Image Rejection Capability Research Articles

Stimulated Brillouin Scattering Based Image-Reject Microwave Signal Harmonic Down-Converter

We propose and demonstrate a photonic microwave signal harmonic down-converter with image rejection capability via stimulated Brillouin scattering (SBS). A dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM) is driven by a radio frequency/image (RF/IM) signal and a local oscillation (LO) signal to realize equivalent phase modulation and 4th-order double sideband modulation respectively. The optical carriers from the two arms of the DP-DPMZM can cancel out each other after polarization combining, thereby increasing the useful optical signal power in photodetection. Since the beating notes between the IM-modulated signals and LO-modulated 4th-order sidebands interfere destructively, the down-converted IM signals disappear naturally, which makes the down-converted image parts be suppressed in optical domain. By using an SBS-based dual-band microwave photonic filter to suppress the RF modulated -1st-order sideband and amplify the +1st-order sideband, destructive interference can be broken. Therefore, the RF signal over frequency range of 21-28 GHz can be down-converted to intermediate frequency (IF) band, and the image rejection ratio (IRR) can be also improved to more than 55 dB. Under -160 dBm/Hz noise floor, the SFDR is 105.1 dB·Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> .

Secrecy Performance of Full-Duplex Jamming and Reception Under I/Q Imbalance

Investigating the physical layer security performance of full-duplex (FD) radio transceivers has been the subject of numerous research studies. However, self-interference cancellation that enables full exploitation of FD communications is a crucial aspect that deserves special attention. Hence, in this paper, we analyze the effect of a FD transceiver's in-phase and quadrature imbalance (IQI) on simultaneously jamming the receiver of an eavesdropper and detecting a signal of interest by deriving an expression for the secrecy outage probability (SOP) metric. Through further analysis for some special and limiting cases, performance insights are drawn by showing that the SOP is dependent on the image rejection capability of the FD transceiver and is approximately equal to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\frac{3}{\text{IRR}}(\ln {(\text{IRR})} - 1.83)$</tex-math></inline-formula> , where the IRR is the image-rejection ratio. The accuracy of the derived SOP expression is verified through Monte-Carlo simulations.

Photonic Image Rejection Mixer Based on Polarization Manipulation of a Broadband Optical Source

We propose a photonic mixer with image rejection capability using a broadband optical source (BOS) and polarization processing. Intermediate frequency (IF) signals with image rejection are generated from the local oscillator-modulated and the time-delayed radio frequency (RF)-modulated BOS light. The RF operating frequency is flexibly tunable over a wide range by simply adjusting the time delay. In addition, the proposed system is free from dispersion-induced mixing power fading and bias drift problem. Experimental results exhibit an image rejection ratio of more than 44.6 dB for RF signals from 2 to 18 GHz, while the IF signal is fixed at 800 MHz. Image rejection mixing operation at different IF frequencies and signal power is also confirmed.

A 43–97-GHz Mixer-First Front-End With Quadrature Input Matching and On-Chip Image Rejection

This article presents a wideband millimeter-wave (mmWave) receiver front-end that covers the frequency range from 43 to 97 GHz, supporting the operation in the major parts of the V-, E-, and W-bands. The front-end incorporates a passive mixer-first topology to achieve high linearity and wideband performance. The front-end adopts I/Q generation at the RF port, using a coupled-line coupler (CLC), rather than at the local oscillator (LO) port to mitigate the crosstalk of the overlapping I/Q LO signals especially present at high frequencies. The CLC at the RF input facilitates ultrawide band input matching. The front-end implements the multi-gate gm3 cancellation technique at the IF amplifiers to preserve the linearity and provide gain at the IF section. Image rejection capabilities using a current mode transformer-based IF 90° coupler are implemented on chip and demonstrated with measurements. The front-end prototype is fabricated on the GlobalFoundries 22-nm FD-SOI CMOS process and it demonstrates an ultra-wideband performance across the frequency range 43-97 GHz (2.25:1 bandwidth) with image rejection of up to 32 dB, IIP3 of 1.6-5.2 dBm, and gain of 15 dB. The implementation used is low-IF topology with 3.8-GHz IF frequency and 1-GHz bandwidth. Furthermore, the measurement results show that the front-end supports high-speed modulated signals of up to 6-Gbps 64QAM modulation data.

A Dual-Band Transformer-Coupled Notch Filter Mixer for 2.45-/5.2-GHz WLAN Application

This paper presents a dual-band down-conversion mixer with image rejection feature using transformer-coupled notch filter for 2.45-/5.2-GHz WLAN application. A single center-tapped transformer is integrated to form two differential series inductor–capacitor (LC) resonators as a filter circuit to create attenuation at the image frequencies in eliminating the signal distortion caused by the image signals. Furthermore, an NMOS cross-coupled pair was adopted in the notch filter to improve the image rejection capability due to the presence of negative resistance. Simulated on a standard 130nm CMOS process, the proposed transformer-coupled notch filter mixer achieves a conversion gain of 15.3/10.7 dB, input-referred third-order interception point (IIP3) of − 6.8/− 2.0 dBm and a noise figure of 8.8/14.8 dB for an input RF of 2.45/5.2 GHz with an IF of 500 MHz. The notch filter mixer consumes 5.5 mW of power from a supply voltage of 1.2 V.

Photonic-assisted image rejection mixer based on Hilbert transform in the optical domain using a phase-shifted fiber Bragg grating

A photonic-assisted image rejection mixer is proposed based on Hilbert transform in the optical domain using a phase-shifted fiber Bragg grating (PS-FBG). The image signal and the desired RF signal are converted to the optical domain by carrier-suppressed single-sideband modulation, which is then split into two parts. One part is Hilbert transformed by a specially designed PS-FBG and a 90-deg optical phase shifter and then combined with the other part to directly reject the image signal in the optical domain. The image-free optical signal is downconverted to an intermediate frequency signal by combining it with an optical local oscillator signal and then detecting them in a photodetector. The image rejection capability of the system is analyzed, and an image rejection ratio of 68.0 or 58.6 dB is achieved when the bandwidth of the image signal is 20 or 60 MHz, respectively, while having an acceptable influence on the desired RF signal. Quadrature phase-shift keying (QPSK) signals, 8 phase-shift keying (8PSK) signals, and 16 quadrature amplitude modulation (16-QAM) signals are used to evaluate the image rejection performance. When the bandwidth of the image signal is 18.75 MHz, the error vector magnitudes of the downconverted QPSK, 8PSK, and 16-QAM signals with the same power, modulation format, and bandwidth are 2.5%, 2.5%, and 2.6%, respectively.

Wideband microwave electro-optic image rejection mixer.

We present an electro-optic downconverting mixer with image rejection capabilities. By using a dual-drive Mach-Zehnder modulator (DD-MZM) to modulate an optical carrier with both a signal and a local oscillator, and an asymmetric Mach-Zehnder interferometer (AMZI) to filter the optical spectrum into two separate ports, we generate photocurrents with a phase relationship controlled via direct current (DC) bias voltage applied to the DD-MZM. By choosing these photocurrents to be in quadrature and combining them in a 90-degree electrical hybrid we achieve over 40dB of image rejection, with a 3dB bandwidth of approximately 20GHz limited mainly by the AMZI free spectral range. We demonstrate downconversion of a 1 Gbaud quadrature phase-shift keyed (QPSK) signal even in the presence of a strong interfering image tone.

Radio-Frequency Impairments Compensation in Ultra High-Throughput Satellite Systems

The quest for massive satellite throughput is relentless, motivating the transmission of broadband signals at multiple Giga-Baud rates. Building low-cost, low-complexity user terminals is essential. These competing drivers conspire to cause analog radio-frequency (RF) components to exceed their tolerance limits. Specifically, analog mixers, anti-aliasing filters and amplification in quadrature frequency-conversion architectures create direct-current (DC) offset and in-phase/quadrature (I/Q) imbalance that is strong and frequency-selective. This paper provides two characterization models of analog RF impairments when the frequency offset is present. Novel digital compensation algorithms with immunity to frequency offset are presented, categorized into equalization with image-rejection capability and image cancellation. Adaptive techniques are utilized that operate without a priori knowledge of RF impairments. Two optimization methods are proposed for the multicarrier scenarios that are useful when using known data samples for factory calibration or in decision-directed mode during field re-calibration. Special consideration is given to estimating the frequency offset during initial factory calibration. Extensive computer simulations reveal that the proposed compensators are robust to frequency offset, provide lossless attenuation of imbalance-induced image and remove DC offset, under numerous scenarios. Cases include when the desired carrier is plagued by image interference from more than one source and on-board high-power amplifier is operated near saturation.

High Conversion Efficiency Photonic Microwave Mixer With Image Rejection Capability

A new photonic microwave image rejection mixer that can achieve high conversion efficiency and has a wide bandwidth is presented. It is based on an integrated dual-parallel Mach–Zehnder modulator (MZM) with a 90° polarization rotator on one branch of the modulator. The two modulators connected in parallel are biased at the minimum transmission point to generate two sets of orthogonally polarized radio frequency (RF) and local oscillator (LO) modulation sidebands with the optical carrier being suppressed. Suppressing the optical carrier enables high RF and LO modulation sidebands to be detected by a photodiode without saturation. The LO modulation index is also designed to obtain a high conversion efficiency mixing operation. Experimental results demonstrate frequency downconversion with an image rejection function and a high conversion efficiency of > $-$ 5 dB over a wide 3 to 20 GHz frequency range. A technique for compensating the effect of coupler amplitude and phase imbalance to obtain a high image rejection ratio is also experimentally demonstrated.

Compensation of Delay Mismatch in a Direct Conversion Transmitter

This brief analyzes the effects of the delay mismatch (DM) between in-phase (I) and quadrature (Q) branches of a direct conversion transmitter (DCT) on its image rejection capability. An iterative technique is proposed to compensate for the DM, based on the instantaneous power measurement of the DCT output signal. It is shown that the proposed compensation technique can obtain the true DM value even when the I/Q impairment exists in the DCT. Simulation results show that the proposed technique can effectively compensate for the DM, thereby improving the DCT performance.

A 2.45/5.2 GHz Image Rejection Mixer With New Dual-Band Active Notch Filter

A 2.45/5.2 GHz dual-band Gilbert downconversion mixer with image rejection function is presented, which is implemented using the 0.18 mum CMOS technology. The proposed differential dual-band image rejection circuitry is employed for the 2.45/5.2 GHz WLAN application to effectively diminish the DC power consumption and complexity of circuit design compared to the traditional Hartley or Weaver architectures. Moreover, the cross-connected pair consisted of NMOS and PMOS transistors in the proposed notch filter will further ameliorate the image rejection capability. The IC prototype achieves conversion gain of 10.5/11 dB, IIP3 of -4.9/-5.2 dBm for RF = 2.45/5.2 GHz and IF = 500 MHz while the image rejection ratio is better than 36/45 dB in the whole operation bandwidth.

A Blind $I/Q$ Imbalance Compensation Technique for Direct-Conversion Digital Radio Transceivers

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Although the quadrature mixing radio front-end offers an attractive way to perform frequency translation, its image-rejection capability is severely affected by the gain and phase imbalances (<formula formulatype="inline"><tex Notation="TeX"> $I/Q$</tex></formula> imbalances) between its two analog signal paths. Digital signal processing techniques have widely been proposed to compensate for these mixer imperfections. Of these techniques, the class of blind compensation techniques seems very attractive since no test signals are required. This paper presents a novel <formula formulatype="inline"><tex Notation="TeX">$I/Q$</tex></formula> imbalance extraction technique that uses a Cholesky decomposition of the received signal's covariance matrix to extract the exact imbalances of the front-end. An analysis is also presented on extracting and separating the imbalances of a cascaded imbalanced modulator and demodulator. Both a block-based and an adaptive variant of the technique are proposed, and a performance evaluation over multipath channels is presented. </para>

Image frequency suppression in frequency-scanned direction-of-arrival estimation systems

A novel signal processing approach to the problem of image frequency suppression in wide-band frequency-scanned radio frequency (RF) receiving arrays that employ digital signal processing (DSP) techniques to estimate the direction of arrival (DOA) of incoming radiation has been presented. The conventional approach to image rejection in RF receivers is to employ a front-end RF tuner before downconversion to the intermediate frequency. As DOA processing employs a separate receiver channel for each array element, an RF tuner would be needed behind each element. Clearly for scanned systems at microwave frequencies, this is not a viable option where the tuners would generally have to be implemented in RF hardware. The need for RF tuners can be eliminated by downconversion down to baseband and employing I&Q mixers, which provide an intrinsic image rejection capability. Unfortunately, such a solution requires two analog-to-digital (A/D) converters per array element. An alternative approach is to use image rejection mixers in which case only one A/D converter per array element is needed. The approach also requires only one A/D per array element but achieves the image rejection through a DSP implementation. As a result, use of relatively expensive image rejection mixers is avoided without sacrificing performance. Experimental results are presented that validate the theoretical predictions.