JADAVPUR UNIVERSITY

Department of Electronics and Telecommunication Engineering

MICROWAVE LAB

Title- Study of Gunn Diode Oscillator

Name: Susmit Sanyal

Roll Number: 002110701102
Class: ETCE UG IV
Section: G1

Date of Submission: 01/10/2024

 EXPERIMENT 3
TITLE: Study of Gunn Diode oscillator.

OBJECTIVE:
To study the Gunn diode oscillator and its properties.

APPARATUS REQUIRED:

Sl. No. Item Specification

1. Gunn oscillator X480B

2. Gunn power supply X480A

3. Ferrite isolator X718/X717

4. Frequency meter X710

5. Attenuator X321

6. Crystal detector X310

7. Power meter U181

8. Thermistor mount UA132

9. Coaxial to waveguide
X850
adapter

10. Oscilloscope EC OS768

11. Cables and accessories

THEORY:
A Gunn diode is a passive semiconductor device with two terminals, composed of only an n-doped
semiconductor material, unlike other diodes that consist of a p-n junction. Gunn diodes can be made from
materials that consist of multiple, initially empty, closely spaced energy valleys in their conduction band
like Gallium Arsenide (GaAs), Indium Phosphide (InP), Gallium Nitride (GaN), Cadmium Telluride (CdTe),
Cadmium Sulfide (CdS), Indium Arsenide (InAs), Indium Antimonide (InSb), and Zinc Selenide (ZnSe).
The general manufacturing procedure involves growing an epitaxial layer on a degenerate n+ substrate
to form three n-type semiconductor layers (Figure la), wherein the extreme layers are heavily doped
compared to the middle, active layer.Further, metal contacts are provided at either end of the Gunn
diode to facilitate biasing.
When a DC voltage is applied across the terminals of the Gunn diode, an electric field develops across its
layers, with most of it appearing across the central active region. In the initial stages, conduction
increases as electrons move from the valence band into the lower valley of the conduction band.

The associated V-I plot is depicted by the curve in Region 1 of Figure 2. However, once it surpasses a
specific threshold value (Vth), the conduction current through the Gunn diode decreases, as illustrated
by the curve in Region 2 of the figure.

Region 1
Region 2

Figure 2

This is because, at higher voltages, the electrons in the lower valley of the conduction band move into
its higher valley where their mobility decreases due to an increase in their effective mass. The
reduction in mobility decreases the conductivity, leading to a decrease in the current flowing through
the diode.
The diode shows a negative resistance region in its V-I curve from Peak Point to Valley Point. This
feature is referred to as the transferred electron effect, leading Gunn diodes to be called Transferred
Electron Devices.
In a Gunn Oscillator, the Gunn Diode is situated within a resonant cavity, where the oscillation
frequency depends on cavity dimensions, not the diode. The bias voltage allows for amplitude
modulation.

EXPERIMENTAL SETUP:
PROCEDURE:

1. The equipment is set up as shown in the figure above. It is ensured that the voltage and the pin
diode bias knob of the Gunn Oscillator are turned anticlockwise completely.
2. The Gunn diode oscillator is then connected to the power supply. Make sure that the right
connector is used to supply the Gunn bias. The pin bias cable is connected to the pin diode
connector.
3. Adjust the Gunn oscillator frequency to a practical center frequency, such as 9.5 GHz, by fine-
tuning with a micrometer and calibration chart.

(a) Voltage-current characteristics:

The voltage increases in increments of 0.5 volts, and the respective current is read on the power
supply's panel meter by alternately switching to current and voltage modes. The current values
against voltage are then plotted and compared to Figure 2.

(b) Output power and frequency as a function of bias

1. The Gunn bias is adjusted to approximately 7 volts (just above the threshold voltage). This
adjustment is indicated by a sudden increase followed by a decrease in current to about 300
milliamps.
2. The variable attenuator's attenuation is decreased to produce a moderate deflection on the
power meter. Both the attenuator reading and the power meter reading are recorded (attenuator
readings should be combined with power meter readings).
3. The frequency meter is tuned to obtain the tip in the power meter.
4. The attenuator of the power meter scale should not be disturbed.
5. Now the gunn bias is incremented in steps of 0.5v.
6. At each voltage reading, note the power and frequency by tuning the frequency meter.
 7. The results are used to plot frequency and power as a function of voltage.

(c) Output power as a function of frequency

1. From the results of the above section, the voltage for which power output is maximum is noted and
the gunn bias is adjusted to this voltage.
2. Now the micrometer of the gunn oscillator is moved to one extreme. Care must be taken so that the
micrometer isn't overturned. It has to be made sure that the power output is not less than 5mW at
this end.
3. Frequency and power are noted as in section (b).
4. The micrometer is moved by 0.5mm. The frequency and power are noted again. This is continued till
power falls to about 5mW (in the higher frequency range that is around 11.5GHz). These results are
used to plot power as a function of frequency.

EXPERIMENTAL DATA:

Run 1: V-I characteristics of Gunn Diode

Voltage (V) Current (A)

0 0

0.47 0.05

0.5 0.06

0.7 0.08

0.8 0.1

0.9 0.11

1 0.12

1.5 0.19

2 0.24

2.5 0.29

3 0.33

3.5 0.37

4 0.38

4.5 0.39

5 0.36

5.5 0.35

6 0.34
 6.5 0.33

7 0.32

7.5 0.32

8 0.31

8.5 0.3

9 0.3

9.5 0.29

10 0.29

PLOTS:

Run 2: Electronic tuning of Gunn Diode

Gunn Bias Power Frequency

Voltage (V) (GHz)
(or Current) (µA)

7 54 10.335

7.1 140 10.365

7.2 160 10.365

7.3 136 10.365

7.6 170 10.37

PLOTS:
Run 3: Mechanical tuning of Gunn Diode
Gunn Bias = 6.97V

Biasing length Power Frequency

(mm) (GHz)
(or Current) (µA)

13.5 200 10.51

14 174 10.395

14.5 78 10.29

15 90 10.165

PLOT:
CONCLUSION:

1. V-I characteristics of Gunn diode indicate an increase in the current with an increase in
voltage (positive resistance region). After a certain point, it decreases (negative
resistance region). This point is called the Threshold Voltage.
2. For electronic tuning, we select a voltage close to the midpoint in the negative
resistance system.

3. The frequencies obtained in the electronic and mechanical tuning are resonant.