Theory and Design of Tunable Full-Mode and Half-Mode Ferrite Waveguide Isolators

Abstract

Ferrite isolators are attractive due to their excellent isolation, low loss, good linearity and high power performance. However, these devices usually operate over a single frequency band. Multiband applications are possible if the isolation bandwidth of an isolator can be tuned. This paper presents a tunable waveguide-based full-mode ferrite isolator as well as a more compact half-mode tunable isolator, both fabricated on yttrium-iron-garnet substrates. For the first time, theory and design guidelines for the center frequency, bandwidth and tuning of the ferrite isolators unidirectional magnetostatic surface wave (MSW) mode are presented. The proposed theoretical model reveals that the isolation bandwidth can exceed 100% if the magnetization-to-bias field ratio is higher than 8. While the full-mode design is fabricated using a conventional subtractive technique, the half-mode design is implemented using inkjet printing technology. The full-mode isolator provides a maximum bandwidth of 45% and a peak isolator figure of merit (IFM) of over 65 dB at 7 GHz, whereas the half-mode design has a maximum bandwidth of 59% and a peak IFM of 76.7 dB at 7.5 GHz. The tuning of the centre frequency is from 7 GHz to 10.7 GHz for the full-mode and from 4.4 GHz to 9.9 GHz for the half-mode design using magnetic field strengths up to 2500 Oe and 2400 Oe, respectively. This work demonstrates the versatility of ferrite isolators as tunable mi crowave devices for reconfigurable RF applications.

Decoupling Technique Using Ferrite-Film Loading for 5G MIMO Applications

“…Important goals when using ferrite materials in compact antenna applications are antenna miniaturization and bandwidth enhancement, which are crucial to facilitate sufficient separation between the two antennas in the limited space of MIMO systems [24][25][26][27][28][29]. However, ferrites have low electrical conductivity, which decreases the eddy current losses, making them ideal components for high-frequency devices, such as isolators, circulators, phase shifters, and magneto-optical devices [30][31][32][33][34]. However, this isolation effect has rarely been considered in antenna design, which could benefit the control of interacting electric current distribution on the MIMO antennas.…”

Lightweight Low-Noise Linear Isolator Integrating Phase-Engineered Temporal Loops

“…Isolators can be realized by the simultaneous breaking of time-reversal symmetry and spatial inversion [1][2][3]. Conventional techniques and structures for the realization of isolators include magnetically biased two-dimensional electron gas systems [4], gyroelectric waveguides [5], transistor-loaded transmission lines [6][7][8][9][10][11][12], magnetic ferrites [1,[13][14][15][16][17][18][19], nonlinearity [20], and space-time-modulation [21][22][23][24]. Although these approaches have their own unique advantages and applications, they suffer from distinct limitations and disadvantages that restrict their applications.…”

Directivity Enhancement in Non-Reciprocal Bandpass Filters using an Evolutionary Algorithm

“…N ON-RECIPROCITY, using time-varying transmission lines (TVTL), has recently gained laurels in the design of non-reciprocal devices such as circulators, isolators, gyrators, etc., which traditionally relied on bulky and expensive ferrite components for their operations. [1]- [3]. Lately, the concept of TVTL has documented its proficiency in the design of nonreciprocal bandpass filters (NR-BPF).…”