Antennas Short notes | Electromagnetics - Electronics and Communication Engineering (ECE) PDF Download

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Short Notes on An tennas
1. In tro duction
• An tennas are devices that con v ert electrical signals in to electromagnetic (EM) w a v es and vice v ersa.
• Essen tial for wireless comm unication, radar, broadcasting, and remote sensing.
• Op erate b y radiating or receiving EM w a v es, c haracterized b y parameters lik e gain, directivit y , and
e?iciency .
2. Basic Principles
• Radiation : A ccelerating c harges in the an tenna pro duce EM w a v es.
• Recipro cit y : An tennas p erform equally w ell for transmission and reception.
• F requency Dep endence : An tenna size scales with w a v elength ? = c/f , where c is the sp eed of
ligh t.
• Radiation P attern : Describ es angular distribution of radiated p o w er.
3. T yp es of An tennas
• Dip ole An tenna : Simple, half-w a v elength (?/2 ) wire, omnidirectional in plane p erp endicular to
axis.
• Monop ole An tenna : Quarter-w a v elength (?/4 ) o v er a ground plane, used in mobile devices.
• Lo op An tenna : Circular or square lo op, used for lo w-frequency reception.
• P arab olic Dish : High-gain, directional, used in satellite comm unication.
• Horn An tenna : W a v eguide-fed, broadband, used in micro w a v e applications.
• P atc h An tenna : Flat, compact, used in wireless devices (e.g., Wi-Fi, GPS).
• Y agi-Uda An tenna : Directional, with driv en elemen t, reflector, and directors, used in TV recep-
tion.
4. An tenna P arameters
• Gain : Ratio of radiated p o w er in main direction to isotropic radiator, in dBi.
• Directivit y : Measure of ho w fo cused the radiation pattern is:
D =
4pU
max
P
rad
where U
max
is maxim um radiation in tensit y , P
rad
is total radiated p o w er.
• E?iciency : ? =
P
rad
P in
, accoun ts for losses.
• Bandwidth : F requency range o v er whic h an tenna p erforms effectiv ely .
• Imp edance : Should matc h transmission line (e.g., 50 ? ) to minimize reflection.
• P olarization : Orien tation ofE -field (linear, circ ular, elliptical).
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Short Notes on An tennas
1. In tro duction
• An tennas are devices that con v ert electrical signals in to electromagnetic (EM) w a v es and vice v ersa.
• Essen tial for wireless comm unication, radar, broadcasting, and remote sensing.
• Op erate b y radiating or receiving EM w a v es, c haracterized b y parameters lik e gain, directivit y , and
e?iciency .
2. Basic Principles
• Radiation : A ccelerating c harges in the an tenna pro duce EM w a v es.
• Recipro cit y : An tennas p erform equally w ell for transmission and reception.
• F requency Dep endence : An tenna size scales with w a v elength ? = c/f , where c is the sp eed of
ligh t.
• Radiation P attern : Describ es angular distribution of radiated p o w er.
3. T yp es of An tennas
• Dip ole An tenna : Simple, half-w a v elength (?/2 ) wire, omnidirectional in plane p erp endicular to
axis.
• Monop ole An tenna : Quarter-w a v elength (?/4 ) o v er a ground plane, used in mobile devices.
• Lo op An tenna : Circular or square lo op, used for lo w-frequency reception.
• P arab olic Dish : High-gain, directional, used in satellite comm unication.
• Horn An tenna : W a v eguide-fed, broadband, used in micro w a v e applications.
• P atc h An tenna : Flat, compact, used in wireless devices (e.g., Wi-Fi, GPS).
• Y agi-Uda An tenna : Directional, with driv en elemen t, reflector, and directors, used in TV recep-
tion.
4. An tenna P arameters
• Gain : Ratio of radiated p o w er in main direction to isotropic radiator, in dBi.
• Directivit y : Measure of ho w fo cused the radiation pattern is:
D =
4pU
max
P
rad
where U
max
is maxim um radiation in tensit y , P
rad
is total radiated p o w er.
• E?iciency : ? =
P
rad
P in
, accoun ts for losses.
• Bandwidth : F requency range o v er whic h an tenna p erforms effectiv ely .
• Imp edance : Should matc h transmission line (e.g., 50 ? ) to minimize reflection.
• P olarization : Orien tation ofE -field (linear, circ ular, elliptical).
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5. Radiation Mec hanism
• Driv en b y alternating curren t, pro ducing time-v aryingE andB fields.
• Near field: Reactiv e region close to an tenna ( r <?/2p ).
• F ar field: Radiativ e region where fields deca y as 1/r , used for comm unication.
• Radiation resistance: R
rad
, part of an tenna imp edance con tributing to p o w er radiation.
6. Applications
• Wireless comm unication (cellular, Wi-Fi, Blueto oth).
• Broadcasting (AM/FM radio, TV).
• Radar systems (w eather, military).
• Satellite comm unication and GPS.
• RFID and IoT devices.
7. Practical Considerations
• Size : Smaller an tennas (e.g., patc h) for compact devices, larger for high gain.
• Matc hing : Use baluns or matc hing net w orks to ensure imp edance compatibilit y .
• En vironmen t : Nearb y ob jects affect radiation pattern and imp edance.
• Losses : Conductor and dielectric losses reduce e?i ciency .
• Arra y An tennas: Multiple elem en ts impro v e gain and steerabilit y (e.g., phased arra ys).
8. Conclusion
• An tennas are critical for e?icien t EM w a v e transmission and reception in wireless systems.
• Understanding their t yp es, parameters, and design considerations is essen tial for optimizing p er-
formance in div erse applications.
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