Graph of SBR1(max) and SBR2(max) for different values of SLL samples at f0. The proposed scheme for periodic switching of antenna array elements is shown in Figure 13. Flowchart of the generalized intersection approach algorithm used for far-field amplification.
A common approach in the literature is to directly minimize the cross-polar component of the far field [19, 20]. This is done using Eq. 2) for cross polar pattern masks in the front projector of the generalized IA.
Introduction
Phase compensation techniques based on projection method and convex optimization (phase correction only) for comparing the maximum gain of a phase compensated conformal antenna array were discussed. These fundamental maximum compensated gain limitations of the phase compensation techniques can be used by a designer to predict the maximum broadside obtainable theoretical gain on a conformal antenna array for a specific deformed surface. Another exciting application of conformal antenna array is at the base station in a cellular mobile communication system.
As a result, the radiation pattern of the conformal antenna array changes, as shown in Figure 1. Various methods have been proposed in the literature to compensate for the reduction in directivity and to improve/correct the radiation pattern of a conformal antenna array. In summary, it has been shown that the radiation pattern of a conformal antenna array can be improved with various calibration techniques, signal processing algorithms, sensor circuits, and phase and amplitude adjustments.
Subsequently, compensated gain will be compared to linear flat array using both methods to investigate the gain limitations of these compensated techniques for conformal antenna arrays. Projection Method for Pattern Restoration of Conformal Antenna Array The projection method in [26] and its further exploration in ares.
Computing the distance to the projected elements
The results in [18] indicate that the directivity of conformal antenna array can be reduced by 5–15 dB. This chapter will focus on phase compensation of four-element conformal cylindrical antenna array using (1) projection method and (2) convex optimization method. Projection method for pattern retrieval of conformal antenna array The projection method in [26] and its further exploration in The projection method in [26] and its further exploration is used here to obtain the behavior of the conformal antenna array shown in Figure 2, to describe.
If each antenna element on the cylindrical surface is excited with uniform amplitudes and phases, that is, if excitation weights w n = 1 e j 0° are placed on all elements, then the E-fields radiated by the antenna elements will arrive at the reference plane with different phases. If the E-fields E ±n e j ϕ ±n of antenna elements with the same phase are made to arrive at the reference plane, then constructive interference will result in a wide radiation pattern and pattern recovery to latitude is possible. This will cause the E-fields of antenna elements to arrive at the reference plane with the same phase and will produce a constructive radiation pattern in the +z direction.
To calculate this compensated phase, the antenna elements are projected on the reference plane, and then the distances from antenna elements on the cylindrical surface (shown as black dots) to the projected elements on the reference plane (shown as dashed circles) are calculated. Using the relation between L = r𝛉𝛉 , the angular positions of antenna elements can be calculated, where L = 𝛌𝛌 / 2 is the distance between the elements on the cylindrical surface.
Computing the compensated phase
Array factor expression
Convex optimization for pattern recovery of conformal antenna array The broadside gain maximization problem of a conformal antenna array in Figure 2
Analytical and simulation results
The gain G c (between uncorrected and corrected) and G ref (between corrected and linear) decreases with increasing r. But it is obvious that in all cases. a) Analytical results for phase compensation of a conformal cylindrical antenna array with r = 8 cm. The compensated (corrected) weights were calculated using the projection method in Section 2 and convex optimization in Section 3. Analytical results using Eq. 5) and the CST simulation results using Figure 2 are discussed below. The difference in gain (G ref) between the flat array and the compensated conformal array gain was then calculated and is also given in Table 1.
It can be seen from Figure 4 and Table 1 that the broadside compensated gain Gc of the conformal antenna array is greater than the uncorrected gain and is less than the gain of the flat array using design optimization and convex ( phase correction only ) methods. This is the fundamental limitation of both compensation methods for wide pattern recovery of conformal antenna arrays and should be kept in mind during the design of the conformal antenna array. It should be noted that the convex optimization has more degrees of freedom than the projection method in the sense that the convex optimization yields complex weights (amplitude taper plus phase correction), while the projection method yields only phase correction (one degree of freedom).
However, for latitudinal pattern recovery, convex optimization gives uniform amplitudes (equal to 1) and compensated phases and thus the performance is equivalent to the projection method for lattice pattern restoration. This is an important finding and should be retained in the design phase of conformal antenna arrays.
Conclusion
In the limiting case, when the radius of curvature of conformal cylindrical array increases to 30 cm and above (closer to flat array), the compensated gains increase. a) Analytical results for phase compensation of a conformal cylindrical antenna array with r = 10 cm. In this chapter, phase compensation techniques based on projection method and convex optimization (phase correction only) have been discussed for restoration. a) Analytical results for phase compensation of a conformal cylindrical antenna array with r = 12 cm. The compensated gains of both the methods were compared with linear flat antenna array.
It is shown that the maximum broadside gain recovered with both methods is less than the linear antenna array for severe deformation cases and approaches the gain of linear antenna array for less conformal deformation surfaces. The analytical expressions and the convex optimization algorithm used can be used by a designer to predict the maximum possible compensated gain of a conformal antenna array. a) Analytical results for phase compensation of a conformal cylindrical antenna array with r = 15 cm.
Future work
A note on the fundamental maximum gain limit of the projection method for conformal phased array antennas. Based on various studies, let's consider the main advantages and disadvantages of the operation of the mobile communication system in the millimeter range. The base station is located on a separate mast 3 m high in the geometric center of the service area (see Figure 2).
As it follows from Eq. 2), the direction of the beams deviates whenλ varies, that is, a so-called squinting effect is observed. One of the most promising techniques for designing an RS's PAA is to use IPBFs based on a multiple-beam Butler matrix. The optical output signals of the OMs are fed to a spatial distribution unit based on 88 optical Butler matrix.
In the course of the research, first of all, the accuracy of creating a mmWave 88 integrated OBM is checked. The phase error values for the center and two extreme frequencies of the RF generators.
Venu Madhav and M. Siva Ganga Prasad
Vivaldi antenna
The Vivaldi antenna with its exponentially tapered slot profile is a type of tapered slot antenna (TSA). 1] in his 1974 study introduced the tapered slot antenna as a broadband strip array element capable of multi-octave bandwidths. 3] compared three different TSAs, linearly tapered slot antenna (LTSA), constant width slot antenna (CWSA) and Gibson's exponentially tapered slot antenna, the Vivaldi antenna.
Using a low-dielectric substrate (cu-coated, ε = 2.45) instead of aluminum oxide and the antipodal transition of the slit line. This type of transition offers a relatively wider bandwidth, but the antipodal slit line transition has a major cross-polarization problem.
Principle of operation
- Vivaldi antenna design
- Construction
- Bandwidth consideration
- Fabricated Vivaldi antenna
For military and commercial applications, high-gain, wide-bandwidth antennas are preferred, and Vivaldi antennas or tapered slot antennas (TSA) are the best choice. Problem Statement: The objective is to design single-cavity and dual-cavity Vivaldi antenna operating from 8 to 18 GHz to achieve VSWR less than 3:1 and to compare the antenna performance for single-cavity and dual-cavity Vivaldi antenna. two cavities. Figure 3(a)–(c) shows the front view, back view, and feed arrangement of the dual-cavity Vivaldi antenna.
Figure 4(a) and (b) show the simulated single-cavity Vivaldi antenna and Vivaldi dual-cavity antenna with SMA connector in CST software, respectively. The two substrates are merged into a double layer Vivaldi antenna [8] for both cavities separately. Therefore, the radiation pattern and performance depend on. a) Front view of Vivaldi dual cavity antenna; (b) back view of Vivaldi dual cavity antenna; and (c) feed arrangement of Vivaldi dual cavity antenna.
Figure 6(a) and (b) show the fabricated Vivaldi single-cavity antenna and Vivaldi double-cavity antenna, respectively. These two antennas are tested separately. a) Vivaldi single cavity antenna with SMA connector and (b) Vivaldi double cavity antenna with SMA connector.
Results 1 VSWR
- Return loss
- Return loss measurement
- Anechoic chamber
- Radiation pattern
- Plane patterns
- Gain of the antenna
The measured VSWR for single-cavity antenna and double-cavity Vivaldi antenna are shown in Figure 10(a) and (b), respectively. This is usually expressed as a ratio in decibels (dB). a) Simulated VSWR for single cavity Vivaldi antenna without SMA connector and (b) simulated VSWR for double cavity Vivaldi antenna without SMA connector. The measured return loss for single-cavity Vivaldi antenna and double-cavity Vivaldi antenna are shown in Figure 11(a) and (b), respectively.
Initially, relative gain measurements are performed, which compare to the known gain of the standard antenna. a) H-plane patterns for single-cavity Vivaldi antenna and (b). The simulated gain of a single-cavity Vivaldi antenna ranges from 3.36 to 8.55 dBi over the design frequency band, as shown in Figure 16(a). The simulated gain of a Vivaldi dual-cavity antenna ranges from 2.62 to 8.65 dBi over the design frequency band, as shown in Figure 16(b).
The measured gain diagrams of single-cavity Vivaldi antenna and double-cavity Vivaldi antenna are shown in Figure 17(a) and (b), respectively. The comparison of antenna performance for single cavity Vivaldi antenna and double cavity Vivaldi antenna is reported.
