I have designed few CP antennas on HFSS. I got good return loss and axial ratio values. However the gain is negative in most of the designs. What could be the possible reasons? Anyone else who came across such case and how to overcome this?
Greetings, there is nothing wrong with the antenna which offers negative Gain. Antenna which exhibits negative gain i.e. (uptil -5dB) could be preferably used for near field applications like RFID, still the gain value should not be significantly negative (i.e. -13 dB and so on) for such applications.
- Sometimes the limitations in usage of materials for antenna design for limited frequency is also the case for the negative gain in antenna.
- Incorporation of slots to make the antenna circularly polarized may reduce the effective area (due to slots). so reduction in effective area of antenna is also responsible for reduction in gain.
- Rather to usage of conventional materials for antenna design, people move with growing layers either by sputtering or chemical vapour deposition in such case reducing the sheet resistance of the material grown aids with increasing the radiation efficiency and hence improves the gain.
- Improving the thickness of conductor also aids with the improvement in radiation efficiency and so forth the antenna gain from its negative value.
There are a few possible reasons for negative gain for CP antennas in HFSS:
- Losses. All antennas have some losses, due to resistance in the conductors and the substrate, as well as radiation losses. If the losses are too high, the antenna gain will be negative. This can be especially true for CP antennas, which often have more complex structures than linearly polarized antennas.
- Incorrect design. If the antenna is not designed correctly, it may not radiate efficiently in the desired direction. This can lead to negative gain in that direction.
- Incorrect simulation setup. If the HFSS simulation is not set up correctly, it can produce inaccurate results, including negative gain.
Here are some specific things to check if you are getting negative gain for a CP antenna in HFSS:
- Make sure that the simulation is converged. Increase the number of passes if necessary.
- Make sure that the radiation box is large enough. The radiation box should be at least a quarter wavelength away from the antenna on all sides.
- Check for any errors in the antenna design. Make sure that the dimensions of the antenna elements are correct, and that there are no gaps or shorts in the conductors.
- Check the simulation settings. Make sure that the frequency and port settings are correct.
If you have checked all of these things and you are still getting negative gain, it is possible that there is a bug in HFSS. In this case, you can try contacting Ansys support for assistance.
It is important to note that a negative gain does not necessarily mean that the antenna is useless. For example, CP antennas with negative gain are sometimes used for near-field applications, such as RFID. However, if you are designing an antenna for a long-range application, a negative gain is undesirable.
-Ve gain in dBi means low gain. If we convert it into absolute value then it will be in +Ve only.
The reason can be compactness of structure, mismatch in impedance, more losses.
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