## 1 Introduction  
As the microwave (MW) spectrum becomes more and more crowded, which is synonymous with an increasing electromagnetic (EM) compatibility problem [1], one needs new functional materials for EM coatings, shields and filters, working in specific frequency bands. Such materials should combine high electrical conductivity with good electromagnetic interference (EMI) shielding efficiency (SE), the reciprocal of the transmittance. Small sheet resistance, high optical and IR transparency, ultra-small thickness and ultra-light weight make graphene [2] an excellent candidate for designing such poly-functional materials for EM applications.  
Microwave probing has revealed that even a single graphene monolayer is capable of providing almost 20% of EM attenuation [3]. However, since deposition of graphene on dielectric surfaces of arbitrary shape is still a difficult task, attention of scientists and engineers is currently focused on composite materials filled with graphene nanoplatelets, nanoribbons and flakes that also demonstrate remarkable mechanical, thermal and electromagnetic properties (see [4] and references therein). We have recently suggested an interesting alternative to graphene-based materials by demonstrating that 25 nm thick pyrolytic carbon (PyC) film, which is morphologically close to the nanographite, being many thousands times thinner than skin depth can attenuate a significant part of incident microwave radiation [5]. In contrast to graphene, PyC films can be easily synthesized not only on metal, but also on dielectric substrate [6] of arbitrary shape which makes it very attractive from the technological point of view. Moreover, being 5-100 times thicker than graphene monolayers, PyC film are much more robust than atom layer thick graphene, _i.e.,_ it is hardly influenced by mechanical tension, acoustic waves or an external electric field. The EM response of PyC films can be easily described and characterized in the framework of the conventional techniques allowing quantitative description of their properties. It is also worth noting that coating of a substrate with PyC film is much cheaper than with graphene, _i.e.,_ PyC films are also commercially attractive for a wide range of applications.  
The frequency dependence of transmittance/reflectance in K\({}_{\text{a}}\)-band, 26-37 GHz, for 25 nm thick PyC film was measured in [5]. An experiment demonstrated surprisingly high absorbance (\(\sim\)30%) despite the small sample thickness, which was many thousands times less than the skin depth in metals. The experimental and theoretical description of transmittance/reflectance of PyC films of different thicknesses at the frequency of 30 GHz has been reported recently in our paper [7]. In the current paper, we concentrate on the frequency dependence of absorption, transmission and reflection of PyC films in the K\({}_{\text{a}}\)-band (26-37 GHz). In particular, we address two important points for practical application: (i) dependence of the absorbance/reflectance of PyC film deposited on quartz substrate on the irradiation effect from the PyC or substrate side; and (ii) frequency dependence of the EM properties of binary PyC-quartz structures in the K\({}_{\text{a}}\)-band.