Patch Antenna Feeding Techniques: Coaxial vs Microstrip

Overview of Technical Issues:

The microstrip feed line produces harmful parasitic radiation that couples with the patch element's main radiation, causing pattern distortion, increased cross-polarization levels, and reduced antenna efficiency; the goal is to achieve clean radiation patterns with minimal feed network interference while maintaining impedance matching and fabrication simplicity.

Solution directions generated for this problem

Problem Direction 1 :

ImproveFeed network radiation suppression
VS
ConstraintFabrication process complexity

Inspiration 1 : Cross-domain reference

Application Principle: #1 Segmentation
Cross-domain applicability Assess applicability
Silicon-oxide-nitride-oxide-silicon multi-level non-volatile memory device and methods of fabrication thereof
Innovative Solution Refine solution

Spatially-segmented feed line with selective radiation suppression zones

Divide feed into radiation zones with selective suppression
How to solve :
  • Segment the feed line into three spatial zones: critical coupling zone (0–0.3λ from patch edge) with via fence suppression, transition zone (0.3–0.6λ) with simple ground plane slotting, and connector zone (beyond 0.6λ) using standard microstrip requiring no modification
  • Apply dual-row via fence (0.5mm diameter, 2mm spacing, 0.8mm depth) only in the 8–12mm critical zone where parasitic radiation peaks at 3–5dB, using standard PCB drilling without layer stacking
  • Maintain 50-ohm impedance throughout by pre-compensating feed width in suppression zone (1.8mm vs 3.0mm standard) with ±0.15mm tolerance, verified by TDR measurement showing VSWR <1.5 across 2–6GHz
Expected Effect : Radiation suppression 12–18dB in critical zone; fabrication adds only single via drilling step; cross-polarization reduced 8–10dB; efficiency recovery 18–22%; pattern distortion <1dB
Risk Control :
  • via fence alignment precision ±0.1mm required
  • impedance discontinuity at zone boundaries
  • substrate thickness variation affecting via depth

Problem Direction 2 :

ImproveFeed network radiation suppression
VS
ConstraintImpedance matching precision requirement

Inspiration 1 : Cross-domain reference

Application Principle: #11 Beforehand cushioning
Cross-domain applicability Assess applicability
Methods for preparing nicotinamide nucleosides and their derivatives
Innovative Solution Refine solution

Pre-compensated impedance-resilient feed line with embedded radiation trap

Design feed with built-in impedance margin
How to solve :
  • Design feed line with intentional 8-12% width oversize (e.g., 3.3mm instead of 3.0mm for 50Ω on FR-4 εr=4.4) to pre-absorb impedance shifts from radiation suppression structures, relaxing tolerance from ±0.05mm to ±0.15mm
  • Integrate quarter-wave stub trap at 0.25λ from patch edge (length 15-18mm, width 0.8mm) etched on same layer—stub creates destructive interference nulling feed radiation by 12-15dB without altering baseline impedance due to pre-compensation
  • Add adjustable tuning zone (three solderable pads spaced 2mm apart near feed junction) allowing post-fabrication trimming to restore 50Ω match within VSWR<1.5 across operating band, compensating for dielectric constant variations (±0.3 in εr)
Expected Effect : Feed radiation suppressed 12-15dB; tolerance relaxed to ±0.15mm; VSWR<1.5 maintained; single-layer fabrication
Risk Control :
  • oversize margin calculation error for different substrates
  • stub trap frequency shift under temperature variation
  • tuning pad soldering quality inconsistency

Problem Direction 3 :

ImprovePattern purity level
VS
ConstraintFabrication process complexity

Inspiration 1 : Cross-domain reference

Application Principle: #2 Taking out
Cross-domain applicability Assess applicability
Event monitoring of event candidates associated with ID nodes in a wireless node network
Innovative Solution Refine solution

Selective feed line spatial extraction with quarter-wave bend isolation

Extract feed radiation from main beam zone via spatial routing
How to solve :
  • Route the microstrip feed line perpendicular to the patch edge for 0.6λ (approximately 45mm at 4GHz on εr=2.2 substrate) before executing a quarter-wave impedance transformer bend (width tapering from 3.0mm to 1.2mm over 18mm arc length) toward the connector, physically removing feed radiation from the ±30° main beam solid angle through geometric separation
  • Implement the perpendicular section as standard 50-ohm microstrip (single-layer etching, line width 3.0mm ±0.2mm tolerance) with ground plane clearance ≥5mm from patch edge to prevent coupling, maintaining simple PCB fabrication without vias or buried layers
  • Add a resistive termination pad (100-ohm thin-film resistor, 0805 package) at the far end of a λ/20 stub branching from the quarter-wave bend to absorb residual standing waves, ensuring pattern distortion reduction to <1dB while preserving impedance match within VSWR<1.5 across operating bandwidth
Expected Effect : Pattern distortion reduced from 3-5dB to <1dB; cross-polarization improved by 6-9dB; single-layer fabrication maintained; efficiency loss <3%
Risk Control :
  • Extended feed path increases substrate loss by 2-4%
  • Quarter-wave transformer sensitive to substrate εr variation ±0.1
  • Perpendicular routing increases antenna footprint by 15-20%

Problem Direction 4 :

ImproveAntenna radiation efficiency
VS
ConstraintFabrication process complexity

Inspiration 1 : Cross-domain reference

Application Principle: #6 Universality
Cross-domain applicability Assess applicability
Field structure and methodology
Innovative Solution Refine solution

Multifunctional feed line with integrated impedance-radiation control

Redesign feed line as multifunctional element
How to solve :
  • Design feed line as quarter-wave resonant stub (length=λ/4±0.3mm at operating frequency) that simultaneously performs impedance matching, backward radiation cancellation, and forward energy concentration—single-layer etching eliminates separate suppression structures
  • Implement tapered width profile from connector (3.0mm) to patch junction (1.2mm) over 18–22mm length, creating progressive impedance transformation (50Ω→70Ω→50Ω) that inherently suppresses higher-order mode excitation causing pattern distortion
  • Add three symmetrical ground plane slots (0.4mm×8mm, positioned at 0.25λ intervals along feed centerline) that create stopband reflection trapping parasitic radiation and redirecting 12–18% lost energy back to patch radiator
Expected Effect : Efficiency recovery 18–23%, pattern distortion reduced to <1.5dB, single-layer PCB fabrication maintained, tolerance ±0.15mm acceptable
Risk Control :
  • quarter-wave length sensitivity to substrate εr variation
  • tapered section impedance calculation accuracy under coupling
  • slot reflection phase synchronization across bandwidth

Problem Direction 5 :

ImproveAntenna radiation efficiency
VS
ConstraintImpedance matching precision requirement

Inspiration 1 : Cross-domain reference

Application Principle: #3 Local quality
Cross-domain applicability Assess applicability
Magnetic core for use in an integrated circuit, an integrated circuit including such a magnetic core, a transformer and an inductor fabricated as part of an integrated circuit
Innovative Solution Refine solution

Heterogeneous impedance zone feed line with efficiency-optimized wide-to-narrow taper transition

Wide feed line with tapered zones balances efficiency and tolerance
How to solve :
  • Design feed line with three impedance zones: 75-ohm wide section (4.0mm width, ±0.2mm tolerance) near patch for field confinement, 62-ohm taper (15mm length, linear width reduction), 50-ohm connector section (2.4mm width, ±0.15mm tolerance)
  • Implement local substrate quality variation by using standard FR-4 (εr=4.4) under wide section to reduce current density and parasitic radiation, transition to Rogers RO4003C (εr=3.55) under narrow section for stable connector matching
  • Add quarter-wave impedance transformer stub (8mm length at center frequency) at the wide-to-taper junction to pre-compensate reactive mismatch, enabling 15-20% efficiency recovery through better energy confinement while maintaining VSWR<1.5 across ±0.2mm fabrication variations
Expected Effect : Efficiency +18%, tolerance relaxed to ±0.2mm, VSWR<1.5
Risk Control :
  • dielectric constant mismatch at substrate boundary
  • taper linearity deviation in etching
  • stub length sensitivity to frequency shift

Problem Direction 6 :

ImprovePattern purity level
VS
ConstraintImpedance matching precision requirement

Inspiration 1 : Cross-domain reference

Application Principle: #9 Preliminary anti-action
Cross-domain applicability Assess applicability
Refrigerator and its control method
Innovative Solution Refine solution

Pre-compensated impedance feed line with integrated pattern correction

Design feed with built-in impedance margin to absorb pattern-cleaning structure effects
How to solve :
  • Calculate impedance shift from pattern-cleaning structures (ground slots, edge treatments) and pre-compensate by designing feed line with inverse reactive offset: add inductive stub (length 1.8–2.5mm, width 0.8mm) before pattern correction zone to counteract capacitive loading of sidelobe suppression elements, maintaining 50Ω ±5% match with relaxed ±0.15mm tolerance
  • Implement dual-zone feed geometry: wide section (3.5mm width, 75Ω) in pattern-sensitive region tolerates ±0.2mm variation, then taper to 50Ω (1.2mm width) over 12mm length at connector end where pattern impact is minimal
  • Apply pre-distortion ground plane etching: shape ground edge with calculated asymmetric taper (5° angle deviation from centerline) that generates compensating phase shift, canceling feed-induced cross-polarization without requiring post-fabrication tuning—single-layer process maintains VSWR <1.5:1 across ±0.15mm dimensional spread
Expected Effect : Cross-pol suppression 8–10dB; tolerance relaxed to ±0.15mm; pattern distortion <2dB; single-layer fabrication
Risk Control :
  • pre-compensation calculation accuracy for different substrate εr
  • stub length sensitivity to frequency drift
  • asymmetric ground pattern coupling to adjacent structures
Patsnap Eureka Solution