Jacques and Pierre Curie discovered the piezoelectric effect in 1880-1881, but it would take another century for the predecessor to the modern-day ceramic coaxial resonator-based filter to be designed and described.1 Over the course of that century, and in the decades that followed, advances in materials science and manufacturing technology enabled the primitive ceramics discovered in the 1940s2 to evolve into the compact, temperature-stable, rugged, and complex bandpass filter solutions of the 21st century. Mini-Circuits boasts one of the strongest portfolios of ceramic coaxial resonator filters anywhere in the world, with unparalleled availability to 6 GHz.

RF / microwave filters are essential building blocks of practically every wireless transceiver design. Filters block undesired signals outside the application operating bandwidth while passing in-band signals through to the rest of the signal chain. At a high level, filters can be described by their response, that is, the general shape of the S21 curve in the passband, transition, and stopband. A theoretically ideal filter would have a “brick wall” response, exhibiting 0 dB insertion loss in the passband, infinite rejection beyond the frequency cut-off fc and a transition from the passband to the stopband in 0 Hz

Designers are finding new techniques to improve system performance with Mini-Circuits’ patented reflectionless filters all the time. Among these, supplementing anti-alias filters in wideband ADCs to minimize the effect of switching transients has emerged as a popular use case.

Frequency translation devices such as multipliers and dividers are used to convert frequencies from lower spectrum regimes to higher frequencies, and vice versa. As these devices are intrinsically non-linear, they generate spurious harmonics, which are often filtered to prevent harmonics from appearing in-band. Using conventional, reflective filters creates an undesirable scenario where the out-of-band harmonics are reflected back to the multiplier. The multiplier is also affected by the reactive loading exhibited by a reflective filter at harmonic frequencies (see Figure 1). Given that multipliers have poor output return loss, this combination of effects leads to large ripples in the conversion efficiency of a multiplier chain, and hence, susceptibility to environmental factors.
This issue can be solved by leveraging the unique capabilities of reflectionless filters. To demonstrate this solution, an experiment was conducted with a doubler test circuit and a 4X multiplier chain (see Figure 2). Each experiment was conducted using comparable reflective and reflectionless filters, and the results were then analyzed.

GNSS (Global Navigation Satellite Systems) has become an increasingly prevalent RF application for both military and consumer use. Early GNSS technology, or location-based services (LBS), was developed exclusively for military use and operated with a margin of error of about 10-yards (9.14m), which was sufficient at the time, but limited its suitability for end uses requiring a higher degree of precision. In the time since the first launch of GPS more than 40 years ago, the evolution of the technology has improved precision to the order of 2-3 yards (1.83-2.74m). This advancement of the technology combined with significant miniaturization and cost reduction of LBS-enabled devices has opened up a large and growing commercial market for GNSS services. For example, GNSS is now used in the agricultural market to calculate statistics for weather, soil conditions, and crop health to help farmers maximize their yields and profits. Such innovations have stimulated demand for components that support military, industrial and consumer applications.