PIFA antenna Squint problem

[yefj]

Hello ,I have desighned a PIFA antenna as shown bellow..
But when i did the cut plane i see that it has a squint of 8 degrees.
what could be done to move the beam to 0 degree?
Thanks.

 

[biff44]

you would have to screw around with the ground plane shape to correct for that.
the ground plane needs to be bigger, for instance

and if you actually made one and tested it, you would have to be very concerned about how you connected to the antenna,
so that cable surface currents were minimized

 

[yefj]

pifa antenna is placed on cell phone,
how to chose the ground plane size and antenna location i need to use?
Thanks.

 

[vfone]

Moving the feeding point towards the center of the antenna may help a bit in this regards, but the antenna input impedance may be different.
Why would you need to correct 8 degrees squint, when anyway the mobile phone will rotate and tilt in almost all directions...

 

[yefj]

the problem is that all the articles of PIFA doesnt mention how to plan the groud plane in the simulation.
When i encresed my ground plane to 2*lambda on each direction.
I got the matching and radiation pattern totally ruined.
I dont know why.
When i start building an anteena how to deside what ground plane size to use?
Thanks.

 

[biff44]

the problem is that all the articles of PIFA doesnt mention how to plan the groud plane in the simulation.
When i encresed my ground plane to 2*lambda on each direction.
I got the matching and radiation pattern totally ruined.
I dont know why.
When i start building an anteena how to deside what ground plane size to use?
Thanks.

you seem surprised that when you integrate an antenna design onto a PC board that is chock full of componentes, and oddly shaped, that the antenna pattern is not perfect.
i hope this does not come as a big shock to you, but microwaves are MUCH more complicated than they taught you in school.

an experienced engineer knows their system gain reqiurements, that yield a min/max antenna gain requirement, and figures out how to meet that. they do NOT worry, even a little, that the antenna pattern is not "perfect"

one example, did you simulate a person's hand holding the cell phone case with this antenna inside of it? or did you not bother with that huge effect?

 

[volker@muehlhaus]

I'm a bit surprised that you designed a PIFA with almost square radiator !? The PIFA designs that I know (or created) all have "narrow" wire-like radiators. Are you sure there is no patch-antenna mode in your design?

 

[vfone]

The antenna with narrow strip radiator is an Inverted-F antenna:

Antennas: The Inverted-F Antenna (IFA)

The inverted-F antenna, or IFA, is described. This antenna is a quarter-wavelength resonator, and is commonly used as a mobile or cell phone antenna.

www.antenna-theory.com

when the antenna presented above is a Planar Inverted-F antenna, which use a metal plate for radiation:

PIFA - Planar Inverted-F Antennas

Shorting pins used in patch antennas are discussed. These can add a design parameter or degree of freedome that allows the performance to be tuned. The PIFA (Planar Inverted F Antenna) is discussed.

www.antenna-theory.com

PIFA (the same as IFA) use a shorting pin to the ground. Both types are monopole antennas, where the entire metal will radiate (faithfully), compared to patch antennas where the radiation happen due to fringing fields.
But of course, PIFA has radiation from parasitic fringing fields, when also patch antennas have some parasitic radiation from the metal plate.