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DIY-DualDirectionalCoupler.php   14164 Bytes    26-11-2015 10:14:14


DIY Dual Directional Coupler, 5 - 1000 MHz, 20 dB


An Add-On to our Scalar Network Analyzers



This is not a new invention. It's just a hack together of some (very) nice parts. And the result is an 'even nicer' part. (So we think :-)


DIY Dual Directional Coupler, 5 - 1000 MHz, 20 dB




✈ Hardware Description




This design uses two times an ADC-20-4 or an ADC-10-4 from Mini Circuits. A small printed circuit board was designed to offer adequate 50 Ω traces, as it should go up to 1000 MHz. The termination is done by two resistors 0805, 100 Ω in parallel. We used sma connectors to keep the geometry small. The case was milled from aluminium. Surface coated with nickel. As connectors, you mayst use MC000242 (Multicomp) or 142-0701-411 (JOHNSON).







✈ Performance (2 x ADC-20-4+ assembled)




Figure 1. Coupling (INPUT - INCIDENT) or (TEST PORT - REFLECTED) of the DIY Dual Directional Coupler

Figure 1. Coupling (INPUT - INCIDENT) or (TEST PORT - REFLECTED)


Figure 2. Main Line Loss (INPUT - OUTPUT) of the DIY Dual Directional Coupler

Figure 2. Main Line Loss (INPUT - OUTPUT)


Figure 3. Return Loss: Input of the DIY Dual Directional Coupler

Figure 3. Return Loss: Input


Figure 4. Return Loss: Output of the DIY Dual Directional Coupler

Figure 4. Return Loss: Output


Figure 5. Return Loss: Coupling (INCIDENT or REFLECTED) of the DIY Dual Directional Coupler

Figure 5. Return Loss: Coupling (INCIDENT or REFLECTED)


Figure 6. Directivity of the DIY Dual Directional Coupler

Figure 6. Directivity

Note : The directivity is the difference in dB of the power output of the two coupled ports, when power is transmitted in a constant direction on the main-line.

All measurements done with an hp 8753 ES. We apologise for the de-pixeled graphs. As it seems, that Mini Circuits specifies very diffidently, this dual directional coupler mayst also be used slightly out of range :-)




✈ RF directional coupler 'Quick bleach'




Assuming that the rf source is connected at the input port and the load is connected at the output port, this dual directional coupler outputs a signal at the forward port which is 20 dB lower than the power entering at the input port. Vice versa it outputs a signal at the reflected port which is 20 dB lower than the power entering at the output port. Those 20 dB are referred to as coupling coefficient. An essential feature of directional couplers is that they only couple power flowing in one direction.

The lower the signal at the coupled port, the more signal is available to the through line.

In case the load is not matched to the system impedance, it will reflect power. Therefore the signal at the reflected port is a measure for the impedance of the load.

It is possible to design directional couplers in various ways. Depending on the frequency, the design may use lumped elements, transmission lines or waveguides. The design here uses lumped elements (transformers). Mini Circuits ADC-10-4 or Mini Circuits ADC-20-4.


Read more on Jeff's blog.




✈ Alain explains how a Directional Coupler works








✈ Homebrew 50 Ω Terminations




When building terminations for 50 Ω, several possibilities arise. 1 x 51 Ω, 2 x 100 Ω, 3 x 150 Ω, 4 x 200 Ω, 6 x 300 Ω, [...] In order to see, if there is a difference, we build them using an sma connector and 0603 resistors (the set from Constructiva AG, using Vishay/Yageo 1% thick film resistors). As at very high frequencies solder/flux left-overs may have an influence, the sma connectors have been cleaned with isopropanol. Measurements have been done with an hp 8753 ES, as calibration standard, we used a (new) Huber & Suhner 65 SMA-50-0-36/111 NE.

Configuration S11 at 1 MHz S11 at 1 GHz S11 at 2 GHz S11 at 3 GHz
51 Ω - 39.2 dB - 26.8 dB - 21.4 dB - 17.0 dB
2 x 100 Ω - 60.8 dB - 49.2 dB - 46.2 dB - 45.1 dB
3 x 150 Ω - 56.2 dB - 33.8 dB - 27.9 dB - 26.1 dB
4 x 200 Ω - 65.7 dB - 30.0 dB - 25.2 dB - 22.2 dB
6 x 300 Ω - 59.6 dB - 25.7 dB - 19.0 dB - 16.4 dB

It can be seen, that DIY design and assembly of 50 Ω terminations yields very useable results when considering rf design techniques. The best solution here is 2 x 100 Ω, obviously some parasistic effects add up when using more of those resistors. The Measurement below refers to the 2 x 100 Ω version.


DIY 50 Ω Terminator, S11 DIY 50 Ω Terminator, S11



DIY 50 Ω Terminator




✈ Please cite as :




Dipl.-Ing. Alexander C. Frank, "DIY Dual Directional Coupler, 5 - 1000 MHz, 20 dB"
http://www.changpuak.ch/electronics/DIY-DualDirectionalCoupler.php




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t1 = 3844 d

t2 = 560 ms

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