Coaxial Mode Feed

Coacial mode (for cylindrical wave excitation)

This circuit is used for feeding of RLSA. When a concentric slot arrangement is used with this excitation, the conical beam is radiated because the phase difference is 180deg for symmetrical slots at boresight. When a pencil beam is required, the spiral slot arrangement is used.

• M. Natori, M. Ando, and N. Goto, "A Design of Coaxial-to-Radial Line Adapters in Radial Line Slot Antennas," IEICE Trans., Vol.E73, No.11, pp.1874-1879, Nov. 1990.

Rotating mode (for rotating mode excitation)

A spiral slot arrangement with cylindrical wave excitation can be used in order to radiate the pencil beam at boresight. When the number of the slots are small, the analysis model using periodic boundary walls will not work well. In that case, a concentric slot arrangement with rotating mode (the amplitude is uniform, and the phase is tapered linearly along the phi-direction) excitation is preferable. For rotating mode excitation, a cavity resonator with perturbation elements, a ring slot using microstrip line, a notched annular ring slot on a shorting plate of a rectangular waveguide and a crossed slot on the broad wall of a rectangular waveguide are proposed. At present, a crossed slot on the broad wall of a rectangular waveguide is considered to be a promising candidate becuase the structure is simple, and it does not use dielectric materials.

• Kaoru SUDO, Takuichi HIRANO, Jiro HIROKAWA, and Makoto ANDO, "A Radial Line Slot Antenna Fed by a Rectangular Waveguide through a Crossed Slot," IEICE Trans. Communication, Vol.E86-B, No.10, pp. 3063-3070, October 2003.
• Kaoru SUDO, Akira AKIYAMA, Jiro HIROKAWA, and Makoto ANDO, "A Millimeter-Wave Radial Line Slot Antenna Fed by a Rectangular Waveguide Through a Ring Slot," IEICE Trans. Communication, Vol.E84-C, No.10, pp.1521-1527, Oct. 2001.
• Akira Akiyama, Jiro Hirokawa, and Makoto Ando, "APERTURE COUPLED PLANAR FEED CIRCUITS FOR ROTATING-MODE RADIAL LINE SLOT ANTENNA," APMC pp. 46-49, paper number 203, (Sydney, December 2000)
• Y. Kigure, A. Akiyama, J. Hirokawa, and M. Ando, "A Planar Circuit of a Ring Slot Exciting a Rotating Mode in Radial Line," Proceedings of the 1999 IEICE General Conference, B-1-102, Tokyo, March 1999. (in Japanese)
• Tatsuya Yamamoto, Jiro Hirokawa, Makoto Ando, and Naohisa Goto, "An Analysis of an Electric Wall Type Cavity Resonator for Concentric Array Radial Line Slot Antennas," PROCEEDINGS OF ISAP'96, CHIBA, JAPAN, pp.337-340, Sep. 1996.

Pi-Junctions

for co-phase feed

This figure shows pi-junctions which devide the incident power with co-phase. The distance between the neighboring pi-junctions is a guide wavelength. This divider is called a pi-junction because the power is divided with the figure of pi (Greek character).

• Tsukasa Takahashi, Jiro Hirokawa, Makoto Ando, and Naohisa Goto, "A Single-Layer Power Divider for a Slotted Waveguide Array Using Pi-Junctions with an Inductive Wall," IEICE Transactions on Communications, Vol.E79-B, No.1, pp.57-62, Jan. 1996.
• N. Goto, "A Planar Waveguide Slot Antenna of Single Layer Structure," Technical Report of IEICE, AP88-39, pp.39-43, July 1988. (in Japanese)

for alternating-phase feed

This figure shows T-junctions which devide the incident power with alternating-phase. The distance between the neighboring T-junctions is a half the guide wavelength. This divider is called a T-junction because the power is divided with the figure of T.

• K. Sakakibara, Y. Kimura, A. Akiyama, J. Hirokawa, M. Ando, and N. Goto, "Alternating Phase-fed Waveguide Slot Arrays with a Single-Layer Multiple-Way Power Divider," IEE Proc. Microw. Antennnas Propag., vol.144, No.6, pp.425-430, Dec. 1997.

center feed for alternating-phase feed

This figure shows Cross-junctions which devide the incident power with alternating-phase. The distance between the neighboring Cross-junctions is a half the guide wavelength. This divider is called a Cross-junction because the power is divided with the figure of Cross (+).

The long-line effect is serious because it restrict the bandwidth. Because the total distance between the input and the last slot is reduced with this feed circuit, the band width can become wider. The beam squint due to the frequency variation can be also improved because two beams squint in the opposite directions.

• Se-Hyun PARK, Jiro HIROKAWA, and Makoto ANDO, "A Planar Cross-Junction Power Divider for the Center Feed in Single-Layer Slotted Waveguide Arrays," IEICE Trans. Communication, Vol.E85-B, No.11, pp.2476-2481, November 2002.

Longitudinal Shut Slot

-1st-null beam-tilting, Linearly polarized wave

TE10 wave ->
Magnetic field of a TE10 incident wave and magnetic currents on the slots

These figures show the longitudinal shunt slot arrays. Slot offsets are alternating with respect to the waveguide center axis. The magnetic field of a TE10 incident wave excites magnetic currents on the slots. The physical interpretation is taht the slots cut the electric current on the waveguide wall, and they act as condensers which then prpduce electromagnetic fields outside. Coupling power is controlled by the slot offset, and transmission phase is controlled to be zero (resonant slot) by the slot length. Slot parameters are designed by the unit-cell analysis using the method of moments (MoM). The slot spacings are varied a bit from a half the guide wavelength in order to suppress the total reflection which is the accumulation of reflections from each slot. Normally the phase taper is 360deg*n (n: integer except 0) from the first slot to the last one linearly. As a result, the main beam is tilted because of the phase taper. The radiation pattern is null at boresight because the sum of EM fields radiated from each slot cancels out. In the above example, n=-1 which is called -1st-null beam-tilting.

• Y. Kimura, T. Hirano, J. Hirokawa and M. Ando, "Alternating-phase fed single-Layer slotted waveguide arrays with chokes dispensing with narrow wall contacts," IEE Proc. Microw., Antennas Propag., Vol.148, No.5, pp.295-301, October 2001. (Alternating-phase fed single-layer slotted waveguide arrays)
• K. Sakakibara, J. Hirokawa, M. Ando, and N. Goto, "Periodic Boundary Condition for Evaluation of External Mutual Couplings in a Slotted Waveguide Array," IEICE Trans. Commun.,Vol.E79-B, No.8, pp.1156-1164, Aug. 1996. (Co-phase fed single-layer slotted waveguide arrays)

Leaky-wave (Beam-tilting angle 50deg), Circularly polarized wave

TE10 wave ->
Magnetic field of a TE10 incident wave and magnetic currents on the slots

These figures show leaky waveguide crossed-slot arrays. This antenna radiates a circularly polarized wave in a tilted beam direction. The tilted-beam (50deg) can be realized by a leaky-wave, in which a tilted direction is determined by the difference of phase velocities in the two regions. Mobile DBS reception antenna is one of the applications of this array, which allows horizontal mechanical scanning with flush-mount. This antenna have been released in the market.

• Takuichi HIRANO, Jiro HIROKAWA, and Makoto ANDO, "A Design of a Leaky Waveguide Crossed-Slot Linear Array with a Matching Element by the Method of Moments with Numerical-Eigenmode Basis Functions," IEICE Trans. Commun., Vol.E88-B, No.3, pp.1219-1226, March 2005.
• T. Hirano, J. Hirokawa, and M. Ando, "Design of a Waveguide Crossed-Slot Array with Matching Elements Using the Method of Moments with Numerical-Eigenmode Basis Functions," IEEE AP-S Digest, Columbus, Ohio, US, vol.3, pp.1046-1049, June 22-27, 2003.
• T. Hirano, J. Hirokawa, and M. Ando, "Waveguide matching crossed-slot," IEE Proc. Microw., Antennas Propag., vol.150, no.3, pp.143-146, June 2003.
• T. Hirano, J. Hirokawa, and M. Ando, "Method of moments analysis of a waveguide crossed slot by using the eigenmode basis functions derived by the edge-based finite-element method," IEE Proc. Microw., Antennas Propag., vol.147, no.5, pp.349-353, Oct. 2000.
• J. Hirokawa, M. Ando, N. Goto, N. Takahashi, T. Ojima, and M. Uematsu, "A Single-Layer Slotted Leaky Waveguide Array Antenna for Mobile Reception of Direct Broadcast from Satellite," IEEE Trans. Vehicular Tech., vol.44, no.4, pp.749-755, Nov. 1995.

Teflon (er=2.17, tan d=0.00085 at 10GHz)
Transmission Loss: 0.11dB/cm, Insertion Loss: 0.56/2=0.28dB at 61.25GHz

A parallel plate post-wall waveguide consists of a print circuit board (PCB) with metallized via holes, which simulate rectangular waveguide. Waveguide structures can be easily fablicated in millimeter-wave band. EM fields are concentrated in the waveguide, and do not spread like microstrip lines, which is preferable for electromagnetic compatibility (EMC). A parallel plate post-wall waveguide can reduce conductor loss by increasing the waveguide height, which is impossible using microstrip lines.

A broad band post-wall waveguide to rectangular waveguide converter had been realized. For commercial use, many types of converters which connect between a post-wall waveguide and other transmission lines such as coaxial line, microstrip line and so on are required, and they are under development.

A slotted parallel plate post-wall waveguide array is one of the applications of a post-wall waveguide. There are many kinds of applications such as Butler matrix, waveguide filter and other microwave circuits.

• T. KAI, J. HIROKAWA, and M. ANDO, "Feed through an Aperture to a Post-Wall Waveguide with Step Structure," IEICE Trans. Commun., Vol.E88-B, No.3, pp.1298-1302, March 2005.
• T. KAI, J. HIROKAWA, and M. ANDO, "A Transformer between a Thin Post-Wall Waveguide and a Standard Metal Waveguide via a Dielectric Substrate Insertion with Slits Etched on It," IEICE Trans. Commun., Vol.E87-B, No.1, pp.200-203, January 2004.
• J. Hirokawa, and M. Ando, "Single-Layer Feed Waveguide Consisting of Posts for Plane TEM Wave Excitation in Parallel Plates," IEEE Transactions on Antennas and Propagation, Vol.46, No.5, pp.625-630, May 1998.

Teflon (er=2.17, tan d=0.00085 at 10GHz)
Transmission Loss: 0.037dB/cm at 25.6GHz

The mechanism of a Butler matrix is explained briefly using the above animation. The Butler matrix devides the input power from a port to the output ports with same amplitude but with linear phase taper. The phase taper is different for each input port. Electronic beam scanning can be realized when the Butler matrix is used as a feed circuit for antennas. The above figure shows a 4-Way Butler matrix using post-wall waveguides, whose transmission loss is much smaller than one using microstrip lines.

The mechanism of a Butler matrix is understood by a discrete Fourier transform (DFT) of theDirac delta function and translation rule (F[f(t-t1)]=F[f(t)] exp(j w t1)). The Fourier transform of the Dirac delta function Dirac(t) is 1. When Dirac(t) is translated in the time domain as Dirac(t-t1), the taper in the phase is generated , and its Fourier transform becomes F[Dirac(t-t1)]=exp(j w t1) due to translation rule. Analogous to the discrete Fourier transform, let us correspond the left and right ports on the above figure to the discrete time and frequency axis, respectively. The interpretation is now clear that the output ports are the discrete Fourier transform of input ports. Butler matrix is a microwave circuit which discrete Fourier transforms analog signals. The Fast Fourier transform (FFT) algorithm is used in the Batler matrix, and it is realized by using microwave circuits such as hybrids, phase shifters and cross junctions. Systematic design procedure for the Butler matrix is well explained in the paper (T.N. Kaifas and J.N. Sahalos, "On the Design of a SIngle-Layer Wideband Butler Matrix for Switched-Beam UMTS System Applications," IEEE Antennas and Propagation Magazine, Vol.48, No.6, Dec. 2006.).

• S. YAMAMOTO, J. HIROKAWA, and M. ANDO, "A Beam Switching Slot Array with a 4-Way Butler Matrix Installed in a Single Layer Post-Wall Waveguide," IEICE Trans. Commun., Vol. E86-B, No. 5, pp.1653-1659, May 2003.