The two-diode subharmonically pumped stripline mixer has a pair of diodes shunt mounted with opposite polarities in a stripline circuit between the signal and local oscillator inputs. The circuit has low noise and conversion loss and substantial AM local oscillator noise cancellation.The local oscillator frequency is about half the signal frequency. A novel diode chip, the notch-front diode, which has ohmic contacts on the chip faces adjacent the face containing the diode junctions, was developed for these circuits. The notch-front diode permits the low parasitic reactance of the waveguide diode mount to be achieved in stripline circuits. The best performance for a two-diode subharmonically pumped mixer with notch-front diodes was a 400 K mixer noise temperature, obtained at 98 GHz which is comparable to the best fundamental mixers in this frequency range. The performance over a 47-110-GHz frequency range for this circuit with commercial beam-lead diodes is also presented.

Subharmonically Pumped Millimeter-Wave Mixers

Harmonic techniques are employed to leverage low-cost, ordinary surface mount technology (SMT) to high microwave frequencies where tight beamforming with a small antenna makes reliable, high-accuracy pulse-echo radar systems possible. The implementation comprises a 24 GHz short-pulse transceiver comprised of a pulsed harmonic oscillator employed as a transmitter and an integrating, pulsed harmonic sampler employed as a receiver. The transmit oscillator generates a very short (0.5 ns) phase-coherent harmonic-rich oscillation at a sub-multiple of the actual transmitter frequency. A receiver local oscillator operates at a sub-multiple of the transmit frequency and is triggered with controlled timing to provide a very short (0.5 ns), phase-coherent local oscillator burst. The local oscillator burst is coupled to an integrating harmonic sampler to produce an integrated, equivalent-time replica of the received RF. The harmonic techniques overcome four major problems with non-harmonic approaches: 1) expensive, precision assembly, 2) high local oscillator noise, 3) sluggish oscillator startup, and 4) spurious local oscillator injection locking on external RF. The transceiver can be used for automotive backup and collision warning, precision radar rangefinding for fluid level sensing and robotics, precision radiolocation, wideband communications, and time-resolved holographic imaging.

Short pulse microwave transceiver

To reduce DC offset caused by local-oscillator-signal self-mixing in a direct-conversion receiver, an active balanced harmonic mixer with second-order intermodulation (IM2) canceler was proposed, and a direct downconverter containing the mixer and a 45/spl deg/ phase shifter was fabricated on a BiCMOS chip. The dc offset caused by the self-mixing was measured and found to be smaller than the noise level. A second-order intercept point at the input of +37 dBm was achieved with the IM2 canceler, which is suitable for direct conversion receivers for quadrature phase-shift keying signals containing an amplitude modulation component.

An I/Q active balanced harmonic mixer with IM2 cancelers and a 45/spl deg/ phase shifter

In this paper, the theory of noise and frequency conversion is developed for two-diode balanced and subharmonically pumped mixers. Expressions for the conversion loss, noise temperature, and input and output impedances are derived in a form suitable for numerical analysis. Schottky diodes are assumed, having nonlinear capacitance, series resistance (which may be frequency dependent due to skin effect), and shot and thermal noise. In Part II, the theory is applied to several practical examples, and computed results are given which show the very different effects of the loop inductance (between the diodes) in balanced and subharmonically pumped mixers. It is also shown that the ideal two-diode mixer using exponential diodes has a multiport noise-equivalent network (attenuator) similar to that of the ideal single-diode mixer.

Noise and Loss in Balanced and Subharmonically Pumped Mixers: Part I--Theory

A monolithic even harmonic mixer with a new simplified circuit configuration is described. The mixer employs an antiparallel diode pair, and open and short circuited stubs as filters for separating RF output signal. IF (intermediate frequency) input signal and LO (local oscillator) power from each other. The circuit configuration is suitable for MMICs (monolithic microwave integrated circuits). A 40 GHz band even harmonic mixer is fabricated on a 1.7 mm*2.2 mm GaAs substrate and a conversion loss of 9.5 dB and a suppression of the virtual LO leakage of 75 dB are achieved. >

A 40 GHz band monolithic even harmonic mixer with an antiparallel diode pair

An analytical and experimental investigation of the properties of an antiparallel diode pair is presented. Such a configuration has the following unique and advantageous characteristics as a harmonic mixer: 1) reduced conversion loss by suppressing fundamental mixing products; 2) lower noise figure through suppression of local oscillator noise sidebands; 3) suppression of direct video detection; 4) inherent self protection against large peak inverse voltage burnout. These results are obtained without the use of either filters or balanced circuits employing hybrid junctions.

B.A. Newman

Papers

Harmonic Mixing with an Anti-Parallel Diode Pair