Showing papers on "Linear phase published in 2020"

Liquid crystal integrated metalens with tunable chromatic aberration

Abstract: Overcoming chromatic aberrations is a vital concern in imaging systems in order to facilitate full-color and hyperspectral imaging. By contrast, large dispersion holds opportunities for spectroscopy and tomography. Combining both functions into a single component will significantly enhance its versatility. A strategy is proposed to delicately integrate two lenses with a static resonant phase and a switchable geometric phase separately. The former is a metasurface lens with a linear phase dispersion. The latter is composed of liquid crystals (LCs) with space-variant orientations with a phase profile that is frequency independent. By this means, a broadband achromatic focusing from 0.9 to 1.4 THz is revealed. When a saturated bias is applied on LCs, the geometric phase modulation vanishes, leaving only the resonant phase of the metalens. Correspondingly, the device changes from achromatic to dispersive. Furthermore, a metadeflector with tunable dispersion is demonstrated to verify the universality of the proposed method. Our work may pave a way toward active metaoptics, promoting various imaging applications.

Loss Compensated PCM GeTe-Based Latching Wideband 3-bit Switched True-Time-Delay Phase Shifters for mmWave Phased Arrays

Abstract: This article reports the first implementation of 3-bit millimeter-wave switched true-time-delay (TTD) phase shifters based on phase-change material (PCM) germanium telluride (GeTe). Two TTD phase shifters are presented. The first phase shifter is designed using four monolithically integrated PCM single-pole triple-throw (SP3T) switches to route the signal through delay lines. The insertion loss variation between various states is minimized by integrating two fixed PCM GeTe elements maintained in the crystalline state, along with the optimized width of the delay lines. The PCM switching cells are latching type, thus, consume no static dc power. The SP3T switches are connected back-to-back in two stages to provide a 3-bit phase shift with 20° precision. The second phase shifter is designed using two back-to-back connected PCM single-pole eight-throw (SP8T) switches. Both phase shifters are designed to operate over an 8 GHz wide frequency band with a center frequency of 30 GHz. The devices are fabricated in-house using an eight-layer microfabrication process. The proposed devices are highly miniaturized with an overall device area of 0.42mm 2 and 1.4mm 2 for the first and second phase shifter, respectively. The first phase shifter exhibit a measured average loss of 4.3 dB with a variation of ±0.3 dB and a return loss better than 20 dB, while the second phase shifter demonstrates low average measured loss of 3.8 dB with only ±0.2 dB loss variation and returns loss better than 17 dB at 30 GHz. Both phase shifters provide 180° linear phase shift with lower than 18 ps delay in the worst case.

A Full-Passband Linear-Phase Band-Pass Filter Equalized With Negative Group Delay Circuits

Abstract: A full-passband linear-phase band-pass filter (BPF) equalized with negative group delay circuits (NGDC) is proposed. The NGDCs are utilized to suppress the salient group delay at the edge of the passband of the traditional BPF for achieving the full-passband linear-phase characteristic. To obtain input- and output-port impedance matching, two BPFs loading NGDCs are center symmetrically configured by Wilkinson power dividers. To verify the design concept, a 3-order full-passband linear-phase BPF is designed and fabricated. From the measured results, the GD fluctuation is reduced by 74% from 0.57 to 0.15 ns, return loss is better than 10 dB, and the insertion loss variation is less than 3 dB within the frequency range from 2.142 to 2.804 GHz. The proposed BPF achieves a flat group delay in the whole passband and realizes the full-passband linear-phase characteristic.

Design of Robust Higher-Order Repetitive Controller Using Phase Lead Compensator

Abstract: The performance of conventional repetitive controller (RC) deteriorates under frequency variations and system uncertainties. Due to limited bandwidth, it is also a trivial task to stabilize the conventional RC. This paper proposes a higher-order repetitive controller (HORC) with linear phase lead as a stabilizing compensator and zero-phase tracking error (ZPTE) compensator. The periodic signal generator, used by the HORC, offers relatively high gains in the neighborhood of tuned frequency and its harmonics. Stability conditions for higher-order repetitive (HOR) control system, including the phase lead compensator, are presented. The proposed solution is applied to repetitive current control of a two-level grid-connected inverter. Simulation and experimental results show that the HORC designed using the phase lead compensation is robust to frequency variation in reference/disturbance and system uncertainties.

Feature Extraction for Transient Chemical Sensor Signals in Response to Turbulent Plumes: Application to Chemical Source Distance Prediction

Abstract: This paper describes the design of a low-pass differentiator filter with linear phase and finite impulse response (FIR) for extracting transient features of gas sensor signals (the so-called “bouts”) which are relevant for accurately estimating the source-receptor distance in a turbulent plume. Our current proposal addresses the shortcomings of previous ‘bout’ estimation methods, namely: (i) they were based in non-causal digital filters precluding real time operation, (ii) they used non-linear phase filters leading to waveform distortions and (iii) the smoothing action was achieved by two filters in cascade, precluding an easy tuning of filter performance. The presented filter preserves the signal waveform in the bandpass region for maximum reliability concerning both bout detection and amplitude estimation. Thanks to its FIR design, the filter can be implemented with nonrecursive structures, thus being inherently stable and allowing an easy algorithmic implementation and optimization. As a case study, we apply the proposed filter to predict the source-receptor distance from recordings obtained with a metal oxide (MOX) gas sensor in a wind tunnel. We demonstrate that proper tuning of the proposed filter can reduce the prediction error to 8 cm (in a distance range of 1.45 m) improving previously reported performances in the same dataset by a factor of 2.5. The performance of bout-based features are also benchmarked against traditional source-receptor distance estimators such as the mean, variance and maximum of the response. We also study how the length of the measurement window affects the performance of different signal features and how to tune the filter parameters to make the predictive models insensitive to wind speed. A MATLAB implementation of the proposed filter and all analysis code used in this study is provided.

Noncontact High-Linear Motion Sensing Based on A Modified Differentiate and Cross-Multiply Algorithm

Abstract: The interferometric radar sensor can wirelessly detect the relative displacement motions, owing to its inherent nature of high sensitivity to the moving objects. To overcome the phase ambiguity and discontinuity caused by non-linear phase modulation, approaches such as differentiate and cross-multiply (DACM) were proposed for linear demodulation of the vibration motions. However, the existing DACM algorithm is strongly dependent on the calibration of I/Q output signals, resulting in low tolerance to noise and inaccuracy in detecting motions of large linear displacement. Based on the differentiation and the geometrical theorem of the trigonometric functions, this paper proposes a modified DACM algorithm with simplified expression but much improved performance for high-linear motion detection. Theoretical analysis was presented to introduce the proposed algorithm. Both simulation and experimental results demonstrate that the proposed algorithm is not only free from phase ambiguity, but also superior in several aspects: the stability under a signal to noise ratio (SNR) of 25 dB has been improved by 9 dB and the linearity of measuring large displacement motion has been improved by 32 dB, comparing to the existing DACM algorithm. Moreover, the simplified expression would greatly reduce the computational resources needed for linear phase demodulation.

Highly Linear Phase-Canceling Self-Injection-Locked Ultrasonic Radar for Non-Contact Monitoring of Respiration and Heartbeat

Abstract: A novel phase-canceling demodulation scheme to improve the linearity of a self-injection-locked (SIL) ultrasonic radar is proposed with the goal of solving the null detection problem and accurately sensing large displacements of a moving target. A proportional-integral (PI) controller regulates the phase of the injection signal and cancels the Doppler phase shift by tuning a delay in the received echo signal, and this tunable delay serves as the radar output, which is linearly proportional to the displacement of the target. Without assuming weak injection, the frequency and phase equations for an SIL oscillator are derived, supporting the construction of a plant model and the design of a PI controller. Also, a new ultrasonic radar equation is presented for estimating the radar detection range. The SIL radar with phase regulation is operated in its anti-phase injection mode for better performance. The proposed design is implemented on an FPGA to make a 40 kHz continuous-wave ultrasonic radar. The maximum detectable peak-to-peak motion is up to 120 mm (approximately 14 wavelengths of displacement), with a total harmonic distortion as low as 2.3% for the detection of 1 Hz harmonic motion. The radar is used to detect the human chest movement for non-contact monitoring of the respiratory rate and heart rate. Due to the high linearity and sensitivity, the radar is capable of faithfully detecting the relatively large involuntary body movements and lung movements while still preserving the weak heartbeat rhythm buried in them, with the average error of measured heart rates less than 1 BPM.

Asymmetric coherence gratings.

Abstract: We introduce a class of partially coherent, Schell-type sources whose degree of coherence is represented by a finite series of complex-valued functions. The significance of implementing such a series is due to the fact that one can manipulate the weighting coefficients of its terms having a computationally trivial linear phase of the degree of coherence for obtaining the radiated beams of the same complexity as could only be previously achieved with analytically intractable nonlinear phases. Our examples illustrate new opportunities for modeling asymmetric coherence gratings and lattices.

A new design approach for nearly linear phase stable IIR filter using fractional derivative

Abstract: In this paper, a new design method for digital infinite impulse response ( IIR ) filters with nearly linear-phase response is presented using fractional derivative constraints ( FDCs ) . In the proposed method, design problem of an IIR filter is constructed as the minimization of phase error between the desired and designed phase response of an allpass filter ( APF ) such that the designed lowpass filter ( LPF ) or highpass filter ( HPF ) yields less passband ( ep ) , and stopband errors ( es ) with optimal stopband attenuation ( As ) . In order to have accurate passband ( pb ) response, FDCs are imposed on appropriate reference frequency, where the optimality of these FDCs are ensured by using a new greedy based sorting mechanism. The simulated results reflect the efficiency of the proposed method in term of improved passband response along with better transition width. However, small reduction in As is observed within the allowable limit, when compared to non-fractional design approach, but the designed filter remains immune to wordlength ( WL ) effect.

A novel singular spectrum analysis-based multi-objective approach for optimal FIR filter design using artificial bee colony algorithm

Abstract: Effective filter design plays an important role in signal processing applications. Multiple parameters must be considered to control the over-frequency response of the designed filter. In this study, a novel multi-objective approach is proposed for windowing finite impulse response (FIR) filter design. The windowing FIR filters are commonly used due to its linear phase property, frequency stability and easier implementation. However, windowing method can only control the cutting frequency of filter, and it suffers from the problem of insufficient control of the transition bandwidth, pass and stop band cutoff frequencies. Therefore, the window function was optimized using a novel multi-objective artificial bee colony (ABC) algorithm based on singular spectrum analysis (SSA) to eliminate these disadvantages of the windowing method. The proposed method was compared to three other multi-objective ABC variants. Novel SSA-based multi-objective approach yielded the best performance among four approaches. The proposed multi-objective approach that uses the SSA method has a significant advantage since it does not require user experience, it is not dependent on parameters, and there is no weight determination problem. Also, it does not have sorting and pooling stages that increase the cost of calculation. The obtained results were compared with the published literature studies. The SSA-based multi-objective approach offered better alternative to other literature techniques in terms of calculating the fitness function that deals with finding the most reasonable solution considering all error terms. Finally, the performance of the designed filter was tested on electroencephalography (EEG) signal. The EEG signal was decomposed successfully into subbands using proposed filter design approach. Based on numerical results of this study, the proposed filter provided the low-pass band and stop band ripple, and high stop band attenuation value of all, while having well enough performance.

The Prism: Recursive FIR Signal Processing for Instrumentation Applications

Abstract: This paper provides the mathematical background for the precise, repeat integral signal monitor (Prism), a signal processing network node used in a variety of sensing and instrumentation applications. The key operation is a double Fourier-style integration, which can be implemented recursively using sliding windows and precisely using Romberg integration. The Prism generates one or two outputs; if two are generated, they are orthogonal, analogous to an analytic signal, from which sinusoid properties, such as frequency, phase, and amplitude, can readily be derived. The Prism outputs are finite impulse response (FIR), but the calculation is recursive, resulting in a low computational cost which is independent of filter length. This paper compares the Prism’s computational efficiency with both a least squares FIR filter design and an equivalent Prism filter implemented as a conventional convolution. The advantages of the Prism include design simplicity, low computational cost, and a linear phase response, making it a useful network node for a wide range of instrumentation and signal processing tasks.

A group-delay-compensation admittance inverter for full-passband self-equalization of linear-phase band-pass filter

Abstract: A group-delay-compensation (GDC) admittance inverter (J-inverter) is proposed for the full-passband self-equalization of the linear phase band-pass filter (BPF) The proposed GDC J-inverter consists of a coupled-line section, two resistors, and two short-circuited lines Its group delay (GD) has two local minima located symmetrically at both sides of the center frequency, which can be used to effectively reduce the GD fluctuation at the edge of the passband for realizing the full-passband self-equalized linear-phase BPF The positions and magnitudes of the GD local minima are controllable by adjusting the characteristic parameters of the coupled lines and the short-circuited lines and the values of the resistors To verify the design concept, a 3-order BPF based on the proposed GDC J-inverter is designed and compared with the BPF based on the traditional J-inverter From the measured results, the GD fluctuation of the proposed BPF within the bandwidth of |S21| > −3 dB and the bandwidth of |S11|

High-Speed and High-Resolution Low-Coherence Interferometric Demodulation Without Phase Jumps

Abstract: This letter reports a high-speed and high-resolution low-coherence interferometric demodulation algorithm without phase jumps. The demodulation algorithm utilizes the restored analytic interference signal and discrete Fourier transform to deduce the Buneman frequency estimation formula and obtain the linear phase. The optical path difference (OPD) is demodulated based on the Buneman frequency estimation and total phase method. Phase jump is eliminated by re-calculating the peak index and phase from the amplitude and phase frequency spectrums when the peak index approximates an integer value. The experimental results verify the phase jumps are eliminated. The proposed demodulation algorithm provides a 0.027-nm cavity length resolution of an extrinsic Fabry-Perot interferometer (EFPI) with 5-kHz demodulation rate and 384 data points number of an optical spectrum. The speed limitation experimental results show the demodulation speed can achieve 300 kHz with 256 data points number of an optical spectrum. The proposed demodulation algorithm is very robust and promising for all kinds of low-coherence interferometers.

Elliptical Ring Antenna Excited by Circular Disc Monopole for UWB Communications

Abstract: This research proposes a compact elliptical ring antenna excited by a circular disc monopole (CDM) for ultra-wideband (UWB) communications. In the study, time- and frequency-domain pulse distortions of the antenna in the transmission mode were characterized by magnitude and phase of the antenna transfer function (Hrad). The results showed that the gain and magnitude of Hrad in the boresight direction are sufficiently flat with linear phase response. The average antenna gain is 3.9 dBi over the UWB spectrum. The antenna also exhibits low pulse distortion with the correlation factors (ρ) of 0.98 and 0.93 for the fifth-order derivative Gaussian pulse and modulated Gaussian pulse with 6 GHz band rejection. The CDM-excited elliptical ring antenna possesses several attractive features, including wide bandwidth, flat gain, compactness, low cost, and low distortion.

Low-Power All-Digital Multiphase DLL Design Using a Scalable Phase-to-Digital Converter

Abstract: This work presents a low-power all-digital approach to multiphase delay locked loop (DLL) design by the use of a scalable phase-to-digital converter (PDC) based on asynchronous sampling. The PDC is used as a linear phase detector (PD) with the ability to measure any phase difference leading to a shorter delay line with less power consumption. Two different approaches for the delay cell implementation are investigated. The digitally controlled shunt-capacitor inverter (SCI) delay cell leads to an extremely small design with the delay line being the only analog component, while the voltage controlled current-starved inverter (CSI) delay cell has a lower power consumption and less jitter. The proposed design procedure of the SCI based DLL allows fast simulation using Verilog based models since no analog low pass filter is required. Using the proposed modeling technique for the PDC, the behavior of the DLL can be estimated based on input clock jitter specifications. The SCI and CSI based multiphase DLL designs are fabricated in a 65nm CMOS process operated from a 1.2V supply. The proposed SCI based DLL occupies only 0.0048mm2 of active area and consumes 2.25mW at 2.5GHz input frequency with a 622.6MHz sample clock. The RMS jitter of the circuit is 1.2 ps and 1.4 ps for the DLL loop and the phase shifter loop, respectively. The RMS jitter is significantly reduced with the CSI based DLL to 0.86 ps and the power consumption of 2.64mW at 4GHz input frequency with a 996.1MHz sample clock provides an improved power efficiency compared to the SCI based DLL. As a trade-off, the area is increased to 0.0085mm2 due to the use of a $\Delta \Sigma $ modulator and an analog low pass filter.

Elements Failure Robust Compensation in 2D Phased Arrays for DOA Estimation With M-ary PSK Signals

Abstract: Constant modulus algorithm (CMA) has been widely used in direction of arrival (DOA) estimation for constant modulus signals. However, CMA fails completely when dealing with array elements failure. In this paper we devise an algorithm to solve CMA fault-tolerance deficiency. The compensation of failed elements in 2D arrays is achieved by a Replace , Replicate , Reconstruct and Remove (4R) algorithm. The 4R-2D-CMA starts by replacing a failed-element signal by the nearest operating array element signal, then, after computing the covariance matrix, the corrupted rows and columns corresponding to failed elements in both elevation and azimuth are replicated from their Centro-symmetric counterparts to correct the covariance distortion. Replication step takes advantage of a special structure of two perpendicular Centro-symmetric arrays producing a Centro-Hermitian matrix. Afterwards, a 2D-CMA algorithm is used for decomposition to produce azimuth and elevation directions matrices. After decomposition, a linear phase correction is used before the covariance matrix is reconstructed. Finally, a second decomposition is used to obtain final DOAs. The number of constant modulus (CM) sources is estimated from a robust spectrogram analysis. Results for an SNR of −3 dB with 11% of elements failure show almost full recovery and hence prove the effectiveness of the novel approach.

Implementation and Performance Comparison of Digital Filter in FPGA

Abstract: This paper describes the design of different variants of Finite Impulse Response (FIR) filters, their implementation in Field Programmable Gate Array (FPGA) and the performance comparison using a hardware platform. The coefficients of filters are expressed in signed integer term to design a synthesizable optimal finite word length digital filter. This paper is focused on the design structure, resource usage and occupied silicon space, needed for implementation in FPGA. Multiple types of digital filters are tested using MATLAB out of which two filter design techniques, Gaussian window filter and Least square linear phase FIR filter are considered for illustration. The designed filters are synthesized and implemented using the HDL code generated by ‘hdl coder’ tool of MATLAB. FIR filter is also realized using pre-implemented Soft-IP Core provided by the FPGA manufacturer. Finally the filters are implemented on a hardware platform and compared to study their real time performance and the resource utilization of FPGA.

Design of a Low-Order FIR Filter for a High-Frequency Square-Wave Voltage Injection Method of the PMLSM Used in Maglev Train

Abstract: In position sensorless control based on a high-frequency pulsating voltage injection method, filters are used to complete the extraction of high-frequency response signals for position observation. A finite impulse response (FIR) filter has the advantages of good stability and linear phase. However, the FIR filter designed by using traditional methods has a high order which will cause a large time delay. This paper proposes a low-order FIR filter design method for a high-frequency signal injection method in the permanent magnet linear synchronous motor. Based on the frequency characteristics of the current signal, the requirement that the FIR filter needs to meet were analyzed. According to the amplitude–frequency characteristic of the FIR filter, these requirements were converted into constraint equations. By solving these equations, the coefficient of the FIR filter could be obtained. The simulation and experiment results showed the effectiveness of this low-order FIR filter.

A Wideband True-Time-Delay Phase Shifter with 100% Fractional Bandwidth Using 28 nm CMOS

Abstract: A fully integrated passive true-time-delay (TTD) phase shifter is presented for a wideband phased array antenna using 28-nm CMOS technology. By using a delay-compensation technique, a linear phase characteristic is achieved within a wide frequency range over 8−24 GHz. A combined bridged-tee network (BTN) delay cell is proposed to accomplish the delay compensation with the most significant bit (MSB) at 29.6 ps and the least significant bit (LSB) at 7.4 ps, which are 45° and 180° at 16 GHz, respectively. The measured insertion loss is in the range of 7.8−12 dB with an RMS gain error less than 1.4 dB from 8 GHz to 24 GHz. In addition, the measured RMS TTD phase and delay errors are less than 1.6 ps and 1.5°, respectively, within 8−24 GHz. The chip size of the proposed TTD phase shifter is 0.48 mm2.

Learning FIR Filter Coefficients from Data for Speech-Music Separation

Abstract: An Finite Impulse Response (FIR) filter is a widely used digital filter technology whose impulse response has a finite duration. An FIR filter is usually favored for many reasons such as easy to design, easy to implement on a variety of system architectures. An FIR filter can be easily designed with a linear phase response and its output is more predictable since it doesn't have feedback components. There are both engineer and mathematical methods for designing an FIR filter so that machine learning doesn't play an important role in the FIR filter design. In this paper, we present an alternative to traditional filter design methods to direct learn the FIR filter coefficients from input data with machine learning algorithm. With the proposed algorithm, we can easily design an FIR filter from the input data mixed with designed all spectrum noise signal. To show the capability of this algorithm, an example application of suppressing background music from speech or vice versa is demonstrated in this paper. Despite that the music and speech have a lot of overlap in their spectrum, the filter designed by our algorithm can successfully suppress music or speech in a mixture of music and speech signals.

Linear Phase Design of Piezoelectric Transducers for Acousto-Optic Dispersion Delay Lines Using Differential Evolution for Matching Circuit Optimization

Abstract: A numerical method for providing linear phase response of bulk acoustic wave (BAW) piezoelectric transducers (PTs) of acousto-optic devices is developed. Our approach is based on the analytic approximation of the phase response of the PT with the matching electrical circuit and optimization with a differential evolution genetic algorithm. Simulations and experiments were performed for two typical BAW excitation schemes: direct and reflective. Variance of the group delay in the specified frequency range was reduced by an order of magnitude for reflective excitation of BAWs.

All-pass-based design of nearly-linear phase IIR low-pass differentiators

Abstract: A new approach to the design of the nearly linear phase infinite impulse response low-pass differentiators using a parallel all-pass structure is discussed in this paper. The magnitude and phase re...

A Low-Power, High-Linearity Wideband 3.25 GS/s Fourth-Order Programmable Analog FIR Filter Using Split-CDAC Coefficient Multipliers

Abstract: This article presents a 3.25 GS/s fourth-order programmable analog finite impulse response (AFIR) filter for flexible discrete time analog signal processing (DT-ASP). For wide application of the proposed AFIR filter, it is designed for full bandwidth utilization up to the Nyquist rate, programmable via the multiplier coefficient set. In this implementation of the FIR function, split-capacitive DACs (split CDACs) are adopted as coefficient multipliers, providing high-linearity over the full frequency range and low power consumption. Individual coefficients are digitally controlled with total 7-bit codes, consisting of 6-bit fractional value, and 1-bit for sign selection. The addition is simply implemented in the current-domain. Noise and effects of the time-interleaved operation are analyzed to understand limitations on the dynamic range. The proposed AFIR filter is implemented in 32-nm SOI CMOS technology; the core area of the circuit is 0.1 mm2. Measurement results demonstrate transfer function configurability over all possible low pass filter (LPF), bandpass filter (BPF), and high pass filter (HPF) linear phase coefficient sets. The AFIR filter achieves > 11-dBm third-order input intercept point (IIP3) over the full frequency range with a 0.9-V supply. The maximum power consumption is 10.6 mW.

Design of narrow transition band variable bandwidth digital filter

Abstract: This study presents a novel implementation technique for linear phase variable bandwidth finite impulse response (FIR) filters with a noticeable reduction in transition bandwidth as well as hardware complexity. In this proposition, concept of Farrow structure based design technique is effectively utilised; whereas the fixed sub-filters are constructed from a generalised interpolated bandpass method based low-pass FIR filter by means of different techniques such as interpolation, up-sampling and masking. Simulation results have shown the frequency response characteristics of several variable bandwidth FIR filters, designed with the help of the proposed architecture. Simulation results have shown a drastic reduction of transition bandwidth resulting from the proposed variable bandwidth FIR filters of up to ∼70–80%, when compared with other state-of-the-art filtering techniques, with a significant reduction in hardware complexity of up to ∼50%.

Group Delay of Fractional n+α-Order Bessel Filters

Abstract: In this paper we present the realization of fractional-order analog filter with Bessel approximation, having linear phase response, which is also usually represented by a constant group delay. There are many applications such as analogue video signal processing, radar and sonar receivers, hard disk drive read channel applications, analog front end of biomedical signal processing, where linear phase response is desirable. Optimally designed Bessel filter can provide better transient response in the passband, it reduces overshoot, ringing and provides minimal phase distortion. In this work we research Bessel approximation with the non-integer order $\mathrm{n}+\alpha;\mathrm{n}$ is integer number and $0\lt\alpha\lt1$. The influence of non-integer filter order to the value of the constant group delay of the filter is presented. It is shown that the group delay value can be additionally tuned by changing the parameter α.

Analysis and Design of Reflectarray Antennas Based on Delay Lines: A Filter Perspective

Abstract: The analysis and design of reflectarray (RA) antennas based in delay lines is introduced for the first time from a filter perspective. To this purpose, each unit-cell of the RA is considered as a network composed of two ports, one being the delay line and the other one the free-space. This approach allows to borrow the coupling matrix formalism from filter theory and apply it to design unit-cells exhibiting broadband operation together with very sharp frequency responses. The concept is demonstrated with the aid of planar printed unit-cells coupled to substrate integrated waveguides (SIWs) through slots, a configuration that offers significant advantages to shape its frequency response while providing relatively low loss. With the aim of validation, a third order filter structure integrated in SIW-based unit-cells has been experimentally tested using the waveguide simulator technique, at a center frequency of 9 GHz. Measurements demonstrate a high-quality linear phase variation and range, and large frequency selectivity together with broadband response for the element of about 18%. The experimental results show the feasibility of this approach for the design of broadband reflectarray antennas exhibiting sharp gain responses. To illustrate the concept, a medium size reflectarray has been theoretically designed using the proposed unit cell at 9 GHz, showing a directive beam with 35.8 dB gain, sharp gain selectivity over 18 dB, and confirms the wide band operation with 20.3% bandwidth for a 3 dB gain variation.