Broadband microwave absorber composed of sandwich structure with a lossless medium as the intermediate layer

•A broadband microwave absorber with a sandwich structure was designed with an effective absorption bandwidth of 10 GHz.•Lossless medium (air or paraffin) was used as the intermediate layer, playing a role in regulating the phase of microwaves, resulting in an improvement of impedance matching and broadening the effective absorption bandwidth.•The proportion of microwave energy lost in each layer was given, proving that the addition of paraffin layers can increase the loss of the remaining layers.