# Design of phasing coil for GSM antenna

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#### billano786

##### Super Member
I am trying to design a passive GSM antenna around 900 MHz (for 833-960 Mhz band).

What I am trying to do is to stack one 1/4 wavelength monopole (placed at bottom) with another 5/8 wavelength monopole Placed on top) with a phasing coil (in shape of a helix) between them.

Can anyone help me in design of this phasing coil and ground plane? I alos know the way to calculate gain of this antenna. I am looking for a gain of 3db.

#### mamali

##### Full Member level 4
billano786 said:
I am trying to design a passive GSM antenna around 900 MHz (for 833-960 Mhz band).
What I am trying to do is to stack one 1/4 wavelength monopole (placed at bottom) with another 5/8 wavelength monopole Placed on top) with a phasing coil (in shape of a helix) between them.
thus the antenna should be longer than 7/8 lambda0, about 30cm, isnt problem? (do you have freedome just in one dimesion?, i mean, could you consider another type of antennas, or you insist in using this design?)

marti

#### billano786

##### Super Member
I want to stick to this very design only.

You are right that length of antenna is nearly 30 cm but I do not know calculations for phasing coil (number of turns, dia etc.) and ground plane. I also want to know the way to calculate the gain of it.

All sugesstions are welcome.

#### goxy

##### Full Member level 4
I'm not sure in the 1/4 and 5/8 wavelength elements, they should be about 1/2. Bandwidth can not be so wide because coil is resonant structure, about 100MHZ at vswr<2 is expected.
Ground plane can be replaced with a coupler(tube around first element).
Specify your diameter of elements and coil wire(suggested is about 3-4mm because wider bandwith, but question is can you made :shii: a coil from this wire ).

#### billano786

##### Super Member
What I wish to design is like one shown in figure uploaded. Diameter of wire which I wish to use for making element and coil is 2mm. I can easily make coil from this wire.

I have seen number of antennas like this which one element as 1/4 lambda and other as 5/8 lambda.

I do not want to copy the design of any one of these but the aim is to learn the calculation part of these as I am totally new to RF world and this seems to be a good practical application of electromagnetic theory I learnt .

#### goxy

##### Full Member level 4
look in posted example, structure is very simple and easy for analyze.
You have to calculate coils, elements, balun(coupler) and network parametars. For coils impedance in free space may to use above paper by mamali.
Hellen's equation, balun, network analyze... look at books : "Antenna and EM Modeling with Matlab" by Sergey N. Makarov and "Electromagnetic Waves and Antennas " by Sophocles J. Orfanidis, it's free available on www.ece.rutgers.edu/~orfanidi/ewa (don't forget https://www.ece.rutgers.edu/~orfanidi/ewa/ewa.zip Matlab examples).

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