Questions tagged [antenna-theory]
Designing antennas, selecting antennas for specific applications, properties of a given antenna design.
3
votes
1answer
279 views
Does a parabolic reflector dish change circular polarity?
I've been receiving satellite signals in the L-band (~1.7GHz), recently.
These signals are RHCP. So far, I've been using a DIY helical antenna in axial mode, and a patch antenna with cropped or ...
3
votes
5answers
58 views
Gain difference between half-wave and infinitesimal dipole?
In discussion around another Q&A here, Glenn W9IQ commented:
The directive gain difference between a half wavelength dipole and an infinitesimal dipole is only 0.39 dB
I'm curious where this ...
0
votes
2answers
82 views
If one were to add reflector elements above and below a dipole would it change the direction to horizontal?
Since adding a reflector and a director horizontally to a dipole (as in a three element Yagi) causes the beam to reflect horizontally, what should happen if reflectors above and below the dipole were ...
2
votes
1answer
74 views
Stacking DB8 “bedsprings”
I'm trying to receive a UHF TV signal 86 miles away. Considering the height of the transmitting antenna and the height of the receiving antenna, I should be able to just make line-of-sight between ...
1
vote
2answers
77 views
antenna theory for beginners [closed]
I am new to amateur radio and am having trouble getting my head around antenna theory. Can anyone suggest a good 'introduction to antennas' that doesn't get too technical? Thanks.
2
votes
1answer
62 views
What does co-phasing of cross-polarized antennas mean?
I was working with the 3GPP release 14.6, and it mentioned that modern communication systems have cross polarized antennas, and in order to perform beam-forming we need to co-phase our pre-coder.
Pre-...
4
votes
2answers
52 views
What are the effects of different feed-line incidence angles?
Consider a dipole antenna fed by a coax (say, longer than the antenna) with a signal reasonably close to the dipole's resonant frequency. Various sources say that the feed-line should approach the ...
7
votes
5answers
172 views
Are there formulae to calculate capacitance and inductance of an antenna?
How to calculate internal impedance of a dipole antenna? Its resistance has two components ie wire resistance and radiation resistance, both these can be calculated using formula. Are there formula to ...
3
votes
1answer
78 views
Twisting copper wire for a less-flexible DIY antenna
I am making DIY antenna for a home project. The antenna is going to be "V-dipole" with leg length about 53cm.
Unfortunately, I didn't find a thick copper wire, but I have a lot of thin core from tv ...
2
votes
3answers
84 views
Do PCB antennas suit for NOAA and ADS-B?
I saw many designs for creating DIY antennas for NOAA (~137MHz) and ADS-B (~1090MHz) but never seen it in a PCB implementation.
So I have a rookie question: why nobody uses PCB antennas for such ...
2
votes
2answers
61 views
G5RV Jr. fed with ladder line and coax
I am a new ham and I was just given a G5RV Jr. I have about 20 feet of coax plus about 60 feet of 450 ohm ladder line I can feed it with. Can I extend the G5RV Jr. feed line with the ladder line I ...
1
vote
2answers
52 views
vertical 40m antenna takeoff angle
I built a 40m vertical using the W8AMZ design https://www.amateurradiosupplies.com/v/vspfiles/assets/images/40m_vertical_monopole_-_manual.pdf
Seems to be working for the most part. But I'm not sure ...
1
vote
2answers
73 views
True near field distance for a short monopole antenna?
Antenna properties:
Height x Diameter = 3.3 inches x 1.4 inches
Test Frequency: 900 MHz
(Wavelength = 33 cm or 13 inches)
I see some conflicting formulas to calculate the near field distance for ...
5
votes
4answers
232 views
Why does not a bigger antenna receive more power?
According to http://www.antenna-theory.com/basics/aperture.php, the power received by an antenna depends on the power density of the incoming wave, the wave length (which I consider to be fixed) and ...
2
votes
1answer
144 views
CB Radio Ground Plane (or lack thereof)
Notice the vertical antenna on the truck. I believe this first antenna is referred to as a "dipole", mounted vertically. CB to coax, coax to antenna.
The shell of the truck is fiberglass. Even the ...
2
votes
1answer
111 views
What type of this antenna is it?
Could you please tell me which kind of this antenna is? I supposed it is a modified dipole, but not quite sure. Is there any available equation for calculating the original dimensions of this type of ...
6
votes
1answer
55 views
Two antennas on different sides of a building
I live in the 4th floor of a building with one side facing south and the other north. I am able to use my 2M mobile base transceiver with a mobile magnet mount antenna placed just outside the window. ...
-2
votes
1answer
109 views
How do I understand this figure about antenna pattern? [closed]
Why the back lobes have such a large area??? I think it may be like https://www.cisco.com/c/dam/en/us/products/collateral/wireless/aironet-antennas-accessories/prod_white_paper0900aecd806a1a3e.doc/...
1
vote
1answer
49 views
Can the Q of a loop antenna be changed?
Can the Q of a loop antenna be changed?
If so what are some common techniques? (Formulae appreciated).
3
votes
1answer
68 views
Understanding of NFC Reader Antenna matching
I have been designing a 20 x 20 cm square NFC reader antenna which looks like this:
In order to make it work and detect NFC tags at certain distance, it needs to be matched. To do that I was trying ...
3
votes
1answer
111 views
Is a J-pole an appropriate antenna for mounting to a steel handrail?
Last year, a group of us placed a battery-powered 2m digipeater using a J-pole antenna on a mountaintop. We're planning on doing the same this year except we plan to use a surge arrestor from the feed ...
3
votes
1answer
73 views
Electrical Earth
I have moved to a new flat which is on the 4 floor, luckily the landlord has let me put an OCF dipole outside with coax feeding through an existing hole in the window frame. I'm looking for some ...
3
votes
1answer
57 views
Antenna Patterns and Multipath Effect
It's said that in order to decrease multi-path effects on receiving antennas that your antenna pattern should have a sharp slope near the horizon. Why?
for example this is article mentioned it.(...
4
votes
2answers
208 views
Antenna Efficiency
Intuitively, we all understand that an antenna at fractional wavelengths will not radiate well even with perfect impedance matching systems.
From what I understand the efficiency of antenna has a ...
3
votes
1answer
63 views
Skin effect - rough versus polished surface
Considering "skin effect", does the surface finish of Aluminum tubing have any practical effect on antenna efficiency at HF frequencies (5-30 MHz)?
For example: Aluminum tubing as manufactured - rough ...
4
votes
1answer
159 views
Microstrip Loop Antenna Design
I am trying to design a loop antenna for operation at 2.4 GHz, I would like for it to have above 2.5 dB gain at 2.4 GHz and have relatively good return loss (<-10 dB).
I have started my design as ...
6
votes
4answers
247 views
Why do we distinguish between balanced and unbalanced?
I hear all the time, "you need a balun between your balanced dipole and unbalanced coax to stop the common-mode current" when it seems the proper advice is "you need something to stop common-mode ...
3
votes
1answer
121 views
What is the turn spacing on a Helix Antenna?
I want to do some satellite communication so I thought why not build my own helix antenna.
I found this page:
Helix antenna design and construction details
The most things are clear except for the ...
2
votes
2answers
335 views
How do you calculate the field strength at a given distance?
Given this question from the full license exam in the UK:
What is the field strength at a distance of 7m from an antenna with an effective radiated power of 100W?
in which the answer is:
10 V/m
...
4
votes
3answers
219 views
Can an antenna be too powerful for certain receivers?
I'm brand new to shortwave radio and have been researching what kind of a receiver to get. I'll use it on the antenna I'll build (longwire, 50-100 feet) for shortwave listening; no transmitting. Right ...
3
votes
3answers
302 views
How can I calculate the 1/4-wave monopole impedance dependence on groundplane angle?
I watched this video of a very nice explanation of a simple dipole and 1/4-wave monopole. In that video they show how you can impedance match the 1/4-wave monopole by bending the 4 (virtual ground ...
2
votes
1answer
46 views
How to consider the influence from the PCB that a small antenna is mounted on?
The small antenna itself has an S11 of -3 dB around MICS band (verified with simulation and network analyzer). In application, the antenna is mounted on a transceiver PCB of 30*15*0.8 mm which has 2 ...
2
votes
1answer
214 views
Feedline and balun for 80m horizontal delta loop
I am new to HF. I'd like to put up an 80m delta loop. Due to aesthetic considerations I need to use coax to the shack. If tuned for 3.55MHz, I anticipate having a good SWR on 80m, 40m, and 20m. The ...
3
votes
2answers
179 views
How low can a vertical dipole be mounted?
An answer to this question suggests that raising a vertical dipole sufficiently can create the effect of a phased array. How about the opposite.
How low can a vertical dipole be mounted?
Can a ...
3
votes
2answers
88 views
What is the easiest way to eliminate a beam antenna's backward radiation (rear lobe)?
I tried a metallic reflector which works well in terms of radiation, but considerably degrades the return loss and adds more complexity to the design.
0
votes
1answer
154 views
Gain in long wire antennas
DARA (you know, Hamvention) TNG is looking for projects. Thursday, I will be proposing building and characterizing a vertically-polarized 1 wavelength on a side reentrant rhombic.
Since in doing the ...
1
vote
1answer
156 views
SDR - discone antenna setup
Here's a picture of my SDR receiver setup...
This entire setup lives indoors as I'm not able to put anything up on the roof right now.
My understanding of a discone antenna is that the downward ...
1
vote
1answer
390 views
Designing VLF antenna
I was doing some research about the relation between wavelength and antenna size and shape. I was mostly interested in 15KHz rf range.
Based on my research I found the following:
A squarish shape ...
2
votes
2answers
113 views
Physics behind this decametric radio telescope
I am following this design for a simple decametric radio telescope.
I understand the principle that a radio wave hits the metal inducing an electric current that can be measured, but I do not ...
2
votes
3answers
123 views
Which antenna would you use?
I'm starting to study RF propagation at college, and I'm thinking about what antenna I should choose for this scenario:
The distance between the transmitter and receiver is just 700 meters, and the ...
3
votes
2answers
113 views
Can you create a radio beam with a Faraday cage?
Imagine we have an isotropic antenna at the origin emitting a steady sine wave at frequency $f$. Encompassing the antenna is a sphere of radius $r$ made of a fine copper mesh (with holes $\ll\frac\...
4
votes
3answers
2k views
Aluminum vs copper antenna element lengths
Does the particular metal used in antenna elements make any difference in element length or spacing, i.e. 1/2" aluminum tube vs 1/2" copper tube?
I know that length and diameter have an effect on ...
3
votes
3answers
110 views
Could 8' Marine whip antennas operate on much higher frequencies?
I have backgrounds on electrical communications, but know little about EM/RF.
I would like to install outdoor antennas for experiments (receive only; I do not hold licenses, although I do intend to ...
5
votes
2answers
137 views
Radials on a vertical, spread out evenly or not?
To have a groundmounted quarter wave vertical with a decent efficiency you need at least 16 radials.
So normally you would spread them out on the ground evenly around the base. This would give an ...
0
votes
3answers
222 views
Total cancellation in corporate feed network for patch antenna
I'm trying to build an array of patch antennas in order to receive a GPS signal. The idea is to build 4 patches and connect them with a corporate feed network. An example of corporate feed is this one....
2
votes
3answers
797 views
Feeding a dual-band UHF and VHF Yagi antenna
I just built a UHF Yagi antenna for my HT, and I was thinking about adding VHF elements. If I do, could I just connect the coax directly to both sets of elements without a diplexer?
1
vote
3answers
184 views
Would the antenna described work?
For reception of amateur radio satellites, turnstile antennas (consisting of two crossed dipoles fed out-of-phase) are often used.
I've recently had an idea - what if two half-wavelength dipoles are ...
0
votes
2answers
253 views
Do the radials of a quarter or 5/8 wavelength antennas connect to the braid of the coaxial cable?
I'm studying for my foundation license (in the UK) and I have these diagrams:
Do the radials in a quarter or 5/8 wavelength antennas connect to the braid/shield of the coaxial cable? If so, how does ...
1
vote
1answer
66 views
Resistance of antenna dipoles
A quick question: Is it a disaster if the two legs of a v-dipole antenna are different resistances? Thanks.
3
votes
2answers
658 views
Optimising a small magnetic loop with 1:1 SWR but little radiation
I'm trying to build a small magnetic loop for 5W on at least 40m - 20m following ideas of G4ILO's wonder loop. For this, I'm using coax with a ~2mm copper core and ~1mm spacing to the braid (see 1st ...
