Sum Channel Research Articles

A 24 GHz Amplitude Monopulse Comparator in 0.13 $\mu$m CMOS

This letter presents the design and implementation of a wideband 24 GHz amplitude monopulse comparator in 0.13 mum CMOS technology. The circuit results in 9.6 dB gain in the sum channel at 24 GHz with a 3-dB bandwidth of 23.0-25.2 GHz, and a sum/difference ratio of > 25 dB at 20-26 GHz. The measured input PI dB is -14.4 dBm at 24 GHz. The chip is only 0.55 times 0.50 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (without pads) and consumes 44 mA from a 1.5 V supply, including the input active baluns and the differential to single-ended output stages (28 mA without the input and output stages). To our knowledge, this is the first demonstration of a high performance mm-wave CMOS monopulse comparator RFIC.

Throughput and Channel Access Statistics of Generalized Selection Multiuser Scheduling

To provide a near-optimal low-complexity solution to parallel multiuser scheduling in code-division multiple-access (CDMA), we propose generalized selection multiuser diversity (GSMuD) schemes with multi-code channel assignment and analyze their performance. The proposed GSMuD (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , L) schemes rank a total of L users awaiting transmissions by their signal-to- noise ratios (SNRs) and select the L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> (1les Lc les L) users with the largest absolute (or normalized) SNRs for parallel channel access, which achieve near-optimal sum rate with a low scheduling complexity. The sum and individual channel throughput rates, second order statistics, fairness, and channel access statistics of the proposed GSMuD schemes are derived, taking into account different types of generalized fading channels. Compared to the round robin (RR) scheduling without SNR ranking, the GSMuD with normalized SNR ranking achieves a substantially higher sum rate while maintaining fairness. GSMuD also significantly improves the channel access performance and the degree of fairness than selective multiuser diversity (SMuD), which selects one best user only at each time slot.

Monopulse-radar tracking of swerling III-IV targets using multiple observations

This paper proposes a novel statistical prediction of monopulse errors (Levanon, 1988) for a radar Swerling III-IV target embedded in noise or noise jamming where multiple observations are available. First, the study of the maximum likelihood estimator (MLE) of the complex monopulse ratio for a Swerling III-IV target embedded in spatially white noise allows us to extend the use of the MLE practical approximate form introduced by Mosca (1969) for Swerling 0-I-II cases. Afterward, we derive analytical formulas for both the mean and variance of the MLE in approximate form conditioned by the usual detection step performed on the sum channel of a monopulse antenna. Last, we provide a comparison of target direction of arrival (DOA) estimation performance based on monopulse ratio estimation as a function of the Swerling model in the context of a multifunction radar.

SUM AND DIFFERENCE MULTIPLE BEAM MODULATION TRANSMITTED BY MULTIMODE HORN ANTENNA FOR INVERSE MONOPULSE DIRECTION-FINDING

The sum and difference multiple channels were usually applied to the monopulse system only in a receiver. But this paper presents a technique of multiple beam modulation transmitted by the sum and difference multiple channels. The modulated field is designed as three chip signal vectors whose sum and whose differences are controlled by the gains of antennas,and the angle between the sum vector and the differential vector depends on the phase error between the channels so that the different microwave signals can be transmitted in the different directions. A receiver with single-antenna can extract azimuth and elevation with respect to the transmitter. Simulation results show that the proposed modulation system has been successfully designed to integrate digital communication with direction-finding in the way of the reverse monopulse.

Joint Use of Sum and Delta Channels for Multiple Radar Target DOA Estimation

This paper deals with the problem of estimating the parameters, i.e., complex amplitudes, directions of arrival (DOAs), and Doppler frequencies, of multiple radar targets present in the same range-azimuth resolution cell of a surveillance radar, by joint processing the sum and delta channel data. The AML-RELAX (asymptotically maximum likelihood) estimator previously derived by the authors is extended to a two-channel system scenario. Both the cases of targets having the same Doppler frequencies and different Doppler frequencies are considered. Performance is numerically investigated through Monte Carlo simulation and compared with that of the single channel estimator, which exploits knowledge of the sum antenna main beam only. Performance of the AML-RELAX estimator is also compared with that of two monopulse estimators for single and multiple target scenarios.

Finite-difference time-domain modeling of a corrugated horn antenna as a radar system feed

The design of a reflector-antenna feed for monopulse tracking-radar application is presented. The feed consists of a rectangular-circular mode coupler to isolate the sum and difference channels required for monopulse tracking, and a corrugated horn for a symmetric radiation pattern with low cross polarization. The modeling is carried out using the finite-difference time-domain (FDTD) method, which is well suited for field visualization. The measurements show that the feed performance meets the design requirements and is in close agreement with the FDTD prediction. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 384–387, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21176

A wide-band monopulse comparator with complete nulling in all delta channels throughout sum channel bandwidth

A broad-band monopulse comparator with complete nulling in the three delta channels throughout the sum channel bandwidth is presented in this paper. It is based on a new broad-band 180/spl deg/ hybrid with amplitude and phase balances that are theoretically perfect and frequency independent. Using this 180/spl deg/ hybrid, a microstrip monopulse comparator was realized on a low-cost FR-4 board. The comparator was fully characterized by its eight-port S-parameters to generate the sum and delta channel frequency responses. Over 30-dB null depths was achieved in the three delta channels across the sum channel passband from 1.1 to 3.3 GHz.

A compact Ku‐band monopulse horn

AbstractThe design, manufacture, and testing of a compact Ku‐band monopulse horn is described, with an emphasis on an effort to maximize the return loss of the sum, azimuth, and elevation channels. The results show that the multimode monopulse horn has the required radiation patterns and acceptable return loss for its narrowband operation requirement. The bandwidth is found to be limited by the difficulty of matching the three channels simultaneously. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 9–13, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10357

Bass management system for home theater equipment

A setup to be used in a home theater or sound reproduction system for handling low frequency sound signals with a signal source providing several full bandwidth digital sound channels and at least one digital low frequency subwoofer channel includes a delay-and level control unit at least for each full bandwidth signal channel, which is equipped for a speaker not capable of reproducing low frequency sounds. A first summing stage creates the sum channel by summing the delay-and level controlled signal channels. A second summing stage adds a low frequency subwoofer channel to the sum channel in order to create a digital bass channel. A DA-conversion, amplifying, lowpass-filtering and volume control unit processes the digital bass channel in order to create an analog bass channel.

Probability distribution of complex monopulse ratio with arbitrary correlation between channels

The joint distribution of the real and imaginary parts of the monopulse ratio (MR) is obtained for a monopulse radar with arbitrarily correlated Gaussian noise and non-zero means in the sum and difference channels. The general result is used to consider thresholding and to develop the marginal density for the real part of the MR for the special case of real correlation between the channels.

Monopulse-radar angle measurement in noise

Angle-tracking accuracy in noise or noise jamming was quantified by this author in a previous paper for those monopulse radars which compute the monopulse ratio digitally from baseband signals, and which use those measurements only when the sum-channel envelope exceeds a detection threshold examined here in more detail is the impact of only receiver noise, in the absence of a hostile, electronic countermeasure (ECM) environment. Here, the target is not assumed to be positioned at, or very near, the null of the monopulse ratio. Furthermore, noise levels in the difference and sum channels are not taken to be necessarily equal, where inequality can occur from differences in noise figure between the two channels, or from applying separate and different aperture weighting for difference and sum antenna patterns in a phased-array radar. >

Simultaneous nulling for monopulse array with partially adaptive weights

A new simple method is described for synthesizing low-sidelobe sum and difference patterns with partially adaptive weights. By partially adaptive, we mean that only part of the weights are adapted for simultaneous nulling. These adaptive weights are shared by the sum and difference channels, leading to a significant reduction in the number of variable attenuators/phase shifters used, as compared to the fully adaptive implementation. An objective function is derived that yields different configurations of the shared adaptive weights. Numerical examples are presented to ascertain the efficacy of the new method for both point and extended interference. >

Subarray-synthesized low-side-lobe sum and difference patterns with partial common weights

Methods of synthesizing low-side-lobe sum and difference patterns for linear arrays are described. By subarray beam forming, the sum and difference patterns exhibit a common factor, leading to a simple monopulse estimator. A procedure is proposed for the synthesis of the subarray-based sum and difference patterns which approximate a set of reference patterns in least-squares sense. Supervised nulling is incorporated as a means of suppression of strong interference. To further reduce system complexity, the constraint that parts of the beam-forming weights are shared by the sum and difference channels is imposed. The relationship between the maximum number of common weights allowable and the number of subarrays used is discussed. Numerical results are presented to demonstrate the efficacy of the proposed methods.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Nonbiased geometric centroid for high resolution radar angle tracking

An efficient algorithm is presented for tracking the true and nonbiased geometric centre of an array of scatterers on a single target. This algorithm is specifically designed for the monopulse radar angle tracking system with stepped frequency pulse train. The crosscorrelation function of the sum and difference channels normalised by the autocorrelation of the sum channel is used to calculate the geometric centre of each uniquely separated pair of scatterers. Dividing by the autocorrelation function eliminates the effects of different targets radar cross-sections (RCS), however, the zero separation term of the error function (DC term) is still biased toward the bigger scatterer. The nonzero terms (AC terms) are the down range distance separations between scatterers and are independent of their RCS. By simply dropping the zero separation term, and averaging the remaining terms together, the aimpoint becomes the unbiased geometric centre of the array.

HIGH RESOLUTION MONOPULSE RADAR TRACKING SYSTEM

High resolution radar techniques are applied to the problem of resolving a multiple target array and locating its geometric center without the usual biasing toward the brightest scatterer. This result is accomplished using monopulse radar techniques combined with high resolution stepped frequency pulse train signal processing in an angle tracking noncoherent high resolution radar. The center of each uniquely separated pair of point targets is calculated by examining the crosscorrelation function of the sum and difference channels. The autocorrelation of the sum channel is used to normalize the crosscorrelation data thereby eliminating the effects of the different targets’ radar cross sections (RCS). The zero separation term of the error function (dc term) remains biased toward the bigger scatterer, even after normalization. The nonzero terms (ac terms) are the cross range distances from the antenna’s boresight to each scatterer and are independent of their RCS. By simply dropping the zero separation term and averaging the remaining terms together, the aimpoint becomes the unbiased geometric center of the array.

Monopulse-radar angle tracking in noise or noise jamming

In many monopulse radars, feedback in the angle-tracking servo system is taken to be directly proportional to the monopulse ratio. In those radars, monopulse measurements are conditioned on simultaneous occurrences of receiver sum-channel video exceeding a detection threshold: if a detection fails to occur, the measurement is ignored, and the angle-tracking servo is made to coast. Such conditioning is shown to be necessary in order that the noise power be finite in the servo feedback. The conditional mean value and conditional variance of the monopulse ratio are derived and quantified in terms of threshold level as well as signal-to-noise ratio. The formulation permits the noise covariance between receiver difference and sum channels to be complex rather than only real-valued, so that the sources of noise jamming are not required to be positioned in the receiving-antenna mainlobe and to be copolarized with the antenna response there. Nonfluctuating and Rayleigh-fluctuating target cases are considered and compared, and fluctuation loss is quantified.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Use of difference channel information for detection in monopulse radars

The problem of target detection and acquisition by a monopulse tracking radar is considered. This problem is conventionally addressed using only information in the sum beam. The additional information available in the difference channels may be utilised to give improved performance. Two possible realisations of this concept are presented and analysed in some detail, namely linear combinations of the sum and difference channels, and detection based on the complex indicated angle. Other possibilities are also mentioned as possible areas for future work.

Adaptive nulling in monopulse antennas

Theoretical and experimental results are presented for phase-only nulling in low-sidelobe monopulse antennas. Both results are based on a gradient search algorithm that simultaneously searches for a minimum in the sum and difference channel output powers. The array's beam steering phase shifters double as the adaptive weights. Each element in the gradient is found by changing phase shifter setting by Delta Psi (the phase shifter stepsize) and measuring the change in output power. Then the phase shifter is restored to its original value, and the process repeated for all the remaining array phase shifters. The algorithm iterates as long as each new adaptive weight setting reduces the total output power. If the output does not go down, then Delta Psi is decremented by one setting and the iteration is started again. The algorithm stops when Delta Psi =0. The adaptive weights act as random perturbations to the phase taper of the array. Consequently, the sidelobe level is proportional to the size of the phase perturbations and inversely related to the number of elements. By keeping the adaptive phase shifts small, the average sidelobe level and the main beam gain do not drastically change.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Monopulse Radar Angle Tracking Accuracy with Sum Channel Limiting

The variance of angle tracking error is found for an amplitude-comparison form of monopulse radar when the sum channel contains a limiter prior to the angle error detector. The error expression is valid for any shape of transmitted pulse and any duration of range tracking gate but does assume matched filters in signal processing channels. The procedures used are rigorous and an example of results is worked out for the special case of a rectangular transmitted pulse envelope. It is shown, for rectangular pulses, that achievable angle tracking error variance with sum channel limiting is not more than 2.22 dB larger than the theoretical minimum for any processor and not more than 1.29 dB larger than a similar signal processor that uses a "linear" angle error detector. Results apply for large single-pulse signal-to-noise ratio.

Correction to "Monopulse Radar Angle Tracking Accuracy with Sum Channel Limiting"

Correction to "Monopulse Radar Angle Tracking Accuracy with Sum Channel Limiting"