How I use Caban microwave reflectometer in my projects

Hi! My name is Olesya (leka_engineer). I am a microwave engineer and I write about the development and show my laboratory. Almost two years ago I got my first device measuring S-parameters (more precisely, one of the parameters of the scattering matrix – the reflection coefficient). In Figure 1 – reflectometer Planar Caban R54.

The device operates at up to 5.4 GHz, has a compact body with a nice rubber band (others have reflectometers just a metal case), N-type connector (doesn't creak).

I checked Planar's website and found out that this device discontinued. Too bad. I hope you will still find this article interesting, since the application methods are the same for all reflectometers.

One-port measurements

What can be measured with a reflectometer? The first thing that comes to mind, of course, is antennas. Some time ago we helped with modification of the microwave part in Sher-Khan alarms. Then Caban was very useful for one of the stages of work – we brought out the output from the antenna with a cable, connected a reflectometer to it (Figure 2). This structure was moved around the car interior, and thus the optimal place for installing the system was found. On the other side of the reflectometer, a USB cable is connected, which, in turn, is connected to a laptop. Almost all Planar devices do not have a screen; a laptop, computer or Win tablet is used to visualize measurements.

2 Signaling unit with an extended cable ending with an SMA connector - Tair ADP1A-NF-35M transition - Reflectometer — 2 Signaling unit with an extended cable ending with an SMA connector – Tair transition ADP1A-NF-35M – Reflectometer

During another stage of the work, modification of the antenna in another block, which, unlike the one shown in Figure 2, is placed under glass, Kaban also came in handy. Sher-Khan employees also connected the reflectometer to the antenna output and in online mode (in contact with us) selected the values of inductances and capacities of the matching path, provided that there was glass and possible rain.

3 The process of measuring and adjusting the antenna of the under-window alarm unit

Another single-port microwave device is a load. I wrote about the project for Amitron to develop loads. According to the idea, there were several loads in the line, one of which was supposed to be powerful, but not very high-frequency, up to ~4 GHz. At first, I used a reflectometer to measure the SWR of the load layouts, but it became clear that it could work at a higher frequency. The prototype of the 6 GHz/300 W load Amitron Electronics exhibited at Expoelectronica. By the way, Planar had a very beautiful stand at the exhibition.

Two-port measurements

I admit that I used to always consider the methods of measuring two-port devices with reflectometers as “crutches”, I was sure that nothing worthwhile could be “measured” this way. But recently there was a need to measure a large number of filters “in the field”. A colleague lent me his exactly the same Caban and I was able to connect them to measure the frequency response of the filters. Here it is necessary to clarify that these filters are not a new development, it is known that the SWR of the filters (in the absence of any defects) is quite low in the working band.

4 The process of measuring the filter frequency response

For comparison purposes, and to be sure of the reliability of the results, a part of the filter batch was measured both on the R&S ZVA and by the method described above. Figure 5 shows a comparison of the frequency response of the devices. This article was written by leka_engineer

5a frequency response of filters measured with R&S

5b Frequency response of the same filters, measured using two Kabans

5v comparison of measurements of one filter on ZVA and R54

As can be seen from Figure 5, the only problem is a small noise of the track when measuring with the Kabanov (presumably due to the IF). But the main conclusion is that such the measurements are reliable and correlate very well with measurements on an expensive device.

I would not recommend using this measurement method for initial testing or setting up new developments, for this you need a full-fledged device. But, for example, for testing a batch of products that have been in production for a long time, it is very convenient and relatively inexpensive.

Additionally

The above are classic ways of using reflectometers in work. I can hardly imagine such a situation, but reflectometers can also be used to measure: the phase shift of reflective phase shifters, the frequency dependence of the reflection coefficient module of a blocking capacitor.

Reflectometers can be useful for checking the SWR (OK/is there a break) of two-port devices with a load on the second port (for example, I have a new device, I'd better first check it with a reflectometer quickly at home, to see if there is a defect in the assembly, before going to a large VAC, which I don't have yet).

Thank you for your attention!