Amplitude Imbalance Research Articles

Research on IQ Imbalance Error of Orthogonal Alternating Sampling

In the signal acquisition of complete orthogonal frequency alternating acquisition system, we need to transform the broadband input signal to baseband through analogue orthogonal demodulation. Thus, the IQ imbalance errors will inevitably exist, including amplitude imbalance error and phase imbalance error, resulting in distortion deterioration of reconstruction signals. This paper makes an in‐depth study on such IQ imbalance errors and mathematically deduces the mathematical expressions of imbalance errors and the spurious frequency distribution caused by them, which shows that the positions where the spurious signals appear are closely related to the frequency of input signal and the tuning frequency of analogue quadrature demodulation. Meanwhile, the amplitude and phase imbalance parameters of the channels I and Q are also calculated. Finally, the spurious effects caused by imbalance errors are verified by simulation experiment, and the verification results are consistent with the theoretical derivation results.

A Simple Optimization Method for Generating High-Purity Amplitude and Phase Modulation

We present a simple method for the adjustment of an in-phase (I) and quadrature-phase (Q) Armstrong-type modulator for use as a calibrator in precision noise metrology. The availability of relatively pure levels of both amplitude modulation (AM) and phase modulation (PM) can greatly simplify the optimal alignment and calibration of metrology equipment such as AM and PM noise measurement systems. The phase and amplitude imbalance of the components that constitute an IQ modulator results in an undesired combination of AM and PM. These impairments must be corrected to generate the pure signals required for metrology. Our proposed method corrects for these non-ideal impairments without needing a calibrated IQ demodulator and offers a high-purity AM/PM signal with spurious modulations as low as 1 ppm. We present the calibration procedure and uncertainty analysis of such a modulator when used as a calibrator for a PM and AM noise measurement system.

Compact wideband and harmonic suppressed quadrature coupler using susceptance loaded coupled lines

AbstractIn the paper, a novel type of quadrature coupler with the features of wideband, arbitrary harmonic suppression and small size is proposed, for the first time, by employing susceptance loaded coupled lines. Design equations are derived using the even‐odd mode decomposition analysis. The discussions on arbitrary couplings and harmonic suppressions are also investigated. For demonstration, a prototype with a second harmonic suppression was fabricated and measured. The overall size is 0.19λg × 0.27λg, which is smaller than most of the reported wideband quadrature couplers. Measurement results show that the fractional bandwidth of 40% is obtained under the condition of 15‐dB return loss/isolation, 1‐dB amplitude imbalance, and 90° ± 5° phase difference. The proposed coupler can be a good candidate for wideband applications without using the multi‐cascading and complex miniaturization method.

Highly Miniaturized Dual-band Power Divider based on HMSIW for 5G/ WLAN Applications

A highly compact dual-band power divider (PD) based on the HMSIW structure is investigated in this paper. The dual-band operation is achieved by incorporating an inner modified circular complementary split-ring resonator (MC-CSRR) and outer circular CSRR on the top metal layer of HMSIW. The operating frequency of the PD decreases due to evanescent mode propagation. This assists in miniaturizing the structure apart from the 50% size reduction offered by the HMSIW. By asymmetric placement of two output ports of a PD, it is possible to achieve an unequal PD with an arbitrary power division ratio. To exhibit the proposed idea, two dual-band PD prototypes, one with equal power division and the other with unequal power division are designed, fabricated and experimentally verified. The PD occupies a compact size of 0.128 λg× 0.122 λg, where λg being the guided wavelength at the first operating frequency. The proposed PD with advantages of lower insertion loss, better return loss, minimum amplitude and phase imbalance between the output ports is beneficial for 5G FR1 n78 (3.3- 3.8 GHz) and WLAN (5.17 GHz) communications.

Compact wideband Wilkinson power divider on GaAs integrated passive device technology

In this article, a novel topology of wideband on-chip Wilkinson power divider (WPD) with good insertion loss (IL) performance is proposed and demonstrated on gallium arsenide (GaAs)-based integrated passive device (IPD) technology. The proposed WPD is further analyzed by the even and odd method. To verify the advantage of the proposed WPD against the conventional one, two examples are numerically investigated, showing that the proposed one achieves better performance in terms of IL and isolation. In addition, the proposed design achieves a miniature area and small amplitude and phase imbalance (AI) performance. The fractional bandwidth (FBW) of the proposed WPD is 100% (6-18 GHz), where the magnitude imbalance is less than 0.08 dB and phase imbalance is better than 0.4°. Furthermore, the minimum IL is better than 0.96 dB and return loss is better than 13.7 dB within the core passband. Meanwhile, the isolation of the WPD is better than 17.6 dB. Finally, to further demonstrate our design conception, the proposed WPD has been fabricated on GaAs IPD technology with size of 1.5 × 0.9 mm2, and measured by on-wafer probing. All the simulated and measured results of the proposed WPD are matched reasonably well with each other, thus firmly validating the claimed superior performance of the proposed WPD in the wide operating bandwidth, low IL, and high isolation.

A New Miniaturized Broadband Multiway and Polyphase Differential Phase Shifter on Single-Layer PCB Substrate

A new technique to realize miniaturized broadband multiway and polyphase differential phase shifters is proposed and studied in this article. In contrast to existing designs based on coupled-line and loaded stubs, the multiway phase dispersions are controlled by susceptances of multiple resonant tanks in this work, which can well enlarge the operation bandwidth (BW) and avoid the unachievable physical sizes in strip width and coupling gap over a large phase shift range on the universal reference line topology. In addition, its phase-shift range can be highly extended by properly allocating resonant frequencies of resonant tanks in each path to be specified different values. The theoretical analysis and design formula are studied, and the synthesis method is presented to determine all circuit parameters. By virtue of the quasi-lumped element technology, the proposed multiway phase shifter can be flexibly implemented on a single-layer printed circuit board (PCB) substrate with a very compact size. For demonstration, a five-way differential phase shifter in 0°-180° range has been designed, fabricated, and tested. Over a BW of 80.4%, the achieved phase shifts are 45° ± 4°, 90° ± 5°, 135° ± 5°, and 180° ± 6.3° with low insertion loss (IL) (<1.05 dB) and small amplitude imbalance (<0.29 dB). To the best of our knowledge, this is the tested widest multiway differential phase shifter in the 0°-180° range up until now. Meanwhile, the whole circuit size, including the substrate, is less than 0.30 $λ_{{g}} $ x $0.26λ_{{g}}$ .

Multi-octave linearized RF/photonic link based on orthogonal modulation and optimized demodulation.

In this Letter, we propose and demonstrate a multi-octave linearized analog radio-frequency (RF)/photonic link with orthogonal modulation and optimized demodulation. In our proposed link, the DC-reserved (DCR) digital method is utilized in a parallel Mach-Zehnder-modulator scheme to greatly improve the tolerance to the in-phase/quadrature amplitude imbalance and Q-path DC error, which inevitably exist during digital processing. The fault tolerance and transmission performance of the link are theoretically analyzed and experimentally verified. Compared with the traditional digital-signal-processing method, higher signal-to-distortion ratios can be achieved by the DCR method when the amplitude imbalance and DC errors are considered. As a result, the SFDR2 and SFDR3 (spurious-free dynamic ranges) of our system are measured to be 103.74dB⋅Hz1/2 and 116.31dB⋅Hz2/3, respectively. Furthermore, the linearization of the link is demonstrated by testing the RF signals with various frequencies, which proves the potential in broadband applications.

Dynamic Dispersion-Compensation for Wideband Microwave Photonic Notch Filter With High Rejection and High-Resolution

Interference-based microwave photonic notch filters (MPNFs) provide large rejection through destructive interference of radio frequency signals generated by beating a carrier with the upper and lower modulation sidebands. The two modulation sidebands are designed to have an amplitude imbalance and phase shift of π between them. In many schemes, large rejection is achieved at the desired radio frequency by balancing the amplitudes of the modulation sidebands using stimulated Brillouin scattering (SBS) based gain or loss. However, the combined dispersion of the Brillouin active medium and other components detunes the phase difference between the sidebands away from π, which causes a reduction in the notch depth. Dynamic dispersion control is, therefore, desirable for compensating dispersion-induced notch depth reduction. Here, we report dispersion-compensation exploiting bias-dependent phase of the modulation sidebands of a z-cut intensity modulator. We demonstrate a high-resolution ( ~ 50 MHz) MPNF with a large rejection of $>$65 dB over 1-25 GHz. To demonstrate the applicability of our MPNF in the presence of radio frequency interference, we suppress an interferer by 49 dB without affecting the signal. Such dispersion-compensated MPNFs are of importance in the sphere of Industry 4.0 based applications such as frequency measurement.

Design of a 3.7 GHz, 1 kW CW hybrid radial power divider for LHCD system of SST-1 Tokamak

This paper presents a novel design of an 8-way radial power divider/combiner that exhibits low insertion loss and minimum phase imbalance. The proposed design is realized using combined features of resonant and non-resonant based power dividing/combining structures to reap the benefits of both kinds of designs. The multi-layered power divider is designed to operate at a frequency of 3.7 GHz for possible use in Lower Hybrid systems for fusion applications. The structure is simulated using COMSOL Multiphysics to evaluate its RF and thermal performance. Simulation results indicate that the proposed power divider exhibited an amplitude and phase imbalance of ±0.05 dB and ±0.1° respectively between the peripheral ports. The computed return loss for the input port of the power divider is around 56 dB while the insertion loss is approximately 0.24 dB. Coupled RF-thermal simulation results indicate the capability of this design to handle continuous wave (CW) power of up to 1 kW. The proposed device is intended to be narrowband and would be used in the 1 kW solid state RF source under development at the authors’ institute.

Transceiver Imbalances Compensation and Monitoring by Receiver DSP

In-phase and quadrature (IQ) imbalances in optical transceiver, such as amplitude imbalance, phase imbalance, and IQ skew, can cause serious system performance degradation, especially when high order modulation formats are used. In this work, we present a method to isolate and separately monitor these various impairments from received signals by coherent digital signal processing (DSP). Receiver amplitude and phase imbalances could be compensated and monitored by Gram-Schmidt orthogonalization procedure (GSOP) and receiver skew could be compensated and monitored by a 4 x 4 or 4 x 2 multiple-input and multiple-output (MIMO) equalizer. Transmitter imperfections compensation and monitoring take place behind the residual frequency offset compensation and carrier phase recovery by a 4 x 4 MIMO equalizer based on minimal mean square error (MMSE) criterion. By these methods, we analyze and investigate the interaction of transceiver's impairments impact on each monitor numerically. After that, we conduct an experiment to verify the feasibility of the proposed method. All of these results show that each monitor could operate very robust even when multiple co-exist.

Synthesis of miniaturized filtering coupled‐line trans‐directional coupler with wide suppression band

In this paper, the synthesis of miniaturized filtering coupled-line trans-directional (CL-TRD) coupler with wide suppression band is presented. This coupler is formed by two parallel coupled lines, one capacitor-loaded coupled line, and four sub-circuits. With the introduction of the sub-circuits, extra transmission poles located at the cut-off frequency are generated, resulting in high frequency selectivity. Size reduction is also achieved. Design equations of the filtering CL-TRD coupler are derived using the even-odd mode decomposition analysis and design procedures are provided for guidance. For demonstration, a 3 dB prototype with a size of 0.46 λg × 0.21 λg is designed, fabricated and measured. The measured results validate the 32% bandwidth centered at 1 GHz with more than 10 dB return loss/isolation, less than 0.5 dB amplitude imbalance and 5° phase error. Besides, a 15 dB wide stopband from 1.18 to 5.07 GHz (5.07f0) is obtained with a sharped skirt selectivity.

Fast Alignment Algorithm for Autocalibration in Digital Monopulse Radars

Calibration is important for digital monopulse radars since the target tracking performance would be degraded by the amplitude and phase imbalance among channels. However, the alignment between the radar to be calibrated and the test probe is a challenge, especially for antennas with high gain and narrow beamwidth. In this letter, we propose a fast alignment algorithm for the autocalibration of digital monopulse radars using the gradient ascent method based on the tentative radiation pattern gradient model. We verify the feasibility and the high efficiency of the proposed algorithm by simulations and an experiment of a W-band digital monopulse radar. The elapsed time of the proposed algorithm is 0.01 <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">%</b> of the existing method and requires lower equipment complexity compared with the scanning-based method.

A novel design of compact broadband 4 × 4 Butler matrix-based beamforming antenna array for C-Band applications

In this paper, a compact broadband 4 × 4 Butler matrix (BM) as a feeding network for antenna array is presented and studied. The broadband performance of the BM occurs when it operates in the almost equal difference of phases and coupling throughout the operating band. The different components of the proposed design such as branch-line coupler, crossover, and Schiffman line phase shifter are designed and optimized to be low loss and wideband. The total size of the BM is 37 mm × 47 mm, equal to 0.64λ0 × 0.81λ0 in design frequency at 5.2 GHz. The measurement bandwidth for fabricated structure on the FR4 substrate is 24 % achieved from return loss lower than −10 dB. The beam directions are measured at −15, −43.2, +43, and +15° at 5.2 GHz for each input port 1–4 excitation respectively with the gain value of 10.2 ± 0.2 dB and sidelobe levels of −8.2 ± 1.2 dB. The Final BM exposures phase errors of 3 ± 1.7° with the amplitude imbalance of less than ±1 dB over the operational band.

Ring-Shaped D-Band E-Plane Filtering Coupler

This letter presents a ring-shaped E-plane filtering coupler working at 150 GHz with high performance. The coupler is based on cavity resonators. Unlike the conventional ones, the four resonators in this coupler are all bent along their length direction and connected end to end, forming a closed circle. By adjusting the radius of the circle, three of the resonators work on TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> mode while the other is on TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">102</sub> mode. The coupler can be split through E-plane and the measured response of the coupler has an excellent agreement with the simulation, with a low amplitude imbalance of 0.31 dB, insertion loss of 0.12-0.46 dB, and over 20-dB return loss and isolation.

Design and analysis of low-insertion-loss G-band CMOS four-way Wilkinson power dividers and dual balun

We present the design and analysis of G-band CMOS Wilkinson power dividers and dual balun for G-band communication and imaging systems. Miniature spiral and U-shaped four-way Wilkinson power dividers, which are based on three two-way Wilkinson power dividers, are designed and implemented. Miniature spiral dual balun, which is equivalent to an upper balun and a lower balun in parallel, is also designed and implemented for comparison. These devices are planar and symmetrical, and their main structure is implemented by the 2.34-µm-thick topmost metal to minimize the resistive loss. This leads to low insertion loss, and small amplitude imbalance (AI) magnitude and phase difference (PD) deviation. For instance, the spiral four-way Wilkinson power divider occupies 0.033 mm2 chip area and achieves S11 of − 11.4 dB, S21 of − 6.271 dB, S31 of − 6.445 dB, S41 of − 6.676 dB, and S51 of − 6.111 dB at 180 GHz, one of the smallest chip areas and lowest insertion losses for four-way power dividers with similar operation frequency. The corresponding AI magnitude and PD deviation are 0.565 dB and 3.2°, respectively. Moreover, the spiral dual balun occupies 0.026 mm2 chip area and achieves S11 of − 10.6 dB, S21 of − 7.549 dB, S31 of − 7.1 dB, S41 of − 7.598 dB, and S51 of − 7.352 dB at 180 GHz. The corresponding AI magnitude and PD deviation are 0.498 dB and 5.7°, respectively. The prominent results of the spiral and U-shaped four-way Wilkinson power dividers, and the spiral dual balun indicate that they are suitable for power division/combination in G-band systems.

Compact and broadband directional coupler for high power applications

A compact, flat coupling, and broadband directional coupler are presented for high-power applications in the frequency band of 100 ∼ 1000 MHz. The coupler is mainly composed of two compact semi-flexible coaxial cables with the length of the λ 0/4 (λ 0 is the free-space wavelength at the frequency of 850 MHz), four chip ceramic capacitors, and two air wound inductors that can tune the coupling coefficient. The phase inverter of the coupler is well designed and experimentally validated. The directional coupler exhibits high performance in the whole operation frequency band with low insertion loss (less than 0.3 dB), high directivity (more than 18 dB), and high power (up to 300 W). The amplitude imbalance of the coupling coefficient is less than 0.3 dB. The measured results exhibit good consistency with the theoretical analysis. And the proposed design method can be readily extended to other low-cost, high-power, and broadband directional couplers.

Millimeter-Wave Wideband Waveguide Power Divider With Improved Isolation Between Output Ports

We present a novel compact wideband waveguide T-junction power divider, especially suited for millimeter-wave and THz frequencies. It incorporates substrate-based elements into a waveguide structure to provide the output port's isolation and matching. The internal port is introduced at the apex of the T-junction formed as an E-probe on a substrate. This facilitates efficient coupling of the reflected energy from the output port to a novel thin-film-based resistive termination integrated with the E-probe onto the same substrate and fabricated by means of thin-film technology. A power divider was designed, simulated, and fabricated for the frequency band 150–220 GHz to experimentally verify the theoretical and simulated performance. The results showed excellent agreement between the simulations and measurements with the devices demonstrating a remarkable return loss of 20 dB for both the input and output ports for a three-port device with equal split and isolation better than 17 dB between the output ports. Furthermore, the measured insertion loss is less than 0.3 dB and the amplitude and phase imbalance are 0.15 dB and 0°, respectively. Moreover, the divider's remarkable tolerance to the dimensions and sheet resistance of the resistive material of the built-in absorbing load makes the device a very practical component for millimeter-wave and THz systems, in particular radio-astronomy receivers.

Calibrating the Amplitude and Phase Imbalances in AgileDARN HF Radar

AbstractThe Agile Dual Auroral Radar Network (AgileDARN) radar has been developed as an all‐digital high‐frequency (HF) coherent scatter radar. Based on phased array antenna and digital signal processing techniques, digital beam forming (DBF) is employed for both transmission and reception, which steers toward the desired direction based on the relative phases within the array elements. However, the amplitude and phase imbalances among channels will lead to substantial degradation of DBF performance, including the beam direction deviation, broadening of the main lobe, deteriorated side lobes, antenna gain degradation, and ultimately affects the radar detection accuracy. Here, we present a complete method for calibrating these imbalances in transceivers and linear array elements in AgileDARN radar: internal calibration and external calibration. During the internal calibration, the calibration signals with the same amplitude and phase as the multi‐pulse sequence are sent to all transceivers internally. The variance of the outputs illustrates the transceivers' imbalances and can be processed to implement calibration. Further, the meteor echoes and linear least squares fitting method are employed for external calibration, which calibrates the amplitude and phase imbalances among the cables and phased array elements. The technique has been successfully implemented, and we present the results of measured data observed by the AgileDARN HF radar before and after calibration.

Compact wideband Wilkinson power divider on gallium arsenide‐based integrated passive device technology

In this article, a novel topology of wideband on-chip Wilkinson power divider (WPD) with good insertion loss (IL) performance is proposed and demonstrated on gallium arsenide (GaAs)-based integrated passive device (IPD) technology. The proposed WPD is further analyzed by the even and odd method. To verify the advantage of the proposed WPD against the conventional one, two examples are numerically investigated, showing that the proposed one achieves better performance in terms of IL and isolation. In addition, the proposed design achieves a miniature area and small amplitude and phase imbalance (AI) performance. The fractional bandwidth (FBW) of the proposed WPD is 100% (6-18 GHz), where the magnitude imbalance is less than 0.08 dB and phase imbalance is better than 0.4°. Furthermore, the minimum IL is better than 0.96 dB and return loss is better than 13.7 dB within the core passband. Meanwhile, the isolation of the WPD is better than 17.6 dB. Finally, to further demonstrate our design conception, the proposed WPD has been fabricated on GaAs IPD technology with size of 1.5 × 0.9 mm2, and measured by on-wafer probing. All the simulated and measured results of the proposed WPD are matched reasonably well with each other, thus firmly validating the claimed superior performance of the proposed WPD in the wide operating bandwidth, low IL, and high isolation.

Wideband microwave Doppler frequency shift measurement based on acousto-optic frequency shift and DP-QPSK receiver

Microwave Doppler frequency shift (DFS) measurement is one of the backbone parts in modern radar systems. In this paper, a simple and novel optical approach to implement broadband microwave DFS measurement is proposed. Two carrier-suppressed single-sideband modulation (CS-SSB) modules, which are constituted by two Mach Zehnder modulators (MZMs) and two optical band pass filters (OBPFs) are employed for modulating both transmitted signal and echo signal. Due to the frequency shift by an acousto-optic modulator (AOM), the proposed method converts the DFS signals to the intermediate-frequency (IF) domain for simultaneous estimation of DFS value and direction, which helps to avoid low-frequency interference. Moreover, an integrated dual-polarization quadrature phase shift keying (DP-QPSK) receiver is used to obtain the in-phase and quadrature (I/Q) DFS terms and improve the system stability. In the experiment, the microwave DFS is estimated with a clear direction and a maximum measurement error of 4.9 Hz over an ultra-wide operation frequency from 10 to 40 GHz. The micro-Doppler frequency shift (mDFS) measurement is also carried out to demonstrate the advantage of low-frequency DFS measurement. Excellent system stability is also observed in the experiment, where the corresponding I/Q amplitude and phase imbalance are maintained lower than 2.5 dB and 4.8 degrees during 60 min.