Microwave Doppler Speed Measurement System

1. GuoJianghuai Supervisor: Roland G Clarke       Assessor: Chris Trayner Microwave Doppler Speed Measurement System Transmitting Horn Antenna 2.4GHz Oscillator Introduction Wilkinson Power Splitter A Doppler radar is a special kind of radar which takes advantage of the Doppler effect to achieve velocity data about moving or static objects at a distance. Through beaming a microwave signal towards the desired target, then listening for reflection from the target, after that, analyzing how the frequency of the returned signal has been affected by the object's motion. By doing some data analysis, the variation can have a output of direct and highly exact measurements of the relative speed for the target relative to the radar. The antenna plays an important role in any radar or communication system. An antenna can be treated as a device which is converting a guided electromagnetic wave to a plane wave propagating in free space (transmission), or vice versa (reception). So one side of an antenna acts as an electrical circuit element, but the other side offers an interface with a propagating plane wave. Antennas are intrinsically bidirectional, so they can be used for both transmit and receive functions. Wilkinson power divider is a lossy three-port network having all ports matched with isolated output ports. When the output ports are matched, it has the beneficial property of being lossless. The reason for this is that the power dissipated is only reflected power. The Wilkinson power divider can be manufactured to divide the power into any proportion. However, the case that is considered in this project is the equal-split case, which is also called as 3dB case. Oscillators and frequency synthesizers are the main part of wireless transmitters and receivers. They provide accurate control for frequency conversion and carrier generation. In this project, it uses ROS-3000V oscillatoras the input signal source or Local oscillator. 2.4GHz transmitted Moving target Aims and Objectives Received shifted Doppler frequency The aim of this project is to design and construct a microwave continuous-wave Doppler Radar system to detect and display the speed of an object moving toward or away from the unit. The objectives are construction of microwave and embedded system. Microwave system includes design of Wilkinson power splitter and a low-pass filter. Embedded system deals with changing the frequency of received signal into voltage, investigation of relationship of voltage and velocity and displaying the velocity. In addition, storing and displaying fastest and lowest speed is included. Receiving Horn Antenna Frequency Mixer A mixer is a three-port device, and its main function is to realize the frequency conversion through using a nonlinear or time-varying element. An output which contains the sum and difference frequencies of its two input signals could be generated by a perfect mixer. The procedure of frequency down-conversion which is usually used in a receiver take place in this project. In this situation, the input signal becomes an RF signal, which has a form vRF(t)= cos2πfRFt and the local oscillator signal. the mixer output is composed of the sum and difference of the input signal frequencies which is frequencies of LO and RF signal. Conclusion The project processes as planed, and it works well, even though there is some small system error. Through the design and construction of microwave Doppler speed measurement system, a better understanding and application of microwave theory and embedded system are obtained. Software A C program was designed to implement the functions of a frequency measurement and velocity meter. In this program, it includes frequency measurement, display, data check and key scan function. The reciprocal counter is a counter which always makes a period measurement on the input signal. If frequency information is desired, it can be directly represented by taking the reciprocal of the period measurement. Low pass filter Microcontroller LCD displayer Output speed Comparator Wait for first rising edge Key scan Wait for second rising edge Speed data check LCDs are the prior system for battery-powered (hand-held) applications ranging from wristwatch displays and handheld TVs to laptop computer displays. The reason for this is LCs have properties of low drive voltage, low power consumption, thin form factor, light weight, full-color, full motion video, gray scale with a wide dynamic range, better image quality, and high reliability. A low-pass filter is a filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency. In the operational amplifier circuit shown in the figure, the cutoff frequency (in hertz) is defined as: f =1/(2πRC). If the op amp is not used in a closed-loop, its output will be either high or low. It is be dependent on the polarity of the voltage between its inputs. The basic comparator compares the voltage levels at its two inputs. Typically, the logic levels are suitable for usual logic families such as TTL, CMOS, or ECL. A microcontroller is a small computer on a single integrated circuit containing a processor, memory, and programmable input/output devices. All PIC microcontrollers have a counter that works as a watchdog timer. This timer can be configured with specific bits when the microcontroller is being programmed. Thus the frequency measurement could be achieved by calculating the period. Calculate time during a pulse Work out speed