**3.4 Charger circuit fabrication**

*A Guide to Small-Scale Energy Harvesting Techniques*

**3.3 Antenna simulation**

indicated in **Figure 15**. So knowing that power equals to current times voltage, we obtain 532*μ* W output power for 915 MHz signal. It should be noted that voltage drop in 915 MHz (8.8 V to 3.6 V) is because that by connecting battery to charger circuit, battery charging process starts and in this process power must be constant,

so by increasing the current drawn by the battery, output voltage drops.

Receiver antenna is a broadband type with linearly polarized radiation. Considering that our bandwidth is 500 MHz, according to previous experiences, we

**104**

**Figure 15.**

**Figure 14.**

*Output voltages in 580, 650, 760 and 915 MHz.*

*Output currents in 580, 650, 760 and 915 MHz.*

Test results for our fabricated charger circuit are indicated in **Figure 18**. In terms of experimental results, we obtain 6.89 V of output voltage at the frequency of 915 MHz (which obtained 8.8 V in simulation results), where our input signal is a 0 dbm generated by R&S®SMB100A signal generator. For a 10 kΩ resistive load, load voltage is 2.12 V and we can calculate the output power as 450*μ* W.

**Figure 16.** *Designed U-shape UWB antenna.*

**Figure 17.** *Measured and simulated reflection coefficients of UWB antenna.*

**Figure 18.** *(a) Fabricated charger circuit (b) Circuit test.*
