Ka波段紧凑型TE01-TE11椭圆波导模式转换器的研究(英文)

本文对椭圆波导TE₀₁-TE₁₁模式转换器进行了研究。选择了合适的椭圆波导截面,在椭圆波导纵轮廓线函数中采用了相位重匹配方法,并利用粒子群算法进行了纵轮廓线优化,所设计的椭圆TE₀₁-TEs₁₁模式转换器在28 GHz时的转换效率为99.16%,在27～29.3 GHz模式变换器的效率大于90%,相对带宽为8.2%。所设计的TE₀₁-TEs₁₁椭圆模式转换器的转换段为现有长度的一半。将设计的椭圆模式转换器与两个过渡段相连,并在CST中进行仿真和验证,其结果与理论计算一致。设计出了一个中心频率点为28 GHz的高效、紧凑、高功率椭圆波导TE₀₁-TE₁₁模式转换器。     

Wideband circular patch antenna operated at TM01 mode

The characteristics of a circular patch microstrip antenna with a top-loaded monopole feed are investigated. Air is used as the dielectric substrate. The distance between the radiating patch and ground plane is ~0.15λ₀. The patch is excited in the TM₀₁ mode. An impedance bandwidth (SWR<2) of 50% and an average gain of 5dBi are obtained     

A single-period TE02-TE01 mode converter in ahighly overmoded circular waveguide

A single-period 60 GHz TE₀₂-TE₀₁ mode converter for use in an electron cyclotron heating (ECH) system for magnetically confined plasmas is presented. The mode converter is very compact and has a broad bandwidth and a theoretical conversion efficiency of 97.6%. A method of computing the reflection from converters is presented and used to show that reflection from the single-period mode converter is minimal. Experimental results are consistent with theoretical calculations     

Broadband linearly polarized beat-wave TEm1/TE11 mode converters

Broadband linearly polarized waveguide mode converters have been developed to transform the high-order cylindrical TE_m1 output wave from harmonic gyrotron amplifiers into the more useful TE₁₁ fundamental waveguide mode. The converter's corrugation period is equal to the beat between the two waves and the bandwidth is predicted to be inversely proportional to the number of periods. Four-period TE ₃₁/TE₁₁ and TE₄₁/TE₁₁ converters with an azimuthal perturbation of m_c=4 and m_c =5, respectively, have yielded a peak conversion efficiency of 98% with a bandwidth greater than 3% and a one-period beat-wave converter has been designed to yield 12% bandwidth. However, it has been observed in measurements that the strong coupling in a short converter can lead to a shift of the center-frequency with an accompanying reduction of the efficiency and bandwidth. A two-period TE₄₁/TE₁₁ converter with 5% bandwidth displayed a 5% frequency shift and a conversion efficiency of only 86%     

Input impedance of a coaxial line probe feeding a circularwaveguide in the TM01 mode

By means of the conversion of complex power technique (CCPT), a formally exact full-wave solution is given for the case of a coaxial line probe fending a circular waveguide for TM₀₁ modal excitation. The overall scattering matrix of the coaxial-line-prove-circular-waveguide system is deduced. Numerical results for the impedance as `seen' by the coaxial line are presented and compared with experimental results obtained in the 9.0-11.5-GHz frequency range. Their agreement is reasonably good except at the lower frequencies (<10.0 GHz), where the TM₀₁ mode in the circular guide is close to its cutoff frequency (8.14 GHz)     

High power millimeter-wave TE03 to TM11 mode converters

Transmission of power from 42 ± 0.2 GHz gyrotron (TE₀₃ mode) to tokamak or dummy load requires a set of transmission line components. It includes a set of mode converters that converts circularly unpolarised TE₀₃ mode to polarised HE₁₁ mode. The mode conversion sequence is methodised in two steps; first from TE₀₃ to TE₀₁ mode and then from TE₀₁ to TM₁₁ mode. The proposed mode converters performance depends on the parameters such as waveguide radius, beat wavelength, number of ripples, its perturbation amplitude (η) and bending angle. These parameters are numerically optimised and verified in CST microwave studio. TE₀₃ to TE₀₁ mode conversion is realised by the generation of intermediate mode TE₀₂. The mode conversion length for TE₀₃ to TE₀₂ mode converter is6λ₀, (where λ_b is the beat wavelength of corresponding mode conversion) which converts 99.15% of an incident circular TE₀₃ mode power into TE₀₂ mode power. Next, mode converter converts TE₀₂ mode into TE₀₁ mode with 99.06% efficiency along the optimal length of6λ_b. For TE₀₁ to TM₁₁ mode conversion, two conversion methodologies have been proposed: first using axis arc bend (34.94°) technique to convert TE₀₁ into its analogous degenerate mode with 99.01% conversion efficiency and second using parabolic curve with 90° bend, which gives a conversion efficiency of 97.5%.     

Achievement of pencil-beam radiation from a TM01 modecircular waveguide source

A method employing appropriately placed parallel-metallic plates in the aperture of a TM₀₁ mode circular waveguide source so as to have it produce pencil-beam radiation is described and analyzed. Programmed computations, with experimental verification, are given for the case of a C-Band TM₀₁ source flared out to a conical horn so as to produce moderate (22 dBi) gain. Means of extending the method to achieve higher gains (40 dBi to 60 dBi) and to modify the plate arrangement so as to produce the same effect with a TE₀₁ mode are briefly outlined     

Optimized overmoded TE01-to-TM11 mode converters for high-power millimeter wave applications at 70 and 140 GHz

Mode coupling in bent, oversized, smooth-wall circular waveguides was studied by means of numerical integration of coupled-mode differential equations in order to optimize high-power TE01-to-TM11 mode transducers at 70 GHz and 140 GHz. Such mode transformers are used in the mode conversion sequence TEOn to TE01 to TM11 to HE11 for generating the almost perfectly linearly polarized Gaussian-like HE11 mode from circular electric TEOn gyrotron modes. This quasi-optical HE11 hybrid mode is in many respects ideal for electron cyclotron resonance heating (ECRH) of magnetically confined plasmas in thermonuclear fusion research and for other technical applications. Curvature and ellipticity coupling as well as ohmic attenuation of 6 coupled modes (TE01, TM11, TE11, TE12, TE21, TM21) are included in the coupling matrices. Integral expressions were used for deriving the coupling coefficients for arbitrary modes in bent, smooth-wall waveguide. Lowest level of unwanted spurious modes together with highest transmission efficiency (shortest arc length) is achieved with sinusoidal curvature distribution instaed of constant curvature. The calculated conversion efficiencies of 98.0% at 70 GHz and 95.2% at 140 GHz (interior waveguide diameter D=27.8 mm for 200 kW transmission lines) are in excellent agreement with the measured values of (97.6±0.4)% and (95±1)%, respectively.     

Design of short high-power TE11-HE11 modeconverters in highly overmoded corrugated waveguides

A theoretical parametric study of TE₁₁ to HE₁₁ mode conversion in highly oversized, circumferentially corrugated circular waveguides with different inner diameters is presented for various frequencies in the range of 28 to 140 GHz. The depth of the annular slots is tapered gradually from one half to one quarter wavelength. Computer-aided optimization of converter length, shape of corrugations, and nonlinear slot depth variation has been achieved with a scattering matrix code employing the modal field matching techniques (modular analysis concept). Relatively short mode transducers with matched converter lengths are feasible. The optimum conversion lengths are L₁≈0.5λ_B (short converter) and L₂≈1.2λ_B (long converter), where λ_B is the beat wavelength of the TE₁₁ and TM₁₁ modes in the corresponding smooth-walled circular waveguide. The predicted performances of short and long mode transducers are practically identical. Experimental results taken at 70 GHz (i.d.=27.79 mm) are in excellent agreement with the theoretically predicted performance data. In all cases the HE₁₁ output mode purity is 99% to 99.5%. The maximum cross-polarization and input-reflection levels are below -29 dB and -50 dB, respectively     

A novel tap input coupling structure for a narrow bandpass filterusing TM010 mode of a microstrip circular-disk resonator

This paper discusses a new method to couple into the TM₀₁₀ mode of a microstrip circular-disk resonator. This method can achieve reasonably strong input coupling, which is useful for narrow-band filters with fractional bandwidths of approximately 0.5% and above. A comparison between this newly proposed input coupling structure and the conventional gap input coupling structure will be addressed. A decision threshold for using either the tap input or the conventional gap-coupled input is also explained. Experimental results of a filter fabricated using this novel input coupling structure is also presented     

Design of mode converters for generating the TE11 mode from TM01 vircator at 4GHz

This work reports on measurements and calculations (coupled mode equations) on the conversion of transverse magnetic TM₀₁ vircator mode at 4 GHz to the linearly polarized TE₁₁ mode by means of mode converter systems using a circular waveguide with curvature. The mode converter is composed of a 38.78° bend with 39.07 cm curvature and a 50.78° inverse bend with 25.24 cm curvature in 9 cm internal diameter (ID) circular waveguide. The efficiency of conversion from TM₀₁ to TE₁₁ at 4 GHz exceeds 99%, and the overall efficiency from TM₀₁ to TE₁₁ exceeds 90% over a calculated range of 3.72–4.8 GHz.     

Design of triple mode TE01δ resonator transmissionfilters

The use of triple mode TE_01δ cubic resonators for the design of transmission mode filters is presented. Frequency tuning and coupling between modes are studied experimentally. The tunability of all inter-cavity couplings, necessary for the realization of a wide range of transfer functions, is demonstrated with a 6th degree, 5 MHz wide filter at 2 GHz. With an insertion loss of 0.7 dB in a volume of 260 cm³, the filter presents a 2:1 volume reduction over conventional TE_01δ filters     

Numerical analysis of a TM010 cavity for dielectricmeasurement

The properties of a TM₀₁₀ cavity containing a lossy dielectric material are investigated, using the transmission-line-matrix (TLM) technique with serial nodes in cylindrical coordinates. The cavity operates at 1.1 GHz and has three concentric layers and an air gap between the sample and cavity cover. The influence of this air gap on the Q-factor and the resonant frequency is studied. Compared with the TLM method in rectangular coordinates and uniform grids, the present method is more efficient and easier to program for the analysis of the cavity with cylindrical symmetry. Computed results show that the air gap between the sample and cavity cover is very critical to the accuracy of the measurement of the dielectric property of the sample when the sample diameter is small, but negligible when the diameter is large. Unfortunately, in the case of a highly lossy sample, a small sample diameter must be used to maintain a reasonably high Q-factor. Special techniques are recommended to minimize the error caused by the air gap     

Ka波段准TE01模椭圆型准光模式变换器的理论修正与设计

基于圆电模研究了椭圆型准光模式变换器，并提出用于快速设计椭圆结构准光系统的修正公式。利用修正公式设计的准光系统由椭圆型Vlasov辐射器与准抛物面镜组成。计算仿真结果表明，该椭圆体系所辐射的波束具有辐射方向性更好，副瓣增益更低的特性，并且其尺寸相比于传统的圆体系更小。     

Ka波段TE_（01）模回旋速调管带新型渐变段输出腔设计

利用正余弦拟合的方法和半径渐变波导的耦合波理论,设计出一种Ka波段TE01模回旋速调管带该新型渐变段输出腔。通过Matlab数值计算和HFSS仿真优化,研究了该新型渐变段的传输参数、反射参数、对杂模的抑制等性能指标。仿真结果表明：在渐变段长度为80mm、口径由14mm变化到32mm的情况下,在33～35GHz的范围内该新型渐变的传输参数大于-0.016dB,反射参数小于-55dB,对TE02模的耦合为-25dB和对TE03模抑制在-55dB以下;而该输出腔的中心频率为34.075GHz,Q值为109.6,工作模式TE01模式的模式纯度大于0.94。     

Design and characterization of dispersion compensating fiber basedon the LP01 mode

The practical implementation of erbium-doped fiber amplifiers with gain at 1.55 μm allows long unrepeatered transmission distances. However, in order to realize high data rates over these distances with already installed standard single mode fiber, techniques must be found to overcome the pulse spreading due to the positive chromatic dispersion of the transmission fiber in this window, we review a compensation technique based on propagating the signals through a specially designed fiber with large negative dispersion for the LP₀₁ mode, thereby ending up with zero net pulse spreading. The basis of the concept are discussed and a key figure of merit for dispersion compensating devices is defined. The design and optimization of dispersion compensating (DC) fiber is described with special attention to practical concerns including packaging and manufacturability. We describe experimental fabrication results of DC fiber, results of using the fiber to make compact dispersion compensating modules, and the outcome of recent systems experiments incorporating the fiber     

Two port analysis of dielectric resonator antennas excited in TE01 mode

Results of a numerical and experimental study of the transmission and input reflection coefficients of a two element array of half-split cylindrical dielectric resonator (CDR) antennas are presented. The antenna elements are situated on a ground plane and fed by a coaxial probe. A procedure based on the method of moments (MoM) for the coupling of a body of revolution (BOR) to a non-BOR geometry together with classical microwave network theory is implemented. Some of the numerical results are verified experimentally     

Precision measurement of coupling between microstrip and TE01 mode dielectric resonator

The coupling between a microstrip transmission line and a dielectric resonator with a relative dielectric constant of 80 has been measured as a function of the distance between the resonator and the microstrip. Precision measurement involves the TRL de-embedding procedure, and data fitting to a fractional linear transformation on a complex plane. A comparison is made of covered and uncovered resonators, demonstrating the influence of radiation     

A low-loss bandpass filter using electrically coupled high-Q TM01δ dielectric rod resonators

For a TM_01δ mode dielectric rod resonator placed coaxially in a TM₀₁ cutoff circular waveguide, characteristics such as the resonant frequency, its temperature coefficient, the unloaded Q, and the other resonances are discussed on the bases of accurate calculations using the mode-matching method. The results show that this resonator compares favorably with a conventional TE_01δ mode dielectric resonator, particularly for realization of a high unloaded Q. Analytical results also verify that interresonator coupling between these two resonators can be expressed equivalently by a capacitively coupled LC resonant circuit. A four-stage Chebyshev filter having a ripple of 0.035 dB and an equiripple bandwidth of 27 MHz at a center frequency of 11.958 GHz was fabricated using these resonators. Its insertion loss is 0.5 dB, which corresponds to an unloaded Q of 17000, and no spurious response appears in the frequency range below 17 GHz     

Studies on a few-mode fiber-optic strain sensor based on LP01-LP02 mode interference

We studied a fiber-optic strain sensor based on interference between LP₀₁-LP₀₂ modes of a circularly symmetric few-mode fiber (FMF). A simple theoretical analysis for predicting the performance characteristics of such a sensor is developed. Fiber elongations producing differential phase shift of 2π (δl_2π) between the two modes are measured, which is found to be independent of sensing length of the fiber as predicted by theory. A good agreement between the experimental and theoretical values of δl_2π is observed. Theoretical calculations predict that the sensitivity of such a sensor is maximum for fibers with V=4.82 and increases with the increase in the core cladding index difference Δn