DE2229669A1 - Polarization-insensitive directional coupler for millimeter waves - Google Patents

Description

WESTERN ELECTRIC COMPANY Saleh, A.A.M. -1

New York, NY, 10007 , US A

Polarization-insensitive directional coupler for millimeter waves

The invention relates to a directional coupler for separating an incident wave into at least 2 output waves, one of which Output wave with the incident wave by a transmission coefficient and a second output wave with the incident Wave are linked by a reflection coefficient.

In recent years, the need for directional couplers in the millimeter and sub-millimeter wavelength range has been developing a variety of couplers which are quite similar to the optical frequency coupler. These so-called ; quasi-optical "directional couplers are low loss and facilities of simple construction. However, they are quite sensitive to polarization. As a result of their sensitivity to polarization can the quasi-optical directional coupler according to the prior art only with regard to a required coupling characteristic can be designed for a single polarization. Therefore, their application was primarily limited to systems at where a single polarization was used.

209853/0827

The invention is based on the object of designing a directional coupler of the type specified at the outset so that the restriction falls towards a single direction of polarization, i.e. any waves can also be processed.

The stated object is achieved in that the coupler comprises three adjacent areas, each of which has a predetermined thickness and dielectric constant and that the thicknesses and dielectric constants of the respective areas are selected so that the transmission coefficient and the reflection coefficient of the coupler are independent of the polarization of the incident wave are.

A further development of the invention relates to the fact that the two outer areas have the same thickness and the same dielectric constant exhibit.

A second development of the invention relates to the fact that the thicknesses and dielectric constants of the respective areas are selected in accordance with the following equations: ^. 2

1 - (C ₁ - 1) / COS θ {

209853 / Ijöv

kXo

i T

\ J £, -sin ² 0.

' ^mid

_d - 2jl L

2 2 DD

^sin

-1

where: θ. is equal to the angle between the direction of propagation of the incident wave and the normal to the surface of the first area, k is an integer not divisible by two, Λ. is a wavelength of the electromagnetic energy, R is the reflected portion of the incident energy, d is the thickness of the respective outer areas, c. ₁ their respective electricity constants and d _o and £. are the thickness

it i

or dielectric constant of the area in between.

According to the principles of the invention, three adjoining dielectric plates or layers are used to form a quasi-optical one Directional coupler used. In particular, the thicknesses and dielectric constants of the platelets and the orientation of the coupler to the path of an incident wave is chosen so that the polarized electric field in the plane of incidence of the transmitted portion of the incident wave is equal to the perpendicular to the incident plane polarized field of the transmitted

209853/0827

Part of the incident wave, namely with regard to phase and Amplitude. The plane of incidence is determined by the normal on the surfaces of the layers and the direction of the incident Wave defined. The selection leads to the fact that the dielectric platelets are also chosen to be essentially loss-free The above parameter in the specified manner also ensures that the reflected components of the two waves have the same relative phases and have amplitudes. In addition, since an arbitrarily polarized incident wave can be split into two components can, which are polarized once in the plane of incidence and perpendicular to it, it is obvious that the transmitted components all waves incident on the coupler will and will similarly have the same relative phases and amplitudes the reflected components of all incident waves also have the same relative phases and amplitudes.

As mentioned, in a special embodiment of the invention the two outer dielectric layers of the coupler have the same thickness d and the same dielectric constant Q_, while the middle layer has a different thickness and different dielectric constant ε. In this

Embodiment, the parameters d, d, £, £ are used to

JL Δ ι. Δ

filling predetermined relationships chosen in the following Equations are disclosed in detail.

2098 5 3/0827

Further details of the invention are provided by reference explained to the following description with reference to the drawing, the only figure showing a coupler made of three dielectric Shows layers constructed according to the principle of the invention.

The directional coupler is denoted by the general reference number 11 and has three adjoining dielectric layers 12, 13 and 14. The outer layers 12 and 14 are the same Dielectric constant £; and equal thicknesses d. The one in between or middle layer 13, on the other hand, has a different dielectric constant £ and a different one Thickness d. However, all three layers are considered essential accepted without loss.

The coupler 11 lies along the input direction 15 of the shaft, at an angle of 90 + Θ., Where - #. the angle

ι ι

between the direction 15 and the normal to the surface 16 of the layer 12 is. The one directed along the path 15 and on Wave energy incident on the surface 16 is divided into two output paths or directions 17 and 18 by the coupler. Of the Path 17 is parallel to path 15, while path 18 has an angle of 2 Θ. to route 15 forms. 0. for example, let 45.

In this case the; Directions IG and 18 perpendicular to each other.

2 0 9 8 5 3/0827

In operation, two plane waves polarized perpendicular to each other are generated in the plane of the figure, i.e. the plane of incidence, spread out, directed along the wave path 15. One of these waves has an electric field, which is polarized parallel to the plane of incidence and is represented by the vector E. The electric field of the other wave is polarized perpendicular to the plane of incidence and is represented by the vector E.

The two waves proceed along path 15 and impinge on coupler 11 at surface 16. The coupler 11 divides each wave into two separate waves, one directed along path 17 and the other directed along path 18. The waves directed along the path 18 are referred to as reflected waves, while those directed along the path 17 Waves are referred to as transmitted waves.

The reflected wave resulting from the polarization E, is represented by the vector E in the figure, while the transmitted wave is denoted by the vector E. Both

XL

Waves E, E have the same polarization as their generating wave E. Correspondingly, the reflected and the transmitted wave from the E _(> polarization are denoted by the vector E ₀ and E, respectively

203853/0 ^ 27

pointed out that these waves are polarized in the same direction as their generating wave.

In accordance with the principles of the invention, it has been recognized that the

relative amplitude and phase of E, and E "and the relative ^ - Ir 2r

Amplitudes and phases of E and E are made equal

XL ώΐ

in which the parameters £. , f., d, d in correspondence

1 A χ 2 »

Mood can be selected with the following proportions:

₁ -) ² /

d -

-sin V

sin

-1

• 2 "- sin θ. ι

⁽¹ - ^R)

where k is an integer not divided by two, R the relative one Proportion of the incident wave which is to be coupled along the path 18 and X o is the wavelength of the incident Energy in free space.

20985 3/0827

In the case shown here, the following parameters and equations can be used to write:

^E lr ^E 2r

^E 2

^E l " ^E

where r and t are the transmission and reflection coefficients of the coupler for normal and parallel polarized ones to the plane of incidence Waves defined.

Since a wave of arbitrary polarization walling along path 15 can be split into two waves, one being polarized in the plane of incidence and the other being polarized perpendicular to this plane of incidence, it is readily apparent that the parameters r and t are the transmission and reflection coefficients a ent s for such a wave also represent. Assume, for example, that instead of representing the fields of separate waves, the polarizations E and E are actually the component fields of a single wave with an electric field E, ie: E ₃ - E _{1 +} E ₂ .

209853/0827

The incidence of this wave on the coupler results in transmitted and reflected waves E, E, E, E, as before;

However, it 2a, ± V ciE the previous case is known:

^E lr ^{= rE} l
^E 2r = ^rE 2
^E ! T - * i
^E 2t ^{3 tE} X

Hence the composite reflected and transmitted Waves from E as follows:

In one embodiment of the invention for hybrid surgery (i.e., half of the energy is transmitted and the other stick is reflected) at a frequency of 100 GHz (i.e., λο = 3.0 mm) values of £ = 1.26 and £. = 9.4 were considered satisfactory

JL et

found. A material with the first value of the dielectric constant at a frequency of 100 GHz is Buna-S rubber, while a material with the latter value of the dielectric constant at 100 GHz is aluminum oxide or alumina. Other important dimensions of this embodiment are as follows:

209853/0827

θ. 73.4

d / Xo 0.428

d _o / λο 0, 078

In the illustrated embodiment it was assumed that the waves incident on the coupler 11 are substantially plane waves and that the coupler 11 is substantially unlimited is. It should be noted, however, that the principles of the present invention also apply when the Coupler 11 is limited, for example when it is located within a waveguide link. In these cases you have to however, the equations derived for the thickness and dielectric constants of the coupler layers are modified to the same extent become how the state of the guided wave deviates from the state of the plane wave.

In any case, it is understood that the arrangement described above only one embodiment can apply to many possible embodiments of the invention. Numerous and modified ones other embodiments can be implemented in accordance with the inventive concept without departing from the scope of the invention reach. For example, the dielectric constant, and thicknesses of the first and third dielectric layers instead to be chosen the same, also to be chosen differently.

209853 / ^ 62 "-

Claims (3)

J ₁ I PATENT CLAIMS Directional coupler for separating an incident wave in at least two output waves, one output wave Ie with the incident wave by a transmission coefficient and a second output wave is linked to the incident wave by a reflection coefficient, characterized in that the coupler (11) comprises three adjacent areas (12, 13, 14), each of which has a predetermined one Thickness and dielectric constant, and that the thicknesses and the dielectric constants of the respective regions (12, 13, 14) are selected so that the transmission coefficient and the The reflection coefficient of the coupler (11) are independent of the polarization of the incident wave. 2. Directional coupler according to claim 1, characterized in that the two outer regions (12, 14) are the same Have thicknesses and the same dielectric constants. 3. Directional coupler according to claim 2, characterized in that the thicknesses and the dielectric constant of the respective areas are selected according to the following equations: 209853/0827 I) ² / cos ² β. ^d i ⁼ ~ τ ~ ■ -sin ² Q. 1 ι and ^α 2 2 TT . -1 sin \ / 8 ₂ -sin θ. 1-R IT ^2f i \ (ί ₂ - V) where θ is. the angle between the direction of propagation of the incident Wave (15) and the normal to the surface (16) of the first area (12), k is an integer not divisible by two, A. ο the wavelength of the electromagnetic energy, R the reflected Share of the incident energy, d the thickness of the respective outer areas (12, 14), £ the dielectric constant of each outer areas (12, 14) and d and £ the thickness or the dielectric constant of the intermediate area (13). ? Π 9 8 5 3/0 8 2 7