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.     

A Fast Low-Loss Microstrip p-i-n Phase Shifter

A 4-bit p-i-n phase shifter with low RF attentuation, fast switching time, and low switching power requirements is described. The circuit, made in microstripline, consists of four cells giving phase shifts of 180, 90, 45, and 22.5/sup deg/, respectively. Each cell consists of a 3-dB coupler loaded by two p-i-n diodes. The transmission loss is 1.6 dB /spl plusmn/ 0.2 dB over the operating bandwidth of 11.7-12.2 GHz for a biasing current of only 5 mA/cell. Switching time between phase states is 1 ns.     

A Fast-Switching Low-Loss 12-GHz Microstrip 4-PSK Path Length Modulator

A 4-PSK microstrip modulator operating at data rates of up to 800 Mbits/s at 12 GHz is described. The circuit is made of two cells in series. Each cell consists of a 3-dB branch-line hybrid coupler and two BTL p-i-n diodes. One cell provides 0° or 90° phase shifts, and the Other 0° or 180° phase shifts, so that four carrier phase values are obtained by appropriately exciting the two cells. The switching time of each cell is 200 ps. Simultaneous switching of both cells increases the switching time to a maximum value of 400 ps. The phase waveforms are nearly rectangular at the above-mentioned data rates. RF insertion loss is 1 dB ± 0.1dB for the four phase values over the 11.7-12.2 GHz frequency band.     

Two Simple Methods For The Measurement Of The Dielectric Permittivity Of Low-Loss Microstrip Substrates

Two simple methods are presented for the measurement of the dielectric permittivity of low-loss microstrip substrates. The permittivity associated with a specific length of microstrip may be obtained. The methods are not wasteful of substrate material.     

High-Power Ferrite Circulators

The Faraday rotation and insertion loss of various ferrite-loaded waveguide structures have been studied in order to determine their power-handling capacities. A method of measuring insertion loss to within +-0.05 db is described. Two figures of merit containing this information are defied for the various configurations. The first, defined as the rotation per attenuation, indicates for a given value of rotation the efficiency of power transmission through the device, while the second, defined as the dissipative area per power loss, indicates the power handling capacity of the structure. By utilizing this information, the author has described an X-band ferrite circulator which is capable of handling an average power of 1000 watts. In addition, the design of a 2000-watt gyrator type circulator is indicated.     

Circulators using coplanar waveguide

Bosma's method of analysing stripline circulator operation is modified to suit circulators using coplanar waveguide. One of the circulators designed in this way shows a maximum isolation of 19.1 dB, insertion loss 0.8 dB and VSWR 1.3 or less at a centre frequency of 9.56 GHz.     

Four-Port Crossed-Waveguide Junction Circulators

A detailed account is given of the experimental investigation which has led to the design of 4-port circulators at frequencies from 2.5 to 25 Gc. The complex behaviour of these devices is clarified by establishing the modes of circulation in any particular waveguide passband. The modes are defined in terms of the static magnetic field (H) required, the microwave frequency (f) and the direction of circulation. The shape of the mode characteristic depends upon the ferrite/brass configuration in the center of the junction and the mode charts are given for two possible ferrite arrangements. The fixed-field bandwidths of the two configurations are, respectively, 2-4 per cent and 4-8 per cent. The performances are: isolation (ports 1-4) >20 db, cross-coupling (ports 1-3) >20 db, VSWR <1.2 and insertion loss (ports 1-2), respectively, <0.5 db and <1.0 db for the two configurations. The tunable bandwidth depends upon the mode of circulation and varied from 5 to 15 per cent. The positions of the modes in the waveguide pass-band can be adjusted by changing the diameter of the center ferrite/brass post. This shifting of the center frequency is described in detail for both ferrite arrangements and, for particular modes of circulation, figures are given of the frequency shift per 0.001" change in ferrite and brass diameter.     

Operation of Tracking Circulators

The classic two circulation conditions of a junction circulator obtained by setting the imaginary part of the complex gyrator impedance to zero and evaluating the real part does not ensure that the in-phase and counter-rotating eigennetworks are separately idealized. This paper indicates that the physical and magnetic variables of the tracking circulator described by Wu and Rosenbaum coincides with these special boundary conditions. Specifically, the gyrator resistance for this circulator may be calculated at the frequency for which the in-phase eigennetwork exhibits a short-circuit boundary condtion (using the n=0 and +-3 modes) and the counter-rotating eigennetwork modes exhibit complex conjugate immittances (using the n= -1, +2 and n = +1, -2 modes). The paper includes a new formulation for the Q-factor of this type of circulator which is used to calculate that of the tracking circulator.     

Broadband Strip-Transmission Line Y-Junction Circulators

Broadband circulators have been developed which operate below resonance and cover octave bandwidths in the frequency regions 0.6-8.0 Gc. The interrelationship of voltage standing-wave ratio (VSWR) and isolation between various ports is established without imposing symmetry. The fact that building a three-port circulator is essentially a matching process is used as a basis for a successful experimental development procedure. Empirically determined criteria for broadbanding are reported with particular emphasis placed on the discussion of optimizing saturation magnetization, linewidth, strip-transmission line parameters, and magnetic biasing field. The importance of having a ferrite with low dielectric loss tangent is also discussed. The empirical data are considered in light of theoretical work done in this laboratory and in light of the papers by Bosma.     

A Low-Loss Double-Tuned Transformer

In this letter, we present a state-of-the-art, planar double-tuned transformer using high-, micromachined spiral inductors and integrated capacitors. This circuit provides a 4:1 impedance transformation over a 30% bandwidth centered at 4.06 GHz, with a minimum insertion loss of 1.50 dB. The fabricated circuit occupies a total area of 440 times 500 mum²and finds application in power amplifier and other matching applications. An accurate lumped-element circuit model and design tradeoffs are presented. We believe this is the first implementation of a planar microwave double-tuned transformer.     

Symmetrical Four-Port Edge-Guided Wave Circulators

Four-port microwave-integrated-circuit (MIC) edge-guided wave circulators (BGC) have been designed, fabricated, and tested. A mathematical characterization of the strip conductor's shape as well as a precise mechanical control of the bias inhomogeneity are provided. By means of these two techniques the reproducibility of the device is greatly improved with respect to that of the EGC obtained by the traditional cut-and-try methods. X-band performance data are presented and related to the spatial distribution of the effective magnetic permeability mu/sub eff/ in the ferrite substrate. Experimental evidence is reported that an efficient circulator action occurs when mu/sub eff/< 0 at some point under the central circular shield. The spatial distribution of the RF electric field at the circulator's surface is investigated by a mechanical probing technique. It is found that in the lower part of the operation band, RF fields of considerable amplitude extend in the air in the region between the guiding edge and the substrate's edge.     

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.     

宽带集中元件环行器计算机辅助设计

本文从散射矩阵本征值的频率关系出发,对宽带集中元件环行器所需的设计参数作了优化计算。文中采用乘子法将约束优化问题化为无约束优化问题。计算结果与实验结果较一致并证实了为得到宽带性能实验中出现的隔离双峰的现象。     

The Synthesis of N-Port Circulators

It is shown that there is a certain wide class of three-port network that can be transformed into a circulator by the addition of reactive elements. For such synthesis from a symmetrical three-port junction it is necessary and sufficient for it to be loss-free and for the moduli of the two transmission coefficients to be different. This approach may be used in the design of broad-band circulators. For junctions approximating to an n-port circulator with n>3, it is shown that when the n reflection coefficients are matched by reactive networks in each arm, n particular transmission coefficients also vanish.     

Substrate-Integrated-Waveguide Circulators Suitable for Millimeter-Wave Integration

Over the years, many millimeter-wave circulator techniques have been presented, such as nonradiative dielectric and fin-line circulators. Although excellent results have been demonstrated in the literature, their proliferation in commercial devices has been hindered by complex assembly cost. This paper presents a study of substrate-integrated millimeter-wave degree-2 circulators. Although the substrate integrated-circuits technique may be applied to virtually any planar transmission medium, the one adopted in this paper is the substrate integrated waveguide (SIW). Two design configurations are possible: a planar one that is suitable for thin substrate materials and a turnstile one for thicker substrate materials. The turnstile circulator is ideal for systems where the conductor losses associated with the thin SIW cannot be tolerated. The design methodology adopted in this paper is to characterize the complex gyrator circuit as a preamble to design. This is done via a commercial finite-element package.     

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.     

Varactor-Tuned Lumped-Element Circulators (Correspondence)

In the case of lumped-element circulators, the center frequency of the device can be tuned by altering the lumped capacitance only. It is the purpose of this paper to describe a new voltage-tuned circulator which is obtained by replacing the usual lumped capacitances by varactor diodes. Such a circulator has been tuned over an octave band from 250 to 500 MHz.     

A Low-Loss Diffraction Grating Frequency Multiplexer

A quasi-optical frequency multiplexer based on a blazed diffraction grating is studied. Experimental data, supported by semi-quantitative theoretical considerations, show that the multiplexer is an efficient channel-dropping filter well suited to use in the millimeter wave region. A feature of the grating multiplexer which sets it apart from conventional designs is its ability to drop several channels using a single frequency-selective element, namely, a diffraction grating. This economy of hardware results in a simple, compact structure. The channels of the experimental multiplexer have typical bandwidths of ~540 MHz with loss of ~1 dB. The width of the impulse response at half amplitude is ~1.5 ns. Return loss within a channel is typically 15-20 dB. Comparisons with other millimeter wave multiplexer designs are discussed.