Category: radar Systems

Radar Systems Tutorial Job Search This tutorial is meant to provide the readers to know and understand the working of various Radars that are used for detecting either stationary or non-stationary targets. It also provides the details of various Antennas that are used in Radar communication. So, this tutorial gives the overview of Radar communication. Audience This tutorial is meant for all the readers who are aspiring to learn the concepts of Radar Systems. In some universities, this subject is also called as “Radar Communication”. Prerequisites The fundamental concepts covered in Analog Communication & Antenna Theory tutorials will be useful for understanding the concepts discussed in this tutorial. Learning working make money

Radar Systems – Types of Radars In this chapter, we will discuss in brief the different types of Radar. This chapter provides the information briefly about the types of Radars. Radars can be classified into the following two types based on the type of signal with which Radar can be operated. Pulse Radar Continuous Wave Radar Now, let us discuss about these two types of Radars one by one. Pulse Radar The Radar, which operates with pulse signal is called the Pulse Radar. Pulse Radars can be classified into the following two types based on the type of the target it detects. Basic Pulse Radar Moving Target Indication Radar Let us now discuss the two Radars briefly. Basic Pulse Radar The Radar, which operates with pulse signal for detecting stationary targets, is called the Basic Pulse Radar or simply, Pulse Radar. It uses single Antenna for both transmitting and receiving signals with the help of Duplexer. Antenna will transmit a pulse signal at every clock pulse. The duration between the two clock pulses should be chosen in such a way that the echo signal corresponding to the present clock pulse should be received before the next clock pulse. Moving Target Indication Radar The Radar, which operates with pulse signal for detecting non-stationary targets, is called Moving Target Indication Radar or simply, MTI Radar. It uses single Antenna for both transmission and reception of signals with the help of Duplexer. MTI Radar uses the principle of Doppler effect for distinguishing the non-stationary targets from stationary objects. Continuous Wave Radar The Radar, which operates with continuous signal or wave is called Continuous Wave Radar. They use Doppler Effect for detecting non-stationary targets. Continuous Wave Radars can be classified into the following two types. Unmodulated Continuous Wave Radar Frequency Modulated Continuous Wave Radar Now, let us discuss the two Radars briefly. Unmodulated Continuous Wave Radar The Radar, which operates with continuous signal (wave) for detecting non-stationary targets is called Unmodulated Continuous Wave Radar or simply, CW Radar. It is also called CW Doppler Radar. This Radar requires two Antennas. Of these two antennas, one Antenna is used for transmitting the signal and the other Antenna is used for receiving the signal. It measures only the speed of the target but not the distance of the target from the Radar. Frequency Modulated Continuous Wave Radar If CW Doppler Radar uses the Frequency Modulation, then that Radar is called the Frequency Modulated Continuous Wave (FMCW) Radar or FMCW Doppler Radar. It is also called Continuous Wave Frequency Modulated Radar or CWFM Radar. This Radar requires two Antennas. Among which, one Antenna is used for transmitting the signal and the other Antenna is used for receiving the signal. It measures not only the speed of the target but also the distance of the target from the Radar. In our subsequent chapters, we will discuss the operations of all these Radars in detail. Learning working make money

Radar Systems – Duplexers In two-way communication, if we are supposed to use the same Antenna for both transmission and reception of the signals, then we require Duplexer. Duplexer is a microwave switch, which connects the Antenna to the transmitter section for transmission of the signal. Therefore, the Radar cannot receive the signal during transmission time. Similarly, it connects the Antenna to the receiver section for the reception of the signal. The Radar cannot transmit the signal during reception time. In this way, Duplexer isolates both transmitter and receiver sections. Types of Duplexers In this section, we will learn about the different types of duplexers. We can classify the Duplexers into the following three types. Branch-type Duplexer Balanced Duplexer Circulator as Duplexer In our subsequent sections, we will discuss the types of Duplexers in detail. Branch-type Duplexer Branch-type Duplexer consists of two switches — Transmit-Receive (TR) switch and Anti Transmit-Receive (ATR) switch. The following figure shows the block diagram of Branch-type Duplexer − As shown in the figure, the two switches, TR & ATR are placed at a distance of $lambda/4$ from the transmission line and both the switches are separated by a distance of $lambda/4$. The working of Branch-type Duplexer is mentioned below. During transmission, both TR & ATR will look like an open circuit from the transmission line. Therefore, the Antenna will be connected to the transmitter through transmission line. During reception, ATR will look like a short circuit across the transmission line. Hence, Antenna will be connected to the receiver through transmission line. The Branch-type Duplexer is suitable only for low cost Radars, since it is having less power handling capability. Balanced Duplexer We know that a two-hole Directional Coupler is a 4-port waveguide junction consisting of a primary waveguide and a secondary waveguide. There are two small holes, which will be common to those two waveguides. The Balanced Duplexer consists of two TR tubes. The configuration of Balanced Duplexer for transmission purpose is shown in the following figure. The signal, which is produced by the transmitter has to reach the Antenna for the Antenna to transmit that signal during transmission time. The solid lines with arrow marks shown in the above figure represent how the signal reaches Antenna from transmitter. The dotted lines with arrow marks shown in the above figure represent the signal, which is leaked from the Dual TR tubes; this will reach only the matched load. So, no signal has been reached to the receiver. The configuration of Balanced Duplexer for reception purpose is shown in figure given below. We know that Antenna receives the signal during reception time. The signal which is received by the Antenna has to reach the receiver. The solid lines with arrow marks shown in the above figure represent how the signal is reaching the receiver from Antenna. In this case, Dual TR tubes pass the signal from the first section of waveguide to the next section of waveguide. The Balanced Duplexer has high power handling capability and high bandwidth when compared to Branch-type Duplexer. Circulator as Duplexer We know that the functionality of the circulator is that if we apply an input to a port, then it will be produced at the port, which is adjacent to it in the clockwise direction. There is no output at the remaining ports of the circulator. So, consider a 4-port circulator and connect the transmitter, Antenna, receiver and matched load to port1, port2, port3 and port4 respectively. Now, let us understand how the 4-port circulator works as Duplexer. The signal, which is produced by the transmitter has to reach the Antenna for the Antenna will transmit that signal during transmission time. This purpose will be achieved when the transmitter generates a signal at port1. The signal, which is received by the Antenna has to reach the receiver during reception time. This purpose will be achieved when the Antenna present at port2 receives an external signal. The following figure shows the block diagram of circulator as Duplexer − The above figure consists of a 4-port circulator — Transmitter, Antenna and the matched load is connected to port1, port2 and port4 of circulator respectively as discussed in the beginning of the section. The receiver is not directly connected to port3. Instead, the blocks corresponding to the passive TR limiter are placed between port3 of circulator and receiver. The blocks, TR tube & Diode limiter are the blocks corresponding to passive TR limiter. Actually, the circulator itself acts as Duplexer. It does not require any additional blocks. However, it will not give any kind of protection to the receiver. Hence, the blocks corresponding to passive TR limiter are used in order to provide the protection to the receiver. Learning working make money

Discuss Radar Systems This tutorial is meant to provide the readers to know and understand the working of various Radars that are used for detecting either stationary or non-stationary targets. It also provides the details of various Antennas that are used in Radar communication. So, this tutorial gives the overview of Radar communication. Learning working make money

Radar Systems – Tracking Radar The Radar, which is used to track the path of one or more targets is known as Tracking Radar. In general, it performs the following functions before it starts the tracking activity. Target detection Range of the target Finding elevation and azimuth angles Finding Doppler frequency shift So, Tracking Radar tracks the target by tracking one of the three parameters — range, angle, Doppler frequency shift. Most of the Tracking Radars use the principle of tracking in angle. Now, let us discuss what angular tracking is. Angular Tracking The pencil beams of Radar Antenna perform tracking in angle. The axis of Radar Antenna is considered as the reference direction. If the direction of the target and reference direction is not same, then there will be angular error, which is nothing but the difference between the two directions. If the angular error signal is applied to a servo control system, then it will move the axis of the Radar Antenna towards the direction of target. Both the axis of Radar Antenna and the direction of target will coincide when the angular error is zero. There exists a feedback mechanism in the Tracking Radar, which works until the angular error becomes zero. Following are the two techniques, which are used in angular tracking. Sequential Lobing Conical Scanning Now, let us discuss about these two techniques one by one. Sequential Lobing If the Antenna beams are switched between two patterns alternately for tracking the target, then it is called sequential lobing. It is also called sequential switching and lobe switching. This technique is used to find the angular error in one coordinate. It gives the details of both magnitude and direction of angular error. Following figure shows an example of sequential lobing in polar coordinates. As shown in the figure, Antenna beams switch between Position 1 and Position 2 alternately. Angular error θ is indicated in the above figure. Sequential lobing gives the position of the target with high accuracy. This is the main advantage of sequential lobing. Conical Scanning If the Antenna beam continuously rotates for tracking a target, then it is called conical scanning. Conical scan modulation is used to find the position of the target. Following figure shows an example of conical scanning. Squint angle is the angle between beam axis and rotation axis and it is shown in the above figure. The echo signal obtained from the target gets modulated at a frequency equal to the frequency at which the Antenna beam rotates. The angle between the direction of the target and the rotation axis determines the amplitude of the modulated signal. So, the conical scan modulation has to be extracted from the echo signal and then it is to be applied to servo control system, which moves the Antenna beam axis towards the direction of the target. Learning working make money

Radar Systems – Radar Antennas In this chapter, let us learn about the Antennas, which are useful in Radar communication. We can classify the Radar Antennas into the following two types based on the physical structure. Parabolic Reflector Antennas Lens Antennas In our subsequent sections, we will discuss the two types of Antennas in detail. Parabolic Reflector Antennas Parabolic Reflector Antennas are the Microwave Antennas. A knowledge of parabolic reflector is essential to understand about working of antennas in depth. Principle of Operation Parabola is nothing but the Locus of points, which move in such a way that its distance from the fixed point (called focus) plus its distance from a straight line (called directrix) is constant. The following figure shows the geometry of parabolic reflector. The points F and V are the focus (feed is given) and the vertex respectively. The line joining F and V is the axis of symmetry. $P_1Q_1, P_2Q_2$ and $P_3Q_3$ are the reflected rays. The line L represents the directrix on which the reflected points lie (to say that they are being collinear). As shown in the figure, the distance between F and L lie constant with respect to the waves being focussed. The reflected wave forms a collimated wave front, out of the parabolic shape. The ratio of focal length to aperture size (i.e., $f/D$ ) is known as “f over D ratio”. It is an important parameter of parabolic reflector and its value varies from 0.25 to 0.50. The law of reflection states that the angle of incidence and the angle of reflection are equal. This law when used along with a parabola helps the beam focus. The shape of the parabola when used for the purpose of reflection of waves, exhibits some properties of the parabola, which are helpful for building an Antenna, using the waves reflected. Properties of Parabola Following are the different properties of Parabola − All the waves originating from focus reflect back to the parabolic axis. Hence, all the waves reaching the aperture are in phase. As the waves are in phase, the beam of radiation along the parabolic axis will be strong and concentrated. Following these points, the parabolic reflectors help in producing high directivity with narrower beam width. Construction & Working of a Parabolic Reflector If a Parabolic Reflector Antenna is used for transmitting a signal, the signal from the feed comes out of a dipole Antenna or horn Antenna, to focus the wave on to the parabola. It means that, the waves come out of the focal point and strike the paraboloid reflector. This wave now gets reflected as collimated wave front, as discussed previously, to get transmitted. The same Antenna is used as a receiver. When the electromagnetic wave hits the shape of the parabola, the wave gets reflected onto the feed point. The dipole Antenna or the horn Antenna, which acts as the receiver Antenna at its feed receives this signal, to convert it into electric signal and forwards it to the receiver circuitry. The gain of the paraboloid is a function of aperture ratio $D/lambda$. The Effective Radiated Power (ERP) of an Antenna is the multiplication of the input power fed to the Antenna and its power gain. Usually a wave guide horn Antenna is used as a feed radiator for the paraboloid reflector Antenna. Along with this technique, we have the following two types of feeds given to the paraboloid reflector Antenna. Cassegrain Feed Gregorian Feed Cassegrain Feed In this type, the feed is located at the vertex of the paraboloid, unlike in the parabolic reflector. A convex shaped reflector, which acts as a hyperboloid is placed opposite to the feed of the Antenna. It is also known as secondary hyperboloid reflector or sub-reflector. It is placed in such a way that one of its foci coincides with the focus of the paraboloid. Thus, the wave gets reflected twice. The above figure shows the working model of the cassegrain feed. Gregorian Feed The type of feed where a pair of certain configurations are there and where the feed beam width is progressively increased while Antenna dimensions are held fixed is known as Gregorian feed. Here, the convex shaped hyperboloid of Cassegrain is replaced with a concave shaped paraboloid reflector, which is of course, smaller in size. These Gregorian feed type reflectors can be used in the following four ways − Gregorian systems using reflector ellipsoidal sub-reflector at foci F1. Gregorian systems using reflector ellipsoidal sub-reflector at foci F2. Cassegrain systems using hyperboloid sub-reflector (convex). Cassegrain systems using hyperboloid sub-reflector (concave but the feed being very near to it). Among the different types of reflector Antennas, the simple parabolic reflectors and the Cassegrain feed parabolic reflectors are the most commonly used ones. Lens Antennas Lens Antennas use the curved surface for both transmission and reception of signals. These antennas are made up of glass, where the converging and diverging properties of lens are followed. The frequency range of usage of Lens Antenna starts at 1 GHz but its use is greater at 3 GHz and above. A knowledge of Lens is required to understand the working of Lens Antenna in depth. Recall that a normal glass Lens works on the principle of refraction. Construction & Working of Lens Antenna If a light source is assumed to be present at a focal point of a lens, which is at a focal distance from the Lens, then the rays get through the Lens as collimated or parallel rays on the plane wave front. There are two phenomena that happens when rays fall from different sides of a lens. They are given here − The rays that pass through the centre of the Lens are less refracted than the rays that pass through the edges of the Lens. All of the rays are sent in parallel to the plane wave front. This phenomenon of Lens is called as Divergence. The same procedure gets reversed if a light beam is sent from the right

Radar Systems – MTI Radar If the Radar is used for detecting the movable target, then the Radar should receive only the echo signal due to that movable target. This echo signal is the desired one. However, in practical applications, Radar receives the echo signals due to stationary objects in addition to the echo signal due to that movable target. The echo signals due to stationary objects (places) such as land and sea are called clutters because these are unwanted signals. Therefore, we have to choose the Radar in such a way that it considers only the echo signal due to movable target but not the clutters. For this purpose, Radar uses the principle of Doppler Effect for distinguishing the non-stationary targets from stationary objects. This type of Radar is called Moving Target Indicator Radar or simply, MTI Radar. According to Doppler effect, the frequency of the received signal will increase if the target is moving towards the direction of Radar. Similarly, the frequency of the received signal will decrease if the target is moving away from the Radar. Types of MTI Radars We can classify the MTI Radars into the following two types based on the type of transmitter that has been used. MTI Radar with Power Amplifier Transmitter MTI Radar with Power Oscillator Transmitter Now, let us discuss about these two MTI Radars one by one. MTI Radar with Power Amplifier Transmitter MTI Radar uses single Antenna for both transmission and reception of signals with the help of Duplexer. The block diagram of MTI Radar with power amplifier transmitter is shown in the following figure. The function of each block of MTI Radar with power amplifier transmitter is mentioned below. Pulse Modulator − It produces a pulse modulated signal and it is applied to Power Amplifier. Power Amplifier − It amplifies the power levels of the pulse modulated signal. Local Oscillator − It produces a signal having stable frequency $f_l$. Hence, it is also called stable Local Oscillator. The output of Local Oscillator is applied to both Mixer-I and Mixer-II. Coherent Oscillator − It produces a signal having an Intermediate Frequency, $f_c$. This signal is used as the reference signal. The output of Coherent Oscillator is applied to both Mixer-I and Phase Detector. Mixer-I − Mixer can produce either sum or difference of the frequencies that are applied to it. The signals having frequencies of $f_l$ and $f_c$ are applied to Mixer-I. Here, the Mixer-I is used for producing the output, which is having the frequency $f_l+f_c$. Duplexer − It is a microwave switch, which connects the Antenna to either the transmitter section or the receiver section based on the requirement. Antenna transmits the signal having frequency $f_l+f_c$ when the duplexer connects the Antenna to power amplifier. Similarly, Antenna receives the signal having frequency of $f_l+f_cpm f_d$ when the duplexer connects the Antenna to Mixer-II. Mixer-II − Mixer can produce either sum or difference of the frequencies that are applied to it. The signals having frequencies $f_l+f_cpm f_d$ and $f_l$ are applied to Mixer-II. Here, the Mixer-II is used for producing the output, which is having the frequency $f_cpm f_d$. IF Amplifier − IF amplifier amplifies the Intermediate Frequency (IF) signal. The IF amplifier shown in the figure amplifies the signal having frequency $f_c+f_d$. This amplified signal is applied as an input to Phase detector. Phase Detector − It is used to produce the output signal having frequency $f_d$ from the applied two input signals, which are having the frequencies of $f_c+f_d$ and $f_c$. The output of phase detector can be connected to Delay line canceller. MTI Radar with Power Oscillator Transmitter The block diagram of MTI Radar with power oscillator transmitter looks similar to the block diagram of MTI Radar with power amplifier transmitter. The blocks corresponding to the receiver section will be same in both the block diagrams. Whereas, the blocks corresponding to the transmitter section may differ in both the block diagrams. The block diagram of MTI Radar with power oscillator transmitter is shown in the following figure. As shown in the figure, MTI Radar uses the single Antenna for both transmission and reception of signals with the help of Duplexer. The operation of MTI Radar with power oscillator transmitter is mentioned below. The output of Magnetron Oscillator and the output of Local Oscillator are applied to Mixer-I. This will further produce an IF signal, the phase of which is directly related to the phase of the transmitted signal. The output of Mixer-I is applied to the Coherent Oscillator. Therefore, the phase of Coherent Oscillator output will be locked to the phase of IF signal. This means, the phase of Coherent Oscillator output will also directly relate to the phase of the transmitted signal. So, the output of Coherent Oscillator can be used as reference signal for comparing the received echo signal with the corresponding transmitted signal using phase detector. The above tasks will be repeated for every newly transmitted signal. Learning working make money

Radar Systems – Range Equation Radar range equation is useful to know the range of the target theoretically. In this chapter, we will discuss the standard form of Radar range equation and then will discuss about the two modified forms of Radar range equation. We will get those modified forms of Radar range equation from the standard form of Radar range equation. Now, let us discuss about the derivation of the standard form of Radar range equation. Derivation of Radar Range Equation The standard form of Radar range equation is also called as simple form of Radar range equation. Now, let us derive the standard form of Radar range equation. We know that power density is nothing but the ratio of power and area. So, the power density, $P_{di}$ at a distance, R from the Radar can be mathematically represented as − $$P_{di}=frac{P_t}{4pi R^2}:::::Equation:1$$ Where, $P_t$ is the amount of power transmitted by the Radar transmitter The above power density is valid for an isotropic Antenna. In general, Radars use directional Antennas. Therefore, the power density, $P_{dd}$ due to directional Antenna will be − $$P_{dd}=frac{P_tG}{4pi R^2}:::::Equation:2$$ Target radiates the power in different directions from the received input power. The amount of power, which is reflected back towards the Radar depends on its cross section. So, the power density $P_{de}$ of echo signal at Radar can be mathematically represented as − $$P_{de}=P_{dd}left (frac{sigma}{4pi R^2}right ):::::Equation:3$$ Substitute, Equation 2 in Equation 3. $$P_{de}=left (frac{P_tG}{4pi R^2}right )left (frac{sigma}{4pi R^2}right ):::::Equation:4$$ The amount of power, $P_r$ received by the Radar depends on the effective aperture, $A_e$ of the receiving Antenna. $$P_r=P_{de}A_e:::::Equation:5$$ Substitute, Equation 4 in Equation 5. $$P_r=left (frac{P_tG}{4pi R^2}right )left (frac{sigma}{4pi R^2}right )A_e$$ $$Rightarrow P_r=frac{P_tGsigma A_e}{left (4piright )^2 R^4}$$ $$Rightarrow R^4=frac{P_tGsigma A_e}{left (4piright )^2 P_r}$$ $$Rightarrow R=left [frac{P_tGsigma A_e}{left (4piright )^2 P_r}right ]^{1/4}:::::Equation:6$$ Standard Form of Radar Range Equation If the echo signal is having the power less than the power of the minimum detectable signal, then Radar cannot detect the target since it is beyond the maximum limit of the Radar”s range. Therefore, we can say that the range of the target is said to be maximum range when the received echo signal is having the power equal to that of minimum detectable signal. We will get the following equation, by substituting $R=R_{Max}$ and $P_r=S_{min}$ in Equation 6. $$R_{Max}=left [frac{P_tGsigma A_e}{left (4piright )^2 S_{min}}right ]^{1/4}:::::Equation:7$$ Equation 7 represents the standard form of Radar range equation. By using the above equation, we can find the maximum range of the target. Modified Forms of Radar Range Equation We know the following relation between the Gain of directional Antenna, $G$ and effective aperture, $A_e$. $$G=frac{4pi A_e}{lambda^2}:::::Equation:8$$ Substitute, Equation 8 in Equation 7. $$R_{Max}=left [ frac{P_tsigma A_e}{left ( 4pi right )^2S_{min}}left ( frac{4pi A_e}{lambda^2} right ) right ]^{1/4}$$ $$Rightarrow R_{Max}=left [frac{P_tGsigma {A_e}^2}{4pi lambda^2 S_{min}}right ]^{1/4}:::::Equation:9$$ Equation 9 represents the modified form of Radar range equation. By using the above equation, we can find the maximum range of the target. We will get the following relation between effective aperture, $A_e$ and the Gain of directional Antenna, $G$ from Equation 8. $$A_e=frac{Glambda^2}{4pi}:::::Equation:10$$ Substitute, Equation 10 in Equation 7. $$R_{Max}=left [frac{P_tGsigma}{left (4piright )^2 S_{min}}(frac{Glambda^2}{4pi})right ]^{1/4}$$ $$Rightarrow R_{Max}=left [frac{P_tG^2 lambda^2 sigma}{left (4piright )^2 S_{min}}right ]^{1/4}:::::Equation:11$$ Equation 11 represents another modified form of Radar range equation. By using the above equation, we can find the maximum range of the target. Note − Based on the given data, we can find the maximum range of the target by using one of these three equations namely Equation 7 Equation 9 Equation 11 Example Problems In previous section, we got the standard and modified forms of the Radar range equation. Now, let us solve a few problems by using those equations. Problem 1 Calculate the maximum range of Radar for the following specifications − Peak power transmitted by the Radar, $P_t=250KW$ Gain of transmitting Antenna, $G=4000$ Effective aperture of the receiving Antenna, $A_e=4:m^2$ Radar cross section of the target, $sigma=25:m^2$ Power of minimum detectable signal, $S_{min}=10^{-12}W$ Solution We can use the following standard form of Radar range equation in order to calculate the maximum range of Radar for given specifications. $$R_{Max}=left [frac{P_tG sigma A_e}{left (4pi right )^2 S_{min}}right ]^{1/4}$$ Substitute all the given parameters in above equation. $$R_{Max}=left [frac{ left ( 250times 10^3 right )left ( 4000 right )left ( 25 right )left ( 4 right )}{left ( 4pi right )^2 left ( 10^{-12} right )} right ]^{1/4}$$ $$Rightarrow R_{Max}=158:KM$$ Therefore, the maximum range of Radar for given specifications is $158:KM$. Problem 2 Calculate the maximum range of Radar for the following specifications. Operating frequency, $f=10GHZ$ Peak power transmitted by the Radar, $P_t=400KW$ Effective aperture of the receiving Antenna, $A_e=5:m^2$ Radar cross section of the target, $sigma=30:m^2$ Power of minimum detectable signal, $S_{min}=10^{-10}W$ Solution We know the following formula for operating wavelength, $lambda$ in terms of operating frequency, f. $$lambda =frac{C}{f}$$ Substitute, $C=3times 10^8m/sec$ and $f=10GHZ$ in above equation. $$lambda =frac{3times 10^8}{10times 10^9}$$ $$Rightarrow lambda=0.03m$$ So, the operating wavelength,$lambda$ is equal to $0.03m$, when the operating frequency, $f$ is $10GHZ$. We can use the following modified form of Radar range equation in order to calculate the maximum range of Radar for given specifications. $$R_{Max}=left [frac{P_t sigma {A_e}^2}{4pi lambda^2 S_{min}}right ]^{1/4}$$ Substitute, the given parameters in the above equation. $$R_{Max}=left [ frac{left ( 400times 10^3 right )left ( 30 right )left ( 5^2 right )}{4pileft ( 0.003 right )^2left ( 10 right )^{-10}} right ]^{1/4}$$ $$Rightarrow R_{Max}=128KM$$ Therefore, the maximum range of Radar for given specifications is $128:KM$. Learning working make money

Radar Systems – CW Radar basic Radar uses the same Antenna for both transmission and reception of signals. We can use this type of Radar, when the target is stationary, i.e., not moving and / or when that Radar can be operated with pulse signal. The Radar, which operates with continuous signal (wave) for detecting non-stationary targets, is called Continuous Wave Radar or simply CW Radar. This Radar requires two Antennas. Among which, one Antenna is used for transmitting the signal and the other Antenna is used for receiving the signal. Block Diagram of CW Radar We know that CW Doppler Radar contains two Antennas − transmitting Antenna and receiving Antenna. Following figure shows the block diagram of CW Radar − The block diagram of CW Doppler Radar contains a set of blocks and the function of each block is mentioned below. CW Transmitter − It produces an analog signal having a frequency of $f_o$. The output of CW Transmitter is connected to both transmitting Antenna and Mixer-I. Local Oscillator − It produces a signal having a frequency of $f_l$. The output of Local Oscillator is connected to Mixer-I. Mixer-I − Mixer can produce both sum and difference of the frequencies that are applied to it. The signals having frequencies of $f_o$ and $f_l$ are applied to Mixer-I. So, the Mixer-I will produce the output having frequencies $f_o+f_l$ or $f_o−f_l$. Side Band Filter − As the name suggests, side band filter allows a particular side band frequencies − either upper side band frequencies or lower side band frequencies. The side band filter shown in the above figure produces only upper side band frequency, i.e., $f_o+f_l$. Mixer-II − Mixer can produce both sum and difference of the frequencies that are applied to it. The signals having frequencies of $f_o+f_l$ and $f_opm f_d$ are applied to Mixer-II. So, the Mixer-II will produce the output having frequencies of 2$f_o+f_lpm f_d$ or $f_lpm f_d$. IF Amplifier − IF amplifier amplifies the Intermediate Frequency (IF) signal. The IF amplifier shown in the figure allows only the Intermediate Frequency, $f_lpm f_d$ and amplifies it. Detector − It detects the signal, which is having Doppler frequency, $f_d$. Doppler Amplifier − As the name suggests, Doppler amplifier amplifies the signal, which is having Doppler frequency, $f_d$. Indicator − It indicates the information related relative velocity and whether the target is inbound or outbound. CW Doppler Radars give accurate measurement of relative velocities. Hence, these are used mostly, where the information of velocity is more important than the actual range. Learning working make money

Radar Systems – Overview RADAR is an electromagnetic based detection system that works by radiating electromagnetic waves and then studying the echo or the reflected back waves. The full form of RADAR is RAdio Detection And Ranging. Detection refers to whether the target is present or not. The target can be stationary or movable, i.e., non-stationary. Ranging refers to the distance between the Radar and the target. Radars can be used for various applications on ground, on sea and in space. The applications of Radars are listed below. Controlling the Air Traffic Ship safety Sensing the remote places Military applications In any application of Radar, the basic principle remains the same. Let us now discuss the principle of radar. Basic Principle of Radar Radar is used for detecting the objects and finding their location. We can understand the basic principle of Radar from the following figure. As shown in the figure, Radar mainly consists of a transmitter and a receiver. It uses the same Antenna for both transmitting and receiving the signals. The function of the transmitter is to transmit the Radar signal in the direction of the target present. Target reflects this received signal in various directions. The signal, which is reflected back towards the Antenna gets received by the receiver. Terminology of Radar Systems Following are the basic terms, which are useful in this tutorial. Range Pulse Repetition Frequency Maximum Unambiguous Range Minimum Range Now, let us discuss about these basic terms one by one. Range The distance between Radar and target is called Range of the target or simply range, R. We know that Radar transmits a signal to the target and accordingly the target sends an echo signal to the Radar with the speed of light, C. Let the time taken for the signal to travel from Radar to target and back to Radar be ‘T’. The two way distance between the Radar and target will be 2R, since the distance between the Radar and the target is R. Now, the following is the formula for Speed. $$Speed= frac{Distance}{Time}$$ $$Rightarrow Distance=Speedtimes Time$$ $$Rightarrow 2R=Ctimes T$$ $$R=frac{CT}{2}:::::Equation:1$$ We can find the range of the target by substituting the values of C & T in Equation 1. Pulse Repetition Frequency Radar signals should be transmitted at every clock pulse. The duration between the two clock pulses should be properly chosen in such a way that the echo signal corresponding to present clock pulse should be received before the next clock pulse. A typical Radar wave form is shown in the following figure. As shown in the figure, Radar transmits a periodic signal. It is having a series of narrow rectangular shaped pulses. The time interval between the successive clock pulses is called pulse repetition time, $T_P$. The reciprocal of pulse repetition time is called pulse repetition frequency, $f_P$. Mathematically, it can be represented as $$f_P=frac{1}{T_P}:::::Equation:2$$ Therefore, pulse repetition frequency is nothing but the frequency at which Radar transmits the signal. Maximum Unambiguous Range We know that Radar signals should be transmitted at every clock pulse. If we select a shorter duration between the two clock pulses, then the echo signal corresponding to present clock pulse will be received after the next clock pulse. Due to this, the range of the target seems to be smaller than the actual range. So, we have to select the duration between the two clock pulses in such a way that the echo signal corresponding to present clock pulse will be received before the next clock pulse starts. Then, we will get the true range of the target and it is also called maximum unambiguous range of the target or simply, maximum unambiguous range. Substitute, $R=R_{un}$ and $T=T_P$ in Equation 1. $$R_{un}=frac{CT_P}{2}:::::Equation:3$$ From Equation 2, we will get the pulse repetition time, $T_P$ as the reciprocal of pulse repetition frequency, $f_P$. Mathematically, it can be represented as $$T_P=frac{1}{f_P}:::::Equation:4$$ Substitute, Equation 4 in Equation 3. $$R_{un}=frac{Cleft ( frac{1}{f_P} right )}{2}$$ $$R_{un}=frac{C}{2f_P}:::::Equation:5$$ We can use either Equation 3 or Equation 5 for calculating maximum unambiguous range of the target. We will get the value of maximum unambiguous range of the target, $R_{un}$ by substituting the values of $C$ and $T_P$ in Equation 3. Similarly, we will get the value of maximum unambiguous range of the target, $R_{un}$ by substituting the values of $C$ and $f_P$ in Equation 5. Minimum Range We will get the minimum range of the target, when we consider the time required for the echo signal to receive at Radar after the signal being transmitted from the Radar as pulse width. It is also called the shortest range of the target. Substitute, $R=R_{min}$ and $T=tau$ in Equation 1. $$R_{min}=frac{Ctau}{2}:::::Equation:6$$ We will get the value of minimum range of the target, $R_{min}$ by substituting the values of $C$ and $tau$ in Equation 6. Learning working make money