Microwave transmission line oscillator composition principle and circuit Specific explanation

Basic knowledge of microwave transmission characteristics "microwave" usually refers to the wavelength in - of the electromagnetic waves, corresponding to the frequency range of: -, which is between radio waves and infrared, and can be divided into decimeter waves, centimeter waves, millimeter waves, submillimeter waves. Microwave and low-frequency electromagnetic waves, with all the characteristics of electromagnetic waves, but due to the microwave wavelength is shorter, high-frequency and therefore has many unique properties, mainly in: 1, the description of the method: due to the electromagnetic wave wavelength is extremely short, and the use of components and equipment can be compared to the size of the low-frequency band due to the concentration of energy and its propagation properties with the "road", the concept of "road" to describe. The concept of "road" to describe the use of components known as the centralized parameter components (resistance, capacitance, inductance, etc.); and microwave propagation should be used to deal with the concept of "field", the use of components for the distribution of parameter components (waveguide, resonant cavity, etc.). Therefore, the low-frequency circuit of current, voltage, resistance, etc. is no longer applicable, but the equivalent method of treatment; microwave measurements to power, wavelength, impedance instead of current, voltage, resistance, etc. 2, the method of generation: microwave period in - and the electron tube electron crossing time (about ) similar, so microwave generation and amplification can not be used in the ordinary electronic devices, instead of the structure and structure of the electronic components. Replaced by a completely different structure and principle of microelectronic components - speed control tubes, magnetrons, traveling wave tubes and microwave solid-state devices. 3, optical similarity: as microwaves between radio waves and infrared, so not only has the nature of radio waves at the same time with the nature of light waves: linear propagation at the speed of light, reflection, refraction, interference, 4, strong energy: due to the high frequency of microwave, so the available bandwidth, information capacity, and can penetrate the atmosphere can be widely used in satellite communications, satellite radio and television, cosmic communications and radio astronomy research. Because of these characteristics of microwaves, microwaves in communications, radar, navigation, remote sensing, astronomy, meteorology, industry, agriculture, health care, as well as medicine and other aspects of a wide range of applications. A microwave components Introduction 1. solid-state oscillator (solid-state signal source) microwave oscillator (signal source) is a device that generates microwave signals, commonly found in magnetron oscillators, speed-tuned tube oscillators and solid-state oscillators of several kinds. Magnetron oscillator power volume, commonly used to provide high-power signals; speed control tube oscillator structure is simple, easy to use, but the low efficiency is generally only 0.5% -2.5%, the output power is generally small in, so it is more suitable for laboratory use. Solid-state oscillator is a relatively new type of signal source, can be divided into microwave transistor oscillator, body effect tube oscillator, avalanche diode oscillator. Solid-state oscillator oscillation frequency is high, the highest oscillation frequency of up to several hundred gigahertz; output power up to tens of watts or more, pulse power up to a few kilowatts; tributary power conversion to microwave power is high, up to 50% or more. Here mainly introduces the laboratory commonly used by the body effect diode oscillator. 1963 the United States International Business Machines Corporation found that gallium arsenide and indium phosphide and other materials, such as thin layers with negative resistance characteristics, and thus do not need P-N connection to produce microwave oscillation, its operating principle and usually consists of P-N section of the semiconductor device is different, it is not the use of carriers in the P-N within the Motion characteristics, but the use of carriers in the semiconductor in vivo in vivo motion characteristics, is relying on gallium arsenide materials, "body" within a physical effect (negative resistance effect) so called body effect diode or Geng's tube (Gun tube). Body effect diode by the cut-off attenuator and used to modulate the microwave pulse amplitude PIN modulator. Laboratory commonly used 3cm solid-state signal source frequency adjustment range of about 8.6 a 9.6GHz. Body effect oscillator is the core component of the microwave signal source, I (A) it is the use of semiconductor materials with negative resistance characteristics of gallium arsenide made of gallium arsenide has a two-level structure, on the upper and lower two levels of the difference between the energy level of 0.36Mev; in the different energy levels of the electrons have different effective mass and different Mobility, in which the effective mass of the upper energy level is large mobility is small. When the energy of the lower conduction band of electrons increased to 0.36Mev, the lower conduction band of electrons will be excited to the upper conduction band to go, so that it is in a certain region of the negative resistance characteristics, that is, the emergence of the Voltammetric Curve Figure (1) U (V) as shown in Figure (1): it can be seen that the body effect tube can produce an oscillating current, so that the thickness of Gallium Arsenide is sufficiently small, the body effect tube can produce a similar pulse spikes of the oscillating waveform, oscillation frequency is very high! Waveforms, oscillation frequency is very high, that is, to produce microwave signals. Typical Geng's diode as shown in the figure: by the copper thread (received on the negative pole of the DC power supply), copper base (plus heat sink), ceramic ring (insulating effect), gold wire leads, gallium arsenide sheet, the top cap (positive) composed of if Geng's diode is mounted in the resonant cavity at the appropriate location, as long as it is added to both ends of the DC voltage, you can generate microwave oscillations within the resonance cavity, constituting the microwave negative resistance oscillator. The main performance parameters of Geng diode are as follows Geng's diode's main performance parameters are: operating frequency 10GHz or so, operating voltage 10V, operating current 0.2-0.6A, output power 0.03-0.1W, the maximum voltage withstand capacity of 14V. 2. Isolator is a kind of irreversible attenuator, the forward attenuation of smaller Isolator is an irreversible attenuator, forward attenuation is small, about 0.1dB, reverse attenuation is very large, up to dozens of dB, so only allows microwaves to pass through a single direction, the opposite direction of propagation of microwave resistance absorption. Isolators are often used between the oscillator and the load to isolate and unidirectional transmission. Isolator is generally made of ferrite material, ferrite is a magnetic material, by the bivalent metal manganese, magnesium, nickel, copper, copper, and other oxides and iron oxide firing and become, it has a magnetic material of magnetic conductivity, but also has a high electrical resistivity, generally up to , because of its high electrical resistivity, the electromagnetic field can penetrate into the internal role of the loss is very small, so it is widely used. Isolator attenuator isolator is divided into resonant and field shift type two kinds, resonant power, laboratory commonly used field shift type, it is in the waveguide in the appropriate location to place a piece of both ends of the pointed split shape (in order to reduce the reflection) ferrite sheet, so that its surface and the narrow side of the waveguide parallel to the surface of the absorber (made of graphite powder or nickel-chromium alloy) and the addition of a constant magnetic field is made. In the ferrite plus a constant magnetic field so that the electrons in the ferrite produced by the inlet and at the same time coupled with the constant magnetic field perpendicular to the high-frequency right-rotation or left-rotation polarization of the magnetic field, as a result of the two kinds of magnetic field and the direction of the electron inlet and the opposite direction, respectively, and therefore produce different permeability and and with the size of the constant magnetic field and change, when the thickness of the ferrite sheet, the location of the magnetic field and the strength of the selection of the appropriate, resulting in the non-reciprocity of the Field effect, both when the electromagnetic wave propagating in the waveguide for the right circular polarization when the ferrite presents the permeability for a negative value of the right circular polarization field is "excluded" outside the ferrite, absorbing material surface electric field is 0, almost no attenuation. When the electromagnetic wave propagation in the reverse direction for the left circularly polarized field is "sucked into" the ferrite, the absorbed material surface electric field is absorbed, reverse attenuation is very large. 3. attenuator Attenuator is a resistive device, used to attenuate the microwave power and level. Attenuator can be divided into fixed and variable two kinds, can also be divided into absorption attenuator, rotary polarization attenuator and over limit attenuator. Laboratory commonly used absorption variable attenuator, which is installed in the waveguide can be moved within the attenuator, attenuator is coated with a resistive film on the dielectric sheet dielectric sheet (for example, in the glass sprayed nickel-chromium), move the position or depth of the attenuator can be changed on the degree of absorption of electromagnetic waves, thereby changing the intensity of electromagnetic waves within the waveguide, adjusting the strength of the signal.4. Frequency meter (wavelength meter) is the use of resonant cavities to measure the frequency, it is usually used with a coaxial attenuator to measure the power and level of the waveguide. Frequency components, it is usually selected coaxial or cylindrical waveguide for the resonant cavity made of, and "absorption" resonant frequency meter, its cavity through the coupling element coupled to a straight section of the waveguide, when its cavity detuned, the electromagnetic field in the cavity is extremely weak, this time does not absorb the energy, basically does not affect the propagation of electromagnetic waves within the waveguide, and accordingly connected to the terminal Accordingly, the oscilloscope connected to the end of the oscilloscope to maintain a constant size of the signal output. Move the position of the piston at one end of the resonant cavity to change the length of the resonant cavity, you can change the intrinsic frequency of the resonant cavity. When its intrinsic frequency is the same as the frequency of the microwave, *** vibration absorption occurs, absorbing energy from the electromagnetic field, so that its energy is reduced, the *** vibration absorption peak. Read the indication of the micrometer at this point, check the corresponding frequency from the attached table, and use the relationship between wavelength and frequency to find out the wavelength of the electromagnetic wave in free space. Wavelength table (frequency meter) Load 5 load microwave transmission access to some components of the electromagnetic wave to produce a specific effect, can be divided into matching load and reactance elements (or load). Matching load is usually made in the form of a waveguide, the internal absorption sheet, which is coated with metal fragments of foam (such as platinum) or carbon film dielectric sheet, the medium is generally used glass, ceramic paper, etc., made into a split shape can be slowly absorbed by the microwave, and its shape and size to determine the degree of absorption,. Matching the absorption rate of the load is large almost all the microwave into which the absorption, can be considered non-reflective, VSWR = 1.06. reactance elements including diaphragms, tuning screws and short-circuit piston three. Diaphragm can be divided into: 1) capacitive diaphragm - will be placed in the waveguide so that the electric field is strengthened, equivalent to the capacitor across the line with a double, showing capacitive properties. (2) inductive diaphragm - will be placed in the waveguide due to the diaphragm current so that the magnetic field around the diaphragm is concentrated, equivalent to the cross-connection and double-wire inductors, presenting the inductive properties. (3) Concordance Window - capacitive diaphragm and inductive diaphragm combined together to become the center of the (3) Tuning window - the combination of capacitive diaphragm and inductive diaphragm into a middle hole diaphragm, equivalent to access to a L-C oscillation loop, tuning screw is a rectangular waveguide tube central position when the screw is inserted, the electromagnetic field will be changed: when the insertion of the depth of the shallower (), so that the electric field enhancement, presenting a capacitive; capacitance and inductance are equal to the formation of a series resonance; when the inductive reactance is greater than the capacitive reactance, the presentation of the inductive resistivity. 6) VSW measurement line Measurement line, also called Standing wave measuring line measuring line, also known as standing wave measuring instrument, is used to measure the standing wave distribution law of the instrument, can be divided into measuring standing wave measuring line electric field and measuring magnetic field two kinds. The first commonly used in the laboratory, which consists of a longitudinal slot along the longitudinal section of the straight waveguide with a microwave crystal detector can be moved along the slot with a microwave crystal detector probe probe. Probe through the slot into the transmission line, from which the microwave power to pick up microwave power to measure the microwave electric field strength of the amplitude along the axis of the distribution of the law, the position of the probe can be attached to the measurement line scale or micrometer read out. 7, crystal detector crystal detector core element is the use of semiconductor point of contact diode (also known as microwave diode), its structure as shown in the figure: the shape of the general bullet-shaped shell for the high-frequency aluminum magnet tube; Crystal detector is in the opposite end of the waveguide on the microwave diode, as shown in the figure, the microwave diode will be inserted into the center of the broadside of the waveguide in order to detect the induced voltage between the two broadsides of the waveguide, in order to get a larger detector signal, usually in the short-circuiting piston through the adjustment of its rear end of the position of the diode and the diode spacing is , so that the detector diode is located in the electric field at the maximum. Microwave diode oscilloscope structure schematic 7. Adaptor adaptor is used to adjust the waveguide system to match the state of the device, can be divided into a single screw adaptor, three-screw adaptor and double T-joints adaptor and so on several kinds. Single screw tuner is essentially a rectangular waveguide with a screw, the role of the screw is equivalent to a short-circuit branch connected in parallel at the waveguide cutoff, change the depth of the screw and the location of the waveguide, it can be adjusted to any desired impedance: when inserted into the depth of when it presents an equivalent parallel inductance, when inserted into the depth of when it presents an equivalent parallel capacitance, the value of which is equal to the value of about the time of the series resonance occurs, when the waveguide is in a short-circuit state, in practice, the waveguide is a short circuit. The waveguide is in a short-circuit state, and the insertion depth of the screws does not exceed the resonance depth in practical applications. If three screws are inserted into the waveguide, it constitutes a three-screw tuner, and these two types of tuners are only applicable to the case of small power. Single-screw tuner Double T-head tuner In addition, there are connecting elements, branching elements (E-plane branching, H-plane branching, double T branching and magic T), directional couplers, loopers.