Measurements of insertion loss with a signal generator and a receiver.
(March 9 2013)

The DUTs.

This page describes insertion loss on DUTs presented here: Using the HP8712C network analyzer to measure impedances and losses on 1296 MHz. The impedance data from that page is used to split the measured insertion losses into mismatch loss and dissipative losses below.

The Rx port.

Figure 1 shows the arrangement for insertion loss measurements. The important parts are the circulators. They guarantee that the LNA, an MMIC with 2 dB NF and 40 dB gain always looks into the same impedance (through a filter). That guarantees that the MMIC will always provide the same gain.

In front of the circulators there is a section of semirigid cable which has been squeezed to make the impedance very close to 50 ohms on the female SMA connector which constitutes one side of the test position.

The MMIC is followed by a high level mixer, a ZFY-11 from Minicircuits which is fed with an LO signal from a HP 8657B which is routed through a MMIC amplifier. The output of the mixer is sent to a SDR-IP through a low pass filter.

Figure 1. Insertion loss measurement. Here DUT18 is inserted.

The Tx port.

The 40 dB power attenuator near the upper left corner of figure 1 is connected to a HP8644A which is set to 1296.06 MHz. The short section of 0.5 inch Heliax with screws allows the impedance at the male SMA connector to be tuned to 50 ohms precisely regardless of what 50 ohm unit is connected at the other side of the 40 dB attenuator. (Anything with better than 20 dB return loss.)


The loss measurement is performed by repeatedly insert and remove a DUT. It is essential that none of the RG223 cables that carry 1296 MHz is moved during the process. Moving these cables easily causes several tenths of a dB changes in the signal level. That is due to the impedance changes on bending the cables. The circulators must thus not be moved during a measurement sequence so all the necessary movement will be on the black cable that is gently bent to allow the Tx port to be moved axially without any impedance change. The black cable is 1 meter of Flexiform 401 with an extra screen on it.

Stability issues.

Figure 2 shows the stability at a bandwidth of 100 Hz. The 8644A has less AM noise than the 8657B as can be seen from a comparison between figures 2 and 3.

Figure 2. The stability of the setup shown in figure 1 with the 8657B as LO and 8644A as signal.

Figure 3. The stability obtained when 8644A is used for the LO and 8657b for the signal.

The LO signal level is set to a level where small variations does not affect the mixer gain. This way the AM noise of the 8657B becomes insignificant. The differences are not large however.

As it turns out, the dominating instability is due to variations in the phase noise. By use of a larger bandwidth, 500 Hz instead of 100 Hz, the power of the noise sidebands is largely included in the signal level. At these very high signal levels the receiver noise floor does not contribute despite the wider bandwidth. The stability at 500 Hz bandwidth is shown in figure 4.

Figure 4. With 500 Hz bandwidth and 8644A for the signal source with the 8657B as the LO the stability is quite good. Keeping constant room temperature is very important. One essential part of the set-up is a big fan that keeps steady air-flow on the amplifiers which otherwise get unstable temperatures and variable gain.

This looked good at first, but after starting to do measurements I found that the signal level would suddenly change by perhaps 0.03 dB and sometimes become unstable changing rapidly by about that amount. It was non-trivial to find the reason because there were many reasons.

Level changes happened spontaneously but could also be provoked by hitting the table to introduce small vibrations. The major problems were the following:

  • 1. Touching the DC supply wires to the MMIC in the signal path would trigger small gain variations. Even when the wires were fixed to the table with some tape, touching the wires near the power supply would introduce gain changes. The problem turned out to be incorrectly mounted 4 mm connectors. The multi-stranded wire had ben soldered before it was screwed into the banana plug. Correcting this error made the level less sensitive to touching the DC cables.

  • 2. The gain would change in an irregular way when the 12 V DC supply wire to the MMIC in the signal path was touched. It was no longer sensitive to small vibrations, but it was sensitive to hand capacitance. A decoupling capacitor made no difference. A 3 dB attenuator between the filter and the MMIC cured this problem which therefore is interpreted as self-oscillations in the MMIC due to the near infinite SWR outside the filter passband. This problem was solved by the insertion of a diplexer that attenuates by about 0.2 dB on 432 but that guarantees a reasonable SWR up to 6 GHz and probably much higher.

  • 3. Banging the table still caused big instabilities on the gain. I replaced all cables with semi-rigid or Heliax. That did not improve at all even though bending cables was no longer critical.

  • 4. Small vibrations on the signal path MMIC would cause gain variations. Found that tighting the screws holding the SMA connectors on the MMIC solved this problem.

  • 5. Tightening the screws really hard on the LO MMIC made a further improvement.

  • 6. When the system was left running for longer times there were still spontaneous gain changes and periods of gain intstability noise. Light knocking on every part relieved that the filter was a problem. Tightening the screws really hard helped a little, but tightening the nut to one of the N connectors made a big difference.

  • 7. I had not replaced the cable carrying 15 MHz IF from the mixer to the low pass filter on the SDR-IP. This cable turned out to be extremely sensitive. The reason is that it carries the sum frequency (and even higher frequencies.) Small impedance changes affect the conversion gain of the mixer. This problem was solved by placing the low pass filter directly on the mixer.

  • 8. Still not stable. The last problem I found was the SMA connectors on one of the semirigid cables. The connectors that use the center wire of the cable itself as the male connector pin did not provide a stable contact. (I had cleaned them.) Replacing that cable with one having proper connectors with gold plated pins made the setup stable.

The setup to replace the one in figure 1 is shown in figure 5 where two highly linear amplifiers with 5 dB gain each are added between the mixer and the SDR-14.

Figure 5. Improved insertion loss measurement.


Table 1 gives the impedances of the female port as measured previously and the insertion losses measured with the setup in figure 5 with links to the raw data.

Table 2 gives the impedance of the male port as measured previously together with the insertion losses.

Device    Zre      Zim      Loss     Stddev
         (Ohm)    (Ohm)    (dB)     (dB)
none     49.99    0.02      0.0000    0.0
DUT1     50.54    0.73      0.0348    0.00055
DUT3     48.39   -1.99      0.0242    0.00027
DUT8     68.56   10.56      0.1702    0.00106
DUT13    53.05    2.12      0.0589    0.00083
DUT18    35.16    0.02      0.1921    0.00041
DUT31    48.98   -2.56      0.0624    0.00054
DUT38    51.30  -19.81      0.2137    0.00053
DUT81    67.99    9.25      0.1941    0.0006
DUT83    69.55   13.90      0.2260    0.00037
DUT138   49.44   20.43      0.2608    0.00025
DUT183   33.83   -1.07      0.2456    0.00044
DUT318   47.18   14.67      0.1834    0.00086
DUT381   50.66  -19.16      0.2390    0.00061
DUT813   65.68    7.00      0.1790    0.00060
DUT831   68.50   14.16      0.2587    0.00032

Table 1. Impedances on the female SMA connector with the different DUTs measured by the 8753E and insertion losses from the setup in figure 1.

Device    Zre      Zim      Loss     Stddev
         (Ohm)    (Ohm)    (dB)     (dB)
none     49.98   -0.07      0.0000    0.0
DUT1     50.06   -1.08      0.0348    0.00055
DUT3     48.45   -2.20      0.0242    0.00027
DUT8     71.81    1.26      0.1702    0.00106
DUT13    47.42   -2.30      0.0589    0.00083
DUT18    71.30    2.13      0.1921    0.00041
DUT31    52.41    0.33      0.0624    0.00054
DUT38    73.15    4.81      0.2137    0.00053
DUT81    35.42    3.87      0.1941    0.0006
DUT83    44.49  -18.64      0.2260    0.00037
DUT138   73.82    5.71      0.2608    0.00025
DUT183   45.26  -18.94      0.2456    0.00044
DUT318   68.05   -0.47      0.1834    0.00086
DUT381   34.18    2.49      0.2390    0.00061
DUT813   52.42   15.00      0.1790    0.00060
DUT831   57.36   19.41      0.2587    0.00032

Table 2. Impedances on the male SMA connector with the different DUTs measured by the 8753E and insertion losses from the setup in figure 1.

Simplistic evaluation of data.

As a first attempt the data of tables 1 and 2 was fed into the computer program used for evaluation of the previous less accurate study of insertion losses.

The result was discouraging. Uncertainties were larger than in the previous study. The reason is that tables 1 and 2 on this page contains data from only 3 DUTs and that most of the DUTs have a high SWR.

The dissipative losses of a DUT can be computed from |S21|+|S11| which approaches unity for a low loss DUT. The value has to be slightly less than one and the logarithm times 20 gives the dissipative losses in dB.

The problem is that S11 suffers from a reproducibility problem. When impedances are measured once again the values typically differ by a few tenths of an ohm. In cases where SWR is high (all involving DUT8) a few tenths of an ohm is an unacceptable error. The previous study provides better accuracy despite the 10 times less accurate insertion losses because more DUTs with low SWR were measured.

The data of table 1 and 2 has to be processed differently.

The 85033 calibration kit.

The manufacturer specification is that the return loss of the LOAD is 40 dB or better below 2 GHz in the temperature range 15 to 35 degrees Centigrade. That is equivalent to say that the impedance is within a circle with radius 1 ohm in the Smith chart.

The impedance depends on the temperature, the male LOAD changes by (-0.039 + j0.033) Ohms for a 10 degree temperature change while the female LOAD changes by (-0.046 + j0.006). It seems reasonable to assume that the calibration kit is within 0.95 ohms from the Smith center at 25 degrees.

When the network analyzer is calibrated on the female LOAD and then the female to female adapter of the calibration kit is used to measure the male LOAD, the result is (49.939 - j0.141).


The first case, "none" means that the female connector with impedance (49.99, j0.02) is connected to the male connector with impedance (50.05, -j0.02). The associated voltage reflection coefficient is


Applying the worst combination of points 0.95 ohm away from the measured values gives a reflected power of -34.1 dB at the connection. The reflected power is a loss of 0.0017 dB in transmitted power.

The measured insertion loss of DUT1, 0.0348 dB could therefore be anything between 0.0348 and 0.0365 due to the influence of the calibration kit uncertainty on the measuement with no DUT inserted.

When sending power from the male connector through DUT1 into the female connector, the impedance seen by the male connector is (50.54 + j 0.73). The true impedance carries the error of the calibration kit male load so when computing the dissipative losses, the influence of the calibration kit error does not grow much. One finds that the dissipative losses of DUT1 is in the range 0.0340 to 0.0361 dB due to the uncertainty of the calibration kit. That is the average of the measurement in both directions. The average is less affected than the individual directions. To this comes the error of the insertion loss measurement with a standard deviation of 0.00055 plus a small error due to reproducibility problems with standard SMA connectors. The calibration kit thus gives an error of +/-0.001dB on DUT1.

For DUT8 it is different. Repeating the same math gives a range of 0.0285 to 0.0349 dB for the dissipative loss due to the uncertainties of the calibration kit only. That is +/- 0.006 dB, six times larger uncertainty than for DUT1. This result is approximate, but the underlying physics is simple. The DUT is a two-port. We determine the dissipative losses from the sum of transmitted and reflected power. (If the sum is below one, the rest is dissipative loss.) When the reflected power is very small it is not so critical to know impedances very well but when a significant fraction of the power is reflected, even relatively small errors are important.


We set up a set of unknowns:

ZERR_FEMALE 2 parameters (The error on the female SMA impedance)
ZERR_MALE 2 parameters (The error on the male SMA impedance)
S11_DUT1 2 parameters
S21_DUT1 2 parameters
S22_DUT1 2 parameters
S11_DUT3 2 parameters
S21_DUT3 2 parameters
S22_DUT3 2 parameters
S11_DUT8 2 parameters
S21_DUT8 2 parameters
S22_DUT8 2 parameters

In total 22 parameters for DUT1, DUT3 and DUT8. Based on an initial guess we can compute the insertion loss as well as the impedance in 15 cases for each one of table 1 and table 2. That gives 90 equations. We also need |S11|=|S22| which gives three more equations and that the insertion loss of "none" has to be zero. With table 1 and table 2 as input to duteval-1.0.tbz (6627 bytes) the data of table 3 is obtained. The program sets up the equations and solves the least squares problem of finding optimum parameters. One can set different weights to the phases and to the insertion losses. The experimental uncertainties differ by something like a factor of 100 so the errors have to be weighted correspondingly. It is not very critical.

         Fitted      Experiment     Diff       Fitted   Exp      Diff
          (Ohms)       (Ohms)      (Ohms)        (dB)   (dB)     (dB)
DUT100(50.65  0.51)(50.54  0.73)( 0.11 -0.22)  0.0347  0.0348 -0.000104
DUT300(48.27 -1.99)(48.39 -1.99)(-0.12  0.00)  0.0239  0.0242 -0.000255
DUT800(68.78 10.38)(68.56 10.56)( 0.22 -0.18)  0.1692  0.1702 -0.000980
DUT130(53.01  1.98)(53.05  2.12)(-0.04 -0.14)  0.0608  0.0589  0.001858
DUT180(35.27  0.21)(35.16  0.02)( 0.11  0.19)  0.1935  0.1921  0.001372
DUT310(48.58 -2.74)(48.98 -2.56)(-0.40 -0.18)  0.0597  0.0624 -0.002704
DUT380(50.94-19.91)(51.30-19.81)(-0.36 -0.10)  0.2142  0.2137  0.000537
DUT810(68.06  9.48)(67.99  9.25)( 0.07  0.23)  0.1926  0.1941 -0.001472
DUT830(69.47 14.03)(69.55 13.90)(-0.08  0.13)  0.2247  0.2260 -0.001319
DUT138(49.60 20.26)(49.44 20.43)( 0.16 -0.17)  0.2607  0.2608 -0.000074
DUT183(33.95 -1.08)(33.83 -1.07)( 0.12 -0.01)  0.2468  0.2456  0.001160
DUT318(46.96 14.47)(47.18 14.67)(-0.22 -0.20)  0.1829  0.1834 -0.000467
DUT381(50.69-19.09)(50.66-19.16)( 0.03  0.07)  0.2377  0.2390 -0.001313
DUT813(65.92  6.62)(65.68  7.00)( 0.24 -0.38)  0.1798  0.1790  0.000806
DUT831(68.55 14.73)(68.50 14.16)( 0.05  0.57)  0.2587  0.2587 -0.000015
DUT100(50.63 -0.50)(50.06 -1.08)( 0.57  0.58)  0.0348  0.0348  0.000017
DUT300(48.15 -1.84)(48.45 -2.20)(-0.30  0.36)  0.0240  0.0242 -0.000196
DUT800(71.95  1.40)(71.81  1.26)( 0.14  0.14)  0.1698  0.1702 -0.000406
DUT130(47.56 -2.49)(47.42 -2.30)( 0.14 -0.19)  0.0613  0.0589  0.002360
DUT180(70.73  1.87)(71.30  2.13)(-0.57 -0.26)  0.1929  0.1921  0.000765
DUT310(53.07  0.69)(52.41  0.33)( 0.66  0.36)  0.0597  0.0624 -0.002665
DUT380(73.52  4.88)(73.15  4.81)( 0.37  0.07)  0.2153  0.2137  0.001648
DUT810(35.78  4.17)(35.42  3.87)( 0.36  0.30)  0.1932  0.1941 -0.000914
DUT830(44.61-18.48)(44.49-18.64)( 0.12  0.16)  0.2251  0.2260 -0.000908
DUT138(74.00  6.15)(73.82  5.71)( 0.18  0.44)  0.2611  0.2608  0.000308
DUT183(45.21-17.92)(45.26-18.94)(-0.05  1.02)  0.2466  0.2456  0.000997
DUT318(68.01 -0.50)(68.05 -0.47)(-0.04 -0.03)  0.1856  0.1834  0.002238
DUT381(34.49  2.88)(34.18  2.49)( 0.31  0.39)  0.2382  0.2390 -0.000787
DUT813(52.36 15.02)(52.42 15.00)(-0.06  0.02)  0.1779  0.1790 -0.001111
DUT831(57.11 20.35)(57.36 19.41)(-0.25  0.94)  0.2578  0.2587 -0.000872
Computed insertion loss for [none] =-0.00005
RMS error for insertion loss 0.00127
DUT1 Dissipative loss 0.03447 dB.  Efficiency: (S11)0.99211 (S22)0.99208
DUT1 S11: (  0.005954  0.006432)
DUT1 S21: ( -0.196591 -0.976414)
DUT1 S22: (  0.005597 -0.003828)
DUT3 Dissipative loss 0.02086 dB.  Efficiency: (S11)0.99522 (S22)0.99519
DUT3 S11: ( -0.018343 -0.021574)
DUT3 S21: (  0.690175 -0.719776)
DUT3 S22: ( -0.019263 -0.020107)
DUT8 Dissipative loss 0.02537 dB.  Efficiency: (S11)0.99416 (S22)0.99419
DUT8 S11: (  0.163225  0.073787)
DUT8 S21: (  0.123706 -0.973021)
DUT8 S22: (  0.178941  0.009817)
Sum of dissipative losses for DUT1,DUT3 and DUT8 = 0.08071 dB
Calkit male LOAD error = (-0.088, i 0.141) Ohms
Calkit female LOAD error = (-0.094, i 0.092) Ohms

Table 3.Results from a least squares fit using duteval. The first 15 lines are from table 1, the next 15 lines are from table 2.

The purpose of this investigation was to find the summed loss of DUT1, DUT3 and DUT8 with better precision than obtained previously

The old result was 0.0890 dB to compare with 0.0807 dB. The difference is due to different results for DUT8 which has high SWR and is more difficult to measure. What error limits to set on the new result is beyond my skils.

The RMS error for the computed insertion losses is 0.0013 dB. The result is based on a large number of measurements and is presumably a bit better.

The impedance transformers.

Table 4 is a list of the six combinations that all have the same insertion loss, 0.0807 dB (with a small but unknown error.)

Four of them have VSWR in the range 1.47 to 1.50 and map the impedance plane reasonably well. The remaining two are significantly closer to the Smith chart center and will not be used. They are marked with an asterisk in table 4.

Device     Zre    Zim        Phase   Ideal    Diff     VSWR 
DUT138    73.82   5.71       11       0       11     1.49257
DUT183    45.26 -18.94      -93     -90       -3     1.50320
DUT318    68.05  -0.47       -1      *               1.36114
DUT381    34.18   2.49      169     180      -11     1.46963
DUT813    52.42  15.00       73      *               1.34407
DUT831    57.36  19.41       59      90      -31     1.46996

Table 4.Impedance transformers.