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Design Examples using ProCAP

ProCAP Low-Pass Cross Coupled Filter

 

Before selecting the filter design, it is necessary to select the tab labeled Units so that the design uses the desired units for the filter design.  The design starts with selecting the tab labeled ‘Design’ and the selection of LC Filt.  This brings up a menu for selecting the type of filter: Low Pass, Band-Pass, High-Pass or  Band-Stop. In this case the lowpass is selected and a menu appears for input of the design parameters.  Upon selecting the type of design a menu appears for placing the desired design parameters.  Selecting the tab “Create Circuit File” results in the nodal design appearing in the ProCAP window.

 

Initially every component has a question mark which were removed except for the first and last capacitor.  Then a cross coupled capacitor was added from the first to the last node with a value of 2 pF.  Without the capacitor, the solid red line is shown.  With the capacitor, the dotted line is shown.

 

It may be seen that cross-coupling causes some loss reduction out-of-band.  Usually placing the cross coupled element to an internal node will reduce the increase in the out-of-band loss.  The capacitor labeled C1 was modified to improve return loss.  Cross coupling may be made between any two nodes and may be done for any filter type.

 

ProCAP Diplexer

 

For the Diplexer design, two interdigital filters were designed using Parfil (not all filter types can be imported into ProCAP): one tuned GPS L1 (1575.42 MHz) and one tuned for L2 (1227.6  MHz). Parfil provides for selection in Parfil of the ProCAP file for import into ProCAP. These filters were combined as shown in Figure 1.  The lines from the input to the filters is approximately l/4.  The length may be computed from the Smith chart for the L1 filter.  The S11 plot is shown in Figure 2. Notice that at the L2 frequency (1223MHz) the angle is at 148 degrees . 

 

                Figure 1.  Diplexer layout for filters at L2 and L2                                                                                     Figure 2.  Input S11 for L1 filter

 

Notice that at the L1 frequency the reflection angle is 148 degrees at the L2 frequency. This means in order to rotate clockwise to an open circuit the line from L1 would need to be (180 + 32)/2 degrees long.  For the L1 filter (not shown), the length require for the Line from L1 to the open circuit is 172 degrees and thus the length would be 172 /2 degrees.  To create the actual design the lengths and widths of these lines would be optimized for minimum return loss.  The measured performance of the diplexer is shown in Figure 3.

 

                        Figure 3. Loss and return loss for Diplexer with the L2 filter selected. 

 

Notice that the return Loss for both filters is shown. 

 

Using this design approach a multiplexer may be designed with as many as 30 filters.  Shown in Figure 4 is the performance of a 12 filter multiplexer with the 40 MHz filter selected.  In this case the filters not selected are terminated with 50 ohms.

 

                    Figure 4.  Multiplexer for 12 filters with the 40 MHz filter selected.

 

The following shows the ProCAP partial data input for analyzing the diplexer.

 

MEDIA STRIPL ER=2.2 B=0.2 Th=0.0014 Loss_Tan=0.001 Loss_Fact=1 Rough=50

CKTBLK

STE 2 3 1 W1=0.09969 W2=0.09969 W3=0.09969

SCN5 3 4 5 6 7 8 9 10 11 12 W=0.09969 S1=S12 S2=0.1388 S3=0.1388 S4=S12 L=0.193

SCN5 13 2 14 5 15 7 16 9 17 18 W=0.09969 S1=S12 S2=0.1388 S3=0.1388 S4=S12 L=1.372

SLI 13 19 W=0.09969 L=?0.0148316

SLI 17 20 W=0.09969 L=?0.0168162

STE 18 11 51 W1=0.09969 W2=0.09969 W3=0.09969

SVH 4 0 RAD=0.0325

SEN 6 0 W=0.09969

SVH 8 0 RAD=0.0325

SEN 10 0 W=0.09969

SVH 12 0 RAD=0.0325

SEN 19 0 W=0.09969

SVH 14 0 RAD=0.0325

SEN 15 0 W=0.09969

SVH 16 0 RAD=0.0325

SEN 20 0 W=0.09969

STE 22 23 21 W1=0.09993 W2=0.09993 W3=0.09993

SCN5 23 24 25 26 27 28 29 30 31 32 W=0.09993 S1=S1 S2=0.1551 S3=0.1551 S4=S1 L=0.1201

SCN5 33 22 34 25 35 27 36 29 37 38 W=0.09993 S1=S1 S2=0.1551 S3=0.1551 S4=S1 L=1.088

SLI 33 39 W=0.09993 L=?0.00938354

SLI 37 40 W=0.09993 L=?0.0082533

STE 38 31 52 W1=0.09993 W2=0.09993 W3=0.09993

SVH 24 0 RAD=0.0325

SEN 26 0 W=0.09993

SVH 28 0 RAD=0.0325

SEN 30 0 W=0.09993

SVH 32 0 RAD=0.0325

SEN 39 0 W=0.09993

SVH 34 0 RAD=0.0325

SEN 35 0 W=0.09993

SVH 36 0 RAD=0.0325

SEN 40 0 W=0.09993

SLI 53 52 W=?0.186531 L=?1.29683

SLI 53 51 W=?0.197707 L=?1.01501

DEF3P 53 1 21

TERMINATION 50 50 50

EQUATE

S12=?0.12

S1=?0.138

FREQ(GHz) 1.1 1.7 0.003

MARKERS 1.2 1.25 1.55 1.6

 

ProCAP Lange Couplers

 

Design of three Lange coupler couplers are described: original Lange coupler, Lange coupler unfolded with 4 lines, and a Lange coupler with 6 lines. These are shown in Figures 1 –3. The performance of the unfolded coupler is nearly identical with that of the original coupler design.

 

Figure 1. Original Lange coupler                            

Figure 2. Unfolded Lange coupler 4-line

Figure 3. Unfolded Lange coupler 6-line

 

      Figure 4.  Lange coupler unfolded showing direct path output                                              Figure 5.  Lange coupler unfolded showing coupled path output


The following shows the ProCAP partial data input for analyzing the coupler.

 

MEDIA MSTRIP ER=9.6 H=0.01 CH=0.1 Th=0.0002 Loss_Tan=0.0001 Loss_Fact=1 Rough=55

CKTBLK

MCN4 1 2 3 4 1 2 3 4 W=W S1=S1 S2=S S3=S1 L=L

RES 4 0 R=50

DEF3P 1 2 3

TERMINATION 50 50 50

EQUATE

S=?0.00125

S1=?0.0015

W=0.0026

L=0.098

FREQ(GHz) 4 20 0.12

MARKERS 8 10 12 16

SCALE

 

  

 

ProCAP Ceramic Tapped Combline Filter

 

Using Parfil, A tapped rod coupled combline filter as designed a 10 GHz as shown in the data below.  In order to not have too small a filter, the resonator length was chosen as 80 degrees.  This design uses Aluminum oxide substrate with a loss tangent of .0001.  The rods are formed in the ceramic block by drilling and plating the drilled walls of the ceramic block.  The line width was selected at a fixed width of 0.06 “.

 

                    Tapped Round Rod Combline Filter

    10.000          GHz CENTER FREQUENCY   0.30000                 GHz BANDWIDTH

    0.0500                     dB RIPPLE         5                         POLES

    0.3000    INCHES GROUNDPLANE SPACING    10.000           DIELECTRIC CONSTANT

                                             35.120       OHMS INTERNAL IMPEDANCE

     50.000     OHMS INPUT LINE IMPEDANCE    0.0273       INCHES INPUT LINE WIDTH

     50.000    OHMS OUTPUT LINE IMPEDANCE    0.0273      INCHES OUTPUT LINE WIDTH

     0.0131     INCHES INPUT TAP TO SHORT    0.0131    INCHES OUTPUT TAP TO SHORT

     80.000      DEGREES RESONATOR LENGTH    0.0002      nH INDUCTANCE OF END CAP

     0.0500   INCHES DISTANCE TO SIDEWALL    0.0100 INCHES DIAMETER OF INPUT LINE

     10.000 DIELECTRIC CONSTANT EVEN MODE    10.000  DIELECTRIC CONSTANT ODD MODE

     0.0100  INCHES LINE DIA SIDEWALL-TAP                                       

 

      SECT   ELEMENT       ZOE       ZOO    LENGTH     WIDTH       GAP   END CAP

      NUMB     VALUE      OHMS      OHMS    INCHES    INCHES    INCHES        pF

         1    0.9984    43.182              0.0828    0.0604                0.0770

                                  34.207                        0.1615

         2    1.3745    42.899              0.0828    0.0595                0.0794

                                  35.443                        0.1798

         3    1.8283    42.419              0.0828    0.0587                0.0787

                                  35.443                        0.1798

         4    1.3745    42.899              0.0828    0.0595                0.0794

                                  34.207                        0.1615

         5    0.9984    43.182              0.0828    0.0604                0.0770

 

The design results from Parfil are shown in the plot of Figure 1.  Losses were not included

Figure 1.  Tapped combline filter loss and return loss vs. frequency

 

From Parfil, the ProCAP file is imported as shown in Figure 2.  The ProCAP plotted output also shows the initial computed performance.  The discrepancy is due to the transfer from synthesis to analysis.  This usually results in small changes in the capacitances computed.  In ProCAP, an optimization was performed  in which the capacitances are changed while optimizing for return loss.

 

After optimizing the capacitances,  the resultant frequency response is shown in Figure 3.

 

Figure 3.  Frequency response after optimizing capacitances.  

 

The changes in capacitances are .0012 pF, .00456pF and .00356pF.  These represent changes less than 5 percent.  Some of the 1.8% is due to slightly tuning the center frequency.  In addition for optimum performance the distance to the tap point was shortened by 10 percent.  This frequency response plot includes losses  which are less than 1dB except at one band edge.  The line spacing and widths were not changed.  Generlly better results are obtained from interdigital filters

ProCAP Balanced Amplifier

A Balanced amplifier is one in which two amplifiers are used with hybrid couplers at both the input and output of the two amplifiers.  This result in greatly improved input and output impedances.  The hybrid couplers could be Lange couplers or the more traditional branch line hybrid couplers.  This is illustrated in Figures 1 and 2.

Figures 3 and 4 show the performance of the branch Line hybrid for direct and coupled outputs.  

 

                   Figure 1. Branch Line Hybrid                                                            

 

 Figure 2. Lange Coupler


Figure 3. Branch Line hybrid direct output.                                                  Figure 4. Branch Line hybrid coupled output

 

 The data used for the calculations is as follows:

MEDIA MSTRIP ER=2.2 H=0.03125 CH=0.25 Th=0.0014 Loss_Tan=0.001 Loss_Fact=1 Rough=50

CKTBLK

MLI 1 2 W=W1 L=L1

MLI 1 3 W=W2 L=L2MLI 2 4 W=W2 L=L2

MLI 3 4 W=W1 L=L1

RES 2 0 R=50

DEF3P 1 3 4

TERMINATION 50 50 50

EQUATE

W1=0.0938

W2=0.1538

W3=0.0938

L1=0.7168

L2=0.7058

FREQ(GHz) 2.4 3.6 0.02

MARKERS 2.4 2.7 3.3 3.6

 

Figure 5: Balanced hybrid coupled amplifier circuit illustration

                                           Figure 6. Balanced amplifier circuit performance using branch line hybrids


 The output for this circuit is shown in Figure 6.  The return loss is considerably improved over a single amplifier.  For wide bandwidth circuits, the Lange coupler would be used.