Staircase power distribution of array antenna for UHF band RFID reader

The ultra high frequency (UHF) band spectrum will likely be congested in near future since the next generation wireless as well as Radio Frequency Identification (RFID) system users will witness the use of UHF band technology with increased demand of bandwidth, bit rate, frequency spectrum and power consumption. The alternate solution is the use of millimeter-wave band technology. It is possible to improve data throughput, range resolution and multi-user capability in mm-wave band RFID system. ‘Higher power reception efficiency and lower side lobe level (SLL) of radiation pattern’ is required for RFID system that will increase the tag range and transmission bit rate. At the same time lower SLL will minimize the interference level. Beam pointing error is another problem of UHF band antenna which reduces the tag range and bit rate. These problems can be minimized by using large number of antenna elements. But with UHF band signal it is practically difficult to construct large array antenna; since the array size becomes tremendously larger with the increase of antenna elements. ‘Higher power reception efficiency and lower SLL’ can practically be obtained by using non-uniform power distribution of large number of antenna elements in millimeter wave band. A new and technically better method of beam forming by implementing the concept of staircase power distribution (SPD) of antenna elements at 60 GHz has been investigated and presented in the paper. The SPD method is compared with Gaussian edge tapering method. It was found that the maximum SLL (MSLL) is the lowest in case of SPD. The beam efficiency of SPD is also equivalent to that of Gaussian edge tapering method. It is easier to fabricate a larger number of antenna elements within smaller area with SPD at 60 GHz system; since the antenna size is smaller and the number of different power distribution in SPD case is less and stepwise uniform. Uniform and less number of different power distribution of SPD also minimizes other technical errors.

Multi-beam antenna is an important way to increase the channel capacity of cellular communications. It is available in two ways, one is based on optical methods, such as Luneberg lens and Rotman lens. However, the common problem with this method is that the lens size is too large or difficult to process. Another method is based on beam-forming network composed of coupler and phase shifter, such as Butler matrix. The Butler matrix has been studied for a long time, in the form of microstrip, stripline, or substrate-integrated waveguide. The substrate-integrated waveguide with low insertion loss is mainly used in the higher frequency such as millimeter wave band. The microstrip is mainly used in 4G/5G base stations, suitable for broadband design and process. Low side-lobe level, narrow beams are especially important for multi-beam base station antennas. The traditional Butler matrix is 4 × 4 Butler matrix for 4-beam base stations. However, the traditional Butler matrix can only output equal-amplitude power, with a side-lobe level higher than −13.4 dB. The beam width is too wide due to the few number of antenna. The 4 × 4 Butler Matrix with attenuator can reduce the side-lobe level, but it will increase the insertion loss of the beam-forming network. The 4 × 4 Butler matrix with phase shifter and power divider can form a 4 × 6 Butler matrix, which reduce the beam width beam and side-lobe level. However, for large-angle scanning, not only the side-lobe level, but also the grating-lobe problem caused by the wide-angle scanning and wide antenna spacing needs to be solved. The array with triangle arrangement can reduce the side-lobe and grating-lobe level. A wide-band 4-beam antenna array and beam-forming network for 4G base stations are presented in this paper. Adopting triangular arrangement, the number of antenna in sub-array is increased, and the antenna spacing is reduced, resulting in good side-lobe and grating-lobe level suppression. The output amplitude and phase errors are small over a wide band, with low insertion loss.

This paper presents a new method to calculate slot conductance which takes mutual coupling between the adjacent elements in an array into account. This method is explained for calculating slot conductances of inclined slots in the narrow wall of a rectangular waveguide. Then a slot array with this type of radiating elements is designed for −35 dB side lobe level. The results show that proposed method is excellent to design slot array with low side lobe level. A weak point of inclined slot is high cross polarization. To solve this problem a simple and tunable non-inclined slot is proposed. The proposed method is adopted to design an array using this type of slot. The achieved side lobe level and cross polarization are −33.5 dB and −30 dB respectively over the 9% bandwidth which is suitable for many radar applications.

The development of wideband antennas with low sidelobe level (SLL) is vital for many up-to-date special communication and air traffic control applications. As it has been reported earlier, array antennas have advantages in SLL but are inherently narrower band than reflector antennas. Another question, not easy for array antennas (if being compared with reflectors), is usually the cost. Researchers do their best to extend the bandwidth (BW) of low SLL arrays and reduce their cost. The task to achieve a good SLL is especially difficult in the case of small array aperture because amplitude and phase (A&/spl phi/) errors, the mutual coupling, and edge effects are more influential in this case than for large arrays. In this paper cost effective design approaches are considered for an S-band dipole antenna array with relatively small aperture and potential opportunities are investigated to improve SLL and BW. The cost reduction is provided by use of the printed circuit technology for all antenna components (radiators, beamforming networks, phase shifters) and by minimizing the number of components. The improving of SLL and BW is provided by A&/spl phi/ errors minimization, mutual coupling and edge effect suppression.

In synthetic aperture radar (SAR) imaging, geometric resolution, sidelobe level (SLL) and signal-to-noise ratio (SNR) are the most important parameters for measuring the SAR image quality. The staring spotlight mode continuously transmits signals to a fixed area by steering the azimuth beam to acquire azimuth high geometric resolution, and its two-dimensional (2D) impulse response with the low SLL is usually obtained from the 2D weighted power spectral density (PSD) by the selected weighting window function. However, this results in the SNR reduction due to 2D amplitude window weighting. In this paper, the staring spotlight SAR with nonlinear frequency modulation (NLFM) signal and azimuth non-uniform sampling (ANUS) is proposed to obtain high geometric resolution SAR images with the low SLL and almost without any SNR reduction. The NLFM signal obtains non-equal interval frequency sampling points under uniform time sampling by adjusting the instantaneous chirp rate. Its corresponding PSD is similar to the weighting window function, and its pulse compression result without amplitude window weighting has low sidelobes. To obtain a similar Doppler frequency distribution for low sidelobe imaging in azimuth, the received SAR echoes are designed to be non-uniformly sampled in azimuth, in which the sampling sequence is dense in middle and sparse in both ends, and azimuth compression result with window weighting would also have low sidelobes. According to the echo model of the proposed imaging mode, both the back projection algorithm (BPA) and range migration algorithm (RMA) are modified and presented to handle the raw data of the proposed imaging mode. Both imaging results on simulated targets and experimental real SAR data processing results of a ground-based radar validate the proposed low sidelobe imaging mode.

The impact of the fitness functions: minimizing the RMS / maximum side lobe in the working area of the ACF signal is examined. Also the influence of such genetic algorithm parameters as the population size, the mutation rate, the type of crossover functions and other at the rate of convergence of the algorithm to solve the problem of the signal synthesis with a low level of side lobe is investigated. The main goal of the study is to find the parameters of a genetic algorithm with a minimum search time of a radar signal with given ACF parameters. In this paper, it is shown that using as an optimization function minimizing of the RMS level of the side lobe results in better indicators than when minimizing the maximum side lobe. Also shown are the dependencies of the speed of the algorithm on its main parameters.

Array antennas offer a wide range of opportunities in the variation of their directivity patterns through amplitude and phase control. Peak sidelobe levels may be reduced via amplitude control or weighting across the array aperture. Several authors have made significant contributions in detailing processes for synthesizing these aperture amplitude distributions for the purpose of sidelobe level control. One of the basic trade-offs when implementing amplitude weighting functions is that a trade between low sidelobe levels and a loss in main beam directivity always results. Some of the commercially available pattern calculation programs that can implement sidelobe level control do not provide calculations of the aperture efficiencies given different amplitude weightings. Calculation of the aperture efficiency can be somewhat confusing, particularly with regards to the difference between tapering via attenuation versus redistribution. The purpose of this paper is to define these terms, to provide a review of the proper normalization technique that is important in obtaining accurate aperture efficiency estimation. Descriptions of the amplitude tapers and their utility will be presented. A design example will be presented which will compare theoretical efficiencies with those obtained via finite element method simulation.

An eight element linear iris excited centered broadwall waveguide slotted array antenna is realized at 10GHz using FEM simulator. Different feeding arrangement is illustrated with proper electric field magnitude and phase distribution for obtaining higher gain and lower first side lobe level. 15.01dB gain with zero beam tilt and -14.89dB side lobe level is achieved in center fed case with 2.88dB improvement in side lobe level compared to end fed case.

Endfire arrays such as Yagi antennas can be analyzed in terms of the phase and amplitude distribution in a plane transverse to the axis of the array. A method for controlling the amplitude and phase across the virtual aperture is given. It is shown, in particular, that the virtual aperture area can be increased through the use of parasitic side arrays, and that at the same time control of the illumination function can be retained. Thus, it is possible to increase gain and reduce side lobes simultaneously without supergaining. Measured patterns are shown for three different array types. Type I is a Yagi antenna 6 wavelengths long, tuned for maximum gain by using a modified Hansen-Woodyard condition reported elsewhere. Types II and III are two-dimensional endfire arrays, also 6 wavelengths long. Type II was tuned for very low side lobe level (30 db), and Type III for maximum gain obtainable with a more moderate side lobe level (17 db). The gain of Type II was 30% above that of Type I, while the gain of Type III was 60% above Type I. The method presented demonstrates that controlled excitation of a two-dimensional parasitic array with a single feed (rather than a line source) is feasible.

A microstrip array antenna with low sidelobe level (SLL) for X-band marine radar is proposed. The antenna is composed of a 32-element patch array and a three-layer near-zero-index metamaterial (NZIM). The IABC-Kmeans algorithm, which combines the improved artificial bee colony algorithm and K-means clustering algorithm, is used to optimize the current amplitude of the array elements to obtain a lower SLL. The NZIM is loaded in front of the array antenna to reduce the beamwidth of the E-plane. The antenna is designed and fabricated. The measurement results show that the gain of the antenna at the center frequency is 22.7 dBi, the SLLs of H-plane and E-plane are −30.66 dB and − 26.78 dB respectively, and the half-power beamwidth of H-plane is 5.9°. Compared with the previous similar antenna structures, the antenna has lower SLL under the premise of narrow beam and high gain, which is very suitable for X-band marine radar of small and medium fishing vessels.

A low profile, high gain 32 × 64-slot array antenna with unequal beamwidths in the E- and H-planes and low sidelobes is proposed for vehicular applications in the 71-81 GHz band. The antenna is composed of 512 (16 × 32) 2 × 2-slot subarrays arranged with equal spacing and excited by a nonuniform corporate-feed-network. A two dimensional amplitude-tapering (complying with Taylor distribution) is used to achieve the low sidelobe levels (SLLs). Combined with the different dimensions of the array, the sidelobes and the beamwidths in the E- and H-planes are independently controlled. A prototype slotted waveguide array is fabricated to verify the array properties. Measurements show that the matching of the array is better than -14 dB over the entire bandwidth. The first SLL is lower than -18.9 dB/-24 dB with the maximum 3-dB beamwidth of 2.3°/1.3° in the E-/H-plane, respectively. The peak gain of over 39.4 dBi and the cross-polarization discrimination (XPD) of below -36.2 dB are also achieved. The demonstrated features of high gain, low SLL, and independent controllability of the beam in the E- and H-planes are most desirable for vehicular communications and radars.

To achieve a high gain and low first side-lobe level, variants of linear and planar series fed circular and hexagonal microstrip antenna arrays using the binomial distribution, are proposed around 3000 MHz frequency band, on thinner Arlon substrate (h ~ 0.027λg). The linear 7 × 1 array of circular patches, yields first side-lobe level of −25 dB with a gain of 12.7 dBi, whereas using hexagonal patches, respective values are, −28 dB and 12.9 dBi. The planar 5 × 3 and 5 × 5 arrays using half wavelength and wavelength spacing are presented. An optimum response is obtained in 5 × 5 array for the wavelength inter-element spacing. Here, using circular patches, first side lobe level in the E and H-planes is −29 and −14 dB, respectively, with a peak gain of 17.6 dBi, whereas that using hexagonal patches, the respective first side lobe level in the E and H-planes is −26 and −17 dB, with a peak broadside gain of nearly 19 dBi. Thus using a thinner substrate, proposed series feed binomial planar arrays offer a gain of more than 15 dBi with a lower first side lobe level.

A low-profile phased array antenna with a low sidelobe was designed and fabricated using a genetic algorithm (GA). The subarray distances were optimized by GA with chromosomes of 78 bits, a population of 100, a crossover probability of 0.9, and a mutation probability of 0.005. The array antenna has 24 subarrays in 14 rows, and is designed as a mobile terminal for Ku-band satellite communication. The sidelobe level was suppressed by 6.5 dB after optimization, compared to the equal spacing between subarrays. The sidelobe level was verified from the far-field pattern measurement by using the fabricated array antenna with optimized distance.

The millimeter wave radiation of a dielectric leaky-wave antenna (DLWA) coupled with a metallic diffraction grating with a sinusoidal height profile is experimentally investigated. The interaction between dielectric and grating is contactless and it is from the broad-face of the dielectric line. The measured field patterns are compared with the simulated HFSS patterns. Antenna parameters such as polarization, HPBW, cross-polarization and side lobe levels are measured. The effects of the geometrical parameters of the grating to the radiation are also investigated. Some results are compared with a DLWA which has another diffraction grating profile shape (rectangular). The investigated antenna can be used as a frequency scanning antenna in mm-wave radars because it has low cross and side lobe levels and narrow beam width.

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