Chia-Chan Chang

Design of a Beam Switching/Steering Butler Matrix for Phased Array System

A compact broadband 8-way Butler matrix integrated with tunable phase shifters is proposed to provide full beam switching/steering capability. The newly designed multilayer stripline Butler matrix exhibits an average insertion loss of 1.1 dB with amplitude variation less than ±2.2 dB and an average phase imbalance of less than 20.7° from 1.6 GHz to 2.8 GHz. The circuit size is only 160 × 100 mm2, which corresponds to an 85% size reduction compared with a comparable conventional microstrip 8-way Butler matrix. The stripline tunable phase shifter is designed based on the asymmetric reflection-type configuration, where a Chebyshev matching network is utilized to convert the port impedance from 50 ¿ to 25 ¿ so that a phase tuning range in excess of 120° can be obtained from 1.6 GHz to 2.8 GHz. To demonstrate the beam switching/steering functionality, the proposed tunable Butler matrix is applied to a 1 × 8 antenna array system. The measured radiation patterns show that the beam can be fully steered within a spatial range of 108°.

Design of a Reflection-Type Phase Shifter With Wide Relative Phase Shift and Constant Insertion Loss

reflection-type phase shifter with constant insertion loss over a wide relative phase-shift range is presented. This important feature is attributed to the salient integration of an impedance-transforming quadrature coupler with equalized series-resonated varactors. The impedance-transforming quadrature coupler is used to increase the maximal relative phase shift for a given varactor with a limited capacitance range. When the phase is tuned, the typical large insertion-loss variation of the phase shifter due to the varactor parasitic effect is minimized by shunting the series-resonated varactor with a resistor Rp. A set of closed-form equations for predicting the relative phase shift, insertion loss, and insertion-loss variation with respect to the quadrature coupler and varactor parameters is derived. Three phase shifters were implemented with a silicon varactor of a restricted capacitance range of Cv,min = 1.4 pF and Cv,max = 8 pF, wherein the parasitic resistance is close to 2 Omega. The measured insertion-loss variation is 0.1 dB over the relative phase-shift tuning range of 237deg at 2 GHz and the return losses are better than 20 dB, excellently agreeing with the theoretical and simulated results.

2.45-GHz CMOS Reflection-Type Phase-Shifter MMICs With Minimal Loss Variation Over Quadrants of Phase-Shift Range

CMOS reflection-type phase shifters with minimal insertion-loss variation over quadrants of phase-shift range are presented. Two performance enhancement techniques are proposed. First, the 3-dB quadrature hybrid is designed with a phase-compensated inductively coupled hybrid. Second, an impedance-transformed pi-resonated varactor network is presented to provide a full 360deg phase range, using a MOSFET varactor with limited reactance variation range. The design considerations and simulation are described. Two experimental 2.45-GHz phase shifters were implemented in 0.18-mum CMOS technology. One has a measured phase-shift range of 120deg with the insertion loss of 5.6 plusmn 1.2 dB in 2.33-2.60 GHz and the other has a phase range larger than 340deg with the insertion loss of 10.6 plusmn 2 dB in 2.44-2.55 GHz. Both chips are extremely compact with sizes of 0.72 and 0.66 mm2, respectively, and consume zero dc power.

Design of Stepped-Impedance Combline Bandpass Filters With Symmetric Insertion-Loss Response and Wide Stopband Range

An enhanced stepped-impedance combline bandpass filter employs an array of stepped-impedance resonators with tapped-transformer coupling at input and output is presented in this study. This filter has enhanced performance, including symmetric insertion-loss response around the passband and wider stopband range. The structure is compact and suitable for multilayer realization because it is free of lumped capacitors and has fewer via-hole grounds. The circuit is investigated with the characteristic mode theory of coupled lines to prove the existence of multiple transmission zeros around the passband. Numerous diagrams are given for circuit design purposes. The second- and fourth-order bandpass filters at 2.45 GHz were designed, measured, and compared with the conventional combline structure to demonstrate their performance enhancement.

Novel Design of a 2.5-GHz Fully Integrated CMOS Butler Matrix for Smart-Antenna Systems

This paper presents a novel design of monolithic 2.5-GHz 4times4 Butler matrix in 0.18-mum CMOS technology. To achieve a full integration of smart antenna system monolithically, the proposed Butler matrix is designed with the phase-compensated transformer-based quadrature couplers and reflection-type phase shifters. The measurements show an accurate phase distribution of 45plusmn3deg, 135 plusmn 4deg, -45 plusmn 3deg, and -135 plusmn 4deg with amplitude imbalance less than 1.5 dB. The antenna beamforming capability is also demonstrated by integrating the Butler matrix with a 1 X 4 monopole antenna array. The generated beams are pointing to -45deg, -15deg, 15deg, and 45deg, respectively, with less than 1deg error, which agree very well with the predictions. This Butler matrix consumes no dc power and only occupies the chip area of 1.36 times 1.47 mm2. To our knowledge, this is the first demonstration of the single-chip Butler matrix in CMOS technology.

A 24-GHz CMOS Butler Matrix MMIC for multi-beam smart antenna systems

A 24-GHz 4-way Butler matrix MMIC in 0.18-mum CMOS technology is presented. The multi-layer structure of CMOS process is utilized to monolithically realize the bulky Butler matrix on silicon substrate. Particularly, the multi-layer bifilar transformer is introduced to miniaturize the circuit and reduce the signal loss. The implemented CMOS Butler matrix MMIC only occupies a chip area of 0.41 mm2 (excluding I/O pads). The experimental results show that insertion losses are 2.2plusmn0.6 dB from 23 to 25 GHz and the phase errors are within 6deg. Therefore, by connecting this Butler matrix to a linear array antenna, four orthogonal beams, pointing to -49deg, -15deg, 15deg, and 49deg, respectively, are generated within 0.3deg error.

Magnetocaloric effect in Fe–Zr–B–M (M=Mn, Cr, and Co) amorphous systems

The magnetocaloric effect (MCE) of the amorphous Fe–Zr–B–M (M=Mn, Cr, and Co) ribbons has been investigated. The MCEs of the Fe90−xZr10Bx (x=5, 10, 15, and 20) ribbons are enhanced with small amounts of boron addition. Furthermore, the Curie temperature of the specimens can be decreased to be about room temperature with appropriate Mn and Cr substitutions, but the MCE performance of the specimens drops only slightly. It is also found that the magnetic entropy change of the Co-substitution series of Fe85−yZr10B5Coy ribbons almost remains constant although the Curie temperature is increased to be about 400K for y=5. Therefore, for the application of MCE refrigeration at above room temperature, the Fe85−yZr10B5Coy ribbons are preferred due to the constant MCE and the high refrigeration capacity of about 90J∕kg at the magnetic field change of 10kOe. Moreover, the field dependence of the magnetic entropy change exhibits power dependence for all the studied specimens. In the ferromagnetic range, the exponent is...

A 25-GHz Compact Low-Power Phased-Array Receiver With Continuous Beam Steering in CMOS Technology

A compact low-power phased array receiver with continuous beam steering is presented based on the subsector beam steering technique. The entire beam steering range is divided into five subsectors from four characteristic beams of the Butler matrix. In each subsector the receive beam is steered by weighted combination of the received signals from array antennas. The theory of beam steering is detailed and the relationship of the steered angle with the beam steering factors is derived. The proposed architecture has lower circuit complexity and less power consumption because no challenging CMOS 360° variable phase shifters and multi-phase voltage-controlled oscillators are required. The phased array MMIC implemented in 0.13 μm CMOS technology has 17-21 dB receiving gain and 8.9-10.7 dB noise figure in 25-26 GHz. It consumes lower than 30 mW and takes a small chip area of 1.43 mm2. The continuous beam steering is demonstrated over the spatial range from -90° to +90°.

A fast clutter cancellation method in quadrature doppler radar for noncontact vital signal detection

A fast clutter cancellation technique is proposed for quadrature Doppler radar to robustly detect the vital signals when clutters enter the test environment. The dc offset at baseband varies with the change of test environment, dramatically reducing the accuracy of vital signal detection. To solve this problem, a clutter cancellation generator is employed in the radar receiver. Based on the detected dc offset values in I and Q channels, the generator produces an output signal, anti-phase to the received clutter signal, such that the clutter signal is cancelled at RF frontend. Therefore the time-varying dc offset at baseband is eliminated. The clutter cancellation method is described and the experiment was conducted to demonstrate the proposed method.

A 24-GHz full-360° CMOS reflection-type phase shifter MMIC with low loss-variation

A 24-GHz bi-directional CMOS reflection-type phase shifter (RTPS) with full 360deg phase tuning range and minimal insertion-loss variation is presented. Two circuit enhancement techniques are employed: the broadside-coupled transformer-based hybrid and the pi-type resonated varactor load. The implemented 0.18-mum CMOS RTPS demonstrates a measured phase shift range of 360deg with small insertion-loss variation of plusmn1.2 dB at 24 GHz. The chip is 0.33 mm2 in area and it consumes zero DC power.