Antennas and Propagation (T5-T8)
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45 Terms
The polarization of a patch antenna can be changed by changing
the feeding point location
The uncertainty in the permittivity of the substrate has a high impact on the patch
operational frequency
The narrow bandwidth of a patch antenna is due to
the similarity to a cavity and resonant condition
The efficiency of a patch antenna is
around 30%
The main advantage of microstrip antennas is
their convenience of fabrication and integration with circuits
The fact of obtaining in the process a value of W>L
It is not important as the feeding in the middle of W makes that the lowest resonance is defined by L
How is the physical length of the patch in relation to the length of a corresponding cavity?
shorter
If I wish to keep the same operational frequency with a laminate with higher permittivity I should
decrease L
The formulas to calculate the effective permittivity of the patch and the line are
dependent on the W/h ratio of the antenna and the line respectively
The starting point of the design process is
W
The magnetic field on the aperture
has a electric field associated that is actually Ea
The electric fields in an elemental aperture
are uniform (constant) in all the aperture
The maximum radiatied power density of an elemental aperture is in the direction
Theta=0o
In the mathematical calculation of the radiated power of an elemental aperture
it is assumed that the aperture radiates in the whole 3D space
The directivity of the elemental aperture
is always 4.77 dBi no matter the field value
The maximum directivity of a horn happens when
the product of Aphy x eta_ap is maximum
The directivity of a non uniform aperture depends on
The physical area of the aperture and the level of uniformity of the field in the aperture
For a particular operational frequency in a E-plane horn antenna, if we increase the dimension a
it depends on the original value of a
The orientation (polarization) of the radiated field of a horn
is the same as the mode of the waveguide from which it is derived
For a particular operational frequency in a E-plane horn antenna, if we increase the Le for the same area of the aperture
The directivity increases
If the primary source of a parabolic reflector is a pyramidal horn antenna with the longest dimension being horizontal
The polarization of the reflector is vertical
The basic principle of a reflector antenna is
to make the reflected rays interference constructive by managing path length differences
What of these structures is not a reflector antenna?
a patch antenna
A typical reflector directivity is
35 dBi
The directivity of a reflector antenna
is higher than the primary source
The focal distance is
the r ́ distance from the origin to the point of the paraboloid with theta'=0 condition
Beta is
the maximum angle theta' that covers the paraboloid
The three geometric variables that univocally define a parabolic reflector are
Dr, f and beta
When symmetry happens around z axis in a parabolic reflector
The geometry does not depend on phi
The sweeps of angles thar cover the whole parabolic reflector are
phi' between 0 and 2pi and theta' between 0 and beta
Las pérdidas por reflexión en el suelo
Dependen de la altura de las antenas
La reflexión en el suelo puede dar origen a un aumento de la señal recibida
Verdadero
En la estimación de las pérdidas por reflexión en el suelo …
Se aproxima el coeficiente de reflexión en el suelo
Las pérdidas de enlace crecen con la frecuencia
Si la ganancia es aproximadamente constante con la frecuencia
La ecuación de Transmisión de Friis es válida
En campo lejano y en espacio libre
El radio de las zonas de Fresnel…
Depende de la posición relativa del obstáculo con respecto a las antenas
La ionosfera
Permite comunicación a grandes distancias
La atenuación por lluvia
Se puede estimar utilizando una atenuación por distancia con datos de normas
La atenuación por onda de superficie
Es importante a bajas frecuencias
La absorción molecular
Es importante a altas frecuencias
El modelo de Motley- Keenan es
Indoor
El modelo de Okumura Hata es
semi-empírico
El modelo de Lee es
semi-empírico
El modelo de Ikegami es
Físico
El modelo de Ray Tracing es
Determinístico