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The authors present the design, fabrication and testing of a W‐band monopulse antenna. This antenna consists of three main building blocks: an array with 48 × 48 slots, a tapered corporate‐feed network and a comparator. The comparator has four input ports to generate sum and difference patterns in orthogonal cardinal planes for monopulse operation. A novel octuple excitation is adopted for the corporate network to achieve a side lobe level lower than −20 dB for the sum patterns and simultaneously reduce drastically the manufacturing complexity. Diffusion bonding technology is used for fabrication. Twenty‐four etched copper sheets with a thickness of 0.2 mm are stacked to realise the prototype. The total size of the antenna is 40.76×40.76×1.51λ03 $40.76\times 40.76\times 1.51{\lambda }_{0}^{3}$, with λ0 being the wavelength at the centre frequency (94 GHz). The antenna presents an isolation better than 12 dB among the input ports in the 84–100 GHz band. The realised measured gain is 40.7 dBi at 94 GHz. The measured 3‐dB gain bandwidth is 17.4%. The difference patterns at 94.0 GHz present null depths of −24.0, −18.0, −17.5, and −17.4 dB, in the E‐, H‐, 45°‐, and 135°‐planes, respectively. [ABSTRACT FROM AUTHOR]

Modern K-/Ka-band satellite communications have become increasingly demanding in recent years with regard to the performance of the terminal antenna used in the link. These terminals should be high gain and broadband, as well as guarantee polarization diversity over a large field of view. A low profile is also highly desired to integrate the antenna system into a variety of moving platforms, such as aircraft and trains. An ultra-low-profile continuous transverse stub array is proposed here to tackle these challenges. The antenna array is realized in printed circuit board technology by adopting a contactless transition between the stacked-up layers without resorting to blind or buried vias. The proposed antenna is wideband (impedance matched within the 19–31 GHz band, i.e., ~50%) and provides multibeam radiation for polar angles as far as ±22.5°. The peak value of the gain is 19.7 dBi, and the maximum radiation efficiency equals 50%. Furthermore, the antenna array is combined with a dual-band polarization converter. The latter provides orthogonal circular polarization (CP) in two non-adjacent bands. The overall antenna system performs right- and left-hand CPs within the SatCom downlink and uplink in the K-/Ka-band, respectively. For each polarization, the axial ratio is below 3 dB over 9.47% and 4.42% fractional bandwidths, respectively. [ABSTRACT FROM AUTHOR]

We present the experimental validation of the dual-mode, polarization-agile parallel-fed continuous transverse stub (CTS) antenna architecture introduced in Part I of this two-part paper. The Ka-band dual-mode CTS array described in Part I is characterized when it radiates in horizontal and vertical polarization. To this end, it is combined with two different quasi-optical beamformers operating in a quasi-transverse electromagnetic (quasi-TEM) and in a quasi-transverse electric (quasi-TE1) mode, respectively. The scanning capabilities of both multibeam antenna systems are demonstrated. The CTS array and its feed network comprising corrugated parallel-plate waveguides (CPPWs) are fabricated by additive manufacturing. Measurements show that the dual-polarized CTS antenna works between 29 and 32 GHz in a field of view of about 45°, achieving a peak gain of 31.3 dBi and very low cross polarization. These promising results pave the way for the realization of dual-circularly polarized beam-scanning antennas with application to broadband and compact Ka-band ground terminals. [ABSTRACT FROM AUTHOR]

This article presents an efficient analysis method for a novel continuous transverse stub (CTS) antenna. As opposed to state-of-the-art CTS antenna designs, the proposed architecture achieves circular polarization using a single CTS array and without any polarization converter. The structure consists of long radiating slots/stubs fed by over-moded parallel-plate waveguides. More precisely, the transverse electromagnetic (TEM) mode and the first transverse electric (TE1) mode of the feeding waveguides are used to generate a circularly polarized field. The array is analyzed using a spectral mode-matching method. First, the active reflection coefficient of the infinite array is derived in closed form. A windowing approach is then adopted to compute the radiation patterns of finite-size arrays. Numerical results obtained with this method are in excellent agreement with full-wave simulations, carried out with a commercial software. The performance of this class of CTS antennas has been investigated using the developed model. It is theoretically demonstrated that the proposed array can be designed to attain an axial ratio (AR) lower than 3 dB over a 52.9% relative bandwidth at broadside. Furthermore, the active input reflection coefficient is lower than −10 dB over a 40.8% relative bandwidth, when the array steers its main beam at $\theta _{0}=45^\circ $. This solution is an attractive candidate for next generation satellite communication terminals. [ABSTRACT FROM AUTHOR]

We present here a novel architecture of high-gain continuous transverse stub (CTS) antenna array operating at E-band (71–86 GHz) with reduced sidelobe level (SLL). The antenna consists of an array of 16 long slots excited by a nonuniform parallel-plate waveguide (PPW) corporate feed network. The nonuniform excitation is achieved by the design of asymmetrical power dividers in PPW technology, for which simple analytical models are provided. Full-wave simulations are validated by measurements of a prototype fabricated in aluminum. The SLL is lower than −28 dB in the E-plane. Such an SLL is 15 dB lower than classical parallel-fed CTS arrays. The overall antenna SLL remains below −18 dB over the 75–86 GHz band. Its mean radiation efficiency is 60%, and the maximum efficiency of 85% is reached at 86 GHz. [ABSTRACT FROM AUTHOR]

Wide-angle coverage, fine angular resolution, and low-power consumption are the key characteristics of millimeter-wave short-range wireless systems, such as access points in fifth-generation cellular networks and automotive radars. In this paper, we present a 60 GHz switched-beam antenna system addressing all these requirements. It consists of two identical parallel-fed arrays of eight slots, each fed by a passive pillbox beamformer. A switch network comprising four single-pole-multiple-throw switches excites one of the two arrays at a time and selects the radiated beam. The whole system is fully integrated into a multilayer low-temperature cofired ceramic module. The antenna covers a scan range of about ±39° in one plane using 11 beams between 57 and 66 GHz. The proposed architecture enables the simultaneous achievement of continuous coverage (beam crossover levels of about −3 dB) and of low sidelobe levels. Dedicated numerical tools are used for a preliminary design of the antenna. The design procedure, the technological development, and the experimental results are discussed in detail. [ABSTRACT FROM AUTHOR]

In metasurface (MTS) antennas, a surface wave (SW) is gradually transformed into a leaky wave, owing to the SW interaction with a reactance tensor periodically modulated in the aperture plane. In such antennas, the modulated reactance is typically obtained by subwavelength patches printed on a dielectric substrate. As an alternative technology, we propose the use of a class of metal-only MTSs in the synthesis of the reactance tensor. The absence of dielectric is useful to withstand harsh environments in space applications. The proposed element consists of a metallic cylinder with elliptical cross section, placed on a ground plane and arranged in a square lattice with subwavelength unit cells. This structure is well suited for fabrication by metal additive manufacturing. We have applied the metal cylinders in the design of a right-handed circularly polarized antenna, with broadside pencil beam at Ka-band. The obtained performance has been verified by full-wave simulations. A prototype has been successfully manufactured and measured, showing a good performance. [ABSTRACT FROM AUTHOR]

We present a 2-D Van Atta array for far-field wireless power transfer systems. The antenna array is made up of wideband, wideangle long slots. The monostatic radar cross section (RCS) of the finite array is derived by windowing the aperture field distribution of the corresponding infinite case. It is shown that for oversampled apertures, the array behaves as an ideal Van Atta reflector. Therefore, the proposed solution can collect and reradiate the total power impinging on it from a remote source over a large field of view and bandwidth. The array design is presented and validated through measurements over a relative bandwidth of 24% centered at a frequency of 5.8 GHz. The array consists of four slots, each fed by eight coaxial ports. Coaxial cables are used to connect pairs of feeds in a Van Atta configuration. A bidirectional amplifier is also introduced into the Van Atta scheme to amplify the collected energy before retransmission to a possible moving user for wireless power transfer. Off-the-shelf components are used to implement the bidirection amplifier. The amplifier is matched across the bandwidth of the array and provides 5 dB gain. Monostatic RCS measurements show that the array exhibits −10 dB beamwidths of about 118° and 80° in the E- and H-planes, over the entire bandwidth. In addition, it is shown that when the array ports are terminated with matched loads, the antenna RCS is reduced by approximately −15 dB with respect to the Van Atta case. This experimentally confirms that the array collects the total energy impinging from a remote source. [ABSTRACT FROM AUTHOR]

An amplitude-comparison monopulse slotted waveguide antenna array with a pillbox parabolic quasi-optical beamforming network is proposed in substrate integrated waveguide (SIW) technology in the 24 GHz band. The beamformer is illuminated by a cluster of horn pairs located in the focal plane of the pillbox reflector. Each horn pair is composed of two H-plane sectorial horns connected to a coupler. In-phase and out-of-phase operations of each horn pair allow radiation of the $\Sigma $ and $\Delta $ beams along the antenna scanning plane (E-plane). At the design frequency of 24.15 GHz, the experimental results demonstrate an antenna field of view of ± 26°, with null depth better than −20 dB for all the measured $\Delta $ beams. The antenna gain varies between 21.6 and 20.5 dBi for the $\Sigma $ beams and the measured input reflection bandwidth is about 2.4% for VSWR < 2. [ABSTRACT FROM PUBLISHER]

In this communication, it is shown that a nondiffracting vortex beam (i.e., a higher order Bessel beam with azimuthal phase variation) can be generated in the near field by synthesizing an inward cylindrical traveling-wave distribution over a finite aperture antenna. A radial line slot array (RLSA) is then designed to prove the concept. The collimated vortex beam is excited in the proximity of the RLSA, within a region properly defined by the nondiffracting range of the generated beam. The radial dependence of the longitudinal electric field of the vortex-beam magnitude follows a first-order Bessel function, and its phase presents a linear azimuthal variation. Full-wave results validate the generation of the nondiffractive higher order Bessel beam within the radiative near field of the launcher. [ABSTRACT FROM PUBLISHER]

We proposed a synthesis method to design thinned leaky-wave-based arrays. The array elements are small waveguide apertures opened on a ground plane. A superstrate (impedance sheet, dielectric slab, etc.) is placed above the array. The array elements excite leaky-wave modes between the ground plane and the superstrate, enhancing the aperture efficiency of the final antenna. An iterative optimization procedure based on a convex $\ell_1$ minimization is used to reduce the number of array elements, maintaining the radiated field within a predefined mask. All the embedded element patterns are evaluated for each source through a fast Green’s function spectral approach, taking into account the effects of the mutual coupling during the optimization procedure. The use of a superstrate provides array structures with a reduced number of elements and enhanced aperture efficiency with respect to configurations without superstrate. The level of the grating lobes is also controlled during the optimization. A parametric study is performed to understand the capabilities of the leaky-wave-thinned array varying the reflectivity of the superstrate. As an example, an array of 18 elements working over a 7% fractional bandwidth is synthesized, providing a reduction by a factor of 4 in the number of elements when compared to a configuration with the same requirements, but without superstrate. [ABSTRACT FROM PUBLISHER]

This paper presents a flat, high gain, wide scanning, broadband continuous transverse stub (CTS) array. The design procedure, the fabrication, and an exhaustive antenna characterization are described in details. The array comprises 16 radiating slots and is fed by a corporate-feed network in hollow parallel plate waveguide (PPW) technology. A pillbox-based linear source illuminates the corporate network and allows for beam steering. The antenna is designed by using an ad hoc mode matching code recently developed for CTS arrays, providing design guidelines. The assembly technique ensures the electrical contact among the various stages of the network without using any electromagnetic choke and any bonding process. The main beam of the antenna is mechanically steered over $\pm 40^\circ$ in elevation, by moving a compact horn within the focal plane of the pillbox feeding system. Excellent performances are achieved. The features of the beam are stable within the design 27.5–31 GHz band and beyond, in the entire Ka-band (26.5–40 GHz). An antenna gain of about 29 dBi is measured at broadside at 29.25 GHz and scan losses lower than 2 dB are reported at $\pm 40^\circ$. The antenna efficiency exceeds 80% in the whole scan range. The very good agreement between measurements and simulations validates the design procedure. The proposed design is suitable for Satcom Ka-band terminals in moving platforms, e.g., trains and planes, and also for mobile ground stations, as a multibeam sectorial antenna. [ABSTRACT FROM PUBLISHER]

A multibeam pillbox antenna system incorporating monopulse phase comparison technique is proposed in the 24-GHz band. This low-profile antenna architecture combines the scanning capabilities of pillbox configurations and enhanced resolution of two-quadrant monopulse technique; this approach avoids mechanical orientation of the antenna system for tracking applications. The radiating panel consists of two subarrays of 23 slotted waveguides, with 8 slots per waveguide. The beam is scanned in E-plane over a field of view of \pm \bf 40^\circ , and sum/difference patterns are generated in H-plane. Around the design frequency, \bf f = \bf 24.\bf 15\,\bf GHz, the antenna gain varies between 25 and 21.5 dBi for the central and extreme beams, respectively. The measured null depth is better than - \bf 16\;\textdB for all difference beam patterns. The antenna bandwidth for \bf VSWR < \bf 2 (\textbfS\textbf{ii} < - {\bf 10}\;\textbf{dB}) and isolation better than \bf 10\;\bf dB (\textbfS\textbf{ij} < - {\bf 10}\,\textbf{dB}) is equal to 4.5%. [ABSTRACT FROM PUBLISHER]

This paper introduces a rigorous and effective modeling framework for the continuous transverse stub (CTS) array, based on a spectral Green’s function approach. A multimodal expansion of the equivalent currents over the slots is used to derive an accurate expression for the active impedance of an infinite array. This formula is validated through comparisons with full-wave simulations when the array scans are in principal planes. The mathematical formulation highlights the broadband properties of CTS arrays and accurately predicts the impact of the geometrical parameters on the active impedance, as a function of frequency and scan angle. The discussion of the results provides physical insights to outline effective design strategies. [ABSTRACT FROM PUBLISHER]

A leaky-wave slot array antenna fed by a dual offset Gregorian reflector system is realized by pins in a parallel plate waveguide. The radiating part of the antenna is composed by parallel slots etched on one side of the same parallel plate waveguide. The dual offset Gregorian reflector system is fed by an arrangement constituted by two vias and a grid, also constituted by pins. Also this feed arrangement realizes a leaky type of radiation, this time inside the parallel plate waveguide. A prototype of the antenna has been designed, manufactured and successfully tested. The low profile, low cost and high efficiency of the antenna render it suited for a variety of radar or telecom applications. [ABSTRACT FROM AUTHOR]