Microwave antenna

F) PRINTED (MICROSTRIP OR PATCH) ANTENNA Cont.

DISADVANTAGES

• Narrow band width ( 1% ) , while mobiles need ( 8% ).
• Low efficiency , especially for short circuited microstrip antenna.
• Some feeding techniques like aperture and proximity coupling are difficult to fabricate.
• An array suffers presence of feed network decreasing efficiency , also microstrip antennas are relatively expensive.

F) PRINTED (MICROSTRIP OR PATCH) ANTENNA Cont.

Microstrip Antennas	Reflector Antennas
Preferred for low directivity applications. Lower efficiency. Suffers low efficiency caused by feed network for arrays. Smart antennas, uses electronic scanning when combined with phase shifters. More accurate manufacturing by photo etching. Feeding is by coupling or coax feed lines.	Performed for high directivity applications as the effect of blockage is less. Higher efficiency. Suffers blockage caused by fixation Struts. Uses mechanical scanning . Less accuracy , sometimes parabolic surfaces are rough. Uses other antenna (dipole , monopole, apertures , etc) as a feed.

MICROSTRIP VS. REFLECTORS

G- PHASED ARRAY ANTENNA

• Is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.
• Phased array transmission is use to enhance transmission of radio waves in one direction.
• A phased array antenna is composed of lots of radiating elements each with a phase shifter. Beams are formed by shifting the phase of the signal emitted from each radiating element, to provide constructive/destructive interference so as to steer the beams in the desired direction