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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1answer
54 views

Why do dielectric waveguides support hybrid modes and metallic waveguides do not?

Can anyone explain to me qualitatively why dielectric waveguides (core and infinite cladding) support hybrid modes (E_z and H_z components in the guided wave), while metallic waveguides cannot? I am ...
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3answers
557 views

What's the use of an impedance matching network when the transmission line has the same impedance of the antenna?

I'm designing a PCB including Quectel's BG77 LTE module. In the application note I read: The antenna ports have an impedance of 50 Ω. Then this reference design is proposed for the antenna interface:...
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2answers
98 views

Trace capacitance vs telegraphers equation

I haven't taken a course on transmission lines or RF so bear with me. Using EM we can calculate the capacitance and inductance of traces. I'm somewhat confused on the value of this calculation, though,...
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95 views

Why does the IF of an RF mixer not go down to DC?

Consider this mixer: “SMA Triple Balance Mixer RF/LO Freq. 6-18 GHz IF Freq. 2-8 GHz” If my RF is 18 GHz and my LO is 17 GHz then the IF should be 1 GHz. But the product somehow has a minimum of 2 GHz....
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1answer
51 views

Problem with S parameter calculation

A load of 50Ω is connected in shunt in a 2-wire transmission line of Z0 = Ω 50 as shown in the figure. The 2-port scattering parameter matrix (S-matrix) of the shunt element is: Method 1 The line is ...
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44 views

Input and output impedance matching for the HMC414 amplifier

I have a question about the impedance matching at the input and output of the HMC414 power amplifier. I don't know exactly where to put this matching, and I wouldn't want to make a mistake. The ...
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51 views

What type of polarization does this wave have?

I just took a test today and one of the questions asked was to classify the polarization of a wave. The wave consisted of x/y components $$E = 3\cos(wt-kz) x + 4 \cos(wt-kz) y$$ I classified this as ...
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26 views

Deriving S-Parameters for Hybrid 90° Coupler with Isolated and Delayed P Shorted from 90° Hybrid Coupler S-Param Matrix

I'm trying to derive the s-parameters for a 90 degree hybrid coupler using the s-parameter matrix that is known for a coupler of this type when the ports are configured correctly. In this situation, I'...
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1answer
43 views

The field in a waveguide at exactly the cut-off frequency

Can anyone explain to me qualitatively, what kind of field exists inside a waveguide at EXACTLY the cut-off frequency? I would be grateful if an explanation was given about waveguides with metalic ...
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5answers
1k views

Why do we need to use transmission line theory?

I just started to learn transmission line theory. I'm still confused about a lot of things. Every source says that we need to use transmission line theory when the length of the wire is 1/4 or longer ...
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1answer
63 views

Are microwave SPDT switches typically reciprocal?

This is something of a basic question, but don't want to assume prior to buying an expensive switch. Are microwave (think up to 20GHz) switches typically reciprocal? When reading specification sheets, ...
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1answer
116 views

Decoding/Demodulating audio data in Patent US4877027A [closed]

I'm interested in decoding/demodulation audio/voice data sent using microwave pulses as described in this patent: US4877027A - Hearing system In the patent it's shown that voices or any other audio ...
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1answer
69 views

How to power this RF microwave solid state switch

I have the following RF switch: After googling for several hours, I have found that it is a solid state switch, from DC to 26.5GHz. I've also been able to test that between the golden plated female ...
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2answers
44 views

Design of feed gap of a dipole antenna

I am unsure of the formula used to calculate the feeding gap of a dipole antenna. When I go through some research papers, the formula given to calculate the feed gap of a dipole antenna is L/200. I ...
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1answer
129 views

Are there non-unscrewable microwave oven bulbs? [closed]

I recently emptied a Samsung microwave oven of its components and came across the lightbulb, which appeared at first glance to be fitted in a diamond shaped holder. Though when I looked through the ...
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1answer
40 views

Why can S21 be simply calculated as 2Vout/Vgen?

For one of the four S-parameters - the S21 - why is that S21 can be translated as 2Vout/Vgen? Is there a simple explanation for it?
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24 views

How can I tell whether a waveguide supports hybrid modes or not?

When studying metallic waveguides, it was taken for granted that the TE and TM (and potentially TEM) formed a complete set, that is, any electromagnetic field in the waveguide could be written as a ...
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48 views

Proof of voltage in lossless line

I'm currently a newbie in electronics engineering, and I want to prove the formula for a lossless Transmission lines, but I'm struggling with it. Assuming we know the formulas for U(z) = Ud0(exp(-γ*z)+...
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71 views

Designing a pseudo-Doppler transmitter

I am thinking about creating a CW transmitter based on the pseudo-Doppler effect (educational purposes, nothing special in mind). For this purpose, \$n\$ antennas will be placed in a straight line, ...
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0answers
38 views

Spurious resonance in microstrip transmission line

We were trying to study the broadband response of a microstrip line on a 1.5mm thick Rogers AD1000 substrate whose Dk=10.7 and loss tangent=0.0023 at 10 GHz. The trace width is 1.2 mm. The S21 is ...
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1answer
66 views

Friis Transmission Equation for Wideband Transmission

it's known the following Friis transmission equation: $$P_{rx} = P_{tx} \cdot G_{tx}(f) \cdot G_{rx}(f) \cdot \left(\frac{c}{4 \pi R f}\right)^2$$ It's nice but, as far as I'm concerned, it works only ...
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1answer
107 views

S Parameters Channel Modelling Time domain representation of insertion loss

Below is the insertion loss waveform obtained after S parameter of a channel.The waveform is in frequency domain. May I know what is the equivalent time domain waveform and how to obtain it from this ...
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2answers
65 views

How is the "open" component of the vector analyzer calibration kit made?

I've done some measures of S parameters with a VNA a long time ago. I'm not an expert om this, but I remember the procedure of calibration, which was using, for a single port, the three lumped ...
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1answer
44 views

PCI wifi board (Ubuntu OS) to experiment with microwave signals

I would like to use a PCI WiFi board under Ubuntu OS to experiment with microwave signals. I would like to be able to access the board through the software driver and be able to turn on or turn off ...
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2answers
324 views

Why are transmission lines and waveguides needed for high frequency?

At low frequency, we can just use a piece of wire to connect electrical components, but why are special transmission lines and waveguides needed for high frequency circuits? Also I am confused by the ...
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1answer
63 views

Wire heating from microwave signal

How would one calculate the temperature change in a wire into which a microwave signal of a given frequency and power is applied?
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1answer
72 views

Trace width at high frequency

What trace width and height is required for a 1 A current at 3 GHz? Can the cross section of the trace be smaller than in case of DC or low frequency currents because of the skin effect? Will the ...
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0answers
37 views

Microwave signal / oscillating magnetic field

What is the most effective way of applying a homogeneous oscillating magnetic field at high frequency(3 GHz) to an area of about 5x5mm^2? Helmholtz Coils are not practical due to the high frequency ...
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1answer
120 views

What resistor is needed to discharge a capacitor of about 3kV (inside a microwave)

I've already made a capacitor discharge tool for a 300V capacitor and works fine using the 2 resistors that were on the PCB with the capacitor. I need to upgrade this to discharge a microwave ...
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73 views

B-field strength inside current loop antenna

I want to comprehend the design of a microwave antenna designed by Sasaki et al. (arXiv:1605.04627 [cond-mat.mes-hall]) As can be seen in Fig 2a the magnitude of B is strongest in the center of the ...
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1answer
51 views

Homogeneous magnetic field inside aperture of PCB

I need to create a homogeneous magnetic field of a certain strength across a 10mm diameter opening of a PCB by using a current track on said PCB around the opening. The signal sent through the ...
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3answers
80 views

Coaxial Connector Termination

I am studying microwave engineering at university, but I never had a possibility to try to manufacture anything that I have been learned in my courses. So I have decided to try it by myself. I have ...
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0answers
42 views

De-embedding ceramic filters

I want to design a diplexer using two ceramic filters. S2P files of the filters are not provided. Therefore, I designed a PCB which can be shown below to obtain their S2P parameters. In the first ...
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61 views

Klystron to klystron cascade

I have been studying and working with RF for quite some time. I do not yet have much knowledge on microwave devices, amplifiers and oscillators like magnetrons and klystrons. I know that the klystron ...
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27 views

Two transmission lines with different media

I have some questions about intrinsic impedance and characteristic impedance. I learned the reflection of a wave occurs if the intrinsic impedance of the materials is different. \$ \Gamma = \frac{\...
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3answers
139 views

Near field and far field EMI

I was reading this article on EMI near field vs far field. I am confused on how the Electric field and Magnetic field are separate within the near field and suddenly after a certain distance, these ...
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0answers
103 views

RF transistor amplifier circuit does not work

I have a microwave NPN transistor (MMBR941LT1) which I want to use as an amplifier for a 2.4Ghz signal (from my Wifi router) but it doesn’t work. The signal is captured by a dipole antenna with each ...
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1answer
99 views

Noise Figure of an Attenuator

it is known that the noise figure of an attenuator is equal to its attenuation coefficient L. A proof of this statement is provided here. Basically, it uses the formula (Reference): $$F = 1 + \frac{...
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1answer
104 views

What is the ABCD matrix of an impedance step?

What is the ABCD matrix of the following configuration, where a transmission line with characteristic impedance \$Z_0\$ is connected to another line with characteristic impedance \$Z_1\$ (if we ...
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2answers
235 views

Glass of microwave oven

From a user who "doesn't know" anything about Maxwell's equations. How to explain simply the behavior of a transparent glass of a microwave oven? Lets the light pass ... but blocks the "...
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1answer
141 views

Faraday Cage - Wavelength and hole size

I read about the faraday cages and understood that the size of the holes should be very small than the wavelength of the signal for effective shielding. But I am really confused due to the ...
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1answer
127 views

Why is a microwave oven equipped with a waveguide? [duplicate]

In a microwave oven, the magnetron connects to the waveguide.  Magnetrons produce microwaves, which are guided into the cooking chamber by waveguides. Why don't we directly connect the magnetron to ...
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1answer
26 views

Is there any relation between distance from source to reflector and standing waves?

When two electromagnetic waves (not considering mechanical waves) having the same amplitude and wavelength, moving in opposite directions are superimposed on each other and create standing waves. One ...
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3answers
132 views

What is the difference (and the link) between the RADAR cross section (RCS) and the equivalent area of the target?

Here it is written that: The radar cross section (RCS) σ of a target is the equivalent area seen by a radar. It is the fictitious area intercepting that amount of power which, when scattered equally ...
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24 views

Is it possible to use a Limiting Modulator Driver as an amplifier?

The MTC5525 is basically a Limiting Modulator Driver for driving LiNbO3 modulators, which for me, says nothing, even after googling for 1 hour. But the seller says it can be used as a power amplifier. ...
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6answers
856 views

A few questions on PIRs and other motion detectors

I grew up incorrectly believing that motion detectors (as part of burglar alarm systems) were designed to detect movement, when in actual fact it is the movement of a heated (like body heat) object ...
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5answers
122 views

Can we use any electromagnetic wave (eg: radio wave, light waves etc) for cooking food?

A microwave oven cooks food using microwaves. The oscillating electric field in microwaves rotates the water molecules in our food. As all waves have oscillating electric fields, my question is why we ...
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21 views

How to design a complementary split ring resonator (CSRR)?

I've been looking for references that could help me to design a CSRR with no success. Basically, given a desired resonance frenquency, I want do design/calculate a CSRR that meet the needs ...
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0answers
56 views

What is the difference between a cavity resonator and a faraday cage?

In my internet research, I found that several people believed microwave ovens act as faraday cages and some said they act as cavity resonators.  I know that Faraday cages block incoming electric ...
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1answer
30 views

Power limiter purpose in a receiver

let's consider the following blocks diagram for a receiver of a pulse RADAR (but I suppose my question regards many kinds of receivers) My book says that T/R Lim means a power limiter which is ...

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