1940 IEEE GEOSCIENCE AND REMOTE SENSING LETTERS, VOL. 13, NO. 12, DECEMBER 2016 First-Order Bistatic High-Frequency Radar Power for Mixed-Path Ionosphere-Ocean Propagation Shuyan Chen, Student Member, IEEE, Weimin Huang, Senior Member, IEEE , and Eric W. Gill, Senior Member, IEEE Abstract— A theoretical mixed-path ionospheric clutter model for bistatic high frequency radar is presented. Based on previous monostatic work, the first-order received electric field for bistatic radar is derived by considering the scattering processes on both the ionosphere and the ocean surface. Then, the first-order received power model is developed by incorporating a vertically polarized pulsed dipole antenna. In order to investigate the power spectrum of this ionospheric clutter model and its relative intensity to that of the ocean clutter, a normalized ionospheric clutter power is simulated. Numerical simulation results are compared with that of monostatic radar looking at the same ocean scattering patch. Subsequently, the simulations show how the bistatic angle and the ionospheric conditions affect the power spectrum for this bistatic mixed-path ionosphere clutter. Index Terms— Bistatic configuration, high frequency (HF) radar, ionospheric clutter. I. I NTRODUCTION H IGH-FREQUENCY surface wave radar (HFSWR) is operated as an ocean remote sensing device at fre- quencies between 3 and 30 MHz. By analyzing the received Doppler spectra, various sea parameters, including surface current fields, wave, and wind information may be extracted [1]. Additionally, HFSWR may be used to determine the position, speed, and track of hard targets such as ships and icebergs. The performance of the HFSWR may be significantly impacted by ionosphere clutters. In practice, a portion of the radar radiation may unavoidably travel upward to the ionosphere from the transmitting antenna, and then be partially reflected back to the receiving antennas directly (vertical prop- agation) or via the ocean surface (mixed-path propagation). This ionospheric clutter may have a high enough intensity to contaminate significant portions of the range-Doppler spectra [2]. Therefore, to improve the reliability of an HFSWR system, it is necessary to find methods to identify the unwanted signals in the radar return. One attempt to alleviate the clutter problem involves modeling the scattering processes of radio waves with the ionosphere and ocean surface based on the physical scatter- ing mechanisms. This letter presents a continuation of the Manuscript received April 7, 2016; revised August 2, 2016; accepted October 14, 2016. Date of publication November 1, 2016; date of current version December 7, 2016. The work of W. Huang was supported by the Natural Sciences and Engineering Research Council of Canada under Grant 402313-2012. The work of E. Gill was supported in part by the Natural Sciences and Engineering Research Council of Canada under Grant 238263-2010 and in part by the Atlantic Innovation Fund Award. The authors are with the Faculty of Engineering and Applied Science, Memorial University, St. John’s, NL A1B 3X5, Canada (e-mail: sc5714@mun.ca; weimin@mun.ca; ewgill@mun.ca). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LGRS.2016.2618855 Fig. 1. Geometry of mixed-path propagation for bistatic radar. development of the mixed-path propagation models, which have been investigated for monostatic radar configurations with a pulsed dipole [3] or an FMCW source [4]. Here, the analysis is extended to the bistatic case. Instead of using two full radar systems, the bistatic configuration provides a more economical way to obtain the directional information of the ocean surface characteristics, which involves a single transmitter and two widely separated receivers (one possibly at the transmit location). In Section II, the geometry of the mixed-path propagation for the bistatic HF radar is introduced and the received power model incorporating a pulsed source is derived. Simulations are conducted for varying wind directions and a comparison is made with results from a monostatic configuration in Section III. Section IV gives a brief summary of this letter. II. THEORETICAL DERIVATION A. Electric Field for a Pulsed Bistatic HF Radar The geometry of the mixed-path propagation for the bistatic radar is shown in Fig. 1. The xy plane indicates the mean sea level. The primary source transmitting antenna is taken to be a vertical dipole at the origin (0, 0, 0 + ) and the receiving antenna is at a range of ρ away from the transmitter. Assuming the ionosphere to be a reflecting plane at a height of H /2, the image of the radar source is at a height of H . Note that θ i is the reflection angle, R 1 is the range of free space propagation, ρ 1 is the projection of R 1 onto the xy plane, and ρ 2 is the range of surface propagation. The development of the bistatic mixed-path propagation incorporating a general vertical dipole source begins from the electric field equation found in [3, eq. (10)]. The electric field at the receiving antenna (ρ, 0, 0 + ) when a single scatter occurs at a point (x , y , 0 + ) is given as ( E + 0n ) 1 ∼-kC 0  R i sin θ i e - jkR 1 2π R 1 (∇ε ·ˆ ρ)  ∗ F (ρ 2 ) e - jkρ 2 2πρ 2 (1) where C 0 = ((η 0 l )/c)ω I (ω) is the dipole coefficient for an antenna of length l carrying a current I whose radian 1545-598X © 2016 IEEE. 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