Waveguide Converter Research Articles

Permittivity measurement of high-frequency substrate based on the double-sided parallel-strip line resonator method

With the development of 5G technology, the accurate measurement of the complex permittivity of a printed circuit board (PCB) in the wide frequency range is crucial for the design of high-frequency circuits. In this paper, a microwave measurement device and method based on the double-sided parallel-strip line (DSPSL) resonator have been developed to measure the complex permittivity of typical PCBs in the vertical direction. The device includes the DSPSL resonator, the DSPSL coupling probe, a pressure monitor, a Farran C4209 vector network analyzer (100 K to 9 GHz), and a FEV-10-PR-0006 frequency multiplier (75–110 GHz). Based on transmission line theory, the physical model of the DSPSL resonator was established, and the relative permittivity and loss angle tangent value of the dielectric substrate were calculated using conformal transformation. To excite the resonator, the DSPSL coupling probe with a good transmission effect was designed, which consists of DSPSL microstrip line (MSL) transition structure and an MSL-WR10 rectangular waveguide converter. To reduce the air gap between the sample and the metal guide band and dielectric support block, and to improve test accuracy, a mechanical pressure device is added to the top of the DSPSL resonator. Based on the DSPSL resonator, we have used the device to test four typical PCBs, namely, polytetrafluoroethylene, Rogers RT/duroid®5880, Rogers RO3006®, and Rogers RO3010®. The results show that the maximum error of the relative permittivity is less than 3.05%, and the maximum error of the loss angle tangent is less than 1.27 × 10−4.

O-Band Grating Couplers Using Silicon Nitride Structures

To test silicon photonics component performances, a silicon (Si) grating coupler (GC) is used to couple the light from a single-mode fiber (SMF) into the chip. However, silicon nitride (Si3N4) waveguides have recently become more popular for realizing photonic integrated circuits (PICs), which may be attributable to their exceptional characteristics, such as minimal absorption and low back reflection (BR) in the O-band spectrum. Thus, to test the photonic chip, a waveguide converter from Si3N4 to Si needs to be added to the photonic circuit, which can lead to more power losses and BR. To avoid this conversion, we propose in this manuscript a configuration of a GC based on Si3N4 structures, which can be employed to minimize the footprint size and obtain better performance. The achievement of high efficiency was possibly obtained by optimizing the structural properties of the waveguide and the coupling angle from the SMF. The results demonstrated high efficiency within the O-band spectrum by using a wavelength of 1310 nm. Notably, at this specific wavelength, the findings indicated a coupling efficiency of −5.52 db. The proposed design of the GC consists of a uniform grating that offers improvements regarding affordability and simplicity in manufacturing compared to other GC models. For instance, using a reflector or a GC with non-uniform grooved teeth introduces challenges in fabrication and incurs higher costs. Thus, the proposed design can be useful for improving the testing abilities of the Si3N4 photonic chips used in transceiver systems.

Broadband Resonance-Free Septum Circular Polarizer Operating Above 200 GHz

In this paper, a broadband septum circular polarizer with double inline rectangular-to-semicircular waveguide transformers is proposed, which breaks through the theoretical single-mode bandwidth. Meanwhile, a novel waveguide splitting method is utilized, i.e., the common waveguide and inline waveguide transformers are integrally manufactured. This approach avoids the air gap introduced by the traditional split-block technology, and thus solves the problems of orthogonal-modes leakage and mode resonance caused by the waveguide discontinuity. Therefore, the proposed polarizer possesses the merits of broadband, resonance-free, high consistency of orthogonal modes and low insertion loss. In the polarizer measurement, a circular to rectangular waveguide converter is designed and fabricated. The measured insertion loss of the polarizer is found to be around 0.28 dB in the frequency range of 198~260 GHz, and the in-band return loss is better than 15 dB. Moreover, the isolation of left-hand and right-hand circular polarization ports exceeds 23 dB within 206~260 GHz. The proposed polarizer has widely potential applications in millimeter-wave and terahertz devices such as broadband antennas and radial power combiners.

Broadband Circularly Polarized Conical Corrugated Horn Antenna Using a Dielectric Circular Polarizer.

In this paper, a broadband left-handed circularly polarized (LHCP) corrugated horn antenna using a dielectric circular polarizer is proposed. Circularly polarized (CP) waves are generated by inserting an improved dovetail-shaped dielectric plate into the circular waveguide. Compared with the traditional dovetail-shaped circular polarizer, the proposed improved dovetail-shaped circular polarizer has a wider impedance bandwidth and 3 dB axial ratio bandwidth. A substrate-integrated waveguide (SIW) structure is designed as a wall to eliminate the influence of fixed grooves on the circular polarizer. The simulated reflection coefficient of the dielectric plate circular polarizer is less than -20 dB in the frequency band from 17.57 to 33.25 GHz. Then, a conical corrugated horn antenna with five corrugations and a four-level metal stepped rectangular-circular waveguide converter are designed and optimized. The simulated -10 dB impedance and 3 dB axial ratio (AR) bandwidths of the circularly polarized horn antenna integrated with the polarizer are 61% (17.1-32.8 GHz) and 60.9% (17.76-33.32 GHz), respectively. The simulated peak gain is 17.34 dBic. The measured -10 dB impedance is 52.7% (17.2-27.5 GHz).

Design and Implementation of Ku-Band High Directionality Antenna

In this article, a Ku-band high directivity antenna is designed, which consists of a radiation waveguide section, a mode conversion section, and a coaxial waveguide conversion section. In this article, the theoretical calculation process of antenna components is summarized and supplemented. The calculation method between key technical indexes and structural parameters is established. The key technical parameters of the antenna, including input return loss, half-power beamwidth, gain, and cross-polarization level, are studied and explored. The radiation performance of the antenna can be further improved by optimizing the structural parameters. Finite-element analysis and COMSOL simulation software are used to study. In order to reduce antenna reflection, a method of equal-Q impedance transformation is proposed for rectangular and circular waveguide converters and coaxial waveguide converters. Finally, the proposed feed antenna is processed and verified, and the measured results are in good agreement with the simulation results.

Theoretical and Experimental Investigations on a 90° Compact TM01-TE11 Mode Converter for RBWO

Mode converter is one of the most important devices in the high-power microwave (HPM) applications. To conduct an in-depth research for the orthogonal mode converter, a novel 90° compact TM₀₁-TE₁₁ circular waveguide converter working at 9.7 GHz is proposed in this article. This design innovatively integrates the traditional mode converter with 90° bend techniques based on the mode coupling theory, which ensures a compact structure and high-power handling capacity. Calculated and simulated results illustrate that the maximum conversion efficiency of the converter at central frequency reaches 99.4% when the structure length is 535 mm, and the bandwidth reaches 680 MHz when the conversion efficiency exceeds 95%. For demonstration, a prototype is fabricated, and the corresponding experiments are investigated. According to the S-parameter measurement, it has a high conversion efficiency at central frequency. Meanwhile, the high-power performance is conducted by connecting it with a relativistic backward oscillator (RBWO), and the converter works stably under a maximum output power of 4 GW. The good agreement of the theoretical analyses, simulations, and experimental results indicates the feasibility of the proposed converter.

Resonant Reflectors for Experimental Studies of the Reflected-Signal Influence on the Gyrotron Operation Regimes

Experimental study of the influence of resonant reflection of the operation mode on the gyrotron generation regimes is a topical problem of modern high-power vacuum electronics. In this work, we formulate the requirements for the external resonant reflection system and propose its development variants. We consider resonant reflectors of two types, which are intended for experiments with a gyrotron at the operation mode TE0, 2 at a frequency of 28 GHz. According to the initial requirements, the reflection coefficient of the gyrotron operation mode at the resonant frequency should amount to 5–10% with the reflector quality factor exceeding 15000 in the range 27998–28008 MHz of the gyrotron-frequency tuning by a magnetic field. The first variant of the reflector is a cylindrical cavity at the TE0, 3, 1 mode. The measured reflection coefficient amounted to 6% at a frequency of 27999 MHz with a quality factor of 15000. The tunable two-mirror resonator at the mode TEM0, 0, p (p >> 1) is the second variant. A number of the waveguide converters of the circular-waveguide mode TE0, 2 to the TE0, 1 mode, the TE0, 1 mode to the TE1, 1 mode, and the convertor of the TE1, 1 mode to the linearly polarized Gaussian wave beam are developed and manufactured for excitation of a two-mirror resonant reflector by the gyrotron radiation. During the frequency tuning in the band 27990–28010 MHz, the measured reflection coefficient amounted to 8% with a quality factor of about 40000. The calculated and measured converter characteristics are given along with the measured frequency characteristics of the developed resonant reflectors.

Stabilization of the axisymmetric parts dimensions and shapes

This article reviews the method of increasing the stability of geometrics of non-rigid parts of the “shaft” type. The authors give the grounds for the necessity of treatment by the complex vibro-impact method. The authors also present the unit functional diagram, complete with the automatic control system for the implementation of the proposed method. The unit consists of a self-centering steady rest with a non-flow electrohydraulic drive; a vibro-impact drive with a waveguide converter, a workpiece temperature control device. The control system provides the workpiece axis stabilization and temperature control in the process of axial complex vibro-impacts. The article proves the expediency of using the complex vibro-impact method.

Millimeter-Wave Air-Filled Slot Antenna With Conical Beam Based on Bulk Silicon MEMS Technology

In this communication, a millimeter-wave (mm-wave) air-filled slot antenna with a conical beam at 60 GHz is proposed. The antenna is suitable to be integrated with various IC systems mainly because it is designed and fabricated based on bulk silicon microelectromechanical systems (MEMS) technology. The whole structure is composed of an antenna part and a waveguide to substrate integrated waveguide (SIW) converter. In the antenna part, four meander slots are arranged annularly and excited by a square air cavity. The conical radiation pattern benefits from the out-phase ${E}$ -field excited on slots. An operating bandwidth of 2.17% for S11 < −10 dB and a conical beam peak gain of 3.21 dBi are achieved. The proposed antenna shows its potentials in mm-wave indoor communication.

Radiation output system for planar gyrotron

Gyrotrons with planar resonator cavity offer some advantages over conventional cylindrical ones for submillimetre wavelengths. The radiation in the planar gyrotron should be converted from the mixture of several high modes of the rectangular waveguide into the Gaussian beam with high efficiency. For the experimental 145 GHz gyrotron, a two- channel output is considered. Both channels consist of waveguide converter and two convex mirrors and direct the radiation through the single output window. Calculated total efficiency of the system exceeds 98%.

Bidirectional Mode Slicing and Re-Combining for Mode Conversion in Planar Waveguides

Photonics integrated circuits and planar lightwave circuits are crucial in future high capacity optical communication networks. Such circuits can perform complicated and sophisticated signal processing functions’ on-chip level. However, they should have high bandwidth in order to handle ultrafast data flow and thus achieve high-capacity transmission. One way to achieve such high bandwidth is using few-mode waveguides. Therefore, it becomes mandatory to find a way to convert from current conventional single-mode planar waveguides into few-mode waveguides, and moreover to selectively excite the desired modes within the converted multimode waveguides. In this paper, a novel silica-glass planar waveguide converter is numerically demonstrated for the first time. This device can convert in a bidirectional fashion between single-mode and two, three, or four modes planar waveguides, in addition, to selectively excite the desired mode. The device principle of operation mainly depends on spatial modes slicing and re-combining to achieve the desired higher or lower order modes. That could be accomplished by cascading stages of V-shape and M-shape graded-index planar waveguides. The graded-indices allow for flexible and simple geometrical designs that can split or combine fundamental as well as higher order modes. The finite-difference time-domain numerical method is utilized to verify the device operation and evaluate its performance for each excited mode in bidirectional directions. The device shows good performance over the entire C-band wavelength range with the worst-case magnitude of insertion-loss ≅ 3 dB, polarization-dependent loss ≅ 0.6 dB, and return-loss ≅ 21 dB. It also shows a worst-case cross-talk of ≅ −24.1 dB among the excited high-order modes in the forward direction, and a worst-case mode-rejection ratio of ≅ −23 dB for non-excited modes in the reverse direction. Moreover, the device shows reasonable performance tolerance to variations in V-shape and M-shape waveguide design parameters.

Design and manufacture of the RF power supply and RF transmission line for SANAEM project Prometheus

A 1–5 MeV proton beamline is being built by the Turkish Atomic Energy Authority in collaboration with a number of graduate students from different universities. The primary goal of the project, is to acquire the design ability and manufacturing capability of all the components locally. SPP will be an accelerator and beam diagnostics test facility and it will also serve the detector development community with its low beam current. This paper discusses the design and construction of the RF power supply and the RF transmission line components such as its waveguide converters and its circulator. Additionally low and high power RF test results are presented to compare the performances of the locally produced components to the commercially available ones.

STUDY OF A LEAKY WAVEGUIDE ON HEATING MORTAR BLOCK SYSTEM FOR MELTING SNOW THROUGH QUASI MICROWAVES

The apparatus with electromagnetic waves of frequency 2.45GHz, such as microwave ovens, are mass-produced, therefore an oscillator for the electromagnetic wave of frequency 2.45GHz is inexpensive. We study the heating mortar block system using oscillator of frequency 2.45GHz for melting snow to convert an electromagnetic wave into heat. The heating mortar block system can melt snow in a shorter time than systems with electric heating wires. The heating mortar block system for melting snow needs to be composed of a leaky waveguide for providing electromagnetic waves to the heating mortar blocks. The leaky waveguide has many slots emitting electromagnetic waves on the top surface. In this study, the influences that the figure of the slots gives to quantity of emitted electromagnetic waves are confirmed. First, the characteristic of the single slot on a metal board about emitted electromagnetic waves was confirmed by the S parameter. The metal board that a slot was installed in is connected to a coaxial waveguide, and return loss is measured. When a slot grows longer in the direction inhibiting the electric current in the leaky wave guide, return loss greatly changed. The slot with 60mm long emitted most electromagnetic waves. This length is equal to a half wavelength of the electromagnetic wave of 2.45GHz in the free space. Second, the characteristic regarding emitted electromagnetic waves of the slots that were arranged continually on a leaky waveguide was confirmed by equipment measuring quantity of emitted electromagnetic waves on the leaky waveguide. The equipment measuring the quantity of emitted electromagnetic wave on a leaky waveguide is composed of electromagnetic waves oscillator, a leaky waveguide and a coaxial waveguide converter with the metal board that a slot was installed in. The slot that emitted the most electromagnetic waves on the metal board is 60mm long. Electromagnetic waves that emitted out from each slot on a leaky waveguide is received in a coaxial waveguide converter with the metal board that the slot was installed in. When the length of the slot on the leaky waveguide was 30mm, quantity of emitted electromagnetic waves is stable. In addition, emitted electromagnetic waves have the period that depend on the wavelength in the leaky waveguide when they are reflected in the terminal of the leaky waveguide. However, when they are absorbed in the terminal of the leaky waveguide, the period of emitted electromagnetic waves is lost. This is because there are no stationary waves since there are no reflection waves. The ability of the heating mortar block system for melting snow was confirmed by melting snow piled up in Tsuruoka city, Yamagata prefecture. The heating mortar block system is composed of electromagnetic waves oscillator, leaky waveguide and heating mortar blocks. The slots that emitted electromagnetic waves stably on leaky waveguide is 30mm long. In addition, the rest of electromagnetic waves are emitted at the terminal of the leaky waveguide by the slot of 60mm long. As a result, the heating mortar block system for melting snow has ability of melting snow. However, the heating mortar blocks did not have the equal temperature rise under the influence of the dielectric constant of themselves. It is necessary to make a space between a leaky waveguide and the heating mortar blocks for the equal temperature rise.

On-chip sub-terahertz surface plasmon polariton transmission lines with mode converter in CMOS.

An on-chip low-loss and high conversion efficiency plasmonic waveguide converter is demonstrated at sub-THz in CMOS. By introducing a subwavelength periodic corrugated structure onto the transmission line (T-line) implemented by a top-layer metal, surface plasmon polaritons (SPP) are established to propagate signals with strongly localized surface-wave. To match both impedance and momentum of other on-chip components with TEM-wave propagation, a mode converter structure featured by a smooth bridge between the Ground coplanar waveguide (GCPW) with 50 Ω impedance and SPP T-line is proposed. To further reduce area, the converter is ultimately simplified to a gradual increment of groove with smooth gradient. The proposed SPP T-lines with the converter is designed and fabricated in the standard 65 nm CMOS process. Both near-field simulation and measurement results show excellent conversion efficiency from quasi-TEM to SPP modes in a broadband frequency range. The converter achieves wideband impedance matching (<−9 dB) with excellent transmission efficiency (averagely −1.9 dB) from 110 GHz–325 GHz. The demonstrated compact and wideband SPP T-lines with mode converter have shown great potentials to replace existing waveguides as future on-chip THz interconnects. To the best of the author’s knowledge, this is the first time to demonstrate the (sub)-THz surface mode conversion on-chip in CMOS technology.

Method for Synthesis of ${\rm TE}_{01}\!\!-\!\!{\rm TE}_{11}$ Mode Converter for Gyrotron by the NURBS Technique

A method for synthesis of ${\rm TE}_{01}$ – ${\rm TE}_{11}$ waveguide mode converters is proposed based on the non-uniform rational B-spline technique. An application of the method to a 30.5-GHz serpentine circular waveguide converter of ${\rm TE}_{01}$ – ${\rm TE}_{11}$ mode is given. The serpentine circular waveguide synthesized by the method has coaxial-parallel input and output ports and smooth axial curvature distribution, as well as short length and high conversion. The method offers good solutions to the problems of the mode converter design in the situation where two successive waveguides are asked to fit together strictly.

Rectangular to Circular Waveguide Converter for Microwave Devices Characterization

In this paper, a rectangular to circular waveguide converter is investigated numerically and characterized experimentally for microwave devices characterization. The converter is designed as an excitation method of circular waveguide to produce its dominant mode as the problem of circular waveguide in the excitation process. A WR248 type rectangular waveguide transducer with working frequency of 2.60–3.95GHz for TE10 mode is used as the wave exciter to be converted to a WC248 type circular waveguide. Prior to the fabrication, physical parameters of converter including length of rectangular segment, length of transition segment and length of circular segment are analyzed to obtain the optimum design. It shows that the length of transition segment affects to the return loss of converter and its length to produce TE11 mode of circular waveguide smoothly has to be more than twice of waveguide wavelength. From the result, the length of transition segment is chosen to be 275mm as it demonstrates better return loss compared to other lengths almost in the designated working frequency. To verify the design result, the prototype of converter is then realized and characterized experimentally. Furthermore, some discussion related to the results of experimental characterization is also presented.

Integration of GaN/AlN all-optical switch with SiN/AlN waveguide utilizing spot-size conversion

Spot-size converters for an all-optical switch utilizing the intersubband transition in GaN/AlN multiple quantum wells are studied with the purpose of reducing operation power by improving the coupling efficiency between the input fiber and the switch. With a stair-like spot-size converter, the absorption saturation of 5 dB is achieved with a pulse energy of 25 pJ. The switch is integrated with a SiN/AlN waveguide and spot-size converters, and the structure provides the possibility of an integration of the switch with other functional devices. To further improve the coupling loss between the waveguide and the switch, triangular-shaped converters are investigated, demonstrating losses as low as 2 dB/facet.

DESIGN OF A BROADBAND TRANSITION USING THE CONSTANT IMPEDANCE STRUCTURE APPROACH

Transitions from circular waveguides to rectangular waveguides are used in many situations. One particular case is between the feed of a circular corrugated horn antenna and following rectangular waveguide structures. Since the field patterns are not the same on both sides the conversion from rectangular to circular waveguide always results in a certain amount of power reflected back in one waveguide. Much effort has been put in designing special converters which reduce this effect. For many designs, reflection is reduced by introducing a certain number of waveguide steps. By adjusting the distance between these steps, one can get destructive interference of the returned signal at specific frequencies. In this paper, an alternative approach, the constant impedance structure (CIS) has been chosen. This eliminates the need to design a waveguide converter for minimum return loss at discrete frequencies. The transition obtained by this approach is compared to a transition based on linear surface interpolation.

1×8 fiber-optic switch based on an innovative waveguide converter and a micro torsion mirror

This paper reports a 1x8 fiber-optic switch based on an innovative waveguide converter and a micro torsion mirror. A compact 9-fiber collimator is implemented with the waveguide converter. With the micro torsion mirror aligned to the 9-fiber collimator, light from the central fiber can be steered to any of the other 8 fibers. The introduction of the waveguide converter enables a smaller and faster micro torsion mirror. The switch shows good performance, insertion loss, nonuniformity, and cross talk is <3.02 dB, <0.4 dB, and <-35 dB respectively. Improvements of performance are expected after further optimization.

Study and design of broadband nonuniform ripple-wall TE0n-TE0(n+1) mode converters

Based on the coupled wave theory， this paper presents the design， numerical analysis， and simulation of two types of TE0n-TE0(n+1) ripple-wall waveguide mode converters: a uniform ripple-wall converter and a nonuniform ripple-wall waveguide converter. For the first type，17.17GHz，six-period TE02-TE03 mode converter and 34.30GHz，six-period TE01-TE02 mode converter were operative； and 34.30GHz，six-period TE01-TE02 for the nonuniform one was operative. The design study is focused on the maximization of the conversion efficiency and mode purity coupled with a broad bandwidth. The nonuniform one seems to have a significant advantage over the uniform one， its conversion efficiency reaches 99.5% at center frequency and has a conversion bandwidth of more than 1.5GHz. Simulation results agree well with the theoretical predictions.