Learning Attitude

“A fool thinks himself to be wise, but a wise man knows himself to be a fool”.

-William Shakespeare

Antenna Selection

An Antenna is one of the most critical junctions in any RF communication system. It’s performance determines the quality and the continuity of your data flow in both directions.

Common understanding between the system designer, system integrator, the user and the antenna supplier regarding antenna performance.

Top Ten Antenna Questions

What is the operating frequency range of the system? How much gain is required? What kind of radiation pattern is desired? What is the maximum allowable VSWR? What polarization is required? What type of connector interface is required? How much power will the antenna have to handle? Where will the antenna be mounted? Is a radome required? What is the lifetime of the antenna?

What is the operating frequency range of the system?

Before you can specify an antenna, you must know the approximate center frequency and the bandwidth over which it must operate.

Frequency is dictated by the application and the allocations available.

How much gain is required? Antenna performance is primarily established

by its gain . Most commercial antenna suppliers specify gain in

dBd (gain over a half wave dipole). Another reference at microwave frequencies is

dBi (gain over isotropic radiator) a theoretical antenna that radiates equally well in all directions.

e.g Waveguide without Horn

Common communicationantenna types

Type Typical Gain ranges(dBd)

Dipole Omni

Gain Omni Mobile Whips

Corner ReflectorLog Periodic

HornHelix

Microstrip- patchYagi

PanelParabolic Dish

00

3 to 12-0.6 to +5.5

4 to 103 to 8

5 to 125 to15 3 to 153 to 20 5 to 2010 to 30

What kind of radiation pattern is desired? Define the regions for distribution of power. Omni-pattern but higher gain with sector

antennas. What is the maximum allowable VSWR? VSWR represents the degree with which an

antenna is “matched” to the system impedance. What polarization is required? Many systems are challenged because

interfere with adjoining systems.

What type of connector interface is required? How much power will the antenna have to handle?

Type “N”,TNC and BNC connectors are preferred at higher frequencies because they maintain a good VSWR.

If small size and low power operation from 1-10GHz is anticipated, the SMA connector may be preferred.

Inform the antenna supplier the peak power level and comparison of energy levels.

Where will the antenna be mounted? Is a radome required?

The real impact comes when assessing the total environment and whether the antenna will perform and survive once installed.

What is the lifetime of the antenna? The quality of the antenna will match the

quality of the relationship between you and the one who pays the bills.

Microstrip patch antenna designCreate Substrate

Select the menu item Draw > Box

• enter the box position

– X: -7.0, Y: -4.5, Z: 0.0,

• enter the opposite corner of the box

– dX: 12.0, dY: 9.0, dZ: 0.32

Create the FeedSelect the menu item Draw > Rectangle

• enter the rectangle position

– X: -5.0, Y: -0.2475, Z: 0.0

• enter the opposite corner of the rectangle:

– dX: 7.0, dY: 0.495, dZ: 0.0

Dipole design

Pole 1 Dimensions

Center position : 0 ,0 ,0.5

Start position : 0 ,-1 ,0.5

Height=30

Pole2 Dimensions

Center position : 0 ,0 ,-0.5

Start position : 0 ,1 ,-0.5

Height= -30

References

www.astronwireless.com/topic-archives-selecting-antennas.asp

HFSS user manual www.antenna.be/art4.html