E plane tee – axis of its side arm is parallel to the electric field in the main branch.E arm is also called series arm and main arm is called collinear arm. If fields of same magnitude and phase are entered through the opposite sides of main arm then net field in the side arm is zero. If fields entering through opposite sides of main arms are opposite in phase then maximum field will come out through the side arm
H plane tee – side arm is parallel to H filed. H arm is also called parallel arm. Wave coming out of the side arm is additive some of the waves entering the opposite sides of main arm
Magic tee is also called hybrid tee, which is the combination of E arm and H arm. Port 1 and 2 are collinear arms, port 3 is H arm and port 4 is E arm. Wave leaving the H arm is sum of the wave entering through the opposite directions of collinear arm and wave leaving through E arm phasor difference of two input waves
Rat race junction – also called hybrid ring coupler. Used in both RF and microwave system. In its simplest form it is a 3dB coupler and is thus an alternative to a magic tee. Unlike magic tee it doesn’t need any matching structure
Directional coupler is hybrid wave guide. It is a four port device where one port is terminated with matched load. Directivity of directional coupler is the ratio between power output in the coupled auxiliary arm to the power flowing through uncoupled auxiliary arm. Directivity is expressed in decibel. coupling factor is the ratio between power entering main arm to the power coupled in auxiliary arm
Slotted waveguide section – used to sample standing wave in wave guide. Position of the slot doesn’t influence field in the waveguide
Attenuator – is used to provide suitable power level and to isolate source from rest of the equipment. Both fixed and variable attenuators are used.
VSWR meter is a low noise tuned amplifier voltmeter, calibrated in db . It requires a square modulated output
Phase shifter – it consist of a piece of a wave guide and a dielectric material placed inside the waveguide parallel to the axis of the electric vector of TE10 mode . when the dielectric materials moves from the edge of the waveguide to centre then phase of the field changes
Wave guide bends and twists – direction of wave guide can be changed by bends and twists. If broader dimension is bended H field is affected. If smaller dimension is bended E field is affected
Application of magic tee – matching device, isolator, phase shifter, transmit receive switch in radar
Micro wave frequency ranges from 1 GHz to 1000 GHz (0.1 cm to 100 cm). Circulator are used to isolate transmitter and receiver section in radar. Ferrite is used in circulators.Aerial multiplexing equipment is used when traffic requirement exceeds 960 telephone circuits or one television circuit. Aerial circulators are 3 port device used to separate transmitted and received signals when both signals have same polarisation. Here transmitted signals are injected through port A and they are emerged at port C, sometimes it will emerge at port B. received signals are emerged at port C.
If received and transmitted waves have opposite polarisation, then bipolar filters are used for separation. Cavity resonator is a tuned circuit. it is a metallic cavity with silver or gold plating on the interior of the surface. It have high Q (thousands). Klystron used for frequency modulation. Magnetron used for pulse modulation. The modes in a reflex Klystron give the same frequency but different transit times. Klystron operates on the principle of velocity modulation
IMPATT and TRAPATT can be used to generate micro wave signal. TRAPATT diode has higher efficiency than IMPATT diode. TE10 is dominant mode in rectangular waveguide, TE 11 in case of circular waveguide. TEmn and TMmn are possible modes in waveguide. In TM wave m and n are nonzero integers . in TE wave m and n may become zero. M and n represents number of half period variations in x and y axis respectively. Wave angle at cut off frequency is always 90 degree. TEM wave travel along the axis of the guide. TEM wave doesn’t have cut off frequency, so it works in all frequencies. Its wave angel is 0. TEM has no interaction with the guide
For handling large microwave power, the best medium is rectangular waveguide. CFA-Crossed Field Amplifier uses an axial magnetic field and radial electric field. Most of the power measuring microwave devices measure average power. HEMT used in microwave circuit is a low noise Amplifier. A waveguide section in a microwave circuit will act as a high pass filter.
PIN diode can be used as a microwave switch. Tunnel diodes is suitable for very low power oscillator. The noise produced in a microwave tube due to random nature of emission and electron flow is called Shot noise. Transit time noise is important at microwave frequencies. The cavity magnetron uses strapping to prevent mode skipping. The front end of an amplifier chain in manufacture of a communication system is kept immersed in liquid nitrogen to Improve its noise figure. Travelling wave tube (TWT) can be used for amplification of microwave energy. TWT provide more bandwidth than klystron.
The cavity resonator is equivalent to an LC resonant circuit. A high-power microwave pulse of the order of megawatts can be generated by magnetrons. Klystron oscillators are most often used in the frequency range of 3000 to 30000 MHz
Ferrite emitter allow microwave to pass in only one direction. In reflex klystron, If the reflector voltage is made slightly less negative, then frequency will decrease. Frequency of klystron depends on the resonant cavity. Isolator allows a microwave signal to travel in one direction with virtually no loss, but severely attenuates if a signal travels in the opposite direction
In TWT input signal is feed into cathode end of the helix. Traveling-wave tube Is used at frequencies in the order of 8000 MHz. The main benefit of using microwaves is more spectrum space for signals. Magnetic field is introduced into waveguide by a probe. Hot carrier is a popular microwave mixer diode. Gunn diode is a popular microwave oscillator. In a klystron amplifier, velocity modulation of the electron beam is produced by catcher cavity. Magnetron is commonly used in radars.
In TWT, electron beam is density-modulated by helix. Baseband repeater is an active microwave radio repeater which can provide drops and inserts.The microwave beam curves the same of the earth when the value of the correction factor is infinity. Magnetron is most widely used radar transmitter, Periscope antenna has shorten waveguide length. cut-off frequency of a waveguide is the lowest frequency that waveguide operates. Attenuator is used in the traveling wave tube to prevent oscillation
multicavity klystron is not a good low level amplifier because of noise. Cross-field amplifier is a microwave tube with high efficiency. TWT is sometimes preferred to the multi-cavity klystron amplifier because of higher bandwidth of TWT. Telemetry is a microwave communication system which operates at 2 GHz. Cavity magnetron uses strapping to prevent mode jumping
Choke flange may be used to couple two waveguides to compensate for discontinuities in joints. Circulators allow one antenna to feed two transmitter and two receiver simultaneously. Glass tube of a TWT may be coated with aquadag to provide attenuation. Parametric amplifier must be cooled to improve noise performance