# A Broadband Ultra High Frequency (UHF) Fat-Dipole Antenna for Digital TV Applications
## 1 Introduction  
Digital TV (DTV) 3.0 guidelines in Brazil [1] propose the use of indoor multiple-input multiple-output (MIMO) antennas for reception and transmission, aiming to increase data throughput while using the same channel. To cover the entire allocated band of 230 MHz in the UHF range, centered at a frequency of 585 MHz, a broadband response is required (39% fractional bandwidth). The size consideration is significant: a classical half-wavelength dipole at the central frequency of this band measures approximately 25 cm in length. This dimension is already substantial for a single element and becomes even more pronounced when considering a two-element MIMO array. In addition to performance and size requirements, the construction of these antennas must be as simple as possible to ensure that they are low-cost enough for mass production. All these factors must be taken into account during the design process. UHF antennas typically occupy large areas due to their resonant wavelengths. One approach to achieve operation with electrically shorter lengths utilizes the space-filling properties of fractal structures [2]. The antenna in this study is an improved version of a former found in [3], where a fat-dipole planar antenna is introduced with optimized dimensions for reduced areas, but with not much emphasis on the low-coupling requirement necessary for MIMO. The previous design, in turn, was based on a fractal approach for broad bandwidth response, combining the ideas from [4, 5] varying dimensions along the dipole length and with fat strips operating as planar dipoles. Antennas intended for MIMOapplications, in particular, require high electromagnetic isolation to generate uncorrelated signals. Several studies have explored methods to decrease coupling without increasing inter-element spacing, such as T-shaped slots etched on the ground plane layer of an inverted F antenna (IFA) array [6]. In terms of similar antennas close to this frequency range, a bow-tie element excited by a microstrip balun achieved a band from 0.85 GHz to 3.25 GHz; however, the implemented solution is not fully planar [7]. When the structure is allowed to be 3D, this extra degree of freedom enables a larger potential for broad bandwidths, such as using two metallic plates excited by a discone-like monopole excitator, resulting in a band between 30 MHz and 3000 MHz [8]. The use of active devices associated to broadband non-Foster networks that implement negative slopes with respect to the frequency resulted in a planar inverted F antenna (PIFA) element covering the 100 MHz to 500 MHz range [9]. Another approach [10] achieved the low profile characteristic at the VHF range by loading a half-loop antenna with ferrite bars (frequency range 30 MHz to 300 MHz). Considering situations where the antenna is embedded, a U-shaped monopole DTV element was placed inside a laptop with reduced dimensions, taking advantage of the the mutual interaction with the internal chassis structure and resulting in an operational range from 470 MHz to 780 MHz [11]. With the aim of DTV applications as well, a quasi-Yagi antenna using two planar layers was implemented (470 MHz to 806 MHz, considering the VSWR below 2 criterion), whereby its final dimensions were 24 cm by 20 cm [12]. For the particular case of embedded Digital TV antennas (DVB-H) with a band ranging from 470 MHz to 750 MHz in mobile terminals, ref. [13] describes the use of non-resonant capacitive coupling element (CCE)-type antennas, where the radiation efficiency is sacrificed in order to achieve elements that fit into small volumes. For the same DVB-H application, another solution intended to be used in the receiver had a planar folded radiating patch with a folded parasitic arm, covering the 470 MHz to 806 MHz range (VSWR \(<\) 3 or insertion loss \(<\) 6 dB) [14]. This article reports on the design process of a planar antenna for DTV applications, intended for deployment in a 2 \(\times\) 1 MIMO array.