Design of A Beamforming Circular-polarization Waveguide Antenna Array

Integrating antennas into a load-bearing airframe structure has the potential for profound improvements in the capability of military and commercial airplanes, by allowing for substantially increased radiator and array size with reduced weight or drag penalties. Reducing the size of array elements can significantly improve the mechanical performance of the loadbearing antenna. The novel single element spiral slot cut in the broad-wall of a WR-90 rectangular waveguide proposed in this paper is smaller than a quarter of the operating wavelength (half of the size of a conventional rectangular slot). The small antenna element enables a slotted waveguide array to be realized without significantly degrading the mechanical performance in load bearing applications. The proposed spiral slot is compared with conventional rectangular slots and exhibits comparable performance in terms of total efficiency (representing coupling from waveguide mode to the slot) and peak realized gain. Total efficiency and peak realized gain of the spiral slot in travelling wave mode are significantly higher than those of a quarter wavelength rectangular slot element which has near zero radiation. The simulated results were validated by manufacturing the spiral slot placed on the broad-wall of a rectangular waveguide. Realized gain patterns of the spiral slot measured at the design frequency corroborate reasonably with the simulations.

The leaky-wave antennas in the form of closely spaced transverse slots cut in a broad wall of rectangular waveguide were investigated. The thickness of waveguide walls and interaction between slots were taken into account in numerical calculations.

The possibilities of control of polarization and energy characteristics of the X-slots cut in the broad wall of rectangular waveguide with a complex load at the end and with the dielectric heterogeneity of the input waveguide section with a slot investigated. Numerical and experimental investigation of energy and polarization characteristics of such systems are performed. Changing the parameters: the dielectric heterogeneity, position its relative the slot and changing complex load allow to adjust X-radiation field with circular polarization, with a high emissivity and low VSWR at the input.

The admittance of an untilted slot in the narrow wall of a rectangular waveguide is calculated by including the actual external structure. The slot is excited by two tilted thin wires inside the waveguide. The slot is also allowed to extend into the two broad walls of the waveguide to make it sufficiently long for resonance to occur. The external slot admittance is evaluated by using a spectrum of two-dimensional solutions, a method which can handle the arbitrary cross section of the external structure, The analysis predicts that if both the slot and the wires are tuned to resonance, the transmission coefficient gets constant phase over a wide-frequency band. The results also show that resonance can be obtained for any slot length by adjusting the wire length, and this relation between the lengths is presented. The distance between the slot and the wires needed to maximize the radiated power is also shown; some results are confirmed by measurements.

A method is described to accurately analyze horizontal and vertical slots cut in the wall of a cylindrical waveguide. The interior and exterior regions of the guide are analyzed by using a spectrum of two-dimensional solutions (S2DS method). In addition, the finite thickness of the waveguide wall is also taken into account. To accelerate the convergence of the spectral integrals in the S2DS method, the asymptotic behavior of the integrands in these integrals is identified. The reflection and transmission coefficients for horizontal and vertical, rectangular slots in the broad wall of a rectangular waveguide are computed.

In terahertz communication systems, amplifiers and other components can induce non-linear distortion in terms of amplitude and phase, resulting in system performance degradation. This paper presents a terahertz metamaterial waveguide to mitigate amplitude and phase distortions in some terahertz systems. A simple method based on free-space analysis is proposed for designing metamaterial waveguides in an enclosed space. The quasi-periodic metamaterial structures, which feature I-shaped resonant patterns, are integrated onto the inner walls of rectangular waveguides. The phase and amplitude of electromagnetic waves within the waveguide can be modulated by varying the dimensions and number of these resonators. Utilizing the effective medium theory and the equivalent circuits, the metamaterial waveguide’s phase and absorption modulation mechanisms are analyzed. Based on the proposed structure, a metamaterial waveguide with I-shaped resonators is designed and fabricated, and its abilities to modulate the phase and absorption of terahertz waves around 0.2 THz are demonstrated.

Rectangular waveguide slot arrays are commonly used in several microwave antenna systems. The slots are most often located in the broad wall of the rectangular waveguide, arranged longitudinally parallel with the waveguide axis, because this provides good control of the excitation of each slot over a large dynamic range by adjusting the offset of the slot from the center line of the waveguide. However, longitudinal slots can only radiate electrical fields that are transversely polarized with respect to the waveguide axis. If longitudinal (or dual) polarization is required, the slots (or half of them) must be located transverse to the waveguide axis. Transverse resonant slots in the broad wall are too strongly excited for use in large arrays, so transverse narrow slots in the narrow wall are preferred. In the latter case the slots are not excited unless they are tilted or coupled to tilted parasitic elements like wires or posts inside the waveguide. The purpose of the present paper is to analyse an untilted narrow wall slot excited by two tilted wires. An improved and extended analysis in which the slot extensions into the neighboring two broad walls are included, is described. The virtual cylinder method is applied to the calculation of the external admittances of the slot using wedge dyadic Green's functions and entire-domain basis functions in order to get good convergence of the integrals of the spectral domain formulations.

A high power, high gain, and beam-steerable array antenna for high-power microwave applications is presented in this paper, which is fed by rectangular waveguides. A C-shaped slot on the narrow wall of the rectangular waveguide is applied to couple energy from the waveguide to the helical unit, which is used to radiate circularly polarized microwave. 2-D beam scanning is achieved through fewer control units. Simulation results indicate that a 2-m-long linear array achieves a gain of 26.3 dB, an aperture efficiency of 90.43%, and a power-handling capacity of 96.5 MW. A prototype of 20 × 15 array shows the beam scanning range is about ±35° in both typical vertical planes, while the gain decreases by less than 2.0 dB.

A compact and wide-band transverse slot antenna array in the broad wall of a rectangular waveguide partially filled with an H-plane -dielectric slab is presented in this paper. By partially filling an H-plane dielectric slab in the waveguide, the inter-element spacing between slots is reduced to be about 0.8 free-space wavelengths to avoid grating lobes. In addition, the partially filled material provides extra flexibility to adjust the slot impedance as desired within a relatively wide frequency range. A new feeding network is designed for this antenna array, which can prevent the shift in the pointing angle of the array's main radiation beam with the change of frequency. Experimental data for a 2/spl times/4 antenna array operating at X-band show that stable radiation pattern over a wide frequency range can be obtained. The measured gain is 16.9 dB at 10 GHz and the fluctuation is less than 2 dB over a frequency band of 1.5 GHz. The slot array's 10-dB return loss bandwidth is 13% and the cross-polarization level is better than -25 dB.

The resonant length versus offset of a dielectric‐covered narrow square ended slot is studied. The slot, located in the broad wall of a rectangular waveguide, is excited by a single mode. The external field is matched to the internal field by the Galerkin method concept. Corrections due to finite wall thickness are also included.

In this paper, the admittance characteristics of a dielectric filled inclined slot in the narrow wall of a rectangular waveguide have been calculated. By enforcing the continuity of the tangential magnetic field through the slot aperture, an integral equation with the tangential electric field in the slot as the unknown is obtained. An entire domain method of moments (MoM) is used to solve the integral equation. Numerical results show that the slot can resonate without penetrating onto the top and bottom broad walls of the waveguide. It has also been shown that the resonant frequency (length) and the resonant conductance of the slot depend on the dielectric constant of the material filling the slot. The computed results are shown to be in good agreement with those obtained by HP‐HFSS. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 222–226, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10876

The research of millimeter wave waveguide antenna array is urgently needed by the country, but due to the limitation of insufficient processing precision of traditional processing technology, there are still some problems in the realization of large millimeter wave waveguide antenna array, which affects the national scientific and technological progress and the country’s economic development. Aiming at the realization of the large millimeter wave waveguide antenna array, this paper takes 220GHz waveguide antenna array as the research object, combining the MEMS technology that can achieve micron-level processing accuracy with the design of 220GHz waveguide antenna array, and determines the 220GHz waveguide antenna array based on MEMS technology. The design method of 220GHz antenna is simulated by HFSS. The designed 220GHz antenna has a bandwidth of 210GHz~220GHz, a gain of 31dB, a standing wave lower than 1.8, and good electrical performance. Through research, this article reveals a new implementation method for millimeter wave waveguide antenna arrays, realizes the high gain design of millimeter wave waveguide antenna arrays, and establishes a complete set of millimeter wave waveguide antenna array implementation processes, which will provide a better solution for future millimeter wave waveguide antenna arrays. The research on large arrays of waveguide antennas has laid the foundation and provided a new idea for the design of large arrays of millimeter wave waveguide antennas.

A method to reduce cross-polarization (X-pol) of narrow wall slotted waveguide is presented. A 10 inclined slot array cut in the narrow wall of a rectangular waveguide with the element spacing of d = 0.64Aµ 0 operating in Ku-band is employed. The proposed slotted waveguide antenna consists of a perforated-metallic plate which acts as a polarization filter. The polarization filter reduces the maximum cross-polarization level by 10 dB at the design frequency of 14 GHz and 5 dB over the frequency band 12 GHz to 18 GHz.

Slot radiators are popular because of their compactness. However, design of slot arrays for a given application is highly involved. In addition, design of slot arrays, which do not result in EMI either in radar or in communication, is much more complicated. It is well known that for the sake of radiation the slots in the narrow wall of standard rectangular waveguide are made to incline in order produce horizontally polarized radiated fields. However, the resonant slot length cannot be accommodated due to dimensional considerations of the waveguide. Hence the slots are extended into the broad wall to accommodate resonant length. These two aspects are: i) extra length in the broad wall, ii) inclination of the slot in the narrow wall, create EMI due to the presence of cross polarized field components. It is possible to suppress such undesirable field components to escape from the presence of EMI by connecting a T-arm so that slot couples power into the T-arm so that slot couples power into the T-arm instead of free space. The T-arm has to be carefully designed with appropriate orientation to meet the requirements of polarization. E and H plane junction are conventionally used and they are analyzed by several authors. However, to design planar arrays consisting of slot coupled waveguide junctions, there is a need to twist the T-arm by an appropriate angle. That means it results in a waveguide junction in which both slot and T-arm are inclined. In the present work, the waveguide junction, which is suitable for the design of planar structures, is considered and the data on the effects of waveguide dimensions on the overall admittance characteristics is presented. The overall admittance is numerically evaluated from the derived analytical expressions as a function of dimensions of feed waveguide. The change in waveguide dimensions for the feed waveguide has become necessary in order to make the overall structure resonate. An expression for the admittance is derived from the knowledge of self-reaction and discontinuity in modal current. The self-reactions in the feed and coupled guide are separately obtained from TE and TM mode considerations. In the evaluation of admittance the energy stored in the primary guide is also considered. The data on the variation of normalized conductance and susceptance as a function of frequency for different feed guide dimensions and different slot and coupled arm inclinations are presented in this work.

A novel double-ridged slot array antenna on the broad side of a single-ridged rectangular waveguide has been developed. The design is based on using a single-ridged waveguide as a series feed for an array of transverse slot radiators located along its broad wall. The main lobe radiation direction is 60 degrees and the gain is 10 dB. The waveguide broadwall dimension that is needed for the main lobe direction is 25% smaller than that for the rectangular waveguide. The main lobe scanning as a function of frequency is +or-2 degrees and the antenna standing wave ratio is better than 1.62:1 over the 5% bandwidth. >