ANT - 0000

UNDERSTANDING AND FINDING THE INVISIBLE ANTENNAS IN YOUR DESIGN

By Henry W. Ott Henry Ott Consultants Livingston, NJ 07039 (973) 992-1793

www.hottconsultants.com hott@ieee.org

HOC ELECTROMAGNETIC COMPATIBILITY

© Henry W. Ott2000

ANT - 01028

CONVENTIONAL WISDOM

Conventional Wisdom Says: If it Looks Like a Duck and If it Walks Like a Duck and it Quacks Like a Duck, it Probably is a Duck

EMC Wisdom Says: If it Radiates Like an Antenna and it Receives Like an Antenna and it Doesn’t Look Like an Antenna, it Probably Still is an Antenna

HOC ELECTROMAGNETIC COMPATIBILITY

© Henry W. Ott1998

ANT - 01033

OVERVIEW

• ! Describe the Basic Types of Antennas

• ! Understand What Configurations (Electrical & Mechanical) Form Antenna Structures

• ! Learn to Look at Your Design as if it Was an Antenna

• ! Understand What Parameters Affect the Radiation

• ! Learn to Avoid Using Antenna Configurations in Your Design

• ! If You Must Use an Antenna Structure, Know How to Minimize it’s Radiation Efficiency

HOC ELECTROMAGNETIC COMPATIBILITY

© Henry W. Ott1998

ANT - 01001

MISC. ANTENNAS

Fringing Fields Produce Radiation

Unshielded Center Conductor

Metallic Patch Above Ref. Plane Slot in a Metal Plate

Reference Plane

Slot Antenna

Patch or Microstrip Sleeve Antenna Antenna

HOC ELECTROMAGNETIC COMPATIBILITY

© Henry W. Ott1998

ANT - 01002

BASIC ANTENNA STRUCTURES

! Wire Antennas

— Dipole

— Loop

! Aperture Antennas

— Slot

— Horn

HOC ELECTROMAGNETIC COMPATIBILITY

© Henry W. Ott1998

ANT - 01007

CHARACTERISTICS OF ANTENNAS

• ! Size

• ! Bandwidth

• ! Polarization

• ! Antenna Factor or Gain

• ! Radiation Pattern

• ! Front to Back Ratio

• ! Effective Height or Aperture

• ! Radiation Resistance

HOC ELECTROMAGNETIC COMPATIBILITY

© Henry W. Ott1998

ANT - 01003

DIPOLE ANTENNA

• ! A Dipole Requires Two Parts

• ! What About a Monopole?

• ! If You Do Not Provide the Second Part, The Antenna Will Find Something to Serve the Purpose (Usually The Largest Piece of Metal Nearby)

• ! It is Better to Provide the Second Half of The Dipole Intentionally, at Least Then You Know What and Where it is

• ! The Way to Make an Antenna, is to Have an rf Potential Between Two Different Pieces of Metal

• ! To Prevent the Radiation, Tie the Two Halves of the Antenna Together So That They Are at the Same Potential and, Therefore, Cannot Radiate.

HOC ELECTROMAGNETIC COMPATIBILITY

© Henry W. Ott1998

ANT - 01037

INTENTIONAL RADIATORS

Dipole

V

Monopole

V

Reference Plane

Radiates as Good as a Dipole & is Half as Long

Top Hat

V

Reference Plane

Radiates Better Than a Monopole (Up to Twice as Much)

HOC ELECTROMAGNETIC COMPATIBILITY

© Henry W. Ott1997

ANT - 01004

MONOPOLE CURRENT DISTRIBUTION

MONOPOLE
Tip 1
Long Antenna ( ≥ λ /4)
Sinusoidal Current
(Current Shown For λ /4)
0.8
0.6
I
Short Antenna
0.4
(< λ /10)
0.2
Feed
Point 0
0 0.2 0.4 0.6 0.8 1
Reference Plane
Relative Current Amplitude
Distance Along Antenna

HOC ELECTROMAGNETIC COMPATIBILITY

© Henry W. Ott1998