**Recent Advanced Applications**

[10] Yang, S. L. S, Kishk, A. A, & Lee, K. F. (2008). Wideband Circularly Polarized Anten‐ na with L-shaped Slot. *IEEE Transactions on Antennas and Propagations*, June. 2008)

[11] Yang, S. L. S, Chair, R, Kishk, A. A, Lee, K. F, & Luk, K. M. (2007). Study on Sequen‐ tial Feeding Networks for Sub-Arrays of Circularly Polarized Elliptical Dielectric Resonator Antenna. *IEEE Transactions on Antennas and Propagation*, February. 2007)

[12] Yang, S. L. S, Chair, R, Kishk, A. A, Lee, K. F, & Luk, K. M. (2006). Single Feed Ellipti‐ cal Dielectric Resonator Antennas for Circularly Polarized Applications. *Microwave and Optical Technology Letters*, November. 2006) page numbers 2340-2345, 48(11) [13] Chair, R, Kishk, A. A, & Lee, K. F. (2006). Aperture Fed Wideband Circularly Polar‐ ized Rectangular Stair Shaped Dielectric Resonator Antenna. *IEEE Transactions on*

[14] Kishk, A. A. (2003). Performance of planar four elements array of single-fed circular‐ ly polarized dielectric resonator antenna. *Microwave and Optical Technology Letters*,

*Antennas and Propagations*, April 2006) page numbers 1350-1352, 54(4)

page numbers 1780-1783, 56(6)

246 Advancement in Microstrip Antennas with Recent Applications

page numbers 321-333, 55(2)

page numbers 381-384, 38(5)

**Chapter 11**

**Planar Microstrip-To-Waveguide Transition in**

Many kind of millimeter-wave automotive radars have been developed [1], [2]. The microstrip antenna becomes a good candidate when radar sensors are widely used in vehicle due to its advantages of low cost and low profile. Generally microstrip antennas are placed on the surface of a radar sensor and are connected to millimeter-wave circuits inside of the sensor via waveguides. Therefore, transitions from waveguide to microstrip line are required, as shown

Rectangular waveguides were one of the earliest types of transmission lines used to transport microwave signals and are still used today for many applications. Because of the recent trend toward miniaturization and integration, a lot of microwave circuitry is currently fabricated using planar transmission lines, such as microstrip or strip line, rather than waveguide. There is, however, still a need for waveguides in many applications such as millimeter wave systems,

Various types of millimeter-wave transitions from waveguide to microstrip line have been proposed. The ridge waveguide type [3], quasi-Yagi type [4], and planar waveguide type [5] have been studied as longitudinal connection of waveguide with microstrip line. With regard to vertical transitions, a conventional type of probe feeding has a wideband characteristic [6], [7], but it needs a metal short block with a quarter-wavelength on the substrate. The replace‐ ment of the metal short block is a patch element in the waveguide to achieve sufficient coupling between waveguide and microstrip line. The slot coupling type [8] achieves coupling between the microstrip line and the patch element in the waveguide by means of a slot, it is composed of two dielectric substrates without a metal short block. The proximity coupling type [9] has been developed more recently. It can be composed of a single dielectric substrate attached to the waveguide. A rectangular patch element on the lower plane of the dielectric substrate

> © 2013 Seo; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

© 2013 Seo; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**Millimeter-Wave Band**

http://dx.doi.org/10.5772/54662

and in some precision test applications.

Additional information is available at the end of the chapter

Kazuyuki Seo

**1. Introduction**

in Figure 1.
