Abstract-This paper presents our research work on designing a dual-band dual-polarized (DBDP) series-fed S/X-band shared aperture antenna (SAA) for synthetic aperture radar (SAR) applications. The proposed SAA DBDP X-band antenna is designed with the concept of series-fed 4-group 2 × 2 planar arrays with high impedance microstrip line feeding in both vertical and horizontal polarizations. By etching out the inner edge elements from 2 × 2 X-band subarrays in all the four-groups, the Sband element could be accommodated. The design evolution stages have been presented. The S-band (3.2 GHz) is best suited for volumetric soil moisture estimation using SAR and X-band (9.3 GHz) best suited for surveillance SAR applications and grain size estimation. To verify the antenna design concept, a prototype is fabricated and measured with both S-parameters and radiation characteristics including gain measurements. The antenna with reflection coefficient |S 11 | < −10 dB has an impedance bandwidth 3.12-3.42 GHz (9.3% BW) in S-band and 9.2-9.36 GHz (1.72% BW) in X-band. The measured isolation lS21l between two different bands in the same polarization is better than 25 dB, and the isolation between two different bands in two orthogonal ports is better than 30 dB. Measured gain of the antenna at S-band is better than 8.5 dBi at V-port and H-port, and X-band is better than 11 dBi at either port. Measured side-lobe level (SLL) at S-band is better than −17 dB at either port, and X-Band is better than −20 dB at either port. The overall size of the S/X-DBDP SAA is 100 × 100 × 1.6 mm 3 . Measured results of the S/X-DBDP SAA show good agreement with the finite integration technique (FIT) based computer simulation technology (CST) microwave studio.
In this study, a compact series-fed center-fed open-stub (SFCFOS) linear array antenna for K-band applications is presented. The antenna is composed of a single-line 10-element linear array. A symmetrical Chebyshev amplitude distribution (CAD) is used to obtain a low sidelobe characteristic against a uniform amplitude distribution (UAD). The amplitude is controlled by varying the width of the microstrip patch elements, and open-ended stubs are arranged next to the last antenna element to use the energy of the radiating signal more effectively. We insert a series-fed stub between two patches and obtain a low mutual coupling for a 4.28-mm center-to-center spacing (0.7λ at 21 GHz). A prototype of the antenna is fabricated and tested. The overall size of the uniform linear array is 7.04 × 1.05 × 0.0563 λg 3 and that of the Chebyshev linear array is 9.92 × 1.48 × 0.0793 λ g 3 . The UAD array yields a |S11| < -10 dB bandwidth of 1. 33% (20.912-21.192 GHz) and 1. 45% (20.89-21.196 GHz) for the CAD. The uniform array design gives a −23 dB return loss, and the Chebyshev array achieves a −30.68 dB return loss at the center frequency with gains of 15.3 dBi and 17 dBi, respectively. The simulated and measured results are in good agreement. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. ⓒ
In this paper, compact linear dual polarized series-fed 1 × 2 linear and 2 × 2 planar arrays antennas for airborne SAR applications are proposed. The proposed antenna design consists of a square radiating patch that is placed on top of the substrate, a quarter wave transformer and 50-Ω matched transformer. Matching between a radiating patch and the 50-Ω microstrip line is accomplished through a direct coupled-feed technique with the help of an impedance inverter (λ/4 impedance transformer) placed at both horizontal and vertical planes, in the case of the 2 × 2 planar array. The overall size for the prototype-1 and prototype-2 fabricated antennas are 1.9305 × 0.9652 × 0.05106 λ0 3 and 1.9305 × 1.9305 × 0.05106 λ0 3 , respectively. The fabricated structure has been tested, and the experimental results are similar to the simulated ones. The CST MWS simulated and vector network analyzer measured reflection coefficient (S11) results were compared, and they indicate that the proposed antenna prototype-1 yields the impedance bandwidth > 140 MHz (9.56-9.72 GHz) defined by S11 < −10 dB with 1.43%, and S21 < −25 dB in the case of prototype-2 (9.58-9.74 GHz, S11 < −10 dB) > 140 MHz for all the individual ports. The surface currents and the E-and H-field distributions were studied for a better understanding of the polarization mechanism. The measured results of the proposed dual polarized antenna were in accordance with the simulated analysis and showed good performance of the S-parameters and radiation patterns (co-pol and cross-pol), gain, efficiency, front-to-back ratio, half-power beam width) at the resonant frequency. With these features and its compact size, the proposed antenna will be suitable for X-band airborne synthetic aperture radar applications.
The design of X/K‐band shared aperture antenna (SAA) single‐linear polarized K‐band, dual‐polarized (linear/circular) X‐band 36‐elements (6×6) planar array antenna with high gain, and low cost for airborne synthetic aperture radar systems is presented. To reduce the complexity and size of the feed networks, the concept of series‐feed centre‐fed open stub array with Chebyshev amplitude distribution of −25 dB side‐lobe levels (SLL) are employed for K‐band design. Two typical frequencies, X‐band and K‐band of 9.65 and 21 GHz, are chosen (frequency ratio of 1:2.176) in this proposed SAA design on a single‐layer printed circuit board. For K‐band design, SLL can be controlled by Chebyshev distribution. The amplitude is controlled by the width of the individual patch in the linear array with left and right symmetries. A 50‐Ω microstrip line with 0.7λ spacing is used in between the patches for the ±25° scan angle requirement. The measured results are consistent with the simulations and provide a matching impedance bandwidth of 10.36/1.45% at X/K‐bands, respectively. The array also has a high aperture efficiency of more than 85%, SLL of (X/K‐bands: −18.9/−25 dB), and gain of (X/K‐bands: 24.2/17.4 dBi).
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