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This paper presents a millimeter wave series-fed microstrip line antenna array with low side lobes. For millimeter-wave beam forming applications, compact series fed arrays with very small horizontal width and low side lobes are very much required. The proposed array consists of a microstrip line with periodically placed stepped inverted-cone stub sections at a guided wavelength spacing. Surface current cancellation at each guided wavelength in an ideal microstrip line can be altered by symmetrically introducing the inverted-cone stub sections on two edges with a half wavelength offset. By controlling the dimensions and location of the inverted-cone stub sections, the equivalent surface currents can be altered and focused on the cone stub sections, resulting in an effective array radiation. The fabricated antenna array is resonating at 28 GHz and has an impedance bandwidth of 1.3 GHz. Peak realized gain of 10.2 dBi is achieved at 28 GHz and the measured side lobe levels are better than −15 dB in the E and H plane. The proposed microstrip line antenna array with low side lobes also benefits from simple fabrication and high integration ability, which makes it attractive for compact beamforming scenarios in millimeter-wave bands.

Aiming to realize series-fed antenna array with good return loss, low sidelobe level (SLL), and small gain variation over a wide bandwidth, this article presents a unified synthesis method of designing series-fed networks (SFNs) under the equal/unequal distributions with the bandwidth enhancement. We find that the return loss and current distribution bandwidths of SFN are dominated by its input reactance slope. The ratio of SFN main line impedance Z0 and antenna impedance ZL plays an important role in it. When the optimal Z0/ZL makes the input reactance slope equal to zero at the center frequency, the bandwidth of SFN can be highly extended by 2–4 times compared with nonoptimal solutions. In this context, four classical types of SFNs are investigated and synthesized. The closed-form optimal formulas for these SFNs are further deduced under the specified element number N and current distributions I1, $\text{I}_{2}, \ldots $ , and IN. For experimental verification, an eight-element series-fed antenna array driven by the SFN with Dolph–Chebyshev current distribution is designed and fabricated based on the proposed design method. By virtue of the improved SFN, the designed series-fed array exhibits enhanced impedance and radiation bandwidths as predicted. The measured results show designed array achieves an impedance bandwidth of 52.2% (3.34–5.70 GHz) with S11 ≤ −10 dB and the radiation bandwidth with SLL ≤ −20 dB is 20.9% (3.85–4.75 GHz). The measured antenna gain is 11.3 dBi with a small variation of 1.3 dB and the efficiency of array is better than 82% over the operational bandwidth of 18.7% (3.88–4.68 GHz). [ABSTRACT FROM AUTHOR]

Due to the asymmetry of the elements’ position distribution and polarization direction, it is a challenge to synthesize difference patterns with large slope and symmetric main-lobe on 3-D conformal beam-scanning arrays with asymmetric radiation aperture. In this article, an approach to synthesize the optimal difference patterns for 3-D conformal arrays with asymmetric radiation aperture is proposed. To determine the limitation region of the main-lobe and sidelobe for a 3-D conformal array, an initial difference pattern is generated by the joint multidimensional vector clustering method. Then, an auxiliary phase function is introduced to convert the nonconvex constraint of the symmetry of the difference beam into a convex one. Finally, an iterative convex optimization is applied to obtain the optimal difference pattern. The optimization progress is finished by extracting the vector field patterns of a simulated antenna element. Two design examples employing hemispherical conformal array (HCA) and conical conformal array (CCA) with asymmetric radiation aperture are implemented to demonstrate the effectiveness of the proposed method. Difference patterns with −20 dB sidelobe level (SLL) and large slope are obtained in both numerical and simulated results of the two design examples. [ABSTRACT FROM AUTHOR]

For automobile radar systems, the antenna array requires a low sidelobe level (SLL) to reduce interference. A low-SLL and low-cost planar antenna array are proposed in this article for millimeter-wave automotive radar applications. The proposed array consists of six linear series-fed patch arrays, a series distribution network using a grounded co-planar waveguide (GCPW), and a bed of nails. First, a hybrid HFSS-MATLAB optimization platform is set up to easily obtain good impedance matching and low SLL of the linear series-fed patch array. Then, a six-way GCPW power divider is designed to combine the optimized linear sub-array to achieve a planar array. However, since CCPW is a semi-open structure, like a microstrip line, the parasitic radiation generated by the GCPW feeding network will lead to the deterioration of the SLL. To solve this problem, a bed of nails—as an artificial magnetic conductor (AMC)—is designed and placed above the feeding networking to create an electromagnetic stopband in the working band. Its working mechanism has been explained in detail. The feeding network cannot effectively radiate electromagnetic waves into free space. Thus, the parasitic radiation can be suppressed. A low-SLL planar array prototype working at 79 GHz is designed, manufactured, and measured. The measured results confirm that the proposed low-SLL planar array has a −10 dB impedance bandwidth of 3 GHz from 77 to 80 GHz and a maximum peak gain of 21 dBi. The measured SLL is −24 dB and −23 dB in the E-plane and H-plane at 79 GHz, respectively. The proposed low SLL array can be used for adaptive cruise control (ACC) system applications. [ABSTRACT FROM AUTHOR]

In this letter, a low-sidelobe-level (SLL) circularly polarized (CP) leaky-wave antenna with A-shaped elements is proposed based on substrate integrated image guide (SIIG). The A-shaped CP radiating element consists of a horizontal linearly polarized (LP) structure and a vertical LP structure. The horizontal LP wave and the vertical LP wave can be excited by a pair of inclined transversal metal strip patches and a longitudinal metal strip patch, respectively. Their phases are orthogonal and amplitudes can be controlled to be equal by adjusting the tilted angle of the horizontal LP structure and the length of the vertical LP structure. Moreover, the longitudinal metal strip patch is modified to the V-shaped strip patch, which can realize the field cancellation, thereby achieving the boresight radiation for such a leaky-wave antenna. Furthermore, a low SLL is realized by controlling the aperture-field distribution to obtain the desired amplitude distribution and the relatively small axial ratio. In addition, because of the short waveguide wavelength of the SIIG, this feedline can be used to achieve the small interelement spacing and element size, thereby realizing the short length of the array. The measured peak gain of this antenna is 12.3 dBic, the SLL is –19.1 dB and the efficiency is 92.3% at the center frequency of 14 GHz. [ABSTRACT FROM AUTHOR]

A grating lobe suppression approach based on the null scanning antenna (NSA) for a sparse phased array is proposed. The NSA provides continuous null scanning and beam steering on two orthogonal planes, by connecting four varactor loaded impedance reconfigurable circuits to the four edges of a square patch antenna, respectively. The NSA is introduced into a sparse phased array and the grating lobe is suppressed by keeping the radiation pattern null of NSA pointing at the angle of the grating lobe during beam scanning. Meanwhile, the beam direction of NSA is steered to a wider angle with the variation of null angle. The main lobes during beam scanning are located within the 3 dB beamwidth of NSA. Thus, the sidelobe level (SLL) and scan loss over the wide scanning region are improved considerably. A $2\,\,\times \,\,4$ sparse phased array with NSA is designed and measured for verification. Both simulated and measured results indicate that the SLL of the sparse phased array with NSA can be suppressed below −9.3 dB within the scan range from −76° to 75°. The maximum realized gain during beam scanning is 17 dBi, with an aperture efficiency of 69.86% and a maximum gain fluctuation of 4.4 dB. [ABSTRACT FROM AUTHOR]

A series-parallel hybrid-fed microstrip array antenna design is presented for X-band low-probability intercept (LPI) marine radars. Contrary to traditional counterparts, the proposed antenna has improved impedance and radiation bandwidth from 9.1 to 9.6 GHz to accommodate pulse compression and frequency diversity for LPI radars. The antenna structure consists of $24\times4$ patch elements with horizontal polarization. The two halves of the structure are fed in parallel and each arm is fed in a series-series feed network to achieve low sidelobe level (SLL) of −26.5 dB. The manufactured antenna has a gain of 24.0 dBi with half-power beamwidth (HPBW) of 4.5° and 21.5° in azimuth and elevation, respectively. The measured gain flatness is ±0.3 dB over the radionavigation band and ±1.0 dB over the entire band. A novel grid baffle structure with capacitive surface impedance is proposed and implemented to provide high isolation over the target bandwidth. The maximum and average isolations between transmit and receive antennas are measured as 65 and 62 dB, respectively. The proposed antenna is very suitable for dual-mode pulsed and continuous-mode LPI marine radars. [ABSTRACT FROM AUTHOR]

In this letter, a planar broadband higher-order mode millimeter-wave (MMW) microstrip patch antenna array with low sidelobe level (SLL) is presented. For the antenna element, antiphase-TM30 mode is excited by unequally etching the radiating patch with two transverse slots. Meanwhile, an SIW-based pin-loaded slot coupling feeding structure is introduced to achieve merits of broadband, low cross polarization, and low backward radiation. Then, a one-eight power divider with in-phase unequally tapered amplitude distribution is adopted to excite an eight-element array with SLL. The GCPW–SIW transition structure is also selected to achieve broadband impedance matching. Finally, both element and array antenna are optimized and fabricated for verification. For the antenna array, the measured −10 dB impedance bandwidth is from 25.1 to 31.3 GHz (22%) with a maximum gain of 14.6 dBi at 29.5 GHz and a 3 dB gain bandwidth of 27.9%. The measured SLLs at 26, 28, and 30 GHz are all less than −20 dB. [ABSTRACT FROM AUTHOR]

A W-band integrated tapered array antenna with series feed is presented. To reduce the fabrication cost, the antenna is designed on a single layer with the standard printed circuit board (PCB) process. In the array design, a novel coplanar waveguide (CPW) feeding structure is proposed to simplify the feeding network and fabrication by avoiding three-way power divider and via process. Considering the interconnection reliability and cost, the wire-bonding technique is used to connect the integrated circuit (IC) and antenna. To compensate for the parasitic effect of the bond wire and enhance the bandwidth of the antenna with interconnection, an LCL compensation structure is introduced and codesigned with the array antenna, achieving wideband-impedance feature. To demonstrate the validity of the design, several prototypes of the proposed antennas are implemented and measured. The measured results show that the array antenna with wire-bonding interconnection achieves a fractional impedance bandwidth (|S11| < −10 dB) of 13.2%, sidelobe level less than −15 dB at 100 GHz, and ~15 dBi gain. The simulated radiation efficiency is larger than 80% from 98 to 104 GHz. With our designed 100 GHz CMOS radar transceiver, the proposed antenna is used to detect the human vital sign. [ABSTRACT FROM AUTHOR]

This paper introduces the concept of the sparse array into the design of a wide-angle scanning phased array to obtain the low sidelobe level (SLL). The adopted array element is a half-mode substrate integrated waveguide slot array, which can radiate a high-gain and wide-beam pattern in the E-plane. A 16-element phased array with an optimized non-periodic array element arrangement, which is obtained by a semi-full-wave simulation-based synthesis method, is designed and studied. Compared with two periodic arrays with the same array element and element number, the sparse one exhibits the advantage of low SLL. Besides, the designed phased array has an ultra-low profile of only about 0.017λ0. A prototype is fabricated and measured, and measured results show that the proposed array can scan its main beam from -70° to +70° with a realized gain higher than 18.2 dBi and peak SLL lower than -15 dB.

This article presents a design of a single-polarization, $4\times 4$ microstrip patch antenna array, operating at the $K_{a}$ -band. An integrated microstrip network with the aid of using feeding probes excites the antenna array. Simulation and measurement results show that the array operates in a wideband frequency range (return loss RL ≥ 15 dB) from 32 to 36.4 GHz with a low sidelobe level (SLL ≤ −15 dB). To obtain a wide bandwidth, each antenna is fed with a capacitive patch and enclosed by an integrated metallic cavity. Here, we show that an antenna array with an SLL could be achieved by mirroring and feeding the radiating elements with equal excitation. The design is also applicable to a dual-polarized antenna, as it does not only lower the sidelobe level but also improve the cross-polarization without increasing the circuit complexity. An antenna prototype has been realized with an experimental bandwidth better than 3 GHz and a sidelobe level of −15.6 dB. These excellent measured results prove that this method with a simple design approach is feasible for an antenna array with high suppression of sidelobe and cross-polarization. [ABSTRACT FROM AUTHOR]

A design procedure for traveling-wave series-fed microstrip array with a low sidelobe level (SLL) was proposed. To control the radiated power while suppressing the reflection for each antenna element, three types of microstrip antenna elements were introduced, and design parameters were studied. To validate the design procedure, a traveling-wave series-fed array was designed to operate at 76.5 GHz. The performance of the array was measured at an anechoic chamber. The results show stable gain and half-power beamwidth (HPBW) over the frequency range of 75 and 78 GHz, where the SLL was consistently lower than −17 dB. [ABSTRACT FROM AUTHOR]

A novel iterative convex optimization approach is proposed for the synthesis of low-sidelobe 4-D heterogeneous arrays in the presence of mutual coupling effect. To realize wide bandwidth and wide-angle scanning, a tightly coupled dipole element (TCDE) is selected as the basic element. Due to the strong coupling between antenna elements, the active element pattern (AEP) and active reflection coefficient (ARC) are included in the proposed approach in order to evaluate the overall mutual coupling and port matching. Specifically, a nonconvex programming problem in terms of the given maximum sidelobe level (SLL), the ARC or reflected power at the center frequency, and the given maximum sideband level (SBL) at sidebands is established. After the application of some mathematical transformations, the nonconvex programming problem is decomposed into a convex optimization problem at the center frequency and an iterative convex problem (ICP) at sidebands. Owing to the efficiency of the convex optimization, the two problems can be efficiently solved. The proposed approach is applied to synthesize low-sidelobe patterns while minimizing the SBL in a 32-element cone-shaped 4-D heterogeneous array. The simulated and measured results verify the effectiveness of the proposed approach and show the advantages (improved gain) of the heterogeneous array. [ABSTRACT FROM AUTHOR]

A via-loaded microstrip magnetic dipole antenna with enhanced bandwidth and gain is proposed and investigated. The antenna is constructed on a long microstrip antenna with three edges shorted and one edge opened. The open aperture is equivalent to a magnetic dipole, which serves as the radiation source. In the long cavity, two modes are generated, in which the lower one is half-TE110 mode and the higher one is half-TE310 mode. By loading two sets of shorting vias around the null voltage points of the half-TE310 mode, the resonant frequency of the half-TE110 mode is shifted upward. Then, the two modes are merged to achieve an enhanced bandwidth. Moreover, the superposition of the far fields of the two modes results in a narrowed unidirectional beam, a reduced sidelobe level (SLL), and therefore, an improved gain. The theoretical investigation is validated with simulation results. A prototype of the antenna is fabricated and measured. Measured results show that the proposed antenna with a low profile of $0.027\lambda _{0}$ ($\lambda _{0}$ is the wavelength in free space) has an impedance bandwidth of 9.1%, and a peak gain of 10.2 dBi. [ABSTRACT FROM AUTHOR]

A two-dimensionally (2-D) scanning multibeam array with planar structure and low sidelobe level (SLL) is realized in this paper. It is for the first time that the SLL of 2-D scanning multibeam array is properly addressed. To suppress the SLL, a $4 \times 16$ beam-forming network (BFN) is proposed in this paper. Different from the existing schemes, such BFN can provide tapered illuminations in two orthogonal directions and thus can be applied to realize low-SLL 2-D scanning beams. The proposed $4 \times 16$ BFN is formed by interconnecting two sets of sub-BFNs, each of which is stacked by several $2 \times 4$ Butler matrices (BMs). Like other 2-D scanning schemes, the preliminary $4 \times 16$ BFN is of 3-D topology so that it is challenging to be integrated into planar substrate integrated waveguide (SIW) structure. Facing this problem, some modifications of the proposed topology are conducted. Operation principle, simulation, and experiment of a planar, low-SLL 2-D scanning multibeam array operating at 28 GHz are illustrated, which can help to demonstrate its feasibility for millimeter-wave applications. [ABSTRACT FROM AUTHOR]

A W-band hybrid array with a compact size and a high efficiency is presented. With the aid of the joint design of the series-shunt feeding network and substrate integrated waveguide (SIW) blocked slots array, the array with 16 × 56 slots can be divided into eight areas, and then the bandwidth of impedance, gain, and radiation pattern can be improved effectively. Moreover, it has both the advantages of low profile over traditional SIW planar array and low loss over traditional air-filled rectangular waveguide (ARW) slot array. Due to the utilization of back-feeding technology of the proposed hybrid array instead of planar SIW divider, it could save a lot of area for radiating energy and lowering the insertion loss, thus resulting in the gain values higher than 30.7 dBi during the entire operational frequency coverage. It is corresponding to the total efficiency of 26.5%, which is higher than the traditional W-band SIW array due to the usage of the back feeding to conserve the radiation acreage and reduce the insertion loss. By designing the SIW slots array and series-shunt feeding network simultaneously, low sidelobe level characteristics of −16 and −20 dB in E- and H-planes have been successfully accomplished, respectively. [ABSTRACT FROM AUTHOR]

A leaky-wave antenna array with a low sidelobe level (SLL) fed by the substrate-integrated image guide (SIIG) is proposed in this letter. First, the single-layer printed circuit board (PCB) technology is applied here to fabricate the SIIG. The technology not only reduces the fabrication complexity, but also avoids the air gap between the substrate and the metallic ground. A method is introduced here to reduce the additional loss of the single-layer PCB-based SIIG caused by the air holes on the metallic cladding in the perforated regions. As the waveguide wavelength of the SIIG is short, small element spacing can be realized by utilizing this kind of feeding line. Besides, metallic strips with an optimal length-to-width ratio placed on top of the SIIG are employed as radiation elements, which exhibit strong radiation abilities and large controllable range of the leakage constant. Considering these conditions, this type of antenna can realize a low-SLL characteristic within a short length and achieve high gain at the same time. An example antenna with the vertical polarization is designed and measured to validate the theory. A single-layer transition between a coaxial probe and the SIIG is also designed to excite the antenna. The measured gain of the antenna is 14.4 dBi at 13.6 GHz with −19.2 dB SLL, and the radiation efficiency is 84.5%, considering the insertion loss of the feeding line. [ABSTRACT FROM AUTHOR]

A periodic leaky-wave array antenna with circular polarization and low sidelobe level (SLL) for millimeter-wave application is proposed. The unit cell of the array consists of four circular split rings located on both sides of a low-loss substrate, and a planar Goubau line is used to excite the split rings to generate radiation. The antenna can realize an impedance bandwidth larger than 67%, and the 3 dB axial-ratio bandwidth is about 8.9%. The maximum gain is about 18 dBi. To reduce the SLL, the leakage loss factor α along the radiation aperture is tapered, using beamforming technique, by controlling the aperture field distribution into a cosine function. The results show that the SLL of the proposed antenna is about 6 dB lower than that of the antenna with uniform aperture field distribution. The antenna was fabricated and measured, and the experimental results are in good agreement with those of simulation. [ABSTRACT FROM AUTHOR]

A low-sidelobe air-filled slot array is proposed and fabricated using silicon micromachining technology for millimeter-wave application. As is well known, the high-permittivity silicon prohibits the silicon-based antenna from having good performance. Here, this problem is addressed through manufacturing air-filled antenna on silicon substrate. An eight-way unequal power divider is adopted to excite eight air-filled slots and the excitation coefficients present a taper. At the end of the power divider, an air-filled substrate integrated waveguide cavity is used to improve antenna performance and suppress wave leakage, and eight silicon cuboids are stretched into the cavity beneath each slot to acquire good impedance matching. The input interface is selected as the ground-signal-ground structure to facilitate antenna-in-package solution that requires the integration of the antenna and chips or integrated circuits. The three-layered antenna is fabricated using through-wafer etching, gold-plating, optical alignment, and wafer bonding processes. The measured −10 dB impedance bandwidth is 1.27 GHz, and a measured fan-shaped beam at 58.5 GHz with a broadside gain of 11.95 dBi and a sidelobe level of 18.6 dB is obtained. The 3-dB beamwidth is about 14° in H-plane and 8-dB beamwidth is more than 175° in E-plane. [ABSTRACT FROM PUBLISHER]

A dual-polarized (DP) shared-aperture frequency-scanning continuous transverse stub (CTS) antenna with wide scanning range is presented in this paper. In order to mitigate the open stopband and realize continuous beam-scanning including broadside, a novel "L"-type CTS radiation element is proposed. An equivalent circuit model is established to analyze the input impedance and reflection coefficient of the proposed CTS element by using the transmission line theory. The antenna array consists of an orthogonally arranged shared-aperture DP-CTS radiation array and the corresponding linear source generators (LSGs). The amplitude tapering of Taylor distribution is applied to suppress the sidelobe level (SLL). A metallic LSG is designed to reduce the transmission loss with a tapered feeding probe being adopted to broaden the bandwidth. A 12-element prototype is simulated and fabricated. A reasonable agreement between simulation and measurement is achieved. Experimental results show that the DP antenna has an impedance bandwidth of 8 ∼ 14 GHz and a port isolation higher than 21 dB. The scanning ranges for both polarizations are from −73° to 20° with a maximum gain of 23.9 dBi and a SLL lower than −16.6 dB. The proposed DP-CTS frequency-scanning antenna could be applied in radar detection systems. [ABSTRACT FROM AUTHOR]