A lumped component programmable delay element for Ultra-Wideband beamforming

Design of Lumped-Component Programmable Delay Elements for Ultra-Wideband Beamforming

Abstract: We introduce a ladder filter-based programmable time-delay element for beamforming in ultra-wideband (UWB) systems. Such a lumped-element realization becomes possible by approximating e -std as a ratio of polynomials (based on Taylor and Pade expansions). When compared with conventional methods based on the tapped delay-line architecture, the proposed technique achieves lower power dissipation, higher delay range and resolution, and better area efficiency. A prototype delay line designed for the 3.1-10.6 GHz UWB range achieves a delay range of 140 ps and a gain range of -30 dB to +10 dB. Fabricated in a 0.25 μm SiGe BiCMOS process, the delay element occupies an active area of 1 mm 2 and consumes 53 mW from a 2.5 V supply. A four-antenna beamforming system using the delay element can achieve a scanning range of ±61 ° with 0.86 ° resolution for an antenna spacing of 15 mm.

2-D-IIR Time-Delay-Sum Linear Aperture Arrays

Abstract: A uniform linear array (ULA) digital beamformer with enhanced selectivity (interference rejection) over conventional true-time delay-sum (TTDS) beamforming is proposed for scanned aperture applications. Conventional TTDS transfer function, which contains only zero-manifolds, is modified by introducing complex pole-manifolds based on 2-D infinite impulse response (IIR) digital beam filters, thereby achieving enhanced selectivity for the same number of antennas in the ULA. For a ULA of 64 antennas, desired direction of arrival (DOA) 30° and interference DOA -60° from array broadside, a relative improvement in signal-to-interference ratio (SIR) of 7 dB is verified. For 128-element ULA, interference DOA -10°, a relative improvement in SIR of 5-10 dB is obtained for the desired DOA in the range 10°-90°. The projected improvements are independent of the weights of the conventional phased-array, TTDS, or filter-sum beamformer used because the method does not change the zero-manifolds of the original array pattern.

Characterization of Indoor Channels with Directional Antennas and Performance Evaluation

Abstract: Recently UWB beamforming attracts significant research attention to obtain spatial gain in the form of antenna array. It is commonly believed that directional antenna based communication could improve the system performance. In order to further make clear the relationship between system performance and the antenna radiation pattern, UWB indoor channels extracted from practical measurements are combined with circular horn antenna to characterize the channel properties and to evaluate the system performance. The direction related channel parameters like angle of departure (AOD) and angle of arrival (AOA) are obtained by SAGE algorithm from the measurement results. Using directional antenna with a certain half power beamwidth (HPBW), the channel delay will decrease because the multipath components the receiver could collect are reduced. In the line of sight (LOS) environments, the channel capacity increases with the beamwidth decreasing and is always larger than that of an omnidirectional antenna. Similarly, the bit-error-rate (BER) performance of RAKE receiver is improved with the beamwidth becoming smaller. However in the non-line of sight (NLOS) environments, the conclusions are not so simple. The capacity and BER performance are not always better with directional antennas. And the variation trend between the system performance and the antenna beamwidth disappears. This is mainly because that there exist no dominant strong path components like in the LOS environments. This reminds us that when antenna beamforming is used to obtain array gain, the beamwidth should be carefully designed to obtain optimal performance, especially in the NLOS environments.

Indoor channel measurements and capacity evaluation with directional antennas

Abstract: Recently UWB beamforming attracts significant research attention to obtain spatial gain in the form of antenna array. It is commonly believed that directional antenna based communication could improve the system performance. In order to further make clear the relationship between system performance and the antenna radiation pattern, UWB indoor channels extracted from practical measurements with omnidirectional antenna are combined with circular horn antenna to evaluate the channel capacity. In the line of sight (LOS) environments, the channel capacity increases with the antenna beamwidth decreasing and is always larger than that of omnidirectional antenna. However in the non-line of sight (NLOS) environments, the capacity is not always better with directional antenna. And the change consistency between the capacity and the antenna beamwidth disappears. This reminds us that when antenna beamforming is used to obtain array gain, the beamwidth should be carefully designed to obtain optimal performance, especially in the NLOS environments.

An Integrated Ultra-Wideband Timed Array Receiver in 0.13 $\mu{\hbox{m}}$ CMOS Using a Path-Sharing True Time Delay Architecture

Abstract: A fully integrated CMOS ultra-wideband 4-channel timed array receiver for high-resolution imaging application is presented. A path-sharing true time delay architecture is implemented to reduce the chip area for integrated circuits. The true time delay resolution is 15 ps and the maximum delay is 225 ps. The receiver provides 11 scan angles with almost 9 degrees of spatial resolution for an antenna spacing of 3 cm. The design bandwidth is from 1 to 15 GHz corresponding to less than 1 cm depth resolution in free space. The chip is implemented in 0.13 mum CMOS with eight metal layers, and the chip size is 3.1 mm by 3.2 mm. Measurement results for the standalone CMOS chip as well as the integrated planar antenna array and the CMOS chip are reported.

Silicon-Based Ultra-Wideband Beam-Forming

Abstract: Ultra-wideband (UWB) beam-forming, a special class of multiple-antenna systems, allows for high azimuth and depth resolutions in ranging and imaging applications. This paper reports a fully integrated UWB beam-former featuring controllable true time delay and power gain. Several system and circuit level parameters and characterization methods influencing the design and testing of UWB beam-formers are discussed. A UWB beam-former prototype for imaging applications has been fabricated with the potential to yield 20 mm of range resolution and a 7deg angular resolution from a four-element array with 10 mm element spacing. The UWB beam-former accomplishes a 4-bit delay variation for a total of 64 ps of achievable group delay with a 4-ps resolution, a 5-dB gain variation in 1-dB steps, and a worst case -3-dB gain bandwidth of 13 GHz. Overall operation is achieved by the integration of a 3-bit tapped delay trombone-type structure with a 4-ps variable delay resolution, a 1-bit, 32-ps fixed delay coplanar-type structure, and a variable-gain distributed amplifier. The prototype chip fabricated in a 0.18 mum BiCMOS SiGe process occupies 1.6 mm2 of silicon area and consumes 87.5 mW from a 2.5-V supply at the maximum gain setting of 10 dB

Efficient Scalable Modeling of Double- $\pi$ Equivalent Circuit for On-Chip Spiral Inductors

Abstract: This paper presents an efficient technique to generate a scalable double-pi circuit model for spiral inductors. The double-pi equivalent circuit is widely used to build an inductor library because of its high accuracy over a wide frequency range. However, direct parameter extraction for the double-pi model and scalable fitting for each parameter are complicated due to the large number of circuit elements. The proposed method performs a scalable modeling using a relatively simple single-pi model and converts the model to the double-pi model according to the physics-based conversion algorithm. For this purpose, physical relations between the single-pi and double-pi equivalent circuits for a spiral inductor have been derived. The proposed technique is verified by developing a scalable inductor library using 0.13-mum CMOS technology.

Power and Area-Efficient Adaptive Equalization at Microwave Frequencies

Abstract: We present a low power analog adaptive equalization technique suitable for combating inter-symbol-interference at very high data rates. The proposed technique, which we term the lumped parameter equalizer, addresses several of the problems associated with conventional microwave equalizers based on the tapped delay line structure. The theory is given, and simulation results comparing it with the performance of ideal tapped delay line filters are shown. Circuit implementations are discussed, along with the effect of nonidealities on equalizer performance.