In the world of EMI-EMC there is an essential need to measure conducted as well as radiated RF power. Additionally, measurement of RF power is required for design, development and maintenance of various systems of communications; radar etc. An exhaustive literature survey is carried out on various methods of RF power measurement. Based on the analysis of the literature survey, an optimized way of RF measurement is conceived and converted into a realizable measuring system. In the new approach, demerits of the traditional methods are minimized. The proposed RF power meter consists of a matched input section, a central RF measuring unit and a display meter. It can measure RF power ranging from micro watts to few hundred watts. In the developed prototype meter, a frequency range up to 500 MHz is considered which can be further extended up to several GHz in futuristic prototypes. The developed RF power meter is a low cost, easy to operate and portable.
The power supply unit consists of a 9V battery(energizing circuit), 1.2 amps is used to derive the required 5V for the circuit through a regulator (IC 7805). This gives low cost, high reliability, reduction in size and excellent performance.
The Display Meter Section consists of an LED driver, LM3914, manufactured by National Semiconductors that senses analog voltage levels and drives 10 LED’s, providing a linear analog display. A single pin changes a moving dot to a bar graph. Current drive to the LED is regulated and programmable eliminating the need of resistors.
The RF measuring section consists of 8-pin logarithmic amplifier, AD8307, manufactured by Analog Devices. It is an 8-pin DIP which provides a dynamic range of 92dB to ±3dB. An extremely stable and ready to use IC, it does not require any significant external components. This IC provides us with a basic dynamic range extending from approximately -75dB up to +17dB, with a simple input matching network the range can be lowered to -88dBm to +3dBm. Inside the IC, there are six main amplifier/ limiter stages, each having a gain of 14.3dB and small signal bandwidth of 900MHz. The AD8307 is built on an advanced dielectrically isolated, complementary bipolar process. This also has three top-end detectors, placed at 14.3dB taps on a passive attenuator, handle the upper third of 90dB range.
The RF power meter makes accurate RF power measurements in both electric and magnetic fields. It is packed with an extremely stable IC so the results are accurate and it provides a good repeatability. Here, in this case the logarithmic amplifier used supports for only a certain range, but this range can be increase according to the will and wish of the person. It comes in handy for a lab technician who can measure the RF power in a matter of minutes without much expense from his pocket. It can be used in labs to measure RF power. The display meter consists of LED’s which is not only cost effective but also gives a long working period.