Questions tagged [microwave]
Microwaves are radio waves with a frequency from 300MHz to 300GHz which corresponds to a wavelength of one meter down to one millimeter. Often in RF engineering however it is used to refer to a narrower region such as 1 to 100GHz.
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How does this coupler work?
I've bought a few 50MHz-6GHz directional couplers (SEDC-10-63+,) each for 75$. Here is a picture of this expensive coupler:
Unfortunately one of these couplers was not working from the beginning so I ...
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Time Domain Measurements with Vector Analyzer
In my university I have done some time domain measurements with a VNA (by using the transform operation of the instrument). Precisely, I have selected the measurement of the real part of S11 while ...
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Definition of quality factor as function of frequency
I have seen that some electrical components (which contain R,L,C elements) datasheets shows the curve of the quality factor Q with respect to frequency, and not simply its value at the resonance ...
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Meaning of coupling factor for a resonance cavity
I was reading this paper about resonant cavities, and on page 6 it introduces the concept of coupling factor β, which is defined as the ratio between the power loss in the total circuit (including the ...
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Can a Unilateral Amplifier be Unstable?
When designing microwave amplifiers, stability is an important factor to consider. Stability is usually measured with the K factor. In a unilateral network, S_12 = 0, and this makes the K factor ...
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Magnetic field expression in a rectangular waveguide
I was reading the chapter of Fundations of Microwave Engineering (Robert E. Collin) about transmission lines and waveguides, and I have a question about the electromagnetic field in a rectangular ...
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How to block / lessen EM-radiation/signal from home Wi-Fi router? [closed]
1) What materials and how can I use to completely block radiation from two antennas of my WiFi router?
2) What materials and how can I lessen by 20-50% radiation/signal from the third router antenna?
...
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Attenuators in Waveguides
Let's consider for instance a rectangular waveguide with TE01 mode.
As shown here, a possible attenuator may be realized with a metal card placed so that it is tangential to the electric field. Here ...
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Reflection Coefficient with Electric Field and Voltage
In different situations the input reflection coefficient (of a waveguide, of a transmission line etc) is defined differently.
Wikipedia says:
The reflection coefficient may also be established ...
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Measurement of Isolation in a Directional Coupler
I want to measure the isolation of the following directional coupler (for more details of that specific component, go here).
Isolation can be evaluated through the scattering parameter S21, but how ...
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Importance of EM to microwave design?
I am curious, how important is a general understanding of electromagnetics to microwave circuit design?
I have looked at Pozars book which provides some background on EM and transmission lines in the ...
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Example of computation of S matrix
Let's consider the slide 1 of this material.
I have understood the computation of S11, but not that of S21.
I do not understand:
- why there is the circuit with V and two impedances Z0 and there is ...
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Measurement of Resistor Parasitics Inductance and Capacitance
I have seen people doing some measurements of parasitic capacitance and inductance of some resistors, by using a vector analyzer and analyzing the graph of S11 with respect to frequency.
To get this ...
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Computation of the Scattering Matrix of a Transmission Line
let's consider this transmission line (with losses) in which a and b denote respectively the reflected and the incident waves at each port:
This exercise asks to find its scattering parameters ...
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Orientation of loop antenna (receiving mode)
I have done some measurements through a loop antenna similar to that shown in the following picture (all the information included does not refer to my antenna, it is a picture used only to show its ...
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Voltage on a Transmission Line with Ideal Conductors
Let's consider a transmission line with Perfect Electric Conductors.
We know that if an external AC source is applied, we get a voltage waveform between the conductors which is function of the ...
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TEM Propagation in Infinite Ferrit Medium
I have realised a question on Collin's Foundations of Microwave Engineering book which is related to TEM propagation in infinite ferrit medium.
I could not find a way to establish to relate positive ...
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Transmission Line with Short Circuit and Inductor as Loads
let's consider this situation in which the two ports of a transmission line are connected to a short circuit and to an inductor:
The transmission line is supposed to be lossless. My book makes a ...
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Scattering Matrix with Power Waves and Voltage Waves
I read that for a given N-port network there are two different conventions about defining the incident and reflected waves.
This is the first convention:
This is the second convention (we see that ...
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Evaluation of the dominant mode in a waveguide
In a waveguide, the dominant mode is defined as the propagation mode with the lowest cutoff frequency.
Now let's consider a structure in which the lowest cutoff frequency occurs for two different ...
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Time Domain Analysis with Vector Network Analyzer
I have done some measurements with a VNA in time domain (by using the transform operation of the instrument). Precisely, I have selected the measurement of S11 (reflection coefficient at port 1 of the ...
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What is the switching/amplifier component in a 2.4 GHz wifi microwave transmitter
I know that it is hard for the transistors that i know to switch at high frequency but the latest microprocessors and microwave transmitting chips use GHz frequency, what is the gain element there (...
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Building a personal RF anechoic chamber in a large walk-in closet?
What would one need (besides many foam absorbers) to build an in-home small anechoic chamber for transmissions in the UHF to L-bands (specifically 500Mhz - 2 Ghz), and what resources would you point ...
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Vector Analyzer: what is IF bandwidth?
I noticed that if I set IF bandwidth low, the measures done with a vector analyzer are better (with higher SNR) but it is slower.
Precisely, what does it happen when I change it? Can you explain me ...
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Propagation Constant Expression in a Transmission Line
let's consider a generic transmission line:
Its wave vector Kz is equal to:
where
Then, I read also that it is true that:
where does this relation come from?
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Low and high impedance of low pass stepped impedance filter
I'm designing a low pass chebyshev filter using stepped impedance.
I'm using the book 'Microstrip Filters for RF/Microwave Applications' as a reference.
I have difficulty understanding how low and ...
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Waveguides Equivalent Circuits
I was reading in a book how to derive the equivalent circuits for TE, TM, TEM modes of a generic ideal (without losses) waveguide. After some computations, it found this equivalent circuit for TE ...
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Magnetron Working Principle
I was reading this simple description of magnetron working principle.
Can you explain me why when electrons go near the cavities, they start to resonate at microwave frequency? I do not see the link ...
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Tuning Resonant Cavities
I have seen that some resonant cavities are equipped with some external screws, called tuners, which can be used to vary the resonance frequency.
Can you explain me the physical reason with which to ...
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Charge Distribution on a Microstrip Line
let's consider a microstrip line connected to a voltage source V0 (applied between the strip and GND plane). According to foundation for microwave engineering (collin) book, the surface charge density ...
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Microstrip Voltage Boundary Condition
I was reading some notes about a microstrip line. Here the scheme with the reference system:
In this scheme (sorry for the bad quality of the picture) the upper strip is represented as a charge sheet ...
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Coaxial Cable Resonance
let's consider a coaxial cable of length L and see what happens at port 1 when port 2 is left open. Let's consider what is written on these slides:
1) I do not understand the reason of this graph. In ...
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Frequency dependence of S21
I have done a measurement with a vector analyzer in which I have connected a certain coaxial cable to the two port of the instrument.
Precisely, I have got a measure of the phase of S21 of this type:...
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Phase of Scattering Parameters
I do not understand the meaning of the phase of scattering parameters.
Let's consider for instance a two port network, and let's focus on S21.
I know that its absolute value represents a ratio ...
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What is this microwave component?
I am at-home electronics hobbyist and tend to salvage majority of the components I use from old/broken items. Recently I took apart a microwave and desoldered most of the the components from it. I ...
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Can an electric resonator (like a microwave) be used to effectively heat things other than water at different frequencies?
For example, could you determine the resonant frequency of slag in an ore sample and melt it by putting it in an electric resonator at the appropriate frequency?
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Why do microwave ovens use magnetrons?
With a lot of advancement in solid state electronics and signal manipulation, isn't it easier to simply take high amplitude signals with frequencies near 1 MHz and multiply the signals using diodes ...
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Quality factor and frequency bandwidth in a matching network
It is known that the quality factor appears in the formulas for transformation of an impedance series bipole to a parallel one. A simple example is this one:
Now I have three questions:
I have ...
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Design of attenuators in microwave systems
A thin dielectric strip is coated with a resistive film to attenuate microwave signals. However, the dielectric strip is tapered at both ends to reduce reflections. Why does the dielectric strip even ...
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What is a terminal plane in high frequency circuits?
The term "terminal planes" come up very frequently in books on microwave circuits. What exactly does the term mean?
The closest answer I have got is
A terminal plane, or reference plane, is the ...
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Cut-off frequency in ideal waveguides
it is known that in an ideal waveguide (with a perfect electric conductor and with non-dispersive and non-conductive dielectric) there is a cut-off frequency, for each mode, such that for higher ...
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Excitation of a resonant cavity
let's consider this picture in which a cylindrical resonant cavity is excited through a waveguide.
I have some questions:
1) Why is it called "Magnetic Coupling"? I thought this excitation simply ...
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Get expressions of E and H fields at a boundary from expression of surface current - Pozar ex 1.11
I am bringing whis question because, even though I have the solutions manual from the exercises of the book "Microwave Engineering 4th edition", by David M. Pozar (one of the Bible books for microwave ...
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Characteristic Impedance without transmission lines
let's consider this three port power divider:
I saw somewhere that the reflection coefficient Г11 can be calculated with the formula Г11 = (Zin - Z0)/(Zin + Z0), where Z0 = 50 Ohm.
Now my questions ...
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Deriving microstrip stub equations
Do anyone know how to derive the microstrip stub equations for all four microstrip below ?
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AD8318 Maximum Input Voltage
let's consider AD8318, a chip which contains a logarithmic amplifier, often used for power measurements.
I have read its datasheet and there is a thing that I do not understand: no maximum input RF ...
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Peak Current in a transmission line
Let's consider a transmission line (which drives a generic load ZL) connected to an AC voltage source.
If we know that the peak voltage of the source is equal to Vp, how can we evaluate the peak ...
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Coax characteristic impedance measurement
How is physically possible to get the value of the characteristic impedance of a certain coaxial cable?
Precisely, in my case I have a coax of 50Ohm impedance, and I need to cut it and connect some ...
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Wave Propagation in Transmission Lines
let's consider this image (from AAC book, see here)
The author wanted to show that a transmission line propagates not only voltage and current waves, but also an electromagnetic wave in the space ...
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Antenna's resistance: meaning and evaluation
When I studied elementary antenna's theory, I saw that the resistance (for simplicity let's consider only the resistive terms) of an antenna Ra is made of:
1) a parasitic resistance Rl, which causes ...
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