Common Local Oscillator Research Articles

Development of the Q-band ECE imaging system in the large helical device

In this study, we developed the Electron Cyclotron Emission Imaging (ECEI) system with the Q-band in the Large Helical Device (LHD). ECEI measurement makes it possible to obtain the spatiotemporal structure of magnetohydrodynamics (MHD) instabilities in the high-β plasma. Although there were several difficulties for realizing the multi-channelization, such as local oscillator (LO) optics and an expensive high-power LO source, we have solved these problems by developing a Local Integrated Antenna array (LIA) which has an internal LO supply, using a frequency doubler integrated circuit on each channel, instead of a conventional Horn-antenna Mixer Array (HMA) with common LOs. In addition, we have made some improvements to enhance the quality of the measurement signal. First, we developed and introduced notch filters that prevent the strong Electron Cyclotron Resonance Heating (ECRH) stray signal from being mixed into the measurement circuit. Second, the position of the doubler built in the printed circuit board was reconsidered to prevent the mixing of higher harmonic components into the mixer. Also, we have adopted the Logarithmic detector (LOG detector) to deal with the wide dynamic range of the plasma fluctuation. After these improvements, for the first time, we could successfully obtain the initial results of the two-dimensional temperature distribution and its fluctuation distribution in the LHD.

Massive MIMO with Transceiver Hardware Impairments: Performance Analysis and Phase Noise Error Minimization

In this paper, we investigate the impact of hardware impairments (HWIs) on the performance of a downlink massive MIMO system. We consider a single-cell system with maximum ratio transmission (MRT) as precoding scheme, and with all the HWIs characteristics such as phase noise, distortion noise, and amplified thermal noise. Based on the system model, we derive closed-form expressions for a typical user data rate under two scenarios: when a common local oscillator (CLO) is used at the base station and when separated oscillators (SLOs) are used. We also derive closed-form expressions for the downlink transmit power required for some desired per-user data rate under each scenario. Compared to the conventional system with ideal transceiver hardware, our results show that impairments of hardware make a finite upper limit on the user’s downlink channel capacity; and as the number of base station antennas grows large, it is only the hardware impairments at the users that mainly limit the capacity. Our results also show that SLOs configuration provides higher data rate than CLO at the price of higher power consumption. An approach to minimize the effect of the hardware impairments on the system performance is also proposed in the paper. In our approach, we show that by reducing the cell size, the effect of accumulated phase noise during channel estimation time is minimized and hence the user capacity is increased, and the downlink transmit power is decreased.

Incoherent clocking in coherent radio interferometers

Radio interferometer arrays are instruments requiring real-time synchronisation of all array elements to capture and align the observed source wavefront prior to further processing such as correlation and/or beamforming. One method is to deliver a frequency, from a common central local oscillator (LO), using a round-trip phase-stable distribution system such that each element has its own phase-stable copy of the clock with required real-time fidelity for down-conversion and digitisation. The method described here involves equipping each array element with its own independent ‘eLO’ and sending a ‘tracer’ of it to a central site, where the difference between the elements’ eLOs and the central ‘cLO’ is measured. The digitised data from each element is corrected at the central site according to the measurement, before correlation/beamforming. The advantage of this method is that only a ‘trace’ of eLO, needed to measure the rate of change of eLO relative to cLO integrated over a measurement interval, needs to be conveyed over this tracer link, rather than the frequency itself, thereby requiring lower link temporal fidelity and bandwidth.

On the Possibility of Breaking the Heterodyne Detection Quantum Noise Limit With Cross-Correlation

The cross-correlation sensitivity of two identical balanced photodiode heterodyne receivers is characterized. Both balanced photodiodes receive the same weak signal split up equally, a situation equivalent to an astronomical spatial interferometer. A common local oscillator (LO) is also split up equally and its phase difference between both receivers is stabilized. We show by semi-classical photon deletion theory that the post-detection laser shot noise contributions on both receivers must be completely uncorrelated in this case of passing three power splitters. We measured the auto- and cross-correlation outputs as a function of weak signal power (system noise temperature measurement), and obtain a cross-correlation system noise temperature up to 20 times lower than for the auto-correlation system noise temperature of each receiver separately. This is supported by Allan plot measurements showing cross-correlation standard deviations 30 times lower than in auto-correlation. Careful calibration of the source power shows that the auto-correlation (regular) noise temperature of the single balanced receivers is already very near to the quantum limit as expected, which suggests a cross-correlation system noise temperature below the quantum limit. If validated further, this experimentally clear finding will not only be relevant for astronomical instrumentation but also for other fields like telecommunications and medical imaging.

Low-noise correlation measurements based on software-defined-radio receivers and cooled microwave amplifiers.

We present a microwave correlation measurement system based on two low-cost USB-connected software defined radio dongles modified to operate as coherent receivers by using a common local oscillator. Existing software is used to obtain I/Q samples from both dongles simultaneously at a software tunable frequency. To achieve low noise, we introduce an easy low-noise solution for cryogenic amplification at 600-900 MHz based on single discrete HEMT with 21 dB gain and 7 K noise temperature. In addition, we discuss the quantization effects in a digital correlation measurement and determination of optimal integration time by applying Allan deviation analysis.

Capacity of SIMO and MISO Phase-Noise Channels With Common/Separate Oscillators

In multiple antenna systems, phase noise due to instabilities of the radio-frequency (RF) oscillators, acts differently depending on whether the RF circuitries connected to each antenna are driven by separate (independent) local oscillators (SLO) or by a common local oscillator (CLO). In this paper, we investigate the high-SNR capacity of single-input multiple-output (SIMO) and multiple-output single-input (MISO) phase-noise channels for both the CLO and the SLO configurations. Our results show that the first-order term in the high-SNR capacity expansion is the same for all scenarios (SIMO/MISO and SLO/CLO), and equal to $0.5\ln (\rho)$, where $\rho$ stands for the SNR. On the contrary, the second-order term, which we refer to as phase-noise number, turns out to be scenario-dependent. For the SIMO case, the SLO configuration provides a diversity gain, resulting in a larger phase-noise number than for the CLO configuration. For the case of Wiener phase noise, a diversity gain of at least $0.5 \ln(M)$ can be achieved, where $M$ is the number of receive antennas. For the MISO, the CLO configuration yields a higher phase-noise number than the SLO configuration. This is because with the CLO configuration one can obtain a coherent-combining gain through maximum ratio transmission (a.k.a. conjugate beamforming). This gain is unattainable with the SLO configuration.

Fiber-optic radar calibration

A simple fiber-optic radar calibration target is described. Its operation is based on a wideband fiber, a laser transmitter that is directly modulated by the down-converted radar signal and an optical diode receiver recovering said signal. Further up-conversion having a common local oscillator with the first mixer ensures fidelity of the calibration return. Measured useful bandwidth exceeds 200 MHz and practically any radar RF frequency can be handled when suitable mixers are employed. Amplifiers can be added to the down-converted path as desired to compensate for the fiber loss. Modulation and LO sweep provide easy ways of introducing artificial fluctuations and Doppler frequencies. Particularly pulsed radars are readily tested with the proposed scheme as no restrictions are posed by the radar's TR-switch delays.

A study on precise troposphere measurement system by use of beam-transferred common local oscillator method

The authors have been observing a satellite broadcast wave (12 GHz) that is almost continuously transmitted for 24 hours, and examining the change of the satellite orbit and the meteorological changes on the wave propagation path. For the simple and precise measurement of those changes, the authors investigated and developed a common local oscillator method using two receiving antennas, based on the principle of the radio wave interferometer. In order to improve the accuracy of the observation, however, the baseline of the interferometer must be extended. Then, difficulties arise in connection with the extension of the baseline, such as the transmission loss of the local signal to be fed from outside to the converters at the foot of the antenna, or the space for installing the transmission line. From such a viewpoint, we consider a method in which two receiving antennas are placed close to each other at an end of the baseline, and the broadcast wave from the satellite is beam-transferred from the reflector placed at the other end. A basic experiment was performed. It was found that the direction and length of the baseline can be set flexibly by just moving the reflector. The provision of the common local signal is made easy since the antennas are placed at the same site. This paper discusses the observation system using the reflector and the change of the satellite orbit, and the change of the received signal due to the effect of the troposphere, as derived from the obtained data. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(5): 1–10, 2001

Troposphere measurement systems using the offset beam method and common local oscillator method

Troposphere measurement systems using the offset beam method and common local oscillator method

Troposphere measurement systems using the offset beam method and common local oscillator method

Troposphere measurement systems using the offset beam method and common local oscillator method

A multibeam SIS mixer module for a focal plane array receiver

The integration of many receiver units into a receiver array is a common method of improvement of imaging systems. This approach, well known in the mm band for Schottky mixer arrays, has not so far been developed for Superconductor - Insulator - Superconductor (SIS) junction mixers, which give the best sensitivity in the short mm wave range and in the submm range. We demonstrate for the first time a practical low noise multibeam receiver module using SIS mixer technology. The basis for the integration of several SIS mixers with a common local oscillator source is given by the saturation of the SIS receiver noise dependence upon local oscillator power. The module comprises three identical SIS mixers integrated with a common local oscillator, coupled through a three branch waveguide directional coupler. The multibeam module has been developed for a focal plane array receiver of the 30 meter radio telescope of the Institut de Radioastronomie Millimetrique (IRAM).

Phase-referencing in “cluster-cluster” VLBI mode

VLBI between sites with multiple antenna elements, fed from a common local oscillator, holds the prospect of solving for astrometric and geodetic parameters in a new way. The Cluster-Cluster observing mode allows simultaneous observations of multiple sources on the separate “sub-baselines” between sub-elements from one site to the other. The differential analysis benefits from the total cancelation of the temporal structure of the non-geometric contributions (e.g. instrumental terms and the propagation medium). We describe the current status of the analysis of observations in June 1995 using this technique with the WSRT and VLA arrays.

A GPS Attitude Determination System

In 1991 Trimble Navigation introduced a Global Positioning System (Gps)-based attitude determination receiver capable of 3-axis solutions with accuracy to several milliradians for airborne, sea and land platforms. This paper discusses the physical, architectural, and operational features of this receiver system. Analysis of system performance will also be reviewed for various configurations and user applications. The Trimble Navigation attitude determination receiver uses differential carrier phase techniques to determine azimuth, pitch and roll angles of a 3-antenna array. This product is designed to operate in a variety of user applications and to withstand rugged operating environments. Trimble Navigation has expanded its proven GPS sensor architecture to incorporate three independent RF sections and additional processing channels to measure and process the differential phase between antennas on two orthogonal baselines. Direct measurement of differential phase utilizing a common local oscillator provides highly accurate relative phase data. The navigation and attitude processor computes azimuth, pitch, and roll angles as well as position, velocity and time. The solution accuracy and stability statistics are sensitive to various parameters. Antenna baseline length, signal multipath, platform dynamics and filtering are investigated. Test data from static and various dynamic platforms are also presented.

Performance evaluation of coherent subcarrier multiplexed optical distribution systems with common local oscillators

Coherent subcarrier multiplexed local distribution systems using a common local oscillator (LO) in which the LO is provided by a distribution centre instead of locally generated at the subscriber premise are described. Both single and multiple optical carrier systems are considered. Because of the low path loss in a local optical network, a common LO system is possible with a LO shared by many subscribers, and indeed provides many advantages. First, a simplified receiver is achievable which eliminates a tunable LO, an automatic frequency control (AFC) circuit, a polarisation controller, and an optical coupler. Secondly, the system cost is decreased due to the reduction of components. Thirdly, laser phase noise and intermediate frequency (IF) drift are expected to be minimised. Fourthly, because no active optical components are placed at the subscriber premises, the system reliability is increased. Fifthly, the common LO system can be expanded with optical amplifiers without increasing the number of LO and simultaneous amplification of the message, and LO signals are achievable. By sharing high power, highly frequency stabilised, and very narrow linewidth LO lasers provided by the centre, it is expected that a simple and reliable coherent optical distributing network can be constructed by using common LO.

Impact of local oscillator intensity noise on performance of coherent subcarrier multiplexing system using common local oscillator (CLO)

The impact of local oscillator intensity noise on the performance of a coherent subcarrier multiplexing (CSCM) system using a common local oscillator (CLO) is analysed. For a given LO power, RIN noise, and thermal noise, the CNR can be expressed in terms of x, the ratio of σsh2 + σth2 over σRIN2 and, for x ≪1, the CNR decreases as LO power increases; for x ≫ 1, the CNR increases as the LO power increases; as x approaches 1, there exist an optimum value of local oscillator power and a corresponding maximum CNR. For a system with RIN = –150dB/Hz, Ps = –20dBm, β = 0.02, N = 40, NF = 3dB and B = 10MHz, the (PLO)opt is found to be –4dBm and {CNR)max 22.5dB.

Coherent optical ring using common local oscillator

A coherent optical ring distribution system using a common local oscillator is investigated. The results show that equal IF signal for all the nodes can be easily achieved and there exists an optimum branch coupling ratio to achieve a maximum IF signal. In addition, equal IF signal to noise ratio is achievable when the signal and LO have limited output powers.

A comparison of quadrature and single-channel receiver processing in adaptive beamforming

A performance comparison between two different types of receivers in an HF adaptive array application is presented. The data used for the study were recorded using a bistatic HF radar located in the central valley of California. Eastword-looking transmissions were generated using a continuous sweep-frequency (chirp) format with a sweep repetition rate of 60 Hz. Backscatter signals, produced by a one-hop forward ionospheric path followed by a one-hop ionospheric return path were received using eight adjacent 32-element linear subarrays spanning a total linear aperture of 2.5 km. Single-channel receivers at each of the eight subarrays were employed for deramping and conversion to baseband. The overall system bandwidth was 960 Hz, and a common local oscillator was used for the receivers. All adaptive processing was carried out off-line using digitized data recorded simultaneously at the eight receiver outputs. The objective of the study described in this paper was to compare the results obtained using the receiving system described above with those which would be obtained using quadrature receivers at the subarray outputs. In the latter case, dual common local oscillator injection, with a 90\deg phase difference, is employed to obtain two receiver outputs, (in-phase and quadrature components) for each receiver. The component outputs then each have a bandwidth equal to one-half that of the single-channel receiver or 480 Hz for both the in-phase and quadrature signals. One advantage of quadrature reception is that a single real multiplying weight can be used at the two outputs to obtain a frequency-independent gain and phase-shift across the received bandwidth, a property which is not easily obtained for all azimuths in the single-channel receiver structure. The study described in this paper was undertaken to quantitatively determine the importance of this difference in an adaptive beamforming system. The approach taken was to synthesize quadrature receiver signals from the recorded single-channel data using Hilbert transform methods. Comparisons between the two receiving systems were then carried out using identical data sets. The results obtained illustrate that minor differences (less than 5 dB) exist in the processed outputs provided that the same number of adaptive degrees of freedom are used in the two processors. As a result, decisions as to the specific form of a receiver to be used in an HF radar should be based on considerations relating to ease of implementation rather than the overall performance of the adaptive processor.

Design Concept for an All-Channel Transistorized TV Tuner

This report describes a design concept and its implementation for an all-channel transistorized TV tuner with common RF amplifier, mixer and local oscillator for both VHF and UHF TV bands. The VHF and UHF tuned circuits of each stage are mounted on a common wafer of the channel selector. Interaction between the VHF and UHF tuned circuits is eliminated by the novel use of ferrite beads and shielding. The result obtained by this design concept is a low cost, compact and simple all-channel TV tuner with single knob tuning capability. This work was done at Hazeltine Corporation, Hazeltine Research Division (Plainview, N.Y.), under a contract with Hazeltine Research, Inc.

The Double Super-Heterodyne Principle Applied to Dielectric Measurements

By use of two mixers and a common variable local oscillator, a super-heterodyne receiver, such as General Radio Wave Analyzer No. 736-A, can be converted to serve simultaneously as generator and detector. Such an arrangement provides: (1) single dial tuning, (2) absolute freedom from relative frequency drift, (3) the possibility of very narrow band tuning and, thus, improved signal-to-noise ratio. Circuits to accomplish this are described for the range 0–16 kc which occupy no more space than a conventional oscillator, which they replace. Extension of the frequency range to 0–600 kc is possible by simple changes and the use of an RAK-7 commercial receiver, although in this case single dial tuning is not possible. These circuits are particularly useful for automatic balancing dielectric bridges, but should also be very useful in work with vibration and sound, and for filter and amplifier frequency response.