Ultra-wideband Radio Frequency Research Articles

RF MEMS on the radar

This article gives an overview of applications of radio frequency (RF) microelectromechanical system (MEMS) technology in radio detection and ranging (radar). RF MEMS components for radar include attenuators, limiters, (true-time-delay) phase shifters, transmit/receive (T/R) switches and tunable matching networks. Radar subsystems that benefit from RF MEMS technology include active electronically scanned arrays (T/R modules), passive electronically scanned arrays (lenses, reflect arrays, subarrays, and switched beamformers), and radomes. Using a bottom-up approach, the figures of merit for RF MEMS technology are related to the figures of merit for radar subsystems. The article also discusses ultrawideband RF MEMS reflect array and T/R module design as examples. First, electronically scanned array, radar and RF MEMS fundamentals are briefly introduced.

A Systolic Array 2-D IIR Broadband RF Beamformer

A systolic architecture is proposed for the real-time implementation of broadband 2-D IIR beam filters having applications in ultra-wideband (UWB) radio frequency (RF) antenna arrays. Real-time throughputs of one-frame-per-clock-cycle are achieved. A finite-difference time-domain computational electromagnetic model of a typical indoor propagation environment is used to illustrate that the method significantly reduces the bit error rate of the simulated communication system in the presence of multi-user interference, thereby demonstrating the potential application of the architecture in RF communications.

Low-Capacitance and Fast Turn-on SCR for RF ESD Protection

With the smaller layout area and parasitic capacitance under the same electrostatic discharge (ESD) robustness, silicon-controlled rectifier (SCR) has been used as an effective on-chip ESD protection device in radio-frequency (RF) IC. In this paper, SCR's with the waffle layout structures are studied to minimize the parasitic capacitance and the variation of the parasitic capacitance within ultra-wide band (UWB) frequencies. With the reduced parasitic capacitance and capacitance variation, the degradation on UWB RF circuit performance can be minimized. Besides, the fast turn-on design on the low-capacitance SCR without increasing the I/O loading capacitance is investigated and applied to an UWB RF power amplifier (PA). The PA co-designed with SCR in the waffle layout structure has been fabricated. Before ESD stress, the RF performances of the ESD-protected PA are as well as that of the unprotected PA. After ESD stress, the unprotected PA is seriously degraded, whereas the ESD-protected PA still keeps the performances well.

Phase-Only Matched Filtering of Ultrawideband Arbitrary Microwave Waveforms via Optical Pulse Shaping

We demonstrate compression of ultrawideband (UWB) microwave arbitrary waveforms via phase-only matched filtering implemented in a programmable hyperfine resolution optical pulse shaper. We synthesize spread-time UWB electrical waveforms and utilize programmable microwave photonic phase filters to impose the opposite of a waveform's spectral phase on its spectrum. This enables us to compress an UWB microwave waveform to its corresponding bandwidth-limited pulse duration via phase filtering. As an example, we present compression of a linear frequency-modulated electrical waveform with > 15 GHz frequency content with almost 200% fractional bandwidth with ~ 733 ps temporal window to a 40-ps duration pulse with more than 14-dB gain in peak power. Our technique is programmable and we believe it is applicable to a wide range of arbitrary spectral phase modulated UWB radio frequency (RF) waveforms.

Dual-Antenna RF CMOS Front-End for Interferer Removal in Ultra-Wideband Systems

Many ultra-wideband (UWB) systems are challenged by strong jammers and narrowband interferers. Using two antennas, we demonstrate a robust UWB radio frequency (RF) front-end design in a 0.25 μm mixed-signal complementary metal oxide semiconductor (CMOS) technology. The proposed realization is capable of adaptively removing a high-power, narrowband interferer early in the receiver chain avoiding front-end saturation and preserving UWB signal power. The early interferer removal resulting in interferer-free demodulation is based on the least mean squares (LMS) algorithm and achieved through a novel combiner low-noise amplifier and noise optimized filtering. Circuit level RF simulations of the proposed circuitry indicate a maximum improvement in signal-to-interference ratio of 39.6 dB.

Joint scale-lag diversity in wideband mobile direct sequence spread spectrum systems

We consider the effect of mobility on a wideband direct sequence spread spectrum (DSSS) communication system, and study a scale-lag Rake receiver capable of leveraging the diversity that results from mobility. A wideband signal has a large bandwidth-to-center frequency ratio, such that the typical narrowband Doppler spread assumptions do not apply to mobile channels. Instead, we assume a more general temporal scaling phenomenon, i.e., a dilation of the transmitted signal's time support. Based on a uniform ring of scatterers model, we determine that the wideband scattering function, which quantifies the average scale spreading, has a "bathtub-shaped" scale profile. We compare the performances of a scale-lag Rake and a frequency-lag Rake, each capable of leveraging the diversity that results from mobility. Such analysis applies, for example, to ultra-wideband (UWB) radio frequency channels and underwater wideband acoustic channels.

Filter-free ultrawideband generation based on semiconductor optical amplifier nonlinearities

A filter-free scheme for ultrawideband (UWB) generation with single semiconductor optical amplifier (SOA) is proposed and demonstrated. A pair of polarity-reversed optical pulses is generated due to cross gain modulation (XGM) in the pump-probe scheme, whereas the amplified pump pulse becomes sharp at its leading edge such that the power peak is shifted forward. Hence, the combination of the pump and probe signals at the SOA output is quasi-monocycle shape. Our scheme is an improved scheme to avoid exploiting optical filters and time-delay devices. The generated UWB radio frequency spectrum shows good stability when the input probe power varies from −10 dBm to 6 dBm, the probe wavelength varies in the whole C-band, and the bias current varies from 100 mA to 240 mA. Although the generated quasi-monocycle deviates from a standard Gauss monocycle to some extent, the frequency spectrum conforms to the UWB regulation. Two SOAs with different XGM dynamics are compared in generating UWB signals.

A WiMedia UWB Transceiver for 4-HD Channel Streaming

Ultra-wideband (UWB) systems use wide band-width of 3.1 to 10.6 GHz to provide ultra high data-rate for wireless applications. Implementation of UWB RF transceiver in the 3-5 GHz band (mandatory mode) makes big challenges that must be solved by circuit and system techniques. The proposed radio frequency (RF) transceiver, which is implemented in 0.13 mum complementary metal-oxide semiconductor (CMOS) technology, is a part of a three-chip solution, but later it will be one chip solution which includes RF, modulation and demodulation (modem), and medium access controller (MAC). The proposed WiMedia RF transceiver system can transmit and receive 4- high-definition (HD) channel streaming simultaneously.

Petaloid antenna for passive UWB-RFID tags

An ultra-wideband (UWB) antenna designed with a petal-shaped structure is presented. Its measured impedance bandwidth of 10 dB return loss is from 6.6 to 17.5 GHz whereas the size is just 18×16 mm. The radar cross-section and scattered waveforms of the proposed petaloid antenna are theoretically studied using the finite-difference time-domain (FDTD) method. Its backscattering of antenna mode is comparable to that of structural mode, and the scattering pattern is almost omnidirectional. This antenna is suitable for passive ultra-wideband radio-frequency identification (UWB-RFID) tag applications.

Design and analysis of an ultrawide-band distributed CMOS mixer

This paper presents the design and analysis of a novel distributed CMOS mixer for ultrawide-band (UWB) receivers. To achieve the UWB RF frequency range required for the UWB communications, the proposed mixer incorporates artificial inductance-capacitance (LC) delay lines in radio frequency (RF), local oscillator (LO), and intermediate frequency signal paths, and single-balanced mixer cells that are distributed along these LC circuits. Closed-form analytical model for the conversion gain of the mixer is presented. Furthermore, a comprehensive noise analysis of the proposed distributed mixer is carried out, which includes calculation of the mixer noise figure (NF) and derivation of the optimum number of stages, n, minimizing the NF. The designed mixer is capable of covering the RF and LO frequencies over a wide range of frequencies from 3.1-8.72 GHz. A two-stage distributed mixer has been fabricated in a 0.18-/spl mu/m CMOS process. Experiments show a conversion gain of more than 2.5 dB for the entire range of the frequencies. The dc power consumption is 10.4 mW.