Design and fabrication of a nonradiative dielectric waveguidecirculator

A technique is described for constructing a high-performance nonradiative dielectric waveguide (NRD guide) circulator for use at 50 GHz. A mode suppressor, which serves to reduce unwanted modes to a negligible level, was devised and used to improve circulator performance significantly. A half-wavelength step transformer was installed at each port of the circulator to increase the operational bandwidth. The insertion loss of this circulator is less than 0.3 dB, and the 20-dB isolation bandwidth is about 2.6 GHz. Characteristics of the NRD guide circulator are analyzed based on an equivalent circuit representation. This analysis considerably facilitates the design procedure of the circulator     

Circulators Using Planar WYE Resonators

An important class of commercial three-port circulator relies for its operation on a junction resonator consisting of the symmetrical connection of three open-circuited transmission lines. A feature of this resonator is that it may be quarter-wave coupled to form a circulator with a moderate specification (25-percent bandwidth to 25-dB return loss points) and physical dimensions of the order of directly coupled conventional circulators (using a disk resonator). For circulators for which the in-phase eigennetwork may be represented by an ideal short-circuit, the equivalent circuit is a one-port network which may be formed from a characterization of the constituent resonator. This feature is used in this paper to study the equivalent circuit of junction circulators using planar WYE resonators. The derivation of the equivalent circuit parameters is supported with the design of a 4-GHz quarter-wave-coupled stripline circulator.     

Equivalent Circuit Representation for the E-Plane Circulator

The resonator structure employed in an E-plane circulator may be described by a series-resonant circuit as opposed to a parallel circuit in the case of comparable H-plane devices. This is shown to result in a change of the direction of circulation at the edges of the circulator passband. Employing the equivalent circuit representation methods to increase the bandwidth of the E-plane circulator are discussed.     

A Compact Broad-Band Thin-Film Lumped-Element L-Band Circulator

Impedance matrices including magnetic losses are developed for a number of lumped-element ferrite-loaded symmetrical three-port junctions. The scattering matrix eigenvalues corresponding to these matrices are determined as functions of frequency and circuit parameters and are used to analyze these three-ports with emphasis on their properties as circulators. A very compact broad-band thin-film lumped-element circulator is derived from the idealized equivalent circuit. An experimental model approximately represented by this circuit is shown to have a 20-dB isolation bandwidth of greater than 30 percent with an insertion loss of less than 0.6 decibel. A switchable circulator which requires no magnetic-field switching is treated using this same analytical approach. It is suggested that this type of analysis together with additional experimental refinement of equivalent circuits will lead eventually to a computerized design of lumped-element circulators.     

宽带X波段波导结环行器的研究

为了满足某系统的要求,需研制带宽在X波段达4GHz（40％）的宽带波导结环行器。文中采用Y形脊波导中心结形式,采用三阶等宽切比雪夫阶梯阻抗匹配器实现环行器宽带阻抗匹配,并利用HFSS软件优化环行器结构。设计的环行器实验结果为：在8．4GHz至12．4GHz范围内,插损不大于0．3dB,隔离不小于20dB,驻波不大于1．2。环行器设计结果与实验结果基本一致,表明该设计方法正确,设计的环行器满足系统宽带要求。     

Complex Gyrator Circuit of an Evanescent-Mode E-Plane Junction Circulator Using H-Plane Turnstile Resonators

The E-plane circulator is of considerable practical interest but its development has lagged somewhat compared to that of the more common H-plane device. The purpose of this paper is to experimentally investigate the eigenvalue problem and the complex gyrator circuit of an E-plane evanescent-mode junction loaded with one or two H-plane turnstile ferrite resonators symmetrically coupled by three standard rectangular waveguides. The condition for which the eigenvalues of the demagnetized junction are in antiphase has been met with the physical variables at hand, but the more important one for which they are also commensurate has not. A transformer coupled device using quarter-wave-long impedance sections at each port is also described. Its frequency coincides with the even solution of two coupled resonators.     

Broad-Banding and Changing Operation Frequency of Circulator

Broad-banding of a circulator and changing of operation frequency of a lumped-element circulator are discussed. The point of broad-banding is to represent the circulator in a distributed element equivalent circuit. The improvement of the relative bandwidth was between 10 and 20 percent. The point of changing of operation frequency is to use a variable capacitance diode instead of a fixed one. The result is that the operating frequency changed from 120 to 220 MHz with a bias voltage change from 2 to 10 V.     

Wide-Band Operation of Microstrip Circulators

Octave bandwidth operation of Y-junction stripline and microstrip circulators is predicted using Bosma's Green's function analysis. The width of the coupling transmission lines is found to be a significant design parameter. Theoretical and experimental results are presented which show that wide lines and a smaller than usual disk radius can be used to obtain wide-band operation. A microstrip circulator is reported which operates from 7-15 GHz. Also presented are an analysis of the input impedance and an approximate equivalent circuit for the Y-junction circulator which shows the relationship between Bosma's equivalent circuit and that of Fay and Comstock.     

The Synthesis of Symmetrical Waveguide Circulators

A method for synthesizing symmetrical waveguide circulators by adjusting the eigenvalues of the scattering matrix is described. This procedure is particularly useful for the design of very compact circulators in the form of waveguide junctions containing ferrite obstacles. Permissible structural symmetries for a circulator are listed, and a standard form for the scattering matrix of a symmetrical circulator is defined. The synthesis procedure is then described in detail, stating the conditions to be imposed on the scattering matrix eigenvalues, and an expression is obtained for the changes in the eigenvalues due to the placing of anisotropic material within the junction. By applying the theory to Allen's 4-port turnstile circulator, it is shown that the use of a matched turnstile junction and a reflectionless Faraday rotator is not essential. The theory is also applied to the design of novel 3- and 4-port circulators, and two 6-port circulators, one of which may be used as a 5-position waveguide switch, are described. Some experimental results are presented for a compact 3-port circulator in the form of an H-plane Y junction, in 1 inch by 1/2 inch waveguide, containing a ferrite post obstacle. This circulator, which operates with a bias field of approximately 25 oersted, has a useful bandwidth of 3 per cent. Greater bandwidths would be expected in a Stripline or a fin-line version of this device.     

Synthesis of octave-band quarter-wave coupled semi-trackingstripline junction circulators

The complex gyrator circuit of stripline circulators using tracking junctions which satisfy the physical and magnetic variables of the Wu and Rosenbaum boundary conditions, is a nearly frequency independent octave-band resistive network. Such a junction may exhibit two minimas in its reflection coefficient when matched by a two section impedance transformer. However, a third minima may be realised by utilizing a complex rather than a real gyrator circuit. This paper summarises this class of semi-tracking solution in a simple way as a preamble to the design of a degree-3 quarter wave coupled circulator. The overall frequency behaviour of this class of junction has been separately evaluated by combining the electromagnetic and network problems (in conjunction with a two step impedance matching network)     

A Lumped-Element Circulator without Crossovers (Short Papers)

It is proposed to construct a simple "crossoverless" Iumped-element circulator, which can be made without sophisticated thin-film processing. The circulator can be described by a "delta connected" equivalent circuit. A simple capacitor arrangement can be used to influence the three eigenvalue phases of the circulator independently, thus permitting this circulator to be maximized systematically. A set of computer-generated eigenvalues gives insight into the behavior of the device under varying operating conditions. Preliminary measurements using a very simple pattern on a 0.650-in-diam ferrite substrate show a 20-dB bandwidth of 10 percent and an insertion loss < 1 dB (0.3 dB/min) at L band.     

A Study of the Noise-Temperature Performance of a Satellite Communications Low-Noise Amplifier Subsystem

The heart of the low-noise ampfifier (LNA) subsystem is the parametric amplifier which consists of a parametric amplifier proper and a circulator. The LNA subsystem can be simplified into an equivalent circuit, to evaluate its noise-temperature performance by assuming that it consists of a parametric amplifier proper and a circulator, which in its overall sense includes the additional components of the input line as elements in one arm of the circulator. Using this simplified equivalent circuit, the noise-temper ature performance is analyzed theoretically and provides a precise value for the LNA subsystem noise-temperature degradation, the noise-temperature increase of the earth-station receiving system caused by connecting an actual antenna to the subsystem and the measurement error of the HOT/COLD load noise temperature measurement method.     

The Frequency Behavior of Stripline Circulator Junctions

The frequency dependence of the circulation equations for Y-junction stripline and microstrip circulators is investigated, and a new set of design curves is generated for the frequency-independent forms of the circulation condition's roots for both below- and above-resonance cases. Using this new set of curves, the wide-band design predicted by Wu and Rosenbaum and Bosma's narrow-band design are analyzed and compared. Quantitative arguments for the effect of the junction parameters on the bandwidth are given. To support the arguments, the theoretical junction performance of the 7-15 GHz "continuous tracking" circulator reported by Wu and Rosenbaum is calculated and compared with the theoretical performance of a 24 GHz circulator junction designed using the same method. Experimental results also are presented for the 24 GHz design. An analysis for the effect of the ferrite thickness on impedance matching is also included.     

94-GHz 4-Port E-Plane Junction Circulator (Short Paper)

A 4-port junction circulator for use in 94-GHz E-plane integrated circuits is investigated. The design incorporates an E-plane X-junction of standard metal waveguides with a single ferrite disk on one of the narrow walls of the junction plus a metal plunger extending into the junction from the opposite side. The plunger is used to tune the n = 0 mode to the circulator center frequency and additionally can be used to tune the circulator center frequency over several gigahertz without critically degrading circulator performance, Minimum insertion loss of 0.65 dB was typical in a series of 12 plunger-tuned circulators with adjacent port isolation better than 20 dB, and crossport isolation better than 15 dB over nearly a 1-GHz bandwidth.     

Lumped Element Y Circulator

A lumped element Y circulator using ferrite, having a mesh mechanism in place of the center conductor of an ordinary Y strip line circulator, is proposed. A theory is developed relating to bandwidth, insertion loss, and temperature dependence of the reactive energy and the tensor permeability of ferrite, and the bandwidth enlargement is discussed on the basis of the equivalent network. The size of the circulator is approximately 1~2 cm in diameter for VHF and UHF bands and the characteristics are, for example, about 50 percent bandwidth for 20-dB isolation, 2-dB insertion loss at 600-Mc/s center frequency. It is also shown that the insertion loss has its minimum value at a definite bandwidth and, as a practical example, a circulator is described with 0.25 dB of insertion loss and 6.5 percent bandwidth at 700 Mc/s.     

Insertion Loss of 3-Port Circulator with One Port Terininated in Variable Short Circuit (Short Papers)

The insertion loss between ports 1 and 3 of a 3-port circulator with port 2 terminated in a short circuit varies about twice the single path loss. The purpose is to give approximate simple upper and lower bounds for this loss in terms of the single path insertion loss of the junction. One application of this arrangement is encountered in the connection of a filter and equalizer by a single circulator. The final result indicates that, in the absence of circuit losses, the double path loss varies between one and three times the single path loss.     

The Design of Planar Circulators for Wide-Band Operation

The stripline circulator used in microwave integrated circuits (MIC) is considered one of ferrite planar circuits (two-dimesional circuits). We investigated the optimum shape of a planar circulator for wide-band operation, perceiving the wider freedom of the planar structure in circuit design. The wide-band planar circulator, designed using the powerful contour-integral method is triangular shaped with slightly concave sides. The 20-dB isolation fractional bandwidth of the designed circulator is about 52 percent.     

Novel unilateral circuits for MMIC circulators

A circuit which is equivalent to a four-port circulator with one port terminated, called a quasi-circulator, is proposed. The quasi-circulator can replace a conventional circulator even though it is not a complete circulator. Examples of novel three-port unilateral circuit modules, called quasi-circulator modules, which are the main part of the quasi-circulator are presented to realize very wide band circulators in monolithic microwave integrated circuit (MMIC) form without using ferrite materials and external magnets. The proposed modules are composed of an active out-of-phase divider and an active in-phase combiner or an active in-phase divider and an active out-of-phase combiner. The modules have many variations. All are very small and operate over a very wide frequency range. Two types of quasi-circulator modules that have very broadband operation up to X or Ku band are demonstrated. A quasi-circulator is also demonstrated. It is shown how an active circulator is realized by quasi-circulator modules     

Synthesis of Negative Resistance Reflection Amplifiers, Employing Band-Limited Circulators

This paper presents a theory for single-stage circulator-coupled negative resistance reflection amplifiers based on proposed realistic circuit models for frequency-dependent band-limited circulators and broadband negative resistance devices such as the tunnel diode. In particular, gain bandwidth limitations are derived which are imposed by both the inherent resonance associated with the nonreciprocal circulator junction and the reactive parasitic associated with the active device. These limitations are generally more restrictive than past results which assumed a "perfect" frequency-independent circulator and took into account only the device parasitic. In addition, a synthesis procedure is presented for realization of an absolutely stable amplifier with a prescribed nth-order Butterworth or Chebyscheff approximation to an ideally flat band-pass power gain characteristic. The approach employed is based upon the theory of reflection coefficient equalization between two reactively constrained resistances representing the pass band circulator and device immittance models. In addition, a band rejection out-of-band stabilizing network is absorbed in the pass band equalizer in accordance with an over-all synthesis procedure. Finally, the theory is verified by the construction and testing of an L-band tunnel diode amplifier having third-order maximally flat power gain centered at 1.46 Gc/s and with half-power bandwidths (430 Mcls and 355 Mc/s at 10 dB and 16dB midband gain) within six percent of those predicted by theory.