What Are Microstrip Components?

Microstrip components are passive and active circuit elements fabricated on a dielectric substrate using microstrip transmission line technology, where a conducting strip on one surface of the substrate, a ground plane on the opposite surface, and the dielectric between them form the basis for signal routing, power splitting, filtering, and impedance transformation. They are the building blocks of planar microwave and RF circuits, found in radar front ends, wireless base stations, satellite payloads, and measurement instruments. Because they share the same photolithographic fabrication process as printed circuit boards, microstrip components can be integrated with microstrip antennas and MMIC devices into a single planar assembly.

The component set traces back to foundational microwave circuit work in the 1950s and 1960s at institutions such as MIT Lincoln Laboratory and Bell Telephone Laboratories. The relationship between transmission line length and electrical response, quarter-wave impedance transformation and the coupled-line properties that enable bandpass behavior, were established analytically before the microstrip form factor existed and were adapted to planar substrates as fabrication techniques matured.

Power Dividers and Combiners

Power dividers split an input signal into two or more output ports at a defined amplitude and phase ratio; power combiners perform the inverse, summing inputs coherently at a single output. The Wilkinson divider, proposed by Ernest Wilkinson in 1960, remains the dominant topology for equal-split and unequal-split designs. It uses two quarter-wave transmission line sections and an isolation resistor connected between the output ports; at the design frequency, the output ports are matched and isolated simultaneously. As shown in the IEEE Xplore paper on compact Wilkinson dividers with harmonic suppression, modifications using lumped elements or stepped-impedance resonators can suppress harmonics and reduce the physical footprint by more than 80 percent compared to a conventional λ/4 design.

The Gysel divider extends the Wilkinson topology by moving the isolation resistors to ground rather than floating them between ports, improving power handling and enabling independent placement of the terminations on the board.

Thick Film Inductors

Thick film inductors are spiral or meandered conducting elements printed on ceramic or low-temperature co-fired ceramic (LTCC) substrates using screen-printed conductor pastes, typically silver or gold palladium. They occupy little area relative to equivalent microstrip stubs, making them attractive for lumped-element realizations at frequencies below about 6 GHz where quarter-wave microstrip sections would be physically large. Thick film technology is described in the IEEE Xplore chapter on planar circuit design in RF and Microwave Circuit Design, which covers how printed inductor quality factor and self-resonant frequency depend on conductor geometry, substrate permittivity, and via connections to the ground plane.

Thick film inductors are used alongside microstrip transmission lines in miniaturized Wilkinson dividers and branchline couplers, where lumped-element segments replace distributed quarter-wave sections to reduce overall circuit size without substantially compromising insertion loss or isolation performance, as demonstrated in the Scientific Reports study on size-reduced Wilkinson designs.

Applications

Microstrip components have applications in a range of fields, including:

• Cellular base station feed networks, distributing transmit power across antenna array elements
• Radar transmit/receive modules, combining and splitting signals between amplifiers and antenna subarrays
• Satellite transponders, routing signals between multiple uplink and downlink frequency bands
• Test and measurement, as internal power splitters in vector network analyzers and spectrum analyzers
• Medical imaging, feeding phased arrays in microwave-based breast cancer screening systems