Four-port Junction Research Articles

Recent modeling for the ITER ion cyclotron range of frequency antennas with the TOPICA code

This paper documents the analysis of the ITER ion cyclotron resonance heating (ICRF) launcher using the TOPICA code, throughout recent years’ design activities. The ability to simulate the detailed geometry of an ICRF antenna in front of a realistic plasma and to obtain the antenna input parameters, the electric currents on conductors and the radiated field distribution next to the antenna is of significant importance to evaluate and predict the overall system performances. Starting from a reference geometry, we first investigated the impact of some geometrical and numerical factors, such as the Faraday Screen geometry or the mesh quality. Then a final geometry was the object of a comprehensive analysis, varying the working frequency, the plasma conditions and the poloidal and toroidal phasings between the feeding lines. The performance of the antenna has been documented in terms of input parameters, power coupled to plasma and electric fields. Eventually, the four-port junction has also been included in TOPICA models.

High-Power Ridge Waveguide Four-Port Junction Circulator Based on Composite Post Resonators

An X-band high-power ridge waveguide (RW) four-port junction circulator is proposed in this article. It adopts two three-port RW junction circulators connected by a compact RW-to- coaxial-line transition in series with a parallel configuration topology. The composite post resonators are utilized in the three-port circulators. The theoretical analysis of composite post resonator and the design methods of the circulator have been demonstrated in detail. The RW transmission line, parallel configuration topology structure, and compact transition form make the cross-sectional size of the four-port circulator less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.9\lambda \times 0.95\lambda $ </tex-math></inline-formula> at the central frequency of 10 GHz. Measurements show that the 12-dB isolation bandwidths of the circulator are 40% with an insertion loss of 0.2–0.7 dB. High-power tests show that its peak power capacity can reach about 7 kW.

Dual-Band Direct Conversion Receiver With Additive Mixing Architecture

A dual-band direct conversion receiver based on additive mixing architecture for low-cost and multi-mode wireless communication systems is proposed. The proposed receiver consists of two active four-port junctions for additive mixing and one-stage dual-band polyphase filter for quadrature LO signal generation. Each four-port junction is fabricated with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.18~\mu \text{m}$ </tex-math></inline-formula> CMOS technology and configured by an active balun, two buffer amplifiers, two active combiners and two power detectors. The proposed polyphase filter is implemented using type-I architecture adopting one-stage and R-LC resonance type for low power and dual-band operation. The phase and amplitude calibration schemes are also integrated to effectively correct I/Q mismatch within the proposed architecture. The calibration ranges for the phase and amplitude mismatches show 8° and 14 dB, respectively. The validity of the proposed receiver based on additive mixing method is successfully demonstrated by demodulating 16-QAM signals with 40 Mbps at the dual band of 900 MHz and 2.4 GHz.

A Compact $E$ -Plane Four-Port Junction Circulator

A compact E-plane four-port junction circulator is proposed in this letter. It consists of an X-shape waveguide junction, two X-shape ferrite disks with fillets, and several matching metal posts. Based on the combinations of the TM210 and degenerate TM±110 modes, a four-port gyromagnetic resonator is realized. By introducing the tuning elements, the bandwidth is improved. Measurements show that from 8 to 9 GHz, the return loss is better than 18 dB, the isolation is better than 17 dB, and the insertion loss is 0.3-0.6 dB. Measurements agree well with the simulations. Its cross-sectional size is less than 0.86λ× 0.72λ at 8.5 GHz. High-power test shows that its pulsed power capacity is no less than 28 kW.

A Four-Port Microwave Phase Detector at $X$ -Band Based on MEMS Power Sensors

A four-port microwave phase detector based on MEMS power sensors at $X$ -band (8–12 GHz) is proposed in this paper. It consists of two power dividers, two power combiners, two phase shifters, and two MEMS power sensors. Four power dividers/combiners and two phase shifters compose a four-port junction to expand the phase detection range. A thermoelectric power sensor and a capacitive power sensor compose the MEMS power sensor for low and high power measurement. Two types of power sensors can improve the measurement range and enhance the overload capacity. This microwave phase detector is fabricated by GaAs monolithic microwave integrated circuit technology. Experiments show that its return loss is better than −10 dB, and the isolation is better than −13.2 dB over $X$ -band. Measured results of the phase shift fit well with the calculated results in an entire cycle of −180°~+180°. The phase detection sensitivities are $16.62~\mu \text{V}$ /° and 23.94 aF/°, and the response times are 0.408 ms and less than 20 ms for the two types of sensors, respectively. The dynamic range of phase detector can be expanded up to 4 W, which is almost quintuple our previous works.

3D electromagnetic optimization of the front face of the ITER ICRF antenna

In the framework of the ion cyclotron resonance heating (ICRH) antenna development for ITER, a design based on an external matching concept has been proposed [1]. We present in this work a series of electromagnetic simulations of this design performed with the commercial code CST Microwave Studio [2]. On the one hand, we explore how various geometrical modifications of some parts of the antenna (the straps and the four-port junction) can practically double the RF power coupled to the plasma. This optimization is supported by transmission line analysis. On the other hand, we treat the important question of the opportunity to tilt the straps in the toroidal direction to follow the plasma curvature as close as possible. We show that a configuration with two toroidal segments is sufficient and that further segmentation is not necessary. This work also underlines significant progress in the realism of ICRH antenna modelling and the importance of considering realistic load shaping in the models.

A New Range Finder Based on a Four-Port Junction

The design and performance of a prototype range finder based on a four-port junction are presented. The four-port junction is used as a precision phase detector. The system proposed presents advantages such as compact size, low cost, low consumption, and low computational time. The principle of operation, the sensor and the results are described in this paper.

High-Power CW Klystron for Fusion Experiments

A 3.7-GHz 700-kW klystron in continuous-wave (CW) operation has been developed to upgrade the lower hybrid RF plasma heating power in a tokamak up to 10 MW. The klystron is equipped with a diode gun, a five-cavity RF structure, two BeO-disk RF windows, and a large-size X-ray-shielded hypervapotron collector. The output power is recombined in a four-port junction which we also developed. The tube is designed to deliver 620-kW CW RF power with a mismatched load (VSWR = 1.4) and 700-kW CW with a matched load. Several prototypes have been built with successive design improvements. The major improvement was to change one single RF output into two RF outputs. The most recently built prototype meets all design specifications at 73.1 kV and 20.7 A, with an efficiency of 47% on a matched load and 40% with a 1.4 : 1 VSWR load, worst case phase. The power losses dissipated in the body have been measured as low as 17 kW, which corresponds to the RF heating and implies low beam interception. The measured temperatures of the output cavity noses and collector wall have been kept below 130degC and 200degC, respectively, which results in large thermal margin.

Isolator using a ferrite-coupled-lines gyrator

The theory and design of an isolator based on a new concept using a section of axially magnetised ferrite coupled line (FCL) are presented. The isolator consists of a resistive four-port junction cascaded with an open- or short-circuited section of FCL representing a gyrator circuit. Design procedures for microstrip and slot-line configurations are described. The main feature of the isolator is its multiple reversing of operating direction with frequency. Application of the microstrip FCL section to the design of a gyrator is considered. The performance of the isolator is predicted by cascading S-matrices of the microstrip FCL gyrator and resistor circuit. The simulated scattering characteristics of the proposed isolator confirmed the correctness of the concept of the proposed novel nonreciprocal device.

Analysis of the X-junction between two rectangular waveguides and a circular waveguide

The paper describes a method for the analysis of the four-port junction (X-junction) between two rectangular waveguides and a circular waveguide. The method is based on the computation by an efficient technique of the generalized admittance matrix (GAM) of the structure (conveniently divided into subblocks) with no restrictions on the geometrical dimensions, a typical analysis with about 100 modes in the overall structures requires 1-4 s per frequency point on a typical medium-power workstation.

S matrix of a broad wall coupler between dissimilar rectangular waveguides

The paper describes a method of moment analysis of a four-port junction between two dissimilar rectangular waveguides coupled through either a longitudinal slot or a transverse slot on the common broad wall. The Green's function approach has been used to obtain the scattered field inside the primary and the secondary waveguide for both cases. The coupled integro-differential equations, arising from the continuity of the tangential component of the magnetic field at both the interfaces of the slot, are transformed into matrix equation using entire domain sinusoidal basis functions in conjunction with global Galerkin's technique. The results obtained using the present method have been compared with the results available in the literature. The theoretical results on the magnitude and phase of the scattering parameters have been compared with the experimental results for the case of a longitudinal slot coupler with moderate offset from the centerline. The use of global sinusoidal basis functions gives a much faster rate of convergence compared to the use of subsectional basis functions. The equivalent loading of a single slot derived in the paper can be effectively utilized to design a multiaperture coupler. >

High-power, low-recovery-time switched pin diode duplexer at Ku band

High-power duplexer consisting of a four-port ferrite junction circulator and two-stage switched PIN diode limiter with appropriate driver circuit is designed and developed for a low-recovery-time requirement. Insertion loss of 1.5 dB, isolation of 70 dB and recovery time of 40 ns are achieved at a 10-KW peak, 200-ns pulsewidth at Ku band.

Application of the Solutions of Certain Boundary Value Problems to the Symmetrical Four-Port Junction and Specially Truncated Bends in Parallel-Plate Waveguides and Balanced Strip-Transmission Lines

Three boundary value problems involving parallel-plate waveguides terminated in various combinations of electric and magnetic walls are investigated. The analysis leads to infinite sets of linear algebraic equations, which are appropriately truncated and solved on an electronic computer. The results are applied to several problems: to the scattering matrix of the symmetrical four-port junction of parallel-plate or rectangular waveguides; to the symmetrical four-port junction of center strips of a balanced strip-transmission line; to a specially truncated right-angle bend in paralIel-plate and rectangular waveguides; and to mitred bends in strip-transmission lines.

Design and Development of X-Band Ferrite Components

ABSTRACTThis paper describes a four-port X-band junction waveguide circulator and an X-band field displacement isolator. The circulator employs a right angled H-type junction of two X-band waveguides. A full height cylindrical post of R-4 ferrite surrounded by a full height teflon cylinder is symmetrically placed at the junction. Hitherto, no 4-port waveguide circulator using this ferrite-dielectric condiguration has been reported in the literature. This circulator has a bandwidth of more than 500 mc/s. Maximum isolation approaches 40 db. and minimum insertion loss is negligible (less than 0·2 db.). Effects of dielectric loading on the circulator performance are also presented.This paper also describes an X-band field displacement type isolator which has a bandwidth of 1·5 kMc/s. for less than 1 db. insertion loss and greater than 20 db. isolation.