Design of wideband double-sided printed dipole antenna for C- and X-band applications H. Rmili, J.M. Floc’h and A. Khaleghi A wideband double-sided printed dipole antenna is presented for C- and X-bands. The proposed structure consists of a microstrip-fed annular-ring dipole with a central disc dipole printed on the top side of a substrate, and a modified annular-ring dipole, a connecting strip line and the ground plane printed on the bottom side. The antenna gives a wide resonant bandwidth that extends from 5 to 12.8 GHz, with a fractional bandwidth of 87.6%. Experimental and simulation results are presented and discussed in detail. Introduction: With the rapid progress in modern communication system technology, the requirements for broadening frequency band- width have increased for both commercial and military applications. Wideband antennas are desirable in personal communication systems, small satellite communication terminals, and other wireless applica- tions. In particular, communication systems that operate in the C- and X-bands are normally designed using separate antennas for each band. Since it is becoming more and more important to use such systems in one setting, it is desirable to design a single antenna that operates in both frequency bands [1]. To comply with this requirement, compact high-performance broadband planar antennas are needed. Recently, various types of patch antennas have been studied to meet the increasing trend for wideband antennas, and several techniques for size reduction and bandwidth enhancement have been proposed [2, 3]. The most important broadbanding techniques for microstrip patch antennas [4–6] are use of thicker and=or high permittivity substrates, shaping the patch, use of aperture coupling, mounting reactive loading, and use of parasitic elements or coupled resonators. In particular, the double-sided printed dipole-antenna [4, 7], which permits the use of coupled or stacked resonators, is one efficient structure for bandwidth enhancement. This structure is simple and easily fabricated, with easy integration into solid-state devices. In addition, the use of annular-ring patches is also one of the effective shaping techniques to improve the impedance bandwidth of microstrip printed antennas [5, 6]. In this Letter, we combine these two techniques in order to design a novel wideband printed dipole antenna operating in C- and X-bands. The antenna was fabricated and characterised by determining the impedance matching characteristics, the impedance bandwidth, and the radiation patterns. The impedance matching and the impedance bandwidth can be tuned by adjusting different design parameters. L/2 L/2 R 5 R 4 R 2 R 3 R 1 z x top view bottom view W 1 W W 2 W 2 W 3 L 1 L 2 L 3 S S Fig. 1 Printed dipole antenna Dimensions, mm: L ¼ 75, W ¼ 50, L 1 ¼ 15, W 1 ¼ 6, L 2 ¼ 5, W 2 ¼ 1, L 3 ¼ 21.5, W 3 ¼ 10, S ¼ 1, R 1 ¼ 6, R 2 ¼ 7, R 3 ¼ 8.6, R 4 ¼ 10, R 5 ¼ 12 Antenna design: The proposed antenna was etched on CuClad substrate with h ¼ 0.8 mm and e r ¼ 2.17. The design parameters of the optimised structure are summarised in the caption of Fig. 1. The dimensions of the antenna are 75  50 mm. On the top side of the substrate, an annular ring of inner radius R 2 and an outer radius R 3 , with a central disc of radius R 1 is printed. The annular-ring dipole (R 2 , R 3 ) is fed by a strip line of width W 1 . The printed radiator on the bottom side of the substrate is obtained from a circular-ring, with an inner radius R 4 and an outer radius R 5 , by adding a rectangular element of dimensions L 1  W 1 and by subtracting a thin vertical slot of width S as shown in Fig. 1. This radiator was connected through a microstrip line of width W 2 to a rectangular ground plane of dimensions L  W 3 . The antenna was modelled, using IE3D method of moment code, in order to realise a wideband antenna which operates in both C- and X-bands. The main optimised parameters design are the radius R 1 of the central disc, radii R 2 and R 3 of the of the annular-ring printed on the top side of the substrate, and radii R 4 and R 5 of the modified annular-ring printed on the bottom side of the substrate. Fig. 2 shows the simulated return loss variation for different lengths of L 1 . From the simulated results in Fig. 2, we can remark that the lower resonant frequency can be tuned by varying the length L 1 of the rectangular element. This lower frequency at around f 1 ¼ 5 GHz shifts when we modify L 1 from the optimised value 15 mm, and by maintaining a constant coupling distance S of 1 mm between the ground plane and the rectangular element (L 1  W 1 ). In fact this frequency shift with L 1 is due to the modification of the resonating path, whereas the variation of the impedance matching at the lower frequency of the wide band, with L 1 , is due to the modification of the coupling condition between the exciting-rectangular element and the central disc. –35 –30 –25 –20 –15 –10 –5 0 4 6 8 10 12 14 L 1 = 15 mm L 1 = 14 mm L 1 = 16 mm return loss, dB frequency, GHz Fig. 2 Simulated return loss for proposed antenna with different rectangular length L 1 simulation measurement –35 –30 –25 –20 –15 –10 –5 0 4 6 8 10 12 14 return loss, dB frequency, GHz Fig. 3 Measurement and simulation results of antenna return loss ELECTRONICS LETTERS 14th September 2006 Vol. 42 No. 19