10.4 Antenna Gain, Aperture Antennas & Horns, ERP/EIRP, Radiation Patterns

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10 Chapter 10: Practical Antennas & Arrays

10.1 Resonant Dipoles, Inverted-Vs, and Multiband Wire Antennas 10.2 Quarter-Wave Verticals, Ground Systems, and Radiation Efficiency 10.3 Parasitic Arrays, Yagi-Uda Antennas, and Quad Arrays 10.4 Antenna Gain, Aperture Antennas & Horns, ERP/EIRP, Radiation Patterns

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16.1 Biological Effects of RF Energy and ARPANSA Exposure Standards 16.2 Safe Separation Distances, Power Density, and Duty Cycles 16.3 Station Electrical Safety, Battery Hazards, and Safe Headphone Use 16.4 Mast and Tower Construction, Power Line Clearance, and Lightning Protection

10.4 Antenna Gain, Aperture Antennas & Horns, ERP/EIRP, Radiation Patterns

Key Takeaways Explain This Topic AI

Antenna gain measures power directivity and efficiency relative to a standard: an isotropic radiator ( 0 dBi 0\text{ dBi} 0 dBi ) radiates uniformly across all 4 π 4\pi 4 π steradians, while a half-wave dipole ( 0 dBd = 2.15 dBi 0\text{ dBd} = 2.15\text{ dBi} 0 dBd = 2.15 dBi ) concentrates energy broadside, establishing the conversion G dBi = G dBd + 2.15 dB G_{\text{dBi}} = G_{\text{dBd}} + 2.15\text{ dB} G dBi ​ = G dBd ​ + 2.15 dB .

Effective Radiated Power (ERP) references a half-wave dipole, whereas Effective Isotropic Radiated Power (EIRP) references an isotropic radiator ( EIRP = ERP × 1.64 \text{EIRP} = \text{ERP} \times 1.64 EIRP = ERP × 1.64 or + 2.15 dB +2.15\text{ dB} + 2.15 dB ); Australian Advanced licensees are bound by statutory limits such as 5 W 5\text{ W} 5 W PEP EIRP on 472 − 479 kHz 472-479\text{ kHz} 472 − 479 kHz .

Aperture antennas radiate through an opening or reflecting surface. A horn flares a waveguide to improve its transition to free space and increase directivity; aperture size, illumination and phase error determine the radiation pattern.

Parabolic reflector dish antennas collimate spherical waves from a focal feed horn into planar wavefronts, delivering power gain G = η a ( π D / λ ) 2 G = \eta_a (\pi D / \lambda)^2 G = η a ​ ( π D / λ ) 2 and half-power beamwidth θ − 3 dB ≈ 70 ∘ ( λ / D ) \theta_{-3\text{dB}} \approx 70^\circ (\lambda / D) θ − 3 dB ​ ≈ 7 0 ∘ ( λ / D ) , where practical illumination efficiency ( η a \eta_a η a ​ ) ranges from 55 % 55\% 55% to 70 % 70\% 70% .

Microwave amateur and Earth-Moon-Earth (EME) operations across 1.2 GHz 1.2\text{ GHz} 1.2 GHz to 24 GHz 24\text{ GHz} 24 GHz utilize high aperture gains ( > 35 − 45 dBi > 35-45\text{ dBi} > 35 − 45 dBi ) and sub-degree pencil beams to overcome severe round-trip free-space and lunar path losses exceeding 250 dB 250\text{ dB} 250 dB .

Last updated: November 2026

10.4 Antenna Gain, Aperture Antennas & Horns, ERP/EIRP, Radiation Patterns

Radio communication across the electromagnetic spectrum depends fundamentally on launching radio frequency energy into space in controlled spatial distributions. An antenna does not amplify power; rather, it acts as an electromagnetic transducer that concentrates transmitter power into preferred spatial directions. On High Frequency (HF) and Very High Frequency (VHF) bands, directional control is achieved primarily through wire arrangements and parasitic elements. At Ultra High Frequency (UHF) and microwave frequencies, where wavelengths contract to centimeters and millimeters, radio amateurs utilize aperture antennas , including horn antennas and parabolic reflectors . Mastering antenna gain references, radiation patterns, aperture physics, and Effective Isotropic Radiated Power (EIRP) is essential for advanced amateur communications, satellite tracking, and Earth-Moon-Earth (EME) weak-signal operations.

Antenna Gain References: dBi vs. dBd and ERP vs. EIRP

Antenna gain expresses the power density radiated in the direction of maximum beam intensity relative to the power density produced by a reference antenna supplied with identical input power. Gain incorporates both directional concentration (directivity) and electrical efficiency: G = η rad × D antenna G = \eta_{\text{rad}} \times D_{\text{antenna}} G = η rad ​ × D antenna ​ Gain Reference Comparison

• Isotropic Radiator (dBi) Half-Wave Dipole (dBd)
• Theoretical Dimensionless Point Resonant Wire in Free Space
• Radiates Uniform Sphere Toroidal Figure-Eight Pattern

. : .

• : /|\ : ( ( | ) )
• : -- O -- : ( ( | ) )
• : \|/ : ( ( | ) )
• ' : '
• Directivity = 1.0 (0 dBi) Directivity = 1.64 (2.15 dBi)
• 1. The Isotropic Radiator ( 0 dBi 0\text{ dBi} 0 dBi ) and Half-Wave Dipole ( 0 dBd 0\text{ dBd} 0 dBd )

Isotropic Radiator ( dBi \text{dBi} dBi ): A hypothetical, lossless point source radiating uniformly across all 4 π 4\pi 4 π steradians. At distance r r r , power flux density is S iso = P tx / ( 4 π r 2 ) S_{\text{iso}} = P_{\text{tx}} / (4\pi r^2) S iso ​ = P tx ​ / ( 4 π r 2 ) . It possesses a reference gain of 0 dBi 0\text{ dBi} 0 dBi .

Half-Wave Dipole ( dBd \text{dBd} dBd ): A real resonant wire dipole in free space. Because a dipole produces toroidal radiation with zero emission along its wire axis, broadside power density is 1.6406 1.6406 1.6406 times greater ( + 2.15 dB +2.15\text{ dB} + 2.15 dB ) than an isotropic radiator: G dBi = G dBd + 2.15 dB G_{\text{dBi}} = G_{\text{dBd}} + 2.15\text{ dB} G dBi ​ = G dBd ​ + 2.15 dB G dBd = G dBi − 2.15 dB G_{\text{dBd}} = G_{\text{dBi}} - 2.15\text{ dB} G dBd ​ = G dBi ​ − 2.15 dB

2. Effective Radiated Power (ERP) and Effective Isotropic Radiated Power (EIRP)

Delivered transmitter power ( P del P_{\text{del}} P del ​ ) equals transmitter output power minus transmission line and connector attenuation. Directional radiated power is quantified in two formats:

Effective Radiated Power (ERP): Power referenced to a resonant half-wave dipole: ERP = P del × 10 G dBd / 10 \text{ERP} = P_{\text{del}} \times 10^{G_{\text{dBd}} / 10} ERP = P del ​ × 1 0 G dBd ​ /10

Effective Isotropic Radiated Power (EIRP): Power referenced to an isotropic source: EIRP = P del × 10 G dBi / 10 = ERP × 1.6406 \text{EIRP} = P_{\text{del}} \times 10^{G_{\text{dBi}} / 10} = \text{ERP} \times 1.6406 EIRP = P del ​ × 1 0 G dBi ​ /10 = ERP × 1.6406

Under the Australian Radiocommunications (Amateur Stations) Class Licence, Advanced licensees may operate up to 400 W 400\text{ W} 400 W PEP transmitter output. In designated bands with shared services—such as 472 − 479 kHz 472-479\text{ kHz} 472 − 479 kHz ( 630 m 630\text{ m} 630 m )—statutory limits are explicitly framed as radiated limits ( 5 W 5\text{ W} 5 W PEP EIRP).

Radiation Patterns, Lobes, and Beamwidth

An antenna's spatial radiation pattern plots electric field intensity or relative power density in spherical coordinates, sliced into the E-plane (containing the electric field vector) and H-plane (containing the magnetic field vector). Directive Radiation Pattern

• Main Lobe
• /=======\
• Side Lobe / \ Side Lobe
• (==) | +0 dB | (==)
• \ | | /
• \=====( Feed )=====/
• \ /
• \=======/
• Back Lobe
• Lobes, Front-to-Back, and Front-to-Rear Ratios

Main Lobe: The primary beam containing peak power density.

Side Lobes: Unwanted secondary radiation peaks caused by aperture edge currents and phase cancellation limits.

Back Lobe: Residual radiation directed 180 ∘ 180^\circ 18 0 ∘ opposite the main beam.

Front-to-Back ( F / B F/B F / B ) Ratio: Ratio of main lobe peak power to power radiated at 180 ∘ 180^\circ 18 0 ∘ azimuth.

Front-to-Rear Ratio: Ratio of main lobe peak to the highest side or back lobe across the entire rear hemisphere ( 90 ∘ 90^\circ 9 0 ∘ to 270 ∘ 270^\circ 27 0 ∘ ).

Half-Power Beamwidth (HPBW)

The Half-Power Beamwidth ( θ − 3 dB \theta_{-3\text{dB}} θ − 3 dB ​ ) is the angular separation between pattern points where radiated power density drops to half ( − 3 dB -3\text{ dB} − 3 dB ) of the main beam maximum: HPBW = ∣ θ 2 − θ 1 ∣ (both edge points are at half power) \text{HPBW}=|\theta_2-\theta_1|\quad\text{(both edge points are at half power)} HPBW = ∣ θ 2 ​ − θ 1 ​ ∣ (both edge points are at half power)

Aperture Antennas: Fundamental Radiation Physics

Unlike wire antennas that radiate via oscillating conduction currents along thin metallic elements, aperture antennas launch electromagnetic waves through a physical opening or surface into free space. Waveguide -> Gradual horn flare -> Radiating aperture -> Far-field beam

• larger aperture amplitude and phase
• shape the beam
• Waveguide-to-Space Transition

An open waveguide can radiate, but its abrupt termination presents a radiation load and produces a broad beam. A horn gradually enlarges the guide into a radiating aperture, improving the transition to free space and increasing directivity.

Free-space intrinsic wave impedance is: η 0 = μ 0 ε 0 ≈ 376.73 Ω \eta_0=\sqrt{\frac{\mu_0}{\varepsilon_0}}\approx376.73\ \Omega η 0 ​ = ε 0 ​ μ 0 ​ ​ ​ ≈ 376.73 Ω

This does not make the aperture a simple junction between two uniform transmission lines. Its reflection cannot be found just by substituting free-space and guided-wave impedances into a two-resistance reflection formula.

Horn aperture fields are not generally uniform in phase. A short horn with a wide flare has appreciable phase error because paths to the aperture edge are longer than paths to its centre. Aperture dimensions and horn length therefore trade compactness against gain, beamwidth and sidelobes.

Microwave Horn Antenna Topologies Horn Antenna Topologies

• Pyramidal Horn E-Plane Sectoral H-Plane Sectoral
• Flared in E and H Flared in E only Flared in H only

• /=====\ /=====\ /===========\
• / \ | | / \
• / \ /=====\ /===============\
• |===========| / \ | |
• | | /=========\ | |
• \===========/ \=========/ \===============/

Pyramidal Horn: Flared simultaneously along both the E-plane and H-plane walls. Fed by rectangular waveguide, it produces symmetric pencil beams and moderate gain ( 12 to 25 dBi 12\text{ to }25\text{ dBi} 12 to 25 dBi ). It is the global standard for antenna test range calibrations.

E-Plane Sectoral Horn: Flared only along the electric field vector dimension (narrow waveguide wall), keeping the H-plane dimension constant. Produces a fan-shaped beam that is narrow in elevation (E-plane) and broad in azimuth (H-plane).

H-Plane Sectoral Horn: Flared only along the magnetic field vector dimension (broad waveguide wall). Produces a beam that is narrow in azimuth (H-plane) and broad in elevation (E-plane).

Conical Horn: Flared from a circular waveguide feed. Ideal for circular polarization and corrugated feed horns, delivering extremely low cross-polarization and symmetric radiation patterns.

Parabolic Reflector (Dish) Antennas

For forward gains exceeding 30 to 50 dBi 30\text{ to }50\text{ dBi} 30 to 50 dBi , microwave stations employ parabolic reflector antennas . A feed horn positioned at the focal point illuminates a paraboloidal metallic dish, collimating spherical wavefronts into planar wavefronts. Dish Feed Architectures

• Prime-Focus Feed Cassegrain Feed
• Feed Horn at Focal Point Convex Subreflector at Focus

• \ \
• \ \ Subreflector
• \ \ (\)
• +---[ Feed Horn ] +----------+
• / / [ Feed Horn ]
• / / (At dish apex)
• / /
• Feed Architectures: Prime-Focus vs. Cassegrain and Gregorian

Prime-Focus: The feed horn sits directly at the focus in front of the dish. While structurally simple, feed support struts and transmission lines obstruct the radiating aperture, producing blockage loss and high side lobes.

Cassegrain Configuration: Employs a convex hyperboloidal subreflector placed near the focus. The feed horn mounts at the vertex of the main dish. Shorter waveguide runs reduce feeder loss and its contribution to receiver noise temperature.

Gregorian Configuration: Employs a concave ellipsoidal subreflector placed past the focal point, providing similar electrical advantages.

Aperture Illumination Efficiency and Edge Taper

Total power gain depends on the effective aperture area ( A e A_e A e ​ ) relative to physical aperture area ( A p = π D 2 / 4 A_p = \pi D^2 / 4 A p ​ = π D 2 /4 ): A e = η a A p A_e = \eta_a A_p A e ​ = η a ​ A p ​

The aperture efficiency ( η a \eta_a η a ​ , typically 55 % − 70 % 55\%-70\% 55% − 70% ) balances two opposing effects:

Aperture Illumination Taper: Uniform illumination maximizes aperture utilization but causes severe spillover loss.

Spillover Loss: Feed energy missing the reflector edge adds thermal noise from the warm earth ( 290 K 290\text{ K} 290 K ). An edge taper of − 10 dB -10\text{ dB} − 10 dB to − 12 dB -12\text{ dB} − 12 dB at the dish rim provides optimal compromise.

Quantitative Formulas for Parabolic Dishes

For a circular parabolic dish of diameter D D D at wavelength λ \lambda λ :

1. Parabolic Dish Gain G = 4 π λ 2 A e = η a ( π D λ ) 2 G = \frac{4\pi}{\lambda^2} A_e = \eta_a \left(\frac{\pi D}{\lambda}\right)^2 G = λ 2 4 π ​ A e ​ = η a ​ ( λ π D ​ ) 2 G dBi = 10 log ⁡ 10 [ η a ( π D λ ) 2 ] = 20 log ⁡ 10 ( π D λ ) + 10 log ⁡ 10 ( η a ) G_{\text{dBi}} = 10 \log_{10}\left[\eta_a \left(\frac{\pi D}{\lambda}\right)^2\right] = 20 \log_{10}\left(\frac{\pi D}{\lambda}\right) + 10 \log_{10}(\eta_a) G dBi ​ = 10 lo g 10 ​ [ η a ​ ( λ π D ​ ) 2 ] = 20 lo g 10 ​ ( λ π D ​ ) + 10 lo g 10 ​ ( η a ​ )

2. Half-Power Beamwidth (HPBW) θ − 3 dB ≈ 70 ∘ λ D \theta_{-3\text{dB}} \approx 70^\circ \frac{\lambda}{D} θ − 3 dB ​ ≈ 7 0 ∘ D λ ​

Amateur Microwave Allocations & EME Communications

Amateurs deploy aperture antennas across microwave allocations:

1.2 GHz 1.2\text{ GHz} 1.2 GHz ( 23 cm 23\text{ cm} 23 cm ) & 2.4 GHz 2.4\text{ GHz} 2.4 GHz ( 13 cm 13\text{ cm} 13 cm ): High-speed digital links, Wi-Fi experimentation, and amateur satellites (QO-100 uplink).

5.7 GHz 5.7\text{ GHz} 5.7 GHz ( 6 cm 6\text{ cm} 6 cm ) & 10 GHz 10\text{ GHz} 10 GHz ( 3 cm 3\text{ cm} 3 cm ): Terrestrial line-of-sight and rain-scatter DX records exceeding 500 km 500\text{ km} 500 km .

24 GHz 24\text{ GHz} 24 GHz ( 1.2 cm 1.2\text{ cm} 1.2 cm ) & 47 GHz 47\text{ GHz} 47 GHz : Precision millimeter-wave propagation.

Earth-Moon-Earth (EME / Moonbounce): Bouncing microwave signals off the lunar surface requires overcoming round-trip path attenuation exceeding 250 − 270 dB 250 - 270\text{ dB} 250 − 270 dB . Amateurs deploy dishes with gains ≥ 35 dBi \ge 35\text{ dBi} ≥ 35 dBi and HPBW under 2 ∘ 2^\circ 2 ∘ , necessitating precision azimuth/elevation tracking rotators.

Step-by-Step Worked Calculation: 10 GHz EME Parabolic Dish Design

An Australian Advanced amateur designs a 10.368 GHz 10.368\text{ GHz} 10.368 GHz ( 3 cm 3\text{ cm} 3 cm ) Earth-Moon-Earth station. The installation features a prime-focus dish of diameter D = 2.40 m D = 2.40\text{ m} D = 2.40 m illuminated by a circular horn feed with an aperture efficiency of η a = 60 % \eta_a = 60\% η a ​ = 60% ( 0.60 0.60 0.60 ). A 10.368 GHz 10.368\text{ GHz} 10.368 GHz solid-state power amplifier delivers P tx = 50 W P_{\text{tx}} = 50\text{ W} P tx ​ = 50 W PEP into a low-loss waveguide feed with 0.80 dB 0.80\text{ dB} 0.80 dB attenuation. Worked Problem Layout

• [ 50 W SSPA ] ===( Waveguide Loss = 0.8 dB )===> [ Feed Horn ] ===> [ 2.4 m Dish ]
• f = 10.368 GHz η_a = 60%

Step 1: Calculate Wavelength λ = c f = 2.9979 × 10 8 m/s 10.368 × 10 9 Hz ≈ 0.028915 m = 28.915 mm \lambda = \frac{c}{f} = \frac{2.9979 \times 10^8\text{ m/s}}{10.368 \times 10^9\text{ Hz}} \approx 0.028915\text{ m} = 28.915\text{ mm} λ = f c ​ = 10.368 × 1 0 9 Hz 2.9979 × 1 0 8 m/s ​ ≈ 0.028915 m = 28.915 mm

Step 2: Determine Physical and Effective Aperture Area A p = π D 2 4 = π ( 2.40 ) 2 4 ≈ 4.5239 m 2 A_p = \frac{\pi D^2}{4} = \frac{\pi (2.40)^2}{4} \approx 4.5239\text{ m}^2 A p ​ = 4 π D 2 ​ = 4 π ( 2.40 ) 2 ​ ≈ 4.5239 m 2 A e = η a A p = 0.60 × 4.5239 m 2 ≈ 2.7143 m 2 A_e = \eta_a A_p = 0.60 \times 4.5239\text{ m}^2 \approx 2.7143\text{ m}^2 A e ​ = η a ​ A p ​ = 0.60 × 4.5239 m 2 ≈ 2.7143 m 2

Step 3: Calculate Dish Power Gain and Gain in dBi G = 4 π λ 2 A e = 4 π ( 0.028915 ) 2 × 2.7143 ≈ 40 , 796 G = \frac{4\pi}{\lambda^2} A_e = \frac{4\pi}{(0.028915)^2} \times 2.7143 \approx 40,796 G = λ 2 4 π ​ A e ​ = ( 0.028915 ) 2 4 π ​ × 2.7143 ≈ 40 , 796 G dBi = 10 log ⁡ 10 ( 40 , 796 ) ≈ 46.11 dBi G_{\text{dBi}} = 10 \log_{10}(40,796) \approx 46.11\text{ dBi} G dBi ​ = 10 lo g 10 ​ ( 40 , 796 ) ≈ 46.11 dBi

Step 4: Calculate Half-Power Beamwidth θ − 3 dB ≈ 70 ∘ × λ D = 70 ∘ × 0.028915 m 2.40 m ≈ 0.843 ∘ \theta_{-3\text{dB}} \approx 70^\circ \times \frac{\lambda}{D} = 70^\circ \times \frac{0.028915\text{ m}}{2.40\text{ m}} \approx 0.843^\circ θ − 3 dB ​ ≈ 7 0 ∘ × D λ ​ = 7 0 ∘ × 2.40 m 0.028915 m ​ ≈ 0.84 3 ∘

Step 5: Calculate Net EIRP Along Main Beam

Delivered transmitter power: P del = 50 W × 10 − 0.80 / 10 = 50 × 0.8318 ≈ 41.59 W P_{\text{del}} = 50\text{ W} \times 10^{-0.80 / 10} = 50 \times 0.8318 \approx 41.59\text{ W} P del ​ = 50 W × 1 0 − 0.80/10 = 50 × 0.8318 ≈ 41.59 W

Effective Isotropic Radiated Power: EIRP = P del × G = 41.59 W × 40 , 796 ≈ 1 , 696 , 705 W ≈ 1.70 MW EIRP \text{EIRP} = P_{\text{del}} \times G = 41.59\text{ W} \times 40,796 \approx 1,696,705\text{ W} \approx 1.70\text{ MW EIRP} EIRP = P del ​ × G = 41.59 W × 40 , 796 ≈ 1 , 696 , 705 W ≈ 1.70 MW EIRP EIRP (dBW) = 10 log ⁡ 10 ( 41.59 ) + 46.11 dBi = 16.19 dBW + 46.11 dBi = 62.30 dBW \text{EIRP (dBW)} = 10 \log_{10}(41.59) + 46.11\text{ dBi} = 16.19\text{ dBW} + 46.11\text{ dBi} = 62.30\text{ dBW} EIRP (dBW) = 10 lo g 10 ​ ( 41.59 ) + 46.11 dBi = 16.19 dBW + 46.11 dBi = 62.30 dBW

The 2.4 m 2.4\text{ m} 2.4 m parabolic reflector concentrates 50 W 50\text{ W} 50 W of RF power into a razor-sharp 0.84 ∘ 0.84^\circ 0.8 4 ∘ pencil beam, generating 1.70 Megawatts 1.70\text{ Megawatts} 1.70 Megawatts EIRP to conquer lunar path loss.

Comparison Table: Directional and Aperture Antenna Architectures

Antenna Topology Operating Spectrum Typical Gain (dBi) Beamwidth (HPBW) Radiation Mechanism Primary Amateur Applications

Half-Wave Dipole HF / VHF ( 1.8 − 146 MHz 1.8 - 146\text{ MHz} 1.8 − 146 MHz ) 2.15 dBi 2.15\text{ dBi} 2.15 dBi ( 0 dBd 0\text{ dBd} 0 dBd ) 78 ∘ 78^\circ 7 8 ∘ (E-plane) Conduction currents on resonant wire Omnidirectional baseline, regional HF

Yagi-Uda Array HF / VHF / UHF ( 14 − 432 MHz 14 - 432\text{ MHz} 14 − 432 MHz ) 7 − 16 dBi 7 - 16\text{ dBi} 7 − 16 dBi 30 ∘ − 65 ∘ 30^\circ - 65^\circ 3 0 ∘ − 6 5 ∘ Parasitic induction & re-radiation Point-to-point HF/VHF DX, satellite tracking

Pyramidal Horn Microwave ( 1 − 40 GHz 1 - 40\text{ GHz} 1 − 40 GHz ) 12 − 25 dBi 12 - 25\text{ dBi} 12 − 25 dBi 15 ∘ − 40 ∘ 15^\circ - 40^\circ 1 5 ∘ − 4 0 ∘ Waveguide mouth aperture flare Dish feedhorn, antenna test range standard

Sectoral Horn Microwave ( 1 − 24 GHz 1 - 24\text{ GHz} 1 − 24 GHz ) 10 − 18 dBi 10 - 18\text{ dBi} 10 − 18 dBi Asymmetric ( 10 ∘ × 60 ∘ 10^\circ \times 60^\circ 1 0 ∘ × 6 0 ∘ ) 1D waveguide flare (E- or H-plane) Microwave beacon coverage, sector illumination

Prime-Focus Dish Microwave ( 1.2 − 24 GHz 1.2 - 24\text{ GHz} 1.2 − 24 GHz ) 25 − 45 dBi 25 - 45\text{ dBi} 25 − 45 dBi 1.5 ∘ − 8 ∘ 1.5^\circ - 8^\circ 1. 5 ∘ − 8 ∘ Paraboloidal aperture collimation Terrestrial microwave DX, satellite TV/links

Cassegrain Dish Microwave ( 5.7 − 76 GHz 5.7 - 76\text{ GHz} 5.7 − 76 GHz ) 35 − 55 dBi 35 - 55\text{ dBi} 35 − 55 dBi 0.5 ∘ − 3 ∘ 0.5^\circ - 3^\circ 0. 5 ∘ − 3 ∘ Dual reflector (parabola + hyperbola) Weak-signal EME moonbounce, deep-space work