共查询到20条相似文献,搜索用时 15 毫秒
1.
An efficient method for the determination of the scattering matrix of TE11-to-HE11 corrugated cylindrical waveguide mode converters has been developed, based on the representation of the fields inside the corrugations by a small number of radial waveguide modes. Numerical results show that the method, when compared to the usual mode-matching techniques, reduces the computation time without loss of accuracy 相似文献
2.
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 相似文献
3.
The TE11-mode excitation of a concentric circular iris of finite thickness in a circular waveguide is analyzed by Galerkin's method with even and odd excitation. Agreement between calculated and measured dominant mode scattering parameters is generally within experimental accuracy 相似文献
4.
In this paper the time-domain surface impedances of an homogeneous absorber layer, are given for the vertical and horizontal polarizations, or respectively for the electric field perpendicular or parallel to the incidence plane. It turns out that the application of the concept in finite difference time-domain (FDTD) in absorbing surface impedances boundary conditions, gives results in good agreement with analytical Fresnel reflection coefficients. 相似文献
5.
A 90° microstrip bend with an arbitrary miter is characterized using the finite difference time-domain (FDTD) method. In this method, to simplify computations, the microstrip structure is enclosed by four electric walls; thus radiation effects are neglected. Time histories generated by FDTD techniques are Fourier-transformed to yield broadband scattering parameters of the microstrip bend. A miter is introduced to improve the transmission characteristics of the bend, and an optimal miter length is found such that the reflection from the microstrip bend over a broad frequency range is minimized 相似文献
6.
If the discrete Fourier transform of the step response of a network is taken, a large truncation error results, since only a finite number of samples is used. This error is usually removed by first differentiating the waveform, with consequent noise enhancement. The letter shows that the error may also be removed at discrete frequencies, simply by first subtracting a ramp from the step response. 相似文献
7.
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 相似文献
8.
In this work, we present an innovative approach for designing small-scale microcavity resonators. By introducing a gold cladding around the structure, we may significantly reduce the mode volume and simultaneously increase the cavity's quality Q-factor. By making use of the TE011 mode, as opposed to the more traditional HE111 mode, we may further reduce the mode volume while taking advantage of decreased loss into the metal layer due to the optimal polarization choice. We demonstrate a means to design and optimize the cavity geometry to obtain desired spectral characteristics through the use of particle swarm optimization, and we present a cavity operating at 1.5 mum with a Q value exceeding 300 000 and a modal volume of less than 0.9(lambda/n)3. 相似文献
9.
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。 相似文献
10.
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) 相似文献
11.
Designs of compact quasi-periodic and aperiodic TE0n-TE 0n-1 circular waveguide converters for use with gyrotrons in an electron cyclotron heating (ECH) system are developed by analytically and numerically solving the coupled-mode differential equations. Quasi-periodic mode transducer designs which convert the TE02 mode to the TE01 mode, and in some cases also include a taper (waveguide radius reduction), are developed. A 60-GHz aperiodic mode converter-taper combines a 6.35-cm-2.779-cm waveguide diameter taper and a TE02-TE01 mode converter. A 140-GHz aperiodic mode converter-taper combines a 6.35-cm-2.779-cm waveguide diameter taper and a TE03-TE02-TE01 mode converter. The resulting designs are highly efficient (conversion efficiencies ⩾99.4%), are shorter, have a broader bandwidth than previous designs, and have a waveguide radius greater than or equal to 1.389 cm over the entire length of the transducer to allow for high-power transmission. Experimental results consistent with theoretical calculations are presented 相似文献
12.
本文对黑体辐射泵浦CO_2激光和N_2O激光由于CO和H_2O的加入所引起的激光功率变化进行了理论和实验研究.CO的加入可使的N_2O激光功率增加28%. 相似文献
13.
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 L 1≈0.5λB (short converter) and L 2≈1.2λB (long converter), where λB 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 相似文献
14.
The design and experimental studies on a corrugated circular cyclindrical waveguide antenna that is feed-excited in the TE11 mode with suppressed far-out sidelobes are reported. To reduce the spillover in the region 90°⩽&thetas;⩽180°, an attempt was made to introduce circumferential corrugations on the outer surface of the waveguide wall. The design criterion used was that a minimum of 11 corrugations per wavelength were used, and in all there were 25 corrugations. The reason for selecting 25 corrugations was to ensure that the conduction currents induced on the outer walls of the guide were attenuated substantially and did not contribute to the far-out sidelobes. Measured E-plane and H-plane radiation patterns of the feeds and the corrugated waveguide are presented 相似文献
15.
It is shown that due to the similarity of the structures of the TEM cell and the finned waveguide, the closed-form expression for the cutoff frequency of the TE10 mode in the finned waveguides can be used to calculate the cutoff frequency of the TE01 mode in the symmetric TEM cells. The results obtained by the expression given agree with various numerical methods to within 1%. The results calculated by this expression are compared with those obtained by an approximate analytical expression 相似文献
16.
Jingwen Qiu Wei Hong D.N. Wang Dingshan Gao Ying Wang Yuhua Li 《Optical Fiber Technology》2011,(6):580-585
Light scattering by a micro-channel intersecting core of a single mode fiber (SMF) has been investigated by use of two dimensional time-domain finite difference (2D-FDTD) method and the numerical results are in good agreement with those reported in the experiments. The transmission properties of the SMF with such a micro-channel can be attributed to the combined results of scattering effect and FP resonance effect. It is suggested that the SMF with micro-channel of about 4–6 μm in diameter can be effectively used for refractive index sensing with a high refractive index resolution up to ∼10−5. 相似文献
17.
CO2 waveguide lasers `hoot' when, instead of the solitary resonator mode expected from a homogeneously broadened gas laser, two or more resonator transverse modes laser simultaneously on a common laser line. The unwanted mode or modes, even if very faint and present only occasionally, can impede heterodyne measurements where a clean frequency spectrum is required. The authors report measurements of transverse-mode beat frequencies from a small RF-excited CO2 laser with a hybrid Al/Al2O3 square-bore waveguide and plane mirrors; these frequencies alter with mirror tilt by up to 70 MHz mrad-1. A minimum beat frequency is seen when the laser is well assigned. The authors suggest that a model of the misaligned resonator may help to identify the faint modes responsible for hooting 相似文献
18.
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 相似文献
19.
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 相似文献
20.
M. E. Kaliberda L. N. Litvinenko S. A. Pogarsky 《Journal of Communications Technology and Electronics》2010,55(5):505-511
Diffraction of axially symmetric H 0m and E 0m modes by a system of annular slots in the hollow inner conductor of a coaxial waveguide is considered. The space inside a slot and between the slots is filled with a dielectric. Diffraction of H 0m and E 0m modes by the end of a semiinfinite circular waveguide placed coaxially in a circular waveguide of larger diameter is solved as the key problem. The obtained solution is used in the analysis of structures with a finite number of equispaced discontinuities. The solution is obtained with the operator approach. Dependences of the reflection coefficient of this structure on the slot width and the spacing of discontinuities are analyzed. 相似文献