Side-Lobe Level Reduction of Half-Mode Substrate Integrated Waveguide Leaky-Wave Antenna

Here, a wide‐angle phase‐frequency scanning linear array composed of leaky‐wave antennas (LWAs) is proposed. The unit cell of the proposed LWA element consists of microstrip lines and grounded vias. By increasing the scanning rate based on theoretical analysis, wide scanning range with low gain fluctuation of the LWA element is achieved. For gain enhancement, the LWAs are arranged along their length to form a linear array. A method combining theoretical derivation and numerical calculation is used to obtain a high efficiency and low sidelobe level (SLL) of the array. To verify the design method, a linear LWA array is designed, fabricated and measured. The main beam of the LWA array can scan from to in frequency band of 9.3–11.6 GHz with gain fluctuation less than 2 dB and SLL less than dB. The measured results are in good agreement with the simulated results.

This paper investigates the reduction of side lobe level in antenna arrays. Reduction of side lobe level in antenna arrays has some limitations including fixed width of the beam. We have modeled the side lobe level reduction as an optimization problem using simulated annealing technique for side lobe level reduction of a specific beam width. The advantage of this method compared with other methods is that it can get out of local minimums and converge to the optimized answer. Efficiency of simulated annealing algorithm in pattern extraction of desired circular antenna, which is used frequently in modern telecommunication and radar systems, is investigated and the results are compared with that of genetic and evolutionary algorithms. Key words: Simulated annealing, antenna array, circular array, non-uniform antenna array, side lobe level.

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.

In this paper, a new approach of designing single layer Substrate Integrated waveguide (SIW) based planar leakywave antenna for X-band (8-12 GHz) application is presented. The beam scanning range of the final prototype is found to be $85^{\circ}(-60^{\circ}$ to $25^{\circ})$. This design consists of a new type of unit cell, which is the combination of three transverse and three longitudinal rectangular slots. These slots are arranged periodically. The peliodic loading of these slots incorporates capacitive coupling, which is further responsible for a wide range of scanning. The designed antenna is showing a high impedance leakv-wave region. The most challenging task for a leaky-wave antenna is continuous beam scanning from the backward-to-forward with a broadside radiation patterns. In this paper, the designed LWA achieves this task with a significant reduction in side lobe level (SLL) and cross-polarization. The final prototype with directive beam and stable gain characteristic in the desired frequency band is designed. It is found from the radiation pattern that SLL for all the frequency is below -15 dB and cross polarization level of $-\mathbf{1 8}$ dB. A thorough analysis of dispersion diagram of the unit cell and radiation characteristics using fundamental TE<inf>10</inf> mode of SIW is conducted using a full-wave EM-simulator.

Steering of main beam of radiation at fixed millimeter wave frequency in a Substrate Integrated Waveguide (SIW) Leaky Wave Antenna (LWA) has not been investigated so far in literature. In this paper a Half-Mode Substrate Integrated Waveguide (HMSIW) LWA is proposed which has the capability to steer its main beam at fixed millimeter wave frequency of 24GHz. Beam steering is made feasible by changing the capacitance of the capacitors, connected at the dielectric side of HMSIW. The full wave EM simulations show that the main beam scans from 36° to 57° in the first quadrant.

A comprehensive survey of the reconfigurable leaky-wave antennas (LWAs) is made in this paper. Beam-steering and unique radiating features of LWA are highlighted particularly. Therefore, the radiation mechanism of different types of LWA, including uniform, quasi-uniform, periodic, and metamaterial LWAs are discussed in detail. The guiding structures for realizing LWAs, namely microstrip, waveguide, substrate integrated waveguide (SIW), and half-mode SIW (HMSIW) are investigated as well. Basic concepts of electronic beam-scanning LWAs are also introduced, and several state-of-the-art reconfigurable LWAs are studied thoroughly. The investigated reconfigurable LWAs are suitable for beam-scanning applications due to their compactness, ease of implementation, reasonably high gain, and relatively wide beam-scanning range, as will be demonstrated through this comprehensive review.

A low-cost multilayer antenna is proposed for the next-generation automotive radar systems at millimeter waves. The antenna consists of a multilayer half-mode substrate integrated waveguide (HM-SIW) leaky-wave antenna (LWA) based on a dielectric layer with periodic perforations. Its stack-up consists of a 0.5-mm-thick Rogers 4350B substrate and two 1.0-mm-thick FR4 substrates assembled by 1.4-mm-diameter alignment pins and fixations. Measurements of a 126-mm-long fabricated prototype revealed a −10-dB impedance bandwidth of 6.9 GHz, covering the 22 GHz to 28.9 GHz band. The measured gain equals 15.5 dBi at 24 GHz, resulting in a total efficiency of more than 85%. Moreover, the measured radiation patterns in the [22–26] GHz band exhibit an average 3-dB beamwidth of 11.5° and sidelobe levels (SLL) better than 20 dB up to a scan angle of 20°.

This paper presents a method for sidelobe level (SLL) reduction, return loss improvement, and bandwidth enhancement in notch-loaded TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sub> mode rectangular patch antennas. In this method, a fractal-slot is introduced in the center of notch-loaded patch to remove the unwanted out-of-phase current regions. It is shown that a combination of the fractal-slot and notch loading technique can achieve significant improvement in SLL, return loss, and bandwidth of notch-loaded TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sub> mode without compromising gain or symmetry of radiation patterns. Moreover, the method also gives an additional degree of freedom to improve the impedance matching without changing the feed location. A prototype of the antenna is fabricated to verify the proposed method. The proposed antenna shows a measured gain of 13 dBi with a low SLL of −16 dB. Furthermore, it shows symmetrical patterns in both planes with cross-polarization (X-pol) levels of less than 35 dB. An under-sampled <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> array of the proposed antenna is also presented by utilizing its low SLL property to simplify the complexity of feed networks in high gain array antennas. The array offers the same directivity and SLL as that of an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times 8$ </tex-math></inline-formula> array of fundamental mode rectangular patch elements in the same area.

Reducing size and side lobe level (SLL) is essential for resonant cavity (RC) type antenna. This paper proposes a PRS-less RC antenna with compact size, low profile and sidelobes. It is the first attempt to apply a hybrid cavity with a dielectric slab and a shaped ground with power manipulation (SGPM) function. Different from traditional un-equal power dividers utilized in array, herein, we proposed the SGPM to manipulate power distribution on the radiation aperture of a RC antenna. In addition, due to the utilization of the dielectric slab, intrinsic partially reflection can be occurred at the aperture interface between the dielectric and air. This achieves RC response while eliminating the usage of a separate partially reflective surface (PRS), which is often independently required in a conventional RC antenna. For validation, a prototype using the proposed design method is fabricated and measured. Its profile is 0.25 λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub>. The SLL of the design is less than 18 dB across the operating band. Its peak aperture efficiency can reach to 69.1%. The overlapped operating bandwidth exceeds 13%. Compared to other RC antennas, the proposed design has characteristics of miniaturization, wideband, PRS-less, low SLL and low-profile.

A low profile cavity-backed dual-band antenna based on half mode substrate integrated waveguide (HMSIW) technology is designed. HMSIW technology is used to make semicircular resonant cavity. An additional resonance can be generated by loading a U-shaped strip outside the radiation aperture of HMSIW cavity, thus realizing the dual-band performance. The reflection characteristics of single-band and dual-band HMSIW cavity-backed antennas are studied. The simulated results show that the resonant frequencies can be controlled easily by changing the antenna parameters. The proposed antenna has the characteristics of low profile, high gain and low cross polarization.

Bandwidth optimization and side-lobe levels reduction in PC radar using Legendre orthogonal polynomials

Non-uniform Concentric Circular Antenna Array Design using IPSO Technique for Side Lobe Reduction

This letter presents a millimeter-wave (mmW) continuous transverse stub (CTS) leaky-wave antenna (LWA) with pencil-beam broadside radiation, high scanning-rate, and low sidelobe levels (SLLs) characteristics. A parallel-plate waveguide (PPW) meander delay line is employed to control the phase constant of the proposed LWA. By adjusting the length of the transverse electromagnetic TEM-mode PPW delay line, the phase difference between adjacent radiating elements can be altered, achieving flexible control of scanning-rate. Match stubs close to the radiation slots are utilized to suppress the open stopband, which help enlarge the beam scanning range. A linear source generator excited by multiple ports with amplitude tapering is employed to generate the quasi-TEM wave. Combined with additional amplitude tapering among the CTS radiation slots, low SLLs at both principal planes are realized. Experimental results show that the LWA with 12 radiation elements has a scanning range of -68° to 42° over the frequency range of 26-34 GHz (a scanning-rate of 13.75°/GHz) with SLLs lower than 13.5 dB/16.6 dB and a peak gain of over 22.5 dBi.

A novel substrate integrated waveguide (SIW)-based leaky-wave antenna (LWA) is presented for backward endfire radiation and wide range backward scanning from backward endfire to near broadside. Wide backward range, high gain, lower sidelobe levels are achieved by properly designing the radiating slots and unit cell. The presented design provides the measured backward endfire (-90°) gain of 9.5 dBi at 16.7 GHz and the measured gain of 17.4 dBi at 19.8 GHz. Gain increases with frequency as the beam begins to move away from backward endfire to near broadside providing 80° of wide backward scanning range. Sidelobe levels and return loss are well below -10 dB. A prototype of the proposed design is fabricated. The measured results are in good agreement with simulated ones.

In this paper, we simply analyzed the advantages of conformal antenna array, and proposed a method to realize conformal antenna array of airborne with high gain and low side-lobe level (SLL). We designed a Vivaldi antenna unit, which's work frequency is 400MHz~800MHz. Conducting the experiment with HFSS by choosing the Dolph-Chebyshev synthesis method and using its E surface to dispose, which showed that this method can reach the design target. Secondly, aiming at the limited application of uniform linear array (ULA) in the actual project application, studied the effect of non-uniform linear array (NULA), the experiments showed that due to the adoption of the sub-array, some of the SLL become large, and the SLL maximum value is inversely proportional to the number of units in sub-array, Finally, this paper put forward the cross array, it not only overcome the limit to disposal for antenna unit width, but also reduce the requirement for wing size to achieve large array, the experiment proves that it almost has no obvious influence on array performance by this method.