Radar engineering details are technical details pertaining to the components of a radar and their ability to detect the return energy from moving scatterers — determining an object's position or obstruction in the environment.
Radar sensors are classified by application, architecture, radar mode, platform, and propagation window. Applications of radar include adaptive cruise controlautonomous landing guidance, radar altimeterair traffic managementearly-warning radarfire-control radarforward warning collision sensingground penetrating radarsurveillanceand weather forecasting. The angle of a target is detected by scanning the field of view with a highly directive beam.
This is done electronically, with a phased array antennaor mechanically by rotating a physical antenna. The emitter and the receiver can be in the same place, as with the monostatic radarsor be separated as in the bistatic radars.
Finally, the radar wave emitted can be continuous or pulsed. The choice of the architecture depends on the sensors to be used. An electronically scanned array ESAor a phased arrayoffers advantages over mechanically scanned antennas such as instantaneous beam scanning, the availability of multiple concurrent agile beams, and concurrently operating radar modes.
Design choices are:. A constant phase shift over frequency has important applications as well, albeit in wideband pattern synthesis. The range and velocity of a target are detected through pulse delay ranging and the Doppler effect pulse-Doppleror through the frequency modulation FM ranging and range differentiation.
The range resolution is limited by the instantaneous signal bandwidth of the radar sensor in both pulse-Doppler and frequency modulated continuous wave FMCW radars. Bistatic radars have a spatially dislocated transmitter and receiver. In this case sensor in the transmitting antenna report back to the system the angular position of the scanning beam while the energy detecting ones are with the other antenna. A time synchronisation is crucial in interpreting the data as the receiver antenna is not moving.
Monostatic radars have a spatially co-located transmitter and receiver.
It this case, the emission has to be insulated from the reception sensors as the energy emitted is far greater than the returned one. Radar clutter is platform-dependent. Examples of platforms are airborne, car-borne, ship-borne, space-borne, and ground-based platforms. The radar frequency is selected based on size and technology readiness level considerations.
The radar frequency is also chosen in order to optimize the radar cross-section RCS of the envisioned target, which is frequency-dependent. Radar modes for point targets include search and track. Radar modes for distributed targets include ground mapping and imaging. The radar mode sets the radar waveform.
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Stimson: "Introduction to Airborne Radar, 2nd Ed. Lacomme, J.This paper presents a new high-performance five-element monopulse feed with a simple comparator network for Cassegrain reflector applications. The radiating element is a tapered dielectric rod fed by a circular waveguide which is in turn excited by a printed dipole.
The center element is used for the sum pattern, while top and bottom elements are used for the elevation difference pattern, and left and right elements for the azimuth difference pattern. Out-of-phase excitation for the difference pattern is obtained by antisymmetrically placing two dipoles and combining their outputs with a power combiner.
The optimally designed feed has been fabricated and measured. Measurement shows that the feed has the maximum sum pattern gain of Monopulse antennas of single- or dual-reflector type have widely been employed for telemetry of aerial vehicles [ 1 — 3 ]. The feed is a key element in any monopulse reflector antenna and various designs have been proposed, which can broadly be classified into multiple-element, multiple-aperture, and multimode single aperture configurations.
In a monopulse feed, a comparator network is required to form simultaneously a sum and two difference patterns. The comparator network has usually been realized by using rectangular waveguides or printed transmission lines. Folded hybrid tees or magic tee structures are often applied to the multimode-type feed [ 45 ]. In the planar-type monopulse feed, the plate-laminated waveguide comparator can be used [ 6 ]. The above comparator structures are very complicated requiring extensive design work and high fabrication cost.
Monopulse feeds employing four or five dielectric rods have been investigated in [ 78 ]. Compared to horn-type feeds, they have such advantages as structural simplicity and ease of simultaneous optimization of the sum and difference patterns.
In this letter, we present a new high-performance five-dielectric-rod monopulse feed with a simple comparator network, which is suitable for dual-reflector antenna applications.
Employed in our design is a simple comparator consisting of printed dipoles, coaxial cables, and power combiners. The design and realization of the proposed feed are described in the following.
Figure 1 a shows the overall structure of the proposed feed employing five dielectric rods fed by a circular waveguide, which is in turn excited by a printed dipole. The dielectric rods are modelled by the polycarbonate material having a dielectric constant of 2. For a minimum blockage of a reflector antenna, it is desirable to feed the circular waveguide with an end launcher.
To this end, a coaxial probe-fed transverse wire or an axial ridge can be employed. In this paper, we employed a printed dipole for its ease of design, easy polarization rotation, possibility of dual polarizations, and precise fabrication by chemical etching.
The power-handling capability of the proposed feed is limited by the printed transmission lines and the coaxial cables.
Construction of the proposed feed. Figure 1 b shows the electric field directions in each radiator and the topology of the comparator network. The center rod S provides a sum pattern, while the horizontal D 2 and D 4 and vertical D 3 and D 5 pairs generate the azimuth and elevation difference patterns, respectively. The printed dipole is fed by a panel-mount SMA probe connector.
For the sum channel, the dipole output is routed to an SMA connector at the rear of the feed assembly. For the difference patterns, two dipoles are connected to the input of a coaxial power combiner using a pair of phase-matched coaxial cables and the combiner output is routed to the rear of the feed assembly.
Coaxial cables and power combiners are placed inside a cylindrical metal housing. Figure 2 shows dimensional parameters of the designed feed.
The proposed feed is designed in the following steps.With the steady improvements in tracking radar technologies over the past twenty years, the diameter requirements for antennas has been reduced to match the improvements in transmitter power and receiver sensitivity.
This has led to a need for shorter feeds for use in Cassegrain configurations. Antenna feeds have recently been developed for use at C-band, which are fabricated from cast waveguide components and optimized to tight phase characteristics.Highly Advanced Monopulse Radar System Installed At Berhampur
As a long-standing manufacturer of monopulse comparators, the development of an antenna feed was the next logical step in the extension of the product range. The choice of horn design was crucial to achieving a compact feed design. The first C-band feed was developed for a nine-foot reflector and used a four-horn arrangement directly on the outputs of the comparator.
This gave a small footprint to the feed that reduced blockage of the main reflector; however, the beamwidths in the elevation and azimuth difference patterns were excessive, resulting in high sidelobe levels.
The next generation feeds incorporated two auxiliary horns each in both the azimuth and elevation planes resulting in an eight-horn design. The sum pattern was unaffected by the new arrangement and gave similar performance to the earlier design. The delta patterns were significantly narrower giving reduced sidelobe levels, even though the footprint was increased. The company's compact comparator uses four waveguide tees connected via four extension waveguides to the central four horns.
The C-band version is capable of handling up to 1MW peak power at normal atmospheric pressure. It is designed for operation up to 30 PSIA, and should be pressurized to maintain a dry atmosphere inside the waveguide. Sum, elevation and azimuth ports are provided as waveguide flanged interfaces.
Isolation between any two ports is 35 dB minimum. When fitted to an antenna, cross polarization ratios of 30 dB minimum and an error channel null stability of less than 0. The auxiliary horns are connected to a power combiner network that includes the tees that are part of the central comparator.
The two horizontal horns are combined with the azimuth signal from the comparator while the two vertical horns are combined with the elevation signal. All the interconnecting waveguide are phase matched during manufacture. A final test in an anechoic chamber allows the beam patterns from the main and auxiliary horns to be set coincident, thus providing accurate combining to give the maximum possible null depth.
When fitted to an antenna, null depths of 35 dB minimum are achieved with typical values greater than 50 dB. The first eight-horn feeds used coaxial cables to connect the auxiliary horns to the power combiners. This resulted in a very compact feed, especially in the version fitted to the eight-foot reflectors, as shown in Figure 1.
Further development has replaced the cables with waveguides, which, in addition to providing lower insertion loss, also provide better protection against the environment. Although the earlier feeds were exclusively for C-band operation, versions have been developed for X-band using the company's range of precision investment castings. Compared to a multimode horn the eight-horn array is much shorter in overall length. This allows the C-band version to be fitted in antennas with reflector diameters down to eight feet, without the comparator protruding far behind the dish.
When fitted into a or foot reflector, as shown in Figure 2extension waveguides are fitted to increase the overall feed length. These are used to improve the phase balance of the comparator, resulting in improved antenna performance.
Micro Metalsmiths Ltd.Documentation Help Center. The Monopulse Feed block forms the sum and difference channels used for amplitude monopulse directing finding. Sum and difference channels are derived from signals received by an array. You can feed these channels into the Monopulse Estimator block. Input signal, specified as a complex-valued M -by- N matrix, where M is the number of samples or snapshots of data, and N is the number of array elements.
If the array contains subarrays, then N is the number of subarrays. The size of the first dimension of the input matrix can vary to simulate a changing signal length. A size change can occur, for example, in the case of a pulse waveform with variable pulse repetition frequency.
When you set the Monopulse coverage parameter to Azimuththe steering direction is a scalar and represents the azimuth steering angle. When you set the Monopulse coverage parameter to 3Dthe steering direction vector has the form [azimuthAngle; elevationAngle]where azimuthAngle is the azimuth steering angle, and elevationAngle is the elevation steering angle.
Units are in degrees. Sum-channel signal, returned as a complex-valued M -by-1 column vector, where M is the number of rows of X. Azimuth-difference channel signal, returned as a complex-valued M -by-1 column vector, where M is the number of rows of X. Elevation difference-channel signal, returned as a complex-valued M -by-1 column vector, where M is the number of rows of X. To enable this output port, set the Monopulse coverage parameter to 3D. Estimated direction of target, returned as a real-valued 2-by-1 vector in the form [azimuth,elevation].
To enable this output port, select the Output angle estimate check box. Signal propagation speed, specified as a real-valued positive scalar. The default value of the speed of light is the value returned by physconst 'LightSpeed'. Units are in meters per second. Coverage directions of monopulse feed, specified as 3D or Azimuth. When you set this parameter to 3Dthe monopulse feed forms the sum channel and both azimuth and elevation difference channels.
When you set this parameter to Azimuththe monopulse feed forms the sum channel and the azimuth difference channel. Squint angle, specified as a scalar or real-valued 2-by-1 vector. The squint angle is the separation angle between the sum beam and the beams along the azimuth and elevation directions. When you set the Monopulse coverage parameter to Azimuthset the Squint angle parameter to a scalar. When you set the Monopulse coverage parameter to 3Dyou can specify the squint angle as either a scalar or vector.
If you set the Squint angle parameter to a scalar, the squint angle is the same along both the azimuth and elevation directions. If you set the Squint angle parameter to a 2-by-1 vector, its elements specify the squint angle along the azimuth and elevation directions. Select this check box to output an estimate of the target direction angle using the ANG output port. Click this button to create a Monopulse Estimate block based on the parameters in this block.
Block simulation, specified as Interpreted Execution or Code Generation. If you want your block to run as compiled code, choose Code Generation. Compiled code requires time to compile but usually runs faster. Interpreted execution is useful when you are developing and tuning a model.
You can change and execute your model quickly.Click here to go to our main page on antennas. Click here to go to our page on monopulse antennas. Click here to go to our page one hybrid couplers. New for October ! A monopulse antenna has four feeds, which can be horns or other radiators. We'll use the convention of the Cartesian coordinate system, where the quadrants are labeled starting in the upper right, then go counterclockwise, in this case.
Monopulse comparators can be made with either degree or 90 degree hybrid couplers. We'll show you both ways! Below is a schematic representation of a monopulse comparator using degree rat-race couplers. We've labeled the signals as they go through the network, so you can follow the arithmetic. You could try to find a better explanation of this important antenna concept somewhere else on the web, but you never will!
Check it out, someone stole this figure and published it in Microwave Journal article! The lengths of lines labeled " L1 " don't matter, but they must remain the same phase. The same goes for " L2 " lines. With all monopulse comparators, anything that introduces phase or amplitude errors on the four inputs is going to kill the response.
So when you are laying this out, pay attention to every little detail, make the four inputs EXACTLY the same, and keep as much symmetry as possible. We used Eagleware's Genesys program to simulate a rat-race comparator network, including response versus azimuth angle. We found it slightly awkward to use, especially in perfoming the comparator circuit math, which ideally is done using vectors but Eagleware insists that you first convert everything to real and imaginary parts first.
We used 1 mm for the quarter-wavelength, which works out to a center frequency of about Below is the schematic of the rat-race hybrid that we generated in Genesys:. The plots below shows some of the S-parameter frequency responses of this four-port rat-race network, in this case, the magnitude of the transmission between port 1 and the other three ports. Note that port 1 is the "sum" port, which means that a signal into this port splits equally to in-phase signals to ports 2 and 4.
A New High-Performance Monopulse Feed with a Simple Comparator Network
Port 3 is the "difference" port, which would also split equally into two signals at ports 2 and 4, but they would be anti-phase degree difference. Now it's time to build the comparator network. We know that we need a better figure below. Ports 1, 2, 3 and 4 are the antenna quadrant inputs A, B, C and D. The transmission lines TL1, TL2, and TL3 are used to add phase when the monopulse is tipped off of boresight we'll explan this below. Following the arithmetic of the rat-race, signals at ports 2 and 4 are summed at port 1, and subtracted at port 3, for hybrid network N2 top left.
Here are the equations we came up with to compute the sum and deltas responses using Genesys:.The best and most concise description of monopulse tracking I have ever seen.
Please share the post. Part 1. These signals are processed in monopulse processor which carries out mathematical operations on them to derive Tracking Errors which represent the angular difference between Physical position of antenna axis and the Target from which the signal is emanating.
We divert for a few moments from the topic of Monopulse to clarify the pattern. This is because when the pattern is measured in field it is the voltage output of RF detector which simply gives output proportional to the amplitude of the signal irrespective of the phase.
So it is always positive. In reality the detector input has a negative polarity in the 1 st sidelobe and again positive polarity in 2 nd sidelobe and so on for subsequent sidelobes. Detector output rectifies negative voltage and so the output is always positive as inthe figure on top.
One should keep this in mind because the monopulse concept requires a clarity on phase of the pattern and so we will use only the patterns similar to this figure and not the patterns which are represented only in positive region. We will study the actual composition of Monopulse comparator in a subsequent post.
For the present we understand that the input to it a vector quantity as shown in above figure rather than only the positive humps seen during pattern plotting.
Both outputs are simultaneously plotted in third figure. Notice that the output is ZERO near target and is proportionately positive as we go away from axis in one direction and is proportionately negative as we go away in other direction. Moreover the output is very linear in w. If this voltage is given to the control system then the control system will always bring the antenna towards the target automatically. One more very important observation to be made is what happens to the A - B output if angular difference is large?
Notice that the output changes direction beyond the zone confined with RED lines in previous figure. This will result in false indication of angle outness beyond this zone and will in fact drive the antenna away from target and bring it to rest near zero output which is far away from the real target. Back to Main Index. Unknown January 17, at AM. Unknown June 21, at AM. Unknown January 9, at PM. Newer Post Older Post Home.
Subscribe to: Post Comments Atom.Click here to go to main page on beam-forming networks. Click here to go to our main page on antennas. Click here to go to our page on monopulse comparators. A monopulse antenna is one method of realizing a tracking radar. The word "monopulse" implies that with a single pulse, the antenna can gather angle information, as opposed to spewing out multiple narrow-beam pulses in different directions and looking for the maximum return.
The monopulse uses four antennas or quadrants of a single antenna. They can be horns, or sections of a flat plate array of radiators, or even subarrays of an active electrically scanned antenna AESA phased array.
The elements are all steered together mechanically on a gimbal or electrically using phase shifters in the case of AESA. The target is illuminated by all four quadrants equally. A comparator network is used to "calculate" four return signals. The sum signal has the same pattern in receive as transmit, a broad beam with highest gain at boresight; the sum signal is used to track target distance and perhaps velocity. The elevation difference signal is formed by subtracting the two upper quadrants from the two lower quadrants, and is used to calculate the target's position relative to the horizon.
The azimuth difference signal is formed by subtracting the left quadrants from the right quadrants and is used to calculate the target's position to the left or right. A fourth signal, called the "Q difference" is the diagonal difference of the quadrants; this signal is often left to rot an a termination, so the typical monopulse receiver needs only three channels. Sometimes only a two-channel receiver is used, as the two difference signals are multiplexed into one with a switching arrangement.
Here's a block diagram of a monopulse antenna, including the comparator network. The blue squares represent degree hybrid couplers such as rat-races. You can follow the simple arithmetic as the analog signals are added and subtracted to form the four receiver channels. According to convention, elevation angle is. What happens when the target is not along the boresight of the radar? Let's look at the geometry of target with respect to angle, for a simple monopulse where only two antenna elements horn perhaps are used.
The target is some distance L from the upper quadrants of the monopulse antenna. It is slightly farther away l from the lower quadrants, which varies as the sine of the angle and the distance separating the antennas.
Let's look at the sum and difference outputs versus elevation angle from boresight. In this case we will space the antennas one wavelength apart, and did the math using a combination of Eagleware Genesys to model the tranfer function of the comparator network and Excel to model the horn.