High Frequency Communication and Sensing: Traveling-Wave Techniques
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One is shown blue in Fig. The focal lengths corresponding to the focal points can be different from each other. Compared to an optical lens, the delay line network comprises the actual lens position dependent phase shift , while the parallel plate waveguide corresponds to the free space region between the focal plane and the lens surface. If additional beam ports are needed, focal spots are found on an approximately circular arc between and beyond the exact foci.
In principle, the usable beam and antenna port contours extend to the point of their intersection dashed in Fig.
Online High Frequency Communication And Sensing: Traveling Wave Techniques 2014
The edges between the end points of the port contours are terminated grey in Fig. Rubber absorber glued on top of 1 to 2 cm of microstrip line is a practical termination for millimeter waves.
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From the input parameters, such as desired phase shift, focal lengths and geometry and transmission line parameters the positions of the antenna ports and the lengths of the delay lines are determined. In case that more beam ports than the 3 ideal foci are required, a numerical optimization of the positions of the additional beam ports is conducted. The result of the solution of the analytical design equations is shown in Fig. The beam ports are located on the left and the antenna ports are on the right circles. The delay lines are indicated by the horizontal lines at the antenna ports.
The front faces of the tapers are also shown in Fig.
We use the total phase error sum of absolute values of the phase deviation versus position to determine the location of the non-ideal focusing points beam ports numerically. The same procedure is also employed at the ideal beam port foci and antenna ports  -. Here, the results are restricted to two ports on one side of the lens; for the other two ports, the outcome is symmetrical.
The dark spots give the location of the beam and antenna port foci.
In our example, good phase accuracy is found for location tolerances of a few hundred micrometers. Generally, the light yellow regions indicate total phase deviations of a few degrees, which would generally be acceptable.
The white line indicates the phase shift of the antenna signals. It is interesting to note that the low phase error regions at the beam ports have the form of an elongated valley. As long as the beam port is on the bottom of this valley, low phase errors are obtained. From this observation, we can postulate a new design paradigm: the longitudinal orientation of the beam port feeding tapers should be along these valleys.
In this case, uncertainties in the position of the phase centers of these tapers will have little influence on the lens performance, as the phase center of the taper will in any case be on its symmetry axis. Classically, the beam port faces are oriented tangentially on a circle around the center of the antenna port contour position 0,0 in Fig. Comparing the electrical lengths of the lens and delay line structure using the ideal focus points with the desired phase distributions on the antenna ports yields a very good agreement, as shown in Fig. The design of the feed tapers has to be conducted with some care.
The length of the tapers should be fixed to a value which ensures good matching, e. As the design is optimized empirically, the width of the tapers may change during the design process. As shown in Fig. The radiation characteristics of the tapers are calculated assuming a uniform E-field distribution at the front face. Taking into account the propagation path length and the overlap between beam and antenna port radiation patterns, the transmission properties of the lens and beam pointing losses are calculated.
With these results, the lens is empirically optimized for optimum transmission. Typically we find that the focal lengths of on- and off-axis focal points should be equal. In addition, lateral extensions of beam and antenna port contours should also roughly be equal compare Fig. With the overall size of the lens the focusing of the port tapers can be controlled, as a larger feed will focus the radiation more strongly towards the middle of the opposite face of the parallel-plate waveguide.
This may be used to control the sidelobe level. Finally, the complete lens design can be validated in a 2. The design in Fig. The figure is drawn to scale. The lens combined with element antenna columns is depicted in Fig. Then, sinus-shaped sections are added, with which the specific delay is realized. The loss of the lens with delay line network amounts to approx.
Different focal lengths were tested, as can be seen in Fig. If the size of the parallel-plate waveguide is made larger, the delay line network becomes shorter. We employ a novel routing scheme, which consists of a number of lines and circular arcs. This network is generally smaller than the conventional one and induces less radiation loss due to the larger radii of the arcs compare Fig. Additionally, multiples of a guided wavelength are added towards the outer antenna ports, so that an additional amplitude taper comes in effect.
This normally reduces the sidelobe level. As can be seen, the pattern of the latter can be reproduced quite well by the inner four beams of the Rotman lens, but the overall gain of the Rotman-lens based antenna is smaller. The Rotman lens with delay line network induces losses of 6. The design with 8 beam ports resulted from the empirical optimization of the lens performance. The desired 4 beam ports would occupy only a small part of the beam port contour, so additional ports were added.
If the beam ports were increased in size, their radiation into the parallel-plate waveguide would be too much focused and would not illuminate the antenna ports at the edges sufficiently. Even from the early beginning in automotive radar the key driver of all these investigations has been the idea of collision avoidance. Currently these systems are moving from autonomous cruise control and crash warning to real pre-crash reaction.
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Control systems of the vehicle throttle, brakes act when the radar system detects an unavoidable collision. The future concept of these systems is to create a virtual safety belt around the vehicle with multiple sensors, enhancing the current scenario towards the goal of autonomous driving. To achieve this goal, higher resolution radars and better accuracy is required. A frequency of about GHz is proposed here because radar antennas with better resolution and narrower beams than the actual 77 GHz sensors can be developed.
Also, the very high frequency allows an easy integration, because the antenna size is very small. In addition, this band has been investigated as a serious candidate for future automotive radar systems Schneider, The proposed antenna consists of a number of parallel patch columns, which are driven by a corporate feed network printed on one side of a grounded substrate as shown in Fig. Patches are connected by high impedance lines, while the main feeder is a 50 Ohm microstrip line.
This feeding concept enables beam steering in an easy way and the area consumption is kept low.
In this arrangement, the main lobe points to the broadside direction, which is usually required in an automotive radar antenna sensor. Moreover, as the main feeder is a corporate line, this direction is independent of the frequency.
Sidelobe level in elevation should be low, as it determines the amount of clutter that the final system may have. The performance in this aspect was improved by using a tapered power distribution across the patch column, so more power is concentrated in the broadside direction.
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This is done by changing the width of the patch along the column. For the single element, a patch antenna was chosen, because of its flexibility and easiness of design and fabrication. For designing the whole array, first a single cell was optimized for operation at a frequency of GHz see 3. The array calculator of HFSS was then used for finding the right number of cells for a 12 dBi gain array.
The last patch was designed with an inset to allow an easy control of the whole antenna matching. Results of matching show very good agreement between the simulated design and the measured one. The matching bandwidth Fig.
calsonosmang.tk Best matching is moved in frequency with respect to the original design due to inaccuracies of the lab-scale fabrication. Nevertheless, the fabrication process can be optimized because the behavior of the photolithography and etching process is very predictable.