538 



ANTENNAS AND RF COMPONENTS 



Fig. 10-12 Cross Section of Rectangular Waveguide, Showing Width a Which 

 Governs Cutoff Wavelength. 



there is a definite cutoff wavelength. At wavelengths greater than cutoff 

 for a particular mode, the transmission line will not propagate energy in 

 that mode. 



The lowest-order mode or dominant 7node is that waveguide mode having 

 the longest cutoff wavelength (or lowest cutoff frequency). In rectangular 

 waveguide this is the T£io mode (Fig. 10-llc), which has a cut-off wave- 

 length Xc of la (Fig. 10-12). The T^ao mode (Fig. 10-1 Id) is the next 



15 



I 10 



9 5 



C3 



9 10 11 



FREQUENCY (kMc) 



13 



Fig. 10-13 Plot of Guide Wavelength vs. Frequency for RG-52/U or WR90 

 X-Band Waveguide, Showing Cutoff Frequencies for TEio and TE20 Modes. 



