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ELEC 351 Notes Set #15Assignment #7
Problem 8.3 Normal incidenceProblem 8.16 Normal incidenceProblem 8.27 Oblique incidenceProblem 8.28 Oblique incidenceProblem 8.40 Waveguide modesProblem 8.41 Waveguide modes
Do this assignment by November 16.
The final exam in ELEC 351 is December 13, 2018 from 2:00 to 5:00.
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Figures from: http://www.antenna-theory.com/tutorial/waveguides/waveguide.php
Rectangular Waveguide
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Magic Tee = 3 dB Splitter
3 dB Splitter
Apply a signal to arm 3, and half the power emerges from arm 1 and half from arm 2.
Apply a signal to arm 4 and half the power emerges from arm 1 and half from arm 2.
Sums and Differences
Apply signal #1 to arm 1 and signal #2 to arm 2.
Arm 3: signal #1 plus signal #2 Arm 4: signal #1 minus signal #2.
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Diplexer = separate signals at two frequencies
WikipediaA diplexer is a passive device that implements frequency-domain multiplexing. Two ports (e.g., L and H) are multiplexed onto a third port (e.g., S). The signals on ports L and H occupy disjoint frequency bands. Consequently, the signals on L and H can coexist on port S without interfering with each other.L port= the lower frequencyH port= the higher frequencyS port= the sum of the two frequencies
Television diplexer consisting of a high-pass filter (left) and a low-pass filter (right). The antenna cable is connected on the back to the screw terminals to the left of center.Designed and built by Arnold Reinhold
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Waveguide diplexer: separate signals at two frequencies
βWaveguide diplexer links point to point systemsβhttp://www.mwrf.com/passive-components/waveguide-diplexer-links-point-point-systems
Output channel 3:18.7 to 19.1 GHz
Output channel 2: 17.7 to 18.1 GHz
Input: both channelsChannel 2: 17.7 to 18.1 GHzChannel 3: 18.7 to 19.1 GHz
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Waveguide Diplexer: 12.05 and 13.90 GHz
Irene Ortiz de Saracho Pantoja, , Ku Waveguide Diplexer Design For Satellite Communication, Universidad Politechnica de Madrid, 2015
12.05 GHz
13.9 GHzInput: both 12.05
GHz and 13.9 GHz
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Orthomode Transducer (OMT) Combine two linearly polarized signals into one signal with
a horizontal and a vertical component. Two input ports in rectangular waveguideLinearly polarized signals of equal amplitude and 90 degrees out of phase.
One output port in circular waveguide which will feed a circular horn.The output port is circularly polarized by adding the signals at the two input ports with a 90 degree phase shift between them.
Source: Widipediahttps://en.wikipedia.org/wiki/Orthomode_transducer
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OMT designed by PhD student Mohamed Abdelaal
Port 1: common portSquare waveguide,Circular polarization
Port 2Rectangular waveguideHorizontalpolarization
Port 3Rectangular waveguideVerticalpolarization
Mohamed Abdelaziz Mohamed Abdelaal,βDesign and Analysis of Microwave Devices Based on Ridged Gap Waveguide Technology for 5G Applicationsβ, ECE Departmet, Concordia University, April 2018.
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Standard Waveguide SizesD.M. Pozar, Microwave Engineering, 3rd edition, Wiley, 2005.
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Rectangular and Circular Waveguide
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General Solution of Maxwellβs Equations for Transmission Lines and Waveguide
Convention: ba >
( ) ( ) ( ) zjzz
zjyy
zjxx eyxeaeyxeaeyxeaE Ξ²Ξ²Ξ² βββ ++= ,Λ,Λ,Λ
( ) ( ) ( ) zjzz
zjyy
zjxx eyxhaeyxhaeyxhaH Ξ²Ξ²Ξ² βββ ++= ,Λ,Λ,Λ
( ) zjzz eyxeE Ξ²β= ,
Ulaby 7th edition Section 8.6
ππ = ππ ππππ is the phase constant in the dielectric filling the waveguide.π½π½ is the phase constant for waves travelling in the waveguide.
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TEM, TE and TM Modes
TEM field = transverse electric and magnetic field, hence zero axial components: 0=zE 0=zHand
TE field = transverse electric field, hence zero axial component of the electric field:
TM field = transverse magnetic field, hence zero axial component of the magnetic field:
0=zE
0=zH
( ) ( ) ( ) zjzz
zjyy
zjxx eyxeaeyxeaeyxeaE Ξ²Ξ²Ξ² βββ ++= ,Λ,Λ,Λ
( ) ( ) ( ) zjzz
zjyy
zjxx eyxhaeyxhaeyxhaH Ξ²Ξ²Ξ² βββ ++= ,Λ,Λ,Λ
( ) zjyy eyxeE Ξ²β= ,( ) zj
xx eyxeE Ξ²β= , and
( ) zjyy eyxhH Ξ²β= ,( ) zj
xx eyxhH Ξ²β= , and
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Rectangular Waveguides
( ) ( ) ( ) zjzz
zjyy
zjxx eyxhaeyxhaeyxhaH Ξ²Ξ²Ξ² βββ ++= ,Λ,Λ,Λ( ) ( ) ( ) zj
zzzj
yyzj
xx eyxeaeyxeaeyxeaE Ξ²Ξ²Ξ² βββ ++= ,Λ,Λ,Λ
β’TE modes have , solve forβ’TM modes have , solve for
0=zE0=zH
( ) zjzz eyxhH Ξ²β= ,
zjzz eyxeE Ξ²β= ),(
We will show that if we know the axial components, we can find the transverse components from Maxwellβs curl equations:
ππππ2 = ππ2 β π½π½2 where ππ = ππ ππππ and π½π½ is the phase constant for waves travelling in the waveguide.
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All the Field Components
Ξ²jzβ
ββ
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Relationship of the Transverse Components to the Axial Components
If we know the axial components, then we can find the transverse components.
If we know and , then we can find
We can prove this from the Maxwell curl equations: zE zH xE yE xH yH
HjE ΟΒ΅β=Γβ ( )EjH ΟΞ΅Ο +=Γβand
zjyy eeE Ξ²β=
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Maxwellβs Curl EquationsWrite out all three components of
And all three components of
To show that:
HjE ΟΒ΅β=Γβ
( )EjH ΟΞ΅Ο +=Γβ
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Find the Transverse ComponentsAssume that we know the axial components, and , then
find the transverse components,zE zH
yHxHxE yE
Use k for the wave number in the material filling the waveguide:
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Transverse in terms of axial:
Ulaby 7th edition page 384
Repeat the derivation for π»π»π₯π₯ on the previous page to get π»π»π¦π¦, πΈπΈπ₯π₯ and πΈπΈπ¦π¦:
πΈπΈπ₯π₯ =βππππππ2
π½π½πππΈπΈπ§π§ππππ
+ πππππππ»π»π§π§ππππ
πΈπΈπ¦π¦ =ππππππ2
βπ½π½πππΈπΈπ§π§ππππ
+ πππππππ»π»π§π§ππππ
π»π»π₯π₯ =ππππππ2
πππππππΈπΈπ§π§ππππ
β π½π½πππ»π»π§π§ππππ
π»π»π¦π¦ =βππππππ2
πππππππΈπΈπ§π§ππππ
+ π½π½πππ»π»π§π§ππππ
If we can find πΈπΈπ§π§ and π»π»π§π§, then we can find all the other field components.TE Modes: Assume πΈπΈπ§π§ = 0 and find π»π»π§π§TM Modes: Assume π»π»π§π§ = 0 and find πΈπΈπ§π§
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Convention: ba >
Rectangular Waveguide: TE Modes
β’ The axial component of the electric field is zero:β’ Find the axial component of the magnetic field
0=zEzH
( ) ( ) zjyy
zjxx eyxeaeyxeaE Ξ²Ξ² ββ += ,Λ,Λ
( ) ( ) ( ) zjzz
zjyy
zjxx eyxhaeyxhaeyxhaH Ξ²Ξ²Ξ² βββ ++= ,Λ,Λ,Λ
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Wave Equation for the TE Modes
( )yxhz ,
( ) ( ) ( ) zjzz
zjyy
zjxx eyxhaeyxhaeyxhaH Ξ²Ξ²Ξ² βββ ++= ,Λ,Λ,Λ
Find
where
Look at the z component:
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The field βπ§π§(ππ, ππ) must satisfy this wave equation!
To find βπ§π§(ππ,ππ), we must satisfy the wave equation and satisfy the boundary condition that πΈπΈπ‘π‘π‘π‘π‘π‘ = 0 at the surfaces of the waveguide walls.
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Separation of Variables (ELEC365)
Dispersion equation:where and ¡ΡΟ=k
andLet where πππ₯π₯ and πππ¦π¦ are constants.
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Separation of Variables Solution
The field βπ§π§(ππ, ππ) satisfies the wave equation.
What values of πππ₯π₯ and πππ¦π¦ satisfy the boundary conditions?
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Boundary Conditions
For the TE solution, the axial component πΈπΈπ§π§ is zero everywhere.
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Find and in terms of : xE yE zH
( ) zjzz eyxhH Ξ²β= ,
leads to
where
βββ
=y
Hk
jE z
cx ΟΒ΅2
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Satisfy the Boundary Conditions
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Waveguide Modes
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Find the Phase Constant mnΞ²
The value of the phase constant depends on the waveguide mode:
Dispersion equation:where and ¡ΡΟ=k
222ckk β=Ξ²
2222yx kkk ββ=Ξ²
2222
,
β
β=
bn
amknm
ΟΟΞ² 222
,
β
β=
bn
amknm
ΟΟΞ²
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Cutoff Frequency for Mode m,n
mnΞ²For mode m,n to propagate, must be a real number:
22
,2
+
=
bn
amf mnc
ΟΟ¡ΡΟ
The limiting frequency is called the βcutoff frequencyβ mncf ,
22
, 21
+
=
bn
amf mnc
ΟΟ¡ΡΟ
22
, 21
+
=
bn
amf mnc ¡Ρ
If the frequency is greater than the βcutoff frequencyβ, then mode m,n propagates.
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Below Cutoff Waveguide
If the frequency is less than the βcutoff frequencyβ, then mode m,n attenuates.
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Propagation or Attenuation?22
, 21
+
=
bn
amf mnc ¡Ρ
For frequency greater than the cutoff frequency :
β’ is real
β’So the waveguide mode propagates with phase factor
f mncf ,
nm,Ξ²zj nme ,Ξ²β
For frequency less than the cutoff frequency :
β’ is imaginary:
β’So the waveguide mode attenuates with attenuation constant πΌπΌππ,π‘π‘
f mncf ,
nm,Ξ² mnnm jΞ±Ξ² β=,
( ) zzjjzj nmnmnm eee ,,, Ξ±Ξ±Ξ² ββββ ==
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Dominant Mode22
, 21
+
=
bn
amf mnc ¡Ρ
2
10,1
21
=
afc ¡Ρ
ba >
Lowest cutoff frequency: m=1,n=0
Convention:
Next higher cutoff frequency: m=0,n=1 or m=2,n=0?2
01,1
21
=
bfc ¡Ρ
Below , no waveguide mode propagates and the waveguide is said to be βcutoffβ.
10,cf
Between and the next higher cutoff frequency, only one waveguide mode propagates, which is the TE10 mode, and TE10 is said to be the βdominant modeβ.
Above the next higher cutoff frequency, more than one mode can propagate and the waveguide is βovermodedβ.
10,cf
2
20,2
21
=
afc ¡Ρ
ππππ,10 =1
2ππ ππππ
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Example
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(seventh edition page 368)
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For TE modes (πΈπΈπ§π§=0) we have found π»π»π§π§ = π΄π΄ cos
ππππππππ
cosππππππππ
ππβπππ½π½ππ,πππ§π§
so
πΈπΈπ₯π₯ =βππππππ2
π½π½πππ‘π‘πππΈπΈπ§π§ππππ
+ πππππππ»π»π§π§ππππ
=βππππππ2
πππππππ»π»π§π§ππππ
πΈπΈπ¦π¦ =ππππππ2
βπ½π½πππ‘π‘πππΈπΈπ§π§ππππ
+ πππππππ»π»π§π§ππππ
=ππππππ2
πππππππ»π»π§π§ππππ
π»π»π₯π₯ =ππππππ2
πππππππΈπΈπ§π§ππππ
β π½π½πππ‘π‘πππ»π»π§π§ππππ
=ππππππ2
βπ½π½πππ‘π‘πππ»π»π§π§ππππ
π»π»π¦π¦ =βππππππ2
πππππππΈπΈπ§π§ππππ
+ π½π½πππ‘π‘πππ»π»π§π§ππππ
=βππππππ2
π½π½πππ‘π‘πππ»π»π§π§ππππ
Find the transverse field components.Given π»π»π§π§, find πΈπΈπ₯π₯, πΈπΈπ¦π¦, π»π»π₯π₯, and π»π»π¦π¦ .
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Substitute π»π»π§π§ = π΄π΄πππ‘π‘ cos
ππππππππ
cosππππππππ
ππβπππ½π½πππππ§π§
to find the transverse field components πΈπΈπ₯π₯, πΈπΈπ¦π¦, π»π»π₯π₯, and π»π»π¦π¦:
Homework: show that
πΈπΈπ₯π₯ = π΄π΄πππ‘π‘ππππππππππ2
ππππππ
cosππππππππ
sinππππππππ
ππβπππ½π½πππππ§π§
πΈπΈπ¦π¦ = π΄π΄πππ‘π‘βππππππππππ2
ππππππ
sinππππππππ
cosππππππππ
ππβπππ½π½πππππ§π§
π»π»π₯π₯ = π΄π΄πππ‘π‘πππ½π½πππ‘π‘
ππππ2ππππππ
sinππππππππ
cosππππππππ
ππβπππ½π½πππππ§π§
π»π»π¦π¦ = π΄π΄πππ‘π‘πππ½π½πππ‘π‘
ππππ2ππππππ
cosππππππππ
sinππππππππ
ππβπππ½π½πππππ§π§
Ulaby 7th edition page 388
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Wave Impedance for TE Modes
Define the βwave impedanceβ as
ππππππ =πΈπΈπ₯π₯π»π»π¦π¦
=
βππππππ2
ππππ πππ»π»π§π§ππππβππππππ2
π½π½ πππ»π»π§π§ππππ
=πππππ½π½
For mode m, n the phase constant is
π½π½πππ‘π‘ = ππ2 βππππππ
2β
ππππππ
2
So the wave impedance can be calculated as ππππππ,πππ‘π‘ =
πππππ½π½
=ππππ
ππ2 β ππππππ
2β ππππ
ππ2
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In general: π»π»π§π§ = π΄π΄πππ‘π‘ cos
ππππππππ
cosππππππππ
ππβπππ½π½πππππ§π§
πΈπΈπ₯π₯ = π΄π΄πππ‘π‘ππππππππππ2
ππππππ
cosππππππππ
sinππππππππ
ππβπππ½π½πππππ§π§
πΈπΈπ¦π¦ = π΄π΄πππ‘π‘βππππππππππ2
ππππππ
sinππππππππ
cosππππππππ
ππβπππ½π½πππππ§π§
π»π»π₯π₯ = π΄π΄πππ‘π‘πππ½π½πππ‘π‘ππππ2
ππππππ
sinππππππππ
cosππππππππ
ππβπππ½π½πππππ§π§
π»π»π¦π¦ = π΄π΄πππ‘π‘πππ½π½πππ‘π‘ππππ2
ππππππ
cosππππππππ
sinππππππππ
ππβπππ½π½πππππ§π§
Field Configuration in the Dominant Mode
Dominant mode, m=1,n=0: π»π»π§π§ = π΄π΄10 cos
ππππππππβπππ½π½10π§π§
πΈπΈπ₯π₯ = 0
πΈπΈπ¦π¦ = π΄π΄10βππππππππππ2
ππππ
sinππππππππβπππ½π½10π§π§
π»π»π₯π₯ = π΄π΄10πππ½π½10ππππ2
ππππ
sinππππππππβπππ½π½10π§π§
π»π»π¦π¦ = 0
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πΈπΈπ¦π¦ = π΄π΄10βππππππππππ2
ππππ
sinππππππππβπππ½π½10π§π§
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Power Flow in the Dominant Mode
byax β€β€β€β€ 0,0 dxdyasd zΛ=
zjx e
axAajH 10cos10 Ξ²Ο
ΟΞ² β=
zj
cy e
axA
akjE 10sin2
Ξ²ΟΟΒ΅Ο ββ=
( )β«β« β Γ= dxdyaaHaEP zxxyy ΛΛΛ21 *
10
( )β«β« β β= dxdyaaHEP zzxy ΛΛ21 *
10
( )β«β« β
β= β dxdye
axAaje
axA
akjP zjzj
c
1cossin21
1010 10210
Ξ²Ξ² ΟΟΞ²ΟΟΒ΅Ο
ππ10 = π΄π΄ 2 πππππ‘π‘3ππ
4ππ2π½π½10 watts Homework: do
the integration!
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7. Design a rectangular waveguide such that the operating frequency of 10.4 GHz is 20% above the cutoff frequency for the dominant mode. Also, the cutoff frequency of the next higher waveguide mode must be 10% above the operating frequency. The waveguide is filled with air.
7.1) What is the cutoff frequency for the TE10 mode?
7.2) What is the βaβ dimension?
7.3) What is the βbβ dimension?
7.4) Find the phase constant for the dominant mode at the operating frequency.
7.5) Find the wave impedance for the dominant mode at the operating frequency.
7.6) How many modes can propagate in the waveguide at 20 GHz?
Question from an old final exam:
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7.1) What is the cutoff frequency for the TE10 mode?We are told that the βoperating frequency of 10.4 GHz is 20% above the cutoff frequency for the dominant modeβ, so 10.4 = 1.2ππππ,10, where the cutoff frequency isππππ,10 = 10.4
1.2= 8.667 GHz.
7.2) What is the βaβ dimension?
ππππ,πππ‘π‘ = 12ππ ππππ
πππππ‘π‘
2+ π‘π‘ππ
ππ
2and for air-filled waveguide c = 1
ππ0ππ0= 30 cm/ns
ππππ,10 =302ππ
1ππππ
2
+0ππππ
2
=302ππ
ππππ
=15ππ
15π‘π‘
= 8.667
ππ = 158.667
= 1.731 cm
7.3) What is the βbβ dimension? βThe cutoff frequency of the next higher waveguide mode must be 10% above the operating frequency.βSo the next higher cutoff frequency is 1.1x10.4=11.44 GHz.
The next higher cutoff frequency might be ππππ,01 or might be ππππ,20
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ππππ,πππ‘π‘ =302ππ
ππππ1.731
2+
ππππππ
2
ππππ,01 =302ππ
0ππ1.731
2
+1ππππ
2
=302ππ
ππππ
=15ππ
= 11.44
ππ = 1511.44
= 1.311 cmCheck: what is ππππ,20?
ππππ,20 = 302ππ
2ππ1.731
2+ 0ππ
ππ
2= 30
2ππ2ππ
1.731= 30
22
1.731= 30
1.731= 17.33 GHz
Since this is higher than 11.44 GHz, choose ππ = 1.311 cm
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7.4) Find the phase constant for the dominant mode at the operating frequency.
π½π½,πππ‘π‘ = ππ2 β πππππ‘π‘
2β π‘π‘ππ
ππ
2
Where ππ = ππ ππππ = 2ππππππ
= 2πππ₯π₯10.430
= 2.178 rad/cm (with ππ = 1ππππ
= 30 cm/ns)
π½π½,10 = ππ2 β 1πππ‘π‘
2β 0ππ
ππ
2= ππ2 β ππ
π‘π‘
2= 2.1782 β ππ
1.731
2= 1.024 rad/cm
7.5) Find the wave impedance for the dominant mode at the operating frequency. ππππππ = ππππ
π½π½= 2πππ₯π₯10.4π₯π₯109π₯π₯4πππ₯π₯10β7
102.4= 682.0 ohms
7.6) How many modes can propagate in the waveguide at 20 GHz?
ππππ,πππ‘π‘ =302ππ
ππππ1.731
2+
ππππ1.311
2= 15
ππ1.731
2+
ππ1.311
2
ππππ,01 = 11.44 GHz, propagates at 20 GHzππππ,20 = 17.33 GHz, propagates at 20 GHz
ππππ,02 = 15 01.731
2+ 2
1.311
2= 22.88 GHz, does NOT propagate
ππππ,11 = 15 11.731
2+ 1
1.311
2= 14.35 GHz propagates
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7.5) Find the wave impedance for the dominant mode at the operating frequency.Continued:
ππππ,21 = 15 21.731
2+ 1
1.311
2= 20.76 GHz does NOT propagate
ππππ,12 = 15 11.731
2+ 2
1.311
2= 24.47 GHz does NOT propagate