SICL

Substrate Integrated Coaxial Line

  • Shielded structure, non-dispersive
  • easy to integrated

Microstrip lines:

  • Easy to fabricate
  • not shielded
  • loss due to radiation and cross-talk

Strip Lines:

  • lateral leakage
  • cross-talk

Composition

  • A conductive thin film sandwiched between two grounded dielectric layers and side-limited by two rows of metallic via holes (Fig.1)

  • Propagate TEM mode similar to strip line

  • Lateral shielding (侧面的) due to metallic holes avoids the propagation of the unwanted parallel-plate mode , which could be excited by any discontinuity, causing leakage and interferences with other lines.

  • First upper mode: TE10 mode, same as SIW, because central conductor does not affect its model field structure. why?

  • Suppose above is true. Cut-off freq of TE10 mode

    A D S is shown in Fig.1. Usually, D and S is restricted by manufacturing technologies. Thus, A could be adjusted to control the TE10 freq.

  • Characteristic impedance Z0

    For TEM wave, Z0 is freq. independent. Thus Z0 could be controlled by the ratio between 2H and W.

Example

Unimodal operation at 4GHz

Reference

[1] F. Gatti, M. Bozzi, L. Perregrini, K. Wu, and R. G. Bosisio, “A Novel Substrate Integrated Coaxial Line ( SICL ) for Wide-Band Applications,” in 36th European Microwave Conference, 2006, no. September, pp. 1614–1617.

SIW/SISW

Dispersive— not suitable for wideband applications

Review of substrate-integrated waveguide circuits and antennas, 2010, K.Wu

  • For higher frequency, like millimeter-wave, the microstrip lines and coplanar waveguides presents high transmission and radiation losses.

  • SIW has been applied in several microwave components

  • Application in frequency over 30 GHz cases is much less, because the technology needed to manufacture the miniaturized dimensions, losses and material selection restricts.

SIW structure

SIW circuits and antennas review

2 Structure

2.1 Operation principles

Usually $TE_{n0}$ modes are supported, but TM modes are not supported by SIW, due to the gaps between the metal vias: in fact, transverse magnetic fields determine longtitudinal surface currents, which are subject to strong radiation due to the presence of the gaps.

The following figure shows the field distribution of TM11, TM21 mode in rectangular waveguide. It could be seen that the the E field terminates at the transverse wall. Due to the gaps between metal vias, the field will leaked outside the SIW.

The estimation for the effective width of SIW is

where d is the diameter of the metal vias, w represents their transverse spacing and the s ithe longitudinal spacing ( shown in the following figure)

(2) could be refined in many relations.

2.2 Loss mechanisms

loss is critical when SIW works at millimeter wave freqs.

Three loss sources:

  • conductor loss —-> finite condutivity of the metal walls
  • dieletric loss —> lossy dielectric material
  • possibly radiation loss —> energy leakage through the gaps

Solutions:

  • For condutor loss: increase substrate thickness (attenuation constant proportional to the inverse of substrate thickness)
  • Dielectric loss: use better material. dimesion changes won’t help
  • Radiation loss: radiation losses can be kept reasonably small if s/d<2.5, with s/d= 2 being the recommended value.

Insertion loss could be significantly increased by the effect of surface roughness in condutors.

Loss comparison between SIW, Microstrip, CPW: generally comparable losses compared to traditional planar transmission lines.

2.4 Size and bandwidth

width of SIW—> cutoff freq of fundamental mode

operation bandwidth —> one octave ( from cutoff freq f1 of TE10 TO cutoff freq f2 of TE20 mode

  • SIFWL: reduce size by more than 2, slightly larger losses
  • HMSIW:
  • SISW: improve bandwidth, 7.5 - 18GHz (with 40% bandwidth enhancement)
  • Ridge SIW: the ridge was implemented through a row of thin, partial-height metal posts located in the centre of the longer side of the waveguide. 4.9 - 13.39 GHz, with 73% bandwidth enhancement. There is a lot has been done to further improve the bandwidth. …

3 SIW passive circuits

3.1 Filters and couplers

inductive post:

Metal post(柱) or screw（螺钉） extending across a waveguide parallel to the E field, to add inductive susceptance in parallel with the waveguide for tuning or matching purposes.

Reference: https://www.radartutorial.eu/03.linetheory/tl16.en.html

iris:

diaphragm consisting of thin overlapping plates that can be adjusted to change the diameter of a central opening.

3.2 Transitions

4 SIW active circuits

Oscillators, Mixers, Amplifiers

5 SIW antennas

  • SIW slotted antenna [1]

  • leaky-wave antennas

    • longitudinal spacing leakage [2]
    • Based on TE20 mode[3]

  • Modified Vivaldi radiator [4]

  • Cavity-backed SIW antennas

    • slotted SIW cavity fed by a CPW[5]

    • slotted SIW cavity with meander line and fed by a MS line[6]

    • Ku-band xxx, 2 by 2 array of metal patches[7]

  • H-plane sectoral horn antenna, with dieletric loading, high gain and narrow beamwidths [8]

Reference:

[1] Yan, L., Hong, W., Hua, G., Chen, J., Wu, K., Cui, T.J.: ‘Simulation and experiment on SIW slot array antennas’, IEEE Microw. Wirel. Compon. Lett., 2004, 14, (9), pp. 446–448.

[2]Deslandes, D., Wu, K.: ‘Substrate integrated waveguide leaky-wave antenna: concept and design considerations’. Asia-Pacific Microwave Conf. Proc. (APMC’05), Suzhou, China, 2005

[3] Xu, F., Wu, K., Zhang, X.: ‘Periodic leaky-wave antenna for millimeter wave applications based on substrate integrated waveguide’, IEEE Trans. Antennas Propag., 2010, 58, (2), pp. 340–347

[4] Cheng, Y.J., Hong, W., Wu, K.: ‘Design ofa monopulse antenna using a dual V-type linearly tapered slot antenna (DVLTSA)’, IEEE Trans. Antennas Propag., 2008, 56, (9), pp. 2903–2909

[5] Luo, G.Q., Hu, Z.F., Dong, L.X., Sun, L.L.: ‘Planar slot antenna backed by substrate integrated waveguide cavity’, IEEE Antennas Wirel. Propag. Lett., 2008, 7, pp. 236–239

[6] Bohorquez, J.C., Pedraza, H.A.F., Pinzon, I.C.H., Castiblanco, J.A., Pena, N., Guarnizo, H.F.: ‘Planar substrate integrated waveguide cavity-backed antenna’, IEEE Antennas Wirel. Propag. Lett., 2009, 8, pp. 1139–1142

[7] Awida, M.H., Fathy, A.E.: ‘Substrate-integrated waveguide Ku-band Wirel. Propag. Lett., 2009, 8, pp. 1054–1056 cavity-backed 2 × 2 microstrip patch array antenna’, IEEE Antennas

[8] Wang, H., Fang, D.-G., Zhang, B., Che, W.-Q.: ‘Dielectric loaded substrate integrated waveguide (SIW) – plane horn antennas’, IEEE Trans. Antennas Propag., 2010, 58, (3), pp. 640–647

6 SIW active antennas