Spherical retrodirective array

This paper derives the characteristics of a spherically-shaped retrodirective space array. The array can receive an incoming signal over4pisteradians, amplify, frequency translate, and modulate this signal, and then return it in the direction of the incident wave. The directivity of the array for every angle of incidence corresponds to the area illuminated by the incoming wave. In the array the retrodirective characteristic is obtained by a phase inversion technique that is realized in tunnel-diode image frequency converters. A circular cross section of the spherically-shaped retrodirective array is analyzed. The analysis is extended to the spherically-shaped array. It is shown that the effective aperture of a spherical array is smaller than the illuminated area. This reduction occurs because of a tapered amplitude distribution and a symmetrical phase error proportional to the frequency difference between incident wave and reradiated wave at the image frequency. The output spectrum of the converters in the array contains not only the image frequency signal but additional frequency components as well. Because of the phase characteristics of the spectral components, only the image frequency signal when reradiated by the array elements will add coherently in direction of the incident wave. The reradiation of the other frequency components is not collimated.     

An active integrated retrodirective transponder for remoteinformation retrieval-on-demand

A retrodirective transponder based on a novel compact phase-conjugating mixer with conversion gain has been developed. The active circuit uses one port for both incoming and outgoing signals, enabling a reduction of circuit size, and the balanced structure provides suppression of undesired signals. By using a modulated local oscillator, the circuit can modulate the received signal in order to retransmit local information to the remote site. A microstrip antenna is integrated with the phase conjugator and the whole system was fabricated on a single substrate, enabling a one-card system. A four-element prototype array with 0.5λ₀ array spacing demonstrated excellent measured retrodirectivity. Additionally, a simplified binary-phase-shift-keying signal transmitted by the array is recovered successfully at the source location, demonstrating great potential for remote tagging and wireless sensor applications     

New 5.8-GHz circularly polarized retrodirective rectenna arrays for wireless power transmission

This paper proposes two new circularly polarized retrodirective rectenna arrays, including a 2 /spl times/ 2 array and a 4 /spl times/ 4 array. A proximity-coupled microstrip ring antenna is used as the retrodirective rectenna array element, which can automatically block harmonic signals up to the third order from reradiating by the rectifying circuit. These arrays are printed on a Rogers Duroid 5880 substrate of /spl epsiv//sub r/=2.2 with a two-layer structure, with a total thickness of 1.5748 mm (or 62 mil). The new retrodirective rectenna array can track the incoming power source signals automatically and is less sensitive to the power incident angle variations, i.e., main-beam alignment deviation. It can provide a nearly constant dc output voltage within /spl plusmn/10/spl deg/ and 90% dc output voltage within /spl plusmn/45/spl deg/. The conversion efficiencies of the two arrays are 73.3% and 55%, respectively, when the power density is 10 mW/cm/sup 2/. The retrodirective rectenna array can be used in the low-power density applications for microwave wireless power transmissions.     

Digital wireless sensor server using an adaptive smart-antenna/retrodirective array

A wireless sensor server is developed based on a reconfigurable active smart-antenna/retrodirective array. The system can serve as both a retrodirective array transponder and a smart-antenna receiver simply by changing the frequency of the local oscillator applied to the mixers, enabling it to utilize its hardware best to suit its communication environment. When operating as a direct-conversion receiver, the receiver array successfully demodulates a quaternary phase-shift keying (QPSK) modulated signal with circuit gain of 7 dB, and E/sub b//N/sub 0/ for BER=10/sup -4/ is approximately 12 dB without any error correction. In the retrodirective array mode, the system provides 20 dB circuit gain and 20 dB radio-frequency/intermediate-frequency isolation at the center frequency as well as phase conjugation, exhibiting excellent retrodirectivity. The mixers perform phase conjugation and modulation simultaneously, enabling the transmission of locally stored data. The local data is successfully extracted by an interrogator.     

2D phase-conjugated retrodirective array with information carrying capability

A new two-dimensional (2D) phase-conjugated retrodirective array with star-shaped antenna elements is proposed. The phase conjugators provide high isolation of -48 dB between RF and IF ports when RF/IF signals share the same ports in a balanced hybrid. By on-off keying modulation of the local oscillator (LO), the new 2D phase-conjugated retrodirective array can reflect the signal back to the interrogator with the modulation signal carried on it for information exchange. Experimental results show that this array can achieve 2D retrodirectivity within 120deg angle of wide scan range at arbitrary signal polarisation and injection direction     

Dual-polarization frequency-modulated laser source

Diode-pumped 1.3-/spl mu/m as well as 1.06-/spl mu/m Nd:YAG lasers have been operated with two orthogonally polarized modes at slightly different frequencies. The frequency difference, controlled by an intracavity electrooptic crystal, may be modulated. Thus, two polarized-outputs are obtained; one at a constant frequency, and the other frequency-modulated. This is a novel source for frequency-modulated heterodyne detection systems where the reference (local oscillator) frequency originates from the signal laser itself and is automatically locked to it.     

A 1.5-V direct digital synthesizer with tunable delta-sigma modulator in 0.13-/spl mu/m CMOS

In direct digital synthesizer (DDS) applications, the drawback of the conventional delta sigma (/spl Delta//spl Sigma/) modulator structure is that its signal band is fixed. In the new architecture presented in this paper, the signal band of the /spl Delta//spl Sigma/ modulator is tuned according to the DDS output frequency. We use a hardware-efficient phase-to-sine amplitude converter in the DDS that approximates the first quadrant of the sine function with 16 equal-length piecewise second-degree polynomial segments. The DDS is capable of frequency, phase, and quadrature amplitude modulation. The die area of the chip is 2.02 mm/sup 2/ (0.13 /spl mu/m CMOS technology). The total power consumption is 138 mW at 1.5 V with an output frequency of 63.33 MHz at a clock frequency of 200 MHz (D/A converter full-scale output current: 11.5 mA).     

A 16-element two-dimensional active self-steering array using self-oscillating mixers

A 16-element two-dimensional (2-D) retrodirective array using self-oscillating mixers (SOMs) is presented. SOMs allow for easier implementation of larger 2-D arrays by eliminating the complex local-oscillator (LO) feed structure. A 4 /spl times/ 4 element retrodirective array using SOMs is demonstrated at an LO frequency of 7.68 GHz. Each element is phased locked at the LO frequency with an accompanying RF frequency isolation of 17.9 dB between adjacent horizontal elements and 22.2 dB between adjacent vertical elements. A -10-dBm external injection-locking signal is applied to reduce the phase noise of the 16-element array to -68.2 dBc/Hz at 10-kHz offset. Retrodirectivity is observed in the /spl phi/=0/spl deg/, /spl phi/=-45/spl deg/, and /spl phi/=-90 plane for scattering angles of /spl theta/=-15/spl deg/, /spl theta/=0/spl deg/, and /spl theta/=+30/spl deg/.     

Balanced subharmonic mixers for retrodirective-array applications

The drawback of conventional Pon retrodirective antenna systems is the requirement of a local oscillator (LO) working at approximately twice the receive frequency. This limits the use of these systems to rather moderate frequencies where such an oscillator can be obtained. To overcome this problem, a new phase conjugate mixer topology is proposed, whereby the use of a harmonic mixer instead of the conventional fundamental type effectively halves the LO frequency requirement. Another significant problem of conventional Pon phase conjugate mixers is the small spacing in frequency, typically only a few 0.1% of the carrier frequency, between RF, IF, and LO frequency. In this paper, we have overcome this problem by introducing a double balanced structure with a novel phasing strategy. The phasing circuit automatically cancels the RF and LO signal at the system's output port, giving 36-dB RF/IF, and 34-dB LO/IF isolation for a 970-MHz IF and 990-MHz RF signal. The new mixer structure proposed here is an attractive proposition for use in retrodirective antenna arrays significantly enhancing their potential for application in the millimeter-wave frequency range     

A 10-bit wide-band CMOS direct digital RF amplitude modulator

This paper describes a low-distortion wide-band CMOS direct digital RF amplitude modulator, which uses a 10-bit linear interpolation current-steering digital-to-analog converter (DAC) and a Gilbert-cell-based mixer to generate an amplitude modulated RF signal directly. The linear interpolation increases the attenuation of the DAC's image components. The reconstruction filter is, therefore, eliminated. The DAC's differential current signals are directly sent to the mixer, which improves the linearity of the modulated RF signal. Thus, the RF transmitter structure is simplified, and the low distortion is achieved. This modulator is suitable for system-on-chip (SOC) design and is easily scalable. The chip was fabricated in a 0.35-/spl mu/m 3.3-V double-poly triple-metal CMOS process. The core size of the chip is 0.52 mm/spl times/0.68 mm. With a 3.3-MHz modulation signal, a 50-MHz clock, and a 1-GHz carrier, the distortion components are below -53.81 dBc, and the attenuation of the image signal is 47.45 dB. The output power is -6.5 dBm, and the total power consumption is 159.8 mW.     

Tracking antenna architectures based on a planar two-portmicrostrip patch mixer antenna

This paper describes the behavior of a compact two-port integrated mixer active antenna element with low cross polarization, high two-port circuit isolation, and good mixer detection sensitivity. Using this element as an elemental building block, a self-tracking antenna array has been realized which uses an in-band carrier signal for self calibration. The array is relatively insensitive to absolute carrier power level and is capable of tracking incoming signals over ±80°. By minor alteration of the antenna topology, a minimum complexity variant of a heterodyne retrodirective array has been demonstrated over a ±40° retransmission angle. Finally, the use of the antenna in conjunction with an injection-locked voltage-controlled oscillator (VCO) is included in order to demonstrate ±35° phase-shifterless beam steering     

A four-input beam-forming downconverter for adaptive antennas

A four-input beam-forming downconverter for adaptive antennas is described. It consists of 2-bit variable gain amplifiers (VGAs), 5-bit local oscillator (LO) signal phase shifters using double RC-bridge circuits, and mixers. The VGAs adjust gain deviation between signal paths. A differential-signal-to-eight-phase-signal converter is employed as a part of the LO phase shifter to reduce the chip size. A maximum phase error of 4.1/spl deg/, which is less than 1/2 LSB, is achieved. This error value indicates that the required phase shifter accuracy and the necessary isolation between the VGAs has been achieved. This beam-forming IC is applicable to receivers with adaptive antennas, and is expected to help to reduce the costs of adaptive antenna systems.     

Photonic RF phase shifter for harmonic downconversion in phasedarray antenna beam-forming applications

A photonic integrated-optic RF phase shifter for harmonic downconversion in phased array antenna beam-forming applications is presented. The subsystem consists of two integrated optic Mach-Zehnder interferometers fed with a combined signal from the receiving antenna and the local oscillator. This device achieves both phase shifting and harmonic downconversion of incoming RF signals     

A 75-dB image rejection IF-input quadrature-sampling SC /spl Sigma//spl Delta/ Modulator

Quadrature sampling of intermediate frequency (IF) signals is subject to the well-known problem of gain and phase mismatches between the in-phase (I) and quadrature (Q) channels. This paper presents an IF-input quadrature-sampling switched-capacitor (SC) /spl Sigma//spl Delta/ modulator that circumvents the I/Q mismatch problem by time-sharing between the I and Q channels the critical circuit components, namely, the sampling capacitor and the capacitor of the first-stage feedback digital-to-analog converter (DAC). In addition, a clocking scheme that is insensitive to I/Q phase imbalance is used. A third-order single-loop 1-bit low-pass modulator has been designed and fabricated in a 0.35-/spl mu/m CMOS process with an active area of 0.57mm/sup 2/. The experimental results show that the modulator achieves an image-rejection ratio (IRR) of greater than 75dB throughout a 200-kHz signal bandwidth.     

Bow-tie retrodirective rectenna

A novel bow-tie retrodirective rectenna designed at 5.8 GHz is proposed. The new retrodirective rectenna combines a traditional rectenna with a retrodirective array. The new retrodirective rectenna array can automatically steer its main beam towards the power source and hence is not sensitive to the power incident angle changes. It can provide a constant DC output voltage within /spl plusmn/10/spl deg/ and 90% DC output voltage within /spl plusmn/30/spl deg/. The conversion efficiency of the arrays is 84% when the power density is 10 mW/cm/sup 2/.     

A retrodirective antenna array using a spatially fed localoscillator

This work investigates a spatially fed local oscillator (LO) for a retrodirective antenna array. Compared to conventional planar transmission-line feed networks, the spatial feed offers a more flexible array layout and easier implementation, especially in large two-dimensional (2-D) arrays. This method of delivery involves radiating the LO through free space to the back-side of the array where it is received by slot-coupled patch antennas and delivered to the mixing elements. A four-element linear retrodirective array utilizing this approach is demonstrated at an LO frequency of 10.7 GHz. Retrodirectivity is observed at scan angles from -40° to +40°     

Photodiode-integrated microstrip antenna array for subterahertz radiation

The radiation characteristics of subterahertz (sub-THz) electromagnetic waves emitted from an antenna array integrated with photodiodes are investigated. The element of the fabricated array antenna was a 300-GHz microstrip antenna integrating a uni-traveling carrier photodiode. It was observed that the beamwidth of a 3 /spl times/ 1 antenna array is about half that of the single microstrip antenna. We also confirmed that the radiation direction changed by 20/spl deg/ when 2/spl pi//5 of phase difference was added to the input optical signal for each antenna element. These results demonstrated that sub-THz waves emitted by each element of the array were coherently superimposed and the power combining of the sub-THz radiation occurred in the microstrip antenna array. The measured output power of each radiation element is about 120 /spl mu/W, and a total output power of 1 mW can be estimated for a fabricated 3 /spl times/ 3 array in an ideal radiation condition.     

方向回溯天线发展现状

与时间反演系统的时间反转原理类似,方向回溯天线基于相位共轭原理实现系统的相位反转,从而完成系统的自动波束聚焦,是一种新型的波束自跟踪天线。本文由方向回溯天线的性能和应用两个方面出发,介绍了近十年方向回溯天线的研究现状,具体包括方向回溯天线的极化特性、频率特性、新结构等性能,以及方向回溯天线在无线功率传输、射频识别、电子对抗等领域的应用,探究了方向回溯天线的发展趋势。     

A multicarrier GMSK modulator with on-chip D/A converter for base stations

A multicarrier Gaussian minimum shift keying (GMSK) modulator with a 14-bit on-chip digital-to-analog (D/A) converter is presented. The design contains four GMSK modulators, which generate GMSK modulated carriers at the user-defined center frequencies. In wireless base stations, the modulated transmit signals are usually combined at the RF frequency after power amplification. The multicarrier modulator combines four GMSK modulated signals in the digital domain, thereby eliminating the need for an antenna microwave combiner. A new digital ramp generator and output power-level controller performs both the burst ramping and the dynamic power control in the digital domain. The maximum dynamic performance is obtained by multiplexing two D/A converters with output sampling switches. The digital multicarrier GMSK modulator is designed to fulfill the derived spectrum and phase-error specifications of the GSM 900/1800/1900 base stations for pico-, micro-, and macrocells. The die area of the chip is 26.8 mm/sup 2/ in 0.35-/spl mu/m CMOS (in BiCMOS) technology. Power consumption is 706 mW at 3.3 V with 52 MHz.     

A 13-b 1.1-MHz oversampled DAC with semidigital reconstruction filtering

A digital-to-analog converter (DAC) composed of a cascaded digital /spl Sigma//spl Delta/ modulator and the combination of a semidigital/digital finite-impulse response (FIR) and an infinite-impulse response (IIR)-SC/RC filter is described. The architecture enables the analog linear reconstruction of 16/spl times/ oversampled digital signals. With the analog section implemented in CMOS 0.18-/spl mu/m and the digital part programmed into a field-programmable gate array (FPGA), the modulator plus reconstruction filter achieves a peak SNR of 78 dB. The spurious-free dynamic range reaches 80 dB and stays better than 73 dB within the 1.104-MHz signal band. A missing-tone-power ratio of 70 dB, demonstrated for a signal with 15-dB peak-to-average ratio, proves that the solution is suitable for ADSL-CO transmitters.