ELECTRONICS LETTERS 15th March 2001 Vol. 37 No. 6 Linearly polarised radial stub fed high performance w ideband slot antenna P.H. Rao, V.F. Fusco and R. Cahill A wideband printed slot antenna fed by a radial stub operating over the mobile communication bands PCN (1.716–1.880GHz) and UMTS (1.9–2.0GHz and 2.1–2.2GHz) is presented. The impedance bandwidth of the antenna achieved for a VSWR ≤ 2 is 34% and the radiation patterns remain stable over the entire frequency band of operation (1.7– 2.4GHz) with cross-polarisation levels of less than –20dB. Simulated and measured radiation pattern and return loss results are presented. Introduction: A major advantage of the slot antenna over dipole antenna configurations is the higher bandwidth that can be achieved and the lower feed interaction effect with respect to radiation pattern influence. To achieve operation over a broad band of frequencies, various methods of feeding the slot antenna have been attempted [1, 2]. In this Letter we show that by using a radial stub as a series element on a 50 Ω feeder line we can achieve a wide impedance bandwidth match and stable radiation patterns over the frequency range 1.7–2.4GHz, covering PCN, UMTS and Bluetooth frequencies. Antenna configuration and design: The antenna designed at 2.2GHz as centre frequency, consists of a printed slot on a 2λ 0 × 1.5λ 0 (L × W) ground plane fed by a 50 Ω microstrip transmission line loaded with an open circuited radial stub. The antenna was fabricated on a double-sided etched Taconic material of ε r = 2.5 and height (h) 1.57mm. Considering the known broadband advantages of the series radial stub [3], the 50 Ω microstrip feed line was loaded with a radial stub in series to excite the slot antenna. Optimisations were carried out using HFSS [4], and the dimensions of the stub and the position of the stub on the feeder line (Figs. 1a and b) were varied in order to improve the impedance match over a broad range of frequencies while simultaneously achieving useful radiation patterns. Two tuning stubs of width (W 1 ) 5mm and length (L 2 ) 3.2mm are added on the feeder line at (d 2 ) 29mm from the feed point to match the impedance at the higher frequency band edge. Fig. 1 Wideband linearly polarised slot antenna a Antenna geometry b Feed geometry L′ = 0.9λ 0 , W′ = 0.16λ 0 , L 1 = 104mm, α = 90°, W″ = 4.5mm Fig. 2 Comparison of measured and simulated return loss of wideband slot antenna ——— measured ··········· simulated Fig. 3 Comparison of normalised measured and simulated E-plane radia- tion patterns at 2.0GHz (10dB circles) measured, co-polarisation simulated, co-polarisation ——— measured, cross-polarisation – – – – simulated, cross-polarisation Fig. 4 Comparison of normalised measured and simulated H-plane radia- tion patterns at 2.0GHz (10dB circles) measured, co-polarisation simulated, co-polarisation – – – – measured, cross-polarisation –·–·–·– simulated, cross-polarisation