David M. Lin

Electronic Warfare Receiver with Multiple FFT Frame Sizes

An electronic warfare (EW) receiver based on fast Fourier transforms (FFTs) with different frame sizes is presented. With a given sampling frequency, an FFT-based EW receiver can improve its frequency estimation by increasing the FFT frame size; however, such an increase has detrimental effects on its time-of-arrival and pulse width estimations. By applying multiple FFTs with different frame sizes, the proposed EW receiver can achieve high time and frequency resolutions simultaneously.

Digital wideband phased array calibration and beamforming using time reversal technique

A 16-channel digital wideband phased array without antenna is characterized using impulse response measurement. A chirp signal is used as probing signal. By careful chirp design, impulse response at sub-band is measured for all the channels. Spectral domain response showing dispersive phase and magnitude reveals significant imbalance among the channels. Based on time reversal technique principle, spectrum-modified time reversal impulse response is calculated. This time reversal response is applied to the chirp probing signal to verify the bandpass characteristics of the sub-band, and the waveform coherent waveform. It is also applied to the CW pilot tone to verify digital beamforming gain.

Mono-bit digital chirp receiver using mono-bit IFM (instantaneous frequency measurement) receiver as a core

This paper describes the design and intricacies of a wideband digital chirp receiver utilizing a one-bit ADC (Analog to Digital Converter) to measure the carrier frequency and chirp rate of unknown received signals which have very high chip rates. The core of the chirp receiver is composed of monobit IFM receivers which are low cost and very accurate.

Wideband signal detection by employing differential sampling rates

A wideband electronic warfare digital receiver design is proposed. The design utilizes the frame-based FFT algorithm commonly implemented in traditional electronic warfare (EW) encoder design [1]. The frequency coverage in traditional digital receiver designs is limited to a single Nyquist zone due to the desire to eliminate aliasing effects from multiple Nyquist zones that generate frequency ambiguities. The proposed design is based on a two-channel structure that allows M Nyquist

Angle of arrival measurement using wideband linear phased array

A radio frequency (RF) signal detection algorithm is developed based on two- dimensional Fast Fourier Transform (FFT) on phased array time series data. The sensitivity is calculated based on two-frame signal detection criterion. A collection system consisting of a linear phased array and multiple wideband digital receivers is utilized. Simulation results are presented based on the system parameters of the channelization frequency plan including the frequency range, LO, mixer, and sampling frequency. Experimental angle of arrival data are processed, and the results are shown to be in good agreement with the simulation results.

Two signal high dynamic range and high resolution wideband digital receiver using beat frequency

This paper describes how to build a wideband digital receiver using 2 FFTs with bit-reduced kernels and beat frequency resulting from the square of the sampled input data. It reduces the computation time, increases the instantaneous dynamic range, and improves the frequency resolution if compared with a typical fix point FFT approach. Without losing the generality, a 10 bit A/D converter, 2.56 GHz sampling rate, and 256 points of data processing are used for illustration of this approach. The Matlab simulations are used to compare the new approach with the approach using a 10-bit fix point FFT. The simulation results are tabulated.

Digital linear chirp receiver for high chirp rates with high resolution time-of-arrival and time-of-departure estimation

The use of chirp signals in modern radar and ranging systems have numerous benefits. They are extensively used to improve signal-to-noise ratio and range resolution. The performance capabilities of these signals are directly related to their time-bandwidth product, i.e., the duration and bandwidth of the pulse. Ultra-wideband chirp signals are further desirable because they span a large bandwidth, making them resistant to narrowband environmental interference. The accurate detection and measurement of high chirp signals is difficult due to the necessity of a high-sampling analog-digital converter, a target measurement platform with high computational power, and a time-of-arrival (TOA) estimator with high temporal resolution. The difficulty of the problem is further compounded with the requirement that no a priori knowledge of the signal, noise, or operating environment is known. This paper presents a practical approach and implementation of a high linear chirp rate receiver and TOA estimator pair capable of detecting and measuring stationary radio frequency pulses as well as linear chirp rates up to 1.18 GHz in 400 ns. The high-resolution TOA algorithm and linear chirp receiver have been prototyped, synthesized, and placed and routed for a Virtex 6 SX475 FPGA.

Wideband phased array calibration method for digital beamforming

Previous study has used chirp signals to characterize the RF response of a multi-channel RF receiver [1]. The results showed a significant channel imbalance. After applying a time-reversal filter, the channel imbalance was remedied and both phase and amplitude were realigned among the channels. In the present study, the RF response of a complete multichannel receiver with antenna was characterized. A 1-8 GHz phased array antenna was mounted in an anechoic chamber and a chirp signal was used to measure the frequency response of each channel as a function of azimuth angle. Each channels response was equalized using a time-reversal filter derived from the measured data and a combined beam pattern was formed. Time-reversal filters that steer the beam were also generated and it was found that sidelobe level worsened with larger steer angles. A simple mutual coupling model was proposed to explain the beam pattern feature.

Directional wide band time reversal digital beam forming FIR filter design using bore-sight calibration data

The time reversal wide band digital beam forming and calibration technique is briefly described. New techniques using the bore-sight probing RF signal alone to derive the time reversal FIR (Finite Impulse Response) filter set are discussed. In the digital beam forming simulation, a set of 50-tap FIR filters measured from a 16 channel of 1 to 8GHz tunable 500Mhz bandwidth front end digitized system is used as RF front end. The simulation results of the previous time reversal approach and new approaches are compared.

Detection and sensitivity analysis of compressed sensing electronic RF receiver

Compressed sensing (CS) technique has been applied in various areas of signal processing including RF signal processing. It is attractive due to its potential wideband coverage with reduced sampling rate. We conduct performance analysis of compressed sensing in receiver application. The compressed sensing uses two modulations and sampling schemes: non-uniform sampling (NUS), and Pseudo Random Code (PRC). Two algorithms are used to process the compressed signals: OMP (Orthogonal Matching Pursuit) and PE (Parameter Estimation). Signals detection sensitivity is analyzed through probability density function and the detection threshold according to the predetermined false alarm rate. Methods to remedy issue caused by modulations are proposed, and the sensitivity simulation results are also presented. The comparison of the one-signal detection sensitivity using remedy version of OMP and PE on the NUS modulation schemes are also presented and discussed. Sensitivity analysis for variable measurement matrices is then presented.