Yuanxun Ethan Wang

In this paper, a novel parametric receiver design with an electrically small bow-tie antenna is proposed to achieve low noise performance over a broad bandwidth. Specifically, we propose to match the electrically small antenna directly to a parametric amplifier, without using any intermediate impedance matching network to avoid the addition of noise to the receiver. The parametric amplifier, which is driven by a high frequency pump voltage, exhibits a high impedance, time-varying capacitive load to the dipole. Therefore, the low frequency signal voltage from the dipole is detected as it modulates the capacitance of the varactor diode bridge. The signal is being amplified and upconverted to the proximity of the pump frequency at the output with minimum contamination of noise in the process. The complete noise theory of such parametric receivers is presented and validated against nonlinear circuit simulation results. A monolithically integrated varactor diode bridge is custom designed and fabricated with InGaAs HBT process. The varactor bridge provides capacitive match to that of an electrically small bow-tie that has a diameter of 47.6cm. Based on this design, a parametric receiver prototype is constructed and tested with incident signals from 10MHz to 100MHz. Measurements show at least 2dB improvement in its best noise figure and 4 times of the 10dB noise figure bandwidth compared to that of the conventional self-resonant electrically small antenna that has the same form factor.

This paper presents a novel method to design ultra-miniaturized antenna leveraging on the radiation of electron spin precessions (E-Spin). The antenna operates at the ferromagnetic resonance frequency of a normally biased ferrite disc where the input of RF energy is transferred to circularly polarized radiation of E-Spin efficiently. We propose an analytical process for estimating the quality factor of the E-Spin antenna. The analysis can predict the theoretical resonance frequency and radiation efficiency given the dimension and material properties of the ferrimagnetic materials. We also validate our analysis with static magnetic field simulation, full-wave simulation, and measurement on the prototype antenna with an yttrium-iron-garnet disc. The results show that we can create an antenna resonating at 3.350 GHz with the smallest size (ka=0.20 for radiating element / ka=0.40 for the entire structure) among the state-of-the-art. The antenna features a much wider axial ratio bandwidth compared to the state-of-the-art, the circular trajectory of the precession of magnetic moment dictates the circular polarization of radiated field. The antenna achieves -4.91 dB gain and a -10 dB bandwidth of 17 MHz in the measurement. Furthermore, by controlling the external biasing magnetic field, the center frequency of the E-Spin antenna can be tuned by 175 MHz with minor variation on the gain. The design demonstrates a new method for realizing ultra-miniaturized circularly polarized electrically small antennas, where the low stored energy improves bandwidth–efficiency product at ferromagnetic resonance. The operating frequency is set by the magnetic bias-controlled ferromagnetic resonance, that allows continuous frequency tuning 10.3 times wider than its static bandwidth.

Filters used for modulated RF signals are often matched bandpass filters that have larger bandwidths than that of the modulation. Therefore, the time constants of the filters must be shorter than the symbol periods. This paper presents an idealized theoretical model for Phase-Sensitive Dynamic Filters (PSDF), a class of emerging filters that can be tuned in real time, as fast as the symbol rate of a signal but with time constants longer than the symbol periods. With the foreknowledge of the frequency and phase shifts of a given signal, such filters are capable of filtering across multiple symbols of a constant envelope and compressing the noise bandwidth to a fraction of the modulated signal bandwidth. The transient response of the filters can be longer than the symbol rate of the signal. This can mathematically be modeled by infinite impulse response (IIR) filters with long time constants yet fast time-varying complex coefficients in the feedback path. Phase-sensitive dynamic filters preserve energy across symbols and also exhibit phase-sensitivity. The proposed models indicate that PSDFs can be employed in applications such as rejection of self-interference in the front ends of full-duplex communications systems. Such systems pave the way for the possibility of higher isolation and robustness compared to other prototypical approaches in dynamically changing systems.

A new versatile modeling method has been proposed for simulations of three-dimensional (3-D) arbitrarily shaped RF magnetic components. The simulations are accomplished through the hybrid computations of electrodynamics and micromagnetics, where the Maxwell’s equations and Landau-Lifshitz Gilbert (LLG) equation are jointly solved. The method solves the Maxwell-LLG system based on the mesh cells of fixed material distributions in space. The field variables are computed with the FDTD method through the leap-frog-processing (LFP). In the modeling, a Yee cell implementation allows the boundary conditions on the material surfaces to be satisfied with the Maxwell equations coupled with the LLG equation effectively. The implementation also utilizes a material mapping (MM) solution to determine the material property of each mesh element generated by the ray-casting method (RCM). Moreover, a double damping perfect matching layer (PML) technique is implemented as the absorbing boundary condition of the simulations, where the ferromagnetic material can extend into the PML regions. The parallel programming technique is utilized for the FDTD-LFP to improve the computational efficiency. The numerical solution has proven to be effective and stable even for simulations of RF devices in resonances with low loss ferromagnetic materials.

Electrically small antennas face a seemingly insoluble dilemma. As engineers make headway in efficiency by boosting the device quality factor (Q), the bandwidth necessarily drops. Any wins in bandwidth conversely deteriorate the already low efficiency. The result is that cutting edge designs that boast of high efficiencies also have notoriously low bandwidths. This is untenable for commercial and military applications. One future platform that exemplifies this is the mechanical resonance based piezoelectric antenna array. The high Q piezoelectric material allows even a single 1D bar element to be four orders of magnitude more efficient than an optimized 3D metallic antenna at the same form factor but at a bandwidth roughly 1/1000th of the operating frequency. This work presents a method of partially overcoming these bandwidth deficiencies by utilizing a mechanical tuning method unique to piezoelectric antenna arrays. In such devices, the array spacing alters the stiffness of the piezoelectric elements which thus alters the resonance frequency without significantly diminishing the efficiency. Thus, a frequency band may be scanned by mechanically altering the array spacing. This frequency band is referred to as the mechanically tuned half-power bandwidth (MT-HPBW), which is roughly two orders of magnitude larger than the traditional HPBW. Additional improvements in bandwidth are realized by utilizing multiple resonance modes. An algorithm capable of performing full-wave simulations on such piezoelectric antenna arrays is presented with modifications with respect to previous work. Computational and design guidance is also provided based on the authors' own experiences.

In this publication, we present the design and realization of a novel tunable bandpass filter utilizing a cascaded parametric amplifier architecture, configured in a way that increases the tunable bandwidth and produces gain. The filter is based on a two-stage design comprising of an upconverter and a downconverter in series with each other. The mixing is done using varactor diodes, known for high conversion gain and low-noise capabilities. The amplifiers are used to upconvert the signal to a fixed resonant idler, and then downconvert the signal back to its original frequency resulting in a narrow passband and out-of-band rejection. The prototype is configured using a hybrid MMIC-PCB approach and is demonstrated over the tunable frequency range of 1.1~2.1GHz, with an up to 5dB gain at the passband, a noise figure of 3.8dB, and over 30dB suppression out-of-band.

Impedance match to a high-Q load with a passive network is fundamentally narrow band as its linear, time-invariant (LTI) property is subject to the Bode-Fano limit. However, such a limit may be partially lifted for frequency modulated signals when a time-varying matching network is used whose reactance varies continuously following the instantaneous frequency of the signal. The mismatch, however, may increase for high-speed modulations as the result of transient changes of energy balance among the different reactive components. As the information bandwidth of a modulated signal is primarily determined by the modulation speed, a general theory quantifying the modulation speed limit for such dynamic impedance matching is derived based on circuit laws. The analyses are applied to parallel LC resonators with one type of time-varying reactance, two types of time-varying reactance, and gyrator coupled time-varying reactance. The analyses are validated with nonlinear circuit simulations. It is concluded that while a single type of time-varying reactance can help to broaden the modulation rates of impedance matching, two paired types of time-varying reactance (inductance and capacitance) can lift the modulation speed limit completely. Furthermore, when a pair of single-type time-varying reactance coupled with a gyrator is used, the modulation speed limit can be similarly removed. In general, the gyrator adds another dimension in dynamic impedance matching in either lowering the resonant frequency or suppressing the mismatch. The proposed theory can be applied to the dynamic matching of electrically small antennas, which may help to achieve a radiation efficiency bandwidth product that goes beyond the limit imposed by its radiation quality factor, whose lower bound is defined by the famous Harrington-Chu’s limit.

Antenna miniaturization is currently facing increased performance demands while simultaneously lacking a computational framework to drive robust designs. Future platforms must radiate farther, at lower frequency, and be increasingly compact. While mechanical resonance based piezoelectric antenna arrays are a viable candidate, detrimental mutual depolarization effects arise that must be characterized by multi-scale simulations, coupling the elastodynamic and EM wave physics. This work presents an algorithm capable of performing such full-wave simulations to provide design guidance to engineers wishing to mitigate mutual depolarization. The relevant dynamic systems of equations are discretized and put into a Finite Difference Time Domain (FDTD) scheme. This scheme exhibits electrodynamic unconditional stability and features heavily graded meshes to directly tackle the time and length scale disparity between the mechanical and EM waves. The algorithm was validated by comparison with experimental data and analytical solutions. Additionally, the algorithm compared well with predicted values for depolarization. Simulations demonstrated that spacing within piezoelectric antenna arrays should not be made too small, as to induce undue mutual depolarization, or too large, as to not allow sufficient elements to contribute to array dipole moment. Computational guidance is also provided based on the authors’ own experiences.

The design of magnetic filters for millimeter-wave (mmWave) applications is of interest due to the expanding demand for higher-frequency spectrum utilization. This article focuses on modeling and designing mmWave filters using M-type barium hexaferrite (BaM). A systematic design methodology is proposed, beginning with the construction and optimization of BaM resonators to achieve suitable energy coupling coefficients. These optimized resonators are subsequently coupled to form bandpass filters. An equivalent circuit model is developed to quantify the efficiency of coupling between electromagnetic (EM) waves and ferrimagnetic resonance (FMR), offering a robust performance metric for BaM resonators. The practical implementation involves planar printed-circuit-board (PCB)-based BaM resonators and filters. The fabricated bandpass filter, with in-plane dimensions of 3.8 $\times $ 2.7 mm and an out-of-plane dimension of 0.51 mm, exhibits an insertion loss of 6 dB and achieves a 3-dB bandwidth of 190 MHz at 41.5 GHz. These results validate the feasibility and efficacy of the proposed design methodology, indicating significant potential for advancements in the development of high-performance magnetic filters.