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To meet the packaging requirements of terahertz (THz) communication systems, a microstrip line (MSL) to rectangular waveguide (RWG) transition is proposed in this paper. In the transition, the MSL is connected to the corrugated substrate integrated waveguide (CSIW) by a tapered MSL for quasi-TEM to TE10-like mode conversion on substrate, which requires no via holes or shaped dielectric, and is easy to process in THz bands. Then, the CSIW is straightly connected to the RWG transformer and converted to standard RWG, resulting in a compact structure. The working principle of the proposed transition is analyzed, and the influence of several important parameters on the S-parameters of the transition is discussed. A single transition is designed for the 325–500 GHz operation, the S11 better than −14.5 dB and S21 better than −1.03 dB have been achieved in the entire frequency band.

A novel millimeter-wave (mm-wave) wideband circularly polarized (CP) horn antenna using iris polarizer is reported. By introducing the metasurface concept, the electrical contact problem at the mm-wave band for waveguide-separated components of high-performance CP horn antenna is eliminated. The influence of air gaps on polarizer and whole horn antenna loaded and unloaded metasurface is analyzed and explained. According to simulation, small air gaps of the metal-to-metal contacting plane would not harm the horn performance after loading the metasurface, which means the proposed method can achieve a better tolerance of manufacturing and assembly errors and is more suitable for high-frequency CP horn design. For validation, the proposed horn antenna has been fabricated and its performance is evaluated. The measurement results are in good agreement with the simulation results. The experimental results of 37.8% bandwidth from 75 to 110 GHz for both the axial ratio (AR) $\vert S_{11}\vert dB are achieved.

A millimeter-wave (mm-Wave) wideband dual circularly polarized (CP) antipodal septum antenna is proposed. By introducing two antipodal septum blames in widened rectangular waveguide and the corresponding feeding network, the operating bandwidth of the septum antenna is enhanced. The working principle of the generation process of dual CP is explained by a three-port model with three excitation conditions. In addition, the asymmetrical radiation pattern of the classical polarizer consisting of square waveguide and single septum caused by the high-order modes is explained and eliminated. To verify the design, the proposed antenna has been fabricated and measured. An operating bandwidth of 37.4% for reflection coefficients less than −13.8 dB, isolation better than 22 dB, and axial ratio (AR) value less than 3 dB is achieved.

A millimeter-wave (mmW) wideband circularly polarized (CP) antenna based on an air-filled waveguide is proposed. By introducing two symmetrical ridges in the septum antenna, the proposed antenna can obtain a more compact antenna aperture than the septum antenna based on a rectangular waveguide (from 0.99 $\lambda \,\,\times1.25\,\,\lambda $ to 0.66 $\lambda \,\,\times0.91\,\,\lambda $ ). In addition, the high order modes are suppressed to less than −20 dB from 55 to 70 GHz. Then, the sharp corner in the axial-ratio (AR) and gain plots of the septum antenna based on a waveguide are eliminated. A simulated operating bandwidth of 16.4% for both $\vert \text {S}_{11}\vert dB and AR < 3 dB within half-power beamwidth (HPBW) is achieved from 56 to 66 GHz. To verify the design, the proposed antenna has been fabricated and measured. The differences between simulations and measurements caused by flange are evaluated. The measured operating bandwidth of 20.9% is achieved from 60 to 74 GHz

A type of millimeter-wave antenna array with flexible design is proposed for a variety of applications at 60 GHz. The antenna array can be adjusted to be linearly or circularly polarized by simply changing the radiation part of the antenna array. High gain, wideband, and high radiation efficiency characteristics can be achieved by adopting a low insertion loss feeding network and broadband antenna elements. For the linearly polarized antenna array, simulation results show that the impedance bandwidth of the 2×2 antenna subarray reaches 21.6%, while the maximum gain achieves 15.1 dBi and has a fluctuation of less than 0.4 dBi within the working bandwidth. Simulation results of the 8×8 linearly polarized antenna array show a bandwidth of 21.6% and a gain of (26.1±1) dBi with an antenna efficiency of more than 80%. For the 8×8 circularly polarized antenna array, simulation results show that an impedance bandwidth of 18.2% and an axial ratio (AR) bandwidth of 13.3% are obtained. Gain and efficiency of up to 27.6 dBi and 80% are achieved, respectively. A prototype of antenna array is fabricated, and results are compared and analyzed.

This paper presents a wideband dual-circular-polarization (dual-CP) antenna with high port isolation based on a grooved-wall CP horn combined with an orthomode transducer (OMT) in the W-band. A pair of grooves on the inner wall of the horn serves as an inbuilt polarizer within the horn antenna, which is capable of generating both left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) without any septum. The continuous linearly-tapered groove design also allows this multi-section grooved-wall CP horn to achieve low reflection coefficients over a wide bandwidth, thereby realizing wideband dual-CP with high port isolation when it is used together with a wideband OMT. A prototype of the proposed dual-CP antenna is designed in simulation and measured in an experiment. The simulated and measured results agree very well, showing that port isolation > 32.5 dB over 31.6% bandwidth from 80 GHz to 110 GHz is achieved with axial ratio (AR) < 2.8 dB and reflection coefficient < –20 dB for both LHCP and RHCP. Rotationally symmetric radiation patterns over the entire operating bandwidth are also observed with a measured gain of 19.6±2 dBic.

A practical compact antenna test range (CATR) requires good quiet zone quality for antenna characterization. This paper addresses the phase profile of the CATR quiet zone from the known intensity pattern of spatial domain and Fourier domain based on a combined alternating projection algorithm. The proposed algorithm is composed of Gerchberg–Saxton (GS) and Hybrid Input–Output (HIO) algorithms and the two algorithms with spatial phase perturbation (SPP) work collaboratively or independently under predesigned conditions. It is observed that the algorithm with random initial phase guess can always converge to an optimal solution by performing a series of hierarchical optimizations of the problem. The numerical results are in good agreement with simulated results in different frequency bands, overcoming the phase retrieval limitation of local convergence in the iterative process. Furthermore, to validate the effectiveness and robustness of the proposed procedure, the related discussions corresponding to different sampling areas in Fourier domain and different signal to noise ratios (SNRs) are given.

In this paper, the authors present a broadband transition from the standard WR-10 rectangular waveguide (RW) to a groove gap waveguide (GGW) in the W-band. The transition structure is based on electromagnetic band gap (EBG) technology where two EBG units are used, which are responsible for the transition and forming the transmission line. Metal pins in the E-plane together with the back surface of the transmission line create a forbidden band, which prevents power leakage between the connecting parts. Small air gaps will not harm the transition performance according to the simulation, which means it has a better tolerance of manufacturing and assembly errors and, thus, has advantages for mm-wave contactless connections. A back-to-back transition prototype was designed, fabricated and measured. The length of the GGW is 39.6 mm. The measured |S11| is better than &minus, 13 dB and the measured |S21| is better than &minus, 0.6 dB over 76.4&ndash, 109.1 GHz, covering a bandwidth of 35.3%.

A millimeter-wave wideband circularly polarized (CP) horn antenna with no requirement of an orthogonal mode transducer feeding is reported. The horn antenna has a simple structure, which consists of an antipodal curvedly tapered slot antenna and a circular waveguide. The CP principle of the horn is explained. A series of parametric studies was carried out to estimate the effect of key parameters, and the design procedure is also presented. The measured results are in reasonable agreement with the simulation results. The experimental results indicate that the proposed antenna can achieve a bandwidth of 40% (50–75 GHz) for both the axial ratio $S_{11} dB. The proposed antenna is easy to manufacture and is a good candidate for the low-cost wideband CP horn antenna.

A novel millimeter-wave (MMW) endfire wideband circularly polarized (CP) antenna with simple structure is reported. By introducing two symmetrical septum blades filled in the widened rectangular waveguide, the proposed antenna can obtain a 40% bandwidth for both axial ratio (AR) $S_{11} dB. The CP operating mechanism of the antenna has been explained, using a three-port structure. The parametric studies for all of the antenna parameters are carried out to estimate their influences on antenna performance. The sharp corner in the AR plot is also explained by mode analysis. Its influences on the radiation pattern, gain, and reflection coefficient at this frequency point are evaluated. The proposed antenna has been fabricated and measured. The simulation results are in good agreement with the measurement results. Furthermore, this antenna is an appropriate choice for designing a MMW high-efficiency wideband antenna array. An $8 \times 8$ array with 64 equal amplitude and phase wave ports in HFSS has been designed to evaluate the array performance, which shows that the array can achieve 40% operating bandwidth without considering the bandwidth of feeding network. The simulated aperture efficiency of the array is above 85.34% from 50 to 75 GHz.

In this paper, a novel circularly polarized end-fire septum antenna based on substrateintegrated-waveguide (SIW) is proposed in the 60-GHz band. By introducing four symmetrical tapered curved air slots in three stacked open-ended SIW layers, the antenna can obtain an operating bandwidth from 57.2 to 63.4 GHz for both AR 11

In this paper, a millimeter-wave multi-folded frequency-dependent progressive phase shifter based on substrate-integrated-waveguide (SIW) is proposed. The equations based on SIW TE10 mode characteristic are applied to design the parameters of the phase shifter. An end-fire magneto-electric dipole with wide beam width is employed as the radiating element. By combining the antenna element and the phase shifter together, a frequency beam scanning antenna array is proposed and analyzed, using mathematical calculation based on phase array theory. A prototype of the proposed array has been fabricated and measured. The theoretical calculation of radiation pattern of the array is verified by full-wave electromagnetic solver Ansys HFSS and measurement. The measurement results show that the array can achieve a wide scanning range from -18° to 32°, gain variation less than 2.9 dBi, and radiation efficiency around 50% from 57 to 63 GHz. With the advantages of simple and compact structure, wide beam scanning range, and low-cost processing, the proposed array would be a good candidate for millimeter-wave wireless communication.

The authors propose the concept, analysis, and design of frequency tunable band-pass filters operating in the terahertz band. The proposed structure is composed of two metal tapped line and five metal-contacted graphene hairpin resonators transferred onto a dielectric. This structure implements low insertion loss and frequency tunability by adequately controlling DC bias applied on the graphene. An efficient synthesis method has been presented, through combining classical microwave filter theory and the electrical properties of graphene. The theoretical and extracted resonance frequency of resonator (f 0), external quality factor (Q E) and coupling coefficient (Kij ) are utilised to determine the filter circuit dimensions. Then the authors proposed two examples with different operating bandwidths to validate the theoretical design. The potentially high losses of graphene is also evaluated.

This paper presents and characterizes a novel antipodal linearly tapered slot antenna for generating the circularly polarized (CP) field. By introducing two symmetrical slots on the top and bottom layers of a rectangular WR-15 waveguide, we could obtain circular polarization with an axial ratio bandwidth of 34.1%. The waveguide was used to feed the proposed antenna with very wideband impedance matching. The antenna can achieve impedance bandwidth of 40% for S(1,1)

The Fast Fourier Transform is a fundamental tool in scientific and technical computation. The highly parallelizable nature of the algorithm makes it a suitable candidate for GPU acceleration. This paper focuses on exploiting the speedup due to using the half precision multiplication capability of the latest GPUs' tensor core hardware without significantly degrading the precision of the Fourier Transform result. We develop an algorithm that dynamically splits the input single precision dataset into two half precision sets at the lowest level, uses half precision multiplication, and recombines the result at a later step. This work paves the way for using tensor cores for high precision inputs.

The concept and analysis of a graphene-metal beam-reconfigurable terahertz (THz) loop antenna are presented. The hybrid graphene-metal implementation is proposed to combine (i) dynamic surface conductivity tunability using different DC bias voltages and (ii) high radiation efficiency enabled by metal. The loop antenna which employs an artificial mu-negative transmission line provides the horizontally polarised omnidirectional radiation. The graphene-metal loop around the centre ring acts as a reflector. Changing the DC bias of different position of graphene to control the position of resonance can effectively adjust the beam direction. The proposed concept and achieved performance, computed using realistic material parameters, are extremely promising for beam scanning at THz frequencies.