Abstract ¾ Dielectric waveguides rectangular cross section made of dielectrics, ferrites, and semiconductors are experimentally studied at frequencies 30 - 120 GHz. Devices (passive and active) based on these waveguides (attenuators, phase shifters, switches, dividers, couplers and etc.), also some systems using elaborated devices have been created. The advantages of the reported waveguides as follows: broad band, simple construction, low loss and price cost.

As a result of these advantages dielectric waveguides with electrically and optically controlled ferrite and semiconductor insertions are of interest for millimeter wave radars, communication, image and introscopy systems.

Index Terms ¾ Millimeter Waves, Semiconductor, Ferrite.

I. INTRODUCTION

Dielectric waveguides (DW) are regarded as perspective transmission lines for the millimeter (MM) wavelength especially for short MM waves because of low loss and dimensional tolerance requirements as well as broader band compared with the traditional MM transmission lines [1-4].

Presently there are about dozen types of DW. We investigated only rectangular cross section DW on low permittivity substrate or on metal substrate - image DW (IDW), and nonradiative DW [5]. All these waveguides were made of low loss dielectrics, ferrites and semiconductors.

Ferrite and semiconductor DW (FW and SW) allow us to realize electrically and optically controlled devices [4,6,7].

2. MATERIALS FOR DW, FW and SW

The parameters of low loss dielectrics, ferrites and semiconductors used for DW, FW and SW fabrication are shown in Table. The measurements of these parameters were carried out using beam waveguide spectroscopy methods [8,9]. Here n - refractive index, loss tangent, l-wavelength.

Table

#	Material	n±0.3 %	tanx 10^-3	l, mm
1	PTFE	1.437	0.63	0.63
2	Polyethylene	1.512	0.62	1.0
3	SiO₂ (ceramic)	1.820	1.70	0.75
4	SiO₂ (fused)	1.951	1.47	0.86
5	Al₂O₃ (ceramic)	3.031	1.30	0.95
6	Ferrite (NiZn)	3.65	1.52	1.3
7	Ferrite (Li)	3.95	1.24	2.16
8	Ferrite (FeY)	3.88	0.75	2.16
9	Si(r>10⁴Ohm cm)	3.42	0.08	1.41
10	GaAs(r>10⁷Ohm cm)	3.61	0.2	2.2

Expression

allows to estimate losses in DW made of materials of the Table. So in the case of SW using high resistive Si losses may be about 1 dB/m or less for frequencies f < 300 GHz.

DW section made of TGS crystal are used as polarization filter. TGS parameters for the waves propagating along three crystallographic axes were measured to be n₁=2.74, =0.62; n₂=2.31, =8×10^-3; n₃=2.91, =1.5×10^-2, respectively, l=1.1 mm.

Table shows that the difference between refractive indexes of ferrites, Si and GaAs is very small. So no problem to connect FW and SW without reflection and radiation of power. Also the discontinuity in connection DW made of Al₂O₃ and FW or SW is very small.

3. DEVICES BASED ON DW

Main components for frequencies 26- 48, 80-120, 115-145 GHz have been elaborated. Components based on PTFE, SiO, Al₂O₃, Si, GaAs, NiZn, and FeY ferrites have been fabricated (DW- rectangular waveguide transition sections, directional couplers, power dividers, frequency and polarization filters, attenuators, phase shifters, nonreciprocal devices, interferometers, modulators and ets.) [10,11].

IDW made of Al₂O₃ ceramics had insertion loss from 8×10^-3 dB/cm (f =26 -38 GHz) to 1.3×10^-1 dB/cm (f =115 -145 GHz). DW using Si (»10^-4) had insertion loss 10^-2 dB/cm
(f » 100 GHz ).

Complete set of devices for frequency range 26 -37 GHz has been fabricated on the basis of NiZn FW with formed PTFE substrate. Transition from metal rectangular waveguide to FW total losses are less than 0.2 dB. For 3 and 4 port switches two T -bridges were used based on square cross section FW, metal gratings, and coil for magnetic field control. Switching loss in such Faraday effect device is less than 0.6 dB, channel isolation 20 dB.

Rectangular cross section FW with the same coil is used as a magnetically controlled phase shifter without polarization rotation. The section was made of NiZn ferrite ( n= 3.71, =8×10^-3 at frequency 230 GHz, saturation magnetization = 5000 G) and has aspect ratio a/b = 0.5. In this case the degeneracy of modes and ( y axis is parallel to broad side of FW ) is suppressed and no Faraday rotation. We use mode because the phase shift for mode is more and the insertion loss is less then for mode. In FW section of cross section 1.3 ´ 2.6 mm (section length 46 mm) the phase shift per unit length was 120 degrees/cm up to 420 deg/cm depending on current I in the coil. The total insertion loss was 0.4 - 0.5 dB.

The phase shifters were also tested at frequencies 37 - 120 GHz using panoramic network analyzers. These phase shifters had matching tapers fabricated from ferrite. The total length of phase shifters were about 60 mm. The cross section of aspect a/b = 0.5 was chosen from the condition =1,7-1.9, were l₀ is the central wavelength of the operating frequency range. Each coil comprised about 60 winds. The measured phase shift j weakly depends on frequency for j £90⁰ (I = 0.2 -0.3 A). The total loss depending on frequency increases from 0.5 dB at 37 GHz to 2 dB at 115 GHz. The level of orthogonal polarized mode was less than -20 dB up to phase shift 420 degrees. The phase shift per unit length was 80 -90 deg/cm and coil current was less than 1 A.

Another method to create phase shifters is to use thin films of some paraelectric materials deposited on DW. We investigated (Ba, Sr)TiO₃ films of 0.5 mkm thickness on sapphire. Under control voltage 0 -2.5 V/mkm e decreases in 1.5 -2.0 times at frequency
10 GHz [12]. So it is possible to realize phase shifters with phase change (by ) at 1.5 dB insertion losses.

SW made of Si was used as optically controlled attenuator and modulator. Optical control was realized by light emitting diode (LED) which was placed over the surface of the SW.

The insertion loss a₀ (including transition to metal waveguide losses) did not exceed 1.2 dB for frequencies 25 -37 GHz and 2.2 dB for 80-120 GHz. The maximal a (for LED current I =0.5 A) was more than 17 and 20 dB respectively.

The same devices operated as modulators up to frequency 80 kHz.

Isolators consisted of FW were elaborated. In these isolators the energy concentration in DW depends on the direction of wave propagation. The direct wave propagates practically without losses in DW. The reverse wave propagates in FW and is irradiated into absorber. These devices have insertion losses from 0.9 dB at frequencies 25 -40 GHz to 1.8 dB at frequencies 115 -145 GHz. Return losses are more than 12 dB, VSWR is less than 1.35.

A nonreciprocal frequency filter based on the NiZn ferrite disc with axial magnetization was fabricated. The filter had maximum attenuation of 21 dB at frequency 131 GHz, rejection band 1 GHz at the 18 dB level, VSWR <1.4, and the insertion loss less than 1 dB.

Receiving and transmitting subsystems consisting of an IDW, a ferrite isolator, a directional coupler, an optically controlled attenuator, a modulator, and magnetically controlled frequency filter have been elaborated for the frequency range 80 -120 GHz. Insertion losses up to 3.5 dB, VSWR<1.4, isolation more than 14 dB, attenuation range is 15 dB. The dimensions are 20´40´120 mm³, and the weight is 200 grams.

NDW was investigated as device for dielectric materials properties measurements. We used resonant method in NDW. Between main NDW and NDW with sample under test we had air space. This space allowed to change tunnel coupling between main NDW and NDW with the sample. The wave propagating in the sample reflects totally from its back wall. So we have resonator with tunnel coupling. For measurement of we change coupling ( by changing air space between main NDW and NDW with the sample ) up to critical coupling when resonator becomes nonreflecting.

Real part of refractive index n is expressed from equation connecting n and the resonant frequencies of the resonator. This method is good for dielectric samples of small cross section.

CONCLUSION

The results of the experimental study confirm the feasibility of the above -mentioned passive, nonreciprocal, optically and electrically controlled devices based on DW, FW, and SW with characteristics acceptable for practical applications. The devices can be realized both as separate subsystems and as a parts of communication, measuring, testing, and other MM range systems. This work was supported by IRE/RAS and CNPq.

REFERENCES

[1] R.M.Knox, P.P.Toulios, Integrated circuits for the millimeter through optical frequency range, Proc. of Symposium on Submillimeter Waves. Polytechnical Inst. of Brooklyn, N-Y, pp. 495-515, 1970

[2] T.Itoh, Inverted strip dielectric waveguide for millimeter wave integrated circuits, IEEE Trans. on MTT, vol.. MTT-24, pp. 821-830, Nov. 1976

[3] I.Wolff and K.Solbach, Dielektrische Bildleitungen, Aachen, Verlag H, Wolff, 1982

[4] V.V.Meriakri, B.A.Murmuzhev, M.P.Parkhomenko, Millimeter wave dielectric strip waveguides using ferrites and semiconductors, MMET Conference Proc., Kharkov, Ukraine, pp. 253-255, September 1994.

[5] T.Yoneyama, S.Nishida, Nonradiative dielectric waveguide for millimeter wave integrated circuits, IEEE Trans. On MTT, vol. MTT-29, # 11, pp. 1188-1192, 1981

[6] V.V.Meriakri, B.A.Murmuzhev, M.P.Parkhomenko, Millimeter wave dielectric strip waveguides and components based on ferrites and semiconductors, Proc. of MIOP 95, pp. 211-213, Sindelfingen, Germany, 1995

[7] B.A.Murmuzhev, V.V.Meriakri, Millimeter wave low-power electronic and optoelectronic devices based on dielectric, ferrite and semiconductor waveguides, Proc. of SPIE, vol. 2722, pp. 270-272, 1996

[8] V.V.Meriakri et. al., Submillimeter beam waveguide spectroscopy and its applications, Problems of modern radio engineering and electronics, edd. By V.A.Kotelnikov, pp. 179-197, Nauka, Moscow, 1982

[9] V.V.Meriakri, Material properties in the millimeter range, MSMW 98 Symposium Proc., vol.,1, pp.121-123, Kharkov, Ukraine, 1998

[10] V.V.Meriakri and M.P.Parkhomenko, Millimeter wave dielectric strip waveguides made of ferrites and phase shifters based on these waveguides, Electromagnetic waves and electronic systems, vol. 1,no 1, pp. 89-96, 1996

[11] V.V.Meriakri, B.A.Murmuzhev, M.P.Parkhomenko, Millimeter wave devices based on dielectric, ferrite and semiconductor waveguides, Proc. Intern. Microwave and Optoelectronics Conf., 1997 SBMO/IEEE MTT-S, vol. 2, pp.431-433, Natal, Brazil, 1997

[12] Y.M.Poplavko and V.V.Meriakri, High-permittivity microwave dielectrics, Electromagnetic waves and electronic systems, vol. 2, no 6, pp. 35-43, 1997.