Quarter-wave corrugated transformer for broadband matching of a corrugated feed

This paper describes a broadband technique for obtaining the transformation TE
11
→ HE
11
at the input of a corrugated feed. Usually, this transformation is obtained by operating the feed in the vicinity of a frequency, coi, corresponding to one of the zeroes of the input surface reactance since the feed input reflection, ρ
t
vanishes at ω
1
. Here we use a matching transformer to produce ρ
t
≃ 0 at two frequencies simultaneously, i.e., at ω
1
and a much lower frequency, ω
0
. Using two sections of corrugated waveguides, with a total of eight teeth and ω
0
≃ 0.63 ω
1
, the measured reflection, ρ
t
, is about −40 dB in the vicinity of both frequencies ω
0
and ω
1
, and it remains less than −30 dB over the entire frequency range 0.60 ω
1
< ω < 1.04 ω
1
. This makes the corrugated feed suitable for simultaneous operation at the 4- and 6-GHz terrestrial microwave radio bands.