## 1 Introduction  
Microwave absorbers (MAs) are widely used in a variety of fields ranging from military devices to civil electronics, for eliminating unwanted electromagnetic (EM) radiation or reducing EM pollution [1; 2; 3]. Therefore, the study of the absorber has always been the focus of scholars all over the world. Classical microwave absorbers such as Salisbury screen [4; 5] and Jaumann [6; 7] absorbers are designed according to the principle of resonant absorption, and their thicknesses are limited by one-quarter of the wavelength. However, the electromagnetic wave absorbers based on metamaterials can break this limitation effectively. At the same time, because of their excellent designability, metamaterial absorbers have been widely investigated and developed greatly since they came into being, and many breakthroughs have been made [8; 9; 10]. Since their appearance, metamaterial absorbers have gradually developed from the single-frequency absorption of electromagnetic waves [8] to multi-frequency absorption [11; 12] and even broadband absorption [13; 14; 15]. This absorption property has developed from the polarization sensitivity and normal incidence to polarization-insensitive and wide incidence angle stability [16; 17]. The absorption bands have gradually extended from the initial radio frequency and microwave bands [18; 19] to terahertz [20; 21; 22], infrared [23; 24; 25] and even visible bands [26; 27]. Among them, optically transparent metamaterial absorbers have attracted a lot of attention because of their significant and extensive potential applications [28; 29; 30], such as radio frequency identification systems [31; 32; 33], electronic toll collection (ETC) systems [34], observation windows in stealth aircraft and electromagnetic shielding of rooms [35]. In recent years, more and more efforts have been devoted to developing optically transparent broadband absorbers. For optical transparent absorbers, researchers mainly focus on two aspects: how to effectively improve the absorbent bandwidth, and the visible light transmittance. [PERSON] et al. developed a transparent ultrawideband absorber based on a patterned resistive metasurface that had an efficiency of greater than 90% for a frequency band spanning 4.3-18.7 GHz [36]. However, the average visible light transmittance of the absorber is only 65%. [PERSON] et al. developed a high transparency broadband absorber by standing up closed-ring resonators that had an average optical transparency of around 82% [37]. The bandwidth with an absorption greater than 90% ranges from 5.5-19.7 GHz. However, this absorber is sensitive to polarization and can only achieve these properties under particular polarization. Furthermore, the preparation process of this absorber is complex and its pattern contour is obvious. Among the published transparent absorbers, most of the resistive films are designed on the surface of the structure without considering their actual use, which will shorten the service life of the absorber because it can easily be destroyed in the process of use. Such design also makes the pattern contour obvious. Therefore, it is necessary to develop a wide-band transparent absorber with a simple fabrication process, high optical transmittance, low profile and good environmental adaptability. In this paper, a new highly transparent, polarization-insensitive broadband absorber has been designed, fabricated and characterized. The novelty of the proposed absorber is three-fold. First, all patterned indium tin oxide (ITO) resistive films are designed within the structure, which can significantly improve the low profile and service life of the absorber. Second, the use of thin ultra-white glass with higher visible light transmittance enables our absorber to obtain higher optical transmittance (average transmittance, 85.7%) and less total thickness (0.0883 at the lowest operational frequency), which helps to improve the light environment and practicability of the absorber in practical applications.