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Notch Filters
Low insertion loss notch filters (~0.1 dB) are essential for modern defense and wireless systems requiring high spectral fidelity. Spectrum Control’s designs enable receivers to detect low-power targets and distinguish signals in interference-heavy environments. These filters help identify weak communications and extract valuable intelligence in crowded spectra.
Visit our Notch Filter Customization Tool today to optimize your demanding filter requirements.
Our database of low-loss notch filter designs (0.1 dB) helps eliminate the need for additional gain when Size, Weight, and Power (SWaP) initiatives are in place. Low-loss band-reject filters from Spectrum Control also suppress harmonics at the receiver front end when complex pulse or chirp signals are cascaded in the receive-side chain. A flat amplitude response is critical to prevent distortion and unwanted spurious modulation.Spectrum Control’s line of low-loss band-reject filter designs delivers insertion loss as low as 0.1 dB while optimizing pole-placement strategies to achieve maximum rejection in a compact design.
These low-loss notch filters (0.1 dB) also help maintain receiver sensitivity in crowded wireless spectra. Excessive insertion loss can lead to unwanted heat, requiring additional cooling strategies or heavier metal packaging to prevent thermal runaway. Low-loss notch filters from Spectrum Control improve signal-to-noise ratio
(SNR) performance by providing a lower-loss path for weak signals. They maintain spectral purity without introducing harmful bit-error-rate (BER) degradation. Spectrum Control also offers Rapid Filter options, providing band-reject filters in both Chebyshev and Elliptic responses to meet critical demand requirements.
Notch filter frequency response
Lumped Element Lowpass Filters
Spectrum Control’s superior low-loss (0.1 dB) lumped element lowpass filters are ideal for applications where size and weight are critical. Our filter engineers are experts in lumped element design techniques and employ a range of innovative methods to meet today’s demanding specifications.
- Lightweight surface-mount packages for airborne applications
- Silver plating to reduce insertion loss
- Integral shielding for improved isolation
- Strategically placed poles for maximum rejection
- Multiple topologies integrated within a single package for broad frequency coverage
| Frequency | 10 MHz to 3000 MHz |  |
| Size | Small | |
| Cost | Low | |
| Harmonics | No Spurious Passbands | |
| Power Handling | Up to 100 Watts | |
Built from discrete inductors and capacitors, these lowpass filters cover frequencies from HF through portions of S-band (approximately 10 MHz to 3 GHz). Because discrete components are much smaller than the operating wavelength, lumped element designs achieve a more compact footprint than cavity filters. As distributed-element structures, cavity filters must scale with wavelength and can exhibit spurious passbands or re-entrant responses.
Spectrum Control's lumped element lowpass filters avoid these re-entrant modes, delivering cleaner roll-off characteristics and fractional bandwidths ranging from approximately 10% to 90%, performance that is difficult to achieve with narrowband cavity topologies. Easily tuned using air-spaced inductive coils and built from standard off-the-shelf components, they provide a lower-cost, highly customizable alternative to cavity filter designs.
Spectrum Control’s lumped element filters are designed using discrete inductors and capacitors, covering HF, VHF, UHF, L-band, and portions of S-band (approximately 10 MHz to 3000 MHz). Below 1000 MHz, wavelengths are relatively long; distributed-element filters like cavity filters must be at least a fraction of the operating wavelength, which can make cavities physically larger than other topologies such as lumped elements.
Because discrete capacitors and inductors are much smaller than the operating wavelength, lumped element filters can achieve a smaller footprint than cavity designs.
Distributed-element filters, such as cavity filters, can exhibit spurious passbands, harmonic passbands, or a re-entrant response because their performance depends on the physical dimensions of the structure relative to the wavelength.
By contrast, Spectrum Control’s lumped element filters are smaller than the operating wavelength and therefore do not exhibit re-entrant modes or undesirable harmonic passbands, resulting in a cleaner response. They can also achieve very wide fractional bandwidths (roughly 10% to 90%), which can be difficult to replicate with narrow-band cavity-style topologies.
Lumped element filters are relatively easy to tune by adjusting poles using air-spaced inductive coils. Because these designs typically use standard, off-the-shelf discrete elements and don’t require complex specialized machining (unlike cavity filters), they generally offer lower cost and high customizability.
Cavity Lowpass Filters
Spectrum Control's cavity lowpass filter designs deliver industry-leading insertion loss as low as 0.1 dB, combined with high power-handling capability of up to 400 watts. Through careful process control and component selection, our engineers have developed specialized techniques, including intermodulation suppression, to meet the most demanding customer requirements:
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Lightweight aluminum alloy construction reduces overall unit weight | |
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NADCAP-controlled gold and silver plating processes | |
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Proprietary temperature-drift control, holding stability to under 1 ppm/°C | |
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Cross-coupled pseudo-elliptic topology improves close-in rejection with no insertion loss penalty | |
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Custom resonator geometry boosts peak power-handling capacity | |
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Silver-plated resonators and cavity interiors achieve higher Q than standard plating options | |
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Shock- and vibration-resistant stabilizing structures using low-dielectric-constant materials |
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Frequency
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10 MHz to 3000 MHz
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Size
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Small
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Cost
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Low
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Harmonics
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No Spurious Passbands
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Power Handling
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Up to 100 Watts
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These pseudo-elliptic lowpass filter designs reduce the pole count required to meet rejection targets, resulting in smaller, lower-cost filters. The same techniques can also be applied to passband group delay equalization or extended stopband rejection. |
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Spectrum Control's low-loss (as low as 0.1 dB) cavity lowpass filters are recognized worldwide for their innovative topologies when performance cannot be compromised. They combine high-Q designs with creative engineering techniques to reduce size while maximizing power-handling capability. |
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Trusted worldwide in demanding RF applications, Spectrum Control's cavity lowpass filters achieve ultra-low insertion loss of as little as 0.1 dB. High-Q resonator technology, combined with space-efficient designs, delivers excellent power handling in a compact footprint, making these filters an ideal choice wherever performance cannot be compromised. |
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Spectrum Control bandpass cavity filters offer ultra-low insertion loss (0.1 dB) because they have very low internal resistance, due in part to plating that is often silver. This means Spectrum Control cavity filter designs are more efficient and better able to handle radiated signal power. Spectrum Control cavity filters can handle thousands of watts; their larger physical surface area compared with lumped element filters, along with the use of air dielectrics, helps prevent arcing that could destroy a traditional lumped element filter. |
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Spectrum Control cavity filters, with their high unloaded-Q designs, can achieve incredibly narrow fractional bandwidths with very steep skirts. This allows Spectrum Control cavity filters to pass a narrow band while heavily attenuating tones just a few MHz away from the band edge. Spectrum Control bandpass filters in a cavity topology are often designed from Invar, which offers a very low coefficient of thermal expansion. This helps ensure Spectrum’s frequency response doesn’t drift as ambient temperatures change, unlike some other manufacturers’ designs. |
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With a Spectrum Control bandpass filter in a cavity topology, the solid metal housing acts like a Faraday cage, preventing EMI from leaking out and external noise from another channel from leaking in. Known for unparalleled attenuation levels, Spectrum Control cavity filters can provide massive attenuation (100+ dB), which is normally difficult to achieve due to parasitic coupling. Unlike some other filter manufacturers, Spectrum Control offers unique resonator designs, like the one pictured here, to reduce overall size and increase peak power handling. |
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Spectrum Control bandpass filters use unique design approaches to reduce unit size, one of which is iris coupling. Iris coupling transfers electromagnetic energy between adjacent cavities through precisely shaped apertures in the cavity walls. These apertures behave as reactive shunt inductances or capacitances, increasing coupling between resonators and shaping the overall filter response. |
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Spectrum’s pseudo-elliptic designs incorporate cross-coupling to create transmission zeros, resulting in enhanced rejection performance. Unlike Chebyshev or Butterworth designs, where rejection increases gradually as you move farther from the center frequency, Spectrum Control pseudo-elliptic filters use cross-coupling to force the signal to zero at specific nearby frequencies, creating a steeper skirt between the passband and the stopband. |
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Spectrum Control bandpass filters can incorporate a unique low-dielectric-constant stabilizing structure to reduce overall sensitivity to shock and vibration. Even microscopic shifts in resonator positions can induce microphonics or frequency modulation. If a support structure like the one shown to the left had a higher dielectric constant, even a small movement caused by heating could produce a significant shift in center frequency. These innovative structures from Spectrum Control mitigate shifting effects through three primary mechanisms: they reduce electromagnetic disruptions, add mechanical damping and stiffness, and use low-dielectric materials to reduce mass and weight, making them less likely to shift. |
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Spectrum engineers routinely use an integrated cleanup low-pass filter to provide extended stopband performance. An integrated cleanup low-pass filter is a complementary filtering stage whose primary role is to suppress multiple harmonic resonances and spurious tones in resonant cavity structures. Without a cleanup low-pass stage, a transmitter could leak high-power harmonics that may interfere with out-of-band receivers. |
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Tightly controlled conductor spacing and surface finish yield very high power-handling capability. Spectrum Control bandpass filters utilize tightly controlled conductor spacing. Cavity filters are naturally high-Q filters; by design, they store significant electromagnetic energy within their resonators or sections. The space, or distance, between the resonator and the interior cavity walls is critical to optimizing power-handling capability. |
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Using silver plating on our resonators and cavity interiors reduces loss and provides higher Q values than the less expensive plating methods used by other filter manufacturers. Due to its atomic structure, silver has the highest electrical conductivity of any metal. In high-Q Spectrum Control cavity filters, Q is partly defined by the ratio of stored energy to dissipated energy. Using a more conductive finish such as silver directly reduces the amount of energy lost as heat, resulting in higher Q and lower insertion loss. |
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Spectrum Control bandpass filters use innovative cross-coupling techniques to achieve optimal rejection by introducing electromagnetic energy between non-adjacent resonators, creating signal paths that cancel at specific frequencies. Spectrum Control also incorporates bimetallic resonators to improve temperature stability, minimizing frequency drift caused by thermal changes that can alter cavity dimensions and shift the center frequency across the band. |
Advanced SAW Filters
Spectrum Control continues to deliver advanced SAW technology for today’s military and commercial markets. These SAW filters, operating at frequencies up to 1600 MHz, offer a range of outstanding features, including:
- Low insertion loss below 2 dB
- Shape factors below 1.1:1
- Fractional bandwidths up to 60%
- 100% tested
- Pre-aged at 100°C
- Gold wire bonds used on all ball bonds to reduce loss
- Silicon thermoset resin to dampen stray acoustic energy and reduce distortion
- Superior group delay performance, as low as 8 ns unit-to-unit
For a view of our SAW Filter models, click here.
Radar Applications for SAW Products
Another branch of SAW technology, particularly for radar applications, uses filters that deliver a linear change in delay across a defined passband. When paired with digital signal processing, SAW-based systems can track targets very effectively, using dispersive SAW delay lines and filters in both the transmitter and receiver to perform pulse compression and expansion. Spectrum Control SAW filters feature extremely steep skirts to isolate signals of interest in crowded or contested spectrum, and defense-grade designs are engineered to withstand shock, vibration, and temperature fluctuations. Low-loss SAW filters also provide ultra-flat group delay, which helps preserve the precise timing required for advanced missile guidance platforms.
Block diagram for a typical radar system for target detection.
Pulse-compression radar uses dispersive (chirp) filters in both the transmit and receive sections to expand the transmitted waveform and compress the received return, enabling shorter-duration, lower-peak-power transmissions while maintaining sensitivity through improved signal-to-noise ratio. In modern radar applications such as AESA (active electronically scanned array), the antenna electronically steers radio waves without moving the antenna, with each element connected to a compact computer-controlled module that performs both transmit and receive functions.
AESA radars can transmit multiple RF beams at multiple frequencies simultaneously and spread emissions across a wider spectrum, making them harder to detect over background noise while still enabling high-performance operation for ships and aircraft. SAW filters also provide bandpass filtering across many defense applications, including IF filtering in superheterodyne receivers, IF filtering within software-defined radios (SDRs), and IFF, where low-loss designs can deliver high selectivity and low distortion in a smaller, lower-cost form factor than alternative technologies. In superheterodyne receivers, SAW filters are often used as the RF and IF bandpass filters to suppress transmission leakage and interference at RF, and to provide highly selective channel filtering at IF.
Block diagram of a superheterodyne receiver.
Spectrum Control low-loss SAW filters are also used in transceiver systems and are commonly employed in duplexers within transmit/receive designs.
Block diagram of a generic transceiver circuit.
Ceramic Lowpass Filters
Spectrum Control designers are experts in the application of multiple filter topologies, including creative mixed-topology approaches that can be integrated into a single design. High-complexity ceramic filters, such as a six-pole, 2100 MHz design with a 45/0.5 dB shape factor of less than 3:1, demonstrate exceptional performance while delivering strong value.
- Gold-plated surface-mount packages improve solderability and corrosion resistance
- Alternative coupling structures offer superior performance
- Capacitive coupling arrays provide enhanced reliability and repeatability
- Ceramic resonator designs as small as 2 mm reduce overall filter footprint
- Lead-free solders are used to comply with strict RoHS standards
- Select designs are laser-sealed using Spectrum Control’s in-house sealing methodologies
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3D Glass Lowpass Filters
Spectrum Control continues to advance filter technology with the release of its new ultra-miniature glass filters. These high-Q filters, operating at frequencies up to 10 GHz, offer a range of outstanding features, including:
- Low insertion loss below 2 dB in many designs
- Rejection levels up to 70 dB
- Group delay of 1 ns across temperature
- Input power handling up to 1 watt
- Customization to meet demanding requirements
Suspended Substrate Filters
Spectrum’s low-loss suspended substrate filters enable complex transfer functions by integrating multiple filter topologies within a single package. Spectrum Control’s expert engineers optimize low-loss suspended substrate designs to meet demanding performance requirements. Suspended substrate features include:
- Expertise in combining lumped and distributed elements within a single suspended substrate design, providing enhanced unloaded Q and exceptionally low insertion loss
- Gold vias for superior isolation
- Cauer pole–placed transfer functions that yield low insertion loss performance
- Integrated cleanup low-pass filters for improved broadband performance
Technical Questions
Should a bandpass filter be placed before or after the LNA in an RF front end?
If the LNA has a low input power (damage) threshold, place the filter before it to protect against saturation from out-of-band interference. However, the filter’s insertion loss will increase the system noise figure. If the incoming signal is very weak, placing the LNA first allows its gain to mask the filter’s noise contribution. The downside is that any interferers will also be amplified before filtering.
Filter → LNA: Improved linearity, higher system noise figure, protects the LNA from out-of-band signals
LNA → Filter: Lower system noise figure, increased risk of LNA saturation
How does amplitude distortion in bandpass filters impact bit error rate (BER), especially in 64-QAM or 128-QAM schemes?
Filter responses such as Butterworth provide a smooth, flat amplitude characteristic, while Chebyshev and Cauer (elliptic) functions exhibit ripple and uneven weighting. This amplitude variation can distort the signal in the time domain, causing pulse spreading where one symbol overlaps into the next. The resulting intersymbol interference (ISI) can increase bit error rate.
How does simulating the entire board layout, not just the filter, prevent integration issues?
Full-layout simulation using tools like HFSS can identify unintended coupling (crosstalk), where input and output traces interact and potentially bypass the bandpass filter. At higher frequencies, such as 5G and emerging 6G bands, copper landing pads can behave as capacitive elements, detuning the filter’s band edges. Including pad geometries and surrounding structures in the simulation helps account for parasitics and provides a more accurate representation of interface impedance.
What are some items I can include as quick fixes in a checklist?
Tighten all connectors (as shown in the image below) to the manufacturer’s specified torque. Under-tightening can create air gaps, leading to impedance mismatches, while over-tightening can damage the internal dielectric and permanently compromise the integrity of the connector.
Verify connector torque (for SMA/SMP types). As frequency increases beyond UHF, layout precision becomes critical. Excess solder on pads or traces can alter the local impedance, which is typically designed for 50 ohms. Solder buildup can introduce additional capacitance near the pads, changing impedance and creating small reactive elements before or after the filter termination.
What are the primary filtering challenges for FR3 and the new 6G spectrum?
The 6G spectrum is still evolving but is expected to span roughly 7–24 GHz. It is not a single band, but a broader spectrum strategy. Designers working in FR3 will face increasing trade-offs between insertion loss and selectivity in an increasingly crowded spectrum. With dense carrier environments and minimal guard bands, high selectivity becomes critical, often driving the use of elliptic (Cauer) filter responses to mitigate adjacent-channel interference.
At these frequencies, implementation details, such as connector launches, board transitions, interposers, and antenna effects, become just as important as the filter design itself. Even small imperfections can degrade overall system performance and negate filter improvements.
