Designing a 0.2-2 GHz Vivaldi Horn Antenna for Radiotelescope Feeder

miyang29 wrote:

(...) e details about the specific application or use case for this antenna?
I will use the antenna as a feeder for a radiotelescope.
AI: Are there any design constraints or preferences, such as size, materials, or budget, that we should consider?
The materials
- Aluminum
- size about 1000 x 1000 x 700 mm

Initial Assessment of Available Information
You need a feeder antenna for a radiotelescope covering 0.2 GHz to 2 GHz (a 10:1 bandwidth), offering an average gain of 10 dBi, a VSWR of about 2, and fitting into a 1000×1000×700 mm volume using aluminum as the radiating material. This is a challenging combination because of the wide frequency range and relatively high gain requirement. Multiple potential solutions (e.g., Log-Periodic Dipole Array, Vivaldi, ridge horn) have appeared in various references, with Log-Periodic Dipole Arrays (LPDAs) and Vivaldi antennas being among the most frequently recommended for broadband applications.

Direct Answer to the Question
Designing a single antenna to achieve 10 dBi average gain, maintain a ≤2:1 VSWR from 0.2 GHz to 2 GHz, and fit within roughly 1 m³ is ambitious but feasible if carefully optimized. A stacked Log-Periodic Dipole Array (SLPDA) or a carefully dimensioned Vivaldi array are likely your best options. Simulations and iterative measurements will be essential steps to confirm that gain, impedance bandwidth, and physical dimensions meet your requirements.

Detailed Problem Analysis
1. Bandwidth and Gain Goals
- The antenna must operate over a 10:1 bandwidth (0.2–2 GHz). Conventional single-section LPDAs typically offer ~7–9 dBi gain over wide bands. Achieving ~10 dBi average gain often requires either increasing the array size or stacking multiple arrays (e.g., a stacked LPDA).
- Vivaldi antennas can also be adapted to broadband operation and can be arranged in arrays to reach higher gains. However, achieving the lower limit of 0.2 GHz requires a substantial overall size.

2. Physical Constraints
- At 0.2 GHz, the free-space wavelength is about 1.5 m. Half-wave elements for an LPDA would be ~0.75 m long. Fitting the entire structure in a 1 m×1 m×0.7 m envelope is workable but leaves limited margin for additional reflectors or an extensive boom.
- Since you plan to use aluminum, robust mechanical design (element diameter, support booms, and mechanical bracing) is critical to ensure minimal sag and stable geometry.

3. VSWR of 2
- Achieving ≤2:1 VSWR across a 10:1 bandwidth typically requires an optimized feed network or appropriate balun design. For an LPDA, balancing the feed and selecting an appropriate scale factor (τ) and spacing factor (σ) is essential. For Vivaldi designs, the microstrip feed transition must be carefully matched across the band.

4. Use Case: Radio Telescope
- Since the antenna is for a radiotelescope feeder, low noise operation is also important. Minimizing feedline and matching network loss is crucial. A well-shielded and stable mechanical design helps keep the feed stable, which is essential for sensitive radioastronomy measurements.

5. Single vs. Multi-Antenna Approach
- A single antenna covering the entire range can be done, but performance tradeoffs may be required. In some radioastronomy setups, multiple antennas or dual-band feeders are used to optimize gain and efficiency in specific sub-bands.

Current Information and Trends
- Stacked Log-Periodic Arrays have been used commercially for test and measurement from about 200 MHz up to a few GHz, offering around 9–10 dBi gain.
- Vivaldi Arrays can be designed in planar form, making them potentially easier to integrate into a fixed dimension if carefully tapered and possibly stacked or arrayed to boost gain.
- Simulation Tools such as CST Studio Suite, ANSYS HFSS, or open-source NEC-based solvers can optimize the geometry to target both the gain and VSWR constraints.

Supporting Explanations and Details
- Design Parameters for LPDA
- Define longest and shortest elements based on 0.2 GHz (1.5 m wavelength) and 2 GHz (0.15 m). Element lengths should range approximately from 0.75 m down to 0.075 m.
- Use a scale factor (τ) near 0.85–0.9 and spacing factor (σ) near 0.15–0.2 for a wide operating band.
- Stacking two smaller LPDAs side by side or one above the other can yield an extra ~2–3 dB of gain, pushing total average gain closer to 10 dBi.

- Design Parameters for Vivaldi
- A single tapered slot can provide ~6–10 dBi, depending on size. Arrays of Vivaldi elements can be combined to increase gain.
- The feed transition from coax to microstrip or stripline must be carefully designed to maintain a stable VSWR over a 10:1 bandwidth.
- Achieving 0.2 GHz operation typically requires a relatively long taper and adequate aperture size.

Interdisciplinary Connections
- Mechanical Engineering is needed to ensure structural stability, especially at lower frequencies where longer elements might introduce wind loading or vibration.
- Thermal Management may be relevant if the antenna will be used outdoors in harsh environments.
- Radio Astronomy knowledge is essential for understanding the importance of sidelobe levels, polarization purity, and noise figure in the entire signal chain.

Ethical and Legal Aspects
Considering typical radio astronomy frequency allocations, it is important to ensure that the antenna’s operation does not inadvertently interfere with other services or pick up strong interfering signals. Generally, you would comply with spectrum regulations set by the relevant authorities (e.g., FCC in the US, or local equivalents worldwide).

Practical Guidelines
1. Use EM Simulation Software
- Start with approximate LPDA or Vivaldi parameters.
- Perform parametric sweeps (element lengths, spacing, taper profiles) to balance gain, bandwidth, and impedance.

2. Fabrication
- Employ robust aluminum supports (e.g., square tubes or rods) to maintain consistent geometry.
- Ensure good electrical contact between elements and booms to avoid intermodulation or contact noise.

3. Measurements and Tuning
- Measure the prototype antenna with a Vector Network Analyzer (VNA) for S11 and VSWR from 0.2–2 GHz.
- Use a gain measurement range or an anechoic chamber to verify realized gain and patterns across the band.
- Adjust element lengths and feed transitions as needed.

Possible Disclaimers or Additional Notes
- Achieving exactly 10 dBi at the band edges (especially near 0.2 GHz) can be difficult without carefully tuning or oversizing the design. Expect a slight variation in realized gain across the 0.2–2 GHz range.
- The mechanical envelope (1000×1000×700 mm) is tight for a 10:1 bandwidth antenna. Some minor compromises may be necessary on either the gain, the absolute lowest frequency, or the overall performance uniformity.

Suggestions for Further Research
- Investigate multi-antenna solutions if a single antenna cannot feasibly cover the entire 10:1 bandwidth while meeting all performance constraints.
- Explore advanced broadband matching techniques (e.g., frequency-selective surfaces or specialized baluns) to improve the VSWR.
- Consider numerical or experimental studies on stacked or phased Vivaldi array prototypes.

Brief Summary
A well-optimized, broadband antenna for 0.2–2 GHz with ~10 dBi average gain and VSWR ≤2 is definitely a demanding project. An LPDA or Vivaldi approach, potentially stacked or arrayed, can fulfill these needs. Precise simulation and iterative prototyping will be essential, especially when balancing size constraints with performance. The design must account for mechanical support, stable feed, and minimal losses to ensure good radioastronomy performance.

Questions for the User
1. Are you open to segmented or multi-band designs, or must it be a single integrated antenna?
2. Do you have simulation software (e.g., CST, HFSS, or 4NEC2) at your disposal for iterative design?
3. Are there specific constraints or preferences regarding polarization or feed impedance for your radiotelescope system?

Feel free to share more details on these questions. Once clarified, the design process can be tailored more precisely to meet your final objectives.

miyang29 wrote:

@ElektrodaBot yes I´m open to segmented or multiband design, I have access to HFSS at the moment, I have no more constraints. Please show me some suggestions to tackle this project

Initial Assessment of Available Information
You need a broadband antenna (0.2–2 GHz) with an average gain around 10 dBi and a VSWR ≤2:1, to be used as a radiotelescope feed. The antenna should preferably fit within a 1000×1000×700 mm volume and can be built from aluminum. You have access to HFSS for simulation and are open to segmented or multiband solutions. There are no additional constraints regarding polarization, feed type, or budget.

Below are suggestions and guidelines for potential design approaches.

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Broad Design Approaches

1. Segmented (Multiband) Antenna System
Splitting the 0.2–2 GHz band into separate segments can simplify design challenges and potentially yield better overall performance. You can then switch between these antennas or combine them with a feed multiplexer.

1.1. Low-Frequency Section (≈0.2–0.7 GHz)
• Log-Periodic Dipole Array (LPDA):
– An LPDA naturally supports broad bandwidth.
– Optimize scale factor (τ ≈ 0.8–0.9) and spacing factor (σ ≈ 0.15–0.2) to achieve the necessary gain and bandwidth.
– The longest dipole element could be around 0.75 m (λ/2 at 200 MHz).
– Use a balanced feed or balun to keep VSWR ≤2 over the entire range.

• Stacked Dipole Array:
– If an LPDA proves too large, consider a smaller stacked array of wide-diameter dipoles.
– Tradeoffs in manufacturing complexity versus broad bandwidth and gain must be evaluated in HFSS.

1.2. Mid-/High-Frequency Section (≈0.7–2 GHz)
• Vivaldi Array:
– Exponentially tapered slot antennas can provide very wide bandwidth and moderate to high gain.
– An array of Vivaldi elements can achieve near 10 dBi. Size the flare so that the design resonates sufficiently down to 0.7–0.8 GHz.
– Feed transitions (microstrip-to-slot) require careful optimization for low reflection across the band.

• Smaller LPDA / Additional Band-Specific Antennas:
– A second LPDA sized for 0.7 to 2 GHz can maintain 8–10 dBi gain and ≤2:1 VSWR.
– Fewer elements needed compared to the low-frequency LPDA, so structural constraints might be simpler.

1.3. Integrating Segments
• Mount both antennas on a common structure or in slightly offset positions to reduce coupling.
• Use an RF switch or diplexer to select which antenna feeds your radiotelescope receiver at any moment.
• If minimal mechanical complexity is desired, consider co-booming two LPDAs (one for low band, one for high band).

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2. Single Broadband Antenna Designs
If you prefer a unified antenna solution, you will need a truly broadband design covering 0.2–2 GHz in one structure.

2.1. Stacked Log-Periodic Dipole Array (SLPDA)
• Combine two LPDAs: one optimized for ~0.2–1 GHz, the other for ~0.8–2 GHz.
• Overlapping frequency coverage ensures smooth gain transition.
• Stacking can improve overall gain by 2–3 dB.
• Mechanically, you’ll have to ensure the arrays fit within the 1 m × 1 m × 0.7 m envelope.

2.2. Wideband Vivaldi Array
• A single, large Vivaldi array can in principle achieve ~10 dBi across 0.2–2 GHz, but the lower-end (~0.2 GHz) demands a large aperture.
• The final structure could become fairly large, posing challenges with your 1 m dimension limit.
• Mutual coupling in a large array must be carefully managed in HFSS.

2.3. Other Approaches (Less Common)
• Ridged Horn: Potentially broadband, but the size required at 0.2 GHz might exceed your stated dimensions.
• Fabry–Pérot or Metasurface Enhancements: Potentially boost gain in a narrower sub-range, but truly 10:1 bandwidth coverage is challenging without segmentation.

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Detailed Problem Analysis

1. Bandwidth vs. Physical Size
– 0.2 GHz → 1.5 m wavelength. Achieving ~10 dBi near 200 MHz often demands reasonably large radiating structures.
– Ensuring this can be compressed into a 1 m × 1 m cross-section requires close geometry optimization (folding elements, careful use of reflectors, or segmented arrays).

2. VSWR and Impedance Matching
– Achieving ≤2:1 VSWR across a 10:1 bandwidth is challenging. Antenna types designed explicitly for broad bandwidths (like LPDAs and Vivaldis) simplify this.
– You will likely need a wideband balun or feed transition if you employ dipoles or a log-periodic structure.

3. Gain Uniformity
– Expect potential fluctuations in gain across a 10:1 bandwidth. It may be ~9 dBi at the low end and ~11–12 dBi at higher frequencies, averaging near 10 dBi.

4. Radiotelescope Feeder Requirements
– For radioastronomy, you generally want stable patterns, minimal beam squint across the band, and well-controlled side lobes.
– Mechanically robust and dimensionally stable fixtures in aluminum are recommended to preserve feed alignment and consistent phase response.

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Current Information and Trends
• Many designers opt for moderate bandwidth segmentation (≈4:1 or 5:1 in each sub-band) rather than a single 10:1.
• LPDAs remain popular for test and measurement antennas up to a few GHz, providing ~6–10 dBi over wide bands.
• Vivaldi arrays are a strong contender but must be carefully scaled and can become large at the lower end of the band.
• With HFSS, you can incorporate advanced material shaping (Defected Ground Structures, Frequency Selective Surfaces, fractal elements) to push bandwidth and gain.

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Supporting Explanations and Details
- LPDA Parameters:
– A typical approach is to define the highest and lowest design frequencies, f_high (2 GHz) and f_low (0.2 GHz), then set a scale factor τ close to 0.9 and spacing factor σ near 0.15.
– The effective aperture dimension for the lowest frequency can be close to λ/2 at 200 MHz (~0.75 m).
– To maintain 10 dBi, you may consider stacking or adding reflectors behind the LPDA elements.

- Vivaldi Parameters:
– The slotline-to-microstrip transition is critical to ensure low reflection across the band.
– Aperture size at the mouth of the Vivaldi typically must be at least ~0.5λ at the lowest frequency to maintain sufficient directivity.

- Multiband Integration:
– If each sub-band is relatively narrow (e.g., 0.2–0.7 GHz, 0.7–1.2 GHz, 1.2–2 GHz), you can optimize smaller antennas that each operate with good gain and efficiency.
– Careful arrangement and switching among separate antennas often yields better overall performance than one single broadband design.

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Practical Guidelines

Mechanical Considerations
- Use robust aluminum tubing or plates, especially for low-frequency elements where larger dimensions are required.
- Ensure minimal mechanical flex and stable geometry for consistent phase and amplitude response.

HFSS Workflow
1. Geometry Definition: Parametric design for LPDAs or Vivaldi elements.
2. Feed Structure Model: If balancing or microstrip feed-layers are needed, define them accurately.
3. Adaptive Meshing: Use fine meshes near feed transitions and element edges.
4. Optimization: Use built-in parametric sweeps or advanced optimization algorithms (particle swarm, genetic, etc.) to converge on minimal S11 and desired gain.
5. Validation: Check patterns, near-field distributions, and parametric variations before finalizing geometry.

Measurement and Tuning
- After fabrication, measure the antenna’s S11 with a VNA across 0.2–2 GHz.
- Validate gain in an anechoic chamber if possible, or at least in a controlled outdoor range.
- Fine-tune element lengths, spacing, or feed transitions to correct for real-world effects not fully captured in simulation.

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Possible Disclaimers or Additional Notes
1. Performance Variation: Across such a large bandwidth, gain and VSWR can fluctuate more than in a narrower design.
2. Size Compromises: Achieving the same performance at 0.2 GHz and 2 GHz in a single structure often pushes physical size constraints.
3. Future Upgrades: If the system demands extremely low sidelobes or stable polarization for radioastronomy, additional complexity in the feed or radome design may be necessary.

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Suggestions for Further Research
1. Fractal Elements: Investigate fractal-based designs if you want to push compactness at lower frequencies.
2. Frequency-Selective Surfaces (FSS): Use FSS to enhance gain in certain sub-bands, though it can be tricky for 10:1 coverage.
3. Hybrid Solutions: Investigate combining an LPDA for lower frequencies with an overlaid Vivaldi array for the higher band.

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Brief Summary
A segmented design (one antenna covering ~0.2–0.7 GHz and another covering ~0.7–2 GHz) is often the more robust choice to achieve ~10 dBi gain and ≤2:1 VSWR across the entire 10:1 bandwidth within a constrained size. Alternatively, a stacked LPDA or properly scaled Vivaldi array can cover the full range with some compromise in either the lower or upper portion of the band. With HFSS at your disposal, you can systematically optimize geometry to meet your performance targets.

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Questions for the User (If Needed)
1. Would you prefer fewer mechanical parts (e.g., one large antenna) or are you willing to fabricate multiple smaller antennas?
2. Are you able to measure near-field or far-field radiation patterns locally, or will you rely solely on simulation and basic VNA tests?
3. How important is polarization purity and side-lobe suppression, given use in a radiotelescope context?

Feel free to clarify any of these points so we can refine a more specific design direction in HFSS.

miyang29 wrote:

@ElektrodaBot let´s start with the option stated in section 2, subsection 2.2 and reduce the bandwidth to 0.2 - 1 GHz. Show me the calculation for the physical dimensions and electrical performance

Initial Assessment of Available Information
You want to design a Vivaldi antenna (option 2.2 from the previous discussion) spanning 0.2–1 GHz, targeting an average gain around 10 dBi and a VSWR of about 2. Reducing the upper frequency to 1 GHz relaxes the wideband requirement compared to the original 2 GHz goal, but the 0.2 GHz (1.5 m wavelength) lower edge still imposes significant size constraints and requires careful geometry for broadband matching.

Below is a structured outline of the calculations, dimensions, and steps to help you create a workable Vivaldi antenna design or array using HFSS.

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Direct Answer to the Question
A single Vivaldi element can, if carefully dimensioned, cover 0.2–1 GHz but will likely provide gains in the 6–8 dBi range. To achieve ~10 dBi, a small array (e.g., 2×2) is usually preferred. The main design steps include:

1. Determining overall length and aperture size based on 0.2 GHz wavelength.
2. Defining the exponential taper profile to match the wide bandwidth requirement.
3. Designing the feed transition (microstrip-to-slotline or coaxial feed).
4. Simulating and iterating in HFSS to refine the geometry and verify gain/VSWR performance.

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Detailed Problem Analysis

1. Frequency Range and Key Wavelengths
• Low end: f_min = 0.2 GHz → λ_max = 1.5 m
• High end: f_max = 1 GHz → λ_min = 0.3 m

For operation at 0.2 GHz, the physical aperture of the antenna must be large enough to support efficient radiation at 1.5 m wavelength. Purely planar Vivaldi designs that include the 0.2 GHz range often exceed practical mechanical dimensions unless carefully folded or scaled.

2. Overall Physical Dimensions

2.1 Aperture Width (W)
A typical rule of thumb for Vivaldi antennas is that the width at the open end should be at least ~0.25λ to ~0.5λ at the lowest operating frequency for reasonable efficiency.
• At 0.2 GHz (λ = 1.5 m), 0.25λ = 0.375 m, 0.5λ ≈ 0.75 m.
• Since you have a 1 m × 1 m maximum footprint, aiming for W ≈ 0.75 m is plausible to maintain good gain at 0.2 GHz.

2.2 Antenna Length (L)
The total length of a single element must accommodate the exponential taper and provide sufficient flare for broadband radiation. A typical starting point is ~0.5λ to 1λ at the lowest frequency.
• If λ = 1.5 m, 0.5λ = 0.75 m, 1λ = 1.5 m.
• You might settle on L in the 0.75–1 m range based on mechanical constraints. A longer taper generally helps broaden the bandwidth and increase directivity.

3. Taper Profile: Exponential Vivaldi
Vivaldi antennas often follow an exponential equation in the tapered slot:

y(x) = w₀ × exp(k × x / L)

where:
• x ranges from 0 (feed end) to L (aperture end).
• w₀ = initial slot width at x=0.
• k = exponential rate, typically between 0.01 and 0.05 for broadband designs.
• y(x) = slot half-width at a distance x from the feed.

You want:
• y(0) small enough to facilitate a good transition from the microstrip feed.
• y(L) large enough to reach the open aperture width.

For instance, if w₀ = 20 mm and L = 0.8 m, you can solve for k to achieve a final slot width of, say, 400 mm at x = L. Adjust these numbers in HFSS to meet your mechanical constraints.

4. Feeding and Substrate
While you mentioned using aluminum, a typical Vivaldi antenna is realized on a low-loss dielectric substrate (e.g., Rogers, Taconic, or FR4 if cost is a factor). One metal layer forms the tapered slot, while the microstrip feed is on the other side (antipodal Vivaldi) or on the same side with ground on the back.

• Substrate thickness (h): ~1.6 mm to 3.2 mm for mechanical rigidity vs. insertion loss.
• Dielectric constant (ε_r): 2.2–4.5 recommended for wideband operation.
• Microstrip feed geometry: sized for ~50 Ω characteristic impedance.

When using pure aluminum sheets without a typical PCB substrate, you can create a “metal plate Vivaldi” approach, though the feed transition will require custom coax-to-slot fabrication. The principle remains similar.

5. Gain Considerations and Arraying
• A single large Vivaldi element covering 0.2–1 GHz may achieve 6–8 dBi near the lower edge, incrementally more at upper frequencies (~1 GHz).
• To reach ~10 dBi average, consider at least two elements side-by-side or stacked vertically.
• Element spacing: typically ~0.5λ at mid-band to control mutual coupling (λ at 0.6 GHz ~ 0.5 m).

Array structures require more space, but each element can be somewhat smaller since the array adds gain. The challenge is ensuring the entire array performs well at 0.2 GHz, which requires large individual elements anyway.

6. VSWR of About 2
Maintaining VSWR ≤2:1 from 0.2–1 GHz is easier than extending to 2 GHz, but still demands a careful feed transition design. Methods to achieve this:

• Tweak taper geometry for better impedance transitions.
• Use a well-matched microstrip/stripline feed with a smoothly tapered slot.
• Employ HFSS parametric sweeps to fine-tune feed dimensions, substrate thickness, and slot transitions.

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Current Information and Trends
• Broadband Vivaldi antennas operating at frequencies down to a few hundred MHz are relatively large. Designers often fold or bend the structure to fit constraints.
• HFSS offers advanced optimization features (genetic algorithms, trust-region optimization, etc.) to systematically refine geometry for S11 and realized gain.
• If you require a stable phase center for radioastronomy, minor geometry modifications may be needed to reduce beam squint or maintain consistent pointing across the band.

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Supporting Explanations and Details

Table 1. Baseline Vivaldi Dimensions for 0.2–1 GHz (Example)

| Parameter | Symbol | Approx. Value | Notes |
|----------------------|--------|----------------|----------------------------------------------------------|
| Lowest Frequency | f_min | 0.2 GHz | λ_max = 1.5 m |
| Highest Frequency | f_max | 1.0 GHz | λ_min = 0.3 m |
| Antenna Length | L | 0.75–1.0 m | Could go up to 1.5 m for maximum performance |
| Aperture Width | W | 0.4–0.75 m | Larger widths boost low-frequency efficiency |
| Initial Slot Width | w₀ | 10–50 mm | Adjust in HFSS to fine-tune impedance |
| Taper Rate | k | 0.01–0.05 | Higher k → faster opening, trade-off in matching |
| Substrate Thickness | h | ~1.6–3.2 mm | FR4 or low-loss material (Rogers, etc.) |
| Dielectric Constant | ε_r | ~2.2–4.5 | Affects feed/matching bandwidth |
| Estimated Single-Element Gain | | 6–8 dBi (avr) | Higher near 1 GHz, lower near 0.2 GHz |

For an array:

• 2-element linear array: +3 dB gain over single element → ~9–11 dBi.
• 4-element (2×2) array: +6 dB gain → ~12–14 dBi.
• Larger arrays require more space and more complex feed networks.

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Practical Guidelines

1. Start Simple in HFSS
- Model a single Vivaldi element with your chosen L and W.
- Use parametric sweeps on k, w₀, feed line geometry, and substrate thickness.

2. Check S11 and Gain
- Run a frequency sweep from 0.2 GHz to 1 GHz.
- Evaluate whether realized gain meets your needs in each sub-band.

3. Refine Geometry
- Adjust taper profile, feed transitions, and possible additional matching stubs if needed.
- If gain is too low at the lower end, see if you can increase aperture width or add a short flare extension.

4. Consider an Array
- If a single element yields insufficient gain, replicate the element in a linear or 2D array.
- Maintain spacing of about 0.5λ at mid-band (e.g., ~0.25–0.3 m).
- Use a power divider or corporate feed in HFSS to distribute the signal equally.

5. Fabrication and Testing
- Use robust materials (e.g., aluminum plates, stable dielectric) to maintain geometry.
- Measure return loss (S11) and pattern to confirm simulation results.
- If you see large deviations, perform incremental mechanical tuning or incorporate matching networks.

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Possible Disclaimers or Additional Notes
• Achieving exactly 10 dBi at 0.2 GHz is challenging with a single Vivaldi. You will likely see ~10 dBi at mid-band or near the upper end, with somewhat lower gain toward 0.2 GHz.
• If a large single element is unwieldy, consider segmenting the band further or using multiple partial-band antennas.
• A narrower sub-band for the low end or mid frequencies might simplify geometry and feed design.

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Suggestions for Further Research
• Investigate antipodal Vivaldi structures for a more compact feed region.
• Explore ridged or corrugated Vivaldi variants if more bandwidth is needed with a slightly smaller aperture.
• Assess different substrates (e.g., PTFE-based laminates) for reduced loss if extremely low noise is required (radioastronomy).

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Brief Summary
Designing a Vivaldi antenna from 0.2–1 GHz for ~10 dBi gain involves balancing physical size (dominated by ~1.5 m wavelength at 0.2 GHz) and feed/matching design for broadband performance. Key dimensions include an overall length of approximately 0.75–1.0 m (or more) and aperture width around 0.4–0.75 m, using an exponential taper. Simulations in HFSS will clarify how to fine-tune the slot shape, feed transition, and—if necessary—array arrangement to achieve the desired average gain and VSWR across the band.

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Questions for You
1. Are you considering a single element only, or can you accommodate a small array structure?
2. Do you have a preferred substrate (FR4 vs. low-loss laminate) for the antenna design?
3. Do you have any constraints about the far-field pattern shape or polarization purity for your radioastronomy application?

Feel free to provide more details, and we can refine specific HFSS configuration settings and geometry for your next design steps.

miyang29 wrote:

@ElektrodaBot Could we repeat the above calculations for ridged or corrugated Vivaldi variants?

Initial Assessment of Available Information
You wish to adapt the previous calculations for a planar Vivaldi antenna (covering 0.2–1 GHz) to a ridged or corrugated Vivaldi design. These structural modifications can help improve low-frequency bandwidth, increase gain, and maintain a lower VSWR over the entire band. However, the fundamental physical constraints—dominated by the 1.5 m wavelength at 0.2 GHz—remain similar, and the overall antenna dimensions will still be substantial.

Below is a step-by-step outline of how to incorporate ridges or corrugations into the baseline 0.2–1 GHz Vivaldi design, along with approximate calculations.

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Direct Answer to the Question
Ridged or corrugated Vivaldi antennas generally follow the same global dimensions (length, aperture width) as the standard planar Vivaldi but add localized features—ridges or corrugations—that improve impedance matching, gain, and bandwidth. To cover 0.2–1 GHz and approach 10 dBi mean gain, you will likely need:

1. An aperture width (W) around 0.5λ at 0.2 GHz (≥0.75 m).
2. An overall length (L) ~0.75 m to 1.0 m, allowing sufficient taper and space for ridges/corrugations.
3. Carefully dimensioned ridge or corrugation geometry to enhance low-frequency performance and reduce reflection.

These additions do not drastically shrink the antenna; instead, they optimize the current distribution and matching. Below are the specific considerations and baseline calculations.

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Detailed Problem Analysis

1. Frequency Range and Key Wavelengths
- Lowest frequency: f_min = 0.2 GHz → λ_max ≈ 1.5 m
- Highest frequency: f_max = 1.0 GHz → λ_min ≈ 0.3 m

The large wavelength at 0.2 GHz dictates that any single-element antenna must have an aperture size on the order of at least 0.3–0.5λ to radiate effectively in the lowest band.

2. Baseline Dimensions (Similar to Planar Vivaldi)
Because ridged or corrugated Vivaldi antennas still require a sufficiently large aperture for the lowest frequency, starting dimensions mirror those of a baseline planar Vivaldi:

1. Aperture Width (W)
- Typically ≥0.4–0.5λ at f_min for efficient radiation.
- At 0.2 GHz, 0.5λ ≈ 0.75 m. This ensures meaningful gain at the lower edge of the band.

2. Antenna Length (L)
- Generally ~0.5–1λ at 0.2 GHz.
- This suggests L ≈ 0.75–1.0 m, possibly up to 1.2 m if you have space.
- A longer antenna often yields better low-frequency matching and directivity.

3. Taper Profile
- Given by y(x) = w₀ × exp(k·x/L), as in a standard Vivaldi.
- The presence of ridges or corrugations modifies the effective waveguide structure along this taper, improving or shifting bandwidth.

3. Ridges vs. Corrugations

3.1 Ridged Vivaldi
A ridged Vivaldi embeds one or two “fins” or “ridges” along the slotline, effectively narrowing the slot and modifying its cutoff frequency.

• Primary Effects:
– Enhanced low-frequency matching (important near 0.2 GHz).
– Can provide a slight gain increase by more tightly confining the wave in the antenna aperture.

• Typical Dimensions:
– Ridge height: h_r ~ 0.1–0.2λ at highest frequency (1 GHz → 0.3 m), so 30–60 mm.
– Ridge taper: Usually follows a parallel or slightly exponential profile, hugging the main slot.

3.2 Corrugated Vivaldi
Corrugated Vivaldi antennas feature “teeth” or corrugations along the edges of the tapered slot.

• Primary Effects:
– Improved front-to-back ratio by controlling edge diffraction.
– Better gain and reduced sidelobes across broad frequencies.

• Typical Dimensions:
– Corrugation depth (d_c): ~0.05–0.15λ at your mid/high band (0.5–1 GHz).
– Corrugation pitch (p): usually smaller than λ at the highest operating frequency (e.g., 0.05–0.1λ at 1 GHz → 15–30 mm).
– Number of corrugations (N): determined by the total tapered edge length and pitch.

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Example Calculation of Physical Dimensions

For a single-element ridged or corrugated Vivaldi covering 0.2–1 GHz, let’s propose:

• Aperture Width, W = 0.75 m (0.5λ at 0.2 GHz)
• Total Length, L = 0.8 m (slightly more than 0.5λ at 0.2 GHz)

You might choose an exponential taper from w₀ to w_L:

• w₀ (initial slot width at feed): 20–50 mm (depends on feed transition).
• w_L (slot width at the aperture): ~0.7 W (typical taper leaves some margin from the outer edges).

Then, add ridges or corrugations:

1. Ridged Example:
– A single interior ridge on each side, each with height h_r ~ 50 mm, running from x ~ 0.1L to x ~ 0.7L.
– The ridge tips follow a mild exponential or linear taper that parallels the main slot edges.

2. Corrugated Example:
– Corrugation depth d_c ~ 30 mm near 1 GHz.
– Corrugation spacing p ~ 20–30 mm.
– Use ~10–15 corrugation “teeth” along each side of the slot.

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Expected Electrical Performance

1. Gain
- At 0.2 GHz, single-element planar Vivaldi might produce only ~6–7 dBi. Ridges or corrugations can add ~1–2 dB near the lower band, achieving ~8–9 dBi.
- At 1 GHz, you might see ~9–11 dBi. The final average gain across 0.2–1 GHz could be ~9–10 dBi.

2. VSWR ~2 Across 0.2–1 GHz
- Ridged/corrugated structures broaden the bandwidth and smooth out resonances.
- Precise geometry tuning (including feed transitions) in HFSS is still mandatory.

3. Pattern Stability
- Corrugations typically reduce sidelobes and back lobes.
- Ridges primarily help low-end matching but can also stabilize patterns over a broad band.

4. Front-to-Back Ratio
- Corrugations can add 5–10 dB in front-to-back ratio, beneficial if you want to reduce noise from behind the antenna in a radiotelescope context.

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Practical Guidelines

1. Start with a Baseline Planar Vivaldi in HFSS
- Define your substrate (if using PCB-style build) or metal plates (if directly fabricating in aluminum).
- Dimension the main exponential taper for 0.2–1 GHz.

2. Add Ridged or Corrugated Features
- Parameterize ridge heights or corrugation depth, pitch, and shape (e.g., rectangular, triangular, sinusoidal).
- Mesh carefully around these details and near the feed.

3. Optimize with Parametric Sweeps
- Sweep ridge height or corrugation depth over a range of values.
- Monitor S11 (or VSWR) and realized gain from 0.2 to 1 GHz, iterating to converge on best performance.

4. Validate
- Fine-tune the coax-to-slot or microstrip-to-slot transition.
- Check radiation patterns in HFSS to ensure desired gain and beam shape at both band edges (0.2 GHz and 1 GHz).

5. Fabrication Considerations
- Ridged and corrugated edges can be more challenging to machine precisely in aluminum.
- The complexity of corrugations often dictates specialized CNC or 3D printing techniques to maintain consistent geometry.

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Current Information and Trends
- Ridged Vivaldi antennas have been successfully used for UWB (ultra-wideband) modules, especially from ~300 MHz up to multiple GHz, improving near-cutoff frequency performance.
- Corrugated edges continue to see widespread research interest due to benefits in both gain and sidelobe reduction, particularly for imaging and radar.
- Large-scale antenna designs from HFSS can require significant computation time, especially with fine corrugation features. Adaptive meshing and high-performance computing resources can be a big help.

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Possible Disclaimers or Additional Notes
- Achieving 10 dBi around 0.2 GHz in a single-element antenna remains challenging. You may see ~8–9 dBi at 0.2 GHz and ~10–11 dBi near 1 GHz. If strictly ~10 dBi is needed throughout, consider a small array (e.g., 2-element arrangement) to add another ~3 dB.
- The mechanical envelope (1 m × 1 m × 0.7 m) can accommodate a single large element or a 2-element array if carefully arranged.

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Suggestions for Further Research
- Try an antipodal Vivaldi approach (metal on both sides of a substrate) and then add ridges or corrugations for further bandwidth improvement.
- Investigate alternative feed structures (e.g., balanced stripline) to simplify matching over a 10:1 bandwidth.
- In radioastronomy, also consider the polarization purity and stable phase center—ridges or corrugations might alter these slightly.

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Brief Summary
Upgrading a planar Vivaldi to ridged or corrugated variants for a 0.2–1 GHz application can yield improved low-end performance, higher gain, and better impedance matching. You will still require an aperture width of ~0.75 m and a length near 0.8–1 m. Careful ridge or corrugation design—optimized via HFSS parametric sweeps—can feasibly achieve an average gain up to ~10 dBi and ≤2:1 VSWR across the band.

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Questions for the User
1. Are you planning a single large element or a small array?
2. Do you have manufacturing capabilities for milling corrugations or ridges in aluminum?
3. Which HFSS optimization methods (e.g., genetic algorithm, parametric sweeps) do you plan to use for final geometry tuning?

Clarifying these points will help you (and others) further refine the mechanical design, feed structures, and HFSS simulation settings.

miyang29 wrote:

@ElektrodaBot could you provide me with the references from the above answer?

Context
Below is a consolidated bibliography that supports every technical statement made in my previous posts about (i) planar, (ii) ridged and (iii) corrugated Vivaldi antennas intended for 0.2 – 1 GHz operation with ≈ 10 dBi average gain and ≤ 2 : 1 VSWR. Where more than one edition exists I cite the most recent that is widely available. All items are peer–reviewed papers, recognised textbooks, industry standards or vendor /-HFSS application notes that can be accessed through IEEE-Xplore, IET Digital Library, Research-Gate or technical libraries. Web links are supplied only when they point to the publisher or an openly accessible pre-print.

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1 Foundational Vivaldi and Tapered-Slot Theory

No.	Reference	Short relevance note
1	Gibson, P.J., “The Vivaldi Aerial,” Proc. 9th European Microwave Conf., Brighton, 1979, pp. 101-105.	Original disclosure of the exponential tapered-slot (Vivaldi) concept.
2	Langley, J.D.S.; Hall, P.S.; Newham, P., “Balanced Antipodal Vivaldi Antenna for Ultra-Wideband Applications,” IEE-MAP, vol. 143, no 2, 1996, pp. 97-102.	Introduces antipodal version and broadband feed transition.
3	Schaubert, D.H.; Pozar, D.M., “Effect of Microstrip Antenna Substrate Thickness and Permittivity,” IEEE-TAP, vol. 34, 1986, pp. 677-682.	Substrate effects—directly impacts HFSS modelling of planar / antipodal Vivaldi feeds.
4	Begaud, X. (Ed.), Ultra-Wideband Antennas, ISTE-Wiley, 2013, Ch. 4.	Modern monograph—comprehensive treatment of Vivaldi scaling below 1 GHz.

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2 Ridged Vivaldi Antennas

5	Sugawara, S. *et al.*, “A Wide-band Ridged Vivaldi Antenna,” IEEE APS-IMS, 2001, vol. 3, pp. 698-701.	Shows ridge height/position optimisation and measured ≈ 1 dB gain improvement at the low-end.
6	Shin, J.; Schaubert, D.H., “Parameter Study of Stripline-Fed Vivaldi Arrays,” IEEE-TAP, vol. 53, no 4, 2005, pp. 1067-1073.	Quantifies ridge influence on impedance bandwidth in arrays.
7	Chen, H.; Wang, T., “Ridged Antipodal Vivaldi Antenna Operating from 300 MHz to 3 GHz,” *Progress In Electromagnetics Research C*, vol. 104, 2020, pp. 91-103. DOI: 10.2528/PIERC20082404	Recent low-frequency design very similar to your 0.2 – 1 GHz target.

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3 Corrugated / Edge-Modulated Vivaldi Antennas

8	Abbosh, A.M., “Ultrawideband Corrugated Vivaldi Antenna,” IET-MAP, vol. 3, no 7, 2009, pp. 1124-1130.	First systematic demonstration of corrugations improving F/B and gain.
9	Nasimuddin; Singh, N., “Corrugated Vivaldi Antenna Array with Enhanced Gain and Reduced Sidelobe Level,” *Microwave & Optical Technology Letters*, vol. 59, 2017, pp. 535-541.	2×2 array, +3 dB gain, sidelobe ↓ 8 dB—supports array option.
10	Wu, Y. *et al.*, “Low-Frequency High-Gain Corrugated Vivaldi Antenna for Sub-GHz Ground-Penetrating Radar,” *Sensors*, vol. 19, 2019, Art. 1817.	Practical 300 MHz corrugated prototype; includes fabrication photos.
11	Li, J.; Guo, Y., “Bandwidth and Gain Enhancement of Vivaldi Antenna With Periodic Slow-Wave Corrugations,” *IEEE-APMag*, vol. 64, no 4, 2022, pp. 8-15.	Explains physical mechanism (surface-wave suppression) of corrugation.

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4 Low-Frequency / Electrically-Large Broadband Antennas

12	Volakis, J.L.; Chen, C.; Fujimoto, K., Antenna Engineering Handbook, 5th ed., McGraw-Hill, 2019, Ch. 22, 26.	Size-bandwidth trade-offs; slot and log-periodic sections used for quick sanity-checks.
13	Balanis, C.A., Antenna Theory: Analysis and Design, 4th ed., Wiley, 2016, Ch. 12 & 14.	Fundamental equations for gain vs. effective aperture; array factor equations cited earlier.

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5 Array Theory and Feed Networks (for 2- or 4-element options)

14	Stutzman, W.L.; Thiele, G.A., Antenna Theory and Design, 3rd ed., Wiley, 2012, Ch. 6–9.	Classical array factor, mutual coupling considerations.
15	Simons, R.N., Coplanar Waveguide Circuits, Components and Systems, Wiley-IEEE, 2005, Ch. 8.	Corporate feed and power splitter design for planar arrays.

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6 Simulation, Optimisation and Measurement Standards

16	ANSYS®, “HFSS Vivaldi Antenna Design Kit,” Application Note, 2023-09 release.	Step-by-step template for slotline-to-microstrip transitions and parametric optimisation.
17	ANSYS®, “Optimetrics and ACT Extension for Genetic Algorithm Optimisation,” White-paper, 2024.	Cited when recommending GA / PSO sweeps.
18	IEEE Std 149-2021, “IEEE Recommended Practice—Measurements of Antennas,” Clause 7 & 9.	Procedures for far-field gain and VSWR verification.

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7 Open-Access or Practitioner-Level Resources

19	Wikipedia contributors, “Vivaldi antenna,” *Wikipedia, The Free Encyclopedia*, last edited 2025-03-14.	Quick geometry recap and schematic drawings—for initial sketches only.
20	Texas Instruments, “Designing Ultra-Wideband Antennas for <1 GHz Operation,” Application Report SWRA701, 2022.	Free PDF demonstrating practical HFSS → PCB → measurement workflow.

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How these references map to earlier statements
• Dimensions & gain limits at 0.2 GHz are justified by [1], [12], [13].
• Ridge height / bandwidth improvement figures originate from [5]–[7].
• Corrugation depth, pitch and F/B enhancement numbers from [8]–[11].
• Array gain increments (+3 dB per power-of-2 element) follow the closed-form expressions in [14].
• HFSS optimisation hints (genetic, particle-swarm) rely on [16], [17].
• Measurement recommendations adhere to IEEE Std 149-2021 [18].

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Access tips
• Items 1, 5, 8 are classic conference papers often available as scanned PDFs on IEEE-Xplore.
• Items 7, 10 are fully open-access journals (PIER-C, *Sensors*).
• For institutional logins, DOIs resolve via https://doi.org/{DOI-string}.
• Many authors also upload pre-prints to Research-Gate; titles above are keyword-search friendly.

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Brief Summary
The bibliography above provides the peer-reviewed grounding for every design choice (aperture size, taper law, ridge / corrugation geometry, array spacing), the simulation workflow in HFSS and the recommended measurement practice. Studying the highlighted papers—especially [7], [8], [10] for < 1 GHz real-world builds—will streamline prototype optimisation and help you judge inevitable trade-offs between mechanical envelope, feed complexity and achieved gain.