Dear Gautam,

To increase the received power,

you have to:

Increase the the transmitted power by increasing the radio frequency power Po generated by the oscillator. Assuming DC conversion efficiency of about 80 percent for class C operation, then you have to supply your oscillator with a DC power supply of  Po/0.8, Assuming rf transmission efficiency of about 0.8 near field short distance transmission, them the received power will be Pox 0.8. Then you convert it to DC with efficiency of about 0.9, which results in an a DC output power of Pdco= Po x0,8x0.9= 0.72 Po. This value must be equal to 5Vx.5 = 2.5 w.

Then Po= 2.5/0.72= 3.7 w which give a DC power at the transmitter of 3.7/ .8=4.4 w,

Since the voltage is 12 volt the you have to supply a DC current or the transmitter of 4.4/12= 360 mA. Then you have to to be sure of input dc current withdrawn from the transmitter power supply and the Dc conversion efficiency of your oscillator. You have to use the proper power transistor to work as an oscillator and operate in class c operation by the proper DC operating point.

I want 5v and 500ma current at receiver

This specification requires 10 Ohms source resistance (5V / 0.5 A) to drive the mobile charger. The receiver antenna impedance should be considered and suitable matching circuit should be used. You need to add free space loss.

What should be the current of 12 V supply of transmitter ?

This depends upon the losses. Actual loss has to be measured.

As an example, if losses are 10 dB, then the transmitter power should be 25 Watts. The input to transmit antenna should be at least 25 Watts. The transmitter current will be 25 Watts / 12 V.

The above is an example, you need to adjust transmit power based upon the actual losses.

Hi Gautam,

I would like to help but you did not give me enough information. I would need to know the DC voltange and DC current required to operate your transmitter. If you need more than 12 volts, then use a DC to DC converter to get higher voltage. There might be an integrated circuit already made for your application. The converter is a series of solid state switches with capacitors arranged to multiply the voltage. These switch at high frequencies to avoid the need for large capacitors.

Good luck,

Steve

From the circuit view point better use a little oscillator with moderate power and a pure power amp as 2nd stage! This gives you much better options than an oscillator alone. The PA transistor sizes, the bias voltage, the osc drive power,  the supply voltage and matching network determine how much power goes into antenna.