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The power amplifier is to be used on the transmitter subsystem of the wireless surveillance system. The function of the power amplifier is to amplify the transmitter signal from the Band Pass Filter which is then transmitted by the antenna. The Friis transmission formula can be used to determine the gain and output power level of the power amplifier based on the desired range of the system. Based on earlier signal strength experiments conducted, it is known that a 2.4 GHz signal has a 10 dB loss per 5 ft. FCC regulations for the transmitter power level for the 2.4 GHz ISM band is 100 mW. The transmitter power level had to be lower than the maximum allowed legal power level. After discussing the matter with the project advisor, it was advised to conduct power level measurements for the system to get a better idea of the losses present in the system. To conduct the experiments a system similar to the proposed system was set up in the laboratory. The components available in the RF laboratory were used to set-up the system. The system was set-up as shown in the Block Diagram. The ZHL2000 Power Amplifier was used to set-up the system. Power level measurements were performed at every node of the system. Table 1 and Table 2 show the several power level measurements for the transmitter and receiver respectively.
The power amplifier to be used for the system were to be ordered from commercial vendors. After evaluating the data obtained from the experiments, the power amplifier to be used can be selected based on its gain and power output at the operating frequency. The precise output power level of the power amplifier also depends on the power level of the input to the amplifier. The data collected earlier helped determining the amplifier to be selected based on the gain and power calculations conducted.. Table 3 and Table 4 show the power amplifier calculations data. After much deliberation, it was decided to use three power amplifier in series to get the desired gain and power level. The amplifiers to be used were two ERA-3sm and one ERA-5sm in series. The amplifiers are manufactured by Minicircuits corporation. The layout and the series amplifier circuit were to be designed and fabricated in the RF lab.
Friis Transmission Formula
. Pav1 and Pav2 denote the average transmit and receive powers respectively. If the separation between the antenna apertures is d (d > rmin ). D1 and D2 are the directivities of the transmit and receive antenna respectively. According to this formula, the received power is inversely proportional to d2. A plot of the power received versus 1/d2 should be a straight line. For example, if the receive antenna were placed at twice the distance from its original position, the power received by the antenna would drop to one-fourth of its original value.
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