The requirements for circulators for use in combination with microwave and millimeter-wave integrated circuits are reviewed, with special emphasis on modules for phased-array antennas. Recent advances in broadbanding and in miniaturization are summarized. Novel types of circulators that are fabricated by attaching a ferrite disc and a suitable coupling structure to the surface of a dielectric of semiconductor substrate (quasimonolithic integration) are described. Methods for achieving complete monolithic integration are also discussed. >

Circulators for microwave and millimeter-wave integrated circuits

In this article, we provide a comprehensive review of past and present efforts in the field of microwave nonreciprocity with an emphasis on the most commonly used nonreciprocal devices, namely gyrators, isolators, and circulators. After discussing the origin and history of such efforts, we elaborate on the pros and cons of four distinct approaches to break reciprocity which include magnetic biasing of ferrite materials, intrinsic nonreciprocity of solid-state devices, nonlinearities with geometric asymmetries, and finally, periodic spatiotemporal variation. We subsequently pay due attention to the spatiotemporal approach and show that the recently emerging proposals to achieve magnet-free nonreciprocity with linear, periodically time-varying circuits can compete with traditional ferrite devices and even outperform them in several metrics, thus opening the door to exciting venues for miniaturized low-cost and high-performance nonreciprocal devices with numerous applications ranging from full-duplex communications and quantum computing to biomedical imaging and radar systems.

Microwave Nonreciprocity

The useful operating range of circulators has been extended by avoiding the "low-field loss" problems usually associated with operating at frequencies smaller than the magnetization frequency f/sub M/, through the use of a device configuration that assures a nearly uniform internal magnetic field. Performance data on experimental stripline circulators using single-crystal YIG or Li-ferrite disks and external YIG (or Li-ferrite) domes (for achieving a nearly uniform internal magnetic field) are summarized and compared with theoretical expectations. Reasonably good circulator performance is observed in the frequency range from 2.8 to 10.20 GHz for the circulator based on YIG and in the frequency range from 5.8 GHz to 18 GHz for the circulator based on Li-ferrite. The external ferrite domes improve the performance significantly when the frequency is near the lower edge of the operating band.

Broad-Band Stripline Circulators Based on YIG and Li-Ferrite Single Crystals

The authors report on the fabrication and testing of millimeter-wave microstrip/stripline Y-junction circulator operating at K/sub a/ band. By exploiting the properties of high-anisotropy magnetic field, external magnetic field requirements are reduced. The design of microstrip/stripline circulators involves calculations of the radius of the ferrite disks and the port suspension angles in terms of the microstrip dielectric constant and saturation magnetization of the ferrite material. In addition, the operation frequency is determined largely by the uniaxial anisotropy field of the barium-strontium hexagonal ferrite. >

Self-biasing circulators operating at K/sub a/-band utilizing M-type hexagonal ferrites

This chapter contains sections titled: Complex Gyrator Circuit of Weakly Magnetized Junction Circulator Very Weakly Magnetized Gyromagnetic Resonator Weakly Magnetized Gyromagnetic Resonator Moderately Magnetized Gyromagnetic Resonator The Degree-2 Circulator Gap Effects in Circulator Assemblies Suspended Planar Resonator Passband Frequencies of a Three-Port Junction in Immittance Plane Open Walls Spinwave Instability in Magnetic Insulators Frequency Doubling in Ferrites Second-Order Intermodulation in Magnetic Insulators Temperature Stability of Magnetic Insulators Below the Kittel Line Third-Order Intermodulation Products in Nonlinear Devices

The Stripline Circulator: Theory and Practice

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.

The Frequency Behavior of Stripline Circulator Junctions

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The Frequency Behavior of Stripline Circulator Junctions