The sideband that has the maximum response indicates the sector of the field-of-view that the signal comes from and provides a coarse estimation of the arrival direction. Thirdly, the received signals of two identical 4D arrays are phase-compared, and multiple sum-difference patterns are formed with one sum-difference pattern for one sector.
Note that, in Figure 7, the power patterns of the two subarrays are the same and their phase patterns differ by a phase difference of . Direction Finding Antennas 14-1 The use of radio for direction-finding purposes (RDF) is almost as old as its application for com-munications. where represents the complex excitation weighting for the th element at the th sideband and is the time modulation frequency. The experimental results show that this novel monopulse system provides unambiguous direction finding over a spatial field-of-view of ±60° with very low computational complexity. The full array is divided into two subarrays. – Display results in a real-time graphical interface . However, the contradiction between precise angle estimation and large field-of-view was not addressed in these papers. Figure 12 shows the calibrated for different sideband signals. The RDF41 can work as pseudo doppler as well as amplitude…
It can be seen that the received signals of the two subarrays have the same amplitude, and the only difference is the phase response. The measurement error for a spatial field of ±65° is shown in Figure 16. The 4D antenna array is demonstrated for the application of direction finding over a wide field-of-view in this paper. Overview . However, the low SNR performance of the received signals in 4D arrays increases the measurement errors.
The phase-comparison monopulse is defined in terms of receiving beams with different phase centers [1] and is adopted as the type of monopulse in this paper. The SNR of the received signal decreases with the increase of . As a result, multiple pairs of sum-difference patterns with different pointing directions are formed at different sidebands.
As a result of time modulation in 4D arrays, sidebands are generated at multiples of the time modulation frequency. Firstly, the large field-of-view is divided into several sectors. Unlike conventional arrays operating in 3-dimentional (3D) space, the 4D antenna arrays are formed by introducing a fourth dimension, time, into the array design, which can be realized by time-modulating conventional arrays with RF switches. This work was supported by the Natural Science Foundation of China (Grant no. where is the received signal voltage of a single element, is the element space, is the subarray distance, and refers to the free space wave number at the operating frequency. To extract the angle bearing information of the transmitted signal, the exported signals are processed in the following way, as shown in Figure 13.
The time modulation frequency is set to be KHz. We will be providing unlimited waivers of publication charges for accepted research articles as well as case reports and case series related to COVID-19. In this paper, a novel phase-comparison monopulse based on the 4D antenna array is presented. Traditional monopulse systems used for direction finding usually face the contradiction between high angle precision and wide angle-searching field, and a compromise has to be made. The active element pattern is the radiation pattern of an element when it is located in the array with other elements matched perfectly [24], taking into account the effect of mutual coupling between array elements. The waveforms of the two received signals of subarray 1 and subarray 2 are shown in Figure 14(a), and their corresponding spectra are shown in Figure 14(b). These sideband signals can either be suppressed or be enhanced through the optimization of the exciting time sequences [7–13].
In Section 4, an experimental system composed of 4D arrays is built, and the experimental results and corresponding signal processing steps are presented in detail.
<< For accurate angle measurement, the active element patterns of the dipole array are firstly measured without time modulation. %�쏢
In fact, since tangent and sine functions are both periodic functions, any that satisfies Equation (3) is the basic direction-finding equation, which relates the difference-sum ratio to the bearing angle , with the distance of the two subarray as the parameter. In order to steer the multiple beams to the directions of zero and pole points shown in Figure 5, the DE algorithm is used to optimize the time sequence of each subarray. The number of the sideband having the maximum amplitude response is designated as .
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Equation (5) differs from the array factor (1) of a conventional array by the time factor . 3 0 obj For a signal coming from different directions, the corresponding can be used. In Section 3, the novel monopulse system based on a 4D array is presented and its working principle is analyzed. In order to maximize the signal-to-noise ratio (SNR) of the received signal, a set of band-pass filters can be mounted between the antenna elements and RF switches to filter out the noises outside the center band. �����?
��g� Direction Finding Using Multiple Sum and Difference Patterns in 4D Antenna Arrays, School of Electronic Engineering, University of Electronic Science and Technology of China (UESTC), Chengdu 611731, China, International Journal of Antennas and Propagation, W. B. Kendall, “Unambiguous accuracy of an interferometer angle-measuring system,”, L. G. Bullock, G. R. Oeh, and J. J. Sparagna, “An analysis of wide-band microwave monopulse direction-finding techniques,”, E. Jacobs and E. W. Ralston, “Ambiguity resolution in interferometry,”, H. E. Shanks and R. W. Bickmore, “Four-dimensional electromagnetic radiators,”, W. H. Kummer, A. T. Villeneuve, T. S. Fong, and F. G. Terrio, “Ultra-low sidelobes from time-modulated arrays,”, S. Yang, Y. Since its inception in the 1959 [5], many researchers have paid great attention to this novel technology, especially during the past decade [6–19]. For a plane wave with a frequency of and the incident angle of with respect to the broadside of the array, the array factor of the 4D array can be given as By comparing the amplitude of the difference signal with that of the sum signal, the difference-sum ratio can be obtained, and thus the direction of the signal can be easily determined. Other ambiguity resolution techniques include the use of multiple frequencies, baseline rotation or frequency modulation, and so forth. By looking up the difference-sum ratio shown in Figure 12, the ratio +0.137 corresponds to a wave coming from the direction of °; thus the measurement error is 0.5°.
In order to realize a SNR equivalent to that of a conventional array, a set of BPFs must be added after the elements to filter out the noise outside the center band and avoid the aliasing effect, when the bandwidth of the incoming signal is wider than the modulation frequency.
The full 4D array is divided into two subarrays and the differential evolution (DE) algorithm is used to optimize the time sequence of each subarray to generate multibeams at the center frequency and low sidebands. Figure 11 shows the calibrated sum-difference pattern at , +1, +2, and +3 sideband. As the distance between the subarrays becomes larger, the slope of the difference-sum ratio becomes steeper and more zeros and poles are formed. Since the horn as the transmitted antenna is at a fixed position, the 4D array is rotated every 5° from −65° to 65° to simulate the situation where the signal comes from a spatial angle. B. Gan, A. Qing, and P. K. Tan, “Design of a uniform amplitude time modulated linear array with optimized time sequences,”, S. Pal, S. Das, and A. Basak, “Design of time-modulated linear arrays with a multi-objective optimization approach,”, L. Poli, P. Rocca, L. Manica, and A. Massa, “Time modulated planar arrays—analysis and optimisation of the sideband radiations,”, L. Poli, P. Rocca, and A. Massa, “Sideband radiation reduction exploiting pattern multiplication in directive time-modulated linear arrays,”, L. Poli, P. Rocca, G. Oliveri, and A. Massa, “Harmonic beamforming in time-modulated linear arrays,”, Y. Tong and A. Tennant, “A two-channel time modulated linear array with adaptive beamforming,”, A. Tennant and B.
Direction Finding Antenna Arrays for the Randomly Located Source Houcem Gazzah and Jean-Pierre Delmas Abstract We consider the problem of sensor placement for estimating the direction of arrival of a narrow-band source randomly located in the far-field of a planar antenna array. In Figure 14(b), the maximum amplitude response appears in the +2nd sideband, which indicates that the wave comes from the sector around ° and the difference-sum ratio should be chosen as a reference. Accordingly, is given by
A sinusoid signal of 2.6 GHz is sent to the horn antenna and transmitted. For the wave coming from the direction of −60° to 60°, the measurement error is less than 2°. The sideband that has the maximum response provides a rough estimation of signal direction.
As a set of suitable BPFs are not available and not used in the experiment, the SNRs of the received signals are not high enough, especially for the signals from the edges of the field-of-view. When a plane wave impinges on the array with an angle measured from broadside, the received signals or voltages of the two subarrays can be written as The advantage of the proposed technique is that it can achieve direction finding over a much wider field-of-view by adding a set of RF switches to a conventional array. However, these methods either require extra antenna element, receiver electronics and additional installation space, or require the increased complexity or computation time. where denotes the amplitude of the difference signal at th sideband, denotes the amplitude of the sum signal at th sideband, and is the equivalent complex excitation weighting for the th element at the th sideband, calculated by (8). As can be seen, the at different sideband are not the same any more. The time modulation technique in 4D arrays is used to generate multiple beams at different sidebands and the phase-comparison monopulse is used to generate the sum-difference patterns. Take the case where the transmitter is in the 30° direction as an example. A classic and simple type of monopulse is the phase-comparison monopulse, which uses the measured phase differences of two antennas’ outputs to establish the target bearing.
/Filter /FlateDecode The spectra of the two received signals can be computed using the fast Fourier transform (FFT) algorithm and their spectra response is then examined. With frequency range options from 20 MHz to 18 GHz and twin receiver channels, Arrays provide simultaneous monitoring, DF and geolocation capabilities.
In this paper, the time modulation technique in four-dimensional (4D) antenna array is introduced into the conventional phase-comparison monopulse to form a novel direction-finding system, in which both high angle resolution and wide field-of-view are realized.
Then the multibeams of the two subarrays are phase-compared with each other and multiple pairs of sum-difference beams are formed at different sidebands and point to different spatial angles. is a valid solution for (3). Some monopulse systems based on the 4D arrays have been conceptually designed and numerically verified [16–19]. <> There are two types of monopulse systems, namely, amplitude-comparison monopulse and phase-comparison monopulse. If the angle-searching range is inside the field from −14° to 14°, it is easy to determine the angle as is monotonic inside this small field.
As can be seen, these patterns are different due to mutual coupling effect, the ground plane, and so forth.
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