표 2. | Table 2. 3차원 마이크로파 홀로그래피의 다양한 분류 | Classification for 3D microwave holography.

Classification criteria	Type	Characteristics
Scanning aperture	Rectangular synthetic aperture[35]	Simple integral equation, small processing amount
	Cylindrical synthetic aperture[58]	Complex integral equation, large processing amount, better performance
Working frequency	UWB(Confocal method)[46]	Reflection coefficient
	Single (Holography)[47]	Transmission coefficient, better resolution
Inline holography	Beam splitter used[49]	Millimeter-wave
Phase	Indirect holography[38]～[51]	Phase not in use, simple system
	Direct holography[38]	Phase in use, better resolution
Reconstruction	Qualitative[44]	Normal method
	Quantitative[44]	Point-spread function, better accuracy
Linearization of inversion algorithm	Born approx[50]	Worse
	Rytov approx[50]	Better
Phase compensation	Phase compensation holography[56],[57]	Better image quality
Mutiple frequency	Mutiple frequency holography[65],[66]	Fast processing time, good image quality