Questions tagged [antenna]

Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g. TV or radio) waves. -Wikipedia

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Why does an antenna trace have this shape?

I'm wondering why an antenna has a board trace that follows a certain "squiggly" shape. This doesn't have to apply to only antennas; I'm sure that there are other components that have changing paths ...
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42 votes
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Why is 50 Ω often chosen as the input impedance of antennas, whereas the free space impedance is 377 Ω?

In order to efficiently deliver power to a different part of a circuit without reflection, the impedances of all circuit elements need to be matched. Free space can be regarded as a further element, ...
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40 votes
7 answers
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How does an antenna radiate (how do currents flow through the wire)

I don't understand how antennas radiate a signal. I understand the basics of antennas (wavelength, electron E field, etc.), but I simply don't understand how a current can go through a wire that doesn'...
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38 votes
4 answers
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How can a 9mm square antenna pick up GPS?

I'm confused again. Per various antenna dipole calculators online, and if GPS uses 1.575 and 1.228 GHz signals, the dipole antenna needs to be on the order of 10 cm. Yet Adafruit has (or had) tiny ...
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38 votes
3 answers
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Can people act like antennas?

I was watching my oscilloscope as I was holding a very short wire attached to the probe. It was showing about 0 voltage (small spikes) until I touched the metal. When I touched the metal, the scope ...
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37 votes
7 answers
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Why is an inductor not a good antenna?

[An antenna must have] current flowing along its length, so that the resulting fields radiate that energy into space. (Receiving antennas are just this process in reverse). [This] explains why ...
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37 votes
2 answers
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How does a chip antenna work?

There are many guides to using chip antennas, with and without baluns, PCB layout considerations, etc., but I've been unable to find any information on how chip antennas work at a fundamental level, ...
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32 votes
8 answers
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Why don't we use lenses for RF?

Radio waves are a class of electromagnetic waves. Light also is a class of electromagnetic waves. By shaping a material in which the speed of light changes, we can bend the propagation direction of ...
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31 votes
5 answers
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Can I build a camera that is sensitive at 2.4GHz?

I want to build a camera obscura as an art project that produces photos of WiFi signals. The idea for now is to build a 125cm x 125cm x 125cm Faraday cage (using fine copper mesh) with a centered hole ...
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26 votes
7 answers
5k views

Is it possible to generate light with an antenna?

An antenna (e.g. a dipole) is able to radiate at a certain frequency thanks to the EM field generated by a current provided by a signal generator at such a frequency. So, for instance: Voltage source ...
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26 votes
4 answers
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Is an omnidirectional antenna a must for a cell phone?

I have read somewhere (but unfortunately I am not able to remember where) that cell phones do need an omnidirectional antenna. If it is so, what are the reasons for that? Why a normal directional ...
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24 votes
8 answers
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Is it possible to receive information if the received power is below the noise floor?

This relates to my previous question, which I think I have asked in the wrong way: How to insert background EM noise into pathloss equation? I wasn't really interested in detectability of the signal,...
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24 votes
8 answers
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What is a 50-ohm antenna? How would you make one?

This is an intentionally very open ended question. What does it mean for an antenna to be a 50-ohm antenna at some frequency? How do you make a 50-ohm antenna for say 433.92MHz? What are the options? ...
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Why is the reflector on this millimeter-wave antenna spinning?

The WIRED YouTube video Inside Facebook's Quest to Beam the Internet Via Solar Drone and article Inside Facebook’s First Efforts to Rain Internet from the Sky show a dish antenna (starting after 02:00)...
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24 votes
4 answers
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True GPS Location - At the Antenna or Receiver Chip?

Suppose I have a GPS unit attached to an antenna through a 50 meter coax cable. How would the location as calculated by the GPS unit be affected by the cable length? As a bonus question, how would ...
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24 votes
1 answer
876 views

What is the purpose of the elements of this antenna?

I have a 5GHz 23dBi Wi-Fi panel antenna which has the geometry shown in the images below. I have been quite curious as to the purpose of this bizarre antenna design. The elements have such unique ...
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23 votes
2 answers
11k views

Via fences for noise reduction of a chip antenna?

I'm working on a 4-layer PCB that has a wifi module and a chip antenna, the antenna is placed at the corner of the PCB and the copper beneath it is removed, I see that via fences are used on the ...
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21 votes
1 answer
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Designing a GSM PCB antenna

Before someone complains about my crappy design I should tell you that my knowledge on antennas or RF is near zero. I recently worked on a project that required a GSM module. After testing it on a ...
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19 votes
3 answers
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Can I break a radio tranceiving device by operating it with no antenna connected?

People tell me I shall not use my CB-radio station without an antenna connected or it will result in damage of the device. Is this true and why is this?
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19 votes
5 answers
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What do I need in order to build and test a ferrite rod antenna for a specific frequency?

I am trying to piece together what I'd need for a small hobby project. I'd like to build something that is basically the equivalent to a home made avalanche beacon finder. Avalanche beacons transmit ...
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18 votes
4 answers
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Why does 1/4 wavelength have a ground plane and 1/2 wavelength needs none?

Why does 1/4 wavelength have to have a ground plane and 1/2 doesn't? I know that an antenna that has half a wavelength does not need the ground plane (example a dipole antenna) and when using a ...
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17 votes
4 answers
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Why are wifi antennas covered in plastic?

Couldn't it be like a radio antenna (wifi is radio after all), telescopic and without any encasing?
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17 votes
6 answers
60k views

433MHz quarter-wave length antenna: longer is better?

I am trying to conduct an RF project using XY-MK-5V / XY-FS modules: link here My problem is that even though most blogs and Google searches for these modules use a quarter-wave length antenna (...
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16 votes
6 answers
4k views

Can antennas be viewed as light sources?

Clearly antennas are nothing but a device to radiate the electrical energy through electromagnetic waves. Since visible light is also simply a certain range of frequencies, isn't it more easier to ...
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16 votes
3 answers
4k views

What does the radiation from an antenna look like?

Just out of curiosity, I searched for antenna on Google Images, and what usually shows is something like this. So I really thought that an antenna radiates in a circular and equal pattern. But as I ...
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3 answers
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What is this circuit diagram found on an FM transmitter?

This is the circuit diagram on the transmitter at a local FM radio station I clean at (I'm a janitor,) but I'm also studying electrical engineering. I'm puzzled by the circuit diagram on the ...
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16 votes
3 answers
11k views

How does a Theremin "antenna" work?

I always assumed that the shape of the antennas was important; a vertical monopole for pitch and a horizontal loop for volume, thinking that this minimized their interference with each other. But it ...
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15 votes
5 answers
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Are antennas specified for a certain frequency?

"LTE 868 MHz Antenna" Why does 868 MHz stand for? Are antennas specified for a certain frequency or is it necessary for something like input type? For example, I want to transmit a 40 MHz RF ...
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15 votes
8 answers
37k views

Are TV coaxial cables compatible with WiFi antennas?

If I replace an old, roof-mounted TV antenna with a 2.4GHz WiFi (IEEE 802.11) antenna; can I use the existing coax? Or will I need to run all new cable?
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15 votes
2 answers
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Through-Glass WiFi Antenna

I used to install a lot of in-car UHF radios & hands-free cell phone kits. I mostly worked on trucks & commercial utility vehicles fitted with bull bars, upon which I would mount a big, bulky, ...
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15 votes
1 answer
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PCB clearance/keepout area surrounding wireless antenna

Suppose a PCB antenna or chip antenna is integrated onto a board design with a wireless IC, e.g. a Zigbee or Bluetooth module. What are some guidelines regarding clearance/keepout area on the PCB ...
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14 votes
4 answers
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How does a GPS antenna have only two connections yet have all this circuitry inside?

This GPS module I have broke (just gets hot and won't work) so I took it apart and am amazed to see all of this circuitry under the ceramic antenna but only two connections (gnd and signal). When ...
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14 votes
1 answer
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Need help with selecting an antenna for PCB

I have designed a pair of circuits which utilize the QAM-TX2-433/QAM-RX2-433 transmitter/receiver. So far everything is hooked up on solderless breadboards, with just a length of wire for antennas. ...
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13 votes
4 answers
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Why would a time signal receiving watch have an airplane mode?

I've been looking at radio controlled watches online. I noticed that some radio controlled Casio watches have an 'airplane mode', which disables GPS and terrestrial time signal reception: Now, why ...
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13 votes
6 answers
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Simulate bad cell phone reception in the lab

I'm currently developing an internet of things device that utilizes a uBlox SARA-U260 gsm/3G modem. In field testing, we have had significant software/firmware issues due to poor cell phone reception ...
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13 votes
4 answers
27k views

How do you build your own RFID reader?

What's involved in building your own RFID reader? As you guys would know industrial RFID readers aren't cheap, how do you energise the antenna, then read back the output?
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13 votes
3 answers
10k views

How does a wifi antenna work in full-metal laptops?

As far as I understand, metallic covers of devices like MacBook Air should shield the interior from electromagnetic waves rather effectively. Even if a wifi antenna is right behind the screen, the ...
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13 votes
3 answers
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What's the purpose of such weird wiring inside this smart card?

Here's a scan of a stripped MIFARE Ultralight smart card That's some plastic film with (I assume aluminum) foil wiring acting as the antenna for both powering the chip and providing radio ...
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13 votes
5 answers
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How is it possible to have a 5W transmitter driving 50 ohms with a 12V supply?

So let's say you have a circuit, which generates a carrier wave at some frequency (let's say 27MHz) and it's connected to a 50 ohm dummy load (which I gather is equivalent to an antenna for circuit ...
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13 votes
5 answers
8k views

Antennas and Ground Planes

I'm looking at this datasheet for the ANT-433-HETH antenna. In the box labeled "Suggested Board Layout" I see a dimension labeled "Minimum Distance to Ground Plane" of 0.5 inches. I always thought ...
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13 votes
2 answers
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Why do some radio antennas require a path to ground and some do not?

I'm currently learning the basics of radio and have noticed that some radios, such as crystal radios, have a monopole antenna that is essentially a wire buried in the ground. However, other radios, ...
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12 votes
3 answers
9k views

Do square wave exist?

If we send a square waveform through an antenna, will we get square electromagnetic waves with electric and magnetic fields looking like squares? Also, since there is an abrupt/almost jump in ...
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11 votes
5 answers
84k views

Does higher dBi mean further range, for an antenna?

I recently purchased this (ridiculously expensive) Bluetooth module for my Arduino from SparkFun. On the item's page it says that it has been tested at 100 m. I contacted SparkFun for info about ...
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10 votes
2 answers
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Difference between Hirose U.FL and IPEX connectors

Both these connectors are used to connect antenna to Mini PCI cards. Wikipedia does not explain the difference between those naming issues: U.FL, IPEX, IPAX, IPX,[1] AMC, MHF and UMCC is a ...
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2 answers
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What piece of technology is able to record the exact phase of microwaves?

I had this question on the physics community, but I thought this would be appropriate to cross-post here. I read that in VLBI, the signals of microwaves (on the millimeter scale) are recorded and ...
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10 votes
3 answers
8k views

Directionality and gain: yagi versus parabolic antenna

I have a very remote cabin at 1000m (3000f), where I have close to no phone reception, so lately I have been trying to research as much as I can fathom of radio basics, but still without being able to ...
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10 votes
4 answers
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Why can a feedline be cut randomly when the antenna needs a specific length?

With a mobile two-way radio you have the radio, an antenna mount kit and the actual whip antenna. The antenna needs to be trimed to the correct length so to match the freequency you are Tx/Rx on. ...
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10 votes
2 answers
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Which antenna to use if close proximity to metal objects is unavoidable?

In my application, the device is going to be placed on top of a metal disc, less than a centimeter away from the pcb! Now I have prototyped up the device using a nRF24L01+ breakout board with only a ...
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9 votes
2 answers
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Where is the antenna in this remote control board?

This is a PCB of a (radio?) remote control.
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9 votes
5 answers
8k views

Why can only analog signals pass through air (wireless channel)?

I read the following in a book: "When the transmitted signal is passed through the air using electromagnetic waves, it must take the form of a continuous (analog) waveform." Why is this so? Why ...
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