Do It Yourself
Antenna
2.4GHz 40 elements Helical Antenna
Assembly :
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| Final |
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| Matching view 1 | Matching view 2 |
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| Join | Reflector |
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| Fix in front | Fix at middle |
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| Smith chart | Standing wave ratio |
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Firstly, I used the copper plate for the matching network for this helical antenna. Although I can turn the SWR under 1.1, it was still no gain. For the testing, I used a dipole, -10dBm RF signal came from the generator and received this signal by another 2.4GHz dipole and a spectrum analyzer. Two stations had 10 meters distance. I used it for my reference and compare with my homemade 2.4GHz helical. I felt so sad. It had not any large different. Just 2 to 3dB more. ( Please see the photos on the last page for detail.) During the matching alignment, one time when I forgot to connected the matching network to the helical, just with the join between the N-type connector and network. It still match!! This means that the network is a dummy load, not really a complete circuit for matching. So I am now prepare the next method, series a 1/4 wavelength coaxial stub for match. My helical antenna is 200ohms - j 14ohms. But by the simulation, the result is 140ohms +/- j 0ohms. According to these values, it is possible to match for less than SWR = 1.5 with series 30mm Zo = 75 or 93 ohms coaxial. I remember that some cable is 93 ohms. I will test it again later. |
| Detail for alignment | : | Step | Copper plate dimension | Impedance | |
| 1) | (mm) | (ohm) | |||
| 2) | N.C. | 200 - j 14 | |||
| 3) | 17 x 71 x 73 | 140 + j 13 | |||
| 4) | 20 x 71 x 73 | 135 + j 10 | |||
| 5) | 17 x 70 x 70 x 5 | 130 + j 8 | |||
| 6) | 17 x 70 x 70 x 10 | 100 + j 6 | |||
| 7) | 17 x 70 x 70 x 17 | 96 + j 7 | |||
| 8) | 10 x 70 x 70 x 17 | 114 - j 15 | |||
| 9) | 20 x 70 x 70 x 20 | 91 + j 18 | |||
| 10) | 30 x 70 x 70 x 30 | 86 - j 25 | |||
| 11) | 25 x 70 x 70 x 25 | 61 + j 5 | |||
| 12) | 25 x 72 x 72 x 25 | 60 + j 5 | |||
| 13) | 25 x 75 x 75 x 25 | 58 + j 4 | |||
| At last, I modify it to the following polygon but still in 25 x 75 x 75 x 25 and 52 ohms + 0.2 j ohms | |||||
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| b) | Standing Wave Ratio | : | Minimum 1.0753 at 2401MHz (measured by Agilent 8753ES S-parameter network analyzer | ||
| c)
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Element
dimension
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Total 40 elements. AWG 14# copper wire winding on a 1 meter long PVC tube with 40mm inter dia. & 42mm outer dia. | ||
| d) | Reflector | : | 2mm thinkness aluminium plate with 130mm dia. | ||
| e) | Antenna Polarization | : | Circular | ||
| f)
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Antenna
Gain
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Very poor!!! Just 2 to 3 dBd measured by Agilent E4421B RF generator & E4402B spectrum analyzer | ||