Microstrip Patch Antennas S.Mahendrakumar Asst. Prof. (Sl. Gr.) / ECE VCET

Microstrip Antennas Also called “patch antennas”  One of the most useful antennas at microwave frequencies ( f > 1 GHz).  It usually consists of a metal “patch” on top of a grounded dielectric substrate.  The patch may be in a variety of shapes, but rectangular and circular are the most common. 2

Common Shapes of Patch RectangularSquareCircular Elliptical Annular ring Triangular 3

Construction Thickness of the Microstrip is very small t<<λ. Height is Very Small typically it is λ≤h≤0.05 λ. Length of the path is selected between λ/3<L< λ/2. The value of Dielectric constant typically it is 2.2≤ε r ≤12.

Basic Principles of Operation  At a resonance frequency, a strong field is set up inside the cavity, and a strong current on the (bottom) surface of the patch. This produces significant radiation (a good antenna). h PMC z 6

Feeding Methods

Microstrip Feed

Advantages:  Simple  Easy to use with arrays  Easy to obtain input match Inset Feed Microstrip line Feeding Methods 9

Advantages:  Simple  Easy to obtain input match by adjusting feed position Disadvantages:  Significant probe (feed) radiation for thicker substrates Coaxial Feed x z Feeding Methods x y L W (The resistance varies as the square of the modal field shape.) 10

Advantages:  Less line radiation compared to microstrip feed  Can allow for higher bandwidth Disadvantages:  Requires multilayer fabrication Patch Microstrip line Feeding Methods Aperture-coupled Patch (Electromagnetically-coupled Feed) Top view Microstrip line 11

Advantages:  Feed-line radiation is isolated from patch radiation  Higher bandwidth is possible. Disadvantages:  Requires multilayer fabrication Patch Microstrip line Slot Feeding Methods Aperture-coupled Patch (ACP) Top view Slot Microstrip line 12

Aperture-coupled Patch

Microstrip line feed Coax feed 14

Advantages of Microstrip Antennas  Low profile ( Weight & Volumne)  Easy to fabricate (use etching and photolithography).  Easy to feed (coaxial cable, microstrip line, etc.).  Easy to use in an array.  Support both linear & Circular Polarization. 17

Disadvantages of Microstrip Antennas  Low bandwidth (Narrow band)  Efficiency may be lower than with other antennas. Efficiency is limited by conductor and dielectric losses.  Only used at microwave frequencies and above (the substrate becomes too large at lower frequencies).  Cannot handle extremely large amounts of power (dielectric breakdown). 18

Applications  Satellite communications  Microwave communications  Cell phone antennas  GPS antennas  Radar & Military Application  Telemedicine Applications (WBNA) 19

Numerical Tool for Antenna Analysis

 Computer Aided Design software It makes the Design works easy and helps in solving complicated problems.  Widely used software packages are  HFSS (High Frequency Structure Simulator) software developed Ansoft.  IE3D.  CST Microwave Studio.  Microwave office developed by applied wave research.  Numerical Electromagnetic Code (NEC). 21

Numerical Tool for Antenna Analysis  Advantages  It requires less computational time  Implementation is easy  It does not require rigorous mathematical steps  Accuracy is More  Results are closer to the excremental result. 22

Microstrip Antenna Design Using HFSS 23

Design Pro 24

Fabrication Process 25

Fabricated Antenna 26

Antenna Testing Using Network Analyzer 27

Result 28