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To achieve VSWR of 1 at 2.4GHz using a normal mode helical - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.

 Post subject: To achieve VSWR of 1 at 2.4GHz using a normal mode helical
Posted: Thu Apr 28, 2005 11:07 pm 
hi to all,
Can anyone help me to the VSWR of 1 at 2.4GHz. the parameter is as following:
raduis of wire =0.3mm
diamter of helix coil =3mm
pitch angle =37degree
right handed helix

I attached my file here for ur reference.

** Mesh parameters and points
** d = lamda/4 or 0.125m/4= 0.03125
** N = 3 turns
** S = 0.00710207960366(Base on pitch angle =37 degree)
** r = 0.0003m or 0.3mm
** D = 0.003m or 3mm
** h = 0.002m or 2mm
** Max wire segment length = 0.05m or 50mm
** Max Segment Length = 0.0019m (20 segments in 1 coil)
** All values in m


** Tuning Parameter
** #d is the lambda or distance between the 2 helical antenna
** #r is the radius of the helical wire
** #seg is the number of segments on the helix coil
** #s is the spacing between coil turn
** #c is the diameter of the helix coil

** #d = 0.0
** #r = 0.0003
** #seg = 0.002
** #z = 0.0079
** #c = 0.0023

** Wire segment length h
#h1 = 1.0
#h2 = 1.0

#d = 0.0 **Lambda Distance
#e = 0.0 **X coordinate
#r = 0.3 **Helix Radius
#seg = 2.0 **Helix Segment
#s = 7.1 **Turn Spacing
#c = 3.0 **Helix Circumference


** Frequency
#freq = 2.4e9

** Parameters for segmentation
IP #r 50


** Left Side
** Parameters for helix segmentation
LA 1
DP A1 #e -#d #h1
DP B1 #e -#d #s
DP C1 #c -#d #h1

** Right handed helix (1)
HE A1 B1 C1 1 3 #seg

** Define the endpoints and create the wire segment h
DP D1 #c -#d #h2
DP E1 #c -#d 0

LA 2
BL E1 D1


** ** Right Side
** ** Parameters for helix segmentation
** LA 4
** DP A2 #e #d #h2
** DP B2 #e #d #s
** DP C2 #c #d #h2

** Right handed helix (2)
** HE A2 B2 C2 1 3.0 #seg

** Define the endpoints and create the wire segment h
** DP D2 #c #d #h1
** DP E2 #c #d 0

** LA 5
** BL E2 D2

SF 1 0.001

** End of geometric input
EG 1 0 0 0 0

** Specify an infinite ground plane
** BO 2

**Set Discrete Frequency 2GHz-3GHz
FR 10 0 0.51e9 2.6e9

** Voltage gap excitation at a segment
** A2 0 2 1 90 50
A1 0 2 1 90 50
** A2 1 5 1 90

** Calculate surface currents for current display
OS 1 1

** Horizontal far field pattern
FF 1 1 181 1 90 0 2

** End

 Post subject:
Posted: Sat Apr 30, 2005 12:48 pm 

Joined: Tue Apr 26, 2005 6:47 am
Posts: 4
Location: Singapore
since you ar talking about spot frequency at 2.4 GHz you should not find much difficulties to get this VSWR of 1, plat with the number of turns and pitch, you should be able to get it,

please do not stick to the formula dimension play with your hand and see outcome.....................

 Post subject:
Posted: Fri Sep 02, 2005 9:02 pm 

Joined: Fri Sep 02, 2005 7:25 pm
Posts: 34
Location: Hampshire UK
Helix antennas that keep the same pitch all the way to the reflector plane have an impedance of about 140 ohms. This assumes you have the feedpoint right at the point it meets the plane. If you attach a small strip tab along the last quarter-turn as it approaches the feedpoint, shaped to in effect "widen" the helix conductor, making increased capacitance to the plane, you go most of the way to getting a match.

Next step is to feed it with a signal, and slightly compress and adjust the helix at that quarter turn until the VSWR is 1:1, (assumes you a using a VSWR bridge to get the match).

Posted  11/12/2012
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