helix antenna gain dbi
I have a doubt on the gain performance of 3.55GHz for the helix antenna.
As per theory , the gain calculated is about 22dBi but when I do practically , I get 13.5dBi.
Let me explain the way I did to build helix antenna.
According to the spec provided from the website:
www.jcoppens.com/ant/helix/cal.en.php
1) Centre freq: 3.55GHz.
2)Wavelength: 83.3mm
3)Diameter (internal): 29.4mm
4)Conductor Diameter: 1.6mm
5)Spacing winding: 8.3mm
6)Total length: 166.6mm
7)Minimum reflector size: 52mm
8) Reflector / Conductor separation: 0.8mm
Total length of conductor: 1859mm
Theoritical Gain: 22.02dBi
Beamwidth: 36.7 Deg
BW@-3dB 3.453 to 3.753MHz
According to the dimension above , I built the helix antenna using pvc pipe as a support. And I wind the copper coil on the pvc pipe and glue it.
The input impedance of the coil is 155ohms. I believe that I need a stub matching which lambda/4. So it is 2.1cm and I use copper tape of 2.1cm length and solder to the end of copper coil and the other end of copper tape to the centre pin of the connector.
A flat reflector is about 11cm (square flat reflector). I put glue at the bottom of the pvc pipe to the flat reflector.
Then the fixed the helix antenna to the parabolic dish 300mm.
I made 2 helix antenna and fixed it to the 2 parabolic dish 300mm.
I'm transmitting using hp signal generator and receiving from power meter.
According to the practical , I got 13.5dBi using link budget calculation.
But it's not enough. How could I optimize the gain value?
Can anyone help me? Plz....
Waiting for ur reply.
Regards,
Saran
I see that you are using a small spacing between windings. According to the formula that I have, the spacing should be S=0.78*Diameter=22mm.
Shall be a correlation between spacing and pitch angle for optimum performance. This correlation starts to be challenging for frequencies greater than 3GHz.
The input impedance of helix antenna in axial mode is approximately 150 ohms (resistive) and this can be matched to 50 ohms using a λ/4 stub (Z_stub=√(Z_helix*50).
Also for matching can be used a triangle strip line, which dimensions could be tuned using a Network Analyzer.
I didn't understand the exact design of your λ/4 stub and how you achieved the required 87 ohms impedance. If it's a microstrip, the length should be < 21 mm. You may want to check the actual antenna impedance with a network analyzer anyway.
Hi All,
The input impedance of the coil is 155ohms. In order to matching it with 50ohms, we use equation of Zstub= sqrt(Z_helix*50) and the Zstub is 88ohms.
Even after I got the value of 88ohms, I don't see this 88ohms related to the dimension of the λ/4 stub .
Dimension of the λ/4 stub is 2.1cm.
Plz correct me if I did anything wrong . What should I proceed now?
Waiting for ur reply.
Regards,
Saran.
Added after 4 hours 27 minutes:
Hi All,
A small correction on the frequency range.
Actually it is from 3.453GHz to 3.753GHz.
Thanks .
Regards,
Saran
If the stub transmission line uses dielectrica (e.g. coaxial cable or stripline), it's mechanical length is shorter than 21 mm. But I don't know, how you designed it.
Lets make it this way......
The theoretical input impedance of the helical coil is 155ohms. I'm having 50ohms connector.
Before solder the coil to the connector, I believe that I need to add a copper strip in between of the coil and connector, rite......
Copper strip( referred as stub matching which is lambda/4), rite....
Can anyone tell me what and how should I design the stub matching...
Plz give idea to me.
It would be very grateful.....thank you.
Waiting for your reply.
Regards,
Saran