14
votes
Accepted
What is the purpose of the elements of this antenna?
It seems to be a patch antenna array, analogous (among many images you could find googling around) to this one:
Patch antenna arrays are a special kind of microstrip antennas. You can find many ...
7
votes
Accepted
What is difference between resonant and non resonant antennas?
A non-electrically-resonant antenna is when the antenna is used at its optimum "natural" frequency. Example: a half-wave dipole where the incoming signal wavelength corresponds to twice the ...
- 467k
7
votes
Accepted
Why are many radar antenna arrays not rectangular but rather octagonal÷icosagonal?
There are several reasons for those shapes.
First, the cut off/rounded corners make it easier to fit into the nose of an aircraft. This is true of the phased arrays, both active and passive, that are ...
- 10.9k
6
votes
Proper way to combine same-frequency PCB antennas
There is no one correct, there's just correct for your situation.
We live in a universe where energy (and, hence, power) is conserved. So once you've made your antenna reasonably efficient, the only ...
- 46.7k
5
votes
Accepted
Can radio waves be focused to a point using a phased array?
To the extent that "focus" and "point" are meaningful, and for "phased array" of sufficient size:
Sure.
Waves are waves, as long as the medium is linear, they work the ...
- 43.3k
4
votes
What is counterpoise?
A grounded surface forces the potential to be zero everywhere on this surface and has the same effect as if the antenna arrangement were mirrored on the earth's surface. If the distance is correct, ...
- 294
4
votes
Accepted
Which is the cause of "scan losses" in a linear phased antenna array?
Steering any real array off bore-sight induces scan loss, or a loss in directivity. In the image you posted with the multiple beams, that graph is likely normalizing the patterns, hence why they all ...
- 614
4
votes
Proper way to combine same-frequency PCB antennas
If the individual elements are linearly polarized and "omnidirectional" then what they really have is a doughnut-shaped pattern. With the antennas vertical, then they are omnidirectional in ...
- 5,909
4
votes
Does antenna arraying for deep space communications affect the CMB contribution?
You're right. However, remember that coherent addition maximimizing the received signal power means that you would correct the phase of the individual received signals before adding up. In that, you ...
- 98.3k
3
votes
Why do we need array antennas?
Array antennas are the basis for beam forming. With array antennas, you can control the directivity by driving each antenna of the array with a different phase.
- 7,725
3
votes
What is counterpoise?
Each dipole by itself has a toroidal radiation pattern. When combined into an array, the resulting radiation pattern still has two symmetrical lobes. A conductive surface reflects the unwanted lobe ...
- 176k
3
votes
Which is the cause of "scan losses" in a linear phased antenna array?
Array factor does not show scan loss. Array factor is merely a multiplier. It's actually a common mistake for engineers to use the array factor as a gain value. Array factor gain does not change with ...
- 295
3
votes
Does antenna arraying for deep space communications affect the CMB contribution?
It appears to me that since the N arrayed antennas are receiving the
CMB simultaneously from the same small bit of the sky (all are aimed
at the spacecraft along a common line of sight)
Two ...
- 467k
2
votes
Accepted
How are antenna arrays synchronized for direction finding/localisation?
Absolutely, that delay difference has to be compensated for in some way. This is usually done by matching the feed line lengths to all of the antennas so they are identical to within some precision. ...
- 41.5k
2
votes
Distance requirements in antenna arrays?
The minimum array size is a function of the antenna radiation pattern, the signal wavelength and the performance goals for the array. For very close spacing, the antennas may even interact with each ...
- 131
2
votes
Distance requirements in antenna arrays?
can antenna arrays be decreased in size if the antenna elements themselves can be decreased in size?
No, they cannot. The antenna arrays work by constructive and destructive interference where, in ...
- 743
2
votes
Accepted
Rayleigh distance of array antenna
The answer is still $$2D^2/\lambda$$ but we need to define D value correctly.
Rayleigh distance of a single horn antenna can be calculated as shown below.
$$R=\dfrac{4A^2}{\lambda}$$
We can define D ...
- 175
2
votes
Difference between IRS and phased array/reflectarray
Phased arrays have a number of transmitters/receivers in parallel that vary the phase in order to digitally form a lens. This lets the transmitters/receivers adjust its gain in each direction ...
- 17.8k
2
votes
Why are transmitting antennas generally larger than receiving antennas?
This depends on the requirements of the application. In some cases, based on gain requirements, the transmitting antenna is larger in diameter than the receiver while in some cases, it is the opposite....
- 504
2
votes
Do beam-forming devices expect a particular antenna configuration?
There are two classes of beamformer. One type has the antenna configuration hard-coded into its mathematics, and attempts to construct geometrically beams towards wanted sources, and/or nulls towards ...
- 171k
2
votes
Accepted
Derivation of Dolph-Taylor Synthesis
The Chebyshev polynomials can be expressed as:
\$T_n(u) = cos(m cos^{-1}u) \$ for \$-1 <= u <= 1\$ and
\$T_n(u) = cosh(m cosh^{-1}u)\$ for \$ |u| >= 1\$
In Dolph-Chebyshev ...
- 3,446
2
votes
Why is the linear phased array pattern a sinc (visual interpretation)?
Why is the main beam direction orthogonal to the horizontal line connecting the single spherical wavefronts?
If the antenna feeds are synchronous (behavior identical to a diffraction grating with &...
- 14.9k
2
votes
Accepted
Can phased-array (ULA) gain tapering effects be modelled using digital windows?
Yes, that is a valid analysis technique. Remember that a phased array antenna is essentially spacially sampling the incoming RF waveform, which is similar to time domain sampling a signal. So the ...
- 10.9k
2
votes
Accepted
Is an antenna array with a tilted (rotated) antenna element always less optimal than a perfectly aligned antenna array?
When discussing a linear array of elements, assuming the elements are identical (uniform linear array), the pattern can be written as:
$$G(\theta) = G_A(\theta)G_E(\theta)$$
where \$G\$ is the total ...
2
votes
How can polar plots of radiation fields/array factors be made by hand?
Assuming you have a list of amplitude vs angle, you just need to plot these points on paper. Polar graph paper would be best (just Google it to get a source for printing it). Even without polar graph ...
- 16.2k
2
votes
What is the maximum possible aperture efficiency of an antenna?
Theoretically there is no limit. Consider a hertzian dipole, this has a constant gain, hence constant effective aperture, but it can be made as small as you like.
As the size shrinks, the bandwidth ...
- 3,446
1
vote
How reflection occuring in antenna fed by transmission line affects performance?
The impedance of the antenna and the transmission line that feeds the antenna must be matched. If not, there will be standing waves. The reflection coefficient impacts the final power available at the ...
- 504
1
vote
Why are transmitting antennas generally larger than receiving antennas?
Why are transmitting antennas generally larger than receiving antennas?
This question would be applicable only to radio broadcast transmitters and receivers.
A full-size, one quarter or one half ...
- 19k
1
vote
Why are transmitting antennas generally larger than receiving antennas?
There could be any number of reasons, but here is one.
Better signal to noise ratio.
The signal strength at the receiver is dependent on the product of the antenna gain for both the transmitter and ...
- 12.4k
1
vote
Combination of different antennas
Technically, yes, the radiation pattern is the sum of the individual element radiation patterns, adjusted for geometric differences in distance to the receiving point. But you're mixing together ...
- 5,909
Only top scored, non community-wiki answers of a minimum length are eligible