a phase shifter using waffle-iron ridge guides and …...a phase shifter using waﬄe-iron ridge...

A phase shifter usingwaffle-iron ridge guidesand its application to a beamsteering antenna

Hideki Kirinoa), Kazuhiro Honda, Kun Li, and Koichi OgawaGraduate School of Engineering, Toyama University,

3190 Gofuku, Toyama-shi, Toyama 930–8555, Japan

a) [email protected]

Abstract: A mechanical linear sliding phase shifter using waffle-iron

ridge guides (WRG) and its application to a beam steering antenna are

shown. The structure of the new phase shifter is simpler than we have

presented previously in that the number of metal layers has been reduced.

Another advantage of the new phase shifter is that with it simple beam

steering antennas can be realized. This paper explains the principle and the

characteristics of the phase shifter and gives an example of a beam steering

antenna.

Keywords: waffle-iron, phase shifter, beam steering, antenna

Classification: Antennas and Propagation

References

[1] H. Kirino and K. Ogawa, “A 76GHz multi-layered phased array antenna usinga non-metal contact metamaterial waveguide,” IEEE Trans. Antennas Propag.,vol. 60, no. 2, pp. 840–853, Feb. 2012. DOI:10.1109/TAP.2011.2173112

[2] H. Kirino and K. Ogawa, “Metamaterial ridged waveguides with wavelengthcontrol for array antenna applications,” ISAP Intl. Symp. 4E2-1, Digest, 2012.

[3] H. Kirino and K. Ogawa, “A fast and slow wave combined-mode metamaterialridged waveguide for array antenna applications,” EuCAP2013, CA02a.5,Gothenburg, Sweden, Apr. 2013.

[4] E. Pucci, A. U. Zaman, E. Rajo-Iglesias, P.-S. Kildal and A. Kishk, “Losses inridge gap waveguide compared with rectangular waveguides and microstriptransmission lines,” EuCAP2010, C32P1-5, Barcelona, Spain, Apr. 2010.

[5] H. Kirino and K. Ogawa, “Various applications of low-cost phased arrayantennas with mechanical phase shifters,” IEEE-APS Topical Conference onAntennas and Propagation in Wireless Communications, Aruba, Aug. 2014.DOI:10.1109/APWC.2014.6905523

1 Introduction

Low insertion loss phase shifters are key devices for beam steering antennas in the

microwave and millimetre-wave bands. Up till now phase shifters have been© IEICE 2017DOI: 10.1587/comex.2017XBL0006Received January 10, 2017Accepted January 23, 2017Publicized February 14, 2017Copyedited May 1, 2017

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IEICE Communications Express, Vol.6, No.5, 188–193

http://dx.doi.org/10.1109/TAP.2011.2173112




http://dx.doi.org/10.1109/APWC.2014.6905523




manufactured using many semiconductor devices working in those high frequency

bands, which is too costly for consumer devices or small systems. In order to

reduce costs, we proposed a low-cost phase shifter for 76.5GHz radar systems [1],

which employed a new waveguide technology, the so-called Metamaterial Ridged

Waveguide [2, 3] or Gap Waveguide [4]. In this paper we rename this the Waffle-

iron Ridge Guide (WRG). In the WRG there are no metal contacts between the

upper and lower metal plates. Since contact between the metal plates is unneces-

sary, they can be made to slide mechanically with respect to each other, thus

changing the length of the waveguide to realize a phase shifter. In this paper we

propose a new phase shifter and a new beam steering antenna using a WRG with

periodic bumps on the upper metal surface, which is simpler than the ones we have

proposed previously [1].

2 Configuration of the new phase shifter

Fig. 1(a) shows the basic structure of the new phase shifter. This has two special

features. The first feature is the same as that of the WRGs already described in the

literature [1, 2, 3, 4] in which there are many rods and a �=4 high ridge on the lower

metal plate. The second feature is a series of periodic bumps on the surface of

the upper metal plate in line with the ridge. As shown in Fig. 1(a), the height,

thickness, width and spacing of the bumps are h, t, �=8 and �=4, respectively. The

top and bottom levels of the ridge are lower than those of the rods by �=16 in order

that the ridge and the bumps do not come into contact as depicted in Fig. 1(a). In

this paper the depth beside the ridge is different from that in our previous paper [5].

As shown in Fig. 1(a), the new phase shifter has one phase shifting part and

two matching parts on either side of the phase shifting part. The matching parts

have bumps whose height changes linearly between the outside of the phase shifter

and the phase shifting part in order to keep matching when the upper metal plate

is slid.

Fig. 1(b) shows cross sections of the phase shifters for the conditions when

the upper metal plate is mechanically slid with respect to the lower metal plate. The

xy cross sections at z ¼ 0 are shown in (i), (ii) and (iii), and the zx cross sections at

y ¼ 0 are shown in (iv), (v) and (vi), respectively. The arrows in the xy cross

sections indicate the fields generated by RF energy in the WRG, and the lines in the

zx cross sections indicate the current flow in the WRG. The principle of the new

phase shifter can be explained as follows. In (i) and (iv) in which the position of the

bumps is at the centre of the ridge, most of the field is confined between the ridge

surface and the bumps on the upper metal plate, so that the current flow meanders.

In (ii) and (v) in which the upper metal plate has been slid a certain distance, the

field is distributed partly to the bumps and partly to the surface of the upper metal

plate, so that the current flow is slightly straightened and more direct. In (iii) and

(vi) in which the upper metal plate has been slid further, most of the field is between

the ridge and the surface of the upper metal plate, so that the current flow is even

more direct. The above discussion tells us that when the bumps on the upper metal

plate are moved away from the centre of the ridge, the current path becomes shorter.

This shortening of the current path is equivalent to shortening the waveguide, and

© IEICE 2017DOI: 10.1587/comex.2017XBL0006Received January 10, 2017Accepted January 23, 2017Publicized February 14, 2017Copyedited May 1, 2017

189


this is equivalent to increasing the wavelength in the waveguide. Consequently,

sliding the upper metal plate has the effect of phase shifting.

As explained above and shown in the figures, this new phase shifter uses only

two metal plates compared to the one using three metal plates we proposed

previously [1]. Thus, the use of this new phase shifter can reduce costs and the

size of beam steering antennas.

3 Characteristics of the new phase shifter

Fig. 2 shows the characteristics of the new phase shifter, which have been

calculated by EM-simulation for a model with perfect conductivity. The model

has fifteen bumps in the phase shifting part and ten bumps in the matching parts.

Fig. 2(a) shows the input matching and insertion loss characteristics, and Fig. 2(b)

shows the insertion phase shift characteristics. Figs. 2(a) and 2(b) are plotted as

functions of the position of the bumps from the centre of the ridge in the y-direction

for various heights, h, and thicknesses, t, of the bumps. The horizontal axes in

Fig. 2(a) and Fig. 2(b) are normalized by �=8.

(a) Configuration of the new phase shifter.

(b) Phase shift principle.

Fig. 1. Configuration of the new phase shifter and the phase shiftprinciple.


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From Fig. 2(a), we find the following trends and results.

1. With the bumps closer to the ridge the input matching and insertion loss

deteriorate, a trend that increases with the height of the bumps. This shows that

the input matching is very sensitive to the height of the bumps.

2. The worst input matching is less than −10 dB, which means that the matching

part works effectively.

From Fig. 2(b), we find following trends and results.

1. The higher and thicker the bumps are, the bigger the phase shift. The largest

phase shift of more than 11 radians is obtained for bumps with h ¼ �=8 and

t ¼ �=16.

2. The phase shift is very sensitive to the height of the bumps, whereas it is not

very sensitive to the thickness. For example, with h ¼ �=8 and t ¼ �=16,

changing the thickness by a factor of 4 from �=16 to �=64 reduces the phase

shift by 25%, whereas changing the height by a factor of 4 from �=8 to �=32

reduces the phase shift by 95%.

Using the results shown in Fig. 2, we chose h ¼ �=8 and t ¼ �=16 for an

application to a beam steering antenna. This is described in the following section.

4 Application to beam steering antenna

Fig. 3(a) shows the configuration of a beam steering antenna using four phase

shifters. The phase shifters provide the choke parts at the I/O ports using an

impedance converting technique of the quarter-wavelength waveguides that con-

verts the short impedance to an imaginary open circuit and an imaginary short

(a) Input matching and insertion loss characteristics.

(b) Insertion phase shift characteristics.

Fig. 2. Characteristics of the phase shifter.


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circuit sequentially. The choke parts keep the RF energy confined in the region of

the phase shifter when the upper plate is slid. All four phase shifters are on the same

upper and lower metal plates with the distance between adjacent phase shifters

being 3�=4. The RF source is divided into four signals with the same phase and

magnitude, and these are input to the I/O ports. The four signals passing through

each phase shifter are directed to the four antenna elements spaced by 3�=4.

Between adjacent phase shifters, the number of bumps in the phase shifting parts

differs by one. Thereby the differential phase shifts between adjacent antenna

elements remain the same when the upper metal plate is slid. Consequently, when

the upper metal plate is slid, the direction of the main beam, which depends on the

phase changes in the waveguides, changes according to the position of the upper

metal plate.

Fig. 3(b) shows the beam changing characteristics as a function of the position

of the upper metal plate in the y direction shown in Fig. 3(a). The origin is where

the bumps are in line with the centre of the ridge. The height, h, and width, t, of

the bumps are �=8 and �=16, respectively, the number of bumps between adjacent

phase shifters differs by one, and the element spacing is 3�=4. As shown in

Fig. 3(b), a beam steering angle of more than 7 degrees has been obtained.

(a) Configuration of the beam steering antenna.

(b) Characteristics of the beam steering antenna.

Fig. 3. Configuration and characteristics of the beam steering antenna.


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5 Conclusion

A new phase shifter with periodic bumps on the upper metal plate of a WRG is

proposed. By EM-simulation, a phase shift of more than 11 radians can be achieved

when the height, h, and width, t, of the bumps are �=8 and �=16, respectively. The

beam steering characteristics of a beam steering antenna using the new phase shifter

are explained. With h ¼ �=8 and t ¼ �=16, and the number of bumps between

adjacent phase shifters differs by one, and the element spacing is 3�=4, a beam

steering angle of more than 7 degrees is obtained.


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a phase shifter using waffle-iron ridge guides and …...a phase shifter using waﬄe-iron ridge...

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