I.Yu. Ryzhov – Research Scientist, JSC «Corporation «Vega» (Moscow). E-mail: firstname.lastname@example.org
Multi-beam slotted waveguide antennas are widely used in navigational radars mounted on aircrafts and spacecrafts. Such an antenna represents an 2D antenna array of linear symmetrical slotted waveguide travelling-wave antennas and forms four independent beams. Known multi-beam antennas have sidelobe level for about minus 13 dB. Modern navigational radars require slotted waveguide antennas with sidelobe level for minus 20 dB and less.
In the article it was offered to use the law of slot coupling distribution for antenna analysis instead the law of amplitude distribution along the waveguide. It is determined that in the range of −20…−26 dB for sidelobe level and of 3…10% for un-radiated power efficiently to use simple laws of slot coupling distribution such as linear and piecewise linear laws. Using of such laws make it possible to obtain needed values of sidelobe values and un-radiated power in symmetrical linear slotted waveguide antenna with the value of linear antenna efficiency closely to maximum value.
The dependences of far-field characteristics from values of the law of slot coupling distribution coefficients were obtained in program Mathcad. In the case of linear law of slot coupling distribution the far-field characteristics of slotted waveguide antenna depend on values of two law parameters. In the case of piecewise linear laws of slot coupling distribution the far-field characteristics of slotted waveguide antenna depend on values of four law parameters.
To confirm the obtained dependences it was created computational model of the slotted waveguide antenna in program CST Microwave Studio for three variations of antenna parameters: 1) sidelobe level = −20 dB, un-radiated power = 10%; 2) sidelobe level = −23 dB, un-radiated power = 5%; 3) sidelobe level = −26 dB, un-radiated power = 3%.
The difference of values of approriate characteristics obtained in the program Mathcad and in the program CST Microwave Studio for sidelobe level is less than 2%, for beam-width is less than 5% and for un-radiated power is less than 1,4%. Consequently the obtained in program Mathcad dependences are usable for designing of linear symmetrical slotted waveguide antennas with low sidelode level in value range of −20…−26 dB for sidelobe level and 3…10% for un-radiated power.