20-07-2013, 02:48 PM
Determination of coupling and isolation characteristics of a strip-line directional coupler
AIM OF THE EXPERIMENT:-
To determine the coupling and isolation characteristics of a stripline
( or microstrip) Directional coupler.
COMPONENTS REQUIRED:-
Power Supply
VCO
50 ohm Transmission line
Branch line coupler
Parallel line in coupler
50 ohm terminations
Cables with SMA connector
Oscilloscope / VSWR meter / Power Meter
THEORY:-
A two stub branch line coupler is a fundamental direct coupled structure in which the main line is directly bridged
To the secondary line by means of two shunt branches. The length of each branch and their spacing are all quarter
Wavelength in the transmission medium at the center frequency f0.
In a parallel coupled directional coupler the main length ālā of the coupled line section is quarter wavelength in
the transmission medium at the center frequency f0 . All inputs and outputs lines have the same characteristic
impedance
PROCEDURE:-
1. Set up the system as shown in the block diagram
2. Keeping the tuning voltage at minimum and gain control at max, switch on the microwave signal source.
3. Insert a 50 ohm transmission line and check for the output at the end of the system using a
CRO/VSWR meter/ RF power meter.
4. Vary the tuning voltage and check for power supply level using a CRO/VSWR meter
5. Note the output for different VCO frequencies
6. Replace the transmission line with a directional coupler.
7. Check the output at ports 2(through port), measure power output 3(coupled output), and power output at
port 4 (isolated port).
8. Calculated insertion loss, coupling factor and isolation using the formula given.