This paper by R. Chatterjee and N. S. Ganesan from the Indian Institute of Science, Bangalore, focuses on the analysis of microstrip antennas excited at TM_mⁿ mode in the X-band. The authors present a new theory based on the angular spectrum of plane waves and the principle of images to study the radiation characteristics of these antennas. The paper covers several key aspects: 1. **Near Field Analysis**: The authors justify the feasibility of exciting TM_mⁿ mode by analyzing the near field, which shows the non-existence of quasi-TEM mode. 2. **Geometry and Field Distributions**: The geometry of the microstrip structure is described, and the field distributions for different excitation mechanisms are discussed. 3. **Scalar Potential and Field Components**: The scalar potential and field components for the TM_mⁿ mode are derived, considering the propagation constants and boundary conditions. 4. **Experimental Study**: Near field measurements are conducted using a field sampling probe, and the results are presented in figures. 5. **Radiation Characteristics**: The paper discusses the mechanism of radiation, including the role of the ground plane and the concept of image. The angular spectrum of plane waves is used to evaluate the radiation fields, and the directivity, gain, and radiation efficiency are calculated. 6. **Discussion and Conclusions**: The authors conclude that their radiation theory based on the current strip and its image is well justified, and that higher gain and directivity can be achieved with smaller strip widths and substrate thicknesses. The maximum radiation efficiency is about 87% for small values of the aspect ratio (a/b). The 3-dB beam width is generally high, and the study contributes to the understanding of microstrip antenna radiation characteristics.This paper by R. Chatterjee and N. S. Ganesan from the Indian Institute of Science, Bangalore, focuses on the analysis of microstrip antennas excited at TM_mⁿ mode in the X-band. The authors present a new theory based on the angular spectrum of plane waves and the principle of images to study the radiation characteristics of these antennas. The paper covers several key aspects: 1. **Near Field Analysis**: The authors justify the feasibility of exciting TM_mⁿ mode by analyzing the near field, which shows the non-existence of quasi-TEM mode. 2. **Geometry and Field Distributions**: The geometry of the microstrip structure is described, and the field distributions for different excitation mechanisms are discussed. 3. **Scalar Potential and Field Components**: The scalar potential and field components for the TM_mⁿ mode are derived, considering the propagation constants and boundary conditions. 4. **Experimental Study**: Near field measurements are conducted using a field sampling probe, and the results are presented in figures. 5. **Radiation Characteristics**: The paper discusses the mechanism of radiation, including the role of the ground plane and the concept of image. The angular spectrum of plane waves is used to evaluate the radiation fields, and the directivity, gain, and radiation efficiency are calculated. 6. **Discussion and Conclusions**: The authors conclude that their radiation theory based on the current strip and its image is well justified, and that higher gain and directivity can be achieved with smaller strip widths and substrate thicknesses. The maximum radiation efficiency is about 87% for small values of the aspect ratio (a/b). The 3-dB beam width is generally high, and the study contributes to the understanding of microstrip antenna radiation characteristics.