Antenna to operate from 800 MHz - 3 GHz, low efficiency

[SethC]

So I designed this antenna to operate from 800 MHz - 3 GHz. Why is the efficiency of the radiation so low? Will the antenna not radiate at all? Will I need to drive the antenna with a lot of power? It seems that many small PCB commercial antennas are similar in design, so how can they radiate over such large distances?

Attached is my antenna design in IE3D.

 

[Azulykit]

Re: Low Efficiency Antenna?

There are a series of questions here. Low efficiency antennas will radiate, but not as well as a higher efficiency antenna. Putting more power in will mean that more will be radiated. Will it be enough is a system question and depends on the receiver, range and a bunch of other factors. Look into "link calculations" to get a feeling for what needs to be considered.

You are right, there are numerous small antennas on the market and they can be made to work but system adjustments need to be made elsewhere to adjust/compensate for their performance.

My general view is to resist using a (electrically) small antenna if at all possible because the performance is not often inspiring.

I did not look at the specifics of your design.

 

[jian]

Re: Low Efficiency Antenna?

Hi, SethC:

Your antenna is a travelling wave antenna with meander line. At the end of the meander line, you have a distributed matching load. Most of the power is absorbed by the load and some energy is lost in the substrate with high loss tangent (0.013). There is no serious resonance in the structure and very little energy is radiated out. You should have very low efficiency on such an antenna.

Best regards,

 

[SethC]

Re: Low Efficiency Antenna?

Is there anyway to keep the UWB characteristics and still be able to broadcast over a far distance (like cell phones). How do cell phones have such small antenna that simulate to be inefficient, yet they are widely used?

Added after 5 minutes:

How can I make the antenna radiate more power at these frequencies? Should I scrap the design?

 

[jian]

Re: Low Efficiency Antenna?

Hi, SethC:

There are two major sources of losses in a typical antenna: (1) return loss (or the loss due to reflection) and (2) omic-loss. Some people may consider surface wave loss as the 3rd source. However, surface wave will be eventually absorbed by the dielectrics and the ground plane and it can be included into the omic-loss.

For the travelling wave antenna in your example, you are not making use of serious resonances to reduce the return loss. You are using a resistor at the end of the meander line to absorb the power to reduce the return loss. Certainly, the return loss is low while the omic-loss is very high. Therefore, the loss of your antenna is high and you will not get good efficiency.

Most cellular phones are not using wide band antennas. Instead, they are designed to have good resonances at some bands. At those bands, they don't have much omic loss while the good resonances reduce the return loss. It is how they can have high gains at the selected frequency bands. At other frequency bands, the return loss is high and they don't need to care because the antennas are not operating at those bands.

If you want to design a wide band antenna, you might consider to make a wide band resonance and try not to use any resistors in your design.

Regards.

 

[johnson.mike]

Re: Low Efficiency Antenna?

hi sethC,

I think this where, we have to understand how antenna radiates?
General powerdividers,couplers will have good returnloss but they wont radiate as compared to antenna.
And thanks for the explaination given by jian.

Attached here are efficiency and gain of your structure.

regards,
johnson.

 

[byteptr]

Re: Low Efficiency Antenna?

"General powerdividers,couplers will have good returnloss but they wont radiate as compared to antenna. "

Yes, because most part of energy is redirected or guided to the connection ports. An antenna is just a transition between 2 media for EM wave propagation