I want to know about techniques to improve the efficiency of the wireless Power Transmission System based on microwave.
It depend on which characteristic of network you want to improve... If I understood your question well, the first thing comes to mind is increasing the gain of the source... Using PIN-diode modulator would be one way to do it... Or by using some modulation you can enhance the efficiency... clarify your meaning about efficiency... ???!!!!
One can intervene on the gain of the source, matching antenna, pattern of the antennas, modulation type of the signal and topography of the whole system of transmission and reception.
The spread spectrum modulation has an high efficiency in terms of signal noise ratio among the modulation techniques which can be used.
Sir efficiency depend upon gain as we know enhance of gain .we have many method which help to increase gain like change permitivity,super-substrate etc which will improve efficiency.eff=gain* directivity
if u suppress spurious wave radiations generated by fringing field in antenna, the radiation efficiency will increase. So, Try to remove some portions of substrate which are not under the metallic patch in such a way that it doesn't affect antenna layout.
Efficiency have nothing to do with gain nor attenuation. Efficiency is measured in percent and is based on the output = feed pwr - losses.
Efficiency % = ( feed pwer / ( feed pwr - losses )) * 100
However, the bandwidth of a design, especially for antennas, defines the efficiency together with the Q value of the design, so a holistic approach is required.
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To bring up the efficiency, you "simply" need to lower the losses in the transmission line. Changing the gain does NOT change the efficiency unless you are dabbling with metameterials!
Change substrate composition. Another trick is to jack up the impedance far away from 50 Ohms. There is a reason CCTV and TV stuff use 75 Ohms instead of 50 Ohms. If you design your complete solution, why bother using 50 Ohms, chose what's best suited for you! Start using wave guides earlier than using micro strip or substrate based designs.
If you are meaning wireless transmission, then many parameters like antenna gain at both ends, matching with feed/load network, modulation type, path loss etc would matter and each factor has got separate means to increase its value. If it is not wireless, the best way is to use waveguides or rectax (rectangular coaxial lines). These structures are also suitable for low loss feeding pf planar antenna arrays through slots.