Narrow Instantaneous Bandwidth Research Articles

HRR profile estimation using SLIM

In this study, authors address high-range-resolution (HRR) profile reconstruction, when stepped-frequency waveforms are eventually used to maintain a narrow instantaneous bandwidth, resorting to the sparse learning via iterative minimisation (SLIM) paradigm, a regularised minimisation approach with an -norm constraint (for ), providing a variant to the original method. Particularly, the proposed method resorts to the regularised maximum-likelihood estimation paradigm including a term promoting the sparsity of the profile and related to the -norm of the vector containing the scatterers’ reflectivities. A priori information on the interference power level is also accounted for, at the design stage, and, assuming that each range cell under test contains at most one scatterer, the actual active scatterers composing the target are determined by exploiting the Bayesian information criterion (BIC). BIC is also used to automatically select the optimised q , so as to make the procedure adaptive with respect to q . Once the location of the active scatterers has been determined, a least-squares approach is also used to obtain even more precise HRR reconstruction. Furthermore, an efficient algorithm to define optimised frequency hopping patterns, in the presence of a continuous and coordinated feedback between the transmitter and receiver, is presented and assessed. The carried out analysis shows that the SLIM-based procedure presents higher accuracy in the HRR profile recovery than other widely used techniques, i.e. the iterative adaptive approach (IAA). Moreover, results demonstrate that the target range profile estimation capabilities are enhanced, both for SLIM and IAA, when the cognitive paradigm is employed.

Two-dimensional sparse synthetic aperture radar imaging method with stepped-frequency waveform

Stepped-frequency waveforms (SFWs) can use the digital signal processing method to obtain high-range resolution with relatively narrow instantaneous bandwidth, which has been used in synthetic aperture radar (SAR). However, SFWs have the disadvantages of poor antijamming capability and a long period of transmission. Also, in the coherent integration time, some echo data are frequently lost. A two-dimensional sparse imaging method in the space and frequency domains for SAR is proposed based on compressed sensing (CS) theory. A sparse SFW for SAR imaging is formed and analyzed first, which has the advantages of better antijamming capability and a shorter time period of transmission. The range compression is completed by using CS theory. As to the sparse echo data in the space domain, the imaging operator and the CS-based imaging scheme are constructed to simultaneously implement the range cell migration correction and azimuth compression. Compared with the conventional SAR imaging method of SFWs, a much smaller number of frequencies and a smaller amount of imaging data are required for SAR imaging by using the proposed method. Finally, the effectiveness of the proposed method is proven by simulation and experimental results.

Versatile 20 GHz wideband RF digitizer for test and measurement

Wireless device manufacturers are challenged with the test and measurement of ever-evolving complex signals while at the same time contending with shrinking test equipment budgets. For example, modern wireless signals can have bandwidths up to 80 MHz and can vary in operating frequency and amplitude over time. In contrast, affordable spectrum analyzers typically have narrow (up to 10 MHz) instantaneous bandwidth (IBW). This makes analyzing a time-varying wideband signal that is greater than 10 MHz in bandwidth with such narrowband instrumentation require a sweep over several frequency bands. This can yield erroneous measurement results.

Widely Tunable High-Efficiency Power Amplifier With Ultra-Narrow Instantaneous Bandwidth

This paper reports the first power amplifier (PA) that simultaneously achieves a very narrow instantaneous bandwidth (2%) while being tunable over a 38.5% frequency range (2.1-3.1 GHz) with a measured 50%-60% efficiency in the entire band. Such PAs are in great demand for realizing all-digital burst-mode transmitters that are expected to become critical for the future generation of wireless communication systems. Unlike state-of-the-art planar PAs that cannot simultaneously achieve a narrow bandwidth and high efficiency, the presented PA employs a widely tunable high-Q (Q >; 300 over the tuning range) cavity resonator as the output matching network. Furthermore, the tunable multiband matching is performed for both the fundamental frequency and the second harmonic to ensure a high efficiency. The measured PA is implemented with a Cree GaN transistor, and it delivers an output power of ≥ 36 dBm at a gain of ≥ 10 dB. Two-tone testing is further conducted, indicating a good linearity of this PA with an output third-order intercept point greater than 48 dBm over the entire band. This design demonstrates, for the first time, that multiband burst-mode transmitters can be potentially built with widely tunable high-efficiency narrowband PAs.

A Mixed-Signal Matching State Search Based Adaptive Antenna Tuning IC

A closed-loop adaptive antenna tuning unit operating from 850 MHz-2 GHz for multi-band, multi-mode radios is presented. Unlike previous approaches, the proposed module utilizes an analog mismatch detector and a closed-loop mixed-signal matching state search circuit, without the need for an A/D converter. The integrated module is designed and fabricated on a 0.18 CMOS process. When tested on a band-limited shorted patch antenna, the module can perform a scan of 4096 antenna matching states in 4.1 ms, and tune the antenna to a specified narrow instantaneous bandwidth over the entire frequency range.

Eliminating ghost images in high-range resolution profiles for stepped-frequency train of linear frequency modulation pulses

In modern radar systems, using stepped-frequency pulse train is an effective approach to achieve high-range resolution (HRR) with narrow instantaneous bandwidth and low system complexity. However, if the parameters of stepped-frequency (SF) radar (such as single pulse bandwidth, frequency step size and sampling instant) are not prudently designed, ‘ghost image’ phenomenon (also called range ambiguity in some literature) will corrupt the synthetic HRR profiles. The relationship between parameters of the SF radar and the ghost images is provided analytically. A new synthetic range profiling algorithm is developed to generate HRR profiles without ghost images by using the least-squares (LS) estimation. For targets with negligible radial velocities, the new LS profiling algorithm can eliminate the ghost images successfully, and introduces less signal-to-noise ratio loss. With this algorithm, the restriction on the frequency step size is less rigid than the traditional unambiguous criterion. Consequently, a higher range resolution could be obtained. Simulations and field experimental results are also presented.

Electronically Tunable Antenna Pair and Novel RF Front-End Architecture for Software-Defined Radios

This paper proposes a novel RF front-end architecture for software-defined radios (SDRs) based on an electronically tunable antenna pair controlled by an antenna control unit (ACU) consisting of field effect transistor (FET) switches and a field programmable gate array (FPGA). The fundamental gain-bandwidth limitations of electrically small antennas prevent a small antenna from having high efficiency and wide bandwidth simultaneously. In the age of miniaturization, especially in the wireless communication industries, a promising solution to this limitation is to introduce reconfigurable antennas that can be tuned electronically to different frequency bands with both high efficiency and narrow instantaneous bandwidth. This reconfigurable antenna technology not only simplifies current RF front-end architectures, but can be reprogrammed on demand to transmit and receive RF signals in any desired frequency band. This novel RF front-end architecture implemented by a reconfigurable antenna pair can help realize SDRs.

Classification of nonstationary narrowband signals using segmented chirp features and hidden Gauss-Markov models

A method is provided for classifying finite-duration signals with narrow instantaneous bandwidth and dynamic instantaneous frequency (IF). In this method, events are partitioned into nonoverlapping segments, and each segment is modeled as a linear chirp, forming a piecewise-linear IF model. The start frequency, chirp rate, signal energy, and noise energy are estimated in each segment. The resulting sequences of frequency and rate features for each event are classified by evaluating their likelihood under the probability density function (PDF) corresponding to each narrowband class hypothesis. The class-conditional PDFs are approximated using continuous-state hidden Gauss-Markov models (HGMMs), whose parameters are estimated from labeled training data. Previous HGMM algorithms are extended by dynamically weighting the output covariance matrix by the ratio of the estimated signal and noise energies from each segment. This covariance weighting discounts spurious features from segments with low signal-to-noise ratio (SNR), making the algorithm more robust in the presence of dynamic noise levels and fading signals. The classification algorithm is applied in a simulated three-class cross-validation experiment, for which the algorithm exhibits percent correct classification greater than 97% as low as -7 dB SNR.

S-band reflection type variable attenuator

A reflection type variable attenuator is described in this letter. The main component of the circuit is a microstrip 3 dB quadrature coupler. The coupler is used in conjunction with two varactor diodes to vary the attenuation from 2.2 dB to 17 dB over a 40% bandwidth (2.8-4.2 GHz). If married with a programmable voltage controller, the proposed design will provide a low-cost solution for applications with narrow instantaneous bandwidth.