Continuous Transverse Stub Array Research Articles

A Dual-Polarized CTS Array Antenna with Four Reconfigurable Beams for mm-Wave Wind Profile Radar

The wind profiler radar (WPR) system requires a dual-polarized antenna with multiple low-sidelobe and high-gain beams to facilitate the detection of weak signals reflected by atmospheric turbulence. This paper proposes a dual-polarized continuous transverse stub (CTS) K-band antenna with four reconfigurable beams, which comprises a series-fed CTS array and four 1-to-14 power dividers as line source generators (LSGs) to generate a high-quality quasi-TEM wave. The CTS element incorporates a stepped transition radiation stub design and employs a short cutoff stub on the upper surface of the series-fed parallel plate waveguide (PPW) to achieve optimal impedance matching. The entire antenna is an all-metal structure with remarkably low loss, and low-cost standard fabrication processes are employed for the prototype, which achieves fast reconfigurable four-beam scanning to 15°, with a gain of 31.09 dBi and sidelobe levels below −17.6 dB. Measurement results in an anechoic chamber agree well with simulations, demonstrating the antenna’s ease of manufacture, stability, and suitability for wind profile radar applications.

Broadband Continuous Transverse Stub (CTS) Array Antenna for High-Power Applications.

A continuous transverse stub (CTS) array antenna with broad bandwidth and high-power handling capacity is proposed in this paper. The technologies of multi-step impedance matching and T-shaped electromagnetic band-gap (EBG) loading are utilized, which improved the antenna operating frequency bandwidth. An H-plane lens horn is used to feed the CTS array. As a result, a good bandwidth capability of more than 32% is achieved, with a gain variation less than 3.0 dB. The measured sidelobe level (SLL) is below -18 dB in the entire frequency range. Moreover, the power handling capacity of the antenna is more than 80 MW and can reach the GW level after arraying, which indicates that this antenna has application potential in the high-power microwave (HPM) field.

A wideband and high‐gain switched‐beam antenna system using active frequency selective surface

AbstractAntennas using the active frequency selective surface (AFSS) can achieve fast beam‐scanning ability at a low cost. In this study, a switched beam antenna with a high gain and 360° coverage in the horizontal plane is proposed. Twelve columns of AFSS form a cylindrical cavity and are transmissive or reflective to the incident electromagnetic waves under the control of PIN diodes. Benefiting from a coaxial continuous transverse stub array placed at the cavity centre and using 4 units to generate a high gain omnidirectional radiation, the proposed antenna can realise a highly directive switched beam. An antenna prototype is designed, fabricated and measured. Results show that it achieves a |S11| < −10 dB bandwidth of 12.9% and is able to sweep its beam around the azimuth plane with a high gain up to 13.6 dBi at 5.8 GHz working frequency.

Ultra-Low-Profile Continuous Transverse Stub Array for SatCom Applications

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.

A Low-Profile SIW-Based CTS Array with Reconfigurable Four Beams and Dual Polarizations for K-Band Sensing.

A dual-polarized continuous transverse stub (CTS) K-band antenna with reconfigurable four beams and low profile is proposed based on substrate-integrated-waveguide (SIW) design. It consists of a line source generator (LSG) on the bottom surface, a spherical-wave to plane-wave transforming part on the middle layer, and CTS radiators on the top surface. Particularly, the LSG has four SIW-based H-plane horns, and a chip is integrated to switch among the two pairs of horns, so as to transfer the quasi-TEM waves on the bottom surface by a ±10° deflection angle to the middle layer for the CTS radiators on the top surface, resulting in four reconfigurable scanning beams with 10° for two polarizations. The measurements show that it realizes four reconfigurable beams with a 25.8 dBi gain at 24 GHz, verifying the design. The proposed antenna takes into account the advantages of reconfigurable multi-beam, dual polarization, low side lobes, low profile, and high gain, which can be applied to K-band sensing, especially for wind profile radars.

C‐band frequency‐scanning continuous transverse stub array with high gain and low sidelobe level

A C-band substrate integrated waveguide based frequency-scanning continuous transverse stub (CTS) array with high gain and low sidelobe level (SLL) is presented in this paper. The newly suggested linear source generator (LSG) consists of a feeding probe, a main reflector, a sub-reflector, and two metal matching vias. By introducing one matching via on the left side of probe and another one on the right side of the sub-reflector, a broadband LSG is obtained to excite the CTS array with a wide scanning range. The operating mechanism of the two matching vias is analysed. In order to reduce SLL, a serial-fed array with asymmetrically distributed stub width is designed according to Chebyshev distribution for the first time. A prototype of 12-element array is designed, simulated and measured, and excellent agreements are achieved. The measured beam-scanning range is from −52° to 2° within the operating frequency of 5.6–8 GHz, in which |S11| is less than −10 dB. The maximum gain is 22 dBi and the SLL varies between −21 dB and −18.2 dB. The proposed design approach can be applied to other bands and other level distributions. The proposed frequency scanning array has great potentials in radar and detection systems.

A High-gain and Beam-scanning Variable Inclination Continuous Transverse Stub Array Antenna Based on Linear-gradient Stub at Ku Band

A High-gain and Beam-scanning Variable Inclination Continuous Transverse Stub Array Antenna Based on Linear-gradient Stub at Ku Band

Compact line source generator for feeding continuous transverse stub arrays

Abstract Based on a substrate integrated lens (SIL), a compact line source generator (LSG) for feeding continuous transverse stub (CTS) arrays with linear-polarized (LP) beam scanning and dual-polarized (DP) operations is presented in this paper. The SIL consists of metamaterial cells with different sizes being arranged as concentric annulus and is printed on the center surface of two substrate layers. The SIL can convert the cylindrical wave generated by the feed probe of SIW-horn to the planar wave for feeding the CTS array. This rotationally symmetric SIL can be used conveniently to design LSG for feeding CTS arrays with the continuous beam scanning and DP operations, which has been verified by the fabrications and measurements. By simply rotating the SIW-horn along the edge of SIL, the 10-element LP-CTS array obtains a measured beam scanning range of ±35° with the highest gain of 20.6 dBi. By setting two orthogonal SIW-horns at the edge of the proposed SIL, the nine-element DP-CTS array with orthogonal radiation stubs is excited. The DP array obtains the gain of 20.3 dBi at the center frequency with the isolation of 28 dB and the cross-polarization level <−25 dB.

A Low-Profile and Beam-tilted Continuous Transverse Stub Array Antenna at W-band

This paper presents a low-profile, high gain, beam-tilted continuous transverse stub (CTS) array antenna at W-band. The antenna compromises 32 radiating slots and is fed by a parallel plate waveguide (PPW) network with a linear source generator. To deflect the outgoing beam, the principle of linear array scanning is adopted to design inverted T-type structure in each stub to introduce wave path difference. PPW network allows the antenna to obtain lower profile compared to other transmission lines. The design procedure, and the antenna characterization are described. The main beam of the antenna is titled 12 degree in H-plane. The simulation and measured results show that this antenna achieves peak gain of 32.4 dB and a 12 degree beam tilt angle at 99GHz. S11 parameters of the antenna is less than -10 dB in a broadband from 96 GHz to 103 GHz. This antenna has an advantage of miniaturization over other high-gain antenna solutions. The promising performance of this proposed CTS antenna reveals the possible candidate for Millimeter wave (MMW) telecommunication applications.

Wireless communication applications of the variable inclination continuous transverse stub array for Ku‐band applications

A wideband and continuous beam steering variable inclination continuous transverse stub antenna array is presented in the communication. The proposed antenna consists of a continuous transverse stub (CTS) array and a line source generator (LSG). These two parts are designed and optimized separately. The LSG structure is generated by a Pillbox transition. The CTS array is composed of 20 radiating slots and is fed by a corporate-feed network. The corporate-feed network adopts a series-parallel hybrid structure to realize lower profile and high-efficiency performance. The relative rotation movement between the CTS array and the LSG generates a phase gradient on the radiation part such that the proposed antenna can obtain a continuous beam in the upper hemisphere. Based on the array synthesis encryption sampling technology theory, the relationship between the mechanical rotation angle and the beam direction is analysed and obtained. To validate the antenna concept, the antenna is fabricated and measured. The simulation and measurement results are in good agreement. Through the rotation of the CTS array, the designed antenna achieves a ±56°scan. The measured results show that the array can achieve an impedance bandwidth of 16% in Ku-band at the centre frequency of 12 GHz with 67% aperture efficiency. The proposed antenna has the characteristics of low profile, high efficiency, large coverage, and wideband, which is well suited for mobile satellite communication.

A Novel Dual-Polarized Continuous Transverse Stub Antenna Based on Corrugated Waveguides—Part II: Experimental Demonstration

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.

A Novel Dual-Polarized Continuous Transverse Stub Antenna Based on Corrugated Waveguides—Part I: Principle of Operation and Design

Continuous transverse stub (CTS) arrays represent a high-performance and affordable solution for fixed-beam and scanning flat antenna systems, though intrinsically linearly polarized. In these systems, the polarization is controlled using add-on polarization converters or combining cross-connected CTS arrays. This two-part article presents a novel parallel-fed CTS antenna which achieves dual-linear polarization using, instead, a single array and two orthogonally polarized excitation fields. In this article, it is shown that, due to modal coupling, standard parallel-plate waveguides (PPWs) are not suitable as building blocks of the proposed antenna. Therefore, an alternative waveguide, the corrugated PPW (CPPW) is introduced. The dispersion characteristics of such CPPW are investigated. Guidelines to independently design the dispersion properties of the two propagating modes and avoid the excitation of higher order modes are provided. Based on this study, the design and simulated performance of a Ka-band array of eight long slots parallel-fed by a dual-mode CPPW corporate-feed network are described. An extensive experimental validation of the concept is presented in Part II.

Analysis of Circularly Polarized CTS Arrays

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.

Compact Beam-Scanning Flat Array Based on Substrate-Integrated Waveguide

A compact beam-scanning flat antenna array with high gain based on the substrate- integrated waveguide (SIW) is presented in this article. The radiation elements are the continuous transverse stub (CTS) constructed by SIW, which are arrayed on the substrate. The SIW-CTS array has a 4 dB higher gain than the traditional CTS array with the metal parallel plate waveguide and the theoretical explanation is analyzed. A new compact corporate-feed network consisting of an SIW-horn and a flat lens is also proposed. The flat lens could convert the cylindrical wavefront generated by the feed probe and the SIW-horn to a planar wavefront for feeding the CTS array. The Taylor distribution of the feed level made the array has a low sidelobe and high gain. The beam scanning of the array could be realized by simply moving the small SIW-horn along the line across the focal point. An eight-element array is designed, simulated, and fabricated to verify the design. The measured results show that the scanning range is from -35° to 35° with the highest gain of being 20.6 dBi and the sidelobe level of -25.2 dB at the broadside.

High-Performance E-Band Continuous Transverse Stub Array Antenna With a 45° Linear Polarizer

This letter presents a continuous transverse stub (CTS) array antenna with high aperture efficiency, low sidelobes, and cross-polarization characteristics over an E-band. The antenna consists of a full-corporate-feed 32-slot CTS array and a 45° linear polarizer. A multiple-aperture excited parallel-plate waveguide structure works as a linear source generator to generate the quasi-TEM wave with a uniform amplitude distribution over the whole operating band from 71 to 86 GHz. The 45° linear polarizer contains two layers of slots, shifting the linear polarization from the principal E-plane (φ = 90°) to the intended E-plane (φ = 135°). The array antenna achieves the low cross polarization and sidelobe level (SLL) while maintaining high aperture efficiency. Measurement results show that the antenna has an aperture efficiency of over 74% with the peak gains of better than 37.9 dBi over the whole E-band, while the far-field SLLs in the intended E- and H-planes approach the ETSI class IV envelope standard.

Long Slot Array Fed by a Nonuniform Corporate Feed Network in PPW Technology

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.

An $8\times 4$ Continuous Transverse Stub Array Fed by Coaxial Ports

Continuous transverse stub arrays are wideband, wide-scanning antennas consisting of an arrangement of long slots or parallel-plate waveguide apertures radiating in free space. A line source is generally required to feed these arrays. Here, we show that such a line source can be created over the radiating aperture using a two-dimensional (2-D) arrangement of coaxial probe transitions. The coaxial transitions are directly integrated into the parallel-plate waveguides feeding the slots. Such a solution avoids using quasi-optical systems or bulky corporate networks to feed the array. The proposed 2-D feeding scheme also allows steering the main beam of the array. This is an additional benefit with respect to previous designs for which scanning was limited to a single plane. An array of 8 × 4 elements validates the concept at $\text{5.8}\,\text{GHz}$ . Measurements show that the array exhibits a field of view of $\pm{\text{30}}^\circ$ in elevation over the $\text{5.4}\text{--}\text{6.2}\,\text{GHz}$ band, with an active reflection coefficient for the central elements better than $-{\text{10 dB}}$ .

Compact Dual-Polarized Continuous Transverse Stub Array With 2-D Beam Scanning

A dual-polarized (DP) flat antenna array with passive 2-D beam-scanning capability is presented in this paper. The array consists of a DP continuous transverse stub (CTS) array, a flat Risley prism (FRP), and a line source generator. Two sets of CTSs, being constituted by the substrate-integrated waveguide (SIW), share a common aperture and are arranged orthogonally for the DP operation. A novel compact long line source is proposed for exciting this DP-CTS array. The FRP is realized by two linear phase progression phase-shifting surfaces (LPP-PSSs) and is placed above the DP-CTS array. The beam-scanning capability in the azimuth and in the elevation can be realized by rotating simultaneously the two LPP-PSSs in the same and in the opposite directions, respectively. A six-element array prototype is simulated and fabricated. According to the measured results, beam-scanning ranges of 40° in the elevation and 360° in the azimuth are achieved with the maximum gain of 17.8 dBi. The novel contributions from this paper include: 1) a novel compact long line source and 2) the first passive DP 2-D beam-scanning flat antenna array. This array can be extended easily to a higher gain or a circular polarization application.

Millimeter-Wave Low-Profile Continuous Transverse Stub Arrays With Novel Linear Source Generators

This paper presents a new type of continuous transverse stub (CTS) antenna array with a novel linear source generator (LSG). The conventional multilayer parallel-plate waveguide (PPW) feed and pillbox structure are eliminated and replaced with a more compact partially corporate feed network. This helps to achieve a lower profile (or reduction of antenna layers) and high performance of broadband and high efficiency. For validation, two prototypes are demonstrated—one based on hollow waveguides operating at 34–41 GHz (Array-I) and the other based on substrate integrated waveguides operating at 24.5–29.5 GHz (Array-II). Both arrays contain eight radiation slots, fed from a single-layer PPW junction. The required quasi-transverse electromagnetic wave excitations are achieved by using the novel LSG of a jagged cavity structure. The detailed design methodology and analyses are provided in this paper. Measurements show that antenna efficiencies of over 83% and 82% with the peak gains of better than 27.6 and 20.6 dBi are achieved for Array-I and Array-II, respectively. These low-profile CTS designs are well suited for current and emerging millimeter-wave applications such as 5G and point-to-point communications.

An 8 x 4 Continuous Transverse Stub Array Fed by Coaxial Ports

An 8 x 4 Continuous Transverse Stub Array Fed by Coaxial Ports