Reflector Antennas Antenna and Microwave Laboratory In the name of God Babol Noshirvani University of Technology, Iran Reflector Antennas Import video, voice + dipole 60cm

1. Geometry: Paraboloid Sphere/Ellipsoid Hyperboloid

Type 1 : Prime-Focus Antenna 2. Radiation Mechanism: Type 1 : Prime-Focus Antenna Main Reflector: Parabolic Parabola has 2 valuable properties : 1) rays emanating from the focus are all reflected to parallel paths. 2) All paths from the focus to a plane transversal to the aperture at any distance, have the same length. Constructive phase like array, when the reflector is large:physical optic Constructive phase

Type 2 : Offset Reflector Antenna Main Reflector: Parabolic

Type 3 : Cassegrain Antenna Main Reflector: Parabolic Subreflector: Hyperbolic

Type 4 : Gregorian Antenna Main Reflector: Parabolic Subreflector: Elliptic

Type 5 : Offset Cassegrain/Gregorian Antenna

Type 6 : ADE (Axially Displaced Ellipse) Antenna Main Reflector: Parabolic Subreflector: Elliptic

3. Design Procedure: However, Antenna Laboratory of Babol Noshirvani University of Technology Proposes a “Rule of Thumb Method” So Let`s follow that

3. Design Procedure: A) Illumination Taper Illumination loss Spillover loss Illumination taper (dB) = illu loss / spillover loss Ideal (uniform reflector) illumination practical (non-uniform reflector) illumination

Step 1: illumination taper in Reflector 3. Design Procedure: Different illumination taper values Step 1: illumination taper in Reflector Antenna should be somewhat between 10db to 15db. Step 2: Main dish diameter (D) is then calculated (in λ)

3. Design Procedure: fp Step 3: search the market for available Horn Antenna as the feed source. Remember that you can find only some standard pre-fixed antenna, not any size you like ! phi www.atmmicrowave.com D … find the HPBW of Horn in its datasheet. Step 4: 1) set HPBW ≈ 2*phi 2) phi=Arctan[1/(2*(fp/D))] 3) fp is then calculated (in λ). Step 5: check 0.25< fp/D <.65. if not, start again from step 1 with a different value.

3. Design Procedure: fp Step 5: now you can go to the mechanic to build your dish. However you need to give him the depth of the dish (x) rather than its focal point: x= D^2/ (16*fp) x is then calculated. x phi D

HPBW(experimental)≈ 70*λ/D 4. Electromagnetic Properties: Frequency Range: 300 MHz – 100 GHz Bandwidth: 5% Pattern: Pencil beam, 25-50 dBi Gain, (1-10 deg HPBW) Polarization: proportional to the Feed Antenna In a fixed frequency, Larger Size of Dish yields to a greater gain. HPBW(experimental)≈ 70*λ/D

5. Applications: (visual review) Green Bank Telescope which stands near Green Bank, West Virginia The Very Large Array (VLA) at Socorro, New Mexico, United States for Radio Astronomy Applications Space Satellite Antenna

5. Applications: (visual review) Reflector antenna used as radar in fighting ships Air Surveillance Radar at the airport IFF (identification of friend and foe) Reflector Radar

5. Applications: (visual review) Arecibo Observatory is a radio telescope near city of Arecibo in Puerto Rico Its spherical reflector has a 305m dish in diameter. Surface is made of almost 40,000 perforated aluminum panels. Its focal point is 150m above reflector. These devices operate immersed in a liquid helium, to maintain a very low receiver temperature. Arecibo system operates at frequencies from 10MHz (λ=30m) up to 50MHz (λ=6m). 1MW planetary radar transmitter located in a special room inside dome. Contact - 1997

Now, Let`s get familiar with a brand new software: Antenna Magus

Go to CST and simulate a example And complete the work sheet

Reflector Antenna HPBW Design Objectives for the Reflector Antenna set in Antenna Magus: f0 9.4 GHz Feed Antenna HPBW 40 deg Reflector Antenna HPBW your desired (3-6 deg)

Reflector Antenna:

Reflector Antenna: Lg=31.89mm Hg=12.52mm Ha=64.5mm F=468.3mm D=330.3mm Lf=154.8mm Wg=25.04mm Wa=90.3mm S=468.3mm  

Reflector Antenna:

Worksheet Please complete the work sheet to your example: Frequency band : ……… The figure of antenna in CST : ……… The of size antenna in λ and in cm/mm : ……… S11 : ……… (set Z0=75 ohm) Zin (Re and Im) in CST : ……… Surface Current (phase=0 deg) : ……… linear 3D Power Pattern in CST : ……… 2D Power Pattern for theory & CST : ……… HPBW for theory & CST : ………