Non-reciprocal Bandpass Filter Research Articles

Rigorous design and experimental validation of non-reciprocal bandpass filter with ultrawide high reverse isolation bandwidth

This work presents a rigorous design and experimental validation of a non-reciprocal bandpass filter (NBPF) employing time-modulated resonators with progressive phase shift sinusoidal modulation signal to achieve low forward transmission insertion loss (IL) and ultrawide high reverse isolation bandwidth. Analytical design equations have been derived for numerical design of NBPF asl well as providing insights of nonreciprocal frequency response. Additionally, these proposed analytical spectral S-parameters offer the flexibility to design NBPFs with arbitrary termination port impedances. This work also demonstrates a systematic approach to find modulation parameters without relying on optimization methods. It has established empirical relationships between the modulation parameters and the filters specifications to achieve low forward transmission IL and reverse isolation exceeding 15 dB at entire frequency range. The accuracy of the proposed NBPF design has been confirmed by comparing with harmonic balance simulation results of microstrip line NBPF. For experimental validation, three prototypes of NBPF with different termination port impedances are designed, implemented, and manufactured. In experimental results, the frequency of NBPFs can be continously tuned from 1.62 GHz to 1.94 GHz (17.98 %) with maximum forward transmission IL (|S21|) of 5.40 dB and input/output return loss higher than 12 dB. For each frequency tuning state, the reverse isolation (|S12|) exceeds higher than 20 dB across the entire frequency range.

Non-Magnetic Non-reciprocal Bandpass Filter with Quasi-Elliptic Response and Tunable Center Frequency

This paper presents a detailed analytical numerical design methodology and experimental validation of non-magnetic non-reciprocal bandpass filter (NBPF) that exhibits a highly selective quasi-elliptic response in forward direction of propagation. By modulating resonators with progressive phase shift AC modulation signal, unidirectional RF signal propagation (|S21| ≠ |S12|) is achieved. Analytical spectral S-parameters of the proposed quasi-elliptic NBPF have been derived to gain insight nonreciprocal response. Furthermore, empirical relationships between modulation parameters and filter specifications have also been established through numerical simulations, allowing for simplified design process of the NBPF. By varying the resonant frequency of the resonators, a frequency reconfigurable transfer function can be achieved, providing center frequency tunability of NBPF. For experimental validation purposes, a prototype of microstrip line NBPF is designed and manufactured using three time-modulated resonators, which are implemented using transmission line loaded with varactor diodes. The passband frequency can be continuously tuned by changing DC-bias voltage of varactor diodes. The measurement results revealed that passband center frequency is tuned from 1.65 GHz to 1.95 GHz achieving at tuning ratio of 1.182:1, while maintaining the nonreciprocal behavior with two transmission zeros. For all tuning states, in-band minimum insertion loss in forward direction was measured between 3.20 and 4.8 dB, whereas isolation in reverse direction was measured up to 34.5 dB.

Numerical Insight Into the Origin of Nonreciprocity and Performance Enhancement in Nonreciprocal Bandpass Filters Using Evolutionary Algorithm

In this paper, a non-reciprocal filter with enhanced directivity is analyzed methodically, and the filter parameters are optimized using an evolutionary algorithm. The non-uniform spectral dispersion of power among the harmonics in opposite directions is substantiated with the aid of filtering polynomials. These polynomials indicate the origin of at least one transmission zero within the passband in the reverse direction, thereby promoting the non-reciprocal filter response. The filter’s return loss, insertion loss, and isolation characteristics exhibit a trade-off that demands an optimization algorithm to effectuate the judicious choice of circuit parameters. This problem is addressed by designing a 150 MHz lumped element non-reciprocal bandpass filter based on the parameters extracted using an evolutionary algorithm based particle swarm optimization (PSO). The simulated and measured results comply well with the modeling, and the results exhibit maximum directivity of 28.2 dB without degradation in insertion loss (1.1 dB) and return loss (16.2 dB) within the passband. The algorithm can be utilized in designing non-reciprocal filters having different center frequencies and bandwidths.

Numerical Design of Non-Reciprocal Bandpass Filters With the Aid of 3D Coupling Matrix for 5G Bands

In this brief, numerical analysis on spatio-temporally modulated (STM) non-reciprocal bandpass filters is methodically demonstrated to corroborate the underlying phenomenon. The concept of a 3D coupling matrix is illustrated for the first time, which provides an analytical insight into the distribution of RF energy among the intermodulation (IM) products generated in time-modulated resonators. Flagship equations based on coupling matrix are proposed that bypass the tedious analysis of spectral admittance and ABCD matrices. These equations can be modified to design any ordered filters and with varying cross-coupling instances. The experimental validation confirms the accuracy of the numerical equations, and the model can be utilized to further the development in this burgeoning yet eccentric research domain.

Non-reciprocal diplexer and power combiner/divider from topological cavities with both splitting and combining functions

Multiplexers and power combiners/dividers are crucial in many applications of electromagnetic waves including microwave and terahertz communication. Full-duplex communication requires the separation of transmitted and received signals; thus, non-reciprocal multiplexers and power combiners/dividers are very essential. In this work, we present and numerically study a design concept for such non-reciprocal circuits from topological cavities. First, a quad-port circulator is made from a topological cavity and two trivial waveguides, which effectively operates as a non-reciprocal band-pass filter. Then, by parallelly connecting multiple circulators together, topological diplexers and power combiners/dividers are formed. These circuits are non-reciprocal due to the nature of photonic topological insulators, yet unlike the previously proposed non-reciprocal multiplexers or power combiners/dividers, they can both split and combine multiple frequencies or multiple power flows. The topological nature of the proposed circuits also makes them robust to any fabrication error and suitable for practical full-duplex communication applications.

Nonreciprocal Isolating Bandpass Filter With Enhanced Isolation Using Metallized Ferrite

The nonreciprocal bandpass filter has been achieved by utilizing the nonreciprocity characteristics of the magnetostatic surface wave (MSSW) in planar ferrite slabs. In this article, the dispersion relation, impedance, and attenuation of MSSW between the pure and metallized ferrite slabs have been analyzed and compared. Theoretical analysis indicates that the ferrite slab metallized by a thin conductive layer would introduce significant attenuation on the metallized interface, which is MSSW propagating on the isolated direction, while MSSW on the other surface is barely affected. Therefore, nonreciprocal bandpass filter with enhanced isolation can be achieved with metallized ferrite slab. Simulated S-parameters show that a notch in the isolating direction can be obtained at the passing band of the transmitting direction. Experimental results show that the nonreciprocal filter with metallized yttrium iron garnet (YIG) slab (by depositing 100- $\mathbf {nm}$ copper film) exhibits more than 10-dB higher isolation than that with pure YIG slab, while the center frequency, insertion loss, and 3-dB bandwidth maintain almost the same. The center frequency of the filter with metallized YIG slab can be tuned from 7.26 to 8.38 GHz with insertion loss of less than 3 dB, and in-band isolation of more than 30 dB as the dc bias magnetic field is increased from 1.8 to 2.3 kOe. Besides, the nonreciprocal filter has ultra-wide out-band suppression since it utilizes the narrow frequency band of MSSW. The −10-dB out-band rejection exceeds 36 GHz in the upper band and 1 MHz in the lower band.

Frequency Tunable Non-Reciprocal Bandpass Filter Using Time-Modulated Microstrip λ g /2 Resonators

This brief presents a novel frequency reconfigurable microstrip non-reciprocal bandpass filter based on time-modulated microstrip λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> /2 resonators. The modulation is achieved by loading both ends of the λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> /2 transmission line resonators with time-modulated capacitors. The modulation voltage source is connected at the center of the resonator, where there is a natural voltage null, and a single inductor is used to further enhance the biasing isolation. The wideband nature of this isolation scheme enables the tuning of the devices over a wide frequency range. With more than 30-dB RF to modulation isolation, the proposed resonator structure also enables low insertion loss by eliminating RF signal leakage to the modulation ports. A 3-pole bandpass filter example is simulated and measured, showing a minimal insertion loss of 3.9dB, a 20-dB isolation bandwidth of 42 MHz at 1.0GHz, and frequency tuning range of 885-1031 MHz.

Integrated magnetoelectric devices: Filters, pico-Tesla magnetometers, and ultracompact acoustic antennas

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Integrated ferroics for sensing, power, RF, and µ-wave electronics

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