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An analysis of the response of a scanning-beam millimeter-wave correlation radiometer is presented with an emphasis on the spectral signal response. The derivation and subsequent analysis presented here focuses specifically on the effects of the natural oscillation of the signal, called the fringe frequency, as it pertains to rotating sensors. The amplitude and bandwidth of the spectral density are analyzed in multiple cases, including for tracking and nontracking antennas, and for situations in which the antenna beam or the fringe washing function of the correlation radiometer is wide and can be neglected. Closed-form solutions are found for the case where the antennas track the source. Theoretical and simulated responses are given, and experimental results are compared to expected results from the theory for a correlation radiometer designed for security sensing. Measured experimental results show minimal deviation from theoretical calculations, validating the theoretical models derived herein. [ABSTRACT FROM PUBLISHER]

The scanning-beam millimeter-wave correlation radiometer has recently been applied to human presence detection and classification. The natural frequency of the scanning-beam correlation radiometer signal, called the fringe frequency, results from human presence in the scanning beam and must be known in order to filter the signal and provide the best possible radiometric sensitivity. This letter presents new results in estimating the fringe frequency of a 27.4-GHz scanning-beam correlation radiometer by comparing different spectral estimation techniques, including CLEAN, RELAX, PHD, MUSIC, and ESPRIT. Experiments were performed with a human placed beyond the mean detection range of the sensor, resulting in signal power levels below the average power expected in an operational environment. Results show good performance for the CLEAN and RELAX algorithms at fringe frequencies in the range of 15–60 Hz and for the MUSIC and ESPRIT algorithms at fringe frequencies in the range of 60–155 Hz. [ABSTRACT FROM PUBLISHER]

Abstract-The novel application of correlation radiometer theory to the detection of self-luminous objects at close range is presented in the context of human presence detection. Modifications and additions to techniques developed in radio astronomy and remote sensing for close-range terrestrial situations are developed and discussed. To demonstrate the new techniques, a Ka-band correlation radiometer is presented, which detects the presence of a stationary human in an outdoor environment. The correlation radiometer fringe frequency is analyzed in the context of the scanning beam detection system and is estimated using MUSIC and ESPRIT. The visibility, sensitivity, spatial resolution, and dwell time of the system are analyzed. Finally, the correlation response is included in a statistical classifier in conjunction with responses from total power radiometers. Experimental results show improved detection capability over using the total power sensors alone. [ABSTRACT FROM AUTHOR]

A novel method of human presence detection using passive millimeter-wave (MMW) sensors is presented. The method focuses on detecting a standing human from a moving platform in a cluttered outdoor environment using MMW radiometry, which has not been attempted before. Ka -band radiometers are used in the total power mode, as well as correlation mode, which ideally responds well to self-luminous objects such as humans. The intrinsic radiative power from a human is derived, as well as the responses of the total power and correlation modes. A summary of the system hardware design is presented, as well as experimental results. Lastly, a simple Bayesian classification formulation is introduced and shown to produce promising results in classification of humans and nonhumans. [ABSTRACT FROM AUTHOR]

A tunable, electrically small, wire antenna is developed for HF/VHF ground wave transmission. A variable capacitor is serially connected to tune the resonant frequency of the antenna. The optimal position for the placement of the capacitor is evaluated by numerical simulation. The tuning range and sensitivity are also investigated. A prototype antenna is built and tested, and the measured tuning performance is compared to the simulation results. Transmission loss tests are carried out in several nonline-of-sight environments. The measured transmission loss of the tunable small antenna is found to be within 1 to 2 dB of that of a commercial whip across the tested frequency range. [ABSTRACT FROM PUBLISHER]

We report on the use of a genetic algorithm (GA) in the design optimization of electrically small wire antennas, taking into account of bandwidth, efficiency and antenna size. For the antenna configuration, we employ a multisegment wire structure. The Numerical Electromagnetics Code (NEC) is used to predict the performance of each wire structure. To efficiently map out this multiobjective problem, we implement a Pareto GA with the concept of divided range optimization. In our GA implementation, each wire shape is encoded into a binary chromosome. A two-point crossover scheme involving three chromosomes and a geometrical filter are implemented to achieve efficient optimization. An optimal set of designs, trading off bandwidth, efficiency, and antenna size, is generated. Several GA designs are built, measured and compared to the simulation. Physical interpretations of the GA-optimized structures are provided and the results are compared against the well-known fundamental limit for small antennas. Further improvements using other geometrical design freedoms are discussed. [ABSTRACT FROM AUTHOR]

The application of genetic algorithm (GA) optimization to the design and analysis of planar monopole antennas is presented. GA is first used to optimize the impedance matching bandwidth of two particular planar element shapes, the bow-tie (BT) and reverse bow-tie (RBT). The results of this study indicate that the RBT can achieve a significantly wider bandwidth with a much smaller size than the traditional ET. In a follow-on study, GA is used to generate arbitrarily shaped planar monopole designs, which exhibit improved broadband performance and/or reduced size compared with the RBT. The designs generated by the GA demonstrate a better tradeoff between matching bandwidth and electrical size compared with planar monopole designs previously characterized in the literature. Analysis of results from simulation and measurement are presented, which provide insight into the operation of these antennas as well as the key parameters that lead to improved performance. Finally, a performance bound is generated to relate the bandwidth limitation of planar monopoles to size. [ABSTRACT FROM AUTHOR]

This paper describes a new technique to compensate output variations of total power radiometers due to physical temperature changes of the instrument. This technique performs the correction without the addition of expensive microwave hardware required in Dicke switching or many other widely used methods. A characterization period, over which the input antenna temperature is known, indicates the appropriate output adjustment needed for a change in physical temperature of the radiometer. The method effectively corrects the output in an example radiometer system built with inexpensive commercially available parts. For a 30-K variation in physical temperature, the measured data shows an improvement from 60-K peak-to-peak error to 6.9 K with an average absolute error of 1.1 K. [ABSTRACT FROM AUTHOR]

Presents a novel conical monopole antenna composed of multiple wires for the high frequency to very high frequency bands. Characteristics of the antenna; Description of broadbanding and impedance matching techniques used during the design process; Comparison of the performance of the antenna with other electrically small antennas.

Describes a technique developed for enhancing the gain of a wide-flare angle pyramidal antenna horn. Effect of metallic baffles on antenna's performance; Review of pyramidal horn; Description of the experimental horn; Numerical results.