# Computational Design of a Broadband In-Line Coaxial-to-Rectangular Waveguide Transition  
[PERSON]  
1 School of Electric and Computer Engineering, Chungbuk National University,  
Cheongju 28644, Republic of Korea; [EMAIL_ADDRESS] (Q.Z. ); [EMAIL_ADDRESS] (S.X. ); [EMAIL_ADDRESS] (J.H. ); [EMAIL_ADDRESS] (E.-A. ); [EMAIL_ADDRESS] (G.-Y.A. ); [EMAIL_ADDRESS] (D.O. ); [EMAIL_ADDRESS] (C.-S.L. ); [EMAIL_ADDRESS] (B.-C.A.) [PERSON]  
1 School of Electric and Computer Engineering, Chungbuk National University,  
Cheongju 28644, Republic of Korea; [EMAIL_ADDRESS] (Q.Z. ); [EMAIL_ADDRESS] (S.X. ); [EMAIL_ADDRESS] (J.H. ); [EMAIL_ADDRESS] (E.-A. ); [EMAIL_ADDRESS] (G.-Y.A. ); [EMAIL_ADDRESS] (D.O. ); [EMAIL_ADDRESS] (C.-S.L. ); [EMAIL_ADDRESS] (B.-C.A.) 2 Jiangsu Hengxin Technology Co., Ltd., 138 Taodu Road, Yixing 214222, China  
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[PERSON]  
1 School of Electric and Computer Engineering, Chungbuk National University,  
Cheongju 28644, Republic of Korea; [EMAIL_ADDRESS] (Q.Z. ); [EMAIL_ADDRESS] (S.X. ); [EMAIL_ADDRESS] (J.H. ); [EMAIL_ADDRESS] (E.-A. ); [EMAIL_ADDRESS] (G.-Y.A. ); [EMAIL_ADDRESS] (D.O. ); [EMAIL_ADDRESS] (C.-S.L. ); [EMAIL_ADDRESS] (B.-C.A.) 2 Jiangsu Hengxin Technology Co., Ltd., 138 Taodu Road, Yixing 214222, China  
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Bierng-Chearl Ahn  
1 School of Electric and Computer Engineering, Chungbuk National University,  
Cheongju 28644, Republic of Korea; [EMAIL_ADDRESS] (Q.Z. ); [EMAIL_ADDRESS] (S.X. ); [EMAIL_ADDRESS] (J.H. ); [EMAIL_ADDRESS] (E.-A. ); [EMAIL_ADDRESS] (G.-Y.A. ); [EMAIL_ADDRESS] (D.O. ); [EMAIL_ADDRESS] (C.-S.L. ); [EMAIL_ADDRESS] (B.-C.A.) 2 Jiangsu Hengxin Technology Co., Ltd., 138 Taodu Road, Yixing 214222, China  
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[PERSON]  
1 School of Electric and Computer Engineering, Chungbuk National University,  
Cheongju 28644, Republic of Korea; [EMAIL_ADDRESS] (Q.Z. ); [EMAIL_ADDRESS] (S.X. ); [EMAIL_ADDRESS] (J.H. ); [EMAIL_ADDRESS] (E.-A. ); [EMAIL_ADDRESS] (G.-Y.A. ); [EMAIL_ADDRESS] (D.O. ); [EMAIL_ADDRESS] (C.-S.L. ); [EMAIL_ADDRESS] (B.-C.A.) A journal paper on the coaxial-to-waveguide transition dates back to a 1947 work by [PERSON] [2], where various designs of the right-angle transition were presented along with a design theory that includes the transmission line and the characteristic impedance. As one of the fundamental high-frequency devices, the enduring importance of the coaxial transition can be seen in its continued research interest nowadays [3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19]. The in-line coaxial transition has been investigated from the early days of microwave technology developments [1; 2; 3; 4; 5; 6; 7; 8; 9], when the engineering designs were carried out by experiments guided by an elementary theory. Theoretical analysis has been restricted to transitions constructed with a simple rectangular loop mode converter [6; 8]. A right-angle transition employing a single or double continuously tapered ridge was already known in the 1940s [1; 2]. [PERSON] appears to be the first engineer to employ a stepped TEM-TE\({}_{10}\) mode transformer in the design of an in-line coaxial-to-rectangular waveguide transition [3]. In 1957, he achieved a VSWR of less than 1.10 at 2.6-3.8 GHz and a VSWR of less than 1.19 at 4.8-6.5 GHz with his transition. In 1963, [PERSON] used a three-step ridge transformer plus a coaxial quarter-wave transformer to design and test an in-line transition operating at 2.5-4.1 GHz (1.64:1 bandwidth) with a VSWR \(<\) 1.22 or a reflection coefficient \(<-20.1\) dB [4]. [PERSON] and co-workers presented the theoretical analysis and the design of an in-line transition employing an inverted-\(L\) shaped loop probe [5]. Their transition showed a narrow bandwidth. It appears that [PERSON], [PERSON], and [PERSON] are the ones who presented a rigorous theoretical analysis of the inverted-\(L\) shape end launcher assuming a sinusoidal current distribution on the inverted-\(L\) probe wire [6]. Later, [PERSON] improved the theory of [PERSON], [PERSON], and [PERSON] to include more general cases [7].