Microstrip Directional Coupler

 

1. Theory

- Direction coupler extracts a portion of a wave traveling in a direction on a transmission line.

- Applications of directional couplers:

     Transmitted power monitoring

     Reflected power monitoring

 

https://upload.wikimedia.org/wikipedia/en/thumb/3/34/Directional_coupler_symbols.svg/1024px-Directional_coupler_symbols.svg.png

Figure: Directional coupler symbol. P1/P2 = insertion loss, P1/P3 = coupling, P1/P4 =  isolation, P3/P4 = directivity

 

Figure: Microstrip quarter-wave directional coupler topology. Port 1: input, Port 2: through, Port 3: coupled, Port 4: isolated

 

 

 

 

 

 (coupling)

 (through, negative of insertion loss)

 

 

     https://upload.wikimedia.org/wikipedia/en/thumb/0/0e/Stripline_5-section_coupler.svg/1280px-Stripline_5-section_coupler.svg.png  

Figure: Multi-section directional coupler for wideband operation

 

https://upload.wikimedia.org/wikipedia/en/thumb/c/c2/Short_line_directional_coupler.svg/1024px-Short_line_directional_coupler.svg.png   https://upload.wikimedia.org/wikipedia/en/thumb/3/33/Short_line_coupler_unequal_impedance.svg/1024px-Short_line_coupler_unequal_impedance.svg.png https://upload.wikimedia.org/wikipedia/en/thumb/5/58/Short_line_directional_coupler_equivalent_circuit.svg/1280px-Short_line_directional_coupler_equivalent_circuit.svg.png

Figure: Short-section coupled line directional couplers and equivalent circuit representation.

 

2. Applications of the Directional Coupler

 

https://upload.wikimedia.org/wikipedia/commons/thumb/f/f6/Microstrip_Directional_Coupler.jpg/800px-Microstrip_Directional_Coupler.jpg  https://upload.wikimedia.org/wikipedia/commons/d/db/Microstrip_Sawtooth_Directional_Coupler.jpg

Figure: Directional couplers used in microwave devices.

 

Microstrip directional coupler for an X-band motion sensor

CIAS MURENA Plus, https://www.cias.it/en/products/sensors/murena/

Spec.: 24-m range, dual frequency Doppler sensor, 10-11 GHz

    

Figure: Left = MURENA motion sensor, Midde: Intruder detection by motion sensor, Right = Internal view of the 4-element patch array antenna and the motion sensor board.

 

Figure: Block diagram of the MURENA motion sensor [Sanna(2018)]

 

3. Laboratory

 


Figure: Test model of the directional coupler in the MURENA motion sensor [Sanna(2018)]

 

Figure: A 10.5-GHz direction coupler. Substrate: ¥år = 3.5 , tan¥ä = 0.003, h = 0.752, t = 0.035; Coupler: W1=1.7,W2=1.4,S = 0.2, L = 4.2, A = 2.2, H = 4.5 (unit: mm). When the port 1 is the input, the ports 3 and 4 are the coupled and isolated ports respectively.

 

1. Make the structure

2. Simulate the structure with wave-port source with field animation selected.

3. Plot S11, S21, S31, S41 at 9-12 GHz.

4. Find the following values at 10.5 GHz.

     Return loss = (           ) dB

     Insertion loss = (            ) dB

     Coupling = (         ) dB

     Directivity = (         ) dB

5. Find the phases of the following at 10.5 GHz. Move reference planes of the input and output lines by H in the above figure.

     arg(S21) = (             ) deg

     arg(S31) = (             ) deg

6. Display the animated current to understand the operating principles of the directional coupler.