A Gunn diode type MA was chosen for this purpose The answer is to divide the less accurate distance, measured with because of its availability, good performance, and low cost [4], the pair , by the maximum range obtained with and [5]. Details on how a Gunn diode operates can be found in [6]. The bias voltage is applied to the cavity interior via a In summary, using three adequately chosen frequencies, it Bayonnet nut connector BNC directly attached to the external is possible to measure the distance to a stationary target in a part, as shown in Fig.
Inside the resonant cavity, to simple way. Also included in the figure is a threaded drum machined in plastic to move the short circuit so that the oscillating frequency can be accurately varied. A photograph of the oscillator, completely mounted and ready for use, is shown in Fig. This circuit allows the biasing of the Gunn diode in a wide range of conditions. If the polarity and the voltage are correct, the green LED diode lights.
If the biasing polarity is reversed, the red LED lights, the power diode D1N does not conduct, and the output voltage is zero. The programmable linear regulator LM is set to the best bias voltage in this case 14 V for the Gunn diode by varying the value of the potentiometer POT1. If Fig. Module A. To assess the correct operation of the diode inside the resonant cavity, three types of measurements have been per- formed—output power, frequency spectrum, and phase noise of the oscillator.
Previously, the matching of the cavity-diode assembly is verified by measuring the scattering parameters of the oscillator without biasing the diode. The matching found to be better than 20 dB in the whole band. In Fig. As can be observed in this figure, the power exceeds 1. In addition, there are no in-band spurious signals, except one, Fig. Module B. Nulls will occur when the inputs to the magic sideband SSB phase noise of the oscillator measured at tee from each branch are of the same amplitude and phase.
Otherwise, the detected field values will be different from zero. The an- IV. To position the static target based on MFCW radar utilizes a phase bridge or in- target adequately, either at a calibration distance labeled terferometer using a magic tee as the mixer element.
This setup , or at an arbitrary position at distance from the is best described in terms of various modules [3]. It consists of a phase bridge interferometer frequency meter as it is shown in Fig. This procedure must be to detect the phase difference between the signal received repeated for each of the three frequencies.
The second of the interferometer must be balanced in order that the signals signal, RF-SIGNAL-2, propagates through ARM-2, and both that propagate through them will have the same amplitude and signals are combined in the magic-tee waveguide mixer.
For such purpose, the calibrated attenuator labeled The output signal is extracted by means of a crystal detector in Fig. A stable, wideband microwave source with low phase noise and modest cost has been designed, manufactured, and planned for use in teaching laboratories.
Furthermore, a protection circuit has also been designed and built in order to keep the integrity of the Gunn diode during its handling by the students. When the problem of obtaining an adequate microwave source was solved, a waveguide circuit based on a phase bridge was developed to Fig.
Module C. In this experiment, many basic concepts play a role, associated with the theoret- ical contents of regular courses in Electromagnetism and Mi- crowave, taught in Physical Sciences and Telecommunications Engineering.
A similar procedure must be followed for the target at [1] M. Skolinik, Introduction to Radar Systems, 2nd ed. Singapore: Mc- Graw-Hill, , ch. Eaves and E. Ready, Principles of Modern Radar.
New York: for for , and for see Table I. Van Nostrand, , ch. Next, the phase shifts are grouped according to the frequency [3] S. If a voltage is applied to this device, then most of the applied voltage appears across the active region.
The electrons from the conduction band having negligible electrical resistivity are transferred into the third band because these electrons are scattered by the applied voltage. The third band of GaAs has mobility which is less than that of the conduction band. Because of this, an increase in the forward voltage increases the field strength for field strengths where applied voltage is greater than the threshold voltage value , then the number of electrons reaching the state at which the effective mass increases by decreasing their velocity, and thus, the current will decrease.
Thus, if the field strength is increased, then the drift velocity will decrease; this creates a negative incremental resistance region in V-I relationship. Thus, increase in the voltage will increase the resistance by creating a slice at the cathode and reaches the anode.
But, to maintain a constant voltage, a new slice is created at the cathode. Similarly, if the voltage decreases, then the resistance will decrease by extinguishing any existing slice.
The current-voltage relationship characteristics of a Gunn diode are shown in the above graph with its negative resistance region. These characteristics are similar to the characteristics of the tunnel diode. As shown in the above graph, initially the current starts increasing in this diode, but after reaching a certain voltage level at a specified voltage value called as threshold voltage value , the current decreases before increasing again.
The region where the current falls is termed as a negative resistance region, and due to this it oscillates. In this negative resistance region, this diode acts as both oscillator and amplifier, as in this region, the diode is enabled to amplify signals. We hope that you have got an idea of the Gunn diode, characteristics of Gunn diode, Gunn Effect, Gunn diode oscillator and its working with applications in brief.
Here active region is referred to as a middle layer of the device. Due to which the electrons from the 1st layer of the conduction band having almost zero resistivity are transferred into the third layer of the valence band. Because applied voltage has made the electrons to flow from conduction band to valence band. The third layer of Gallium arsenide has the mobility of electrons which is less than that of the conduction band of the first layer.
When the electrons have transferred from the conduction band to the valence band, after some threshold value the current through the device starts decreasing, Due to this the effective mass of electrons starts increasing and thus mobility starts decreasing due to which the current starts decreasing, And this creates the negative differential resistance region in the Gunn diode. In this negative differential resistance region, the current and voltage have an inverse relationship, which means when the current starts to increase the voltage starts to fall.
And when voltage starts to increase the current start to decrease. Gunn diodes are widely used as oscillators to generate microwaves with frequencies range of 1 to GHz. It is a Negative Differential Resistance device as explained above and also they are called as transferred electron device oscillator.
When the DC bias is applied to this diode it behaves in negative differential resistance and generates microwave frequencies. Consequently, the circuit provided below is able to oscillate at low frequencies with the presence of tuned circuit inductance and other circuit connections. Read More: What is the Duty Cycle?
The graph below shows the V-I characteristics of a Gunn Diode with the negative differential resistance region. Initially the Current starts to increase in Gunn diode with the applied bias voltage, At a particular instant, the current starts to decrease and this point is known as peak point.
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