Quick Edit feature is used to increase the search range.

The new Q-range.

The Synthesis Command will be selected again.

The best solution obtained this time. Q3 is higher than before and the solution is more sensitive to component changes.

The second solution obtained.

The third solution obtained.

The artwork of the second solution will be displayed.

The artwork of the second solution.

The second solution will be exported to circuit file.

The solution was exported. The option to close the Impedance-Matching Document will be selected.

The matching network selected has been inserted into the schematic. The Save Command will be used to save the circuit.

The performance of the amplifier will be analyzed.

The transducer power gain response is very flat over the passband and the input match is good (VSWR <= 1.414).

The artwork of the amplifier is displayed. This solution can be realized, but the two double stubs on the input side will be replaced with stepped main-line sections in order to illustrate the features provided.

The Equivalent Stub Command will be used to replace the stubs in the middle of the input network with stepped main-line sections.

The option to replace the first stub with a main-line section is selected.

The stub has been replaced with a main-line section.

The performance with the change is analyzed.

The next stub will also be converted to a main-line section.

The relevant option has been selected.

Both stubs have been replaced with stepped main-line sections.

The artwork of the amplifier after replacing the two stubs.

The input match was degraded by the changes made. The performance will be restored by optimization.

The variables to be optimized will be marked next.

The variables set for optimization are displayed in blue. Optimization bounds will be set next.

The bounds set for the first stepped main-line section.

The bounds set for the next section.

The error function to be used during the optimization will be set up next.

The parameters to be optimized were selected. Note that the stability factor was not included in the error function.

The passband can be changed on this page.

The gain to be optimized is the overall gain (all the matching networks are in place at this point).

The gain window and the weight factors for the gain are specified on this page.

The specifications made for the input and output VSWRs.

The specifications made for the output power. The output power could have been ignored at this point (no variables were selected in the output network).

The error function has been defined.

The command to optimize the circuit will be selected next.

The performance after optimization is displayed. The option to update the circuit with the changes made will be accepted.

The schematic of the optimized input network.

The artwork of the optimized input network.

The input impedance and the output impedance of the amplifier are displayed on a Smith Chart with the normalized gain.

The stability of the circuit will be considered next.

The Rollette (k) and the Sterne (K) stability factors of the circuit are displayed.

The shunt resistance required to stabilize the circuit will be displayed.

The circuit can be stabilized easily by loading its input with a shunt resistor of 330 Ohm (The loss in gain will be less than 1 dB).

The series resistance required on the input of the circuit is not well-behaved.

The line shown will be split in two. The series resistance required for stabilization at this point is small and well-behaved. This was established by experimentation.

The schematic before splitting the 67.7 Ohm line.

The line was split in two. The two lines combined are identical to the original line.

The circuit to the left of the second 67.7 Ohm line must be deleted temporarily to calculate the resistance required for stabilization at this point. The quickest way to do this is to edit the text description of the circuit.

The circuit section of interest has been selected and will be commented out.

The lines of interest were converted to comment lines.

The schematic of the modified circuit will be displayed.

The modified circuit was analyzed.

The series resistance required for stabilization will be displayed.

The series resistance required on the input side is small and decreases monotonically with increasing frequency. 2.2 Ohm in series will be sufficient to stabilize the transistor.

The commented lines will be activated again.

The relevant lines have been selected again and will be activated again.

The schematic view will be opened again.

The restored schematic.

The Dimensions Command was used to display the dimensions of the line selected. The line is 1mm wide. The same width will be used for the thin-film resistor.

A thin-film resistor will be inserted between the two 67.7 Ohm lines.

The resistor was edited to be 1mm wide and 0.2mm long.

The sheet resistance of the resistor will be edited in a text view.

The sheet resistance was changed from 50 Ohm/square to 5 Ohm/square.

The performance of the modified circuit has been analyzed. The resistor inserted (1 Ohm) is not big enough to stabilize the circuit.

The length of the resistor was doubled and the performance was analyzed again. The circuit is now inherently stable. The loss in gain and the change in the input VSWR are minimal.

The circuit will be edited to allow for biasing the gate of the transistor.

A shunt block was inserted into the network after adjusting the lengths of the two 50 Ohm lines.

The shunt network inserted.

The artwork of the modified network.

The length of the selected 50 Ohm line will be increased to prevent coupling between the stubs.

The artwork after the adjustment.

Another shunt block was inserted to allow for feeding the required dc voltage into the circuit.

The circuit after editing the second block.

Parasitics will be added to the 0603 capacitors next.

The same parasitics are specified for the other 22pF capacitor.

The artwork of the circuit.

The selected stub will be bent downwards.

The specifications made for the bend.

The performance of the circuit with the changes made.

The blocking capacitor required will be added next.

The capacitor with its pads and the lines added to model the phase shift through the capacitor.

Lines for modeling the phase shift were added to the other capacitor too.

The length of the lines added will be adjusted in the artwork view.

The specifications made for each of the lines added.

The required cut commands will be added for the phase shift lines in a text view.

The cut commands added for the capacitor selected.

The other capacitor is selected on the artwork in order to add the required cut commands.

The commands after editing.

The performance of the circuit after the adjustments.

The line selected will be shortened.

The values of the lumped components used can be displayed on the artwork. This feature can be toggled on/off by pressing the letter “M”.

The label associated with each lumped component can be moved if necessary (Use the letters “Q”, “W”, “I” and “O”).

The input network will be optimized again to compensate for the changes made.

The stability factor can now be included in the optimization.

The passband page.

The gain selected for optimization.

The window and the weight factors specified for the gain.

The specifications made for the input and the output VSWRs.

The specifications made for the stability factor.

The specifications made for the output power.

The last page of the Error Function Wizard.

The Optimization Command will be selected next.

The optimized performance. The option to update the circuit with the changes made will be selected.

The characteristic impedance values of the two stepped lines were adjusted to be the same.

The performance of the optimized amplifier.

The artwork of the optimized amplifier.

The artwork after further refinement and optimization.

The performance of the final amplifier.