This Electronics Engineering Seminar Topic deals with the following:
LRR- LINE REFLECT REFLECT is a new self-calibration procedure for the calibration of vector network analyzers (VNA). VNA measure the complex transmission and reflection characteristics of microwave devices. The analyzers have to be calibrated in order to eliminate systematic errors from the measurement results.
The LRR calibration circuits consist of partly unknown standards, where L symbolizes a line element and R represents a symmetrical reflection standard. The calibration circuits are all of equal mechanical length. The obstacle, a symmetrical-reciprocal network is placed at three consecutive positions. The network consists of reflections, which might show a transmission. The calibration structures can be realized very easily as etched structures in microstrip technology.
During the calibration [G], [H], which represents the systematic errors of the VNA is eliminated in order to determine the unknown line and obstacle parameters.
Microwave devices are devices operating with a signal frequency range of 1-300GHz. A microwave circuit ordinarily consists of several microwave devices connected in some way to achieve the desired transmission of a microwave signal.
The various microwave solid state devices are,
* Tunnel diodes:
These are also known as Esaki diodes. It is a specially made PN junction device which exhibits negative resistance over part of the forward bias characteristic. Both the P and the N regions are heavily doped. The tunneling effect is a majority carrier effect and is very fast. It is useful for oscillation and amplification purposes. Because of the thin junction and shot transit time, it is useful for microwave applications in fast switching circuits.
* Transferred electron devices:
These are all two terminal negative resistance solid state devices which has no PN junction. Gunn diode is one of the transferred electron devices and which works with the principle that there will be periodic fluctuations in the current passing through an n-type GaAs substrate when the applied voltage increases a critical value i.e. 2-4Kv/cm.
*Avalanche transit-time devices:
These are used for amplification purposes. And the basic principle is the voltage breakdown at the reverse biased PN junction with the supply of electrons and holes.
These microwave solid state devices are used for generation and amplification of microwave signals by means of velocity-modulation theory. The interconnection of two or more microwave devices is regarded as a microwave junction. From the network theory a two-port device can be described by a number of parameter sets, such as the H, Y, Z and ABCD. All these network parameters relate total voltages and total currents at each of the two ports. If the frequencies are in the microwave range, the two port network representation is as shown in FIG: 1.