Showing papers by "Randy L. Haupt published in 2016"

A 6:1 Bandwidth, Low-Profile, Dual-Polarized Ring Array of Spiral Antennas With Connecting Arms

Abstract: In an earlier work, the design of a 2:1 bandwidth dual-polarized phased array of Archimedean spiral antennas with cavity was presented. The reflection coefficient, circular polarization, and grating lobes goals were obtained independently in the design process. The low end of the final bandwidth was constrained to the frequency cutoff of the spiral antenna, at the low end of its bandwidth. In this communication, an extension of the bandwidth of the array is achieved by connecting the spiral antennas of the array. Hence, with the same size, the bandwidth is enlarged almost three times (a total of 6:1). The measurements confirm the simulations. The array can scan up to $\theta=30^\circ$ keeping a low reflection coefficient, good right- and left-hand circular polarization, low-sidelobe levels, and using a low-profile cavity.

Estimating the Bandwidth of Spiral Antenna Arrays

Abstract: An analytical method to estimate the bandwidth of planar phased array of spiral antennas is presented. Three main parameters are considered: circular polarization, reflection coefficient, and sidelobe levels. An application of the method for a planar array of asymmetrical Archimedean spirals is presented for a scan angle of $\theta {= 30^ \circ} $ . The estimated bandwidth and the bandwidth obtained with the simulation results differ in 3.5%.

A testbed for adaptive beamforming with software defined radio arrays

Abstract: Digital beamforming is the heart of adaptive beamforming. Its implementation has been slow due to hardware complexity and expense. This paper proposes a relatively inexpensive approach to digital beamforming using software defined radios. An experimental setup is described and results presented.

Power amplifier and power supply distortion of pulse compression radar chirps

Abstract: This paper examines the effects of time-domain pulse droop on linear FM chirp signals used in pulse compression radar. The radar literature is oddly quiet on how to specify power amplifier droop for a desired level of radar performance, with the result that overly stringent droop specifications (−0.5 dB maximum droop, e.g.) are sometimes imposed on modern phased array radar antennas. Since this drives array cost, mass, and power consumption, it is worthwhile asking how much droop can be tolerated. The present paper analyzes the effects of droop on compressed linear FM chirp waveforms and derives criteria that maintain the fidelity of the matched filter output. The application of a spectral window to control time sidelobes is included in the analysis. We show the perhaps surprising result that chirps are robust to as much as 3 dB of droop. In fact, loss of sensitivity due to reduced energy on the target becomes an issue before significant distortion of the compressed chirp waveform occurs. This work should point the way to sensible droop specifications resulting in more cost effective phased array antennas.

Phase error analysis of a dual polarized concentric ring array

Abstract: In a previous work a dual-polarized non-uniform concentric ring array of spirals has been developed. This array used the sequential rotation technique as a means to enhance the array's axial ratio and the non-uniform concentric rings to reduce the relative side lobe level. In the present paper the effects of realizing the phases of the sequential rotation using digital phase shifters are analyzed, considering both the phase-quantization and the phase-error effects in the broadside radiation of the array. We show that by considering a 2-bit phase shifter with a centered Gaussian error (sigma=5°) in each element of the array the axial ratio is kept under 1dB over the whole bandwidth, with a maximal degradation of 0.85dB when compared with the array without phase-errors or phase-quantization. We also show that the side lobe level suffers a maximal degradation of 4dB for the 2-bit phase shifter, however it is not affected by the phase error.

Phased array far field in the time domain

Abstract: The far field definition used by the IEEE comes from a narrow band formulation (time-harmonic fields). This paper looks at the far field definition from a broadband signal perspective. A time domain definition of far field in terms of the pulse dispersion for large, wideband phased arrays is presented. It is shown that far field in the time domain depends upon the instantaneous bandwidth of the signal.

Low frequency bandwidth in connected spiral arrays

Abstract: Connecting the arms of spirals in a dual circularly-polarized array significantly increases the array bandwidth. The connections decreased the low frequency cutoff from 1 GHz (without connections) to 350 MHz of the original array without connections (1 GHz). In this paper, an analysis at even lower frequencies is carried out revealing that the array is still useful at the original low frequency cutoff divided by 10 (100 MHz).